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Keywords:

  • Gondwana;
  • Pangaea;
  • Permian;
  • Tethys;
  • large igneous province;
  • mass extinction

Abstract

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Background Geology
  5. 3. Methods and Results
  6. 4. Conclusions
  7. Acknowledgments
  8. References
  9. Supporting Information

[1] Voluminous Late Permian flood basalt eruptions are contemporaneous with the mid-Capitanian (260 Ma) and end-Permian (251 Ma) mass extinction events. The Panjal Traps of Kashmir are thought to be correlative to the mid-Capitanian mass extinction however no radiometric age has been determined. We report a single zircon U-Pb laser ablation ICP-MS date of a rhyolite from the lower-middle part of the volcanic sequence. Twenty-four individual zircon crystals yield a mean 206U/238Pb age of 289 ± 3 Ma. The results show that the Panjal Traps are considerably older than previously interpreted and not correlative to post-Neo-Tethys rifting of the Gondwanan margin or the mid-Capitanian mass extinction and are, in fact, correlative to the opening of the Neo-Tethys Ocean. In contrast to other similarly size large igneous provinces, the Panjal Traps are not coincident with a mass extinction event and therefore casts doubt on the direct relationship between continental flood basalt volcanism and ecosystem collapse.

1. Introduction

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Background Geology
  5. 3. Methods and Results
  6. 4. Conclusions
  7. Acknowledgments
  8. References
  9. Supporting Information

[2] Voluminous and rapid outpourings of regionally contiguous flood basalts occur on the order of once every 20 million years since the Mesozoic and are considered to be important contributors to mass extinctions, precursors to continental break-up and the formation of new crust [Coffin and Eldholm, 1994; Ernst et al., 2005; Racki and Wignall, 2005; Campbell, 2007; Bryan and Ernst, 2008]. Spatially and temporally associated volcanic and plutonic rocks covering vast areas of the Earth's crust are referred to as large igneous provinces (LIPs) and, in many cases, are interpreted to represent the physical manifestation of a mantle plume or super plume [Campbell, 2007]. LIPs offer an opportunity to study the complex transfer of mass between the mantle and crust, the petrological evolution of magmatic rocks and also the formation of magmatic ore deposits.

[3] The regular occurrences of LIPs in the geologic record and their probable association with mantle plumes suggest that they are evidence for advective heat transfer during convention of the mantle throughout geological time [Ernst and Buchan, 2003]. It is suggested that there is a correlation between mass extinctions and the formation of LIPs since the Carboniferous [Rampino and Stothers, 1988; Courtillot et al., 1999; Courtillot and Renne, 2003; White and Saunders, 2005; Wignall, 2005] and has led to speculation that there is a, direct or indirect, link between the two. The emission of greenhouse gases (e.g., CO2, SO2, halogens), CO2 degassing from magma-country rock interactions and oceanic anoxia are some of the conditions which LIPs are thought to influence [Wignall, 2001; Racki and Wignall, 2005; Ganino and Arndt, 2009; Wignall et al., 2009]. However, the LIP-mass extinction connection is controversial and not universally accepted [Wignall, 2001, 2005].

[4] The Permian, although relatively short in duration, witnessed many global geological events including the formation of the largest continental LIP (i.e., the Siberian Traps), the most wide-spread mass extinction (∼251 Ma) and possibly the largest supercontinent in Earth history (i.e., Pangaea). Prior to the end-Permian eruption of the Siberian Traps (251 Ma) there are numerous episodes of continental magmatism throughout the Permian including the Emeishan flood basalts (260 Ma), which may have contributed to the mid-Capitanian mass extinction, Central Asian Orogenic Belt (300–250 Ma), Tarim flood basalts (275 Ma), Mino-Tamba flood basalts (280 Ma), Northwest Europe (305–290 Ma) and eastern Australia (305–270 Ma) to list a few [Veevers and Tewari, 1995; Jahn et al., 2000; Zhou et al., 2002; Timmerman, 2004; Menning et al., 2006; Zhang et al., 2010]. The voluminous magmatism that occurred during the Permian is attributed, in some cases, to individual mantle plumes or a super plume [Racki and Wignall, 2005; Isozaki, 2009].

