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Field photos showing the mafic granulites. (a) The retrograde mafic granulite consists of amphibole, garnet and plagioclase, and contains abundant felsic leucosomes; (b) the mafic granulite, consisting of garnet, clinopyroxene, amphibole and plagioclase, was partly retrograded to the amphibolite consisting of amphibole and plagioclase. Note that the coarse-grained red garnet grains are surrounded by dark kelyphitic rims of very fine-grained amphibole and plagioclase. The coins for scale are 1.5 cm across.
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The Himalayan Orogen, resulting from the Tertiary collision of Indian and Asian continents, is a natural laboratory for studying metamorphism, partial melting and granite formation of collisional orogens. However, metamorphic and anatectic conditions and timescales of meta-mafic rocks in the Greater Himalayan Sequences (GHS) in the east-central Him...
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... studied mafic granulite is collected from the core of the EHS (Fig. 1). The granulite body occurs as a layer with a thickness of ca. 30 m within felsic granulites, shows steep to vertical deformation foliation, and contains abundant felsic leucosomes occurring as bands parallel to the foliation of hosting mafic granulite (Fig. 2). Garnet commonly occurs as residual grain in the mafic granulite, and shows a dark kelyphitic rim of very fine-grained amphibole and plagioclase (Fig. 2). The garnet-bearing mafic granulite has been completely transformed into garnet-free amphibolite along the marginal parts of the mafic granulite layer. The concordant bands of ...
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... ca. 30 m within felsic granulites, shows steep to vertical deformation foliation, and contains abundant felsic leucosomes occurring as bands parallel to the foliation of hosting mafic granulite (Fig. 2). Garnet commonly occurs as residual grain in the mafic granulite, and shows a dark kelyphitic rim of very fine-grained amphibole and plagioclase (Fig. 2). The garnet-bearing mafic granulite has been completely transformed into garnet-free amphibolite along the marginal parts of the mafic granulite layer. The concordant bands of leucosomes contain plagioclase, K-feldspar and quartz with or without minor garnet, biotite or ...
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... studied mafic granulite shows a distinct foliation and banded structure, defined by alternating layers of light leucosomes and dark melanosomes (granulite) (Fig. 2). The granulite displays a porphyroblastic texture, and consists of porphyroblastic garnet, and matrix minerals amphibole, plagioclase, quartz, clinopyroxene, orthopyroxene, biotite, rutile, titanite and ilmenite (Figs. 2 and 3). The coarse-grained garnet porphyroblasts have a mineral inclusion-rich core, and a nearly inclusion-free rim ...
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... studied mafic granulite shows a distinct foliation and banded structure, defined by alternating layers of light leucosomes and dark melanosomes (granulite) (Fig. 2). The granulite displays a porphyroblastic texture, and consists of porphyroblastic garnet, and matrix minerals amphibole, plagioclase, quartz, clinopyroxene, orthopyroxene, biotite, rutile, titanite and ilmenite (Figs. 2 and 3). The coarse-grained garnet porphyroblasts have a mineral inclusion-rich core, and a nearly inclusion-free rim (Figs. ...
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... still consider that the zircon rims were formed during the retrograde metamorphism because they have the same age range as the rims with high HREE contents and fractionated HREE patterns. In fact, a considerable amount of garnets are preserved in metastable form during overprint of granulite-to amphibolite-facies metamorphism of the hosting granulite (Figs. 2 and 3). This is probably the reason for the rims of minor zircon grains having low HREE contents and slightly fractionated HREE patterns. ...
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... proposed that the Eocene Himalayan leucogranites were derived from partial melting of the meta-mafic rocks of the subducted Indian continent ( Hou et al., 2012;Zeng et al., 2011), the anatectic condition, degree and timescale of the mafic granulites remain unclear. The studied mafic granulite contains abundant and concordant felsic leucosomes (Fig. 2), providing direct evidence for the partial melting of the mafic granulite. The present study demonstrates that the mafic granulite underwent intensive partial melting during the heating and burial metamorphism and the melt content is up to 14 vol%-16 vol% at the peak-metamorphic stage (Fig. ...
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Citations
... The Namche Barwa complex experienced widespread high-pressure granulitefacies metamorphism directly associated with a continental collision and reached peak P-T conditions of 11-18 kbar and 750-950 °C at ca. 60 Ma (Zhong and Ding, 1996;Liu and Zhong, 1997;Ding and Zhong, 1999) or ca. 40-32 Ma (Ding et al., 2001;Zhang et al., 2010bZhang et al., , 2012Zhang et al., , 2015Zhang et al., , 2018. Exhumation and cooling of these units through medium-P granulite-and amphibolite-facies conditions occurred at P-T conditions of 4-10 kbar and 650-900 °C. ...
