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Schematic illustration of tectonic development of the Himalayan thrust system (vertical exaggeration 6:1). Active faults are shown as bold black lines while abandoned faults are indicated with bold gray lines. Symbols shown correspond to sample positions described in detail in Harrison et al. (1997a, 1998b). Open and closed symbols indicate initial and ®nal positions for the time interval shown. (a) Possible 25 Ma distribution of the protoliths of Greater Himalayan Crystallines (GHC) and Lesser Himalayan Formations (LHF) with respect to Indian cratonic margin after Eohimalayan thickening from ca 50±25 Ma. Future site of the High Himalayan leucogranite (HHL) source region is shown at 25 Ma. (b) Thrusting along the Main Himalayan Thrust (MHT) ¯at and Main Central Thrust (MCT) decollement from 25±15 Ma. Note that this fault system forms immediately above refractory rocks of the Indian craton. (c) Thrusting along MHT ¯at and MBT ramp from 15±8 Ma. Abandonment of the MCT ramp at 15 Ma causes accretion of upper LHF rocks to the hanging wall. (d) Out-of-sequence thrusting in the high Himalaya from 8±6 Ma involving upper LHF (approximately equivalent to reactivated MCT thrust ramp). (e) Activation of MCT-I and further development of MCT Zone (6±2 Ma) leads to accretion of lower LHF rocks to hanging wall. (f) Abandonment of the MCT zone at 2 Ma. Southward transfer of displacement to MFT ramp/MHT decollement. Present predicted positions of HHL and North Himalayan Granite (NHG) source regions are shown by regions shaded white.
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The key to comprehending the tectonic evolution of the Himalaya is to understand the relationships between large-scale faulting, anatexis, and inverted metamorphism. The great number and variety of mechanisms that have been proposed to explain some or all of these features reflects the fact that fundamental constraints on such models have been slow...
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... that slip along the MCT had terminated during the Early Miocene, Harrison et al. (1997a) explained the pattern of geochronological results as due to thrust reactivation during the Late Miocene. A break back from the MBT to the MCT, presumed to have steepened as a result of post-Early Miocene de- formation ( Fig. 5d), could re¯ect a stress increase in the hinterland resulting from an increase in elevation of the Tibetan Plateau during the Late Miocene ( Harrison et al., 1995b) or readjustment of the thrust wedge following signi®cant erosional and/or tectonic denudation of the hanging wall (Dahlen, 1984). Early Miocene slip along the MCT emplaced ...
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... alternative model that ascribed the spatial and temporal variations of granite emplace- ment to continuous slip on a shallow dipping decolle- ment that cuts through crust previously metamorphosed during the Eohimalayan phase (Le Fort, 1996) of collision. They assumed that, immedi- ately prior to collision, the northern Indian margin re- sembled Fig. 5a, and that during the Eohimalayan stage, the Greater Himalayan Crystallines protolith underwent high grade recrystallization and anatexis (see Peà cher, 1989;Hodges et al., 1994Hodges et al., , 1996Parrish and Hodges, 1996;Edwards and Harrison, 1997;Coleman, 1998;Vance and Harris, 1999). As a conse- quence, metamorphism and anatexis in ...
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... model of Harrison et al. (1998b) also employs a ramp-¯at geometry to simulate crustal thickening and assumes that the initiation of the Himalayan thrust system was localized at the boundary between the Greater Himalayan Crystallines and the Indian craton. The slip history they utilized is schematically depicted in Fig. 5. Thrusting begins after the crust has been thickened in response to H25 m.y. of Eohimalayan crustal shortening (Fig. 5a) and proceeds at a constant slip rate of 20 mm/yr. The resulting 250 km of short- ening in the hanging wall is accommodated as follows: slip occurs on the MHT/MCT ramp between 25±15 Ma (Fig. 5b), on the MHT/MBT ramp ...