[5] The Panjal Traps represent a well known Permian continental flood basalt province located in the western Himalaya of Kashmir and its origin and age are debated. There are very few studies which have examined the origin of the Panjal Traps but there are none which addressed the eruption age, consequently, they have remained one of the most contested correlations of the Permian [Nakazawa et al., 1975; Veevers and Tewari, 1995; Wignall, 2001; White and Saunders, 2005]. The Panjal Traps are considered to have erupted at anytime from Late Carboniferous to Early Triassic but more recently they are thought to have contributed to the mid-Capitanian (260 Ma) mass extinction and/or related to post-Neo-Tethys magmatism along the northern portion of the Gondwana margin [Wadia, 1961; Pareek, 1976; Veevers and Tewari, 1995; Wignall, 2001; White and Saunders, 2005; Menning et al., 2006; Wopfner and Jin, 2009]. Therefore the age of the Panjal Traps is very important for constraining the geodynamic evolution of Pangaea and its possible contribution to Late Permian ecosystem collapse.

2. Background Geology

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Background Geology
  5. 3. Methods and Results
  6. 4. Conclusions
  7. Acknowledgments
  8. References
  9. Supporting Information

[6] The Panjal Traps are primarily exposed along the Pir Panjal and Zanskar mountain ranges within the state of Jammu and Kashmir, northern India and are continuous into Kashmir of Pakistan (Figure 1). The Traps are predominantly basaltic in composition with minor amounts of felsic volcanic rocks [Ganju, 1944; Bhat and Zainuddin, 1979]. Ultramafic rocks have been reported within the Karakorum Range and tentatively correlated with the Panjal Traps [Rao and Rai, 2007]. The volcanic rocks are interpreted to have erupted after the deposition of the Late to Middle Carboniferous Fenestella Shale but before the deposition of the Late Permian Gangamopteris Beds which contain lower Gondwana flora [Nakazawa et al., 1975; Wopfner and Jin, 2009]. There are suggestions that volcanism continued until the Early Triassic however those rocks are considered to be a separate unit [Nakazawa et al., 1975]. The reported total thickness of the volcanic rocks is between ∼3000 m in the Pir Panjal Range (western Kashmir) to ≤300 m in the Zanskar Range (eastern Kashmir) with individual flows around 30 m [Middlemiss, 1910; Wadia, 1934; Fuchs, 1987; Chauvet et al., 2008; Wopfner and Jin, 2009]. It was therefore suggested that the volcanic centre was probably located in western Kashmir [Nakazawa and Kapoor, 1973]. There is evidence of both subaerial and subaqueous volcanic eruptions as pillow basalts and columnar jointed flows are observed and suggest that the volcanic rocks erupted within a near-shore, transgressive shallow marine environment. The felsic volcanic rocks are comprised of dacites, trachytes, rhyolites and acidic tuffs and are considered to be the differentiation products of the basaltic rocks although, in many cases, they are below the basalts and preliminary isotopic results suggest separate source origins [Ganju, 1944; Nakazawa et al., 1975; Shellnutt et al., 2011].

image

Figure 1. Location map of the Panjal Traps in northern India and Pakistan (modified from Chauvet et al. [2008]).

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[7] The observation that the Panjal Traps erupted before the deposition of the Gangamopteris beds (containing Gangamopteris kasmirensis) was interpreted to constrain their emplacement to Late Carboniferous however, in some localities the traps were underlain by the Gangamopteris beds [Nakazawa and Kapoor, 1973; Nakazawa et al., 1975; Pareek, 1976]. Nakazawa et al. [1975], supported by observations of Wopfner and Jin [2009], suggested that Panjal Traps are constrained to the Early-Middle Permian (Sakmarian-Artinskian) and that the reports of Early Triassic volcanic rocks are incorrect. Complicating the matter further, several papers interpret the Panjal Traps to be Middle to Late Permian and that they possibly contributed to the mid-Capitanian mass extinction at ∼260 Ma [White and Saunders, 2005; Chauvet et al., 2008]. Other tectonic models suggest the Panjal Traps are correlative to Permian volcanic rocks within the Himalaya which may or may not have been related to the opening of the Neo-Tethys Ocean [Bhat et al., 1981; Bhat, 1984; Veevers and Tewari, 1995; Garzanti et al., 1999; Zhu et al., 2010]. Veevers and Tewari [1995] suggest the Panjal Traps are related to Late Permian (∼250 Ma) magmatism along the Gondwana margin after the opening of the Neo-Tethys whereas Zhu et al. [2010] suggest they were part of a larger volcanic belt which includes the Bhote Kosi basalts and Abor volcanic rocks of India and the Jilong Formation and Selong Group basalts of Tibet and related to the Early Permian rifting of the Neo-Tethys.

