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[Display omitted] • The Halazha pluton is composed of 244 Ma quartz diorites and intruded 233 Ma granodiorites, both containing coeval MMEs. • The formation of MMEs involves two stages of magma mingling. • The Halazha pluton is derived from the partial melting of the juvenile crust. • Amphibole cumulates can contribute to the formation of quartz diorites. Granitoids and coeval mafic microgranular enclaves (MMEs) provide important insights into petrogenesis and crustal evolution. In the eastern sector of the East Kunlun Orogen, the Halazha (HLZ) pluton contains abundant MMEs, recording magma mingling processes. The HLZ pluton comprises quartz diorites and granodiorites, whereas the MMEs have a gabbroic-dioritic composition. This paper provides a detailed description of the petrography and mineralogy of the HLZ pluton and MMEs, and presents new ages and geochemical data. The zircon U–Pb dating results indicate that quartz diorites and granodiorites are ranging from 243 ± 2 Ma to 244.8 ± 1.3 Ma and from 233.3 ± 1.1 Ma to 233.6 ± 1.5 Ma, respectively. The zircon ages of the coeval MMEs are identical to the host rocks, i.e., 244.5 ± 1.1 Ma − 244.5 ± 1.2 Ma, and 233.7 ± 1.3 Ma, respectively. Both quartz diorites and granodiorites contain hornblende, display metaluminous characteristics with average A/CNK values of 0.93 and 0.99, respectively, and thus belong to I-type granite. Both of them are enriched in large-ion lithophile elements such as Rb and Ba and depleted in high-field-strength elements such as Nb and Ta. In addition, they both have low ε Hf (t) values, ranging from −5.6 to −1.7 and −5.4 to −1.79, respectively. Results suggest that HLZ pluton is derived from magmas formed by the partially melting juvenile mafic lower crust. Quartz diorites experienced hornblende accumulation for its low SiO 2 contents. Whereas, the high Sr/Y ratio of granodiorites attributes to the fractional crystallization of apatite. Notably, the crystallization pressure and temperature (average 3.43 kbar and 764 °C) of the hornblende xenocrysts in MMEs is close to it of the hornblende phenocryst in quartz diorite (average 3.68 kbar and 766 °C). This similarity indicates that MMEs in the quartz diorites resulted from magmatic mingling between the mafic magma and the host rock within the deep crust. The hornblende xenocrysts present in MMEs of the granodiorites contain a higher number of inclusions, reveal higher crystallization pressures (average 2.73 kbar) and temperatures (average 825 °C) compared to their host rocks (average 1.35 kbar and 702 °C). These results suggest that MMEs in granodiorites underwent two distinct magmatic mixing processes: the magmatic mixing of mafic magma in the deep crust and then during the upwelling process after this mixed mafic magma entered the granodiorites. [ABSTRACT FROM AUTHOR]

Abstract: Knowledge of the Little Ice Age (LIA) on the Tibetan Plateau (TP) is of critical importance for understanding the climate changes over the past millennium. However, the data associated with the extents and chronologies of TP LIA moraines are highly dispersed in literature. Lack of systematic integration of these data hampers us to further understand the nature of the LIA, especially from a perspective of whole TP. The paper reviews multiple types of dating on LIA moraines to examine the timing and nature of the LIA on the TP. These include ages of radiocarbon 14C, lichenometry, and cosmogenic radionuclide (CRN), by which we can cross-date the same or morphostratigraphically similar landforms. LIA moraines on the TP are usually present a few hundred to thousand meters beyond the contemporary glaciers. The morphological and stratigraphic evidence indicates multiple periods of glacier advance during the last millennium (LIA). At present, available chronology evidence allows to fully compare the timing of the LIA maximum extents. The glaciers reached and retreated from their LIA maximum extents by an asynchronous pattern between different parts of the TP. The majority of glaciers advanced to their LIA maximum extents at late-14th and early-14th century on the southern and northwestern TP, respectively. The glaciers retreated from their LIA maximum extents during 16th to early-18th, late-14th to early-15th and early-16th century on the southern, northwestern, and northeastern TP, respectively. In addition, the glacier advance period of late-18th to early-19th centuries and retreat period of late-19th century are common on the whole TP. Comparison with ice core records suggests that on the TP, the glacier fluctuations responded more strongly to temperature than to precipitation. By comparison of the LIA chronologies from a global perspective, this paper also concludes that the LIA maximum extents occurred commonly earlier on the TP than in North Atlantic and Southern Hemisphere regions, despite of the variability in the timing of LIA maximum extents on the TP and in the North Atlantic regions. Further, more chronology programs, especially in the central TP, are necessarily needed to improve our understanding of the LIA glacier fluctuations. [Copyright &y& Elsevier]