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... thickening and assumes that the initiation of the Himalayan thrust system was localized at the boundary between the Greater Himalayan Crystallines and the Indian craton. The slip history they utilized is schematically depicted in Fig. 5. Thrusting begins after the crust has been thickened in response to H25 m.y. of Eohimalayan crustal shortening (Fig. 5a) and proceeds at a constant slip rate of 20 mm/yr. The resulting 250 km of short- ening in the hanging wall is accommodated as follows: slip occurs on the MHT/MCT ramp between 25±15 Ma (Fig. 5b), on the MHT/MBT ramp between 15±8 Ma (Fig. 5c), and on the MHT and various fault ramps de®ning the MCT zone between 8±2 Ma (Fig. ...
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... is schematically depicted in Fig. 5. Thrusting begins after the crust has been thickened in response to H25 m.y. of Eohimalayan crustal shortening (Fig. 5a) and proceeds at a constant slip rate of 20 mm/yr. The resulting 250 km of short- ening in the hanging wall is accommodated as follows: slip occurs on the MHT/MCT ramp between 25±15 Ma (Fig. 5b), on the MHT/MBT ramp between 15±8 Ma (Fig. 5c), and on the MHT and various fault ramps de®ning the MCT zone between 8±2 Ma (Fig. ...
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... begins after the crust has been thickened in response to H25 m.y. of Eohimalayan crustal shortening (Fig. 5a) and proceeds at a constant slip rate of 20 mm/yr. The resulting 250 km of short- ening in the hanging wall is accommodated as follows: slip occurs on the MHT/MCT ramp between 25±15 Ma (Fig. 5b), on the MHT/MBT ramp between 15±8 Ma (Fig. 5c), and on the MHT and various fault ramps de®ning the MCT zone between 8±2 Ma (Fig. ...
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... crustal shortening (Fig. 5a) and proceeds at a constant slip rate of 20 mm/yr. The resulting 250 km of short- ening in the hanging wall is accommodated as follows: slip occurs on the MHT/MCT ramp between 25±15 Ma (Fig. 5b), on the MHT/MBT ramp between 15±8 Ma (Fig. 5c), and on the MHT and various fault ramps de®ning the MCT zone between 8±2 Ma (Fig. ...
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... (>7608C) predicted for the NHG are reasonably expected to be suciently buoyant and thermally ener- getic to ascend as diapirs into the middle crust, con- sistent with the character of the NHG belt. The ramp- ¯at model is consistent with the observation that the Greater Himalayan Crystallines immediately above the present exposure of the MCT (Fig. 5f) did not experi- ence temperatures high enough to cause widespread melting ( Barbey et al., 1996). Migmatization higher up section may re¯ect imbrication of the Greater Himalayan Crystallines (e.g., Davidson et al., 1997), the advection of magmatic heat associated with leuco- granite emplacement into shallower crustal levels, or a ...
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Exhumation processes of the ultrahigh-pressure (UHP) Tso Morari dome (NW Himalaya) are investigated using structural, petrological, and geochronological data. The UHP Tso Morari unit is bounded by the low-grade metamorphic Indus Suture Zone to the NE and Mata unit to the SW. Three deformation phases (D1, D2, and D3) are observed. Only D3 is common...
The metamorphic architecture of eastern Nepalese Himalaya is characterized by a well-documented inverted metamorphic field gradient, with metamorphic grade increasing northward from lower (LHS) to higher (HHC) structural levels across the north-dipping Main Central Thrust Zone (MCTZ). Peak metamorphic conditions experienced by units at different st...
Citations
... The Miocene leucogranites are widely spread in the Himalayan region and their sources are considered to be products of crustal anatexis (Harrison et al., 1999). Various models have been proposed for the crustal anatexis: thrust and emplacement model (Harrison et al., 1999), radioactive heat accumulation model of the thickened crust (Beaumont et al., 2004) and decompression melting model related to the tectonic activity (Harris and Massey, 1994). ...
