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Being a part of the Paleo- Tethys Ocean, closing of the Buqingshan- Anyemaqen oceanic basin left a rich geologic record in the East Kunlun Orogenic Belt. The genesis and tectonic setting of the granites including quartz monzodiorite, granodiorite and mozogranite is discussed in light of the geochemical and U- Pb chronological data obtained. U- Pb dating studies on zircon from the quartz monzodiorite and monzogranite of the research area yielded ages of 220.11 ± 0.49 Ma ( (Mean Square Weighted Deviates) MSWD = 0.046) and 223.33 ± 0.54 Ma ( MSWD = 0.14), respectively, by Laser Ablation Multiple Collector Inductively Coupled Plasma Mass Spectrometry ( LA-MC-ICP-MS) method. According to sedimentological and structural investigations, the Paleo- Tethys Ocean in the Qimantag region began to close at about 235 Ma, and completely disapperared at about 220 Ma. The three types of granites in this study are considered to intrude the syn- to post-collisional stages. The quartz monzodiorite and granodiorite belong to the I-type granite whereas the monzogranite is of the S-type granite. These two types of granites were formed by different ways of partial melting: first, partial melting of the lower crust took place as a result of asthenosphere upwelling triggered by break-up of the leading edge or tearing of the descending oceanic slab. Subsequently partial melting of the middle-lower crust was caused by the underplating of basaltic magma formed by partial melting of the mantle wedge fluxed by fluids liberated by the oceanic slab dehydration. The magma responsible for the formation of S-type granites appears to have originated from partial melting of the upper crustal material at a shallower level with a clear signature of continental crust. [ABSTRACT FROM AUTHOR]

Early Cretaceous high-Mg adakitic rocks from central Eastern China provide important insights into the thinning mechanism of the over-thickened lithosphere in the Yangtze Block (YB) as well as the North China Block (NCB). The Tanlu fault (TLF), located between the North China and Yangtze Blocks, and has been considered as a prominent pathway of magmas and fluids that resulted in lithosphere thinning of the YB during the Mesozoic–Cenozoic. Here we report the petrology, whole-rock geochemistry, zircon U–Pb geochronology, in situ Hf isotopes, and whole-rock Sr–Nd–Pb isotopes of four high-Mg adakitic intrusions along the TLF in northeastern Langdai. These adakitic intrusions consist of monzodiorite, quartz monzonite porphyry, and quartz monzodiorite. Zircon LA-MC-ICPMS analyses of five samples yield weighted mean 206 Pb/ 238 U ages of 127.58 ± 0.80, 126.90 ± 0.81, 120.71 ± 0.64, 122.75 ± 0.57, and 129.2 ± 1.1 Ma, indicating their emplacement during the Early Cretaceous. The intrusions have intermediate SiO 2 (53.18–65.48 wt%) and high potassium (K 2 O = 3.07–3.95 wt%; Na 2 O/K 2 O = 1.02–1.26) and are classified as shoshonitic to high-K calc-alkaline series. They are characterized by high MgO (1.80–7.35 wt%), Mg # (50–65), Sr (591–1183 ppm), Ni (20.3–143.0 ppm), and Cr (51.40–390.0 ppm) contents, high (La/Yb) N (11.60–28.33) and Sr/Y (27.9–113.5) ratios, and low Y (7.79–22.4 ppm) and Yb (0.60–2.01 ppm) contents, comparable with high-Mg adakites. The samples are enriched in light rare earth elements but depleted in heavy rare earth elements and high field strength elements with slightly negative to positive Eu anomalies ( δ Eu = 0.81–1.30), resembling the features of high-Mg adakitic rocks. Their whole-rock ε Nd( t ) = −16.2 to −15.0, initial ( 87 Sr/ 86 Sr) i = 0.7060–0.7074, low radiogenic Pb ( 206 Pb/ 204 Pb( t ) = 16.208–16.509, 207 Pb/ 204 Pb( t ) = 15.331–15.410, and 208 Pb/ 204 Pb( t ) = 36.551–36.992), and zircon ε Hf( t ) = −36.6 to −16.6 suggest magma derivation from a continental crustal source. The geochemical and isotopic features, in combination with existing geological data, suggest that the intrusions are high-Mg adakites and, by comparison with contemporaneous intrusions in Eastern China, were likely to have been formed by partial melting of over-thickened basaltic lower crust following the delamination of eclogitic lithosphere during the Late Jurassic to Early Cretaceous. It is possible that the TLF played a key role in lithospheric delamination and thinning and in the generation of the high-Mg adakitic rocks. [ABSTRACT FROM AUTHOR]

The Late Cretaceous Mamba granodiorite belongs to a part of the Mesozoic Gangdese continental magmatic belt. No quantitative mineralogical study has been made hitherto, and hence the depth at which it formed is poorly constrained. Here we present mineralogical data for the Mamba pluton, including host rocks and their mafic microgranular enclaves (MMEs), to provide insights into their overall crystallization conditions and information about magma mixing. All amphiboles in the Mamba pluton are calcic, with (Ca+Na)>1.5, and Si=6.81-7.42 apfu for the host rocks and Si=6.77-7.35 apfu for the MMEs. The paramount cation substitutions in amphibole include edenite type and tschermakite type. Biotites both in the host rocks and the MMEs collectively have high MgO (13.19 wt.%-13.03 wt.%) contents, but define a narrow range of Al apfu (atoms per formula unit) variations (2.44-2.57). The oxygen fugacity estimates are based on the biotite compositions cluster around the NNO buffer. The calculated pressure ranges from 1.2 to 2.1 kbar according to the aluminum-in-hornblende barometer. The computed pressure varies from 0.9 to 1.3 kbar based on the aluminum-in-biotite barometer which corresponds to an average depth of ca. 3.9 km. Besides, the estimates of crystallization pressures vary from 0.8 to 1.4 kbar based on the amphibole barometer proposed by Ridolfi et al. (2010), which can be equivalent to the depths ranging from 3.1 to 5.2 km. The MMEs have plagioclase oscillatory zonings and quartz aggregates, probably indicating the presence of magma mixing. Besides, core-to-rim element variations (Rb, Sr, Ba, and P) for the K-feldspar megacrysts serve as robust evidence to support magma mixing and crystal fractionation. This indicates the significance of the magma mixing that contributes to the formation of K-feldspar megacryst zonings in the Mamba pluton. [ABSTRACT FROM AUTHOR]

The intermediate–mafic–ultramafic rocks in the Jianzha Complex (JZC) at the northern margin of the West Qinling Orogenic Belt have been interpreted to be a part of an ophiolite suite. In this study, we present new geochronological, petrological, geochemical and Sr–Nd–Hf isotopic data and provide a different interpretation. The JZC is composed of dunite, wehrlite, olivine clinopyroxenite, olivine gabbro, gabbro, and pyroxene diorite. The suite shows characteristics of Alaskan-type complexes, including (1) the low CaO concentrations in olivine; (2) evidence of crystal accumulation; (3) high calcic composition of clinopyroxene; and (4) negative correlation between FeO tot and Cr 2 O 3 of spinels. Hornblende and phlogopite are ubiquitous in the wehrlites, but minor orthopyroxene is also present. Hornblende and biotite are abundant late crystallized phases in the gabbros and diorites. The two pyroxene-bearing diorite samples from JZC yield zircon U–Pb ages of 245.7 ± 1.3 Ma and 241.8 ± 1.3 Ma. The mafic and ultramafic rocks display slightly enriched LREE patterns. The wehrlites display moderate to weak negative Eu anomalies (0.74–0.94), whereas the olivine gabbros and gabbros have pronounced positive Eu anomalies. Diorites show slight LREE enrichment, with (La/Yb) N ratios ranging from 4.42 to 7.79, and moderate to weak negative Eu anomalies (Eu/Eu ∗ = 0.64–0.86). The mafic and ultramafic rocks from this suite are characterized by negative Nb–Ta–Zr anomalies as well as positive Pb anomalies. Diorites show pronounced negative Ba, Nb–Ta and Ti spikes, and typical Th–U, K and Pb peaks. Combined with petrographic observations and chemical variations, we suggest that the magmatism was dominantly controlled by fractional crystallization and crystal accumulation, with limited crustal contamination. The arc-affinity signature and weekly negative to moderately positive ε Nd ( t ) values (−2.3 to 1.2) suggest that these rocks may have been generated by partial melting of the juvenile sub-continental lithospheric mantle that was metasomatized previously by slab-derived fluids. The lithologies in the JZC are related in space and time and originated from a common parental magma. Geochemical modeling suggests that their primitive parental magma had a basaltic composition. The ultramafic rocks were generated through olivine accumulation, and variable degrees of fractional crystallization with minor crustal contamination produced the diorites. The data presented here suggest that the subduction in West Qinling did not cease before the early stage of the Middle Triassic (∼242 Ma), a back-arc developed in the northern part of West Qinling during this period, and the JZC formed within the incipient back-arc. [ABSTRACT FROM AUTHOR]

It is a puzzle to determine metallogenetic ages in the world. This article uses zircon fission track (FT) dating to probe the mineralizing epochs of Wulonggou (五龙沟) gold ore deposits in eastern Kunlun (昆仑) Mountains. Total of six zircon FT ages have been obtained and can be divided into groups of 235-216 and 197-181 Ma, as well as 162 and 124 Ma, revealing multiple epochs of metallogenetic processes took place in Wulonggou area, mainly first two age groups. The mineralizing ages become lower from northeast Yanjingou (岩金沟) to southwest Hongqigou (红旗沟). The second epoch of 197-181 Ma is first achieved by this work. It is shown that the FT ages consist with other isotopic data and reflect different regional thermotectonic events. [ABSTRACT FROM AUTHOR]