... The Namche Barwa complex was probably initially subducted under the Lhasa terrane before ca. 40 Ma (Ding et al., 2001;Zhang et al., 2010b) and then exhumed to lower-crustal depths at 25-8 Ma (Burg et al., 1998;Ding et al., 2001;Xu et al., 2010;Zhang et al., 2012Zhang et al., , 2015Zhang et al., , 2018 and finally into the upper crust at 10-3 Ma (Burg et al., 1998;Xu et al., 2012;Dong et al., 2015). The final stage of unroofing is documented by zircon and apatite fission-track ages generally younger than ca. ...
... The peak T conditions of the studied metapelites (Milin metasedimentary unit) only reached kyanite-grade metamorphism, but they are higher than the staurolite-grade metamorphism from Palin et al. (2015) and Li et al. (2023). A phase of decompression based mostly on the transition from kyanite to sillimanite has been reported in many areas of the eastern Himalaya (Guilmette et al., 2011;Zhang et al., 2015Zhang et al., , 2018Tian et al., 2016), and related P-T estimates indicate an initial phase of substantial cooling and exhumation of high-grade rocks, followed by exhumation and cooling, similar to the interpretations in our work. ...
We report an integrated comprehensive dataset composed of petrography, pressure-temperature (P-T) calculations, monazite U-Th-Pb ages, and trace-element data from pelitic schists in the eastern Indus-Yarlung suture zone in the Milin area of the eastern Himalaya. These rocks represent the exposure of subduction-related rocks within the eastern Indus-Yarlung suture zone accretionary complex. The dominant mineral assemblages of the pelitic schists are garnet + kyanite + staurolite + biotite + quartz and garnet + kyanite + staurolite + biotite + paragonite + sillimanite with quartz, plagioclase, and ilmenite assemblages. Phase equilibrium modeling of sillimanite-bearing pelitic schists yielded peak P-T conditions of ∼670−680 °C at ∼8.6 kbar, similar to that of kyanite-bearing schists (∼670 °C, ∼8.8 kbar). Monazite grains with complex internal structures retained variable ages ranging from 28 Ma to 15 Ma, which correlate systematically with changes in the concentrations of Y, Th, U, and heavy rare earth elements and ratios of Th/U. Combined with petrologic analysis, we conclude that the pelitic schists experienced a long-lived prograde metamorphism from ca. 28 Ma to ca. 22 Ma. Peak metamorphism occurred in the period 22−21 Ma, followed by quasi-isothermal decompression until 15 Ma. The discrepancies among metamorphic P-T-t paths in the eastern Indus-Yarlung suture zone indicate the presence of not only collision-related regional metamorphism at medium P-T conditions, but also subduction-related high-pressure−low-temperature terranes in the Milin region. These two domains experienced different P-T evolution and tectonic histories and were juxtaposed in the early Neogene during the India-Asia continental collision.
... Previous studies have focused on P-T paths, geochronology and/or partial melting history of these granulites (e.g., Guilmette et al., 2011;Kang et al., 2020). By contrast, studies on the melt compositions (e.g., Zhang et al., 2018) and related MI from the anatectic rocks (e.g., Bartoli et al., 2019;Carosi et al., 2014;Iaccarino et al., 2017) are rare, which limits our understanding on the origin and nature of anatectic melts in the Himalaya. ...
... Melting of metasedimentary and metafelsic rocks generally results from mica breakdown (e.g., Dyck et al., 2020;Groppo et al., 2012;Guilmette et al., 2011;Luo et al., 2022;Sawyer et al., 2011;Zhang et al., 2018). According to our phase equilibrium modelling (Figure 12b), the small amounts of melt produced at P-T conditions below 730 C and 1.24 GPa were derived from partial melting of muscovite plus plagioclase and quartz in the paragneiss. ...
... In addition, leucogranites and associated migmatites along the Himalayan orogen may share some similar features, including timing, source rocks and P-T paths (Weinberg, 2016), and the leucogranites were thought to have derived from partial melting of metasedimentary rocks during crustal anatexis (Gao et al., 2017;Kang et al., 2020;Patino Douce & Harris, 1998;Zhang et al., 2018). Major and trace element compositions of the homogenized glasses in this study are used to try to test the origin model of leucogranites from the Himalayan orogen. ...
