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Due to the unclear tectonic setting of the Jurassic ophiolites within the Bangong-Nujiang suture, how and when intra-oceanic subduction initiated within the Bangong Meso-Tethys remain controversial. Based on the new petrological, geochemical, and geochronological data reported in this paper, ∼190–180 Ma MORB-like ophiolites and OIB-like mafic rocks were identified from the Shiquanhe ophiolitic complex in the western Bangong-Nujiang suture. The MORB-like gabbros exhibit strong light rare earth elements (LREEs) and heavy rare earth elements (HFSEs) depletion and were derived from partial melting of a highly refractory depleted mantle source with limited slab-derived fluids. The OIB-like mafic rocks are enriched in LREEs and HFSEs and were originated from the melting of upwelling asthenospheric mantle without subduction additions. The data for the MORB-like ophiolites reported in this paper and previously published data demonstrate the formation of Early Jurassic fore-arc ophiolites in response to the Early Jurassic intra-oceanic subduction initiation within the Bangong-Nujiang suture. The Early Jurassic OIB-like rocks formed in the extensional tectonic setting, together with regional geological evidence, suggest that the Early Jurassic initial subduction event within the Bangong Meso-Tethys resulted in broad upper plate extension. Our study not only reveals the intra-oceanic subduction initiation age of the Bangong Meso-Tethys but also implies that subduction initiation can cause strong extension in a wider region of the upper plate in the Tethys oceanic system, not just in the fore-arc region. • Discovery of MORB-like fore-arc ophiolite (190–185 Ma) in the Shiquanhe area. • Identifying of OIB-like gabbro-monzonite (185–180 Ma) in the Shiquanhe melange. • Confirming Early Jurassic intra-oceanic subduction initiation in Bangong Ocean. [ABSTRACT FROM AUTHOR]

The Gangdese arc underwent the most intense magmatic flare-up of southern Tibet in the early Eocene (peaked at ∼50 Ma), generating widespread plutonic and volcanic rocks both along and across the arc. However, the dynamic mechanism for the magmatic flare-up is mysterious. This paper systematically analyzed the petrology, mineralogy, geochronology, and geochemistry of the early Eocene volcanic and intrusive rocks in the Pangduo basin in the eastern Gangdese arc. These rocks yielded identical zircon U Pb ages of ∼50 Ma and similar isotopic compositions. The low-silica (< 60 wt%) rocks, including basalt andesite and trachyandesite, result from low degree (2–3%) partial melting of garnet-bearing lithospheric mantle. Based on textural observations and geochemical studies, coupled with Rhyolite-MELTS modeling and zircon trace elements Rayleigh fractionation models, the following research results were obtained. The high-silica rhyolite, ignimbrite, and granite porphyry are the product of limited melt extraction, while the quartz monzonite belongs to the associated residual silicic cumulates. The quartz monzonitic porphyry and trachydacite show a widespread dissolution structure and high formation temperature of ∼850 °C. Whole-rock geochemical mixing model results indicate that they are generated by mixing products of mafic magma, high-silica melts, and remelting melts of quartz monzonite. The volcanic and intrusive rocks in the Pangduo basin are considered as a volcanic-plutonic complex, resulting from the synergistic effect of melt extraction and cognate magma mixing. Both the complex magmatic processes and the early Eocene magmatic flare-up are attributed to mafic magma injection. • The Pangduo volcanic-plutonic complex with various rock types is well exposed in the Pangduo basin, southern Tibet. • The rhyolitic ignimbrite and the quartz monzonite are extracted melts and corresponding residual cumulates, respectively. • Melt extraction and magma mixing via mafic magma injection promote the large-scale magma formation. [ABSTRACT FROM AUTHOR]

