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The petrogenesis of Himalayan leucogranites remains crucial for understanding the thermal and tectonic evolution of the Himalayan orogen. To understand whether they are largely pristine melts of crustal anatexis or have experienced a high degree of fractional crystallization (FC), we present Fe isotopic data of 30 representative Himalayan leucogranites and 9 local metasedimentary rocks. Excepting three garnet leucogranites with low δ56Fe (−0.04‰–0.06‰) that are likely affected by garnet accumulation, tourmaline, and two‐mica leucogranites have largely homogeneous δ56Fe from 0.13‰ to 0.24‰ irrespective of their highly variable SiO2, MgO, and FeOt contents. Combined with observed mineral assemblages and available fractionation factors, this does not support a high degree of FC (with or without assimilation) in their petrogenesis. The elevated δ56Fe relative to the supposed source rocks, represented by metasedimentary rocks and/or metabasite with a δ56Fe value of 0.10‰, by ∼0.07‰, may reflect Fe isotope fractionation during crustal anatexis. This study indicates most leucogranites can provide robust constraints on the conditions of crustal anatexis and thus the thermal and tectonic evolution of the Himalayan orogen. 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. Key Points: The first integrated Fe‐Sr‐Nd isotopical and geochemical data set of Himalayan leucogranites and metasedimentary rocks are presentedIsotopic and geochemical data suggest that two‐mica and tourmaline leucogranites have not experienced a high degree of fractional crystallizationThe low δ56Fe values of garnet leucogranites were likely derived from garnet accumulation [ABSTRACT FROM AUTHOR]

Voluminous Early Cretaceous volcanic rocks in the central Lhasa subterrane provide an ideal opportunity for understanding the mantle–crust interaction and tectonic‐magmatic evolution of the Lhasa Terrane. Here, we report zircon U–Pb ages, geochemical and Sr–Nd–Pb–Hf isotopic data for the Early Cretaceous volcanic rocks, including high‐silica rhyolites (117.2 ± 1.1 Ma) and contemporaneous andesites (114.1 ± 0.8 Ma) in the Sailipu area, central Lhasa subterrane. All these rocks show enriched light rare earth elements (LREE), and radioactive heat‐generating elements (e.g., Th, U, K, and Pb) but depleted high‐field‐strength elements (HFSEs, e.g., Nb, Ta, P, and Ti). The different bulk‐rock Sr–Nd–Pb and zircon Hf isotopic compositions of the rhyolites and andesites suggest that these rocks have distinct magma sources and petrogenetic history rather than an identical source involving assimilation‐fractional crystallization process. The Sailipu high‐silica rhyolites exhibit the characteristics of fractional crystallization and have varying zircon εHf(t) values (−12.2 to +5.2), negative εNd(t) values (−9.5 to −1.6), high and variable initial Sr isotopic compositions ([87Sr/86Sr]i = 0.7047–0.7116) and radiogenic Pb isotopic signatures (206Pb/204Pb = 18.784–18.802, 207Pb/204Pb = 15.722–15.737, and 208Pb/204Pb = 39.382–39.492). A combined process of magma mixing (involving crustal‐derived felsic melts and mantle‐derived mafic melts) and subsequent fractional crystallization were mainly responsible for the formation of these high‐silica rhyolites. The Sailipu andesites show more enriched Sr–Nd isotopic compositions [(87Sr/86Sr)i = 0.7088–0.7154, εNd(t) = −9.9 to −6.7] relative to rhyolites, and less radiogenic Pb isotopic compositions (206Pb/204Pb = 18.632–18.669, 207Pb/204Pb = 15.686–15.689, 208Pb/204Pb = 39.140–39.201). They were likely derived from partial melting of an enriched mantle wedge previously metasomatized by melts derived from subducted sediments. We interprete these Early Cretaceous volcanic rocks as the product of slab break‐off during the southward subduction of the Bangong‐Nujiang Tethyan oceanic seafloor. The dominantly positive εHf(t) and ancient TDMC ages (0.85–1.90 Ga) of Sailipu high‐silica rhyolites further imply that, under the stress relaxation regime, the mantle‐derived melts locally reworked the ancient basement of the central Lhasa subterrane. [ABSTRACT FROM AUTHOR]