Melt inclusions (MIs) in high‐temperature metamorphic rocks provide a unique window into crustal anatexis in collisional orogenic belts and have been widely used to characterize compositions of anatectic melts as well as melting mechanisms. In this study, MIs hosted by peritectic garnet were for the first time identified in an Al 2 SiO 5 ‐free graywacke‐type paragneiss from the Namche Barwa Complex, the Eastern Himalaya, Southeast Tibet. These MIs occur as nanogranites in the rims of porphyroblastic garnet, exhibit negative crystal shapes with an average diameter of ~12 μm and consist of a mineral assemblage of biotite + quartz + plagioclase + K‐feldspar ± muscovite. Re‐homogenization experiments of these nanogranites were conducted at a pressure of 1.5 GPa and temperatures of 800°C, 850°C and 900°C and produced homogeneous glasses at 850°C. The homogenized glasses are strongly peraluminous and calc‐alkalic in composition, with 66.43–71.31 wt.% SiO 2 , 12.64–15.06 wt.% Al 2 O 3 , high alkaline (5.41–7.22 wt.%) and low ferromagnesian (2.72–4.46 wt.%) contents. They are lower in silica and CaO but higher in K 2 O compared with MI produced by fluid‐present melting of metasedimentary rocks, thus indicating fluid‐absent melting. These glasses are also characterized by enrichment of large ion lithophile elements (particularly Cs and Rb), depletion of Ba and Sr, low contents of light rare earth elements (3.6 to 33.7 ppm), high Rb/Sr ratios (6.19–37.3) and low Nb/Ta ratios (2.55–18.7). In combination with phase equilibrium modelling, these compositional features suggest that a sequential dehydration melting of muscovite and biotite was responsible for the production of MI during prograde metamorphism of the studied paragneiss. By compiling MI data published in the literature, we show that dehydration melting of metasedimentary rocks from the Himalayan orogen can produce initial melts with various peraluminous and granitic compositions.
... India-Asia collision may have occurred as a coherent collision along the Himalayas, a diachronous collision from west to east, or a diachronous collision from the center to both sides (Guillot et al., 2008;Ding et al., 2016a;Rehman, 2019). However, published zircon U-Pb ages of the HP metamorphism in the eastern Himalayan syntaxis span from ca. 40 Ma to ca. 10 Ma (Ding et al., 2001;Liu et al., 2007;Booth et al., 2009;Xu et al., 2010;Zhang et al., 2010bZhang et al., , 2015bZhang et al., , 2018Zhang et al., , 2022Su et al., 2012;Zeng et al., 2012;Liu and Zhang, 2014;Tian et al., 2019Tian et al., , 2020. It is unclear whether the large range in metamorphic ages represents long-lived or multistage HP metamorphism. ...
... Zircon and monazite record the retrogression at 29-3 Ma (Liu et al., 2007;Booth et al., 2009;Zhang et al., 2010bZhang et al., , 2015bSu et al., 2012;Tian et al., 2019Tian et al., , 2020. The peak metamorphic assemblages for the mafic granulites of garnet + clinopyroxene + quartz + rutile ± plagioclase or garnet + diopside + meionite + rutile + quartz, which formed under P-T conditions of 1.4-1.7 GPa and 780-900 °C (Ding et al., 2001;Liu and Zhang, 2014;Zhang et al., 2018Zhang et al., , 2022, represent HP mafic granulite-facies metamorphism (O'Brien and Rötzler, 2003). Zircon U-Pb geochronology results show that these mafic granulites experienced HP metamorphism at ca. 40-20 Ma and retrogression at ca. 22-9 Ma (Ding et al., 2001;Xu et al., 2010;Liu and Zhang, 2014;Zhang et al., 2018Zhang et al., , 2022. ...
... The peak metamorphic assemblages for the mafic granulites of garnet + clinopyroxene + quartz + rutile ± plagioclase or garnet + diopside + meionite + rutile + quartz, which formed under P-T conditions of 1.4-1.7 GPa and 780-900 °C (Ding et al., 2001;Liu and Zhang, 2014;Zhang et al., 2018Zhang et al., , 2022, represent HP mafic granulite-facies metamorphism (O'Brien and Rötzler, 2003). Zircon U-Pb geochronology results show that these mafic granulites experienced HP metamorphism at ca. 40-20 Ma and retrogression at ca. 22-9 Ma (Ding et al., 2001;Xu et al., 2010;Liu and Zhang, 2014;Zhang et al., 2018Zhang et al., , 2022. The retrogression of the mafic granulites resulted in the development of clinopyroxene + amphibole + plagioclase + quartz ± orthopyroxene ± ilmenite assemblages as symplectites or as coronas surrounding garnet and clinopyroxene grains, with P-T conditions of 0.5-0.7 GPa and 600-750 °C (Ding et al., 2001;Liu and Zhang, 2014;Zhang et al., 2018Zhang et al., , 2022. ...