[Display omitted] • 432 Ma granites formed in a syn-collisional setting. • 422-411 Ma granites formed in a post-collisional environment. • East Kunlun evolved into a post-collisional stage in the Early Devonian. Middle Paleozoic granitoids in the East Kunlun Orogen of the northern Tibetan Plateau play an important role in deciphering the tectonic evolution of the Proto-Tethys Ocean. This paper presents petrological, whole-rock geochemical, zircon U-Pb geochronological, and Sr-Nd isotopic data for granodiorites, garnet-bearing granites, and syenogranites in the East Kunlun Orogen. These granites have zircon U-Pb ages of 432 Ma, 423 Ma, and 413 Ma, respectively, taken to be their crystallization ages. They have mineralogical and geochemical features of I- (or I-S transition), S-, and A-type granitoids, respectively. Primitive magma of the I-type granodiorite is inferred to be derived from partial melting of a juvenile lower crust, whereas the S-type garnet-bearing granites could be linked to partial melting of greywackes in the middle/lower crust. In contrast, the A-type syenogranite may have been derived from the Neoproterozoic granites at high-temperature and low-pressure conditions. In addition, the 432 Ma I-type granites were likely emplaced in a syn -collisional setting, and the 423–411 Ma S- and A-type granites formed in a post-collisional environment in response to the slab break-off/detachment and asthenosphere upwelling during the Middle Silurian-Early Devonian. These distinct granites suggest that the East Kunlun Orogen evolved into a syn -collisional stage due to the collision between North Kunlun and South Kunlun Terrane during the Middle Silurian (ca. 438 Ma) before experiencing a post-collisional collapse in the Late Silurian to Early-Middle Devonian. These results together with the Silurian orogeny of regional Qilian and Qinling orogens suggest the Proto-Tethys oceans in central China fully closed during Middle Silurian-Early Devonian, and then generated the middle Paleozoic Kunlun-Qilian-Qinling Orogen in East Asia. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Subashi ophiolite in West Kunlun Orogenic Belt was formed at ca. 455–446 Ma. • Geochemical features indicate the Subashi ophiolite formed in a MOR setting. • Mazha-Kangxiwa mélange zone with Subashi ophiolite marks a Proto-Tethys suture. The West Kunlun Orogenic Belt (W-KOB) in the northwestern Tibetan Plateau retains critical information about the tectonic evolution of the Proto- and Paleo-Tethys during the Early Paleozoic to Mesozoic. Although a trench-arc-back arc basin model was used to address the tectonic evolution of Proto-Tethys, records about the evolution of this ocean basin remain ambiguous, particularly no studies about ages and tectonic affinities of ophiolites in the W-KOB are available. In this paper, we present new results on whole-rock elemental and Sr-Nd isotopic composition of basalts, and U-Pb zircon ages of gabbro, diabase and basalt from the Subashi ophiolite. The basalts are characterized by low REE concentrations, depleted LREEs in the chondrite normalized REE patterns, and unfractionated HFSEs in the primitive mantle normalized trace element spider diagrams, resembling normal mid-ocean ridge basalts. They have constant 87Sr/86Sr(i) values of 0.70472–0.70590 and positive ε Nd values of +7.5 to +7.9. Accordingly, it can be concluded that the Subashi ophiolite was derived from a depleted spinel lherzolite mantle source in a mid-ocean ridge setting. Zircon grains separated from basalt, diabase and gabbro have 206Pb/238U ages of 455 ± 4 Ma, 451 ± 6 Ma, and 446 ± 6 Ma, respectively, which are taken to be the crystallization ages of these rocks. Together with previously published data, our new data propose that the Mazha-Kangxiwa-Subashi ophiolitic mélange zone marks the existence of the Proto-Tethys ocean basin during the Early Paleozoic. [ABSTRACT FROM AUTHOR]