[8] The current exposed area of the Panjal Traps is ∼0.01 × 106 km2 however the original total extent of the volcanic rocks is unknown as the region was deformed during the Indo-Eurasian collision [Wignall, 2001]. Ernst and Buchan [2001] estimated the total area of Panjal Traps and other related Permian volcanic rocks of the Himalaya to be ∼0.2 × 106 km2. If the estimate is correct, then Panjal-related magmatism is similar in size to the Emeishan large igneous province (ELIP) of southwestern China and the Columbia River basalts of the northwestern United States.

3. Methods and Results

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Background Geology
  5. 3. Methods and Results
  6. 4. Conclusions
  7. Acknowledgments
  8. References
  9. Supporting Information

[9] Zircons were separated from one rhyolite sample (PJ1-044) collected from the lower-middle flows of the Panjal Traps at 34°02′34.8″N, 74°53′01.6″E. The separated zircons were mounted in epoxy and photographed in backscattered and cathodoluminescence imagery. Some of the zircon crystals are euhedral with oscillary zonation typical of an igneous origin although there are many which are either anhedral or fragmented. The cores of the zircons are commonly darker than the rims giving an appearance of a relic core and younger rim (Figure 2). Zircon U-Pb isotopic analyses were performed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at National Taiwan University in Taipei. The full set-up and methods are described by Chiu et al. [2009]. The laser ablation was preformed using a He gas carrier to improve material transport efficiency. Standard blanks were measured for ∼1 minute and calibration was performed using GJ-1 zircon standard, Harvard reference zircon 91500 and Australian Mud Tank carbonitite zircon. Data processing was completed using GLITTER 4.0 for the U-Th-Pb isotope ratios and common lead. Isoplot v. 3.0 was used to plot the Concordia diagram and to calculate the weighted mean U-Pb age [Ludwig, 2003]. Analyses of twenty four individual zircon crystals form a single concordant age group and yield a mean 206U/238Pb age of 289 ± 3 Ma with a mean square of weighted deviates (MSWD) of 0.75 (Table 1 and Figure 3).

image

Figure 2. Cathodoluminescence photomicrograph of zircons from PJ1-044 showing the individual zircon age and spot location (white circle).

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image

Figure 3. Concordia plot of the LA-ICP-MS zircon U-Pb dating results for PJ01-044.

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Table 1. Zircon LA-ICP-MS 206U/238Pb Age Results for a Rhyolite (PJ1-044) From the Panjal Trapsa
PointAge (Ma)
206Pb/238U1σ207Pb/235U1σ206Pb/238U1σ
  • a

    Standard blanks were measured for ∼1 minute and calibration was performed using GJ-1 zircon standard, Harvard reference zircon 91500 and Australian Mud Tank carbonitite zircon. Data processing was completed using GLITTER 4.0 for the U-Th-Pb isotope ratios and common lead. Isoplot v. 3.0 was used to plot the Concordia diagram and to calculate the weighted mean U-Pb age.

PJ1R-01285±60.300630.011430.045270.00098
PJ1R-02286±60.336590.011190.045440.00101
PJ1R-03291±60.319140.011800.046120.00100
PJ1R-04275±60.349640.011960.043540.00092
PJ1R-05293±70.346950.013570.046480.00107
PJ1R-06283±60.343030.011580.044910.00094
PJ1R-07299±60.371030.010590.04740.00101
PJ1R-08291±60.385260.012650.046120.00104
PJ1R-09293±70.341680.013760.046570.00108
PJ1R-10289±60.333320.009800.045860.00099
PJ1R-11289±60.325810.009880.045780.00098
PJ1R-12282±60.332230.010770.044670.00099
PJ1R-13291±60.290890.009690.046120.00099
PJ1R-14289±60.339820.009920.045830.00098
PJ1R-15284±60.337200.010290.045030.00097
PJ1R-16288±60.334020.009440.045740.00098
PJ1R-17297±70.357330.011960.047220.00109
PJ1R-18290±60.323510.010210.045970.00099
PJ1R-19284±60.319500.008870.045050.00096
PJ1R-20292±80.309720.016440.046360.00122
PJ1R-21293±60.340550.015510.046520.00103
PJ1R-22292±60.328470.009820.046280.00102
PJ1R-23296±60.337240.009570.046960.00101
PJ1R-24289±60.322870.011700.045920.00104

4. Conclusions

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Background Geology
  5. 3. Methods and Results
  6. 4. Conclusions
  7. Acknowledgments
  8. References
  9. Supporting Information