Abstract: Although most porphyry-type deposits are associated with subduction-related magmas within magmatic arc settings, recent research has identified a number of porphyry-type deposits that formed in post-subduction tectonic settings. The newly discovered Habo porphyry Cu–(Mo–Au) deposit in Yunnan, China, formed in a post-subduction tectonic setting and is located in the southwest of the Cenozoic Ailao Shan–Red River continental collision zone. The deposit is associated with the Habo South granite pluton, which consists of three mineralization-related quartz monzonite porphyries and a post-mineralization diorite porphyry. Zircons from the Habo South granite and quartz monzonite porphyries were analyzed by in situ U–Pb LA-ICP-MS, yielding a similiar age of 36Ma, with molybdenite Re–Os isotope dating indicating that the Habo porphyry deposit formed at 35.5Ma. Both magmatism and the associated mineralization at Habo are coeval with porphyry copper deposits in the Yulong metallogenic belt of Eastern Tibet. The Habo South granite and porphyries have SiO2 concentrations of 67.28–73.44wt.%, MgO concentrations of <1.5wt.%, Al2O3 concentrations around 15wt.%, Al2O3/(CaO+Na2O+K2O) (A/CNK) ratios of >1.1, K2O+Na2O concentrations generally between 7 and 9wt.%, and K2O/Na2O ratios of >1.4, showing indicative of high-K magmas. The Habo South granite and quartz monzonite porphyries are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), and depleted in heavy rare earth elements (HREE) and high field strength elements (HFSE), with high Sr and low Y concentrations. They have initial 87Sr/86Sr values of 0.7071–0.7083, with ε Nd(t) values from −5.3 to −3.7. These features are indicative of lower-crust derived adakitic magmas, and are similar to those of mineralized porphyries in the Yulong copper belt in Eastern Tibet. This mineralogical, geochemical, and isotope evidence strongly suggests that the magmas that formed both porphyries and the Habo South granite were derived by partial melting of a region of thickened lower crust, with assimilation of components generated from a region of phlogopite-bearing lithospheric mantle involved during intrusion. The Habo porphyry deposit represents an extension of the Yulong metallogenic belt and formed in response to regional tectonic activity in Eastern Tibet. [Copyright &y& Elsevier]

Abstract: Lincang granite is a batholith located in the Sanjiang region and is an important research subject for understanding subduction and collision during the Paleo-Tethyan period. It is widely exposed in the Lincang Terrane and extends south into Burma. Based on various petrological and geochemical investigations performed from south to north across the Lincang granite, a new set of data, which includes zircon chronological and Hf isotopic data, is presented to discuss the origin of the Lincang granite and its tectonic significance. The Lincang granite is a peraluminous, high-K calc-alkaline body with sub-parallel REE patterns and a strong negative Eu anomaly. This anomaly is characteristic of a post-collision peraluminous S-type granitic batholith. The 200–230Ma formation age of the Lincang granite was determined using LA-ICP-MS zircon U–Pb dating. Thus, it has been confirmed that the granite formed during the late Triassic period, and the formation process lasted for approximately 30Ma. Geochemical and isotopic compositions indicate that the primary magma of Lincang granite most likely originated from a crustal source, and possibly underwent an assimilation–fractionation crystallization (AFC) process during its emplacement. The Lincang granite formed during the continental collision between the Baoshan–Gengma Terrane and the Lanping–Simao Terrane after the northeast subduction of the Paleo-Tethyan Oceanic Plate. Therefore, the late Triassic Lincang granite is important evidence for the closure of the Paleo-Tethyan Ocean. [Copyright &y& Elsevier]

The two basalt flows in Kupukuziman (库普库兹满) Formation of Keping (柯坪) area are the typical products of Permian magmatism. Based on systematic field investigations, we carried out geochemical studies on representative Keping basalts. The results show that the SiO contents in basalts range from 44.69 wt.% to 51.68 wt.%, and the total alkalis range from 4.05 wt.% to 5.5 wt.%, belonging belonging to alkaline basalts. The Ti/Y=468.27-565.35 and TiO=(2.88-3.82) wt.% compared to those of the high-Ti basalts in Emeishan (峨眉山) large igneous province (LIP) (TiO=(3.58-5.21) wt.%, Ti/Y>500, Xiao et al., 2004). The contents of MgO and compatible elements Cr (12.9-18.6 ppm), Ni (13.7-22.7 ppm), and Co (39.6-50.2 ppm) are low, which suggest that the samples have undergone varying grades of fractional crystallization. All the samples have uniform REE and other trace element characteristics, with enriched LREE and LILE relative to HREE and HFS, similar REE patterns without Eu anomaly. The basalts are also show slightly depleted of Ta and Nb. They have higher initial Sr/Sr ratios (0.707 211-0.708 300), lower ɛ( t) values (−2.47 to −4.14), and a narrow range of (Pb/Pb)=37.535 2-38.297 7, (Pb/Pb)=15.435 7-15.517 0, and (Pb/Pb)=17.206 5-17.874 7 ratios. The Ce/Y versus Zr/Nb diagram shows that the parent magmas were originated from low-degree partial melting of the garnet-lherzolite. The analysis results based on geochemical studies seem all point to the same conclusion that the Keping basalts have formed as a product of the interaction between the plume-derived melts and the lithosphere. [ABSTRACT FROM AUTHOR]

Abstract: 40Ar–39Ar step-heating experiments on eleven mineral separates have been conducted on eight volcanic rocks and a granite-porphyry dike from the Yangying and Wuyu basins in the middle Gangdese Belt, southern Tibet. New radiometric ages for sanidine and biotite separates in four volcanic rock samples from Yangying ranges from 10.32±0.07 to 11.40±0.11Ma, whereas plagioclase and biotite separates from a stratigraphic section of the Gaza Cun Formation in the Wuyu basin give ages from 12.57±0.08 to 13.2±0.2Ma. A granite-porphyry which cuts the lower part of the Gaza Cun Formation gives an age of 11.09±0.07Ma, and a dacite from the margin of Wuyu basin gives an age of 15.48±0.11Ma. These age data, in conjunction with geochemical data, suggest that the mid-Miocene post-collisional volcanic rocks from these two basins have both similarities and difference in their petrogenesis. The high [Sm/Yb]N (>7) ratio and high Sr concentration (423–1065ppm) in both suites are consistent with their parental melts derived from partial melting of eclogitized lower crust. However, the Yangying samples are more evolved than the Wuyu samples as manifested by lower MgO, Sr/Sr∗, Eu/Eu∗, and normative plagioclase. It is likely that the source material for the Yangying suite is likely more enriched in K2O than that of the Wuyu suite, perhaps has a greater contribution from metasomatized lithospheric mantle. It is apparent that the post-collisional volcanism in southern Tibet occurred spatially scattered and temporally within a short period in each volcanic basin. [Copyright &y& Elsevier]

Abstract: Ultrapotassic lavas having distinct geochemical compositions (K2O/Na2O >2, K2O >3%, and MgO >3%) are common and widespread on the Tibet Plateau, where they are closely linked to N–S-trending normal faults. The Tibetan ultrapotassic rocks range in age from ~8 to 24 Ma, slightly older than the spatially associated potassic rocks (10–22 Ma). These lavas consist mainly of trachyte, trachyandesite, basaltic trachyandesite, phonolite and tephriphonolite. They have high light rare earth element (LREE) and large ion lithophile element (LILE) concentrations, but are low in high field strength elements (HFSE). They are characterized by having extremely radiogenic Sr (87Sr/86Sr(i ) =0.710719 to 0.736451) and Pb isotopes (206Pb/204Pb=18.449–19.345, 207Pb/204Pb=15.717–15.803, 208Pb/204Pb=39.443–40.168) with unradiogenic Nd isotopes (ε Nd(0 ) =−7.6 to −15) and old Nd model ages (T DM =1.3–2.1 Ga), similar in character to the Himalaya crystalline basement. Their isotopic character is interpreted to reflect subduction of the Indian plate beneath the Lhasa terrane, leading to a highly contaminated mantle source. Delamination of the subducted oceanic/continental materials may have played an essential role in the genesis of the ultrapotassic rocks in the Lhasa terrane. The available geological, geochemical and geophysical data favor a model in which the Indian plate was subducted under southern Tibet. [Copyright &y& Elsevier]

Abstract: The Linzizong volcanic succession (~65–45 Ma) and the coeval batholiths (~60−40 Ma) of andesitic to rhyolitic composition represent a magmatic response to the India–Asia continental collision that began at ~70–65 Ma and ended at ~45–40 Ma with convergence continuing to present. These syncollisional felsic magmatic rocks are widely distributed along much of the >1500 km long Gangdese Belt immediately north of the India–Asia suture (Yarlung–Zangbo) in southern Tibet. Our study of the Linzizong volcanic rocks from the Linzhou Basin (near Lhasa) suggests that syncollisional felsic magmatism may in fact account for much of the net contribution to continental crust growth. These volcanic rocks show a first-order temporal change from the andesitic lower Dianzhong Formation (64.4–60.6 Ma), to the dacitic middle Nianbo Formation (~54 Ma), and to the rhyolitic upper Pana Formation (48.7–43.9 Ma). The three formations show no systematic but overlapping Nd–Sr isotope variations. The isotopically depleted samples with ε Nd(t) >0 indicate that their primary sources are of mantle origin. The best source candidate in the broad context of Tethyan ocean closing and India–Asia collision is the remaining part of the Tethyan ocean crust. This ocean crust melts when reaching its hydrous solidus during and soon after the collision in the amphibolite facies, producing andesitic melts parental to the Linzizong volcanic succession (and the coeval batholiths) with inherited mantle isotopic signatures. Ilmenite as a residual phase (plus the effect of residual amphibole) of amphibolite melting accounts for the depletion of Nb, Ta and Ti in the melt. The effect of ocean crust alteration plus involvement of mature crustal materials (e.g., recycled terrigeneous sediments) enhances the abundances of Ba, Rb, Th, U, K and Pb in the melt, thus giving the rocks an “arc-like” geochemical signature. Residual amphibole that possesses super-chondritic Nb/Ta ratio explains the sub-chondritic Nb/Ta ratio in the melt; residual plagioclase explains the slightly depleted, not enriched, Sr (and Eu) in the melt, typical of continental crust. These observations and reasoning plus the remarkable compositional similarity between the andesitic lower Dianzhong Formation and the model bulk continental crust corroborates our proposal that continental collision zones may be sites of net crustal growth (juvenile crust) through process of syncollisional felsic magmatism. While these interpretations are reasonable in terms of straightforward petrology, geochemistry and tectonics, they require further testing. [Copyright &y& Elsevier]

