SEARCH

SEARCH BY CITATION

Keywords:

  • Crust;
  • geochemistry;
  • arc;
  • orogenic;
  • Japan

Abstract

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Geological Setting
  5. 3. Sample Description and Analytical Techniques
  6. 4. Results and Discussion
  7. 5. Conclusions
  8. Appendix A
  9. Acknowledgments
  10. References
  11. Supporting Information

[1] A new geochemical estimate of the young (mainly Paleozoic age to present) upper crust of the Japan Arc shows a dacitic composition in contrast to the idea that andesite is predominant in active orogenic arcs. Temporal changes in composition are not significant from the Paleozoic age to the present for the Japan Arc. The major element composition is similar to previous models of old cratonic upper crusts. The coincidence in the major elements between young and old crusts indicates that essential mechanisms during crust formation have not changed from the Archean era to the present. In trace element compositions the average young upper crust of the Japan Arc has higher Sb and As concentrations and lower concentrations of alkaline, light rare earth, and high field strength elements with respect to previous models of continental upper crusts. The large degree of constancy of trace element composition in marine sedimentary rocks is in contrast to the large variety in igneous rocks. However, the averages for both accretionary and nonaccretionary sedimentary rocks are almost identical to the average for the igneous rocks of the Japan Arc, with the exceptions of high Sb and As concentrations in unmetamorphosed sedimentary rocks. The compositional homogeneity among different types of rocks on an arc scale implies that recycling processes mechanically mix the arc-derived igneous materials to homogenize the chemical composition during erosion, transportation, sedimentation, accretion, and uplifting. Since the contribution of oceanic crust to the composition of arc crust is small, the recycling processes have not changed the bulk upper crustal composition of the active continental margin except increase the Sb and As from sediments. Instead, the influx of differentiated acidic rocks from depth is essential to characterize the orogenic crust formation of the young Japan Arc. The characteristically low incompatible element content of the Japanese upper arc crust appears inherited from parental magmas derived from a mantle source depleted during a long-term evolution.

1. Introduction

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Geological Setting
  5. 3. Sample Description and Analytical Techniques
  6. 4. Results and Discussion
  7. 5. Conclusions
  8. Appendix A
  9. Acknowledgments
  10. References
  11. Supporting Information

[2] Although the formation of crust is one of the fundamental issues for the evolution of the earth [e.g., Allegre et al., 1983; Armstrong, 1981; Clarke, 1924; Hofmann, 1988; Rudnick, 1995; Taylor and McLennan, 1995], the evolution of crust has been controversial. The models of the composition of the upper continental crust have been studied mainly on exposed old continental crusts [Taylor and McLennan, 1985; Wedepohl, 1995] and in the Canadian Shield [Shaw et al., 1986]. Condie [1993] implied a secular compositional change at the Archean-Proterozoic boundary. He envisaged an Archean upper crust depleted in large ion lithophile elements (LILE) and high field strength elements (HFSE) and heavy rare earth elements (HREE) compared with post-Archean upper crust. However, the HFSE abundance in the Archean upper crust [Condie, 1993] is different from other old upper crust models [Shaw et al., 1986; Taylor and McLennan, 1985; Wedepohl, 1995].

[3] Besides old continental crusts, the crustal composition at active continental margins is not well constrained in spite of their importance as settings where crust is still forming [Arculus and Ruff, 1990; Ellam and Hawkesworth, 1988; Pearcy et al., 1990]. The only data of orogenic upper crust composition were obtained at the Proterozoic-Mesozoic Qinling Orogenic Belt in China [Gao et al., 1992, 1998]. Both of the old central east China cratonic upper crust and the young Qinling Orogenic Belt have essentially similar composition [Gao et al., 1998]. They have high abundance of mafic components and low abundance of K, Rb, and Sr relative to the other old upper crusts [Shaw et al., 1986; Taylor and McLennan, 1985; Wedepohl, 1995].

[4] In this paper, we estimate the young upper crustal composition of the Japan Arc as an active continental margin and arc and compare the results with those for continental crusts previously reported [Condie, 1993; Gao et al., 1992, 1998; Shaw et al., 1986; Taylor and McLennan, 1985; Wedepohl, 1995]. Since these geochemical features must be closely related to the genesis of the Japan Arc, the data obtained in this study are crucial for disclosing the processes operating during the evolution of the arc. From the viewpoint of mass balance we also constrain the sedimentary and igneous processes controlling element distribution in various arc rocks. We focus on the major factors affecting the chemical features of igneous rocks observed in this study to evaluate the role of recycled upper crustal materials during subduction and influx of acidic magma around the Japan Arc.

2. Geological Setting

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Geological Setting
  5. 3. Sample Description and Analytical Techniques
  6. 4. Results and Discussion
  7. 5. Conclusions
  8. Appendix A
  9. Acknowledgments
  10. References
  11. Supporting Information

[5] The Japanese Arc system is composed of two principal arcs: the Northeast Japan Arc and Southwest Japan Arc; and three other subordinate arcs: the Kuril Arc, Izu-Bonin Arc and Ryukyu Arc, which correspond to the eastern part of Hokkaido and Kuril Islands, the Izu and Bonin Islands, and the Nansei and Ryukyu Islands, respectively (Figure 1). The Northeast Japan Arc, Southwest Japan Arc, and Ryukyu Arc were the active margin of the Eurasian continent and share some geologic units. These arcs were sliced off the continent with the opening of marginal seas in the late Cenozoic [Otofuji and Matsuda, 1984; Sibuet et al., 1987; Tamaki et al., 1992]. The Kuril Arc is formed at the margin of a continent presently submerged under the Sea of Okhotsk [Kimura and Tamaki, 1986]. The Izu-Bonin Arc is a modern volcanic arc that was formed during the early Tertiary opening of the Philippine Sea [Seno and Maruyama, 1984]. The Northeast Japan Arc and Izu-Bonin Arc juxtapose with the Southwest Japan Arc at the Itoigawa-Shizuoka tectonic line (ISTL) in the central part of the Honshu Island. The Southwest Japan Arc is further divided by the Median Tectonic Line (MTL) into inner zone (back arc side) and outer zone (forearc side).

image

Figure 1. Outline of geologic setting of the Japan Arc. Base map is modified from a 1:1 million geological map issued by the Geological Survey of Japan [Geological Survey of Japan, 1992]. Abbreviations are as follows: ISTL, the Itoigawa-Shizuoka tectonic line; MTL, the Median Tectonic Line.

Download figure to PowerPoint

[6] The pre-Neogene basement rocks of the Japanese Islands are formed by nappe piles of an accretionary complex of the late Paleozoic-Cenozoic age, and their metamorphic equivalents [Isozaki, 1997]. They are divided into several geologic units with discontinuous ages of accretion [Geological Survey of Japan, 1992]. The accretionary complex consists of a chaotic mixture of exotic blocks and argillaceous matrix. The matrix ages of accretionary complexes are roughly Permo-Triassic, Jurassic, Cretaceous, and Paleogene. The accretionary complex contains exotic blocks of chert, limestone, and basalt whose ages span widely but have systematic relations with those of the matrix sediments. Ophiolites are also included or intercalated in the pile-nappe sequence of accretionary complexes.

[7] The pile-nappe structures of the accretionary complexes are well observed in the outer zone of the Southwest Japan Arc, where the along-arc trending the Cretaceous to Tertiary accretionary complexes show a systematic outward younging arrangement. The zonal arrangement continues until the present accretionary prism at the Nankai Trough, where subduction of the Philippine Sea plate is going on to the north [Ashi and Taira, 1992]. In the north of the Cretaceous accretionary complex a Jurassic accretionary complex is exposed widely. Its tectonic relation to high-pressure-type Sambagawa metamorphic rocks and to the Kurosegawa Serpentinite unit [Nakajima, 1997] is still a matter of debate.

[8] The inner zone of the Southwest Japan Arc is mainly composed of accretionary complexes of Permo-Triassic and Jurassic periods, although the distributions are partly disturbed by the intrusion of the Cretaceous-Paleogene granitoids. A part of the Permo-Triassic accretionary complex has been metamorphosed to high-pressure facies [Isozaki, 1997]. The Cretaceous-Paleogene granitoids are associated with violent felsic volcanism characterized by the extrusion of large volumes of welded tuff [Takahashi, 1983]. The low-pressure-type Ryoke metamorphism and the deposition of the Late Cretaceous shallow marine sediments in the pull-apart basins also took place in relation to this igneous activity.

[9] The Jurassic accretionary complexes and Cretaceous-Paleogene granites are also important components of the Northeast Japan Arc, although most parts are covered with younger sediments and volcanics. Besides exotic blocks in the accretionary complexes, the Paleozoic and Mesozoic sedimentary rocks of epicontinental facies [Saito and Hashimoto, 1982] occur widely in the southern half of the Kitakami Mountains in northern Honshu. Another important component of the Northeast Japan Arc (and of the northern section of the Izu-Bonin Arc) is a thick pile of the Neogene sediments accompanying mafic and felsic volcanic rocks. The Neogene volcano-sedimentary pile, which was formed in relation to the opening of the Sea of Japan [Tsuchiya, 1989], is distributed mainly in the backbone range of the northern half of Honshu, along the Japan Sea coast from Hokkaido to Honshu, and in the Fossa Magna region just in the east of the ISTL [Geological Survey of Japan, 1992].

[10] The Cretaceous-Paleogene sedimentary rocks in central Hokkaido are formed along the Eurasian continent, whereas those in eastern Hokkaido are formed along the margin of a continental crust presently located under the Sea of Okhotsk [Kimura and Tamaki, 1986]. The low-pressure-type Hidaka metamorphic belt in central Hokkaido is considered to be the exposed lower crustal section of a volcanic arc whose uplift was a result of the westward migration of the Kuril Arc [Kimura and Tamaki, 1986; Komatsu et al., 1989].

[11] The Quaternary volcanic rocks and plain sediments cover the basement. The proportions of the Quaternary sediments and volcanic rocks represent 21 and 11%, respectively, of the total surface exposure [Murata and Kano, 1995]. The proportion of the Quaternary volcanic rocks is higher in the Northeast Japan Arc, Kuril Arc, and Izu-Bonin Arc than in the Southwest Arc and Ryukyu Arc.

