Spatiotemporal Variation of the Cretaceous‐Eocene Arc Magmatism in Lhasa‐Tengchong Terrane

It was recognized that two magmatic belts in the Lhasa‐Tengchong terrane formed due to the Mesozoic‐Cenozoic Tethyan evolution. Still, their spatiotemporal variations of magmatic flare‐ups/lulls are rarely discussed. Here we use the new U‐Pb and Lu‐Hf isotopic data of captured zircons and a comprehensive data set to show that the flare‐up of northern magmatic belt has peak ages of 110 Ma in central and northern Lhasa and 120 Ma in eastern Tengchong, possibly related to the tectonic transition from Meso‐ and Neo‐Tethyan double subduction to Neo‐Tethyan single subduction. For the southern magmatic belt, the flare‐ups at 100–85 Ma and 65–45 Ma in eastern southern Lhasa indicate obvious juvenile crustal growth, while flare‐ups at 75–45 Ma in western southern Lhasa and Tengchong record ancient crustal reworking. Such flare‐up variations in the southern magmatic belt possibly resulted from asynchronous changes in the Neo‐Tethyan slab dip.


Introduction
The Lhasa terrane, located in the southern Himalaya-Tibetan orogen, preserves widespread magmatic rocks formed due to Tethyan evolution (Chapman & Kapp, 2017;Kapp & DeCelles, 2019;D.-C. Zhu et al., 2011).Generally, two parallel magmatic belts, the Gangdese belt in the southern Lhasa (SLhasa) and the northern belt in the central and northern Lhasa (CNLhasa), have been previously considered (Lin et al., 2019;D.-C. Zhu et al., 2011).The northern belt is mainly occupied by the early Cretaceous magmatic rocks, whose origins have been variously assigned to flat subduction of the Neo-Tethys, the Meso-Tethyan southward subduction, or syncollision to post-collision processes between the Lhasa and Qiangtang terranes (Hu et al., 2022;Z.-M. Zhang et al., 2021;D.-C. Zhu et al., 2016).On the other hand, the Gangdese continental arc magmatism associated with the Neo-Tethyan subduction, whose origin is not debated, is characterized by flare-ups at 100-85 Ma and 65-45 Ma (Chapman & Kapp, 2017;X. Ma et al., 2022;D.-C. Zhu et al., 2023).During magmatic flare-ups, a major juvenile crust grew through basaltic underplating, fractional crystallization, accumulation, and its remelting under the Gangdese arc (Lu et al., 2022;D. C. Zhu et al., 2022;D.-C. Zhu et al., 2023).However, the causes of the magmatic flare-ups remain controversial, with speculations including slab rollback or subduction of the midoceanic ridge for flare-up at 100-85 Ma and slab rollback or break-off during India-Asia collision for flare-up at 65-45 Ma (X.Ma et al., 2022;X. Zhang et al., 2019;D.-C. Zhu et al., 2023).Recently, the magmatic flareups and derivation from depleted mantle or juvenile crust in the West Burma and Sumatra are considered to resemble those in Gangdese and therefore a 6,000 km Neo-Tethyan continental arc was proposed to align from Gangdese through West Burma to Sumatra and to have concurrent magmatic flare-ups/lulls and juvenile crustal growth related to synchronous changes of the Neo-Tethyan slab dip (X.Zhang et al., 2019).
The Tengchong terrane (TCT), the southeastern extension of the Lhasa terrane, is predominantly occupied by magmatic rocks (Xie et al., 2016;Yang et al., 2012).Except for minor early Paleozoic and Triassic-Jurassic magmatic rocks, the primary magmatism is indicated by flare-ups at 131-111 Ma, 76-64 Ma, and 55-49 Ma (R.-Z. Zhu et al., 2022).The early Cretaceous magmatic rocks in eastern TCT resemble those in the CNLhasa, which when taken together suggest a united northern magmatic belt (Lin et al., 2019).Different from the CNLhasa, the early Cretaceous magmatism in TCT is probably related to the post-collisional process and/or subduction of the Neo-Tethys since detritus provenance revealed closure of Meso-Tethys between the TCT and Baoshan terrane occurred at the late Jurassic-early Cretaceous (J.Zhang et al., 2021Zhang et al., , 2022)).Additionally, although subduction of the Neo-Tethys causes the united southern magmatic belt from Gangdese to western TCT with extensive the late Cretaceous-Eocene magmatism, the arc magmatic flare-ups at 76-64 Ma and 55-49 Ma in western TCT are different from those in Gangdese (Lin et al., 2019;R.-Z. Zhu et al., 2022;D.-C. Zhu et al., 2023).Overall, no matter in the northern or southern magmatic belt of the Lhasa-Tengchong terrane, the magmatism seems to be diverse between Lhasa and Tengchong.
The temporal distribution of magmatic activities has commonly been recorded by zircon ages, which are generally separated from exposed igneous rocks or sediments (Paterson & Ducea, 2015).Recently, captured xenocryst zircons from volcanics have also been employed to reveal magmatic activities that predated the volcanic eruption (Attia et al., 2020;D. Liu et al., 2014).These age records from crystalized zircons from magmatic intrusions, detrital zircons from erosion of magmatic rocks, and captured zircons carried by volcanic eruption can be complementary and give the same general age patterns in previous studies of Gangdese and Cordillera arc (Attia et al., 2020;D. Liu et al., 2014;Paterson & Ducea, 2015;D.-C. Zhu et al., 2023).Therefore, integrating multiple records can enhance our understanding of the temporal and spatial distribution of magmatism.The temporal and spatial framework of magmatism in TCT revealed by exposed rocks needs to be improved because abundant vegetation cover may conceal some critical magmatic records.Uniquely, the complementary age records for exposed rocks can be obtained from captured zircons of the late Cenozoic widespread mantle-derived volcanics in TCT (Guo et al., 2015).Therefore, studying the captured zircons separated from Tengchong volcanics can improve our perception of magmatic distribution in TCT to probe temporal and spatial variations in magmatism on the Lhasa-Tengchong terrane.In this study, we conducted systematic U-Pb and Lu-Hf isotopic analyses on captured zircons from the Tengchong late Cenozoic mantle-derived volcanics.By comparing our results with regional data, we depict the distribution, flare-ups, and source properties of the Cretaceous-Eocene magmatism on the Lhasa-Tengchong terrane.Importantly, we demonstrate spatiotemporal variation of the magmatic flare-ups/ lulls and sources in the Neo-Tethyan continental arc and suggest that such variations are possibly related to asynchronous changes in slab subduction dynamics.