Abstract: The relationship between the breakup of eastern Gondwanaland and the Kerguelen plume activity is a subject of debate. The Cona mafic rocks are widely exposed in the Cona area of the eastern Himalaya of south Tibet, and are studied in order to evaluate this relationship. Cona mafic rocks consist predominantly of massive basaltic flows and diabase sills or dikes, and are divided into three groups. Group 1 is composed of basaltic flows and diabase sills or dikes and is characterized by higher TiO2 and P2O5 content and OIB-like trace element patterns with a relatively large range of ɛNd(T) values (+1.84 to +4.67). A Group 1 diabase sill has been dated at 144.7±2.4 Ma. Group 2 consists of gabbroic sills or crosscutting gabbroic intrusions characterized by lower TiO2 and P2O5 content and “depleted” N-MORB-like trace element patterns with relatively higher, homogeneous ɛNd(T) values (+5.68 to +6.37). A Group 2 gabbroic diabase dike has been dated at 131.1±6.1 Ma. Group 3 basaltic lavas are interbedded with the Late Jurassic–Early Cretaceous pelitic sediments; they have compositions transitional between Groups 1 and 2 and flat to slightly enriched trace element patterns. Sr–Nd isotopic data and REE modeling indicate that variable degrees of partial melting of distinct mantle source compositions (enriched garnet–clinopyroxene peridotite for Group 1 and spinel-lherzolite for Group 2, respectively) could account for the chemical diversity of the Cona mafic rocks. Geochemical similarities between the Cona mafic rocks and the basalts probably created by the Kerguelen plume based on spatial–temporal constraints seem to indicate that an incubating Kerguelen plume model is more plausible than a model of normal rifting (nonplume) for the generation of the Cona mafic rocks. Group 1 is interpreted as being related to the incubating Kerguelen plume–lithosphere interaction; Group 2 is likely related to an interaction between anhydrous lithosphere and rising depleted asthenosphere enriched by a “droplet” originating from the Kerguelen plume, while Group 3 may be attributed to thermal erosion resulting in the partial melting of lithosphere during the long-term incubation of a magma chamber/pond at a shallow crustal level. The Cona mafic rocks are probably related to a progressively lithospheric thinning beneath eastern Gondwanaland from 150–145 Ma to 130 Ma. Our new observations seem to indicate that the Kerguelen plume may have started its incubation as early as the latest Jurassic or earliest Cretaceous period and that the incubating Kerguelen plume may play an active role in the breakup of Greater India, eastern India, and northwestern Australia. [Copyright &y& Elsevier]

Abstract: The Tibetan crust is twice as thick as average continental crust. Crustal compression and shortening as a result of Indian–Asian collision is often considered to be the primary cause for the crustal thickening. In this paper, we show that magmatic contribution is also important. We come to this conclusion by documenting the Paleogene Linzizong volcanic succession (LVS), its coeval granitoid batholiths and the Miocene adakitic rocks along the Gangdese magmatic belt in southern Tibet. It has been widely accepted that the Indian–Asian collision proceeded from a “soft” phase at ∼65–70 Ma to a “hard” phase at ∼45–40 Ma, followed by continued post-collisional convergence to the present. In response to the collision and post-collision convergence are a series of tectono-magmatic events recorded in the Gangdese magmatic belt. These include (1) the syn-collisional LVS volcanism (∼65–40 Ma) and the emplacement of southern Gangdese batholiths (a peak age of ∼50 Ma); (2) a period (∼40 Ma to 25 Ma) that is magmatically quiescent, yet tectonically dominated by active compression and crustal shortening; and (3) the emplacements of post-collisional adakitic rocks (∼25–12 Ma), potassic–ultrapotassic volcanics (∼25–10 Ma) and peraluminous muscovite-bearing granites (∼between 24 and 18 Ma). These three major events contribute in different ways to the crustal thickness. Phase I, formation of the lower juvenile crust from ∼65 Ma to 50 Ma with crustal thickening largely concentrated at ∼50–40 Ma via input of mantle-derived magmas; Phase II, crustal thickening by tectonic shortening at ∼40–25 Ma; and Phase III, retaining crustal thickness, but thinning of the lithospheric mantle since ∼25 Ma in response to crustal extension and upwelling and lateral flow of asthenospheric mantle. We emphasize that collision-induced crustal thickening took place mainly in the period of ∼50–40 Ma and ∼25 Ma, i.e., the period between the late stage of the LVS volcanism and the beginning of the adakitic rock emplacement. Most of the LVS rocks and the collision related granitoids in southern Gangdese have ε Nd >0, attesting to the significance of mantle input, most likely through re-melting of mantle-derived basaltic rocks, including the subducted Neo-Tethyan ocean crust. The petrologic and geochemical characteristics of the Miocene potassic adakitic rocks support the idea that the lower portion of the thickened Tibetan crust is mafic and is genetically associated with the earlier LVS magmatism. We estimate that the mantle material input contributed about 30% of the total thickness of the present-day Tibetan crust. By assuming a pre-collision crustal thickness of ∼35 km, then the tectonic contribution would be about 20 km. [Copyright &y& Elsevier]

Abstract: The distribution of peraluminous granites in Tibet is treated on the basis of the tectonic zones in which they occur, their spatial and temporal distribution, the peak of magmatic activity and the volume of magma intruded. Magmatic activity, with the intrusion of peraluminous granites, was initiated during the Early Jurassic and culminated in the middle Miocene, especially between 20 and 10Ma. Rock types include tourmaline, muscovite and two-mica granites. Magmatic activity in the Gangdise Belt migrated from the east to west and from the south to the north. Episodes of tectonic evolution for the lithosphere of the Qinghai–Xizang (Tibet) Plateau, deduced from peraluminous granite intrusion are: (1) Latest Triassic to Early Jurassic (208–157Ma), representing the subduction phase of the Bangong Co–Nu Jiang oceanic zone; (2) Late Jurassic to Early Cretaceous (157–97Ma), representing the subduction and collision phases of the Bangong–Nu Jiang oceanic zone; (3) Late Cretaceous to early Paleocene (97–65Ma), representing the subduction and initial collision phases of the Yarlung Zangbo oceanic zone ; (4) Paleocene to Eocene (65–40Ma), representing the major collisional stage of the Yarlung Zangbo Oceanic zone and the formation of crust-derived granites; and (5) Oligocene to Recent, representing an intense intracontinental convergence phase. [Copyright &y& Elsevier]

Whole-rock and mineral separate Ar-Ar dating was carried out for the Linzizong volcanic rocks at Linzhou Basin in Tibet to constrain the time span of volcanism and the corresponding stratigraphic sequence. Sampling was based on detailed geologic mapping and stratigraphic sequence of Dianzhong, Nianbo, Pana Formations, systematically from the bottom to near the top. The results indicate that the Linzizong volcanic rocks erupted from Paleocene to middle of Eocene (64.43-43.93 Ma). Among them, the Pana Formation formed from ca. 48.73 to 43.9 Ma, the Nianbo Formation around 54 Ma and the Dianzhong Formation from 64.4 to 60.6 Ma. In combination with evidence from the geochemical characteristics of the volcanic rocks, and from straligraphy in southern Tibet, it is postulated that the age of the lowest member in the Dianzhong Formation of the Linzizong volcanic rock, which overlies unconformably the Late Cretaceous Shexing Formation, likely corresponds to the inception of the collision between Indian and Asian continents in southern Tibet. [ABSTRACT FROM AUTHOR]

Various shaped mafic microgranular enclaves (MMEs) together with several mafic massifs are developed within the Yuegelu granitoid pluton in the eastern part of the Eastern Kunlun. On the basis of detailed field geological surveying and of the results of the petrological and geochemical studies it is suggested that there must be some genetic relationship among the granodiorite host, the MMEs and the hornblende (Hb)-gabbro massifs. Magmatic zircon grains are extracted from samples of granodiorite host rock, Hb-gabbro and the MMEs for U-Pb dating. The U-Pb ages are determined by using SHRIMP II technique, which yields the ages of 242±6 Ma, 239±6 Ma and 241±5 Ma, respectively. The overall correspondence in the U-Pb dating results of them excludes the possibility that the MMEs in the granitoids are solid refractory relics from the source region or that they are xenoliths from the wall rocks. It can also rule out the possibility of a later emplacement of basic magma after the solidification of the granitoids. This dating result indicates that they are the products of magma mixing in early-mid Triassic epoch. Among them the granitoid host is chemically akin to the acidic end member during the magma mixing process, the Hb-gabbro is akin to the basic ones while the MMEs are the incompletely mixed basic magma clots trapped in the acidic magma. Combined with the results from other researches on this pluton it is reasonable to consider that in the mid-Triassic the Eastern Kunlun granitoid belt had undergone a process of magma mixing between the mantle-derived basic magma and the crustal acidic magma which indicates that the injection of mantle materials and energy into the crust and the reactions between them played an important role in the formation of the granitoid rocks. [ABSTRACT FROM AUTHOR]

Fission track (FT) ages of apatite and zircon from four grantie batholiths from Lhasa and Shannan areas are measured. The FT ages of apatite range from 3.2 to 8.3 Ma, corresponding to the uplift rates of 0.12 to 0.20 mm·a[SUP-1] during this period. The uplift height is 580 m, showing that there is not large-scale rapid uplifting in southern Tibet from 3.2 to 8.3 Ma. The zircon FT ages of Lhasa batholith are 25.9 ± 1.7 and 32.7 ± 2.8 Ma, yielding an uplift rate of 0.08 mm·a[SUP-1] between 26 and 33 Ma. Combining this work with other studies, it is suggested that the average uplift rate in southern Tibet is low from the time of collision between India and Asian continents to -3 Ma. The uplift of Tibetan Plateau seems to have finished in multi-stage processes with varied rates. fission track age, uplift rate, Lhasa, Tibet [ABSTRACT FROM AUTHOR]

Examines the geochronology and Nd and Pb isotope characteristics of gabbro dikes of the Loubusha ophiolite in Tibet. Time of formation of the Luobusha ophiolite; Formation of Luobusha ophiolite in an oceanic setting during the Middle Jurassic; Indication of an Indian-Ocean type isotopic affinity.