The timing of high-pressure (HP) metamorphism in the eastern Himalayan syntaxis is important for understanding the India-Asia collisional processes, but it remains elusive. To reveal the metamorphic history of the eastern Himalayan syntaxis, we performed a study of geochronology, trace elements, and mineral inclusions of detrital zircon and monazite from modern stream sediments in the eastern Himalayan syntaxis. Detrital zircon comprise magmatic and metamorphic domains with different zoning. Inherited magmatic zircon domains have high Th/U, low (Dy/Yb)N, and retain ages of 1798−360 Ma. Metamorphic zircon domains with low Th/U, high (Dy/Yb)N, and inclusions of garnet, kyanite, and/or clinopyroxene probably formed under HP conditions. They yield age groups of 49−35 Ma, 33−17 Ma, and 12−7 Ma. The low Th/U and low (Dy/Yb)N metamorphic zircon domains probably formed during retrogression and yield age groups of 27−16 Ma and 10−6 Ma. Detrital monazite yield age distributions similar to those of the low (Dy/Yb)N metamorphic zircon except for the 821−402 Ma inherited cores. The (Dy/Yb)N of 31.6−5.7 Ma monazite decreases with increasing Y content, which indicates that it likely formed under the retrograde stage during garnet breakdown. Based on the oldest metamorphic ages, the initial India-Asia collision occurred no later than 50−44 Ma in the eastern Himalayan syntaxis. The multimodal age patterns of the metamorphic zircon and monazite indicate that the Indian continent underwent multistage HP and retrograde metamorphism in the eastern Himalayan syntaxis. The nearly contemporaneous HP and retrograde metamorphism indicate that the Indian continent continued subducting while the earlier HP metamorphic slices detached and exhumed.
... Resultantly, trace of an actinolite may, therefore, exist (Fig. 5c), where the magnesio-hornblende in eclogitic mafic schists was triggered to replace porphyroblastic omphacite that behaves actinolite (Takasu, 1984). Hence, in the Himalayan orogen, amphibole proximity from metamorphic source terrain cannot be ignored, which is commonly observed in amphibolite, granulite and eclogite facies rock types as layers, lenses, inclusions or symplectites in the mineral assemblages (Wang et al., 2017;Zhang et al., 2018). Further, the TiO 2 content of the amphiboles can also be used to derive a potential source condition. ...
... Calcic amphiboles present in these rocks are characteristically tschermakite to magnesiohornblendeactinolite show consistent Mg # to our study. Likewise, amphiboles of similar Mg # are common in mafic granulite and Tso Morari eclogites developed in the Eastern Himalayan syntaxis and NW Himalaya respectively representing symplectite texture and/or inclusion in garnet (Wang et al., 2017;Zhang et al., 2018). Thus, based on Mg # range, amphibole type and thermobarometry, it can be inferred that the studied amphiboles may be sourced from both igneous and high grade metamorphic rocks exposed along the Himalayan Sequences and LH crystallines in and around the Tsangpo-Brahmaputra catchment. ...
The present study describes results obtained from the chemistry of detrital heavy minerals i.e. pyroxene, amphibole, biotite, garnet, epidote and Fe-Ti oxides in fluvial sediments of the northern Brahmaputra River (Bangladesh) with an aim to determine conditions of their petrogenesis and provenance. The primary and secondary genera of ferromagnesian minerals occurred in calc-alkaline and peraluminous subduction zone. In which, the garnets are Fe-rich, indicating mostly almandine component (Alm65–Pyp16–Grs8–Sps6 averagely), occurred in medium to high grade metasedimentary rocks in the Lesser Himalaya (LH), along the Main Central Thrust (MCT) and the eastern Himalayan syntaxis. Besides, the fingerprint of omphacite and actinolite owe to ascertain the co-existence of garnet developed in ultrahigh-pressure (UHP) eclogites that may also be drained from the Tso Morari massif. Augite to aegirine-augite pyroxenes emphasizes Fe enrichment in basaltic systems and high to ultrahigh grade metamorphic rocks, which are exposed in the LH, Shillong Plateau, Mikir Hills, South Tibetan Detachment System (STDS), eastern Himalayan syntaxis and Tso Morari massif. Geochemistry and thermobarometry of the primary magmatic amphiboles and biotites manifest the source of granitoid and granodiorite like bodies, and their windows are exposed in the Bomi–Chayu, Gangdese arcs and the western Arunachal Himalaya. Again, metamorphosed Fe-Ti oxide minerals are well-exposed along the NE Lesser Himalaya, where magmatic derivative of Fe-Ti oxide minerals were modified through the diffusional processes in low-grade metamorphism (534–562 °C with 10–22.1–10−21.5 fo2). Integrating the aforementioned discussion with the thermochronology, it is evident that the eastern Himalayan syntaxis is the major source of sediment flux, which is carried mostly by the upper Himalayan tributaries i.e. Yigong, Parlung, Dibang and Lohit. Also, the lower Himalayan tributaries i.e. Subansiri and Manas drain the sequestered derivatives dominantly from the Arunachal Himalayan. Tso Morari eclogites (NW Himalaya) have also contribution somewhat of dense minerals to the Tsangpo-Brahmaputra River system. Thus, scrutinizing the fingerprint of single-grain detrital minerals provides key information regarding the source terrains and tectonics of the Himalayan sequences.