3. Sample Description and Analytical Techniques

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Geological Setting
  5. 3. Sample Description and Analytical Techniques
  6. 4. Results and Discussion
  7. 5. Conclusions
  8. Appendix A
  9. Acknowledgments
  10. References
  11. Supporting Information

[12] The surface exposure of the Japan Arc is composed principally of Quaternary sediments (21%), Tertiary sediment (14%), Quaternary volcanic rocks (11%), Tertiary igneous rocks (15%), Cretaceous igneous rocks (12%), and others. Lithologically, the surface exposure consists of 41% igneous rocks, 38% nonaccretionary sedimentary rocks, 17% accretionary complex rocks, and 4% metamorphic rocks [Murata and Kano, 1995].

[13] One hundred and sixty six representative specimens from the Japan Arc were analyzed and subdivided into the 37 geologic groups (Figure 2, Table 1) based on their ages, lithologies, and provinces, as summarized in the 1:1,000,000 scale geologic map [Geological Survey of Japan, 1992]. Individual descriptions are shown in Table A1.

image

Figure 2. Sampling locations. Base map is modified from a 1:1 million geological map issued from Geological Survey of Japan [Geological Survey of Japan, 1992]. Symbols are superimposed for some samples.

Download figure to PowerPoint

Table 1. Major and Trace Element Abundance of 37 Geologic Groups From the Japan Arca
No.GroupbRock NameArea, %nSiO2, %TiO2, %Al2O3, %Fe2O3, %MnO, %MgO, %CaO, %Na2O, %K2O, %P2O5, %LOI, %Sc, ppmV, ppmCr, ppmCo, ppmNi, ppmCu, ppmZn, ppmAs, ppmRb, ppmSr, ppmY, ppmZr, ppmNb, ppm
  • a

    All element values are recalculated on a volatile-free basis to 100%.

  • b

    Symbol (c) with group shows units of accretionary complex. For rock name, (f,na), the felsic nonalkalic; (m,na), mafic nonalkalic, (f,a), felsic alkalic; (m,a), mafic alkalic.

  • c

    Abbreviations of analytical methods except for limestone denoted by footnote c: x, X-ray fluorescence; n, instrumental neutron activation analysis; i, inductively coupled plasma-mass spectrometry.

  • d

    For limestones, analytical methods are the same as the standard JLs-1 in Table 3

  • e

    We analyzed Yb and Lu by using both of inductively coupled plasma mass spectrometry analysis and neutron activation analysis. The data of neutron activation analysis are selected for acidic rocks with insoluble minerals.

Analytical Methodc   xxxxxxxxxx nxxnxxxix,iixxx
1Quaternarysedimentary21.363968.210.6415.775.500.101.973.202.382.160.08(7.43)18.51284113.417289012.874194281307.9
2Neogenesedimentary12.4681573.240.5312.635.430.071.862.371.811.960.11(9.05)14.61266710.82726848.177157211087.4
3Paleogenesedimentary1.897465.690.5514.235.780.141.817.222.062.400.10(11.47)10.8796013.82813758.4882772217010.1
4Cretaceoussedimentary2.718766.020.5012.415.510.121.419.262.322.350.11(9.10)11.3974210.51513655.179248211287.5
5Jurassic-Triassicsedimentary0.505363.790.6213.595.620.102.109.692.361.950.17(7.82)12.81255813.72037742.670337251328.0
6Paleozoicsedimentary0.951563.011.0620.606.860.081.971.792.072.410.14(4.79)27.41956515.22832898.783231361807.3
7(c)Paleozoicsedimentary0.572265.520.6515.284.730.171.606.152.103.550.24(6.47)11.31036922.82414104-1333562819711.6
8(c)Paleozoicvolcanic0.296350.431.6115.1712.120.176.519.803.720.350.13(3.68)49.138422850.6432880-42812552<2
9(c)Paleozoiclimestoned0.08531.810.020.480.180.010.6696.760.010.050.02(42.76)0.414330.28820<322771121<2
10(c)Jurassicsedimentary6.5481167.820.7215.585.110.092.442.202.783.100.16(4.09)13.79611116.246258011.11181592818812.3
11(c)Jurassicvolcanic0.823251.512.9815.8513.160.143.946.933.941.030.53(4.09)37.231010254.651851705.1252725221323.1
12(c)Jurassiclimestoned0.08720.980.010.240.160.010.6197.890.010.050.04(43.14)0.613230.66424<224802922<2
13(c)Jurassicchert0.344388.110.111.631.300.220.597.520.030.410.09(5.91)2.414135.7202625-15688242.7
14(c)Cretaceoussedimentary5.973773.010.5314.084.040.111.530.842.892.910.07(3.65)10.4815312.925207110.21061912217710.7
15(c)Palaeogenesedimentary2.189272.170.5414.264.250.061.631.372.053.590.09(4.30)9.871639.92414687.5127912417011.4
16unknownultramafic0.500446.210.030.858.840.1441.312.560.050.0050.01(4.78)12.44225621051876652<20.56<310<2
17High-T, low-Pmetamorphic1.1201159.701.1014.588.630.603.897.492.021.790.19(2.94)20.113420425.1834292<6653262614615.5
18Low-T, high-Pmetamorphic2.734963.650.9712.838.040.175.325.052.501.280.14(2.33)25.717114628.0557076<638146271065.8
19Quaternaryvolcanic(f,na)6.207669.790.5414.693.740.111.053.143.972.820.13(0.88)11.44275.328565.91032503216010.7
20Quaternaryvolcanic(m,na)4.7551158.050.8416.528.790.153.837.702.911.070.14(0.34)28.62324323.81964763.52829325972.7
21Neogeneplutonic(f,na)0.909267.580.6015.504.140.081.393.523.503.520.17(0.46)10.863288.6911555.71313562415912.5
22Neogeneplutonic(m,na)0.142252.640.5320.537.560.133.9811.802.410.320.10(0.62)26.618111421.0183151<253751630<2
23Neogenevolcanic(f,na)4.200674.850.2813.522.490.060.651.843.133.120.06(7.62)9.222103.14552<3931333713710.7
24Neogenevolcanic(m,na)7.404557.050.9016.957.390.135.056.873.511.910.23(2.95)23.415616825.1643070<253487251307.6
25Quaternary Neogenevolcanic(m,a)0.361153.091.3014.649.020.157.939.432.771.420.26(1.84)28.420939939.314258842.3404502414727.4
26Neogenevolcanic(f,a)0.058176.510.1312.681.180.010.030.214.135.180.007(0.55)1.7<5<50.153<354<221326136693
27Paleogeneplutonic(f)1.192368.570.5015.293.620.071.473.513.932.910.12(0.55)8.667218.69744<273398191386.3
28Paleogeneplutonic(m)0.133150.060.4717.816.290.1010.1212.452.590.100.01(5.22)31.415296543.8768438<232621234<2
29Paleogenevolcanic(f,na)0.369173.410.3813.982.740.090.822.173.752.600.07(1.17)5.43264.34<349<276239201406.8
30Paleogenevolcanic(f,na)0.766251.070.3110.8510.050.1519.086.591.310.510.07(5.57)29.7180121669.95604371<28119836<2
31Cretaceous (Late)plutonic0.619674.580.1913.651.870.040.351.523.294.450.06(0.52)4.61183.13<342<21981434012014.0
32Cretaceous (Middle)plutonic5.017369.500.4115.083.700.071.472.953.413.300.12(0.70)9.353448.411658<21242432112712.5
33Cretaceous (Early)plutonic1.952656.950.9017.268.350.124.027.652.991.600.15(0.79)21.42694127.2173677<24648121907.1
34Cretaceousvolcanic(f,na)3.383373.900.1913.502.680.080.341.923.603.790.04(1.87)6.11052.92<3504.11191522815813.3
35Cretaceousvolcanic(m,na)0.636161.891.1319.348.110.132.761.061.753.730.09(4.10)23.718113718.966341227.21402373721311.8
36Jurassicplutonic(f)0.288269.070.4015.503.620.071.223.043.833.130.12(1.23)4.747136.152616.280450141238.4
37Jurassic-Carboniferous lakesplutonic and volcanic (m)0.007252.570.6918.796.490.096.1210.952.981.210.12(3.61)31.4184100526.1173105505.33739819722.7
 lakes 0.431 
 