The Chakabeishan (CKBS) deposit is the first pegmatite-type Li-Be deposit discovered in the eastern North Qaidam Tectonic Belt (NQTB) of Tibetan Plateau. The correct understanding of its petrogenesis and the precise determination of its formation age are of great significance for further regional prospecting and the discovery of new economically valuable rare-metal deposits. Therefore, a systematic study of texture, major-element composition, and U-Pb dating of columbite-tantalite group minerals (CGMs) in the spodumene pegmatite dyke from the CKBS deposit was undertaken. Three types of CGMs were identified, including concentric oscillatory ferrocolumbite (CGMs-1), homogeneous ferrocolumbite (CGMs-2), and irregular ferrotantalite (minor manganocolumbite) with abundant early ferrocolumbite replacement remnants (CGMs-3). The zoning patterns and chemical compositions in the CGMs record the complex evolutionary history of their host pegmatite from the magmatic stage (CGMs-1, disequilibrium crystallization) to the magmatic-hydrothermal transition stage (CGMs-2, equilibrium crystallization) and then to the late metasomatic stage (CGMs-3, replacement/re-equilibrium). CGMs U-Pb dating results suggest that the spodumene pegmatite dyke (No.15) emplaced at 230.1 ± 2.6 Ma. Subsequently, it experienced fluid metasomatism at 221 ± 5.3 Ma. Based on the new age data and published geochronological data, it can be concluded that the spodumene pegmatite dykes in the CKBS deposit formed in an oceanic subduction-related setting, representing a new metallogenic event in western China. Except for the CKBS deposit, a large number of rare-metal pegmatite dykes have also been discovered in the eastern NQTB, indicating that the eastern NQTB may be an important potential rare-metal metallogenic belt that should be explored in detail and arouse painstaking attention. [ABSTRACT FROM AUTHOR]

Determining the age and petrogenesis of the Mesozoic magmatic rocks may provide crucial evidence regarding the tectonic setting and evolution of the North China Craton (NCC). In this paper, we present new zircon U–Pb ages and geochemical data for bimodal volcanic rocks from Zhuozi area in the eastern Yinshan belt, NCC, to discuss their petrogenesis and tectonic implications. The volcanic rock suite consists of basalts, rhyolites, and trachytes. According to the results of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), the rhyolitic and trachytic rocks have zircon U–Pb ages of 136.9 ± 0.8 Ma and 134.0 ± 1.7 Ma, respectively, representing their eruption ages. The basalts are enriched in large-ion lithophile elements (LILE; Ba, Rb, Sr, and Th) and light rare-earth elements (LREE), and are relatively depleted in high field strength elements (HFSE; Nb, Ta, and Ti). In addition, the basalts are characterized by high fractionations of rare-earth elements (REE), with (La/Yb)N = 24.87–42.85. These features suggest that they were derived from low-degree partial melting of enriched lithospheric mantle metasomatized by subduction-related components. The rhyolitic rocks have low mean Al2O3 (12.26 wt%) and TiO2 (0.14 wt%) contents and Mg# (14.92) values, with relatively low total REE abundances. They have high alkali and Zr, Ce, Y, and Nb contents and high Ga/Al ratios, with notably positive Pb and negative Sr, Ba, and Eu anomalies observed in the primitive mantle-normalized trace element diagram. These features indicate that the rocks exhibit characteristics of A1-type granite and likely derived from the partial melting of a crustal source. The trachytic rocks are show moderate trace elements and SiO2, MgO, Fe2O3T, and TiO2 contents. They were possibly generated by fractional crystallization of the underplating basaltic magmas and assimilated minor crustal materials. The geochemical characteristics, in combination with the regional geology, suggest that the bimodal volcanic rocks formed in an intraplate extensional setting likely associated with the retreat of the subducted Paleo-Pacific plate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Elemental and B isotopic compositions in tourmalines suggest that fluids were unsaturated during the evolution of the CKBS barren pegmatites. • The ratios of Mn/Zn, Mn/Li, Sc/Li and Nb/Sc of tourmalines are useful geochemical criteria for distinguishing the CKBS fertile from the CKBS barren pegmatites. • (Zn + Li) - (V + Sr), Li-Zr/Sr, Sn/10Nb-Li-100Nb and Zn/Sn-Li/10Sc-5Sc are potential elemental groups for discriminating tourmalines of granite-derived pegmatite-type Li-Be deposits from those of other geological environments. To assess the potential of tourmaline as an indicator for pegmatite evolution and exploration, we measured and compared the geochemical compositions in tourmalines of the barren, Be-rich and Li-rich pegmatites from the Chakabeishan (CKBS) deposit, eastern North Qaidam Tectonic Belt, northeastern Tibetan Plateau. Two types of tourmalines from the barren pegmatites are identified: optically homogeneous fine-grain tourmalines (H-Tur) and optically zoned coarse-grain tourmalines (OZ-Tur). Both H-Tur and OZ-Tur are of magmatic origin, showing high Na/(Na + Ca) (0.961–0.990), Y Al (0.389–0.757 apfu) and low Mg/(Fe + Mg) (0.085–0.230). The core-to-rim δ 11B increase within H-Tur and OZ-Tur, together with the enrichment of 11B from H-Tur (crystallized earlier) to OZ-Tur, indicates that fluids were unsaturated in the evolution of barren pegmatites. Compared to H-Tur and OZ-Tur, tourmalines from the Be- and Li-rich pegmatites show higher Nb/Sc (>3:4) and lower Mn/Zn (<1:1), Mn/Li (<3:1), and Sc/Li (<1:500), which are useful indirect criteria of distinction between the fertile and the barren pegmatites. The reliable tourmaline geochemical criteria for further distinguishing the Li-rich from the Be-rich pegmatites are Pb/Sr < 0.11, Nb/Sr < 0.15, and Pb/Co < 4. A compilation suggests that diagrams of (V + Sr)-(Li + Zn), Li-Zn/Sr, Sn/10Nb-Li-100Nb, and Zn/Sn-Li/10Sc-5Sc could discriminate tourmalines of granite-related pegmatite-type Li deposits from those of other deposits and rocks, showing implications for determining prospective areas for further Li-rich pegmatite exploration by using tourmalines recovered from surface sediments. [ABSTRACT FROM AUTHOR]

The article discusses the research study conducted that examines the magmatism and genesis of the Beiya Giant Gold-Polymetallic Deposit, SouthWest China. Topics discussed include problems related to geodynamic setting, origin and petrogenesis of magmatic rocks, high temperature and high salinity conditions to low temperature and low salinity conditions, and temperature decreasing from the porphyry to the wallrock.

The initial Nd and Hf isotope ratios of a 420 Ma post-collisional dioritic-granitic batholith from the Northern Tibetan plateau define a negative trend above and orthogonal to the Ԑ Hf (t)-Ԑ Nd (t) terrestrial array. This uncommon trend offers an insight into the origin of the puzzling Nd-Hf isotope decoupling in the crustal rocks. On this trend, samples depleted in heavy rare earth elements (HREEs, i.e., [Dy/Yb] N ≫ 1) deviate most from the terrestrial array whereas samples with flat HREEs (i.e., [Dy/Yb] N ≥ 1) deviate less or plot within the terrestrial array, pointing to the controlling effect of garnet in the magma source. Ancient garnet-bearing residues after melt extraction will have elevated Lu/Hf ratios and can evolve with time to produce high Ԑ Hf (t) at a low Ԑ Nd (t) value. Mixing of melts derived from such source lithologies (high Lu/Hf) with melts possessing a within-terrestrial array Nd-Hf isotopic composition (low Lu/Hf) best explains the observed trend orthogonal to the terrestrial array. The samples from the Jinfosi batholith with the most decoupled Nd-Hf isotope compositions require a larger degree (> 40%) and ancient (i.e., ≥ 1.8 Gyr) previous melt extraction from their source. It follows that the ancient melts with depleted HREEs complementary to those garnet-bearing residues should have low Ԑ Hf values and plot below the terrestrial array, which is indeed shown by some Archean/Paleoproterozic TTGs. [ABSTRACT FROM AUTHOR]

Melts and fluids derived from subducting/subducted oceanic lithosphere contribute significantly to mantle compositional heterogeneity. Historically metasomatized lithospheric mantle modified by varying materials, especially volatile-rich slab fluids, has been understood to be crucial for the formation of giant ore deposits, thus providing potential prospective areas for mineral exploration. However, it is not straightforward to identify superimposed effects of slab melts and fluids on the sub-continental lithosphere (SCLM) that has experienced long-lived and/or multiple metasomatism. In this study, we present a novel study using Mg and K isotopes, together with radioactive isotopes on mafic post-collisional alkaline potassic rocks (PARs) with the aim of deciphering varying agents contributing to the heterogeneous metasomatism of the SCLM beneath the southeastern Tibetan Plateau. The PARs, formed at ∼36 Ma, are characterized by high abundances of large ion lithophile elements (LILE) but depleted in high field strength elements (HFSE) with high Rb/Sr ratios, indicating a phlogopite-bearing mantle source. We find that features of light Mg (δ26Mg = −0.52 to −0.25‰) and heavy K (δ41K = −0.56 to +0.08‰) isotopes observed in the PARs are largely inherited from their mantle sources with negligible effects of kinetic fractionation, fractional crystallization and crustal level processes. Our modelling reveals that the notable divergence of Sr–Nd–Pb–Mg–K isotope compositions between PAR suites in different tectonic blocks are best understood as resulting from varying contributions of slab-derived components into the overlying mantle lithosphere, including sediment-derived melts, ocean crust-derived supercritical fluids, and marine carbonates. Particularly, their high Th/U ratios and negative correlations between δ26Mg and δ41K values suggest that slab-derived supercritical fluids can dissolve and transport Mg-rich (dolomitic) carbonate into the mantle wedge. [ABSTRACT FROM AUTHOR]

The Ailaoshan orogenic belt is one of the most significant orogenic belts in the southeastern margin of the Qinghai–Tibet Plateau. The widely developed magmatic rocks in this belt preserve the multi-stage tectonic evolution records of the South China Plate. As an important response to the Rodinia breakup tectonic event, the study of Neoproterozoic magmatic rocks in the area is of great significance for reconstructing the Neoproterozoic tectonic process of the Ailaoshan orogenic belt and the tectonic evolution of the South China Plate. Petrology, geochemistry, zircon U-Pb, and Lu-Hf isotopes of the Daping pluton in the Ailaoshan orogenic belt are studied in this paper. The Daping pluton is mainly divided into gabbros and granites. Gabbros and granites belong to the sub-alkaline series, which are relatively enriched in large ion lithophilic elements and depleted in high-field strength elements. The ΣREE contents of the gabbro are low with enrichment in LREEs and depletion in HREEs, and the degree of differentiation of light and heavy rare earth is low, with positive δEu and weak negative δCe anomalies. The ΣREE contents of the granite are low with enrichment in LREEs and depletion in HREEs, and the degree of light and heavy rare earth differentiation is high, with medium–weak negative δEu and weak positive δCe anomalies, suggesting an A2-type granite with A1-A2 transition characteristics. The weighted average age of the gabbro is 816.1 ± 4.1 Ma (MSWD = 0.11), with zircon εHf(t) values of −7.5–5.5. The magma source is a mixture of an ancient crust source and a new mantle source; the weighted average age of the syenogranite is 783.7 ± 8.1 Ma (MSWD = 1.4), with zircon εHf(t) values of −4.3–0.4. The magma source is mainly ancient crustal material (Ailaoshan Group), mixed with a small amount of mantle-derived material; the weighted average age of the monzogranite is 754.8 ± 6.1 Ma (MSWD = 3.0), with positive zircon εHf(t) values of 1.65–10.36. The magma source is a mixture of a large number of mantle-derived materials and a small number of crust-derived materials (Ailaoshan Group). The Daping pluton was formed in the transitional tectonic environment from post-collision to intraplate continental margin rift, corresponding to the Rodinia breakup process in the western margin of the South China Plate. [ABSTRACT FROM AUTHOR]

