Search

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]

[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]

[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]