No.GroupbRock NameArea, %nSb, ppmCs, ppmBa, ppmLa, ppmCe, ppmPr, ppmNd, ppmSm, ppmEu, ppmGd, ppmTb, ppmDy, ppmHo, ppmEr, ppmTm, ppmYb, ppmLu, ppmHf, ppmTa, ppmPb, ppmTh, ppmU, ppm  
Analytical Methodc   iiiiiiiiiiiiiiii,nei,neiiiii  
1Quaternarysedimentary21.36390.614.847420.844.05.3120.04.141.093.600.744.200.792.670.422.790.444.030.5617.27.32.15
2Neogenesedimentary12.468151.158.339217.438.74.4416.93.490.892.810.553.130.581.940.332.010.313.530.4815.96.43.44
3Paleogenesedimentary1.89740.795.741824.550.45.9221.74.091.073.450.623.290.591.880.321.990.335.280.6719.18.51.94
4Cretaceoussedimentary2.71870.643.645923.551.55.9521.84.191.093.520.603.140.571.850.302.110.293.680.5814.46.81.55
5Jurassic-Triassicsedimentary0.50530.683.335821.244.95.3320.13.970.993.520.643.680.662.210.352.150.343.410.5816.98.32.72
6Paleozoicsedimentary0.95150.515.135422.251.46.1924.04.871.313.910.865.120.993.400.543.710.605.710.3615.37.52.11
7(c)Paleozoicsedimentary0.57220.375.858839.179.09.2233.36.651.455.490.874.720.852.630.412.460.365.670.9663.311.62.59
8(c)Paleozoicvolcanic0.29630.310.91263.810.11.658.02.591.072.200.543.380.662.090.332.180.351.49<0.11.60.30.09
9(c)Paleozoiclimestonec0.08530.600.393.51.70.642.00.540.090.400.090.600.120.430.070.300.040.120.071.80.30.51
10(c)Jurassicsedimentary6.548111.466.448729.765.97.5627.15.081.134.300.703.700.672.210.362.610.425.111.0121.113.22.53
11(c)Jurassicvolcanic0.82320.692.023923.244.66.729.36.952.235.351.207.071.233.940.603.790.605.051.672.81.70.41
12(c)Jurassiclimestonec0.08720.050.13011.45.82.007.41.640.241.480.352.360.521.880.291.450.250.500.054.41.00.72
13(c)Jurassicchert0.34430.230.91026.19.61.566.11.230.291.050.191.000.180.530.080.470.070.500.193.71.10.55
14(c)Cretaceoussedimentary5.97370.766.453729.160.56.7524.04.391.053.380.663.530.652.080.352.180.336.290.8219.010.41.98
15(c)Palaeogenesedimentary2.18921.235.666224.151.35.9821.24.011.073.440.542.500.401.190.191.090.175.291.0625.59.21.25
16Unknownultramafic0.50040.330.470.10.30.040.20.070.030.060.010.070.020.040.0050.060.01<0.2<0.10.50.10.01
17High-T, low-Pmetamorphic1.120110.238.448925.151.66.6726.55.251.544.290.824.330.762.420.402.420.383.981.139.86.01.31
18Low-T, high-Pmetamorphic2.73490.278.829912.427.33.8516.13.701.143.180.724.300.812.650.422.580.392.910.377.42.80.64
19Quaternaryvolcanic(f,na)6.20760.486.242321.145.85.6422.04.831.164.230.814.460.842.820.483.240.494.660.9814.110.63.15
20Quaternaryvolcanic(m,na)4.755110.251.43019.021.02.7412.43.151.013.170.593.640.702.300.382.460.382.660.167.02.70.82
21Neogeneplutonic(f,na)0.90920.209.169327.860.17.0126.15.071.394.540.763.980.732.360.382.220.324.471.0922.29.22.94
22Neogeneplutonic(m,na)0.14220.070.21233.28.51.396.71.920.631.460.362.350.421.460.241.540.221.39<0.12.70.320.11
23Neogenevolcanic(f,na)4.20060.418.191325.357.06.8025.75.611.274.920.945.641.043.400.574.000.584.480.8217.910.32.77
24Neogenevolcanic(m,na)7.40450.173.534016.135.34.4717.64.021.303.420.694.080.772.460.422.520.403.250.5513.14.21.67
25Quaternary Neogenevolcanic(m,a)0.36110.251.351338.367.17.4426.55.171.494.760.704.060.722.220.342.140.343.471.976.99.21.60
26Neogenevolcanic(f,a)0.05810.181.2318420640.812819.550.0415.322.3810.291.685.020.805.530.7312.076.1329.530.25.55
27Paleogeneplutonic(f)1.19230.102.465324.551.75.9121.74.031.233.930.583.110.511.800.301.910.294.250.6614.39.12.24
28Paleogeneplutonic(m)0.13310.060.1251.94.50.884.21.300.621.050.281.870.341.150.181.060.160.74<0.11.40.140.04
29Paleogenevolcanic(f,na)0.36910.241.545920.641.34.6016.32.900.972.720.442.350.431.460.252.830.344.550.5614.47.01.73
30Paleogenevolcanic(f,na)0.76620.120.3372.34.70.723.20.840.280.720.181.220.230.810.140.840.140.670.141.30.30.11
31Cretaceous (Late)plutonic0.61960.066.449025.856.96.8325.15.670.714.740.975.590.943.140.553.420.554.341.7430.219.45.40
32Cretaceous (Middle)plutonic5.01730.084.669531.463.78.0929.55.121.124.390.733.600.601.890.311.820.294.001.0522.210.61.90
33Cretaceous (Early)plutonic1.95260.151.835316.837.44.8519.13.941.193.440.653.590.662.030.332.370.333.200.527.74.61.33
34Cretaceousvolcanic(f,na)3.38330.333.151135.270.27.9127.64.750.924.130.764.000.722.490.423.260.504.761.0521.514.72.26
35Cretaceousvolcanic(m,na)0.63611.6519.866437.082.89.4936.47.171.865.551.176.731.193.990.674.350.645.530.9725.511.12.67
36Jurassicplutonic(f)0.28820.292.172334.963.36.6621.83.461.153.840.472.020.411.270.191.270.204.860.4920.214.82.18
37Jurassic-Carboniferousplutonic and volcanic (m)0.00720.151.51248.017.82.4510.52.570.922.220.462.590.491.610.221.470.231.500.132.61.250.30
 lakes 0.431 

[14] The representative rocks were selected to cover the rock varieties and abundance in the group. The sampling strategies: (1) Thirty seven geologic groups are characterized based on their ages, lithologies, and provinces (Table 1). All the 37 geologic groups are distinguishable as geologic units in the 1:1,000,000 scale geologic map [Geological Survey of Japan, 1992]. In Figure 3 the relative proportions of sampled materials with respect to age, outcrop size, and lithology of the rocks are indicated. (2) Samples should cover the areas in both of the NE and SW Japan because of the difference of geologic settings (Figures 1 and 2). (3) We use a linear average within each geologic group (Tables 1 and A1), because the representative rocks in the geologic group are chosen with their abundance on the basis of an enormous amount of existing geologic information. For example, when the volume of both of sandstone and mud stone are comparable in the interest area, we selected the both types for sedimentary rocks. Although the igneous rocks have significant variety in composition, we can select the representative samples based on previous studies. In spite of the small exposed area for metamorphic rocks we analyzed many samples because of their wide varieties. In the extreme case we multiplied the factor to reduce the contribution of exceptional rocks. In the case of accretionary complex we analyzed the representative lithology and will examine the representation using a large-scale geological map in later sections.

image

Figure 3. Bar diagrams of the relative proportions of the sampled materials with respect to age, exposed area percent and lithology of the rocks for 166 analyzed samples. Data of area percent are from a 1:1 million digital geological map issued by the Geological Survey of Japan [Geological Survey of Japan, 1995; Murata and Kano, 1995.

Download figure to PowerPoint

[15] Rock specimens from 300 to 2000 g in weight, depending on their lithologic heterogeneity, were crushed with a jaw-crasher, quartered to 300 g samples of gravel, and powdered under 200 mesh with an automatic agate mortar. Ten major and 35 trace elements were analyzed by routine X-ray fluorescence analysis (used by Togashi and Terashima [1997]), instrumental neutron activation analysis [Kamioka and Tanaka, 1989; Tanaka et al., 1988], induced couple plasma mass spectrometry [Imai, 1990; Ujiie and Imai, 1995], and wet chemistry method (used by Okai [1993]). Loss of ignition (LOI) was measured after ignition under 1000°C for 2 hours. Details of the techniques used are given in Tables 2 and 3. Analytical results for geostandard rocks JB-3 (basalt) and JR-1 (rhyolite) [Ando et al., 1989], and JLs-1 (limestone) [Imai et al., 1996] are also reported with their reference values in Tables 2 and 3 to evaluate the typical precision and accuracy of the analyses.

Table 2. Analytical Techniques Used in This Study and Results for Geostandard Rocks JB-1(Basalt) and JR-1(Rhyolite)a
NameItemsSiO2, %TiO2, %Al2O3, %Fe2O3, %MnO, %MgO, %CaO, %Na2O, %K2O, %P2O5, %Sc, ppmV, ppmCr, ppmCo, ppmNi, ppmCu, ppmZn, ppmAs, ppmRb, ppmSr, ppmY, ppmZr, ppmNb, ppm 
  • a

    Method: XRF; X-ray fluorescence analysis; INAA, instrumental neutron activation analysis; ICPM, inductively coupled plasma mass spectrometry; ICP, inductively coupled plasma-atomic emission; CL, colorimetry; TI, titrimetry.

  • b

    Reference values are from Ando et al. [1989]

  • c

    Reference values are from Imai et al. [1996]

 methodbXRFXRFXRFXRFXRFXRFXRFXRFXRFXRFINAAXRFXRFINAAXRFXRFXRFINAAICPMICPMXRFXRFXRF 
JB-3this study51.291.4617.3211.810.165.239.932.790.770.335.63896538.43619994<214.839527972.7
σ error%0.61.10.90.51.91.50.92.81.32.80.12.680.381.34-316530
referencec50.851.4416.8311.840.165.189.822.810.780.293538360.436.338.81981061.66133952899.42.3
 
JR-1this study75.580.1112.940.930.100.120.694.084.490.025.2<5<50.60<2<331.517.0262284910317.2 
σ error%0.331.23333102.00.8190.2  3  5122.42.24510
referencec75.410.1012.890.960.100.090.634.104.410.025.2<82.30.650.661.43015.9257304610215.5
NameItemsSb, ppmCs, ppmBa, ppmLa, ppmCe, ppmPr, ppmNd, ppmSm, ppmEu, ppmGd, ppmTb, ppmDy, ppmHo, ppmEr, ppmTm, ppmYb, ppmYb, ppmLu, ppmLu, ppmHf, ppmTa, ppmPb, ppmTh, ppmU, ppm
 methodbICPMICPMICPMICPMICPMICPMICPMICPMICPMICPMICPMICPMICPMICPMICPMICPMINAAICPMINAAINAAINAAICPMICPMICPM
JB-3this study0.130.842448.621.33.516.34.21.33.90.754.30.782.50.42.52.810.370.413.6<0.25.41.30.49
σ error%1551.51.2231.22884254542532 684
referencec0.151.12519.120.53.216.64.31.34.60.824.40.842.50.52.42.40.380.382.70.155.51.30.46
 
JR-1methodb1.2318.14419.147.46.1323.65.680.285.21.055.81.063.860.664.35.040.680.835.21.8619.526.59.4
σ error%72.21.91.90.82251468167114132122.233
referencec1.4820.24021496.125.56.20.314.81.16.21.13.90.734.64.60.680.684.71.919.126.59
Table 3. Analytical Techniques Used in This Study and Results for Geostandard Rocks JLs-1 (Limestone)
ItemsSiO2, %TiO2, %Al2O3, %Fe2O3, %MnO, %MgO, %CaO, %Na2O,%K2O, %P2O5, %
  • a

    Method: CL, colorimetry; ICP, inductively coupled plasma-atomic emission; AAS, atomic absorption; TI, titrimetry.