... Reported metamorphic peak P-T conditions range from 11 to 18 kbar and 750 C to 950 C (Booth et al., 2009;Ding et al., 2001;Guilmette et al., 2011;Liu & Zhang, 2014;Liu & Zhong, 1997;Palin Ding & Zhong, 1999;Tian et al., 2016Tian et al., , 2017Zhang et al., 2015). The different constraints on metamorphic ages (from $40 to 1 Ma, Booth et al., 2009;Ding et al., 2001;Peng et al., 2018;Su et al., 2012;Tian et al., 2017;Xu et al., 2012;Zeitler et al., 2014;Zeng et al., 2012;Zhang et al., 2010Zhang et al., , 2012Zhang et al., , 2018, and limited in situ dating of accessory minerals of the NBC (Booth et al., 2009;Liu et al., 2011) impede our understanding of the tectono-metamorphic evolution of the NBC and obscure the relationship between the various driving forces that formed this area. In this study, we applied in situ laser ablation-inductively coupled plasmamass spectrometry (LA-ICP-MS) U-Th-Pb dating, trace element analyses of monazite and conventional geothermobarometry to retrieve the metamorphic P-T-t path of metapelite exposed in the NBC and to shed a light on the discrepancy among the reported metamorphic ages. ...
... The NBC consists of three major formations: (i) the Zhibai Formation, consisting of garnet-bearing gneiss with sporadic boudins of mafic granulite, garnet clinopyroxenite, kyanite-bearing pelitic granulite and garnet amphibolite; (ii) the Paixiang Formation, dominantly consisting of felsic gneiss with subordinate diopside-and forsterite-bearing marble, clinopyroxenite and scapolite diopsidite; and (iii) the Duoxiong-La migmatite (Sun et al., 2004). The previously reported HP granulitic rocks are mainly from the Zhibai formation (e.g., Liu & Zhang, 2014;Liu & Zhong, 1997;Palin Ding & Zhong, 1999;Zhang et al., 2018). Metapelitic rocks in the Zhibai and Paixiang formations are typically interlayered with other metasedimentary rocks, for example, quartzite and metagraywacke, and have broadly undergone ductile deformation. ...
... Otherwise, monazite shows a general trend to a stronger negative Eu anomaly (decrease in Eu N /Eu N * value, Figure 8) at younger ages, which could result from the K-feldspar growth when melting occurred in metapelitic rocks (Rubatto et al., 2013). Therefore, the youngest age yielded by monazite may indicate that the decompressional melting in the NBC ensued to as young as $ 3 Ma, which is consistent with the protracted high-T metamorphism in the NBC (e.g., Koons et al., 2013;Peng et al., 2018;Zeitler et al., 2001;Zhang et al., 2018). ...
Geothermobarometry shows that metapelite samples from Namche Barwa Complex (NBC) reached upper‐amphibolite to near‐granulite facies during the peak metamorphic stage, with similar conditions of ~700–750 °C/8–10 kbar, and then experienced retrograde metamorphism at ~630–700 °C/4–7 kbar. In‐situ monazite LA‐ICP‐MS U‐Th‐Pb dating suggests divergent metamorphism in the NBC: metapelite on the hanging wall of Namu‐La thrust preserved a continuous metamorphic record of >19–3 Ma, whereas metapelite on the footwall yielded age ranges of >18–14 Ma and 8–3 Ma, with a gap in recorded ages between 14 Ma and 8 Ma. Monazite grains in the garnet porphyroblasts, more depleted in the heavy rare earth elements (HREE), yielded the youngest age of ~14 Ma. This is interpreted as the timing of upper amphibolite facies peak metamorphism in the metapelite from the NBC, with the NBC being exhumed coherently thereafter. Furthermore, the discrepancy between reported peak metamorphic ages of high‐pressure granulite (~40–30 Ma, ~25–20 Ma) and mid‐pressure metapelite (~14 Ma, this study) indicate asynchronous subduction‐exhumation processes in the NBC. We suggest that crustal flow has played an essential role in exhumation since ~40 Ma, and recent surficial erosion (<8 Ma) intensified the exhumation of the NBC, with young leucogranite (<10 Ma) resulting from decompression melting. From ~3 Ma to the present, the interplay of erosion and tectonic movement caused ubiquitous rapid uplift, resulting in the concomitant exhumation of various types of rocks and the formation of the spectacular high relief between Yarlung Tsangpo gorge and Namche Barwa Peak.