When impinging on the lithosphere in spreading ridges or intra-plate settings, the asthenospheric mantle can significantly influence plate tectonics. However, the active role of the asthenospheric mantle on subducting slabs remains poorly understood. The main reason for this dispute is the lack of typical geochemical mafic rocks in the subduction zone. In this paper, we first report the Early Jurassic (187 Ma) Yurongguo Nb-enriched basalts in the western segment of the Bangong-Nujiang suture zone. These samples show typical Nb-enriched basaltic features with high Na 2 O, TiO 2 , Nb (>7 ppm), high Nb/Th (average = 11.05), Nb/La (average = 1.37) and Nb/U (average = 72.98) ratios. Unlike the adakite-related Nb-enriched basalts, the Yurongguo Nb-enriched basalts formed from the mixture of magmas derived from upwelling asthenosphere (20–30%) and depleted mantle (70–80%) in the spinel lherzolite region (<70 km). We conclude the Yurongguo Nb-enriched basalts were formed in the fore-arc basin setting with the influence of slab rollback, which occurred under the intra-oceanic subduction. Two southward intra-oceanic subductions may exist in the western part of the Bangong-Nujiang Tethyan Ocean in the Jurassic. The Early Jurassic (200–180 Ma) intra-oceanic subduction formed the fore-arc basin, probably accompanied by asthenospheric mantle activity at the same time, followed closely by flat subduction due to the oceanic plateau. After a period of geological stabilization, the Late Jurassic (170–150 Ma) was the period when the spreading of the little ocean basin ceased, and the second intra-oceanic subduction occurred. We proposed an oceanic plateau-subducted oceanic slab interaction and overriding intra-oceanic subduction model for the Meso-Tethyan subduction in the western Tibetan Plateau. • Yurongguo rocks were formed in 187 Ma, which are the typical Nb-enriched basalts. • OIB (20–30%) and MORB (70–80%) mixed to form the Yurongguo Nb-enriched basalts. • Yurongguo Nb-enriched basalts are the consequence of intra-oceanic subduction. • Oceanic plateau played an important role in the intra-oceanic subduction. [ABSTRACT FROM AUTHOR]

In this paper we present new major and trace element compositions of basaltic rocks in the Gufeng ocean island (GFOI) area in the western segment of the Bangong–Nujiang Suture Zone, northern Tibet. Our aim was to assess the genesis of these rocks and discuss the implications of this new dataset for the evolution of the Bangong–Nujiang Tethyan Ocean. An ocean-island-type double-layer structure comprising a basaltic basement and an oceanic sedimentary cover sequence found within the GFOI provides direct evidence for the interpretation that the assemblage is a typical ocean island. The basalts in the GFOI can be divided into three types (named G1, G2 and G3 basalts), and these basalts range in composition from MORB to OIB types, which is typical of ocean islands. The G1 basalts have MORB-type affinities, possibly indicating the existence of MORB oceanic crust under the GFOI. The G2 basalts represent the early stage of formation of the GFOI, and are produced by the interaction of rising OIB-type basaltic magma and the existing MORB oceanic crust. The G3 basalts are typical OIB basalts and they are the products of the direct eruption of OIB-type basaltic magmas. The G3 basalts have high (La/Yb) N (12.3–14.4), (Ce/Yb) N (10.8–11.8), (La/Sm) N (2.39–2.76), and (Sm/Yb) N (4.89–5.23) ratios, indicating the presence of oceanic lithosphere below the GFOI with a thickness of 50–60 km. Geochemical analyses of the GFOI cherts show that they contain terrigenous material, indicating the GFOI formed close to a continental margin. Norian conodont fossils within the GFOI limestones indicate the GFOI formed during the Late Triassic. These data, combined with geological evidence and a half-space model of lithosphere cooling, where the thickness of the oceanic lithosphere is determined from the age of the lithosphere, indicate that the western segment of the Bangong–Nujiang Tethyan Ocean opened initially in the late Permian, expanded rapidly during the Early–Middle Triassic, and was a mature ocean during the Late Triassic. [ABSTRACT FROM AUTHOR]