... The Miocene leucogranites are widely spread in the Himalayan region and their sources are considered to be products of crustal anatexis (Harrison et al., 1999). Various models have been proposed for the crustal anatexis: thrust and emplacement model (Harrison et al., 1999), radioactive heat accumulation model of the thickened crust (Beaumont et al., 2004) and decompression melting model related to the tectonic activity (Harris and Massey, 1994). It is noteworthy that the emplacement of post-collisional granites in the KB was suggested to be triggered by slab break-off of the Indian Plate during post-collisional setting (Mahar et al., 2014;Awais et al., 2022). ...
... According to Nabelek et al. (2010), magmas produced through strain-related melting, may be episodic because as the partially molted increases, strain heating cease and, only after melts extraction from the molten zone occurs, strain heating can recommence, leading to production of a new generation of partial melts. Episodic strain-related magmatism is suggested by Harrison et al. (1999) to explain the time span of the granitic intrusion in the Central Himalaya. It could explain more than 20 Ma. of syn-transcurrent magmatism in the studied region. ...
... Inverted metamorphism has long been associated with areas of extensive thrust faulting where heat is thought to flow from a hot upper plate to a colder lower plate (Ernst, 1973;Graham & England, 1976;Spear et al., 1995). Some models of Himalayan orogenesis link the anomalous geothermal gradient spatially and temporally with motion along the MCT, whereas others suggest a juxtaposition of previously metamorphosed sequences (Searle & Rex, 1989;Harrison et al., 1999;Hodges, 2000;Dasgupta et al., 2004;Larson et al., 2015). ...
The Himalayan orogen exposes assemblages from low-grade Indian shelf sediments of the Tethyan Formation to eclogite and ultra-high-pressure rocks from the suture zone between the Indian craton and Asian subcontinent. Barrovian-grade pelites in the Himalayan core comprise the Greater Himalayan Crystallines and Lesser Himalayan formations. These units are separated by the Main Central Thrust (MCT), which accommodated a significant amount of convergence. We describe and apply isopleth thermobarometry and high-resolution pressure-temperature (P-T) path modeling to decipher the metamorphic history of garnet-bearing rocks collected across the MCT in central Nepal. Results are compared to with previous reports of conventional rim P-T conditions and P-T paths that used Gibb's method on the same data and assemblages. Predictions of the paths on garnet zoning are also presented for the high-resolution P-T path modeling and Gibb's method using the program TheriaG. Although the approaches yield different absolute conditions and P-T path shapes, all are consistent with the development of the MCT shear zone due to the imbrication of distinct rock packages. Greater Himalayan Crystalline garnets experienced higher grade conditions, making extracting its P-T conditions and paths challenging. Lesser Himalayan garnets appear to behave as closed systems and are ideally suited for thermodynamic approaches.
... Two subparallel leucogranite belts were defined in the Himalayan orogen: the Tethyan Himalayan leucogranite belt in the northern side and the High Himalayan leucogranite belt in the southern side (Figure 1a; e.g. Le Fort 1981;Harrison et al. 1999). Leucogranites in the former belt mainly intruded into the core of the North Himalayan gneiss dome (NHGD) in the THS and have an emplacement age of 46 ~ 8 Ma. ...