Abstract Late Cretaceous magmatism in the southern Lhasa subterrane, Tibet, provides critical constraints on the subduction processes of the Neo-Tethyan oceanic plate. Here, we provide data on the whole-rock geochemistry, zircon U Pb ages, trace element contents, and Hf isotopes of early Late Cretaceous volcanic rocks from Sangri County to Sangye Temple (SS) along the southern Lhasa subterrane. The SS volcanic rocks include basalts, andesites, and dacites. SIMS and LA–ICP–MS zircon U Pb data indicate that the SS dacites were erupted at ca. 95 Ma, coeval with the early Late Cretaceous "flare-up" event in the southern Lhasa subterrane. The SS volcanic rocks belong to the calc-alkaline to high-K calc-alkaline series and have the geochemical features of subduction-related volcanic rocks with negative Nb, Ta, and Ti anomalies. The basalts have similar rare earth element (REE) patterns to E -MORB and are characterized by high Zr abundances (65–190 ppm) and Zr/Y ratios (3.3–6.5). They were possibly derived by high-degree partial melting of mantle peridotite that had been metasomatized by subduction-related fluids with an input of asthenospheric components. Positive whole-rock ε Nd (t) (+2.9 to +3.2) values for the andesites, and their variable Mg# values (35–61) and MgO (2.29–7.32 wt%), Cr (12–232 ppm), and Ni (10–127 ppm) contents can be attributed to medium-degree partial melting of mantle peridotite followed by fractional crystallization of clinopyroxene and olivine. The calc-alkaline SS dacites are similar to adakites with high Sr (663–1188 ppm) and low heavy rare earth element (HREE) and Y (10.7–11.5 ppm) contents. These adakitic dacites have positive whole-rock ε Nd (t) (+2.9 to +3.4) and zircon ε Hf (t) (+8.4 to +14.9) values with relatively high values of Mg# (36–57) and high contents of compatible elements, indicating that they were derived from the partial melting of subducted oceanic slab, and with the ascending magma interacting with mantle wedge peridotite. Our new data indicate a distinct rock association of coeval asthenosphere-component-involved basalts and slab-derived adakitic dacites. Such an association, together with the coeval high-temperature charnockites and high-temperature granulite-facies metamorphism of the charnockitic country rocks in the southern Lhasa subterrane, indicates an anomalous input of materials and heat during the early Late Cretaceous "flare-up" event. Such an event can probably be attributed to the northwards subduction of a Neo-Tethyan oceanic ridge that allowed for contributions from upwelling asthenosphere that differed from the typical results of normal-angle subduction or low-angle/flat subduction and subsequent slab rollback. Highlights • Volcanic rocks erupted at ~95 Ma from the Sangri-Sangye area, southern Lhasa. • Basalts were derived from partial melting of mantle wedge with an asthenospheric component input. • Dacites show the geochemical features of adakites in the SS volcanic rocks. • The SS volcanic rocks were likely the products of Neo-Tethyan oceanic ridge subduction. [ABSTRACT FROM AUTHOR]

A large volume of Early Cretaceous volcanic rocks are exposed in the central Lhasa subterrane, which are essential for models developed for understanding the evolution of Lhasa Terrane. However, the petrogenesis and geodynamic background of these rocks are still in debate. In this paper, we carried out a detailed study on the volcanic rocks of the Zenong Group, including andesite, dacite, and rhyolite from the Coqen area in the central Lhasa subterrane. Zircons from one dacitic tuff yields an age of 115.3 ± 1.1 Ma. All the rocks are enriched in light rare earth elements (LREEs), Th, U, and Pb and depleted in high field strength elements (HFSEs, e.g. Nb, Ta, P, and Ti). The dacite and rhyolite samples are high-K calc-alkaline to shoshonitic and are metaluminous to peraluminous. These felsic samples are characterized by negative ƐNd(t) (−8.9 to −2.1) and ƐHf(t) (−8.1 to −5.6) and have high radiogenic Pb isotopic composition (206Pb/204Pb = 18.6287-19.5578, 207Pb/204Pb = 15.7161-15.7720, and 208Pb/204Pb = 39.1440-40.6253). Particularly, a negative correlation between the ƐNd(t) values and SiO2 contents can be observed in these dacites and rhyolites. Meanwhile, the andesites exhibit similar Sr-Nd-Pb isotopic compositions to dacites and rhyolites (ƐNd(t) = −4.3; 206Pb/204Pb = 18.7119-18.8575, 207Pb/204Pb = 15.7159-15.7203, and 208Pb/204Pb = 39.2944-39.6036). Our new data indicate that different geochemical reservoirs are involved in generating the ca. 115 Ma magmatism in the central Lhasa subterrane. It is likely that dacites and rhyolites are derived from the magma mixing between the ancient basement-derived melts and mantle-derived melts with varying degrees of partial melting. The andesites might originate from partial melting of an ancient lithospheric mantle that have been metasomatized by fluids and/or melts derived from the Tethyan oceanic slab. Our results, together with recent studies, suggest that the Zenong Group volcanic rocks in the Coqen area may represent the magmatic responses to the break-off of the southward subduction of the Bangong-Nujiang Tethyan oceanic slab. [ABSTRACT FROM AUTHOR]