  • b

    Reference values are from Ando et al. [1989]

MethodaCLICPICPICPICPAASTIAASAASICP
This study0.120.0010.0230.0160.00220.655.130.0020.0030.03
σ error%8.39.18.73.12.30.830.3614.36.16.7
Referenceb0.120.0020.0210.0180.00210.6155.090.00190.00300.030

4. Results and Discussion

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Geological Setting
  5. 3. Sample Description and Analytical Techniques
  6. 4. Results and Discussion
  7. 5. Conclusions
  8. Appendix A
  9. Acknowledgments
  10. References
  11. Supporting Information

4.1. Average Upper Crustal Chemical Composition of the Japan Orogenic Arc

[16] We have estimated the average abundance of 45 elements in the exposed Japan Arc (Table 4) from the mean composition of 37 geologic groups listed in Table 1. These groups are statistically weighted according to their frequency in the 1:1,000,000 scale geologic map [Geological Survey of Japan, 1992, 1995; Murata and Kano, 1995] (Table 1). The main Japan upper crust has formed from the Paleozoic until present. As the geologic map was made mainly based on the steep V-shaped valley river cutting outcrops in mountainous area of Japan, the effects of preferential erosion are small. Therefore the surface area integration method should be useful in Japan, even though nonuniform erosion does result in a small bias in surface sampling.

Table 4. Average Composition of the Upper Crust of Japan Arc and Other Modelsa
GroupsNumber in Table 1AreanSiO2, %TiO2, %Al2O3, %Fe2O3, %MnO, %MgO, %CaO, %Na2O, %K2O, %P2O5, %Sc, ppmV, ppmCr, ppmCo, ppmNi, ppmCu, ppmZn, ppmAs, ppmRb, ppmSr, ppmY, ppmZr, ppmNb, ppm
Japan arc upper crust (area weighted average)
total average“1–37”99.6%16667.530.6214.675.390.112.533.902.722.420.12161108415382574.16.5–7.185225261359
pre-Neogene rocks“3–18,27–37”41.7%10867.500.6114.185.110.112.804.022.752.800.11139311816582169.014.9–5.91022062614610
pre-Cretaceous rocks“5–13,36–37”10.5%3864.780.9015.235.850.112.455.162.712.630.191511495193828837.3–8.4962042716711
nonaccretionary sedimentary rocks“1–6”39.9%4369.300.6014.575.530.091.903.612.182.120.1016121501220258510.176192251258
accretionary & matamorphic rocks“7–18”21.3%5967.110.7613.925.670.143.513.632.572.550.1415110155218231787.2–7.9921762516111
igneous rocks“19–37”38.4%6465.920.5715.195.090.102.644.353.352.660.13159980143220612.1–3.391285291319
Neogene-Quarternary igneous rocks“19–26”24.0%3464.010.6815.605.760.112.895.123.432.240.151811571152726642.5–3.671318291349
Paleogene-Cretaceous igneous rocks“27–35”14.1%2669.120.3814.473.990.082.233.073.213.380.08107295123911551.3–2.71262252912611
Upper crust model
Central East China [Gao et al., 1998]b   67.600.6714.105.860.102.603.422.842.660.151510183183933724.5852751819412
Post-Archean [Condie, 1993]c   67.440.5915.054.95 1.933.323.373.220.131490501527   1012753117812
Canadian Shield [Shaw et al., 1986]   67.460.5415.203.150.072.334.283.593.220.167553612.5201562 1143282224627
Upper crust [Wedepohl, 1995]   66.260.5314.934.510.072.294.203.533.520.167543611.81914531.71123232124227
Upper crust [Taylor and McLennan, 1985]   65.70.515.14.930.082.194.23.93.4 11603510.02025711.51123492218911.5d
 
GroupsNumber in Table 1AreanSb, ppmCs, ppmBa, ppmLa, ppmCe, ppmPr, ppmNd, ppmSm, ppmEu, ppmGd, ppmTb, ppmDy, ppmHo, ppmEr, ppmTm, ppmYb, ppmLu, ppmHf, ppmTa, ppmPb, ppmTh, ppmU, ppm 
Japan arc upper crust (area weighted average)
total average“1–37”99.6%1660.615.545821.746.45.5420.84.281.073.650.703.940.722.390.392.570.404.100.7216.98.32.32 
pre-Neogene rocks“3–18,27–37”41.7%1080.625.346325.153.26.2623.04.501.053.770.703.800.682.210.372.420.374.490.9019.210.22.20 
pre-Cretaceous rocks“5–13,36–37”10.5%381.075.043127.057.86.8024.94.851.164.090.703.760.682.210.352.420.384.560.9221.910.52.11 
nonaccretionary sedimentary rocks“1–6”39.9%430.785.844020.243.35.1119.23.931.023.330.663.710.692.320.382.420.383.890.5417.27.02.49 
accretionary & matamorphic rocks“7–18”21.3%590.896.246224.953.06.2523.04.481.133.670.683.640.662.130.342.250.354.850.8517.99.01.72 
igneous rocks“19–37”38.4%640.284.747321.446.05.5821.24.531.103.970.764.330.792.610.442.910.443.900.8416.09.22.48 
Neogene-Quarternary igneous rocks“19–26”24.0%340.314.746818.740.65.0519.84.421.203.920.754.360.822.680.452.940.453.770.6813.26.92.12 
Paleogene-Cretaceous igneous rocks“27–35”14.1%260.224.647725.854.76.4623.74.740.924.060.774.330.752.510.432.900.444.091.1120.813.03.10 
Upper crust model
Central East China [Gao et al., 1998]b   0.313.770035.968.6 31.45.261.25 0.85    2.330.365.280.76399.31.60 
Post-Archean [Condie, 1993]c     71729.563.4 28.85.581.115.200.82    2.360.394.960.971710.42.68 
Canadian Shield [Shaw et al., 1986]     111233.668.2 26.94.690.982.900.50 0.64  1.530.246.03(5.92)1810.72.55 
Upper crust [Wedepohl, 1995]   0.325.968233.067.16.4326.44.800.972.860.512.960.63  1.530.285.921.531710.52.55 
Upper crust [Taylor and McLennan, 1985]   0.203.754829.963.77.0725.94.480.883.780.643.490.802.290.332.190.325.780.92d2010.72.79 

[17] Cretaceous plutonic rocks and Paleogene-Paleozoic accretionary complex rocks are one of the major constitutes of exposed samples (Figures 2 and 3). The plutonic and accretionary complex rocks are tectonically eroded from middle or deep parts of the upper crust of the Japan Arc. The depth of the Conrad discontinuity range from 12 to 22 km in the Japan islands [Zhao et al., 1992]. The original depth of emplacement of Cretaceous plutonic rock in the Ryoke belt and Kitakami Mountains are estimated to be 5–15 km based on contact metamorphism [Okuyama-Kusunose, 1999] and hornblende geobarometry [Takahashi, 1993, 1995]. The depth of accretionary prism attached to NE Japan at offshore of Kitakami mountains is geophysically estimated to be ∼15 km [Finn et al., 1994]. Although some of accretionary complex rocks experienced high-pressure metamorphism at lower crustal conditions up to 30 km [Nakajima, 1997], the area contribution to the exposed average is small (1%, Table 1). Another major constituent of the exposed samples are Quaternary-Neogene sediments and Quaternary-Neogene volcanic rocks, which represent the upper part of the upper crust of the Japan Arc. The Quaternary-Neogene sedimentary basins cover one third of the total area, and their typical depth is 2–3 km [Sumii et al., 1992]. In conclusion, we can assume that the exposed Japan Arc represents the upper part weighted young upper crust of the Japan Arc.

[18] Our calculations indicate that the exposed young upper crust of the Japan Arc has a dacitic composition in contrast to the implicit assumption that the mean composition of igneous rocks in orogenic area is andesite [Taylor and McLennan, 1995]. The dacitic composition of young upper crust of the Japan Arc is rather similar to the representative models of the upper continental crust and shield [Shaw et al., 1986; Taylor and McLennan, 1985; Wedepohl, 1995] (Table 4). The observed small difference between young and old upper crusts could not be explained by the change in the mode of crust formation [Taylor and McLennan, 1995; Ellam and Hawkesworth, 1988] for the evolution of the Japan Arc.

[19] In a strict sense, the young upper crust of the Japan Arc has distinctly higher Sb and As concentration than the previous models of the upper continental crust mainly based on the Canadian Shield [Shaw et al., 1986; Taylor and McLennan, 1985; Wedepohl, 1995; Barth et al., 2000] (Figure 4a). In addition, the Japan Arc has slightly but distinctively lower concentrations of HFSE, LILE, and LREE than these models. Slightly higher concentrations in mafic elements are observed in the Japan Arc. However, low mafic component in the estimates based on the Canadian Shield were interpreted that these estimated is not representative of the upper crust but the middle crust [Gao et al., 1998].

image

Figure 4. The composition of upper crusts according to previous models normalized to the averaged Japan Arc upper crust. (a) Previous models; upper crust [Taylor and McLennan, 1985; Wedepohl, 1995; Barth et al., 2000] and Canadian Shield [Shaw et al., 1986]. (b) Previous models: the Central East China [Gao et al., 1998] and Post-Archean [Condie, 1993], average values of several time windows of post-Archean age from data. Data are from Table 4

Download figure to PowerPoint

[20] As shown in Figure 4b, the upper crust of the Japan Arc is similar to both of the post-Archean upper crust averaged the data of several time windows reported by Condie [1993] and the Central East China upper crust [Gao et al., 1992, 1998]. The upper crust of the Japan Arc is still depleted in HFSE, LILE, and LREE and enriched in Sb relative to the models of the post-Archean upper crust and the Central East China upper crust.