[Display omitted] • Constructed a geochemical big data platform on the Tibetan Plateau. • Using GIS analysis, a filling map of geochemical elements was carried out. • The HF and Nd isotopic packing characteristics were explored. • Multivariate statistics were applied to explore mineralization characteristics. Tibet has received much attention as a pivotal area to explore the genesis of ore deposits. So far, a large number of researchers have conducted a lot of discussions on the geological conditions, genesis, distribution and scale of ore deposits in Tibet, and accumulated a plenty of isotopic test data. Isotopic data can reveal the geological changes of an area and analyze the metallogenic regularity. In this paper, combined with GIS (Geographic Information System) spatiotemporal analysis technology, Hf and Nd isotopic data mapping analysis has been carried out in Tibet. The mapping shows high zircons ε Hf (t) value and high whole rock ε Nd (t) value and low T DM c value on both sides of the Eastern Yarlung Zangbo Suture Zone and the Western Bangong-Nujiang Suture Zone. It indicates that the terranes in these two areas are relatively young and have typical characteristics of Cu and Au mineralization, which are favorable areas for the prospecting of Cu and Au. Combined with the geological fault characteristics of Tibet Plateau, the influence of terrane boundary on the deposit and the relevant characteristics of geochemical elements, three favorable targets for Cu and Au prospecting in Tibet Plateau are delineated by GIS analysis. The results show that the characteristics of isotopic data in Tibet Plateau are quite different in disparate terranes, and the isotopic analysis can quickly delineate the strategic prospecting targets. Therefore, using GIS technology for isotope analysis and metallogenic prediction provides important guiding significance for scientific prospecting. [ABSTRACT FROM AUTHOR]

Abstract: In order to understand soil geochemical exploration in the environment of the high-elevation and -frigid mountainous regions, in this paper, a case study was conducted at Qulong porphyry copper deposit that is located in Tibet Plateau, China. The results show that the contents of As, Sb, Bi, Cu, Mo, Pb increased gradually from coarse soil fraction to fine fraction in all soil horizons. The distribution of Au, Hg, Ag, Co, Ni, and Na2O shows an asymmetrical V-shaped pattern. The −20mesh fraction is the suitable grain size for the soil geochemical exploration to delineate the copper mineralization. From the weathered bedrock to the surface soil layer, the enrichment variations were observed for elements such as Au, Ag, As, Sb, Hg, Pb, Zn, Bi, Mo and W, whereas Mn, Cu, Co, and Na2O leached, and the K2O was content nearly unchanged. [Copyright &y& Elsevier]

[Display omitted] • Provenance is defined for the lakeshore dunes around Co Nag Lake on Tibet Plateau. • The combination of MixSIAR and end-member model can reliably infer the provenance. • Lacustrine and fluvial deposits on the eastern bank are main sources of dune sands. • The coupling of fluvial and aeolian systems promotes the development of sandy land. • Enhanced sand-control project should be taken to protect the Qinghai-Tibet railway. Studies of the provenance of aeolian dunes are crucial for providing knowledge of landscape evolution and developing management strategies to control aeolian desertification. The lakeshore dune is a typical aeolian landform that is widely distributed around the world. However, there has been little work on the provenance and formation mechanism of lakeshore dunes. By comparing the elemental and grain-size compositions of lakeshore dunes and potential sources around Co Nag Lake, this paper combines sediment fingerprinting analysis and end-member modeling. The results identify the provenance of aeolian sands on the eastern bank of Co Nag Lake and draw the following conclusions. (1) The combined use of fingerprinting analysis and grain-size analysis can yield a comprehensive and reliable provenance assessment. (2) The lakeshore dunes on the eastern bank of the lake are primarily derived from lacustrine deposits and fluvial deposits on the eastern bank. The coupling of fluvial and aeolian systems promotes the development of eastern sandy land. (3) Sand-control projects in the Co Nag Lake region should be carried out according to the sources of aeolian sands. It is necessary to strengthen efforts to control lacustrine deposits and sands in gullies. [ABSTRACT FROM AUTHOR]