Abstract: The Lhasa Terrane in southern Tibet is an ideal region to investigate the geodynamic processes of magmatism in relation to slab breakoff. Here we report zircon SHRIMP U–Pb ages and Hf-isotopes, and whole-rock geochemical data from the late Early Cretaceous magmatic rocks around Xainza. The rocks analyzed in this study include basalts, andesites, dacites, and rhyolites from the south of Xainza in the central Lhasa subterrane and the coeval rhyolites in Daguo from the north of Xainza in the northern Lhasa subterrane. The zircon U–Pb data indicate that the Xainza dacites and the Daguo rhyolites erupted contemporaneously at ca. 116Ma, approximately coeval with the Xainza basalts as judged from an adjacent volcanic sequence with systematic compositional change with time. The Xainza basalts are calc-alkaline and display geochemical signatures comparable to those of within-plate basalts rather than typical arc-type basalts. The Xainza andesites and dacites are high-K calc-alkaline and metaluminous to slightly peraluminous. The Daguo rhyolites belong to high-K calc-alkaline–shoshonite and are mostly strongly peraluminous. The whole-rock εNd(t) of the Xainza basalts (−3.5 to 0.6) is markedly different from those of the Xainza andesites (−13.6 to −13.0) and dacites (−9.4 to −9.1). The Daguo rhyolites are high-K calc-alkaline–shoshonite and peraluminous and display geochemical signatures similar to highly fractionated A2-type silicic rocks. Zircons from a rhyolite from Daguo yield εHf(t) values of −1.1 to +4.6, significantly different from those of the Xainza dacites (−8.2 to −4.4). The Xainza basalts are most likely derived from partial melting of an enriched mantle wedge that was metasomatized by subduction-related components, accompanied with significant contributions from subslab asthenospheric mantle. The andesites are generated from partial melting of an ancient lower crust, whereas the dacites are interpreted as the consequences of varying degrees of interaction between the mature Lhasa basement (Al-rich) and mantle-derived melts. The Daguo rhyolites are derived from partial melting of a juvenile crust and experienced significant fractional crystallization. In combination with the other existing data, we suggest that the generation of the ca. 113Ma magmatic rocks around Xainza is most likely triggered by the slab breakoff of the southward subducting Bangong–Nujiang Tethyan Ocean lithosphere. The geological records of the Lhasa–Qiangtang collision zone, particularly the presence of mafic rocks showing within-plate basalt geochemistry, A2-type silicic rocks, and coeval bimodal volcanic rocks in a continent–continent collision zone suggest a petrological association diagnostic of slab breakoff setting. [Copyright &y& Elsevier]

Abstract: This paper reports new zircon LA-ICP-MS U–Pb age and Hf-isotope, whole-rock major and trace element, and Sr–Nd isotope data from Cambrian metavolcanic rocks in the central Lhasa subterrane of southern Tibet. These rocks form a bimodal volcanic suite consisting mainly of silicic metavolcanic rocks with subordinate metabasalts. Five silicic metavolcanic samples dated at ca. 492Ma and one metabasalt sample yielding a near-concordant 206Pb/238U age of 492±4Ma indicate that mafic and silicic eruptions were contemporaneous. The metabasalts are mostly high-K calc-alkaline, enriched in Th, U, and light rare earth elements (LREEs), and depleted in Nb, Ta, Ti, Zr, and Hf, geochemically resembling the Andean arc basalts. The silicic metavolcanic rocks are high-K calc-alkaline and low in Nb and Zr. The metabasaltic rocks have negative whole-rock εNd(t) values (−4.7 to −3.5) and varying zircon εHf(t) values (−0.7 to +7.5), differing significantly from those of the silicic metavolcanic rocks, which yield negative whole-rock εNd(t) values of −8.4 to −7.2 and varying zircon εHf(t) values (−13.9 to −4.6). The metabasaltic rocks are interpreted as resulting from partial melting of an enriched lithospheric mantle source that was metasomatized by subduction-related components, whereas the silicic metavolcanic rocks were derived from basaltic melt-induced anatexis of the ancient Lhasa basement with inherited mantle melt signatures. The Western Qiangtang–Amdo–Tethyan Himalaya situated in the Indian proto-Tethyan margin and the Lhasa and other possible microcontinents or terranes (e.g., Gongshan, Baoshan, Tengchong, Burma, and Sibumasu) paleographically located in the Australian proto-Tethyan margin represent an early Paleozoic Andean-type magmatic arc facing the proto-Tethyan Ocean. The emplacement of the bimodal volcanic rocks and the development of the Cambro–Ordovician angular unconformity in the central Lhasa subterrane can be attributed to slab break-off of the proto-Tethyan Ocean lithosphere following the collisional accretion of microcontinents or terranes located outboard of the magmatic arc (possibly Eastern Qiangtang and South China). [Copyright &y& Elsevier]