[21] Incompatible elements depletion is an essential signature of the upper crust of the Japan Arc. Owing to high mafic components and low K2O concentrations, the Central East China upper crust and the Japan Arc upper crust can be regarded as indicative of an undifferentiated crust (Figure 5a). The low concentration of K2O at the same SiO2 level of the upper crusts, however, is inconsistent with a simple differentiation model from a common parental magma (Figure 5b). The concentrations of the LILE, HFSE, and LREE are lower in the Japan Arc than those in old crusts (Figure 5b, 5c, and 5d). The exceptions are represented by some late Miocene high-HFSE volcanic rocks occurring along the coast of the Sea of Japan (Oki, Northern Kyushu, and Astumi in northeast Japan, Figure 5c). These rocks are related to the postrifting volcanism derived from upwelling mantle source connected to the Miocene opening of the back arc basin [Uto et al., 1994].

image

Figure 5. (a) K2O-Cr, (b) K2O-SiO2, (c) K2O-Nb, and (d) Zr/Yb-La/Yb diagrams for the upper crustal rocks of the Japan. The averaged Japan Arc upper crust and previous models are shown as a reference; upper crust [Taylor and McLennan, 1985; Wedepohl, 1995; Barth et al., 2000], Canadian Shield upper crust [Shaw et al., 1986], Post-Archean upper crust [Condie, 1993], the Central East China upper crust [Gao et al., 1998]. The variation lines by typical fractional crystallization from basalt are shown.

Download figure to PowerPoint

[22] The chemical composition of the young upper crust of Japan Arc seems not to have undergone substantial temporal changes because essentially similar patterns of trace elements normalized to primitive mantle are observed in sedimentary rocks of different ages (Figure 6a). This interpretation is supported by the similarity between our estimate based on the average of all samples and the estimate for pre-Neogene or pre-Cretaceous rocks; the range of the difference is less than 25% (Table 4). Although the Neogene-Quaternary igneous rocks have relatively 8% lower SiO2 and 30% higher MgO than pre-Neogene igneous rocks, they still have dacitic compositions (Table 4). Moreover, the averaged pattern of trace elements normalized to primitive mantle for Quaternary acidic volcanic rocks (SiO2≥62%) agrees with those for the average upper crust of the Japan Arc (Figure 6b). This coincidence implies a large scale of chemical homogeneity in the material input from the mantle throughout the time from the Paleozoic to the present. Therefore we interpret that the exposed Japan Arc represents the whole young upper crust of the Japan Arc.

image

Figure 6. Spidergrams (a) for the averaged sedimentary rocks of various ages, and (b) for the averaged Quaternary volcanic rocks. Data are from Table 4. Normalization values of primodial mantle are from [Sun and McDonough, 1989]. The averaged Japan Arc upper crust is shown as a reference.

Download figure to PowerPoint

4.2. Antimony and Arsenic Enrichment in Sedimentary Rocks

[23] The chemical compositions of average sedimentary rocks are remarkably similar to that of igneous rocks (Table 4, Figure 7a). The relative differences in the average compositions are less than 15% for most incompatible trace elements (LILE, REE, and HFSE) between igneous and sedimentary rocks, and those for Cs, Ta, and U are less than 35%. The relative differences for the major, mafic trace elements and Sr are less than 40%. Exceptionally, the average concentrations of Sb and As in the sedimentary rocks are 2–3 times higher than those in the igneous rocks.

image

Figure 7. Comparison of the average composition (a) the igneous to non-accretionary sedimentary rocks, and (b) the accretionary complex plus metamorphic rocks to non-accretionary sedimentary rocks. Data from Table 4 are normalized to that of the averaged upper crust of the Japan Arc.

Download figure to PowerPoint

[24] As shown in Figure 8a for individual rocks, the concentration of As generally increases with the concentration of Sb. Unmetamorphosed sedimentary rocks show distinctly higher Sb and As concentrations than metamorphosed sedimentary rocks and plutonic rocks (Figure 8b, Tables 1 and 3). Moreover, fine-grained sedimentary rocks have generally higher Sb concentrations than coarse sedimentary rocks (Figure 8a). The systematic difference observed among different lithologies suggests that sedimentation processes, such as surface absorption of As [Belzile and Tessier, 1990] result in the high concentration of As and Sb in the sedimentary rocks. Subsequently, scavenging by the low-temperature hydrothermal fluid results in the low concentration of Sb and As in the metamorphosed sedimentary rocks [Bebout et al., 1999]. Furthermore, in spite of relatively high Sb and As concentrations in some volcanic rocks the average igneous rocks the have the comparable values of Sb and As concentrations with other continental crust models (Table 4). All these facts indicate that the high As and Sb values of the average upper crust of the Japan Arc are not due to any kinds of magmatism, which is unique for recent subduction processes, but are instead due to sedimentation processes.

image

Figure 8. (a) Sb-As and (b) Sb-Na2O diagrams for the individual rocks of the upper crustal rocks of the Japan Arc. Data are from Table A1.

Download figure to PowerPoint

4.3. Sedimentary Rocks as Well-Homogenized Igneous Rocks

[25] The large degree of constancy in the concentrations of trace elements in marine sedimentary rocks (Figure 9) indicates a high degree of homogenization of the clastic sediments during subaerial erosion, transportation, submarine sedimentation, and accretion. The restricted values in Th/U ratios and SiO2 in sedimentary rocks, except for local nonmarine sediments (Table A1), indicating that the redistribution of elements during sedimentation is limited. This would be due to short and steep rivers in Japan. Furthermore, sampling effects for sedimentary rocks are small as results of the homogeneity. On the basis the observed constancy of trace element composition in marine sedimentary rocks, the large chemical variability in igneous rocks, and the coincidence of the average compositions between the sedimentary and igneous rocks of the Japan Arc, it is concluded that the marine sedimentary rocks represent well-homogenized igneous rocks.

image

Figure 9. Trace element compositions of the upper crustal rocks of the Japan Arc against Th concentration. Data are from Table A1. The large degree of constancy in the concentrations of trace elements in marine sedimentary rock is observed.

Download figure to PowerPoint

[26] The igneous rock is an important component of the young Japan orogenic upper crust. The characteristics must result from the repetition of fractionated magma supplies to the crust. Most acidic igneous rocks have distinctly lower Cr component and variable Eu negative anomaly, indicating that fractional crystallization from basaltic and/or andesitic magma is dominant in the Japan Arc. As shown in Figure 10, fractional crystallization is also a fundamental process responsible for some high-silica (75–78% SiO2) igneous rocks. The concentrations of Eu, Sr, Ba, Ca, Mg, and Sc decrease, but the concentrations of REE (except Eu), Y, and Nb moderately increase with decreasing Eu concentration in these high-silica igneous rocks. The concentrations of K, Rb, Si, and Zr remain nearly constant. Batch melting and ideal fractional melting cannot explain the extreme depletion in Eu and Sr, but fractional crystallization involving plagioclase, K-feldspar, biotite, quartz, and zircon can.

image

Figure 10. Composition of high silica igneous rocks (SiO2 = 75–78%) with a Eu negative anomaly normalized to the averaged Japan Arc upper crust.

Download figure to PowerPoint

[27] Melting of sedimentary rocks would be only partial and small. Total or substantial partial melting of sedimentary rocks must be excluded, because of the wide compositional variations in igneous rocks contrast to the compositionally uniform sedimentary rocks. The Th concentration in igneous rocks is not higher than that in the average sedimentary rocks (Figure 9). Hence we must exclude the possibility of even small degree of partial melting. Moreover, a small contribution from sedimentary rocks to the igneous rocks would be compatible with the low 87Sr/86Sr and high 143Nd/144Nd ratios obtained for the Cretaceous acidic rock with respect to their host sedimentary rocks [Shibata and Ishihara, 1979; Terakado and Nakamura, 1984]. In conclusion, the possible contribution of sedimentary rocks is restricted to a small degree of assimilation.

[28] Incompatible element depletion characterizes the upper crust of the Japan Arc. The concentrations of the LILE, HFSE, and LREE in the upper crust of the Japan Arc are lower than in old crusts. These geochemical characteristics are the endogenous inheritance of igneous rocks, because of similarities in average compositions among igneous rocks, sedimentary rocks, and the entire upper crust of Japan (Figure 7). The depletion is typical of arc magmatism [Pearce and Cann, 1973] and is common in young orogenic upper crusts. The characteristically low incompatible element content of the Japanese upper arc crust appears inherited from parental magmas derived from a mantle source depleted during a long-term evolution [Togashi et al., 1992].

4.4. Recycling of the Upper Crustal Materials in Accretionary Complex Rocks

[29] The origin of accretionary complex deposits has been interpreted in two major ways: (1) the deposits associated with the volcanic crust are conveyed from pelagic regions and scraped to the continental side [Karig and Sharman, 1975] or (2) they are derived mostly from continental rocks, and oceanic crust derived from pelagic regions have been selectively subducted under a trench [Moore, 1975]. The present data in this study are meant to provide a key to solving the problem.

[30] We evaluated the average abundance of heterogeneous accretionary complex rocks from compositions of constituting rock types in the Japan Arc. The accretionary complex rocks are composed of shales, sandstones, cherts, basalts, limestones, and their mixture (Figure 9). We examined the idea that a small specimen of shale or mixed rock can represent the average composition of a source area several tens of kilometers square as follows.

[31] Samples from Jurassic accretionary complex of the Tamba Belt in the Ayabe district, SW Japan were systematically collected and analyzed (Table 5). The complex is composed of Jurassic matrix sediments with older exotic blocks and slabs and is divided into two suites: Tamba I and Tamba II. The Tamba I suite consists of A-type mixed rock (clasts of sandstone, bedded chert, and siliceous shale embedded in shale matrix) and slabs, which are composed of chert, shale, and sandstone [Kimura et al., 1989]. The Tamba II suite consists of A-type mixed rock, B-type mixed rock (clasts of basalt embedded in shale matrix), and slabs that are composed of sandstone, shale, chert, and basalt [Kimura et al., 1989]. The compositions of each rock type are statistically weighted to calculate the average composition according to their frequency of surface exposure measured on the basis of the 1:50,000 geological map of the Ayabe district [Kimura et al., 1989].