Abstract: Eocene is a critical time for the elevation of Tibetan Plateau and global climate change, and previous studies suggested that the Eocene elevation was caused by intra-continental subduction of the Songpan–Garze block beneath the Qiangtang block. This paper reports zircon U–Pb age and geochemistry of the Eocene volcanic rocks from the Zuerkenwula mountain area in the northern part of Qiangtang block, and proposes that both slab break-off of the Neo-Tethys oceanic slab along the Bangong–Nujiang suture and intra-continental subduction of the Songpan–Garze block beneath the Qiangtang block caused the extensive partial melting of lithospheric mantle and subducted Songpan–Garze continental crust, which resulted in the significant elevation of the Tibetan Plateau. The volcanic rocks have LA-ICP MS U–Pb zircon age of 40.25±0.15Ma (MSWD=2.1, 2σ), which is contemporaneous with the Eocene eclogites in the Great Himalayan and K-rich lavas in the southeastern Tibet. They display some adakitic characteristics with SiO2 =57.44 to 68.72%, TiO2 =0.38 to 0.81%, Na2O=2.89 to 4.35%, K2O=2.77 to 4.48%, Al2O3 =13.92 to 18.22%, A/CNK=0.69 to 1.03, MgO=0.27 to 5.86% with Mg# ranging from 13.2 to 72.0, strongly depleted in heavy rare earth elements (HREEs) (Yb=0.92 to 1.51ppm and Y=10.1 to 24.1ppm), in combination with their positive Sr anomalies, high Sr/Y ratios and no significant Eu anomalies, which suggest a garnet-in and plagioclase-free source residue. These volcanic rocks can be divided into high-Mg# (>45) and low-Mg# (<45) groups. Both of the two groups share evolved Sr–Nd–Pb isotopic compositions with 87Sr/86Sr=0.707412–0.708284; εNd(t)=−4.0 to −5.7; 206Pb/204Pb=18.7499–18.8189, 207Pb/204Pb=15.7189–15.7384; 208Pb/204Pb=39.166–39.262. The geophysical data and regional geological setting suggest that the low-Mg# adakitic rocks were derived from the decompression melting of a subducted lower continental crust, when low-Mg# adakitic melts in the overlying peridotite mantle wedge captured some olivine crystals, resulting in their elevated Mg# and MgO values. [Copyright &y& Elsevier]

Abstract: Despite more than 30 years’ studies in the Yarlung Zangbo Suture Zone (YZSZ), southern Tibet is still a region of discovery and the geological evolution of the Neo-Tethys here remains controversial. In this paper we present the new field observation, petrography, zircon U–Pb dating and geochemistry of the Zhongba mafic rocks in the western segment of the YZSZ. Zircon U–Pb analyses from a diabase using SIMS (Secondary Ion Mass Spectrometry) yielded a concordant age of 125.7±0.9Ma. All the Zhongba mafic rocks exhibit LREE enrichment (LaN/YbN =4.7–15.8) without Eu anomalies (δEu=0.97–1.01). Their Primitive-Mantle-normalized trace element patterns are similar to those of the average OIB and Hawaii alkaline basalts, as well as other OIB-type rocks already reported in the central-western YZSZ. These observations lead us to suggest the existence of a series of seamounts within the Neo-Tethys during the Early Cretaceous. These OIB-type rocks could be originated from (1) hotspot mantle; (2) near-ridge seamounts by melting-induced mixing of two distinct mantle sources; (3) late-stage magmatism fed by melts that originated from an asthenospheric window due to slab delamination. Combining literature data from the entire YZSZ, which include studies of the MORB- and IAB-type rocks and mantle peridotites, we prefer the third explanation that the OIB-type rocks represent a late-stage magmatic activity above an intra-oceanic supra-subduction zone within the Neo-Tethys. [Copyright &y& Elsevier]