Abstract: The petrogenesis and geodynamic implications of the Cenozoic adakites in southern Tibet remain topics of debate. Here we report geochronological and geochemical data for host granites and mafic enclaves from Wolong in the eastern Gangdese Batholith, southern Tibet. Zircon LA-ICP-MS dating indicates that the Wolong host granites and enclaves were synchronously emplaced at ca. 38Ma. The host granites are medium- to high-K calc-alkaline, metaluminous (A/CNK=0.93–0.96), with high Al2O3 (15.47–17.68%), low MgO (0.67–1.18%), very low abundances of compatible elements (e.g., Cr=3.87–8.36ppm, Ni=3.04–5.71ppm), and high Sr/Y ratios (127–217), similar to those typical of adakite. The mafic enclaves (SiO2 =51.08–56.29%) have 3.83–5.02% MgO and an Mg# of 48–50, with negative Eu anomalies (δEu=0.59–0.79). The Wolong host granites and enclaves have similar Sr–Nd isotopic compositions (initial 87Sr/86Sr=0.7053–0.7055, ε Nd(t)=−2.7 to −1.4), with varying zircon ε Hf(t) values, ranging from +6.0 to +12.6. A comprehensive study of the data available for adakitic rocks from the Gangdese Batholith indicates that the Wolong adakitic host granites were derived from partial melting of a thickened lower crust, while the parental magmas of the mafic enclaves were most likely derived from lithospheric mantle beneath southern Tibet. The Wolong granitoids are interpreted as the result of mixing between the thickened lower crust-derived melts and lithospheric mantle-derived mafic melts, which are likely the protracted magmatic response to the break-off of the Neo-Tethyan oceanic slab at about 50Ma. Our results suggest that the crustal thickening in southern Tibet occurred prior to ~38Ma, and support the general view that the India–Asia collision must have occurred before 40Ma. [Copyright &y& Elsevier]

Abstract: Bulk-rock major and trace element, Sr–Nd isotope, zircon U–Pb and Hf-isotope data are reported for Early Cretaceous igneous rocks sampled along an east–west traverse through the central Lhasa subterrane (E80°00′–E89°) in southern Tibet. These results offer new insights into the pre-Cenozoic geology and tectonomagmatic evolution of the Lhasa Terrane, and provide boundary conditions for the origin and evolution of the Tibetan Plateau. Our new data, together with data from the literature indicate that the Early Cretaceous magmatism in the central Lhasa subterrane lasted for a long period (~143–102Ma) with a magmatic flare-up at ~110 Ma. The latter is accompanied by mafic magmatism in this terrane. The silicic rocks are metaluminous to peraluminous, and enriched in Rb, Th, and U, and depleted in Ba, Nb, Ta, Sr, P, and Ti, with varying initial 87Sr/86Sr (0.7073–0.7209), negative ε Nd(t) (−13.7 to −4.6), and negative to positive zircon ε Hf(t). The andesitic and dioritic enclaves are characterized by initial 87Sr/86Sr of 0.7088–0.7148, ε Nd(t) of −9.9 to −7.8, and zircon ε Hf(t) of −9.5 to −0.2, similar to those of the 110±3Ma silicic rocks. The bulk-rock Sr and Nd isotopic data and zircon ε Hf(t) values indicate an increased contribution of a mantle component in the generation of the Early Cretaceous igneous rocks in the central Lhasa subterrane at ~110Ma. Available bulk-rock Nd- and zircon Hf-isotope data indicate that the crust of the central Lhasa subterrane, at least its oldest elements, was emplaced during the Archean. This further indicates that the central Lhasa subterrane with ancient basement must have been a micro-continental block (i.e., the Lhasa micro-continental block) extending in an east–west direction for >700km (E82°–E89°) with a width of ~100km. The contemporaneous presence of S-type (more crustal source) and I-type (significant mantle input) melts of the Early Cretaceous igneous rocks in this subterrane are interpreted as the consequences of varying extents of interactions between the existing continental crust and mantle-derived melts (including crustal anatexis). We suggest that the mantle-derived melts resulted from southward subduction of the Bangong–Nujiang Ocean seafloor in a syncollisional setting related to the Lhasa–Qiangtang collision, and that the magmatic flare-up with strong mantle input at ~110Ma was genetically associated with the slab break-off of this subducting seafloor. [Copyright &y& Elsevier]