... Wang et al. [100] concluded that thinning of the lithosphere to <90 km was an important factor in the ultra-high-temperature metamorphism. Similarly, the records of high-temperature metamorphic rocks are also found in the Namche Barwa Syntaxis and the Nanga Parbat Syntaxis [101,102]. The formation of the NSRT in southern Tibet is also related to the lithosphere thinning and the asthenospheric upwelling. ...
Postcollisional adakitic magmatism in the Himalayan Orogen provides a probe into the evolution of the collisional orogen. During the Miocene, the Himalayan Orogen underwent a tectonic transition, which was characterized by a series of tectonic events, including the activity of the North-South Trending Rift, exhumation of eclogite, rapid uplift of the orogen, and the extensive adakitic rocks. In this study, we reported the geochemistry and geochronological data of the Kuday dikes intruding into the Tethys Himalayan Sequence near the Sakya Dome of southern Tibet. The Kuday dikes are granitoid porphyries with zircon U-Pb ages of ca. 11 Ma. The Kuday granitoid porphyry dikes have high SiO2 (63.01–68.41 wt.%) and Al2O3 (17.31–19.87 wt.%) but low Mg (0.88–1.41 wt.%), Mg# (36–50), Ni (2.8–19.3 ppm), and Cr (2.9–26.4 ppm), indicating no input of mantle material. They have high Sr (934–1881 ppm), (La/Yb)N (18.84–113.13), and Sr/Y ratios (89.25–305.85) but low K2O/Na2O ratios (0.17–0.79), indicating that they are adakitic affinity. They display initial 87Sr/86Sr ratios of 0.707–0.711 and εNdt values of -3.7–-6.7. These geochemical signatures indicate that the Kuday granitoid porphyrite dikes were derived from the partial melting of the thickened lower crust of the Himalayan Orogen. Partial melting of the thickened lower crust requires additional heat, so the delamination model with lithospheric mantle thinning and asthenospheric upwelling is proposed to explain the formation of the Kuday adakitic rock. The delamination model can also provide a reasonable explanation for the tectonic events during the Miocene in the Himalayan Orogen.
... The GHC, also referred to as the Namche Barwa Complex (NBC) by Zhang et al. (2012), consists of migmatitic orthogneiss, paragneiss, mafic granulite, amphibolite, schist, marble and calc-silicate rock. All the rocks of the GHC underwent high-grade metamorphism and partial melting during the Cenozoic (Zhong and Ding, 1996;Liu and Zhong, 1997;Burg et al., 1998;Ding et al., 2001;Booth et al., 2004Booth et al., , 2009Liu et al., 2007;Xu et al., 2010Xu et al., , 2012Zhang et al., 2010aZhang et al., , 2012Zhang et al., , 2015Zhang et al., , 2018Guilmette et al., 2011;Su et al., 2012;Liu and Zhang, 2014;Tian et al., 2016Tian et al., , 2019Tian et al., , 2020Peng et al., 2018;Kang et al., 2020). ...
... Because the retrograde mafic granulite from the same outcrop as the present studied mafic granulites has been dated using zircon U-Pb method by Zhang et al. (2018), this paper focused on U-Pb ages and trace elements of zircon from the garnet-bearing leucosome of the HP mafic granulites. The leucosome (sample 97-12) occurs as concordant band within the migmatitic granulite (Fig. 2c). ...
... The pelitic and felsic HP granulites in the GHC are characterized by having peak metamorphic mineral assemblage of garnet + kyanite + plagioclase + K-feldspar + biotite + quartz + rutile, commonly with antiperthite (or ternary feldspar) (Liu and Zhong, 1997;Ding and Zhong, 1999;Liu et al., 2007;Zhang et al., 2010aZhang et al., , 2015Guilmette et al., 2011;Su et al., 2012;Xiang et al., 2013;Tian et al., 2016Tian et al., , 2019Tian et al., , 2020. Although migmatitic mafic rocks, including garnet-bearing amphibolite and garnet-free amphibolite, occur widely in the EHS, typical HP mafic granulites, containing garnet, clinopyroxene, plagioclase, quartz and rutile, are rarely reported (Zhong and Ding, 1996;Liu and Zhang et al., 2014;Zhang et al., 2018;Kang et al., 2020). Field observation reveals that the HP mafic granulites show transitional contacts with the hosting amphibolite, characterized by gradual decreasing of garnet and clinopyroxene contents, and increasing of amphibole and plagioclase contents from the granulite to the amphibolite. ...