Contamination is a common scenario of intracrustal magmatic processes that may significantly change the compositions of involved anatectic melts. Here, we present major element and B isotope analyses on tourmalines from the Guowu leucogranite and their host rocks, which allow us to unravel the potential contaminations of the Himalayan leucogranites by metapelite host rocks. Three types of tourmaline have been identified in our samples. Tur-M in the host schist has the highest Mg/(Mg+Fe) ratio (0.52–0.62) and low Al content, suggesting its metamorphic character. Tourmalines in the leucogranite (Tur-L) and in the contact zone between leucogranite and schist (Tur-C) have an identical core-rim texture, and their cores are characterized by the lowest Mg/(Mg+Fe) ratio (0.13–0.18) and high Al content, which are consistent with the composition of magmatic tourmaline in the Himalayan leucogranites. The rims of Tur-L show higher Mg/(Mg + Fe) ratio (0.32–0.45) and moderate Ca, Ti, F contents, reflecting the contribution of the host schist via contamination. The composition of Tur-C rims is similar to that of Tur-M, suggesting a more significant contribution from contaminated schist than that for Tur-L. The different types of tourmaline share consistent B isotope compositions with δ11B ranging from -14 to -12‰. The compositional characteristics of the contaminated tourmaline and the mineral assemblage in the contaminated zone suggest that the involved components derived from the host schist, probably produced by the decomposition of tourmaline, biotite, plagioclase, primarily include Ca, K, Mg, Ti, B and F. In addition, contamination by tourmaline-bearing metapelite may be an alternative interpretation responsible for the peraluminous character of the Himalayan leucogranites. The occurrence of contaminated tourmaline in leucogranites suggests that contamination of host rocks is a possible way promoting the formation of tourmaline in the Himalayan leucogranites, and tourmaline is useful for deciphering the related contamination processes.
... example, if the scenario was similar to the model proposed byHarrison et al. (1999) for the827 Himalaya Orogen, where both features (contacts and isograds) are nearly parallel to each other828 but oblique to the shear zone at the end of the metamorphic peak, then all the lithostratigraphy 829 would be passively rotated during exhumation along the thrust surface, causing an inversion of 830 the layers. This process would generate primary structures with inverted positions, which do 831 not occur at the PN, as mentioned before. ...
Inverted metamorphic gradients are recognized in several Proterozoic to Phanerozoic orogens. However, the mechanisms that are responsible for the formation of these gradients are still a matter of discussion. In the southern Brasília Orogen, an inverted metamorphic gradient is recorded in the Passos Nappe, that comprises a sequence of metasedimentary rocks with minor intercalations of tholeiitic metamafic rocks, metamorphosed under greenschist facies (biotite zone) at the bottom and high-pressure granulite facies at the top. This paper presents a detailed investigation of pressure and temperature conditions along the Passos Nappe by integrating conventional geothermobarometry in metamafic rock and single-trace elements geothermometry (Zr-in-rutile and Ti-in-quartz) in quartzite. Nine lithostratigraphic units are identified in the Passos Nappe, which are informally named A to I, from the bottom to top, adding up to a minimum thickness of 4.56 km. In mafic rocks, the increase of metamorphic conditions is indicated by: (1) chemical variation of amphiboles, from actinolite/edenitic hornblende in Unit C, to pargasitic hornblende in Units E and G, and Fe-pargasite in Units H and I; (2) plagioclase composition varying from An1-13 in Unit C, An15-27 in Unit D to andesine at upper units; and (3) occurrence of clinopyroxene from the top of Unit E upwards. Additional petrographic features in quartzite also corroborate these insights, such as: the increase of grain size of both quartz and rutile, from bottom to top; the morphology of rutile crystals; the mechanism of quartz recrystallization (subgrain rotation dominates in lower units while grain boundary migration dominates in upper units) and the occurrence of rutile needles in quartz in the upper units, which suggest a continuous gradient. Combined application of Zr-in-rutile and Ti-in-quartz geothermometers in quartzite provided the following average temperature and pressure values for each unit: 673 °C and 11.7 kbar for Unit E, 690 °C and 9.5 kbar for Unit G, 747 °C and 11.6 kbar for Unit H and 758 °C and 11.3 kbar for Unit I. Our data indicate that the Zr-in-rutile and Ti-in-quartz systems do not re-equilibrate in metamorphic conditions lower than 600 °C. The extrapolation of these results to the low-grade units indicate: 496 °C and 4.8 kbar at Unit A, 504 °C and 4.8 kbar at Unit B, 502 °C and 4.4 kbar at Unit C. The results obtained with the geothermometer hornblende-plagioclase and the geobarometer garnet-rutile-ilmenite-plagioclase-quartz in metamafic rocks yielded the following average values for each unit: 486 °C and 5.0 kbar at Unit C, 568 °C and 6.0 kbar at Unit D, 622 °C and 8.1 kbar at Unit E, 650 °C and 8.4 kbar at Unit G, 743 °C and 9.4 kbar at Unit H and 723 °C and 11.2 kbar at Unit I. Since the two geothermobarometric approaches are based on independent chemical systems, the results obtained represent robust estimates for the temperature and pressure conditions for the inverted metamorphic gradient of the Passos Nappe. Comparing the inverted metamorphic gradient at the Passos Nappe with classical occurrences at the Himalaya Orogen, it is possible to assume that both origins were similar, which probably involved isotherm inversion due to subduction, channel flow process associated with shear heating and transport of higher pressure rocks over low-pressure rocks by reverse ductile shearing.