Table 5. Major and Trace Element Abundance of the Jurassic Accretionary Complex Rocks From the Tamba Belt, SW Japan
No.RockArea, %SiO2, %TiO2, %Al2O3, %Fe2O3, %MnO, %MgO, %CaO, %Na2O, %K2O, %P2O5, %Sc, ppmV, ppmCr, ppmCo, ppmNi, ppmCu, ppmZn, ppmRb, ppmSr, ppmY, ppmZr, ppmNb, ppm
  • a

    A-type mixed rock (clasts of sandstone, bedded chert, silliceous shale embedded in dark shale matrix).

  • b

    B-type mixed rock (clasts of basalt volcanoclastic rockembedded in shale matrix).

  • c

    A-type mixed rock in Tamba II suite is not analyzed. For the calculation, 1:1 mixture between shale and sandstone is assumed for A-type mix rock.

Tamba I suite
120A-type mixed rocka6969.210.8016.244.540.082.280.531.984.130.2114.21118616.9363884166762820318
122sandstone561.210.5713.514.670.082.4711.205.140.940.2110.1808810.54066532260211416.8
121shale861.491.0020.836.660.082.650.422.304.330.2519.313394205125113165704127716.5
119chert1899.040.050.470.230.000.010.010.030.140.070.9550.683557362
 
weighted average  73.560.6713.633.940.071.910.961.813.270.1912927214322971130722417014
 
Tamba II suitec
125B-type mixed rockb1.255.001.1816.2410.150.237.695.171.902.300.153016152658.32365817054187281228.4
126sandstone3576.290.3513.032.150.030.900.323.912.970.065.941294.11043788222191697.4
127shale2369.100.7216.904.250.061.570.342.754.160.1511.590605.11423771651443221713.2
124basalt1949.982.4814.6113.090.196.3310.422.550.100.2449.233018360.7651311231343381629.1
123chert2295.780.112.210.780.020.350.020.030.590.092.622182.89613021288272.6
 limestone<1                      
 
weighted average  73.820.8011.904.510.072.052.242.522.170.1215105691524466374184231478
No.RockArea, %Sb, ppmCs, ppmBa, ppmLa, ppmCe, ppmPr, ppmNd, ppmSm, ppmEu, ppmGd, ppmTb, ppmDy, ppmHo, ppmEr, ppmTm, ppmYb, ppmLu, ppmHf, ppmTa, ppmPb, ppmTh, ppmU, ppm
Tamba I suite
120A-type mixed rock691.637.866238.695.79.8033.75.581.165.410.683.050.521.790.322.830.515.561.6828.618.43.6
122sandstone50.760.432521.742.65.4020.64.081.143.760.603.360.592.270.372.460.323.410.4511.86.41.9
121shale81.3811.245642.299.111.4441.27.831.396.621.115.741.013.330.564.540.737.071.3718.114.53.6
119chert180.090.5511.74.80.421.60.340.090.310.060.310.050.170.030.160.030.120.11.60.50.7
 
weighted average  1.276.351031.176.17.927.64.680.974.450.592.730.471.620.282.440.434.571.2921.814.22.8
 
Tamba II suitec
125B-type mixed rock1.20.724.438514.731.43.9715.93.671.243.290.663.730.702.080.322.380.423.130.574.73.50.9
126sandstone350.322.667227.658.16.4722.64.000.993.540.522.620.461.440.241.830.294.870.5619.211.41.8
127shale231.559.558829.255.47.4326.75.101.124.320.684.070.772.470.392.350.366.041.0224.513.83.0
124basalt190.550.1159.123.43.6517.34.811.784.080.955.740.983.130.463.480.594.110.6620.70.2
123chert220.471.41806.113.31.565.91.150.321.090.191.020.180.600.100.570.080.510.154.91.90.8
 
weighted average  0.583.237818.337.94.7117.53.530.963.050.532.990.531.690.261.870.303.910.5612.87.31.4

[32] The spidergram (Figure 11) indicates generally similar patterns for shales, sandstones, mixed rocks (aggregate of hand-specimen size), and, to a minor extent, chert. The observed small but distinctive differences in Th/Sc, Th/U, La/Th, La/Sm, and K/Rb would be due to sedimentary processes. The basalts have a quite different pattern, as they are depleted in incompatible elements and have no negative spike for Ta and Nb, probably because of Hot Spot origin [Tatsumi et al., 2000]. The contribution of basalt, however, to the average composition is small, because the basalts have small volume fractions in accretionary complex and are low in incompatible elements. A small specimen of shale or mixed rock could show a representative pattern of elements of the wide source area despite the apparent heterogeneity in different scale from hand-specimen size to a few tens of kilometers.

image

Figure 11. Spidergrams for the constituent rocks of the Tamba Belt, Jurassic accretionary complex of SW Japan. Data are from Table 5; Normalization values of primodial mantle are from [Sun and McDonough, 1989]. The averaged upper crust of the Japan Arc is shown as a reference.

Download figure to PowerPoint

[33] The Tamba 1 suite is characterized by lower Sr and higher Rb, K, and HFSE concentrations than the Tamba II suite, and this is attributed to the higher contributions of acidic rocks to the Tamba I suite. The average compositions of the Tamba I suite, however, are generally similar to those of the Tamba II suite, and both suites are characterized by low concentration of alkaline, light rare earth, and HFSE (Figure 11). The depletion of HFSE observed in the average compositions of the Tamba Belt is a common phenomenon through out the whole area of SW Japan, which has been reported in sandstones of the Tamba and Maizuru Belts [Musashino, 1992] and in shale and chert of the Cretaceous to Paleogene Shimanto Belts from SW Japan [Yamamoto, 1987].

[34] On an arc-wide scale the average accretionary complex rocks and metamorphic rocks are essentially similar to the average nonaccretionary sedimentary rocks and the average igneous rocks (Figure 7b). They are also similar to the total average of the Japan upper crust, although a small bias is observed toward mafic components (Figure 7b). Our data are compatible with the reported nonpelagic origin of Triassic chert of central Japan [Sugisaki et al., 1982]. The MnO/TiO2 ratio is a useful criterion for discriminating environment of marine sedimentary rocks [Sugisaki et al., 1982]. The MnO/TiO2 ratio of the accretionary complex sedimentary rocks is less than 0.5, distinct from the high ratios (0.5–4) of typical pelagic sediments. These results are compatible with field observation, demonstrating that the average percentage of oceanic plate-derived materials in the Jurassic and Cretaceous accretionary complexes is less than 15 and 1%, respectively [Isozaki et al., 1990]. The predominance of arc-derived rocks in the accretionary sedimentary rocks is consistent with the observation of the recent argillaceous sediments on the continental shelf and slope of trench [Sugisaki, 1978, 1984]. These facts suggest that the chemical contribution of oceanic crust and pelagic sediments to the formation of arc crust by accretion is small.

[35] Recycling of the upper crustal materials during subduction process does not change the bulk upper crustal composition of active continental margin, because accretionary complex rocks and metamorphic rocks are mostly arc-derived rocks. Alternatively, influx of magma could control the composition of the upper crust (Figure 12). The exceptions are the addition of Sb and As from sediments. The episodic rapid uplift and erosion moved the sandstone to accretionary complex from the continental margin [Isozaki et al., 1990; Kimura, 1994; Teraoka and Okumura, 1992]. The conclusion from chemical composition is compatible with the thermochronological model that the formation of accretionary complex rocks was episodic and coincides with the igneous events of the Shimanto Belt [Tagami et al., 1995]. No general temporal chemical changes in the compositions of the magma should result in the observed homogeneity in chemical compositions of the young Japan upper crust.

image

Figure 12. Schematic summary of crustal formation at an active arc. Mode of migration of accretionary complex has been adopted from [Tagami et al., 1995]. A recycling of the upper crustal materials during subduction process does not change the bulk upper crustal composition of active continental margin, because accretionary complex rocks and metamorphic rocks are mostly arc-derived rocks. Alternatively, influx of magma could control the composition of the upper crust. No general temporal chemical changes in the compositions of the magma should result in the observed homogeneity in chemical compositions of the young Japan upper crust.

Download figure to PowerPoint

5. Conclusions

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Geological Setting
  5. 3. Sample Description and Analytical Techniques
  6. 4. Results and Discussion
  7. 5. Conclusions
  8. Appendix A
  9. Acknowledgments
  10. References
  11. Supporting Information

[36] The systematic sampling and chemical analysis for the exposed young orogenic upper crust of the Japan Arc revealed the following characteristics: 1. The elemental abundance indicates that the young upper crust of the Japan Arc has a dacitic composition in contrast to the idea that andesite is predominant in orogenic arcs. The young upper crust of the Japan Arc is rather similar to the representative models of the upper continental crust and shield [Taylor and McLennan, 1985; Wedepohl, 1995; Condie, 1993, Gao et al., 1998]. Temporal changes in the average composition are not significant from the Paleozoic age to the present in the Japan Arc, except for some igneous rocks that occurred in relation to the opening of the back arc basin. The observed small difference in the major element between young and old upper crusts indicates that the essential mechanism of crust formation has not changed. High As and Sb values of the average upper crust of the Japan Arc are not due to any kind of magmatism but instead are due to sedimentation processes. 2. Recycling processes mechanically mix the arc-derived igneous materials to homogenize the chemical composition during erosion, transportation, sedimentation, accretion, and uplifting. The idea is supported by the facts (1) both of the averages of chemical composition for accretionary complex rocks and nonaccretionary sedimentary rocks are similar to the average calculated for igneous rocks on an arc-wide scale, except Sb and As, and (2) the large degree of constancy of trace element composition in marine sedimentary rocks is in contrast to the large variety in igneous rocks. Since the contribution of oceanic crust to the composition of arc crust is small, the recycling processes have not changed the bulk upper crustal composition of the active continental margin except increase the Sb and As from sediments. 3. The concentrations of the LILE, HFSE, and LREE in the upper crust of the Japan Arc are slightly but distinctively lower than in the old crust. These geochemical characteristics are the endogenous inheritance of igneous rocks, because of the similarities in average compositions among igneous rocks, sedimentary rocks, and the entire upper crust of Japan. The igneous rocks are composed of voluminous acidic rocks with subordinate basaltic rocks. Most igneous rocks vary along the typical fractional crystallization processes. The contribution of sedimentary rocks to acidic magmas is small, because the amounts of the mafic component included in high silica (SiO2>75%) rocks are distinctly lower than those estimated contribution of sedimentary rocks. 4. We infer that the characteristics of low concentration of the alkaline, light rare earth, and high field strength elements of the upper arc crust are inherited from a parental magma derived from sub-arc depleted mantle source provenance during a long-term evolution.