The Bangong–Nujiang suture zone (BNSZ) is located in the central Tibetan Plateau, and represents the relict of the Bangong–Nujiang Tethyan Ocean (BNTO). This paper presents zircon U–Pb ages and whole-rock geochemical and Sr–Nd isotope data for the ophiolitic rocks from the Rutog, Dongco, Dongqiao, Amdo, and Dengqen areas (from west to east) in the BNSZ. Zircon U–Pb ages obtained from five gabbros and one leucogabbro from the five areas are 169 ± 2, 167 ± 2, 187 ± 2, 184 ± 2, 177 ± 3, and 164 ± 2 Ma, respectively. Mafic rocks (gabbros and basalts) in the BNSZ can be divided into MORB-like and OIB-type, based on geochemical data. The MORB-like rocks are tholeiitic and can be further divided into N- and E-MORB subtypes, marked by depleted and flat REE patterns, respectively. All MORB-like rocks show supra-subduction zone (SSZ) geochemical affinities such as mild enrichment in the large ion lithophile elements and depletion in the high field strength elements, coupled with high and positive whole-rock ε Nd ( t ) values (+ 8.1 to + 5.4). The OIB-type rocks, which formed in the Early Cretaceous (~ 132–108 Ma), are exposed in the Dongco, Dongqiao, and Tarenben areas, and they consist mostly of alkali basalts with within-plate geochemical characteristics and positive ε Nd ( t ) values (+ 5.9 to + 4.5). On the basis of these new data, combined with information from the literature, we further support that the BNTO was an intra-oceanic arc–backarc basin that existed between the North Lhasa subterrane (NLT) and the South Qiangtang subterrane (SQT) during the Early–Middle Jurassic. This basin may have been active until the Early Cretaceous, when the OIB-type basalts erupted. [ABSTRACT FROM AUTHOR]

Eocene magmatic rocks are widespread in western Yunnan, southeastern Tibetan Plateau. However, their petrogenesis and tectonic significance remain controversial. In this paper, we report geochemical and geochronological data of adakite-like rocks from the eastern part of western Yunnan. Zircon U–Pb dating reveals that they were emplaced at ca. 35 Ma. A geochemical study shows that these rocks have high SiO 2 (68.97–72.44 wt.%), K 2 O (4.35–5.87 wt.%) and low MgO (0.61–1.16 wt.%), Y (6.65–12.6 ppm) and Yb (0.58–1.02 ppm) contents as well as high Sr/Y (74–228) and La/Yb (59–131) values, belonging to high-K calc-alkaline to shoshonitic adakite-like rocks. These rocks have high ( 87 Sr/ 86 Sr)i (0.70623–0.70653), low ε Nd (t) (− 4.5 to − 7.5) and slightly low radiogenic Pb isotopic compositions with ( 206 Pb/ 204 Pb)i = 18.042–18.179. Zircons of these rocks show ε Hf (t) values ranging from − 6.3 to + 1.2 and model ages (T DM2 ) of 1513–1035 Ma. The geochemical characteristics indicate that the Eocene adakite-like rocks from the eastern part of western Yunnan were derived from the partial melting of Neoproterozoic mafic rocks underplated in the lower crust of the western margin of the Yangtze Plate with input of mantle-derived potassic–ultrapotassic melt. Integration of published geochemical data clearly shows that zircon ε Hf (t) and whole-rock ε Nd (t) values of Eocene adakite-like rocks from the whole western Yunnan exhibit a trend of westward increase. We infer that the adakite-like rocks from the western part of western Yunnan were derived from the partial melting of late Paleozoic–Mesozoic mafic rocks formed as the lower crust of a continental magmatic arc during eastward subduction of the Paleo-Tethyan Ocean, and the Eocene magmatic rocks in western Yunnan were generated during the removal of thickened continental lithosphere triggered by the India and Asia collision. [ABSTRACT FROM AUTHOR]

Abstract: The Xianshuihe–Xiaojiang fault zone (XFZ) forms a prominent linear NW–SE trending tectonic feature along the southeastern margin of the Tibetan Plateau. The spatial and temporal evolution of the predominantly strike–slip movement along the fault remains unclear, as estimates for the initiation age of its different segments range from 5 to 13Ma. The Jinhe–Qinghe fault (JqF; the south part of the Longmen Shan thrust belt) provides a key for understanding the tectonic role and deformation history of the Xianshuihe–Xiaojiang fault zone in terms of timing, magnitude of displacement, and spatial–temporal evolution. This paper presents research on the structure and chronology of the JqF. The results of a geometric and kinematic study of the Jinhe–Qinghe fault show it to be a thrust fault with a left-lateral strike slip component; The strike slip offset extends at least 13–18km to southwest, based on the shortening of its folds and faulting, and based on stream deflection. Ten apatite fission track apparent ages show a pronounced change in age/elevation gradient at ~17±2Ma, consistent with an abrupt increase of exhumation due to uplift of the hanging wall of the JqF at that time. Combined with the age of deformed Tertiary strata in the footwall of the JqF and the geometric relationships of the JqF with the Chenghai fault and the XFZ, this indicates that the JqF was active between 17 and 5Ma. Based on the fault chronology, geometry, and movement, we suggest that the fault was a transpressional structure at the south end of the XFZ during the period from 17 to 5Ma. [Copyright &y& Elsevier]