Geological Background and Samples
The Lhasa-Tengchong terrane is bounded by the Indus-Yarlung and Myitkyina (MS) suture zones to the south and west, respectively, and the Bangong-Nujiang suture zone (BNS) to the north or east (Figure 1).The Lhasa terrane features an ancient basement for the central Lhasa and a younger and juvenile crust for the southern and northern Lhasa (D.-C.Zhu et al., 2011).The early Cretaceous magmatic rocks in CNLhasa extend southeast into Eastern TCT, while the late Cretaceous-Eocene magmatism is mainly concentrated on the SLhasa-Western TCT (Lin et al., 2019;Xie et al., 2016;D.-C. Zhu et al., 2011).The TCT can be divided into Eastern and Western TCT by the Gudong-Tengchong fault (Figure 2a).The TCT is dominated by the Gaoligong Group, Cretaceous-early Eocene granitic rocks, and late Cenozoic volcanics, with minor Paleozoic and late Cenozoic sediments but lacking Triassic-Oligoene sedimentary strata (BGMRYP, 1990;Xie et al., 2016).The Gaoligong Group is considered as the Meso-to Neo-Proterozoic metamorphic basement (BGMRYP, 1990).In addition, minor early Paleozoic and Triassic-Jurassic intrusive rocks are sporadically distributed in TCT (Xie et al., 2016).As mentioned before, three magmatic flare-ups were identified in the TCT at 131-111 Ma, 76-64 Ma, and 55-49 Ma (R.-Z. Zhu et al., 2022).Late Cenozoic volcanics comprise basic-intermediate-felsic rock assemblages (BGMRYP, 1990), the eruption age of which range from 8 Ma to present (Guo et al., 2015).They unconformably overlie the Gaoligong group, Paleozoic sedimentary rocks and Mesozoic-Cenozoic granitoids (BGMRYP, 1990;Guo et al., 2015).Minor felsic enclaves are also present in some dacites (Figure S1 in Supporting Information S1).Fourteen volcanic samples were collected from the Eastern Tengchong, and 10 from the Western Tengchong (Figure 2a).These volcanic samples comprise 19 basalts, 3 basaltic andesites, and 2 dacites.Representative photographs and sample description of Tengchong volcanic rocks are provided in Supporting Information S1.