In western Yunnan, potassic felsic suites with important Cu mineralization have been interpreted as being genetically associated with the Ailao Shan-Red River (ASRR) shear zone. In this paper, we show that the magmatism is unrelated to the shear zone, but shares many characteristics in common with potassic suites along the Jinsha suture to the north and northwest on the northern Tibetan Plateau, representing a magmatic response to the continued India-Asia convergence since the collision in the early Eocene. These felsic suites include syenite, monzogranite porphyries and granite porphyries. We dated 15 representative samples using zircon U-Pb method that gives a tight emplacement age of ~37–35 Ma. On 45 representative samples, we have done bulk-rock major element, trace element and Sr-Nd-Pb isotope analysis. We use these data, together with zircon Hf isotope data and the literature data on potassic mafic suites in the region to discuss the petrogenesis of these rocks. We conclude that the petrogenesis of the felsic potassic suites is most consistent with a scenario of deep (≥ 40 km) melting of thickened crust. The crustal melting is caused by intrusion and underplating of potassic mafic melts derived from melting of metasomatized mantle lithosphere. The mafic potassic suites in the region result from such mantle melts. Mixing of the mafic melts with the felsic melts explains the syenite and monzogranite porphyries and their extended fractional crystallization gives rise to the granite porphyries. The potassic suites along the Jinsha suture, including those from northern Tibet, western Yunnan and Vietnam, share the same tectonic setting during the Eocene-Oligocene. In response to the continued India-Asia convergence, removal of the lower continental lithospheric mantle triggered by Rayleigh-Taylor convective instability induces asthenosphere upwelling, partial melting of the metasomatized mantle lithosphere. We hypothesize that the eastward migration of the potassic magmatism along the Jinsha suture in the period of Eocene-Oligocene results from eastward thickening and removing of the continental lithospheric mantle along the suture, which, in time and space, correlates with the dischronal subduction of the torn Indian continental slab at ca. 52 Ma along the India-Asia collision zone. • The 35-37 Ma potassic suites in western Yunnan result from lower crust melting. • Their varied felsic compositions result from varying extent of fractional crystallization. • The removal of lithospheric mantle along the Jinsha suture was eastward-migrating. [ABSTRACT FROM AUTHOR]

A series of Cenozoic post-collisional mantle-derived magmas developed in the Southeastern Tibetan Plateau (the SE Plateau), which can be utilized to trace source components and mantle metasomatism, and further constrain the mantle evolution. In this paper, we present a systematic study on petrography, whole-rock major and trace element, Sr-Nd-Pb-Mg isotopes of Miocene-Holocene alkali basalts at the southeastern margin of the SE Plateau. These Miocene-Holocene alkali basalts were the products of the northward extension of the Cenozoic mantle-derived magmatism in Southeast Asia (SE Asia), since they are comparable in terms of geographical distributions, petrographic characteristics, geochronology patterns, and geochemical compositions. The alkali basalts in this study are mainly basanite and trachybasalt, characterized by enriched LILEs, depleted Sr-Nd-Pb isotopes, positive anomaly in HFSEs, and significantly lighter Mg isotopes (−0.51‰ to −0.32‰) relative to primitive mantle. Integrated Sr-Nd-Mg isotopes and seismic tomography suggest a source regions from the mantle transition zone that has been enriched by significant carbonate sediments. The decoupling of high Sr contents and depleted Sr Nd isotopes in the alkali basalts indicate that the mantle carbonation is subjected to recent subduction events and is possibly related to the subduction of the Neo-Tethyan seafloor. The calculated melting temperature of these basalts are generally high (1487–1583 °C), which is consistent with that of Cenozoic basalts in SE Asia (1470–1480 °C) and Hainan island (1480–1530 °C), showing a high-temperature gradient similar to that of mantle plume-related magmatism. Consequently, the generation of Miocene-Holocene alkali basalts is plausibly associated with the Hainan plume. • Sanjiang alkaline basalts are the northward extension of basalts in Southeast Asia. • Sanjiang alkali basalts are originated from the mantle transition zone. • Alkali basalts in the southeastern Plateau originated from the carbonated mantle. • Alkali basalts are related to the Hainan mantle plume. [ABSTRACT FROM AUTHOR]