Abstract: The Lhasa terrane, southern Tibet is where the thickest part of the Earth’s crust occurs as a result of the India–Asia collision. This paper reports zircon U–Pb age and geochemical data of samples collected from the Gangdese batholith, southern Lhasa terrane, a subset of which has already been dated at 65–41Ma using zircon U–Pb geochronology (Ji, W.Q., Wu, F.Y., Chung, S.L., Li, J.X., Liu, C.Z., 2009a. Zircon U–Pb chronology and Hf isotopic constraints on the petrogenesis of Gangdese batholiths, southern Tibet. Chemical Geology 262, 229–245), to constrain the timing and mechanism(s) responsible for crustal thickening beneath southern Tibet. Our new data indicate that the Gangdese magmatism lasted continuously from ca. 65 to 34Ma, during which geochemical evidence for crustal thickening is observed. Crustal thickening is best illustrated by the progressive increase in La/Yb and Sr/Y of the Early to latest Eocene magmatic rocks, associated with the decrease in Hf isotopic ratios of Paleocene to Eocene magmatic zircons. We also identify in this study the oldest (ca. 51Ma), “post-collisional” adakitic granitoids in the Gangdese batholith, interpreted as products from partial melting of underplated basaltic lower crust. Therefore, a thickened crust likely existed by that time, at least locally, in the southern Lhasa terrane, Tibet. [Copyright &y& Elsevier]

Abstract: A ∼500km-long high-pressure metamorphic belt occurs in the Qiangtang Block of northern Tibet. The occurrence of high-pressure metamorphic rocks (eclogite and blueschist) has a significant bearing on the Paleo-Tethys subduction and plate suturing processes. A few studies have been conducted on petrology, mineralogy and geochronology of high-pressure rocks. In this paper we present the results of a geochemical and isotopic investigation on eclogite and blueschist from this belt, and discuss the probable geodynamic implications. Geochemical analyses show that the two rock types, eclogite and blueschist, have grossly similar bulk compositions, but they can be subdivided into two groups based on their TiO2 contents. The low TiO2 (<2.75wt.%) rocks exhibit REE distribution patterns and trace element abundances similar to enriched mid-ocean ridge basalts (E-MORB), whereas the high TiO2 (>2.75wt.%) rocks are more akin to ocean island basalts (OIB). The positive ε Nd(T) values (ranging from 0.4 to 6.3) for all samples suggest that the basaltic protoliths of the eclogites and blueschists were derived from a long-term depleted mantle source. However, their geochemical characteristics require that the source be metasomatized and enriched in large-ion-lithophile and light rare-earth elements shortly before the formation of these basaltic protoliths, like for most OIB and E-MORB of the world. The recognition of oceanic basalts suggests that a Paleozoic ocean should be present in the central Qiangtang Block. This ocean was hypothesized to be the western extension of the Changning–Menglian Paleo-Tethys Ocean in the eastern margin of the Tibetan plateau. The eclogite and blueschist were formed by northward subduction of this Paleozoic ocean in the Triassic. [Copyright &y& Elsevier]

Abstract: The Gangdese Belt is now recognized as an important Cu polymetallic mineralization belt. Recent studies suggest that apart from porphyry copper deposits, polymetallic skarn deposits are another significant deposit type in this belt. In this paper, principal component analysis (PCA) and spectrum–area (S–A) fractal modeling are used to identify geochemical anomalies associated with Cu and Pb–Zn skarn mineralization based on Cu, Pb, Zn and Ag stream sediment data. Firstly, the raster maps of Cu, Pb, Zn and Ag were obtained by multifractal inverse distance weighted (MIDW). Secondly, PCA was used to combine the Cu, Pb, Zn and Ag concentration values. Finally, S–A analysis was used to decompose the first component pattern obtained by the PCA. The results show that major anomalies of Cu, Pb, Zn and Ag are mostly located around mapped intrusions, and along E–W trending faults, where Cu and Pb–Zn skarn deposits favorably occur. These results indicate that: (1) the Gangdese Belt potentially hosts undiscovered Cu and Pb–Zn skarn deposits, and the integrated anomalies for Cu, Pb, Zn and Ag occurring around the intrusions and in the vicinity of faults in the center part of the Gangdese Belt should be further investigated in the next step of mineral resource exploration; and (2) the hybrid method combining PCA and S–A modeling is an effective tool to identify geochemical anomalies. [Copyright &y& Elsevier]