Methods
The cathodoluminescence (CL) images were obtained at the Institute of Tibetan Plateau Research, Chinese Academy of Sciences (ITPCAS).The CL images are presented in Figure S2 in Supporting Information S1.Zircon U-Pb dating was executed by laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) and dated zircons were selected for LA-MC (muti-collector)-ICPMS Lu-Hf isotopic analysis at ITPCAS.Detailed analytical methods see Supporting Information S1.
To comprehensively investigate the spatial and temporal distribution of magmatic rocks from Lhasa to Lohit and Tengchong, we integrated U-Pb age and Hf-Nd isotopic data along with geographical coordinates to assemble a data set encompassing 4,150 Mesozoic-Cenozoic magmatic rocks in the Lhasa-Lohit-Tengchong terrane (Table S3, https://doi.org/10.6084/m9.figshare.24464134).This compilation incorporated recent data compilation by Chapman and Kapp (2017) and D.-C.Zhu et al. (2023), in addition to published Tengchong and Lohit data.We also collected magmatic zircon Lu-Hf isotopic data from the terrane (Table S4, https://doi.org/10.6084/m9.figshare.24464134).In the Lhasa-Tengchong terrane, five magmatic domains are identified within the Lhasa-Tengchong terrane according to their ages, locations, and Hf isotope compositions (Figure 1).Detailed methods see Supporting Information S1.

Ages of Tengchong Captured Zircon
In total, a total of 1,432 zircons from 19 basalts, 3 basaltic andesites, and 2 dacites were analyzed for U-Pb age.Zircons with analysis errors over 4% were filtered out.Zircons with discordance over 10% were rejected, which was calculated based on 206 Pb/ 238 U and 207 Pb/ 206 Pb ages for older than 1000 Ma and 206 Pb/ 238 U and 207 Pb/ 235 U ages for younger than 1000 Ma, separately.Finally, 952 U-Pb ages were used in this study (Table S1, https://doi.S3, https://doi.org/10.6084/m9.figshare.24464134were selected to map in this study.The whole rock ε Hf (t) values were calculated from whole rock ε Nd (t) values, employing the terrestrial array developed by Vervoort et al. (1999) in cases where zircon ε Hf (t) data was unavailable for these rocks.Magmatic rocks are represented by color-coded circles based on their ages from 150 to 40 Ma.Abbreviations: BNS, Bangong-Nujiang suture; IYS, Indus-Yarlung suture; MS, Myitkyina suture; IBS, Indo-Burma suture; SLhasa, the southern Lhasa terrane; CNLhasa, the central and northern Lhasa terrane; WB, the West Burma terrane; TC, the Tengchong terrane; BS, the Baoshan terrane; SGF, Sagaing fault; RRF, Red River fault.org/10.6084/m9.figshare.24464134).Zircons from the Eastern and Western TCT yield U-Pb ages ranging from 3130 Ma to 7.5 Ma and 3232 Ma to 3.9 Ma, separately.Almost of zircons are igneous origins, featuring Th/U values ranging from 0.11 to 4.04 and showing oscillatory zoning in CL images (Figure S2 in Supporting Information S1).Most of zircons having morphology in CL images resemble those from granitic rocks (Corfu et al., 2003).For Eastern TCT, ∼87% concordant zircons are younger than 250 Ma.Two dominant age populations are identified at 140-110 Ma and 75-45 Ma, with a subordinate one at 240-200 Ma and 40-20 Ma (Figure 2c).For Western TCT, ∼59% concordant zircons are younger than 250 Ma.And a dominant age population at 75-45 Ma was observed, with a subordinate age population at 170-150 Ma (Figure 2d).Considering the absence of the Triassic-Oligocene strata in TCT, the Mesozoic-Eocene zircons in these Miocene-Holocene mafic volcanics should be caught/captured from the underlying magmatic rocks.Predictably, most of these age groups of the captured zircons in this study coincide with the age populations of bedrocks in TCT, including 240-200 Ma, 140-110 Ma, and 75-45 Ma (Figure 2e).Additionally, our results reveal two age groups at 170-150 Ma and 40-20 Ma, which are not recognized in currently exposed rocks (Figure 2e).Another significant finding revealed by captured zircons is that magmatic event at 75-45 Ma is widespread in both Eastern and Western TCT, while such a phase of bedrocks is only exposed in Western TCT.