In this paper we present a new model that can explain the large zircon age spectrum of ~ 510 – 420 Ma within a single sample from the Gangcha (Gcha) biotite granodiorite and the Huangyuan (HY) two-mica monzogranite on the northern Tibetan Plateau. The large age spread recorded in zircons is characteristic of granitoid samples from the studied region, which is best explained by the long-lasting magmatism since the onset of continental collision at ~ 500 Ma, followed by slab steepening and the ultimate slab break-off at ~ 450 Ma. These granitoids have a large major and trace element compositional variation, but limited initial Sr (I Sr[450] = 0.709 to 0.715), Nd (Ԑ Nd[450] = − 6.5 to − 3.7), Hf (Ԑ Hf[450] = − 4.3 to 1.5) and Pb ( 206 Pb/ 204 Pb [450] = 17.70 to 17.17; 207 Pb/ 204 Pb [450] = 15.60 to 15.69; 208 Pb/ 204 Pb [450] = 38.04 to 38.73) isotopic variation. The small negative whole rock Ԑ Nd[450] and Ԑ Hf[450] values are most consistent with the granitoid source being dominated by subducted seafloor materials. The inherited zircons with large negative Ԑ Hf[450] values (e.g. − 50) are indicative of input from the lower continental crust and subducted sediments. The correlated variations among major elements, trace elements and radiogenic isotopes are best interpreted as reflecting melting-induced mixing of a compositionally heterogeneous source with superimposed effect of varying extent of fractional crystallization and crustal assimilation. The inherited zircons of Palaeo-Proterozoic age and the Archean crustal model ages signify the involvement of ancient basement rocks. [ABSTRACT FROM AUTHOR]

This paper presents geochemical and age data for Late Triassic lamprophyre, syenite, and granite in the Huata area of the western Yanshan belt of the North China Craton, to provide constraints on the origin and tectonic settings of these Late Triassic igneous rocks. The zircons from the Huata lamprophyres and syenites yielded a mean U Pb age of 203 and 206 Ma, respectively. The lamprophyres are enriched in incompatible elements, with (La/Yb) N = 30.57–33.89, (Gd/Yb) N = 3.54–3.64, and Sr-Nd-Hf isotopic signatures (87Sr/86Sr (initial) = 0.7053–0.7061, εNd(t) = −11.11 to −10.50, εHf(t) = −9.33 to −7.70), consistent with them originating from the low-degree melting of previously metasomatized lithospheric mantle in the garnet-stable area. The syenites display similar incompatible elements to the lamprophyres, but have relatively low (La/Yb) N = 14.26–17.23 and (Gd/Yb) N = 1.81–2.15 ratios. Their Sr-Nd-Hf isotopic compositions (87Sr/86Sr (initial) = 0.7045–0.7050, εNd(t) = −12.10 to −11.35 and εHf(t) = −8.64 to −6.81) were also similar to the lamprophyres, and they are considered to have been generated from the low-degree melting of lithospheric mantle in the garnet-spinel transition zone. The granites have major and trace element patterns and Sr Nd isotopes quite different from the syenites, but are similar to the crust-derived felsic rocks, being enriched in large ion lithosphere elements and depleted in high field strength elements. They are enriched in Nd isotope (εNd(t) = −16.63 to −15.18), and are inferred to have been generated by lower crust anataxis. The presence of igneous rocks in the Huata district indicates that the northern margin of the NCC had already entered a non-orogenic regime by the late Late-Triassic. • Lamprophyres and syenites derive from a metasomatized mantle. • Granites originate from the modified lower continental crust. • The tectonic regime transformed from post-collisional to intraplate at 206 Ma. [ABSTRACT FROM AUTHOR]

The Kejie pluton is located in the north of the Changning-Menglian suture zone. The rock types are mainly biotite-granite. Zircon LA-ICP-MS U-Pb dating indicates that the Kejie pluton emplaced at about 80-77 Ma, Late Cretaceous. The Kejie pluton samples are characterized by high SiO2 (71.68%-72.47%), K2O (4.73%-5.54%), total alkali (K2O + Na2O = 8.21%-8.53%), K2O/Na2O ratios (1.36-1.94) and low P2O5 (0.13%-0.17%), with A/CNK of 1.025-1.055; enriched in U, Th, and K, depleted in Ba, Nb, Sr, Ti, P and Eu. They are highly fractionated, slightly pet aluminous I-type granite. The two samples of the Kejie pluton give a large variation of εHf( t) values (-5.04 to 1.96) and Hf isotope crustal model ages of 1.16-1.5 Ga. Zircon Hf isotopes and zircon saturation temperatures of whole-rock (801°C-823°C) show that the mantle-derived materials maybe have played a vital role in the generation of the Kejie pluton. The Kejie pluton was most likely generated in a setting associated with the eastward subduction of the neo-Tethys ocean, where intrusion of mantle wedge basaltic magmas in the crust caused the anatexis of the latter, forming hybrid melts, which subsequently experienced high-degree fractional crystallization. [ABSTRACT FROM AUTHOR]

Eocene-Oligocene adakitic and non-adakitic shoshonitic felsic intrusions from the southwest margin of the Yangtze Craton provide a crucial geological record for studying crust-mantle interactions at the craton boundary. Despite their significance, the petrogenesis and source properties of these intrusions remain debated. This study suggests that the adakitic and non-adakitic features of these intrusions result from the re-melting of Neoproterozoic juvenile lower crust, as evidenced by zircon U-Pb dating, geochemical analyses, and petrogenetic investigations. The Ninglang-Yongsheng shoshonitic felsic intrusions, characterized by high Mg#, MgO, Ni, and Cr contents, exhibit isotopic characteristics akin to mantle-derived magma and juvenile mafic lower crust. Their U-Pb ages span 32–36 Ma, and they show similar patterns in major and trace elements, rare earth elements (REEs), and isotopes, with enrichment in large ion lithophile elements (LILEs) and depletion in high field strength elements (HFSEs) like Nb, Ta, and Ti. These intrusions also demonstrate significant fractionation between light and heavy REEs, with a modest negative Eu anomaly. Their (87Sr/86Sr) i and ε Nd (t) values range from 0.7060 to 0.7069 and − 4.4 to −1.5, respectively, while Pb isotopic compositions vary slightly. This paper, along with prior research, has developed a genetic model for the Ninglang-Yongsheng shoshonitic felsic intrusions. The adakitic quartz monzonite porphyries likely originated from high-degree partial melting of the juvenile lower crust, whereas the non-adakitic shoshonitic syenite porphyries resulted from lower-degree melting. The composition of the juvenile lower crust may be garnet amphibolite-pyroxenite. This suggests distinct compositional variations within the Ninglang-Yongsheng juvenile lower crust. Moreover, the region's shoshonitic felsic intrusions have assimilated mantle-derived magma. In conclusion, the juvenile lower crust on the Yangtze Craton's southwest margin displays zonal characteristics, with the Liuhe-Beiya area's lower crust showing higher potassium content and more enriched isotopic signatures compared to the Ninglang-Yongsheng region. • Sanjiang adakitic felsic suites formed by re-melting of the juvenile lower crust. • Sanjiang adakitic and non-adakitic felsic suites may have the same origin. • The lower crust along the western margin of the Yangtze craton is heterogeneous. • The thickened lithospheric mantle delamination near the ASRR occurred earlier. [ABSTRACT FROM AUTHOR]

The Ailaoshan orogenic belt, located in the SE margin of the Qinghai–Tibet Plateau, is an important Paleo-Tethys suture zone in the eastern margin of the Sanjiang Tethys tectonic domain. The areas of Mojiang and Zhenyuan, located in the middle part of the Ailaoshan orogenic belt, are the key parts of the Ailaoshan Paleo-Tethys Ocean closure and collision orogeny. The rhyolites outcropped in the Mojiang area, and the granite porphyries outcropped in Zhenyuan area, are systematically studied for petrology, isotope geochemistry and geochronology. The Zircon U-Pb geochronology of rhyolites and granite porphyries give weighted average ages of 253.4 ± 4.2 Ma and 253.3 ± 2.0 Ma, respectively, both of which were formed in the late Permian period. The rhyolites belong to potassic calc-alkaline to subalkaline series. The patterns of the rare earth elements (REE) show a right-inclined seagull-type distribution, and the trace elements plot is right-inclined. The granite porphyries are high potassic calc-alkaline to subalkaline. The REE patterns show a right-inclined distribution, and the trace elements plot is right-inclined, which is consistent with the typical patterns observed in the crust. The peraluminous, highly differentiated and high ASI values suggest that rhyolites and granite porphyries are S-type granites. The zircon εHf(t) of the rhyolites range from −7.22 to −0.72, and two-stage Hf zircon model ages are (TDMC) 1771–2352 Ma, indicating that the magma source area is mainly crust-derived. The zircon εHf(t) of the granite porphyries range from −0.97 to 4.08, and two-stage Hf zircon model ages are (TDMC) 1336–1795 Ma, indicating that the magma is derived from a depleted mantle source and the partial melting of ancient crustal materials. The rhyolites and granite porphyries were possibly formed in the syn-collisional tectonic setting during the late Permian, and their ages limited the time of the final closure of the Ailaoshan Ocean and the initiation of collisional orogeny. [ABSTRACT FROM AUTHOR]

Abstract: The leucogranites in the Baoshan Block of the Tethyan belt in Western Yunnan, are composed mainly of two-mica granite with subordinate muscovite granite. Here we present zircon U–Pb ages from four intrusions that show ages of 448–476Ma suggesting that these rocks were emplaced during the Ordovician. The leucogranites are high-K calc-alkaline and strongly peraluminous, with K2O/Na2O>1 and A/CNK=1.12–1.54. These rocks are enriched in large-ion lithophile elements (LILEs) and light rare-earth elements (LREEs) [(La/Yb)N =1.13–32.4] and Pb, and are depleted in high field-strength elements (HFSEs). They show similar chondrite-normalized REE patterns, with negative Eu anomalies (Eu/Eu*=0.03–0.46). A wide range of zircon εHf(t) values (−9.6 to −2.6) and varying Hf-isotope crustal model ages (2.1–1.6Ga) are also observed. The geochemical signatures indicate that the leucogranites are S-type granites derived mainly from the anatexis of ancient crustal materials. The ages, geochemistry and tectonics in the Baoshan Block and the Lhasa Terrane are closely comparable, suggesting that the Baoshan Block might represent part of an Early Paleozoic magmatic arc in the Gondwana continental margin facing the proto-Tethyan Ocean. The Pinghe granites of the early phase in the Baoshan Block which are coeval with the Cambrian magmatism (ca. 492Ma) identified in the central and southern Lhasa subterranes can be interpreted as products of the slab break-off associated with the subduction of proto-Tethyan oceanic lithosphere. However, the late leucogranite stocks are analogous to the North Himalayan leucogranites, which formed in a short-lived extensional setting caused by the slab break-off associated with the subduction–collision system. [Copyright &y& Elsevier]