Petrogenesis of the Himalayan leucogranite is strongly influenced by conditions which are associated with the tectonic evolution of Himalayan orogen. In this article, we present petrological, geochronological and geochemical results of the Lhozag leucogranites that crop out alongside the South Tibetan Detachment System (STDS) in the east of Himalaya. Zircon U-Pb dating revealed three episodes of leucogranitic magmatism in Lhozag at 17.8 ± 0.1 Ma, 15.1 ± 0.1 Ma, and 12.0 ± 0.1 Ma, respectively. The Lhozag leucogranites show relatively low ε Nd (t), low zircon ε Hf (t) and high initial 87 Sr/ 86 Sr ratios, which are similar to the High Himalayan Crystalline Series (HHCS), indicating that they were derived from the HHCS. The characteristics of relatively high Na 2 O and Rb contents, high Rb/Sr ratios and low CaO, MgO, TFe 2 O 3 , TiO 2 , and Sr contents indicate that both the ca. 18 Ma Lhozag tourmaline leucogranites and the ca. 15 Ma Lhozag two-mica granites were derived from fluid-absent muscovite-dehydration melting of metasediments. The opposite geochemistry characteristics of the ca. 12 Ma Khula Kangri two-mica granites imply that these granites are derived from fluid-present melting of metasediments. Four Khula Kangri two-mica granite samples with relatively lower TiO 2 , TFe 2 O 3 , MgO, and CaO contents, higher Rb concentrations and Rb/Sr ratios could be evolved from the Khula Kangri two-mica granites with relatively lower Rb/Sr ratios. The melting behaviors of the Lhozag leucogranites varied from fluid-absent melting to fluid-present melting, implying that there were P - T - X H2O variations in the deep crust. The tectonic evolution would give rise to variation of P - T - X H2O variation, and subsequent transformation of melting behavior. Our new results display the transformation of melting behavior of the Lhozag leucogranites, which implies the tectonic evolution from earlier N–S extension to later E–W extension in the eastern Himalaya at ca. 12 Ma. [ABSTRACT FROM AUTHOR]

Oligocene and Miocene Himalayan anatexis is generally thought to have been induced by intracrustal heating or processes without the involvement of mantle-derived heat and materials, suggesting that the Himalayan leucogranites are typical examples of purely crustal melts. This study focuses on a Miocene leucogranite at Langkazi within the Himalayan orogen, an intrusion that contains a large number of dioritic enclaves. These enclaves have typical igneous textures, contain acicular apatites, and have back-veining structures, quenched margins, and crystallization ages identical to the hosting two-mica granites, indicating that these enclaves are magmatic. Although the enclaves are evolved, the most primitive samples contain high concentrations of MgO (up to 4.3 wt.%), Cr (up to 159 ppm), and Ni (up to 102 ppm), are strongly enriched in large-ion lithophile elements, are depleted in high-field-strength elements, have negative ε Nd(t) values (–8.6 to –6.1), and have relatively high 87 Sr/ 86 Sr (i) values (0.7085–0.7137), suggesting that they were derived from a relatively enriched region of the lithospheric mantle source. Whole-rock geochemical data indicate that the hosting Langkazi leucogranite formed from magmas generated by the partial melting of metapelite material within the High Himalaya crystalline sequence, and these magmas subsequently mixed with mantle-derived melts that are now represented by the Langkazi dioritic enclaves. This indicates that mantle-derived material played an important role in the generation of the Langkazi intrusions. The whole-rock geochemical compositions of samples from the study area also indicate that the primary melts that formed the Langkazi enclaves were significantly contaminated by the relatively juvenile Himalayan lower crustal material, suggesting in turn that these mantle-derived magmas underwent MASH (crustal melting, melt assimilation, magma storage, and homogenization) processes at the base of crust, introducing heat to the lower crust. This mantle-derived heat may have induced partial melting of the Himalayan lower crust, forming adakite-like magmas. Although the small volumes of these dioritic enclaves suggest that this heat may have assisted the genesis of the north Himalayan granites and the High Himalayan leucogranites, whereas in situ crustal radiogenic heating, shear heating, and decompression melting dominated the melting processes in this region. [ABSTRACT FROM AUTHOR]