Lu-Hf Isotope Compositions of Tengchong Captured Zircon
A total of 585 representative zircons were analyzed for Lu-Hf isotopic compositions.Compared to the exposed bedrocks in TCT, the 140-110 Ma pulse displays a broader range of ε Hf (t) values, ranging from 35.6 to +7.7 (Table S2, https://doi.org/10.6084/m9.figshare.24464134),and part have markedly lower ε Hf (t) values (Figure 2b).Conversely, the majority of the 75-45 Ma zircons contain similar ε Hf (t) compositions to those of rocks except a minor having lower ε Hf (t) values (Figure 2b).Another feature is that, except for the 75-45 Ma zircons in the western Tengchong showing elevated ε Hf (t) values above zero, all other episodes are dominated by enriched isotopic compositions with ε Hf (t) values below zero (Figure 2b).Most of captured zircons have Mesoproterozoic-Mesoarchean T DM C (Table S2, https://doi.org/10.6084/m9.figshare.24464134),which imply that their primary magmas were derived from the partial melting of the ancient crust components.
Although the subordinate Triassic age population was identified by captured zircons, these magmatic activities are not predominant in the Lhasa-Tengchong terrane (D.-C.Zhu et al., 2023).And discussion of that beyond the topic of this study thus we have not further discussed in later sections.

The Northern Magmatic Belt
Magmatism in CNLhasa continued from the middle Jurassic to the late Cretaceous, and magmatic flare-up occurred in the early Cretaceous (Figure 3a).Although the middle-late Jurassic magmatic rocks are rarely exposed in the TCT, our captured zircons data indicated a minor age population of 170-150 Ma (Figure 2d).The early Cretaceous magmatic flareup in Eastern TCT is simultaneous with CNLhasa (Figure 3a), which collectively form the northern magmatic belt in the Lhasa-Tengchong terrane (Figure 1).For the northern magmatic belt, the peak age (∼120 Ma) of magmatic flare-up in TCT is slightly older than that (∼110 Ma) in CNLhasa (Figure 3a).Despite some zircon ε Hf (t) values are up to +10, the averaged zircon ε Hf (t) values lower than 5 suggest that most of their primary magmas in which these zircons were crystalized were derived from the partial melting of the ancient crust (Figure 3a) (Y.Chen et al., 2014;P.-F. Ma et al., 2021;R.-Z. Zhu et al., 2020).Minor zircons having positive ε Hf (t) values can be from those scarce mafic rocks or enclaves in the early Cretaceous felsic rocks in the Lhasa-Tengchong terrane (S.-S.Chen et al., 2017;D.-C. Zhu et al., 2016;R.-Z. Zhu et al., 2020).