The Himalayan orogen, resulting from the Early Cenozoic collision of the Indian and Asian plates, is an ideal vehicle to study active orogenic processes and test geodynamic models of how the crust responds to collisional orogeny. This paper focused on migmatitic high-pressure (HP) mafic granulite and associated leucosome from the Greater Himalayan Crystallines (GHC) in the Eastern Himalayan Syntaxis (EHS) in order to understand the conditions and timescales over which high-grade rocks and partial melts were produced during the Himalayan orogeny. Combining with previous study results from the Western and Central Himalayas and Trans-Himalayan magmatic arc, we obtained the following conclusions: (1) The mafic granulites from the EHS underwent HP and high-temperature (HT) granulite facies metamorphism and partial melting, with peak metamorphic conditions of 15–17 kbar and 820–880 °C. The GHC, at least its western part of the EHS, underwent coherent HP granulite-facies metamorphism. (2) The HP mafic granulites experienced long-lived dehydration melting of amphibole from ∼40 Ma to ∼20 Ma during prograde metamorphism and generated up to ∼16 vol.% partial melt. The variable degrees of dehydration melting of the HP mafic, pelitic and felsic granulites in the EHS generated voluminous granitic melts with distinct compositions, and provided the source for the Himalayan granites. (3) Peak metamorphic pressure of the GHC gradually decreases, whereas the metamorphic temperature progressively increases from the Western to Eastern Himalayas. This indicates that the Indian continental crust deeply subducted into the mantle in the Western Himalaya after the Indo-Asia collision, whereas the Indian crust underthrusted or relaminated beneath the Asian continental crust, and formed the thickened lower crust in the Central and Eastern Himalayas and Gangdese arc. (4) The melts derived from the underthrusted Indian crust probably resulted in isotopic compositional enrichment of the Early Cenozoic mantle- and juvenile crust-derived magmatic rocks of the Gangdese arc.
... In the Sikkim and Yadong region, calculated peak metamorphic pressures of migmatitic granulites of the GHS are particularly different among different studies. Some studies report pressures of at most 8-10 kbar at ∼800°C and assign these rocks to a medium-pressure (MP) metamorphic belt characterized by sillimanite-K-feldspar ± cordierite assemblages (Anczkiewicz et al., 2014;Dasgupta et al., 2004Dasgupta et al., , 2009 (Faak et al., 2012;Rubatto et al., 2013;Sorcar et al., 2014), felsic granulites from Nepal (Groppo et al., 2012;Iaccarino et al., 2015) and Namche Barwa (Guilmette et al., 2011), pelitic granulites from Nyalam (Wang et al., 2016) and Namche Barwa , mafic granulite from Namche Barwa (Zhang et al., 2018), and channel flow model . All the numbers marked on P-T path refer to metamorphic ages in Ma. ...
... Nonetheless, a high-pressure metamorphic stage up to 12-13 kbar also has been estimated for mafic granulites occurring as blocks within pelitic and felsic granulites in the Sikkim area ( Figure 12; Faak et al., 2012), as well as higher metamorphic pressures up to 14-20 kbar for granulitized eclogites in neighboring regions of Nepal and Bhutan Cottle, Jessup, et al., 2009;Groppo et al., 2007;Grujic et al., 2011;Kellett et al., 2014;Li et al., 2019;Lombardo & Rolfo, 2000;Wang et al., 2017;Warren et al., 2011). Recent studies have indicated that the GHS anatectic granulites in the eastern Himalaya commonly experienced high-pressure granulite-facies metamorphism with P-T conditions of up to 12-16 kbar and clockwise P-T paths (e.g., Ding et al., 2001;Groppo et al., 2012Groppo et al., , 2010Guilmette et al., 2011;Kali et al., 2010;Tian et al., 2016;Zhang et al., 2015Zhang et al., , 2018Z. M. Zhang et al., 2010). ...
Revealing the timescales of metamorphic and anatectic processes is central to our understanding of tectonic evolution of collisional orogens. High‐temperature migmatites and leucogranites are well exposed in the Himalayan orogenic core, making it an ideal region to study the timing and duration of partial melting and melt crystallization of the orogen. Here, we report an integrated and comprehensive data set of petrography, U‐Pb age, and trace element data for zircon from a pelitic granulite and associated leucosomes of the Greater Himalayan Sequence (GHS) in the Yadong area, eastern Himalaya. Zircon grains with complex internal structure retain variable ages ranging from 32 Ma to 13 Ma that correlate systematically with changes in the concentrations of Y, Th, U, Hf, Nb, Ta, and HREE, and ratios of Th/U, Eu/Eu*, and Nb/Ta. Combined with petrologic analysis, we conclude that the granulite witnessed high‐temperature metamorphism, melting, and melt crystallization over ∼20 Myr. Prograde, simultaneous increases in pressure and temperature and associated dehydration melting began at least by ∼32 Ma and lasted until ∼24 Ma. Subsequent quasi‐isothermal decompression‐melting occurred between ∼22 and 19 Ma, and late melt crystallization spanned ∼19 to 13 Ma. Large volumes of melt generated during prograde metamorphism could have triggered exhumation of GHS rocks, increasing melt fraction through a positive feedback between exhumation and melting. More comprehensive analysis of different rock types led to more complete and different interpretations for the timing of exhumation and melt crystallization in the Yadong‐Sikkim region and might enable alternate interpretations elsewhere in the Himalayas.