Appendix A

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Geological Setting
  5. 3. Sample Description and Analytical Techniques
  6. 4. Results and Discussion
  7. 5. Conclusions
  8. Appendix A
  9. Acknowledgments
  10. References
  11. Supporting Information

[37] A1

Table A1. (Representative Sample). Source Data for Major and Trace Element Abundance of Rocks from the Japan Arc
 GNo.No.Longitude deg.ELatitude deg.NGeological UnitRock NameSiO2TiO2Al2O3Fe2O3MnO
Analytical Method      xxxxx
 
94-111105140.136.1Joso F.nonmarine mudstone67.310.8119.145.550.08
94-19 113140.136.1Joso F.nonmarine sandstone64.210.7616.896.550.11
94-1 95140.135.9Fujishiro F.marine mudstone65.040.7317.606.950.17
94-14 108140.135.9Fujishiro F.marine sandstone70.070.5214.644.970.09
94-15 109140.136.1Kinoshita F.marine sandstone70.210.5612.266.180.13
94-2 96140.136.1Yabu F.marine mudstone69.010.5815.715.280.08
94-3 97140.335.4Otashiro F.marine mudstone66.150.7616.445.960.07
94-16 110140.335.4Otashiro F.marine sandstone71.940.4313.763.590.07
94-20 114140.136.1Yabu F.marine mudstone69.950.6115.474.470.08
 
Average      68.210.6415.775.500.10
Standard deviation      2.650.132.061.060.03
 
94-62100138.737.4Nishiyama F.marine mudstone66.940.6216.236.240.07
94-8 102141.645.3Koetoi F.marine mudstone78.070.5310.924.040.03
94-4 98140.335.4Kiwada F.marine mudstone61.800.6115.396.210.09
94-17 111140.335.4Kiwada F.marine sandstone69.990.4712.705.180.10
94-5 99140.235.2Miura G.marine mudstone63.390.7316.056.340.07
94-18 112140.235.2Miura G.marine sandstone62.880.5217.186.790.06
94-7 101139.037.6Teradomari F.marine mudstone70.210.6016.865.400.03
94-9 103141.645.3Wakkanai F.marine mudstone79.050.5210.714.070.03
93-30 94136.034.0Kumano G.black shale67.400.7716.876.230.11
92-11 47139.035.5Tanzawa G.cordierite spotted hornfels59.220.9320.735.970.16
94-12 106141.645.2Soya F.nonmarine mudstone70.220.8417.064.540.02
91-18 37137.037.0Otogawa F.glauconite sandstone72.830.265.2715.310.21
91-8 27139.740.0Onnagawa F.siliceous mudstone93.440.173.961.530.01
93-1 65139.740.0Onnagawa F.siliceous mudstone96.060.071.790.920.02
93-2 66138.338.0Nakayama F.glauconite mudstone87.030.317.722.760.02
 
Average      73.240.5312.635.430.07
Standard deviation      11.370.255.683.270.06

Acknowledgments

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Geological Setting
  5. 3. Sample Description and Analytical Techniques
  6. 4. Results and Discussion
  7. 5. Conclusions
  8. Appendix A
  9. Acknowledgments
  10. References
  11. Supporting Information

[38] We thank Hubert Staudigel, Scripps Institution of Oceanography University of California, Ryuichi Sugisaki of Meijo University, Graziella Caprarelli of University of Technology, Sydney, Masumi Mikoshiba of Geological Survey of Japan (GSJ), and Shan Gao, China University of Geosciences for their review of early version of this manuscript. We are grateful to Hirohisa Matsuura, Mitsuru Nakagawa, Hajime Kurasawa, Takashi Nakajima, Nobuyuki Tsuchiya, Masumi Mikoshiba, and Hikari Kamioka of the GSJ for providing samples and to Chisayo Matsue for providing the samples registered in the Geological Museum of the GSJ. We acknowledge Hideki Aoyama and Chiaki Tanaka of the GSJ for processing of sample powders.