[10] The 289 ± 3 Ma age from sample PJ1-044 is the first radiometric age date reported for rocks from the Panjal Traps and has significant implications on the geodynamic development of the Neo-Tethys and the correlations with other volcanic rocks in the Himalaya. Firstly, the age is somewhat similar to Carboniferous-Permian magmatic rocks such as the Malakand (294 Ma), Ambela (297 ± 4 Ma) and Yunam (284 ± 1 Ma) granitoids of the Himalaya [Spring et al., 1993]. Further to the east, Zhu et al. [2010] suggested that the Jilong Formation and the Selong Group basalts in Tibet may be an extension of the Panjal Traps. However, whole rock elemental and isotopic data from the Panjal Traps at Guryal Ravine and Pahalgam in Kashmir are different from the Jilong and Selong basalts and, although they may be contemporaneous, their petrogenetic relationship is yet to be established [Shellnutt et al., 2011].

[11] Secondly, the Panjal Traps cannot be related to the Late Permian (∼250 Ma) post Neo-Tethys rifting of Gondwana [Veevers and Tewari, 1995] and are likely related to the initial opening of the Neo-Tethys Ocean during the Early Permian (Figure 4). Furthermore the interpretation that rifting of the Neo-Tethys began in eastern Gondwana and propagated westward seems unlikely as the Panjal Traps are contemporaneous with rhyodacitic tuffs from eastern Australia [Veevers and Tewari, 1995]. The Panjal Traps could, in fact, be the initial rift zone which propagated linearly eastward and northward and led to the separation of Cimmeria from Gondwana [Metcalfe, 2006]. It is likely that the Early Permian (>270 Ma) rocks in the Himalaya are related to each other in the sense that they are part of a contemporaneous regional tectonic rifting regime which developed over the course of 20 Ma or so along the Tethyan margin of Gondwana but not necessarily petrogenetically related.

image

Figure 4. Paleogeographic reconstructions of Pangaea. (a) ∼290 million years showing the location of the Panjal Traps (PT) and possible rift propagation (red) and (b) after the rifting of Cimmeria from the northern margin of Gondwana (modified from Metcalfe [2006]). North China (NC), South China (SC), Indo-China (IC), western Cimmeria (WC), Lhasa terrane (L), Qiangtang terrane (QI), Sibumasu (S).

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[12] Thirdly, the Panjal Traps are not Middle-Late Permian and therefore could not be a factor in the mid-Capitanian or end-Permian mass extinctions because most continental flood basalt eruptions last ≤10 Ma [White and Saunders, 2005; Bryan and Ernst, 2008]. The absence of a recorded mass extinction [Raup and Sepkoski, 1982] during the Early Permian and the fact that the estimated original area (i.e., ∼0.2 × 106 km2) of Panjal-related magmatism is similar to the ELIP (i.e., ∼0.3 × 106 km2) suggests that either LIPs do not necessarily contribute to mass extinctions or that LIPs must be of a minimum size in order to adversely affect a thriving ecosystem. Considering the Ethiopian flood basalts (i.e., 0.5 × 106 km2) have a larger area than the ELIP and that there was no corresponding mass extinction, coupled with the absence of a mass extinction synchronous with the Panjal Traps, it seems that flood basalt eruptions, strictly speaking, do not directly cause ecosystem collapse but rather some other indirect mechanism or mechanisms (e.g., country rock degassing, bolide impact) are required [Wignall, 2001, 2005; Racki and Wignall, 2005; Ganino and Arndt, 2009; Wignall et al., 2009].

Acknowledgments

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Background Geology
  5. 3. Methods and Results
  6. 4. Conclusions
  7. Acknowledgments
  8. References
  9. Supporting Information

[13] This paper benefitted from the constructive comments of two anonymous reviewers and Michael Wysession. The authors would like to thank Ghulam-ud-Din Bhat and G.M. Zaki for their field assistance and Sun-Lin Chung and Emily Lin for their assistance with laboratory work at National Taiwan University.

[14] The Editor thanks Jason Ali and Michael Rampino for their assistance in evaluating this paper.

References

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Background Geology
  5. 3. Methods and Results
  6. 4. Conclusions
  7. Acknowledgments
  8. References
  9. Supporting Information

Supporting Information

  1. Top of page
  2. Abstract
  3. 1. Introduction
  4. 2. Background Geology
  5. 3. Methods and Results
  6. 4. Conclusions
  7. Acknowledgments
  8. References
  9. Supporting Information
FilenameFormatSizeDescription
grl28516-sup-0001-t01.txtplain text document2KTab-delimited Table 1.

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