The Southern Magmatic Belt
The late Cretaceous-Eocene magmatic rocks widely distributed in the SLhasa and TCT compose the southern magmatic belt (Figure 1), which has been divided into the Western SLhasa, Eastern SLhasa, and TCT segments according to their Hf isotopic compositions.The most striking feature of the southern magmatic belt is that magmatic flare-ups and sources varied between these segments (Figure 3b).The results from bedrock illustrate magmatic flare-ups at 100-85 Ma and 65-45 Ma in Eastern SLhasa (Figure 3b).For TCT, the exposed rocks reveal magmatic flare-ups at 75-60 Ma and 55-45 Ma only in Western TCT, but our captured zircons show a universal flare-up at 75-45 Ma in Western and Eastern TCT (Figures 2c-2e and 3b).For Western SLhasa, magmatic rocks exhibit flare-ups at 75-60 Ma and 55-45 Ma, which are identical to those in TCT instead of Eastern SLhasa (Figure 3b).In summary, the southern magmatic belt is characterized by flare-ups at 100-85 Ma and 65-45 Ma in Eastern SLhasa and at 75-45 Ma in Western SLhasa and TCT segments.
In addition, the highly positive zircon ε Hf (t) values are only present in Eastern SLhasa, which are in contrast to dominantly negative values in Western SLhasa and TCT (Figure 3b).Detailed petrological and geochemical evidence indicate the juvenile crustal growth in Eastern SLhasa at 100-85 Ma and 65-45 Ma (D. C. Zhu et al., 2022;D.-C. Zhu et al., 2023).However, such an obvious crustal growth has not been observed in Western SLhasa and TCT (Figures 1 and 3b), which were occupied by significant reworking of the ancient crust at 75-  S3 and S4, https://doi.org/10.6084/m9.figshare.24464134.45 Ma and characterized by high-K calc-alkaline felsic rocks with dominantly negative zircon ε Hf (t) values (J.Liu et al., 2019;Zhao et al., 2017;R.-Z. Zhu et al., 2022).Two separate seismic profiles also demonstrate different crustal properties with the juvenile crust beneath Eastern SLhasa and ancient crystalline basement under Western SLhasa (Lu et al., 2022;Nábělek et al., 2009).Nevertheless, a few reworking of the ancient crust also happened at some areas of Eastern SLhasa (Ji et al., 2017;D.-C. Zhu et al., 2023).On the other hand, despite reworking of ancient crust dominated the magmatism in Western SLhasa and TCT during 75-45 Ma, the elevated ε Hf (t) values during 60-50 Ma imply an enhanced contribution from depleted mantle melts (Figure 3b) (Y.Wang et al., 2014;Xie et al., 2016).

Early Cretaceous Tectonic Transition From Double Subduction to Single Subduction
Bidirectional subduction of Meso-Tethys during the Jurassic period is supported by recent studies on ophiolite in BNS, arc magmatism, and sedimentary records in CNLhasa and southern Qiangtang terrane (Cao et al., 2016;Li et al., 2019;Tang et al., 2020;D.-C. Zhu et al., 2016).Since the earliest early Cretaceous, collision between the Lhasa-Tengchong terrane and Qiangtang-Baoshan terrane was diachronous, occurring in Tengchong at the early Cretaceous and later in westernmost Lhasa at the late Cretaceous (Fan et al., 2017;K.-J. Zhang et al., 2014;J. Zhang et al., 2021).Meanwhile, the Neo-Tethys was still subducting under the Lhasa-Tengchong terrane (Figure 4a) (Kapp & DeCelles, 2019;J. Zhang et al., 2022).Previous researchers attributed the early Cretaceous magmatism in the northern magmatic belt to (a) the Neo-Tethyan flat-slab subduction (Ding et al., 2003;Z.-M. Zhang et al., 2021), or (b) the results of the Meso-Tethyan evolution: southward subduction of Meso-Tethys, or syn-and post-collisional magmatism after the closure of Meso-Tethys (Kapp & DeCelles, 2019;D.-C. Zhu et al., 2011).During magmatic lull in Gangdese at 150-120 Ma, the formation of Xigaze forearc basin suggests steep subduction of the Neo-Tethys (Dai et al., 2013;Maffione et al., 2015).So, the 150-120 Ma arc magmatism in the northern magmatic belt was probably triggered by southward subduction of Meso-Tethys rather than flat-slab subduction of the Neo-Tethys (Kapp & DeCelles, 2019;D.-C. Zhu et al., 2016).The northern magmatic belt exhibits different age peaks, with 120 Ma in Eastern Tengchong and 110 Ma in CNLhasa (Figure 3a), which is probably related to the diachronous collision between the Lhasa-Tengchong terrane and the Qiangtang-Baoshan terrane.In addition, the dramatically increasing Mg# and ε Hf (t) values since 120 Ma are probably related to post-collision processes during the Meso-Tethyan evolution (Kapp & DeCelles, 2019;R.-Z. Zhu et al., 2022).With the foundering of the Meso-Tethys, the Neo-Tethyan northward subduction exerts the first-order control on the Lhasa-Tengchong evolution.Based on a magmatic lull at 120-110 Ma in Gangdese-Western TCT, extensional magmatism in CNLhasa, and development of 120 Ma arc-back-arc magmatism in Eastern TCT (Hu et al., 2022;Z.-M. Zhang et al., 2021;J. Zhang et al., 2022), we reasonably propose that the combination of flat subduction of Neo-Tethys and post-collisional extension in BNS cause magmatic flare-up in the northern magmatic belt during the early Cretaceous tectonic transition from double subduction to single subduction (Figure 4a).