... Thus, pre-orogenic basins commonly have their original stratigraphy completely modified during deformation (Tavani et al., 2015;Lacombe and Bellahsen, 2016), disturbed also by contemporaneous high-grade metamorphism and partial melting (Collins, 2002), and thrusting of the basement (Lacombe and Bellahsen, 2016). Furthermore, in fold-and-thrust belts, as in the case of the Dom Feliciano Belt in South America, thrust sheets and shear zones make the pre-orogenic reconstruction even more difficult, as allochthonous sheets can be carried over thousands of kilometres, often causing an inversion of the original stratigraphy, and high-grade rocks are placed on top of lower grade ones, as observed in the Himalayas, for instance (Harrison et al., 1999). Nevertheless, some approaches can be chosen to address these problems. ...
This work investigates the pre-collisional (before ca. 650 Ma) history of the Dom Feliciano Belt in southernmost Brazil through geochronological and zircon oxygen isotope study. U-Pb SHRIMP dating of two orthogneiss samples from the Várzea do Capivarita Complex and one metarhyolite sample from the Porongos Complex yielded crystallisation ages of 786 ± 5 Ma, 780 ± 10 Ma and 787 ± 5 Ma, respectively. The mean oxygen isotope values calculated for the ca. 790 Ma zircon cores from the orthogneisses are 8.41 ± 0.13‰ and 8.68 ± 0.14‰, and 8.75 ± 0.72‰ for the metarhyolite. Such values suggest that zircon crystallised in the more evolved magmas, either from the melting of host rocks and sediments or assimilation of crustal material by mantle-derived magmas. The detrital zircon population was analysed in one additional paragneiss sample from the Várzea do Capivarita Complex, and most of the values cluster at 790-750 Ma. The data spread is centred at ca. 790 Ma, which is the crystallisation age of the interleaved orthogneisses. In our interpretation, such dataset suggests a syn-volcanic origin of the paragneiss protolith and, therefore, a volcano-sedimentary origin of the Várzea do Capivarita Complex. The correspondence of geochronological data and zircon oxygen isotope values for the studied meta-igneous samples suggests that the Várzea do Capivarita and Porongos complexes have shared the same igneous history. Therefore, the samples probably represent one magmatic event at different levels of a single basin at ca. 800-770 Ma. Such results bring first-order information about the meaning of tectonic limits in this Gondwana-related belt and implications for reconstructing the pre-collisional history of the orogen.
... Assim, bacias pré-orogênicas comumente têm sua estratigrafia original completamente modificada durante a deformação ( TAVANI et al., 2015;LABOMBE & BELLAHSEN, 2016). Além disso, em cinturões de dobras e cavalgamentos (fold-and-thrust belts), como é o caso da Cinturão Dom Feliciano, fatias de litologias alóctones podem ser transportadas por milhares de quilômetros, muitas vezes causando inversão da estratigrafia original e colocando rochas de alto grau sobre as de baixo grau metamórfico, como pode ser observado nos Himalaias, por exemplo ( HARRISON et al., 1999). No entanto, apesar da dificuldade, algumas abordagens podem ser escolhidas para resolver esses problemas. ...