Abstract: Strongly foliated amphibolite clasts are found embedded within the ophiolitic mélange underlying the Xigaze Ophiolite near Bainang and Angren, Yarlung Zangbo Suture Zone, Southern Tibet. These high-grade amphibolites are interpreted as remnants of a dismembered subophiolitic metamorphic sole that would have formed during the inception of a subduction. They include garnet-clinopyroxene amphibolites, clinopyroxene amphibolites and common amphibolites. Petrographic descriptions, mineral chemistry and thermobarometry of these rocks can be found in a companion paper [Guilmette, C., Hébert, R., Dupuis, C., Wang, C.S., Li, Z.J., 2008. Metamorphic history and geodynamic significance of high-grade metabasites from the ophiolitic mélange beneath the Yarlung Zangbo Ophiolites, Xigaze area, Tibet. Journal of Asian Earth Sciences, 32, 423–437.]. The geochemistry of the amphibolites confirms that their protoliths were igneous mafic rocks of basaltic to pyroxenitic composition that were likely part of an upper oceanic crust. Rare Earth Elements contents are suggestive of an N-MORB origin. However, enriched LILEs and depleted Nb–Ta–Ti when compared to N-MORBs rather suggest a suprasubduction zone influence. A large proportion of the overlying ophiolitic mafic rocks share the same geochemical characteristics, suggesting the protoliths of the amphibolites might have crystallized in the same environment as the Xigaze ophiolitic crust, likely in a back-arc basin. 40Ar/39Ar step-heating dating of hornblende concentrates from three samples yielded ages of 123.6±2.9 Ma, 127.7±2.2 Ma and 127.4±2.3 Ma. These cooling ages are slightly younger or overlapping magmatic and sedimentary ages obtained from the overlying ophiolite. All these new data support a model in which the ophiolitic crust and the protolith of the amphibolites were formed along the same spreading center above a subduction zone. The demise of the early subduction circa 130 Ma forced the inception of a new subduction zone at the SSZ spreading axis, burying SSZ mafic rocks underneath a SSZ ophiolitic mantle. [Copyright &y& Elsevier]

• The host volcanic rocks of the Sinongduo Ag–Pb–Zn deposit erupted at approximately 61.9 Ma. • The sphalerite rich in Ag, In and Cd is a kind of Fe-poor sphalerite that is commonly found in IS epithermal deposits. • The Sinongduo Ag–Pb–Zn deposit is an IS epithermal deposit rather than a LS epithermal deposit. The Sinongduo Ag–Pb–Zn deposit was first defined as a typical low sulfidation (LS) epithermal deposit in the widespread Linzizong volcanic succession (LVS), Gangdese belt, Tibet. This paper we describe the lithology, mineralization, and hydrothermal alteration based on current advances in exploration, and use multiple chemical and geochronology methods, including whole-rock geochemistry (major and trace elements) of ores and the lithocap, the mineral chemistry of sphalerite, and the LA–MC–ICP-MS zircon U–Pb dating of host volcanic rocks to better constrain the genesis of the Sinongduo deposit and give some exploration advice. In the Sinongduo deposit, the host crystal tuff yields a zircon U–Pb age of 61.9 ± 0.4 Ma, indicating nearly simultaneous diagenesis and mineralization. The metallic minerals are mainly FeS-poor sphalerite, galena, pyrite, and minor chalcopyrite, along with silver and silver-based precious minerals. These minerals, particularly FeS–poor sphalerite, pyrite, and chalcopyrite, represent IS states. Mineral chemistry shows that the content of FeS in sphalerite is lower than 4.94 mol% and the Ag concentration is quite high, ranging from 16 to 1798 ppm with a mean concentration of 245 ppm. Low Ga/in ratios (<1) and enrichment of In and Sn in sphalerite imply that the ore-forming fluid is dominated by magmatic water with intermediate temperature. Gangue minerals include the silicic group (quartz and chalcedony), carbonates group (calcite, siderite, ankerite, etc.), and hematite. Alterations, including illite, montmorillonite, and sericite, are widely distributed. The results suggest that the Sinongduo deposit is not a LS epithermal deposit but a typical IS epithermal deposit and we believe that there is potential for Au and Ag exploration. [ABSTRACT FROM AUTHOR]