• Near-critical CO 2 adsorption and adsorption kinetics experiments on shales were measured. • The near-critical CO 2 is found to be 2.528 – 4.663 layers adsorbed in tested shales. • The heterogeneity of adsorption volume distribution was quantified by multifractal analysis. • Avrami's fractional-order model can be employed to determine the adsorption process. • Conceptual models for adsorption mechanism and geological storage were proposed. Studies on the near-critical carbon dioxide (NC-CO 2) adsorption behavior of organic-rich shales are important for shallow shale gas exploration and hydrocarbon recovery enhancement of liquid CO 2 fracturing, which further contributes to geological CO 2 sequestration and global carbon neutrality. We performed CO 2 isothermal adsorption and kinetic experiments on six organic-rich shale samples at a temperature of 303.15 K and pressures of up to 5 MPa to investigate the modeling, multifractality, and kinetics of NC-CO 2 adsorption behavior on shales. The equilibrium data were fitted to the Langmuir, Freundlich, BET, modified BET (M−BET), DA, DR, and OK adsorption models; the multifractality of the isotherms was analyzed; and pseudo-first-order, pseudo-second-order, Elovich, and Avrami's fractional-order models were adopted to analyze the adsorption kinetics. Furthermore, an error analysis technique was employed to compare the accuracies of various models for fitting the experimental data. The results showed that various adsorption models presented different fitting effects; however, the M−BET, Freundlich, and DA adsorption models performed better over the entire studied pressure range. The fitting results of the M−BET model indicated that the number of adsorption layers ranged from 2.528 to 4.663 and had a multilayer adsorption mechanism. The multifractality of the adsorption behavior was described by the generalized fractal dimension and multifractal singularity spectra; we demonstrated that some multifractal parameters characterize the NC-CO 2 adsorption behavior on shales well. Additionally, the TOC, clay, and quartz contents show close covariations with the isothermal adsorption and multifractal parameters. Moreover, the adsorption process was TOC-dependent and subject to Avrami's fractional-order model. Finally, we propose conceptual three-stage adsorption and geological storage models to understand the nature of the NC-CO 2 adsorption behavior of shales. [ABSTRACT FROM AUTHOR]

Abstract: The ∼133Ma volcanic rocks of Sangxiu Formation are distributed in the eastern part of the central Tethyan Himalaya and belong paleogeographically to the northeastern margin of Greater India. These volcanic rocks include alkaline basalts and felsic volcanic rocks. Major and trace element abundances and whole-rock isotopic data for selected samples of these volcanic rocks are used to infer their petrogenesis. Geochemically, the Sangxiu basalts are closely similar to the Emeishan high-Ti basalts. Major and trace element data and Sr–Nd isotopic compositions suggest that the Sangxiu basalts may have been derived from an OIB-type mantle source, with discernable contributions from subcontinental lithospheric mantle (SCLM). The basaltic magmas may have formed as a result of the infiltration of plume-derived melts into the base of the lithosphere in a continental rift setting. The Sangxiu felsic volcanic rocks share most of the geochemical features of A-type granite, and have Sr–Nd isotopic compositions which differ considerably from the Sangxiu basalts, suggesting that they originated from the anatexis of ensialic continental crust. The Sangxiu volcanic rocks may be considered as the consequence of an interaction between the Kerguelen hotspot and the lithosphere of the northeastern margin of Greater India at ∼133Ma, and may represent the initial stage of the separation of Greater India from southwestern Australia. [Copyright &y& Elsevier]

Petrology and SHRIMP U-Pb zircon chronology are reported for the dacite of the Sangxiu Formation in the central segment of Tethyan Himalaya to the southeast of Yangzuoyong Co. Twenty-one measured zircon grains from a dacite sample of the Sangxiu Formation can be divided into two groups, which include long columnar magmatic zircons of 133±3.0 Ma, representing the age of volcanism in the Sangxiu Formation, and inherited zircons consisting of core and overgrowth rim, in which ages of the three cores are 2244±16, 1153±33 and 492±25 Ma respectively; and the age of one overgrowth rim is 132.7±5.2 Ma. These ages are considered to represent the remelting of accretionary crust at different periods resulting from the volcanism of Sangxiu Formation. These volcanic rocks in the Sangxiu Formation, for which age is close to that of Bunbury basalt in southwestern margin of Australia, and older than that of Rajmahal basalt in northeastern India, maybe considered as the products of early activity of the hotspot represented by the Rajmahal basalt. [ABSTRACT FROM AUTHOR]

Miocene ultrapotassic (UP), shoshonitic (P) and calc-alkaline (CA) volcanism is recognized widely over the Tibetan plateau. This volcanism occurred after the end of India’s oceanic lithosphere subduction beneath the plateau. Ambiguities about the distribution and significance of this volcanism arise in part from a paucity of geochronologic and geochemical data. We have sampled two volcanic fields in the Lhasa block: (1) the eastern edge of the Zabuye Salt Lake (central part of the block), (2) the southwestern edge of the Yangbajin Graben. Major and trace elements display high K2O (6.06–6.54%) over a wide range of SiO2 (75.03–55.30%), Na2O (1.32–3.30%) and LREE/HREE enrichment with a significant rare earth element fractionation (26<(La/Yb)n<42) as well as negative Nb, Ta, and Ti anomalies. These features indicate that our samples are chemically identical to the post-collision Miocene UP to P volcanic rocks already identified all over the Tibetan plateau and the southern plateau specifically but distinct from the CA rocks found in the Lhasa block. The Miocene volcanics found in the Lhasa block present greater chemical variation than the rest of the Tibetan plateau. 40Ar/39Ar ages on both sanidine and biotite gave ages ranging from 16.16±0.12 Ma to 16.01±0.12 Ma and 10.60±0.14 Ma to 10.88±0.17 Ma (2σ, excluding systematic errors, relative to Fish Canyon sanidine at 28.02 Ma) for Zabuye Salt Lake and Yangying geothermal field volcanics respectively. These results are consistent with the range of previously published ages from this part of the Tibetan plateau. The presence of N–S-trending dikes and the location of the volcanic fields suggest that local E–W extension in the Lhasa block was coeval. We propose that the synchronous UP, P and CA volcanism in the Lhasa block between 23 and 8 Ma is the result of progressively deepening northward subduction of Indian continental lithosphere producing asthenospheric upwelling. Convective thinning (delamination) of lithospheric mantle fueled by the hot asthenosphere induced partial melting of an enriched sub-continental mantle lithosphere as well as eclogitic lower crust. This mechanism could also explain the local E–W extension observed in the same period (18–10 Ma). We also propose that lateral migration of the deepening Indian continental lithosphere mantle slab could explain the observed younger volcanism in the eastern part of the Lhasa terrane. [Copyright &y& Elsevier]

Presents a study that described the element geochemical subdivision of the middle segment of the Sanjiang River region in China. Aim and principle of element geochemical division; Geochemical division of the strata and volcanic rocks and geochemical characteristics of the various zones; Indicative significance of geochemical division for the distribution of mineral resources and metallogenic rules in the region studied.

The tectonic transition from oceanic subduction to continental collision is a fundamental process during orogenesis. Yet, the nature of this transition and its deep geodynamic processes for the southern Tibetan Plateau remain contentious. This study presents zircon U-Pb-Hf isotopes, whole-rock geochemistry, and Sr Nd isotopes for a quartz diorite intrusion and bimodal dykes from Dagze, combined with compiled data from the southern Lhasa subterrane, to reveal the geodynamic processes of late-stage of Neo-Tethyan subduction. Most of Dagze samples were emplaced between 66 and 64 Ma, while muscovite granite aplite dykes were emplaced between 64 and 60 Ma. They exhibit relatively uniform, depleted Sr Nd isotopes, with ε Nd (t) values ranging from +2.2 to +4.0, positive zircon ε Hf (t) values, and young depleted mantle model ages. Both exhibit compositional characteristics of subduction-related arc magma, marked by the enrichment of large ion lithophile elements and the depletion of high field strength elements. The mafic dykes with relatively low SiO 2 , high MgO, Cr, Ni, possibly originated from a fluid-metasomatized depleted mantle. The quartz diorite intrusion with low MgO, Cr, and Ni was generated by partial melting of sub-arc lithospheric mantle and experienced subsequent fractional crystallization of amphibole, clinopyroxene and orthopyroxene. The granitic dykes originated from partial melting of Gangdese juvenile crust and experienced fractional crystallization dominated by plagioclase. We suggest that the slab rollback and continental collision conjointly controlled the evolution of the latest Cretaceous to Paleocene Himalayan–Tibetan orogeny. Slab rollback of Neo-Tethys commenced around 70 Ma, triggering the partial melting of depleted mantle and juvenile crust, and this process resulted in the formation of Dagze diorites and bimodal dykes with arc affinity. • Diorite intrusion and mafic dykes originated from a fluid-metasomatized depleted mantle. • Granitic dykes originated from Gangdese juvenile crust and experienced fractional crystallization. • Slab rollback of the Neo-Tethys oceanic slab commenced around 70 Ma. [ABSTRACT FROM AUTHOR]

The Tethyan metallogenic domain (TMD), as one of the three major domains in the world, extends over 10000 km from east to west, and has developed several world-class metallogenic belts, such as the Gangdese porphyry Cu belt, the Sanjiang metallogenic belt, the Iran porphyry Cu belt, the Pakistan porphyry Cu belt, the southeastern European epithermal gold deposit belt, and the Southeast Asian Sn belt. The formation and evolution of the TMD is mainly controlled by the multi-stage subduction of Tethys oceanic slabs, the opening and closing of several small ocean basins, and continent-continent collision. The Tethys oceans include the Proto-Tethys (Cambrian-Silurian), Paleo-Tethys (Carbonaceous-Triassic) and Neo-Tethys (Jurassic to Cretaceous), which in turn are formed by rifting from the Gondwana land at different times in different micro-continents. With a series of geological processes such as oceanic opening and closing, continental collision and post-collisional reworking with intraplate deformation, various types of ore deposits are developed in the TMD, including porphyry deposits, epithermal deposits, VMS deposits, chromite deposits, Sn deposits and orogenic gold deposits. The metallogenic processes of the TMD can be categorized into three stages. (1) Oceanic subduction: With the subduction of the oceanic slab and dehydration of basalt and sediments, the asthenospheric mantle was metasomatized with preliminary enrichment in metals under oxidized condition. (2) Continental subduction: Continental collision induced partial melting of the mantle wedge enriched the metals and water in mafic melts, which ascended from subarc depths to the lower crust, locally to the shallow crust for hydrothermal mineralization. (3) Post-collisional reworking: Partial melting of the mafic intrusives in the lower crust produced felsic melts under oxidized and water-rich conditions, which underwent crystal fractionation and transferred water and metals into hydrothermal fluids for mineralization. The large-scale porphyry mineralization in the TMD mainly occurs in the Miocene, which is an important scientific issue worthy of further study in the future. How is the metal enriched in the processes of gradual maturity of the crust, and how does large-scale mineralization occur in a collisional orogen where there is no subduction and dehydration of oceanic slabs anymore to supply S and Cl? These are still important questions in the study of porphyry mineralization in the Tethyan orogen. The application of hyperspectral and mineralogical studies of alteration assemblages is beneficial for prospecting and exploration in the TMD. [ABSTRACT FROM AUTHOR]