The full data is available at the paper:
Reconstruction of a volcano-sedimentary environment shared by the Porongos and Várzea do Capivarita complexes at 790 Ma, Dom Feliciano Belt, southern Brazil - By: Battisti et al. 2022.
The original architecture of pre-collisional environments in collisional scenarios is difficult to reconstruct due to mountain-building processes. This work investigates the pre-collisional (before ca. 650 Ma) history of the Dom Feliciano Belt in southernmost Brazil through the geochronological study of two samples from the Várzea do Capivarita Complex: a tonalitic orthogneiss and a pelitic paragneiss. U-Pb SHRIMP dating of studied orthogneiss yielded a crystallisation age of 786 ± 5 Ma. The Detrital zircon population analysed in the paragneiss shows that most values cluster at 790-750 Ma. The data spread is centred at ca. 790 Ma, which is the crystallisation age of the surrounding orthogneisses. In our interpretation, such dataset suggests a syn-volcanic origin of the paragneiss protolith, and therefore, at least partly, a volcano-sedimentary origin of the Várzea do Capivarita Complex.
... Ruppel and Hodges, 1994;Huerta et al., 1998;Jamieson et al., 1998). Deformational models imply that inverted metamorphic gradients preserve evidence of inverted thermal structures at or near the time of peak metamorphic conditions (England et al., 1992;Harrison et al., 1999;Burg and Schmalholz, 2008). Structural but post-metamorphism models appeal to recumbent folding (Ray, 1947;Gansser, 1964;Searle et al., 1992), thrust imbrication (Frank et al., 1973;Jain and Manickavasagam, 1993), or distributed shearing (Grujic et al., 1996;Hubbard, 1996;Grasemann et al., 1999) of a pre-existing, right-way-up metamorphic sequence in the High Himalaya gneiss sequence, without requiring an inverted thermal gradient at any time. ...
Despite the occurrence of high-grade metamorphic rocks next to and along crustal-scale shear zones, the temporal character of their formation and evolution is difficult to extract. We utilize the major-element diffusion in the compositional re-adjustment of garnet from metapelites in two crustal-scale shear zones as a complementary method to extract cooling rates from deforming/reacting rocks. The two thrust zones, the Nestos Thrust Zone (NTZ) in Rhodope, Greece, and the Main Central Thrust (MCT) in Sikkim, Himalaya, exhibit inverted metamorphic zonation. We applied phase equilibria modelling and geothermometry to constrain the peak- and the post-peak-temperature conditions relevant for the cooling-rate estimates. Results are 50–80 °C/Myr in the footwalls of both thrust zones, in consistency with published estimates using geochronology methods for MCT. However, results are much less (∼0.5–5°C/Myr) for the base of the MCT hanging wall. The estimated cooling rates are between 300 and 2500 C/Myr for the NTZ hanging wall. The exceedingly fast cooling rates indicate the operation of transient and proximal thermo-mechanical processes consistent with the contribution of thrust-related viscous heating during metamorphism. The very slow cooling rate of the MCT hanging wall may reflect a complex thermal history or other overlooked processes.
... Post-Eocene deformation of the India-Eurasia dominant collision zone has brought the convergence system to its current configuration ( Windley, 1983 ) ( Fig. 1 ). The convergence system is prominently characterized by coeval tectonic events during Late Oligocene-Early Miocene epoch to produce some orogen-scale, east-trending fault zones in both the northern Himalayas and southernmost Tibet ( Hubbard and Harrison, 1989 ;Kellett et al., 2019 ;Kellett and Grujic, 2012 ;Li et al., 2008 ;Quidelleur et al., 1997 ;Yin et al., 1999Yin et al., , 1994, as well as the northern Himalayan inverted high-grade metamorphism ( Harrison et al., 1999b ; Ren et al. (2013) ). The inset shows the study area in the larger context of the Tibetan Plateau. ...