Spatiotemporal Variations in the Neo-Tethyan Slab Subduction Drive Arc Flare-Ups
The southern magmatic belt shows spatiotemporal variations in flare-ups and lulls (Figure 3b).Although the causes of episodic arc magmatism remain controversial, one of the most famous hypotheses developed from Cordilleran arc of western North America is that episodic retro-arc lithosphere underthrusting into magmatic source (Chapman et al., 2021;DeCelles et al., 2009;Paterson & Ducea, 2015).Retro-arc lithosphere underthrusting would make isotopic pull-down during magmatic flare-ups, which fail to explain the Neo-Tethyan continental arc episodic magmatism owing to no significant change of averaged zircon ε Hf (t) values during magmatic flare-ups and lulls (Figure 3b).Flare-up at 100-85 Ma in Eastern SLhasa is contributed to rollback of the Neo-Tethyan slab or subduction of the Neo-Tethyan mid-oceanic ridge (L.Ma et al., 2015;Z. Zhang et al., 2010;X. Zhang et al., 2019).However, 100-85 Ma magmatic lulls in Western SLhasa and TCT cannot be explained by subduction of mid-oceanic ridge, either parallel to or oblique to the trench direction.Therefore, dominant mafic rocks and highly positive ε Hf (t) values in 100-85 Ma magmatic flare-up at Eastern SLhasa imply increasing depleted mantle contribution due to Neo-Tethyan slab rollback changing from flat subduction to steep subduction (Kapp & DeCelles, 2019;L. Ma et al., 2015;X. Zhang et al., 2019).At that time, a magmatic lull in Western SLhasa and TCT likely suggests a shallow subduction under these regions (Figure 4b).Subsequently, the change of slab dip from shallow to steep would induce 75-60 Ma magmatic flare-up in Western SLhasa and TCT (Z.Wang et al., 2022;R.-Z. Zhu et al., 2022).During this period, the shallow subduction possibly suppressed arc magmatism and resulted in a magmatic lull in Eastern SLhasa (Figure 4c).Therefore, we propose that alternating steep or shallow subduction of the Neo-Tethys along the southern magmatic belt probably caused this incoherent magmatic flare-ups or lulls during the same period, while repeated steep and shallow subduction of Neo-Tethys across this arc cause episodic magmatism at the same place.The reappearance of mafic rocks and increasing of zircon ε Hf (t) values in the southern magmatic belt after the initial collision of India and Asia at ∼60 Ma and flareup with the peak age of 50 Ma suggest intense heat flow possibly due to slab breakoff during syn-collision (Figure 4d) (L.Liu et al., 2023;D. C. Zhu et al., 2022).