The Tengchong Block within the Sanjiang Tethys belt in the southeastern part of the Tibetan plateau experienced a widespread intrusion of a felsic magmatic suite of granites in its central domain during Late Cretaceous times. Here, we investigate the Guyong and Xiaolonghe plutons from this suite in terms of their petrological, geochemical, and Sr–Nd, zircon U–Pb and Lu–Hf–O isotopic features to gain insights into the evolution of the Neo-Tethys. The Guyong pluton (76 Ma) is composed of metaluminous monzogranites, and the Xiaolonghe pluton (76 Ma) is composed of metaluminous to peraluminous medium- and fine-grained syenogranite. A systematic decrease in Eu, Ba, Sr, P and Ti concentrations; a decrease in Zr/Hf and LREE/HREE ratios; and an increase in the Rb/Ba and Ta/Nb ratios from the Guyong to Xiaolonghe plutons suggest fractional crystallization of biotite, plagioclase, K-feldspar, apatite, ilmenite and titanite. They also show the characteristics of I-type granites. The negative zircon εHf(t) isotopic values (−10.04 to −5.22) and high δ18O values (6.69 to 8.58 ‰) and the negative whole-rock εNd(t) isotopic values (−9.7 to −10.1) and high initial 87Sr/86Sr ratios (0.7098–0.7099) of the Guyong monzogranite suggest that these rocks were generated by partial melting of the Precambrian basement without mantle input. The zircon εHf(t) isotopic values (−10.63 to −3.04) and δ18O values (6.54 to 8.69 ‰) of the Xiaolonghe syenogranite are similar to the features of the Guyong monzogranite, and this similarity suggests a cogenetic nature and magma derivation from the lower crust that is composed of both metasedimentary and meta-igneous rocks. The Xiaolonghe fine-grained syenogranite shows an obvious rare earth element tetrad effect and lower Nb/Ta ratios, which indicate its productive nature with respect to ore formation. In fact, we discuss that the Sn mineralization in the region was possible due to Sn being scavenged from these rocks by exsolved hydrothermal fluids. We correlate the Late Cretaceous magmatism in the central Tengchong Block with the northward subduction of the Neo-Tethys beneath the Burma–Tengchong Block. [ABSTRACT FROM AUTHOR]

[Display omitted] • Monzonite was formed from melts derived from a mantle wedge after fractionation. • The adakitic features of granite are formed by amphibole-dominated fractionation. • Nenjiang ocean experienced slab rollback at ∼375 Ma, and closed at ∼320 Ma. Disputes regarding the subduction process, closure time, and the location of the Nenjiang Ocean have arisen due to limited exposure of late Paleozoic magmatic rocks in the Xing'an block. In this study, we present new zircon U-Pb age, zircon Hf isotope, zircon trace elements and whole rock geochemistry to reveal the evolution process of the Nenjiang Ocean in the late Paleozoic. The Heihe monzonite samples originated from the partial melting of a depleted mantle wedge metasomatized by subduction-related fluids and experienced fractional crystallization of plagioclase and amphibole. The Heihe granites show adakitic affinity, with low contents of compatible elements and U-shaped chondrite-normalized REEs patterns, indicating that the adakitic characteristics of the Heihe granites were formed by amphibole-dominated fractional crystallization. Geochemical modeling shows that the Heihe granite can be generated at a degree of 30–75 % amphibole-dominated fractional crystallization. The geochemical characteristics and genetic type of Heihe granites, associated with coeval sedimentary strata, imply extensional tectonic setting in late Devonian-early Carboniferous. By analyzing the spatiotemporal distribution and geochemical data of the 300–400 Ma magmatic rocks in the Xing'an block, and by conducting locally weighted regression fitting, we propose a geodynamic model. According to this model, the Nenjiang oceanic slab began to rollback at approximately 375 Ma, resulting in the production of the Heihe monzonite and granite. Subsequently, the closure of the Nenjiang Ocean, and collision between the Xing'an block and the Songnen block occurred at around 320 Ma. [ABSTRACT FROM AUTHOR]

Northeast (NE) China underwent complex tectonic processes during the early Mesozoic era, influenced by both the Paleo-Pacific and Mongol-Okhotsk tectonic regimes. However, the dominant factor responsible for the early Jurassic magmatism in the Xing'an block, whether it was the Mongol-Okhotsk or the Paleo-Pacific tectonic regime, remains uncertain. This study aims to investigate the geochemical characteristics, petrogenesis, and geodynamic implications of the early Jurassic A-type granitoids in Heihe, Xing'an block, in order to shed light on the evolution and spatial extent of the Paleo-Pacific tectonic regime. The Heihe A-type granitoids were formed by partial melting of calc-alkaline meta-andesite/basalt under high-temperature and low-pressure conditions. During the later stages of magma evolution, fractional crystallization of K-feldspar played a significant role. The geochemical characteristics of the Heihe A-type granitoids resemble both A 1 -type and intraplate granite, similar to the early Jurassic A-type granites in the Songnen block. The Xing'an block, at least its southeastern margin, was mainly overprinted by the subduction of the Paleo-Pacific oceanic plate during the early Jurassic. This is evidenced by the north-south distribution pattern and the decreasing zirconium saturation temperature from east to west of the early Jurassic igneous rocks in the Xing'an block. The occurrence of early Jurassic various types of A-type granitoids and coeval OIB mafic rocks in NE China could be attributed to the back-arc extension and asthenosphere upwelling triggered by the Paleo-Pacific slab rollback. • The Heihe A-type granitoids were formed by low-pressure melting of juvenile crust. • The Paleo-Pacific tectonic regime was responsible for the Heihe A-type granitoids. • The early Jurassic A-type granitoids in NE China were formed during the slab rollback. [ABSTRACT FROM AUTHOR]

• Four clades with 12 subclades were identified from 205 cox1 haplotypes representing 710 samples data of host insects of Ophiocordyceps sinensis. • The host insects of O. sinensis belonged to 2 genera (Thitarodes and Ahamus) in Hepialidae based on such large and extensive samplings. • Three phylogeographic patterns were uncovered: the co-existence of wide, long-distance dispersal and specific local distribution structures. • The differentiation of host insects of O. sinensis was corresponding to the historical geological uplift events of QTP. A fungus-insect complex, known as DongChong XiaCao, is formed from the infection of the hepialid larvae by the fungus Ophiocordyceps sinensis , which is endemic to the Qinghai-Tibetan Plateau (QTP). Due to previously limited sample collection size, the data about the diversity and structure of the host insect was insufficient and lacked details. The purpose of this study was aimed to discuss the diversity and phylogeography of the host insects of O. sinensis with a large-scale sampling. The mitochondrial cytochrome oxidase I gene (cox1) was sequenced and analyzed among 710 samples representing 88 geographic locations. 205 haplotypes of cox1 were identified from all the 710 samples and 4 phylogenetic clades with 12 subclades were identified. Instead of the single latitude-based divergence suggested previously, three distribution patterns were deduced to correspond to the phylogeographic structures, including but not limited to the co-existence of a wide and specific local phylogeographic distribution structures. Two separate genetic diversity and differentiation centers, namely the northwestern Yunnan and the southeastern Tibet were identified. Dating analyses from three calibrations supported that the divergence of the 4 clades occurred in the Oligocene-Miocene period (30.54–13.66 million years ago) (Ma), which were connected with the second and third geological movements of the QTP (17–25, 8–13 Ma). Our results provide a more detailed understanding of the divergence and distribution patterns of the host insects of O. sinensis. [ABSTRACT FROM AUTHOR]

The Katebasu gold (Au)–copper (Cu) deposit is one of the extra large‐scale Au–Cu deposits discovered in the western Tianshan Mountains in Xinjiang in the recent years. The geological characteristics of the deposit have not been systematically studied and summarized, and there is considerable debate about the deposit type and metallogenic epoch. In this paper, we studied the Katebasu Au–Cu deposit orebody production characteristics, ore mineral composition, structural tectonic, surrounding rock alteration, and metallogenic phases. We identified the deposit types, presented a new discussion on the metallogenic epoch combined with the study of garnet Sm–Nd chronology, and indicate that the deposit type is a skarn type–fracture zone alteration rock type. The skarn‐type Cu–Au deposit is mainly distributed in the fault fracture zone and skarn in the contact zone between the rock mass and marble strata. The fracture zone alteration‐type Au–Cu deposit is mainly distributed in the monzonite granite fracture zone. The mining area has two phases of metallogenesis, which are related to monzonite granite and diorite dykes, respectively, and have a certain degree of superposition in space. The early metallogenesis occurred at 334.3 ± 6.7 Ma. The above results provide direction for regional prospecting. [ABSTRACT FROM AUTHOR]

The northern Guizhou area, located near the southwestern margin of the Yangtze Block and south of the Sichuan Basin, is a promising area for shale gas exploration and development. The discovery of a natural gas accumulation in the Lower Silurian Songkan Formation in the study area is the first discovery of natural gas in this stratum in China, marking an exciting breakthrough in natural gas exploration in northern Guizhou area. This paper presents an investigation of this accumulation using gas geochemistry, including gas composition, carbon and hydrogen isotopes, in context with geological information available for the study area. Our results indicate that the natural gas accumulation in Songkan Formation is probably sourced from the Lower Silurian Wufeng-Longmaxi shale. The δ 13 C(CH 4 ) values range from − 33.9‰ to − 33.2‰, the δ 13 C(C 2 H 6 ) values range from − 37.0‰ to − 36.2‰, and the δ 2 H(CH 4 ) values range from − 157‰ to − 144‰. These results indicate that the gases are of thermogenic origin and are oil-derived. Furthermore, isotopic rollovers seen in the natural gas is similar to that seen in the natural gas from the local Wufeng-Longmaxi shale, which is identified as carbon exchange at high temperature. The δ 13 C(CO 2 ) values range from − 20.8 to − 17.1‰, suggesting that carbon dioxide was mainly generated by thermogenic processes. The fracture investigation indicates that the large development of horizontal fractures in calcareous mudstone is one of the reasons for the high yield of natural gas in Songkan Formation. The petrophysical parameters suggest that limestone with low porosity and permeability effectively prevents natural gas escaping and seals natural gas into calcareous mudstone with horizontal fractures. [ABSTRACT FROM AUTHOR]