Paleogene potassium-rich volcanic rocks (PVRs) are widespread in the southeastern Tibetan Plateau, providing an opportunity to illustrate the architecture of the lithosphere and further constrain the development of the SE Plateau. Their petrogenesis, together with the geodynamic mechanism, remains in dispute. Mg isotopic compositions of the PVRs in western Yangtze Craton, along with new elemental and Sr-Nd-Pb isotopic data, are utilized to elucidate their petrogenesis and reveal the plausible metasomatic and genetic mechanisms. The PVRs give a compositional spectrum from basaltic trachyandesite to trachyte and are characterized by high large ion lithophile elements concentrations, negative anomalies in high field strength elements, and enriched Sr-Nd-Pb isotopes, suggesting an origin of enriched lithospheric mantle. The correlations among varying major oxides and fractional crystallization simulation results jointly reveal fractional crystallization of olivine and clinopyroxene in the magmatic process. The less-evolved PVRs present similar major oxide contents (e.g., Ti, Na, K) to those melts originated from carbonated peridotite + silicate sediment. Apart from enriched Sr-Nd-Pb isotopes, they also show high La/Yb ratios (11.73–58.95), low Ti/Ti* (0.08–0.71), Hf/Sm (mostly <0.70), and varying δ26Mg values (−0.13 to −0.36‰). Combined with the Sr-Nd-Mg isotope numerical simulations, it points out that the mantle source of the PVRs was replenished by a hybrid carbonate-silicic sediment, which was plausibly caused by the Neoproterozoic seafloor subduction. These volcanic rocks also present relatively high K 2 O (3.29–7.50 wt%) and K 2 O/Na 2 O ratios (1.00–2.85). Besides, varying elevated Rb/Sr and low Ba/Rb ratios, together with the La/Yb-Yb non-modal batch melting result, suggest that the enriched mantle source recorded by these PVRs is predominantly constituted by a hybrid phlogopite-bearing garnet-spinel lherzolite. Constrained by petrology studies and seismic tomography, the generation of the PVRs is proposed to be closely associated with the delamination of the thickened lithosphere and thereafter asthenosphere upwelling. • Paleogene K-rich volcanic rocks in the western Yangtze Craton are variably evolved. • These volcanic rocks are sourced from phlogopite-bearing garnet-spinel lherzolite. • Recorded mantle source was replenished by a hybrid carbonate-silicic sediment. [ABSTRACT FROM AUTHOR]

We report petrological and geochemical data on coeval trachybasalts, syenites with enclaves, trachytes, peralkaline rhyolites and peraluminous rhyolites from the Glass House Mountains–Maleny–Noosa area, southeast Queensland, Australia. This rock association and the unique characteristics of the peralkaline rhyolites offer convincing lines of evidence that the petrogenesis of the peralkaline rhyolites is a straightforward consequence of protracted fractional crystallization from basaltic melts of alkali-rich composition. Compared to the common peraluminous rhyolites elsewhere, the peralkaline rhyolites here are characterized by elevated abundances of most incompatible elements, especially the very high Nb (vs. Th) and Ta (vs. U), the very low Ba, Sr and Eu and the extremely high 87 Sr/ 86 Sr ratio. The high Nb and Ta are inherited from the parental alkali basaltic melts. The low Ba, Sr and Eu result from removal of plagioclase during the protracted fractional crystallization. These rocks altogether define a Rb–Sr isochron of ~ 28 Ma, which is similar to Ar–Ar age data on these rocks in the literature. The extremely high 87 Sr/ 86 Sr ratio of the peralkaline rhyolites (up to 1.88) is actually characteristic of peralkaline rhyolites because of extreme Sr (also Eu and Ba) depletion and thus the very high Rb/Sr ratio. That is, the Sr in these rocks is essentially radiogenic 87 Sr accumulated from the 87 Rb decay since the volcanism. We suggest that the petrogenesis of the peralkaline rhyolites from the Glass House Mountain area may be of general significance globally. The coeval peraluminous rhyolites apparently result from crustal anatexis in response to the basaltic magma underplating. The small “Daly Gap” exhibited in this rock association is anticipated during the protracted fractional crystallization from basaltic parent to the more evolved felsic varieties. [ABSTRACT FROM AUTHOR]