Conclusion
The magmatic flare-ups of Neo-Tethyan continental arc are asynchronous on the Lhasa-Tengchong terrane, which are featured by not only juvenile crustal growth but also reworking of ancient crust under basaltic underplating.Spatiotemporal variations in magmatic flare-ups and lulls may result from asynchronous variation in slab dip under the Lhasa-Tengchong terrane.Thanks for the help from Dr. Yahui Yue and Dr. Zaibo Sun with analyses and field sampling, respectively.This study was funded by the National Natural Science Foundation of China (Grant 92055207), the Second Tibetan Plateau Scientific Expedition and Research Program (STEP) (Grant 2019QZKK0703), and the Original Innovation Program of Chinese Academy of Sciences (Grant ZDBS-LY-DQC036).

Figure 1 .
Figure 1.(a, b) The distribution of Cretaceous-Eocene magmatic rocks and Hf isotopic contour on Lhasa-Tengchong terrane topography map.The black dotted line separating SLhasa from CNLhasa based on D.-C.Zhu et al. (2023).The Western and Eastern SLhasa are approximately divided at 87°E according to their Hf isotopic compositions.The Hf isotopic contour map was accomplished utilizing Python with Kriging Method.1941 ε Hf (t) values paired with corresponding longitude and latitude from TableS3, https://doi.org/10.6084/m9.figshare.24464134were selected to map in this study.The whole rock ε Hf (t) values were calculated from whole rock ε Nd (t) values, employing the terrestrial array developed byVervoort et al. (1999) in cases where zircon ε Hf (t) data was unavailable for these rocks.Magmatic rocks are represented by color-coded circles based on their ages from 150 to 40 Ma.Abbreviations: BNS, Bangong-Nujiang suture; IYS, Indus-Yarlung suture; MS, Myitkyina suture; IBS, Indo-Burma suture; SLhasa, the southern Lhasa terrane; CNLhasa, the central and northern Lhasa terrane; WB, the West Burma terrane; TC, the Tengchong terrane; BS, the Baoshan terrane; SGF, Sagaing fault; RRF, Red River fault.

Figure 2 .
Figure 2. Regional geology and magmatism in Tengchong terrane (TCT).(a) Geological map of TCT shows magmatic distribution and sample locations.(b) A plot of ε Hf (t) versus U-Pb age of captured zircons and granitic batholith in TCT.(c, d) Kernel density estimate (KDE) plots of captured zircon ages from Eastern and Western TCT.(e) KDE plots of captured zircon ages and magmatic rock ages from TCT. KDE calculating with adaptive bandwidth was adapted from Sharman et al. (2018).

Figure 3 .
Figure 3. Evolving zircon Hf isotope compositions of different episodes of magmatism in the Lhasa-Tengchong terrane.(a, b) Showing episodic magmatism and their corresponding zircon ε Hf (t) values in the northern and southern magmatic belts, respectively.The Kernel density estimate (KDE) plot outline of ε Hf (t) distribution is depicted by the 90% proportion of zircon ε Hf (t) value points.In KDE plots of magmatic ages, black lines represent captured zircons while the colored areas are rocks.The magmatic ages and their zircon ε Hf (t) values are summarized in TablesS3 and S4, https://doi.org/10.6084/m9.figshare.24464134.

Figure 4 .
Figure 4.The Cretaceous-Eocene tectonic evolution of Lhasa-Tengchong terrane.(a) During 120-110 Ma period, the diachronous closing of Meso-Tethys and the Neo-Tethyan flat subduction collectively controlled magmatism in the northern magmatic belt.Due to the closure of Meso-Tethys occurred at the end of late Jurassic between the Tengchong and Baoshan terranes, subduction of Neo-Tethys triggered ∼120 Ma arc-back-arc magmatism in Eastern Tengchong (J.Zhang et al., 2022).In contrast, ∼120 Ma magmatism in westernmost CNLhasa may resulted from southward subduction of the Meso-Tethys (K.-J.Zhang et al., 2014).(b, c) Changes of subducted slab dip resulted in spatiotemporal variations of arc magmatic flare-ups/lulls in the southern magmatic belt.(d) Indian-Asian collision induced slab break-off and inflow of hot asthenosphere, which caused the peak age of flare-up at 50 Ma in the Lhasa-Tengchong terrane.See abbreviations in Figure 1.