... Both of them contain highly fractionated or evolved granites . The leucogranites intruding into the Greater Himalayas appear as a discontinuous chain of sills and dikes adjacent to the STDS ( Harrison et al., 1999b ;Searle et al., 2003 ). One pluton intruding into the Tethyan Himalayan Sequence penetrated either the axial zone of the gneissic dome or the Tethyan sedimentary sequence ( Fig. 1 ). ...
... Meanwhile, leucogranites of the northern Himalayan domes required a low rate of fluid infiltration ( Guo and Wilson, 2012 ;Le Fort et al., 1987 ) during mantlederived heating ( Zheng et al., 2016 ). The leucogranites in two belts originated either from in-situ partial melting of metapelites ( Harrison et al., 1999b ;Molnar et al., 1983 ;Searle et al., 2003 ) or from a high temperature magma that experienced extensive fractional crystallization after long-distance migration from the locality of anatexis Yang et al., 2019 ). ...
The Late Oligocene-Early Miocene epoch represents a critical stage in the collisional history of the India-Eurasia dominant collision zone. Within this timeframe, a set of tectonic events occurred simultaneously or progressively. However, the key responsible for triggering these nearly coeval events remains unclear. This study used an integrated analysis of both geological and geophysical data to document the tectonic interactions throughout the Himalayan Orogenic Belt from west to east. Deep seismic reflection profiles outline crustal geometry of a decoupled Indian subduction front, and the overlying sheets over the Main Himalayan Thrust (MHT) is evidenced with a sequence of detachment-associated ramp-anticlines. Meanwhile, regional magnetotelluric (MT) profiles document rheologic connections in the form of a high-conductivity anomaly running top-to-the south between the southernmost Tibet and the areas beyond the Yarlung-Zangbo Suture Zone to the south. The overall architecture provides a complete picture of the complex deformation pattern beneath the tectonic convergent system. Together with previous studies in surface geological investigations, we propose that the enhanced duplex stacking of the underthrusting Indian crust increased crustal shortening of the convergent system. The consequent sudden exposure of the northern Himalayan domes released the accumulated stress to trigger the onset of a south-dipping passive roof thrusting through the convergent system to the southernmost Tibetan Plateau. Recognition of this exchange pattern from crustal duplex stacking to passive roof thrusting replenished an understanding of the tectonic interactions of the ongoing India-Eurasia collision.
... Ahmad et al. (2000), Deniel et al. (1987), Inger and Harris (1993), , Richards et al. (2005) and Zeng et al. (2009. Literature data for leucogranites are from Deniel et al. (1987), Gao et al. (2015Gao et al. ( , 2017, Gao and Zeng (2014), Guo and Wilson, (2012), Harrison et al. (1999a), Hou et al. (2012), Hu et al. (2017, Inger and Harris (1993), Ji et al. (2020), King et al. (2011), Lin et al. (2020, , Zeng et al. (2009Zeng et al. ( , 2019, Zhang et al. (2004) and . The endmembers (high Sr/Y granite dike and Himalayan paragneiss) of mixing line are from Ji et al. (2020), whose compositions are listed in Table 1. ...
Plain Language Summary
The Himalayas have been formed from the collision between two tectonic plates. During their formation, the rocks of the continental crust have melted to form leucogranites which potentially provide important information on how the collision process evolves. Several recent studies of rare‐element mineralization associated with these granites have argued that the magmas result from extensive removal of early formed minerals during the cooling of the magma (fractional crystallization [FC]) which, if true, would undermine their usefulness as monitors of the collisional process. In this study, we address this issue through a geochemical approach that combines isotopic data from iron, strontium, and neodymium. Whereas Sr and Nd give information on the source of the magmas, the isotopes of Fe will remain largely unfractionated if the granites result simply from melting the crust but fractionate significantly during FC. Our results reveal very limited fractionation of Fe isotopic compositions for two types of leucogranites, which is inconsistent with the model requiring a high degree of FC but supports the interpretation that they represent largely unfractionated crustal melts. Our study therefore confirms that Himalayan leucogranites can provide reliable probes for the thermal and tectonic evolution of the Himalayan crust.