Abstract: Early Triassic syn-collisional granitoids with mafic magmatic enclaves (MMEs) crop out along the entire East Kunlun Orogenic belt (EKOB) at the northern margin of the Tibetan Plateau. They are andesitic in composition and enriched in light rare earth elements (LREEs) with a flat heavy REE (HREE) pattern. Their average composition resembles that of the bulk continental crust. The enclosed MMEs have the same mineralogy as their host granitoids, but contain a greater mode of mafic minerals (amphibole and biotite), and thus have higher HREE abundances. Zircon U–Pb dating shows that both the granitoid hosts and MMEs have the same crystallization age of ~250Ma and indistinguishable bulk rock Sr–Nd–Pb–Hf isotope compositions (ISr of 0.7080–0.7116, varying 206Pb/204Pbi of 18.53–19.32, essentially constant εNd(t) of −5.3 to −2.1 and a small range of positive εHf(t), mostly 1.7–5.2). The complete isotopic overlapping between the granitoid hosts and the MMEs is understood to reflect that the MMEs are disintegrated cumulates formed at an early stage of the granitoid magma evolution within the same magmatic system. The isotopic data set reveals that the granitoids are variably evolved melts produced by partial melting of the subducted Paleo-Tethyan oceanic crust with terrigenous sediments under amphibolite-facies conditions in response to the continental collision. [Copyright &y& Elsevier]

• The quartz albite porphyry emplaced at 318.6 ± 3.0 Ma in a subduction environment. • The I-type granite quartz albite porphyry originates from the juvenile lower crust. • The northward subduction of oceanic crust generated these intrusions and mineralization. The Linglong porphyry Cu deposit is located in the Dananhu–Tousuquan Arc Belt, adjacent to the large Tuwu–Yandong Cu deposits in Eastern Tianshan, northwest China. In this study, zircon U–Pb, whole rock geochemistry, and zircon Hf–O isotopic analyses were carried out on the Linglong intrusions (i.e., quartz albite porphyry and diorite porphyry). New SIMS zircon U–Pb dating and previous data indicate that the quartz albite porphyry occurred in the Late Carboniferous (318.6 ± 3.0 Ma), younger than emplacement of the diorite porphyry (338–340 Ma) and tonalite porphyry (332–335 Ma) in this area, as well large-scale copper mineralization (331–335 Ma) in Eastern Tianshan. The geochemistry of the quartz albite porphyry intrusions is consistent with calc-alkaline normal arc magmatism, characterized by high SiO 2 (74.82–77.89 wt%), obvious Eu anomalies (0.42–0.52), high Y (21–25.9 ppm) and Yb (2.98–3.67 ppm) concentrations, moderate Mg# values (35–40), but relatively low Sr/Y (6.86–9.52)and low 10,000 Ga/Al values. In situ Hf–O isotopic analyses on zircons show that the quartz albite porphyry rocks have variable ε Hf (t) (+9.0 to + 13.9) and low δ18O values (4.72 to 5.84‰), suggesting a juvenile lower crust derived composition. However, the diorite porphyry intrusions show features of low SiO 2 (57.51–61.12 wt%), minor Eu anomalies (0.82–1.15), strong depletion in high field strength elements (e.g., Nb, Ta, P and Ti), but enrichment in large ion lithophile elements (e.g., Rb, Ba, K and Pb). They also exhibit normal island arc magma geochemical signatures, with high Y (20.9–40.2 ppm), and Yb (2.75–4.64 ppm) concentrations, high Mg# (40–51), and relatively low (La/Yb) N (2.07–4.10) and Sr/Y (5.75–12.13) values, suggesting the melt was derived from the subduction-modified mantle mafic to ultramafic materials. Combined with regional tectonic evolution and our new data, we suggest that the Late Carboniferous magma was generated during the period of the northward subduction of the Paleo-Tianshan ocean plate beneath the Dananhu–Tousuquan island arc. [ABSTRACT FROM AUTHOR]