This paper presents U-Pb zircon geochronology, petrology, and major and trace element, Sr-Nd and zircon Hf isotopic geochemistry of Cretaceous granites and intermediate dykes in the Quanzhou and Xiamen regions of southeastern China. These data are used to investigate igneous petrogenesis and Cretaceous tectonic evolution, and interpret the geodynamics of Palaeo-Pacific slab subduction. Granites in Quanzhou and Xiamen range in age from 133 Ma to 87 Ma, have high SiO 2 and K 2 O contents, low abundances in P 2 O 5 , and an A/CNK index that ranges from 0.97 to 1.09, indicating that they are high-K calc-alkaline metaluminous I-type rocks. Slightly negative ɛ Nd (t) values (− 1.2 to − 4.4), young Nd model ages (0.87 Ga to 1.20 Ga) and positive ɛ Hf (t) values (− 0.5 to + 9.9) of zircon grains indicate that the granites were derived from magmas that melted amphibolite in the middle-lower crust, and which may have assimilated country rocks during emplacement in shallow chambers. The intermediate dykes have no genetic link to the granites and magma mixing was negligible. Eight dyke samples have low SiO 2 and high MgO, Ni and Cr contents. Negative ε Nd (t) values (− 1.5 to − 2.7) and positive ε Hf (t) values (2.7 to 7.6) suggest that the dykes were derived from residual basic lower crust after mafic-crystal accumulation. Two samples of adakite-like dykes are characterised by high Sr/Y ratios (89 to 100) and high SiO 2 , low K 2 O, Ni, Cr contents. In combination with slightly negative ε Nd (t) values (− 1.7 to − 1.8) and positive ε Hf (t) values (2.9 to 4.3), the adakite-like dykes were derived from cumulate basic lower crust which had a mixed source between depleted mantle- and crust-derived melts. Based on our data, combined with previously published work, we suggest that extension-induced middle-lower crustal melting and underplating of mantle-derived basaltic melts were the principal driving mechanisms for Cretaceous granitic magmatism in coastal Fujian Province. Extension was related to subduction retreat whereas steep slab subduction caused underplating of mantle-derived basaltic melts. These processes were coupled and mainly responsible for the tectonic transition during the Cretaceous from compression to extension in the coastal belt of the Cathaysia Plate. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Sandaowanzi volcanic rocks were originated from delaminated lower crust. • The early Cretaceous paleo-Pacific slab rollback caused lithospheric delamination. • The geochemical characteristics of magmatic zircons can imply the magma fertility. The complex and diversified geodynamic mechanism brought massive magmatic activity and gold mineralization in the early Cretaceous in the Great Xing'an Range. The Sandaowanzi gold deposit has a close temporal-spatial correlation with the early Cretaceous magmatism. However, the genetic relationship between the Early Cretaceous volcanic rocks and Sandaowanzi gold mineralization is not well constrained. In addition, the metallogenic geodynamic background of the Sandaowanzi gold deposit remains controversial. Here, the zircon U-Pb geochronology, zircon trace elements, in-situ zircon Hf isotopes, and whole-rock geochemistry of the Sandaowanzi ore-hosting volcanic rocks are reported. The Sandaowanzi volcanic rocks, including andesite and dacite, show variable contents of MgO, Cr, Ni, and adakitic affinity, and are proposed to originate from delaminated lower crust that interacted with lithospheric mantle metasomatized by subduction-related sediments. Besides, it may have experienced fractional crystallization of olivine, clinopyroxene, and amphibole during the early stage of magmatic evolution. Their petrogenesis, combined with other geological evidence, indicates that the Sandaowanzi volcanic rocks were formed during the slab rollback process of the Paleo-Pacific Ocean. Finally, the elemental and isotopic signatures of zircons in the Sandaowanzi magmatic rocks imply that magmas with high water content, high oxygen fugacity, and a high proportion of mantle material contribution produced during 121–123 Ma have the highest mineralization potential, which is consistent with the Rb-Sr isochron ages of ore minerals. The geochemical characteristics of zircons from magmatic rocks in ore deposits provide effective indices for constraining the magma fertility. [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]

Ore deposits in the Southern Lhasa Terrane that formed prior to the India-Eurasia collision are rare. Among them, the formation of the Kelu and Sangbujiala skarn Cu-Au deposits in the Zedong area is associated with a magmatic "flare-up" in the Late Cretaceous (∼95 Ma). However, the tectonic setting, geochemistry, and petrogenesis of the mineralization-related magma of these deposits are not well understood. The biotite granodiorite is the dominant phase in the Kelu and Sangbujiala skarn Cu-Au deposits, and this study reports a set of biotite granodiorite veins (Zircon U-Pb age: 94.1 ± 0.4 Ma) without skarn alteration intruding into the cumulated hornblendite of the Late Jurassic Zedong Terrane. The rocks are adakitic, and have primitive Sr-Nd-Pb isotope compositions ((87Sr/86Sr) i = 0.7040, εNd (t) = +3.1, (206Pb/204Pb) t = 18.457, (207Pb/204Pb) t = 15.564, (208Pb/204Pb) t = 38.215) and zircon εHf (t) values (+9.7 ∼ +13.5). The trace elements of the rocks indicate that they are derived from the magma that originated from the partial melting of the mantle wedge strongly influenced by slab-derived fluids and sediments, and underwent the fractional crystallization of hornblende and plagioclase. The biotite granodiorite magma is rich in water and Cl with high oxygen fugacity (≈ ΔNNO+2 ∼ ΔNNO+4). It crystallizes at low pressure (≈ 157–200 MPa) in a closed system, and the crystallization temperature is inferred to be about 708–733 °C and 588 °C in the early and late stages, respectively. Based on the analysis of zircon data from this study and previous papers, we find that the number of magmatic zircons in the Late Cretaceous Southern Lhasa Terrane began to increase intensively at 95 Ma, accompanied by a leap in εHf (t) values and crystallization temperatures, as well as a sharp decline of (Ce4+/Ce3+) ratios. Those zircons with high εHf (t) values and crystallization temperatures, and low (Ce4+/Ce3+) ratios disappeared at 89 Ma. Therefore, we suggest that the magmatic "flare-up" in the Late Cretaceous (95–89 Ma) Southern Lhasa was triggered by mid-ocean ridge subduction, while the flat subduction occurred during 109–95 Ma and after 89 Ma. • Mid-ocean ridge subduction occurred during 95–89 Ma in the Southern Lhasa Terrane. • Mineralization-related magma during 95–89 Ma is derived from hydrous mantle wedge. • The magma is rich in water and Cl, with high oxygen fugacity. [ABSTRACT FROM AUTHOR]

The lithium isotopic compositions of adakitic rocks and K-rich volcanic rocks in southern Tibet range from + 1.3‰ to + 7.5‰ and − 4.9‰ to + 3.5‰, respectively. The subduction of the Indian Plate beneath the Lhasa Terrane means that traditional lithium isotopic compositions of various reservoirs are unable to explain the aforementioned δ 7 Li data. Therefore, it is necessary to determine the Li isotopic compositions of the different geological endmembers underneath southern Tibet. Here, we report the lithium isotopic composition and concentration of Indian upper and lower continental crust. On the basis of whole-rock major and trace element data and Sr–Nd–Pb isotope data, leucogranites from Luozha and Longzi are considered as representative of Indian upper crust, whereas two-mica granites from Quedang and Dala and granulites and gneisses from Nyalam are considered as representative of Indian lower crust. The Li concentration of Indian upper crust varies from 23 to 45 ppm with a mean of 34 ppm, consistent with a weighted mean Li concentration for the upper crust of 35 ± 11 ppm. In contrast, the Li abundance of Indian lower crust is estimated to be 33–84 ppm with a mean of 58 ppm, much higher than the average Li concentration for the lower crust of ~ 8 ppm because of the high modal abundance of biotite and muscovite. The Li isotopic compositions (+ 0.9‰ to + 5.6‰) of Indian upper continental crust are relatively heavy compared with the average Li isotopic composition of upper continental crust. On the other hand, the Li isotopic compositions of Indian lower continental crust (− 4.4‰ to − 0.1‰) are lighter than those of Indian upper continental crust. The isotopically heavy signature of Indian upper crust is produced by high-δ 7 Li fluids released from the Indian lower crust slab, whereas the lighter signature of Indian lower crust is generated by the partial melting of residual Indian lower crust slab during metamorphic dehydration of Indian lower crust. [ABSTRACT FROM AUTHOR]

Understanding the geological history of the Lhasa Terrane prior to the India–Asia collision (~ 55 ± 10 Ma) is essential for improved models of syn-collisional and post-collisional processes in the southern Lhasa Terrane. The Miocene (~ 18–10 Ma) adakitic magmatism with economically significant porphyry-type mineralization has been interpreted as resulting from partial melting of the Jurassic juvenile crust, but how this juvenile crust was accreted remains poorly known. For this reason, we carried out a detailed study on the volcanic rocks of the Yeba Formation (YF) with the results offering insights into the ways in which the juvenile crust may be accreted in the southern Lhasa Terrane in the Jurassic. The YF volcanic rocks are compositionally bimodal, comprising basalt/basaltic andesite and dacite/rhyolite dated at 183–174 Ma. All these rocks have an arc-like signature with enriched large ion lithophile elements (LILEs; e.g., Rb, Ba and U) and light rare earth elements (LREEs) and depleted high field strength elements (HFSEs; e.g., Nb, Ta, Ti). They also have depleted whole-rock Sr–Nd and zircon Hf isotopic compositions, pointing to significant mantle isotopic contributions. Modeling results of trace elements and isotopes are most consistent with the basalts being derived from a mantle source metasomatized by varying enrichment of subduction components. The silicic volcanic rocks show the characteristics of transitional I–S type granites, and are best interpreted as resulting from re-melting of a mixed source of juvenile amphibole-rich lower crust with reworked crustal materials resembling metagraywackes. Importantly, our results indicate northward Neo-Tethyan seafloor subduction beneath the Lhasa Terrane with the YF volcanism being caused by the initiation of back-arc rifting. The back-arc setting is a likely site for juvenile crustal accretion in the southern Lhasa Terrane. [ABSTRACT FROM AUTHOR]