... GPa and 780-790°C in the presence of melt (Z. M. Zhang et al., 2010Zhang et al., , 2018. ...
The bulk composition of overthickened Tibetan deep crust has been generally believed to be mafic granulite with eclogite at the lowermost crust. However, a granulitic/eclogitic deep crust is in contradiction to geological and geophysical observations in southern Tibet. Here we present petrofabrics and seismic properties of amphibolites from exhumed crustal part of the Indian plate in the eastern Himalayan syntaxis. Our results show strong fabrics of amphibole, nearly random fabrics of plagioclase and strong seismic anisotropies of amphibolites (AVp = 5.6–12.0% and Max. AVs = 5.1–7.7%). Comparing to a deep crust composed of nearly isotropic mafic granulite and weakly anisotropic eclogite, a thick amphibolitic layer in the middle‐lower crust would better account for the strong shear wave splitting (0.2–0.5 s in delay times or 4–15% in S wave anisotropy), the suture boundary parallel faster shear wave polarization, and the widespread postcollisional adakite‐like potassic rocks in southern Tibet.
... 1a, 1b). The Lhasa terrane is composed dominantly of the underlying Precambrian crystalline basement, Paleozoic to Mesozoic marine strata and arc-type volcanic rocks together with Mesozoic and Cenozoic intrusions (e.g., Zhang Z M et al., 2018;Zhu et al., 2013Zhu et al., , 2011Zhu et al., , 2009Pan et al., 2012;Zhang J J et al., 2012;Yin and Harrison, 2000). This trifold tectonostratigraphy was used to divide the entire Lhasa terrane into three belts called the northern, central and southern sub-terranes, separated by the Shiquan River-Nam Tso fault and the Luobadui-Milashan fault, respectively. ...
The Sumdo eclogite-bearing (U)HP metamorphic belt extends over 100 km across the middle part of the Lhasa terrane in southern Tibet, which forms a Permian-Triassic oceanic subduction zone between the south and the north Lhasa sub-terranes, leading to the reinterpretation of the tectonic evolution of the Lhasa terrane in the Tibetan-Himalayan orogeny. Previous studies show that there are significant differences in temperature and pressure conditions of the eclogites in four areas, e.g., Sumdo, Xindaduo, Bailang and Jilang areas. Studying the peak metamorphic P-T conditions and path of eclogite in the Sumdo belt is of great significance to reveal the subduction and exhumation mechanism of Paleo-Tethys Ocean in the Lhasa terrane. In this contribution, eclogite in the Jilang area of the Sumdo belt is chosen as an example to study its metamorphic evolution. The mineral assemblage of the eclogite is garnet, omphacite, phengite, hornblende, epidote, quartz and minor biotite. Garnet has a “dirty” core with abundant inclusions such as epidote, amphibole, plagioclase and a “clear” rim with few inclusions of omphacite and phengite. From the core to the rim, pyrope content in garnet increases while grossular content decreases, showing typical growth zoning. The rim of garnet is wrapped by the pargasite+plagioclase corona, showing amphibolite facies overprint during retrogression. Three stages of metamorphism are inferred as (1) prograde stage, represented by the core of garnet and mineral inclusions therein; (2) peak stage, represented by the garnet rim, omphacite, lawsonite, phengite, and quartz; (3) retrograde stage characterized by decomposition of lawsonite to zoisite, followed by symplectite of omphacite and corona rimmed garnet. A P-T pseudosection contoured with isopleths of grossular and pyrope contents in garnet is used to constrain the near peak P-T condition at 2.85 GPa, 575 °C. In general, the Jilang eclogite shows a clockwise P-T path with a near isothermal decompression process during exhumation. Combined with the age peaks of 583, 911, and 1 134 Ma from the detrital zircons of the country metaquartzite, a continental margin material involving exhumation process at shallow depth after the subduction channel exhumation is inferred for the Jilang eclogite and may further indicate that the subduction direction of the Sumdo eclogite belt is from north to south.