References

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Geological Setting
  5. 3. Sample Description and Analytical Techniques
  6. 4. Results and Discussion
  7. 5. Conclusions
  8. Appendix A
  9. Acknowledgments
  10. References
  11. Supporting Information
  • Allegre, C. J., S. R. Hart, and J.-F. Minster (1983), Chemical structure and evolution of the mantle and continents determined by inversion of Nd and Sr isotopic data, II, Numerical experiments and discussion, Earth Planet. Sci. Lett., 66, 191213.
  • Ando, A., H. Kamioka, S. Terashima, and S. Itoh (1989) 1988 values for GSJ rock reference samples, “Igneous rock series,”, Geochem. J., 23, 143148.
  • Arculus, R. J., and L. J. Ruff (1990), Genesis of continental crust: evidence from island arcs, granulites and exospheric processes,in Granulite and Crustal Evolution,edited by D. Vielzeuf, and P. Vidal, pp. 723, Kluwer Acad., Norwell, Mass.
  • Armstrong, R. L. (1981), Radiogenic isotopes: The case for crustal recycling on a near-steady-state no-continental-growth Earth, Philos. Trans. R. Soc. London, Ser. A, 301, 443472.
  • Ashi, J., and A. Taira, (1992), Structure of the Nankai accretionary prism as revealed from IZANAGI sidescan imagery and multichannel seismic reflection profiling, Island Arc, 1, 104115.
  • Barth, M. G., W. F. McDonough and, R. L. Rudnick (2000), Tracking the budget of Nb and Ta in the continental crust, Chem. Geol., 165, 197213.
  • Bebout, G. E., J. G. Ryan, W. P. Leeman, and A. E. Bebout (1999), Fractionation of trace elements by subduction-zone metamorphism–Effect of convergent margin thermal evolution, Earth, Planet. Sci. Lett., 171, 6381.
  • Belzile, N., and A. Tessier, (1990), Interactions between arsenic and iron oxyhydroxides in lacustrine sediments, Geochim. Cosmochim. Acta, 54, 103109.
  • Clarke, A. W. (1924), The chemical elements,in The Data of Geochemistry, pp. 944, U.S. Geol. Surv., Washington, D. C.
  • Condie, K. C. (1993), Chemical composition and evolution of the upper continental crust: Contrasting results from surface samples and shales, Chem. Geol., 104, 137.
  • Ellam, R. M., and C. J. Hawkesworth (1988), Is average continental crust generated at subduction zones? Geol., 16, 314317.
  • Finn, C., G. Kimura, and K. Suehiro (1994), Introduction to the special section Northeast Japan: A case history of subduction, J. Geophys. Res., 99, 22,13722,145
  • Gao, S., B.-R. Zhang, T.-C. Luo, Z.-J. Li, Q.-L. Xie, X.-M. Gu, H.-F. Zhang, J.-P. Ouyang, D.-P. Wang, and C.-L. Gao (1992), Chemical composition of the continental crust in the Qinling Orogenic Belt and its adjacent North China and Yangtze cratons, Geochim. Cosmochim. Acta, 56, 39333950.
  • Gao, S., T.-C. Luo, B.-R. Zhang, H.-F. Zhang, Y.-W. Han, Z.-D. Zhao, and Y.-K. Hu (1998), Chemical composition of the continental crust as revealed by studies in East China, Geochim. Cosmochim. Acta, 62, 19591975.
  • Geological Survey of Japan (1992), Geological Map of Japan, 1:1,000,000, 3rd ed., Geol. Surv. of Jpn., Tsukuba.
  • Geological Survey of Japan (1995), Geological Map of Japan, 1:1,000,000, [CD-ROM], 3rd ed. Geol. Surv. of Jpn., Tsukuba.
  • Hildreth, W., and S. Moorbath (1988), Crustal contributions to arc magmatism in the Andes of Central Chile, Contrib. Mineral. Petrol., 98, 455489.
  • Hofmann, A. W. (1988), Chemical differentiation of the Earth: the relationship between mantle, continental crust, and oceanic crust, Earth Planet. Sci. Lett., 90, 297314.
  • Imai, N. (1990), Multielement analysis of rocks with the use of geological certified reference material by inductively coupled plasma mass spectrometry, Anal. Sci., 6, 389395.
  • Imai, N., S. Terashima, S. Itoh, and A. Ando (1996), 1996 compilation of analytical data on nine GSJ geochemical reference samples, “sedimentary rock series,”, Geostand. Newsl., 20, 165216.
  • Isozaki, Y. (1997), Constructing two types of orogen in Permo-Triassic Japan: Accretionary versus collisional, Island Arc, 6, 224.
  • Isozaki, Y., S. Maruyama, and F. Furuoka (1990), Accreted oceanic materials in Japan, Tectonophys., 181, 179205.
  • Kamioka, H., and T. Tanaka (1989), The problems in the analyses of geological materials by INAA—An examination of the analytical results of GSJ rock reference samples, J. Geol. Soc. Jpn., 95(11), 835850.
  • Karig, D. E., and G. F. Sharman (1975), Subduction and accretion in trenches, Geol. Soc. Am. Bull., 86, 377389.
  • Kimura, G. (1994), The latest Cretaceous-early Paleogene rapid growth of accretionary complex and exhumation of high pressure series metamorphic rocks in northwestern Pacific margin, J. Geophys. Res., 99, 22,14722,164.
  • Kimura, G., and K. Tamaki (1986), Collision, rotation and back-arc spreading in the region of the Okhotsk and Japan Seas, Tectonics, 5, 389401.
  • Kimura, K., H. Makimoto, and T. Yoshioka (1989), Geology of the Ayabe District, With Geological Sheet Map at 1:50,000, 104 pp., Geol. Surv. Jpn., Tsukuba.
  • Komatsu, M., Y. Osanai, T. Toyoshima, and S. Miyashita (1989), Evolution of the Hidaka Metamorphic belt, northern Japan, in Evolution of Metamorphic Belts, edited by J. S. Daly, R. A. Cliff, and B. W. D. Yardley, Geol. Soc. Spec. Publ., 43, 487493.
  • Moore, J. C., (1975), Selective subduction, Geology, 530532.
  • Murata, Y., and K. Kano (1995), The areas of the geologic units comprising the Japanese Islands, calculated by using the Geological Map of Japan, 1:1,000,000 [CD-ROM], 3rd ed., Chishitsu News, 493, 2629.
  • Musashino, M. (1992), Chemical composition and sedimentary tectonic setting of sandstones with special reference to incompatible elements, Part 1, A case study of the sandstones from the Tamba Belt, Ultra-Tamba zone and Maizuru Belt, Mem. Geol. Soc. Jpn., 38, 8597.
  • Nakajima, T. (1997), Regional metamorphic belts of the Japanese Islands, Island Arc, 6, 6990.
  • Nesbitt, H. W., and G. M. Young, (1997), Early Proterozoic climates and plate motions inferred from major element chemistry of lutite, Nature, 299, 715717.
  • Okai, T. (1993), Geochemical study of carbonate rocks in Chichibu Belt from Kanto Mountains of Japan, Bull. Geol. Surv. Jpn., 44, 351365.
  • Okuyama-Kusunose, Y. (1999), Contact metamorphism in the aureole around the Tanohata plutonic complex northern Kitakami Massif, Northeast Japan; depth of magma chamber of Cretaceous plutonic rocks, J. Mineral. Petrol. Econ. Geol., 94, 203221.
  • Otofuji, Y., and T. Matsuda, (1984), Timing of rotational motion of Southwest Japan inferred from paleomagnetism, Earth Planet. Sci. Lett., 70, 373382.
  • Pearce, J. A., and J. R. Cann (1973), Tectonic setting of basic volcanic rocks determined using trace element analyses, Earth Planet. Sci. Lett., 19, 290300.
  • Pearcy, L. G., S. M. DeBari, and N. H. Sleep (1990), Mass balance calculations for two sections of island arc crust and implications for the formation of continents, Earth Planet. Sci. Lett., 96, 427442.
  • Rudnick, R. L. (1995), Making continental crust, Nature, 378, 571578.
  • Saito, Y., and M. Hashimoto, (1982), South Kitakami Region: An allochthonous terrane in Japan, J. Geophys. Res., 87, 36913696.
  • Seno, T., and S. Maruyama (1984), Paleogeographic reconstruction and origin of the Philippine Sea, Tectonophysics, 102, 5384.
  • Shaw, D. M., J. J. Cramer, M. D. Higgins, and M. G. Truscott (1986), Composition of the Canadian Precambrian shield and the continental crust of the Earth, in The Nature of the Lower Continental Crust, edited by J. B. Dawson, D. A. Carswell, J. Hall, and K. H. Wedepohl, pp. 275282, Geol. Soc. Publ., London.
  • Shibata, K., and S. Ishihara, (1979), Initial 87Sr/86Sr ratios of plutonic rocks from Japan, Contrib. Mineral. Petrol., 70, 381390.
  • Sibuet, J.-C., J. Letouzey, F. Barbier, J. Charvet, J.-P. Foucher, T. W. C. Hilde, M. Kimura, C. Ling-Yun, B. Marsset, C. Muller, and J.-F. Stephan (1987), Back arc extension in the Okinawa trough, J. Geophys. Res., 92, 14,01414,063.
  • Sugisaki, R. (1978), Chemical composition of argillaceous sediments on the Pacific margin of southwest Japan, Geol. Surv. Jpn., Cruise Rep., 9, 6573.
  • Sugisaki, R. (1984), Relation between chemical composition and sedimentation rate of Pacific ocean-floor sediments deposited since the middle Cretaceous: basic evidence for chemical constraints on depositional environments of ancient sediments, J. Geol., 92, 235259.
  • Sugisaki, R., K. Yamamoto, and M. Adachi, Triassic bedded cherts in central Japan are not pelagic, Nature, 298(5875), 644647.
  • Sumii, T., Y. Watanabe, Y. Suzuki, K. Kodama, and M. Tanahashi (1992), Fuel Resources Map of Japan, in Geological Atlas of Japan, 2nd ed., Geol. Surv. Jpn., Tsukuba.
  • Sun, S.-S., and W. F. McDonough (1989), Chemical and isotopic systematics of oceanic basalts: Implications for mantle composition and processes, in Magmatism in the Ocean Basins, edited by A. D. Saunders, and M. J. Norry, Geol. Soc. Spec. Publ., 42, 313345.
  • Tagami, T., N. Hasebe, and C. Shimada (1995), Episodic exhumation of accretionary complexes: Fission-track thermochronologic evidence from the Shimanto Belt and its vicinities, southwest Japan, Island Arc, 4, 209230.
  • Takahashi, M. (1983), Space-time distribution of Late Mesozoic to Early Cenozoic magmatism in east Asia and its tectonic implications, in Accretion Tectonics in the Circum-Pacific Regions, edited by M. Hashimoto, and S. Uyeda, pp. 6988, Terra Sci., Tokyo.
  • Takahashi, Y. (1993), Al in hornblende as a potential geobarometer for granitoids: A review, Bull. Geol. Surv. Jpn., 44, 597608.
  • Takahashi, Y. (1995), Major element geochemistry and mineral chemistry of granitic rocks in Awaji Island—Implications for the zonal distribution of Cretaceous granitic rocks, Inner Zone of Southwest Japan, Bull. Geol. Surv. Jpn., 46, 2340.
  • Tamaki, K., K. Suyehiro, J. Allan, J. C. Ingel Jr., and K. A. Pisciotto (1992), Tectonic synthesis and implications of Japan Sea ODP drilling, Proc. Ocean Drill. Program, Initial Rep. Leg 125, Sci. Results, 127/128, 13331348.
  • Tanaka, T., H. Kamioka, and K. Yamanaka (1988), A fully automated X-ray counting and data processing system for INAA and analysis of rock reference samples, Bull. Geol. Surv. Jpn., 39, 537557.
  • Tatsumi, Y., T. Kani, H. Ishizuka, S. Maruyama, and Y. Nishimura (2000), Activation of Pacific mantle plumes during the Carboniferous: Evidence from accretionary complexes in southwest Japan, Geology, 28, 580582.
  • Taylor, S. R., and S. M. McLennan (1985), The Continental Crust: Its Composition and Evolution, 312 pp., Blackwell, Oxford, England.
  • Taylor, S. R., and S. M. McLennan (1995), The geochemical evolution of the continental crust, Rev. Geophys., 33, 241265.
  • Terakado, Y., and N. Nakamura (1984), Nd and Sr isotopic variations in acidic rocks from Japan: Significance of upper-mantle heterogeneity, Contrib. Mineral. Petrol., 87, 407417.
  • Teraoka, Y., and K. Okumura (1992), Tectonic division and Cretaceous sandstone composition of the Northern Belt of the Shimanto Terrane, southwest Japan, Mem. Geol. Soc. Jpn., 38, 261270.
  • Togashi, S., and S. Terashima (1997), The behavior of gold in unaltered island arc tholeiitic rocks from Izu-Oshima, Fuji, and Osoreyama volcanic areas, Japan, Geochim. Cosmochim. Acta, 61, 543554.
  • Togashi, S., T. Tanaka, T. Yoshida, K. Ishikawa, A. Fujinawa, and H. Kurasawa (1992), Trace elements and Nd-Sr isotopes of island arc tholeiites from frontal arc of Northeast Japan, Geochem. J., 26, 261277.
  • Tsuchiya, N. (1989), Submarine basalt volcanism of Miocene Aosawa Formation in the Akita-Yamagata oil field basin back-arc region of Northeast Japan, Mem. Geol. Soc. Jpn., 32, 399408.
  • Ujiie, M., and N. Imai (1995), Analysis of rare earth elements in standard samples of granitic rocks by inductively coupled plasma mass spectrometry after acid digestion and alkali fusion, J. Min. Petrol. Econ. Geol., 90, 419427.
  • Uto, K.,, E. Takahashi,, E. Nakamura, and, I. Kaneoka, (1994), Geochronology of alkali volcanism in Oki-Dogo Island, Southwest Japan: Geochemical evolution of basalts related to the opening of the Japan Sea, Geochem. J., 28, 431449.
  • Wedepohl, K. H. (1995), The composition of the continental crust, Geochim. Cosmochim. Acta, 59, 12171232.
  • Yamamoto, K. (1987), Geochemical characteristics and depositional environments of cherts and associated rocks in the Franciscan and Shimanto terranes, Sediment. Geol., 52, 65108.
  • Zhao, D., S. Horiuchi, and A. Hasegawa (1992), Seismic velocity of the crust beneath the Japan islands, Tectonophysics, 212, 289301.

Supporting Information

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Geological Setting
  5. 3. Sample Description and Analytical Techniques
  6. 4. Results and Discussion
  7. 5. Conclusions
  8. Appendix A
  9. Acknowledgments
  10. References
  11. Supporting Information
FilenameFormatSizeDescription
ggge68-sup-0001-tab01.txtplain text document12KTab-delimited Table 1.
ggge68-sup-0002-tab02.txtplain text document2KTab-delimited Table 2.
ggge68-sup-0003-tab03.txtplain text document1KTab-delimited Table 3.
ggge68-sup-0004-tab04.txtplain text document5KTab-delimited Table 4.
ggge68-sup-0005-tab05.txtplain text document4KTab-delimited Table 5.
ggge68-sup-0006-tabaA01.txtplain text document2KTab-delimited Table A1.

Please note: Wiley Blackwell is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.