Late Permian Bimodal Volcanic Rocks in the Northern Qiangtang Terrane, Central Tibet: Evidence for Interaction Between the Emeishan Plume and the Paleo‐Tethyan Subduction System

Abstract

Many studies provide compelling evidence for a fossil mantle plume beneath the Late Permian Emeishan large igneous province located near the southeastern margin of the central Tibetan Plateau, a region associated with the Paleo‐Tethyan subduction system. However, little is known about whether direct plume‐subduction interaction occurred during the Late Permian. Here we report geochronological, mineralogical, geochemical, and Sr‐Nd‐Hf‐O isotopic data for the Late Permian (~259–256 Ma) bimodal volcanic rocks (BVRs) in the northern Qiangtang Terrane (NQT), central Tibet. These BVRs consist mainly of basalts, rhyolites, and rhyolitic tuffs. The rhyolites with A‐type affinity were generated by partial melting of newly underplated basalts. Geochemical and isotopic data suggest that two components (ocean island basalt‐type mantle and subducted sediment‐derived fluid) were involved in the generation of the basalts in an extensional back‐arc region. Considering the Permian tectonic evolution of the NQT, we propose that this enriched ocean island basalt‐type mantle was distinct from the Paleo‐Tethyan depleted upper mantle. It most likely originated from Emeishan‐plume material that flowed westward from the South China Block to the nearby NQT, driven by slab rollback‐induced counterflow. The presence of high‐temperature A‐type rhyolites in bimodal back‐arc magmatism also indicates a special subduction setting influenced by a nearby plume. Thus, we propose that the Late Permian BVRs were the result of interaction between the Emeishan plume and the Paleo‐Tethyan subduction system.

Paleomagnetic Constraints on the Origin and Drift History of the North Qiangtang Terrane in the Late Paleozoic

“…When a (sub) equatorial paleolatitude is observed, the choice between normal and reversed polarity is often ambiguous (Huang et al, ). The age of the middle part of our sampling section is dated at ~259 Ma, which is consistent with the age (~259–256 Ma) determined by SIMS U‐Pb zircon dating (Wang et al, ) and has reversed polarity (Ogg et al, ). Therefore, we concluded that our sampling area was more likely located at a paleolatitude of −7.6 ± 5.6°N at ~259 Ma.…”

“…They reliably show similar 206 Pb/ 238 U ages (Figure a), yielding a weighted average age of 259.1 ± 1.4 Ma with mean square weighted deviation = 0.77 (Figure b). The age of ~259 Ma determined by laser ablation sampling and multiple‐collector inductively coupled plasma mass spectrometry (LA‐MC‐ICPMS) dating method is well consistent with the secondary ion mass spectrometer (SIMS) U‐Pb zircon dating results (~259 Ma) for the same volcanic rock from the same bedding (Wang et al, ). Therefore, we confidently conclude that the Nayixiong Fm volcanics most likely erupted at ~259 Ma.…”

“…(c) Geological map of the sampling area (modified from Li, ). (d) Stratigraphic column of the Permian strata showing our sampling unit (modified from Wang et al () based on our observations).…”

First Identification of Late Permian Nb‐Enriched Basalts in Ailaoshan Region (SW Yunnan, China): Contribution From Emeishan Plume to Subduction of Eastern Paleotethys

“…The resultant mantle flow gives rise to the deformation and stalling of the nearby mantle plume (Druken et al, ; Kincaid et al, ), such as in the Yellowstone (Northwestern United States) and Samoa (Southwest Pacific; Druken et al, ; Fletcher & Wyman, ). As a consequence, the slab‐driven mantle flow can entrain ocean island basalt (OIB)‐like enriched plume material and modify the chemistry of the mantle wedge in the subduction zone (Gazel et al, ; Obrebski et al, ; Price et al, ; J. Wang et al, ; Wendt et al, ). For example, the elevated helium isotopic ratios and high Nb concentrations (compared to other high‐field‐strength elements (HFSEs)) in the lavas from the Tonga arc system have been attributed as chemical inheritance from the nearby Samoa mantle plume (Ewart et al, ; Lupton et al, ; Price et al, ; Wendt et al, ).…”

“…He et al, ; Y. Xu et al, ; Y. G. Xu et al, ). The Ailaoshan‐Red River shear zone was originally considered as the western boundary of ELIP (Y. X. Zhang et al, ), yet ELIP‐like basalts and mafic intrusions have been identified in Jinping (southern Ailaoshan region) in western Yunnan and Qiangtang terrane in Tibet (Chung et al, ; J. Wang et al, ; Xiao et al, ; Y. Xu et al, ) and northern Vietnam (e.g., Hoa et al, ), although whether there is any genetic link with the Emeishan plume is still debatable (Halpin et al, ). Paleozoic and Early Mesozoic magmatic rocks associated with the opening and closure of the Paleotethyan Ailaoshan Ocean were well documented in the western Ailaoshan volcanic belts (e.g., Fan et al, ; Jian et al, , ; Lai et al, ).…”