Petrogenesis of the Late Eocene to Early Oligocene Yao'an Shoshonitic Complex, Southeastern Tibet: Partial Melting of an Ancient Continental Lithospheric Mantle beneath the Yangtze Block

Abstract

Cenozoic potassic‐ultrapotassic igneous rocks are widespread in the southeastern Tibetan Plateau. Their petrogenesis and magmatic process remain subject to debate in spite of numerous publications. Almost all of the Cenozoic extrusive and intrusive rocks in Yao'an area, western Yunnan Province, China are geochemically shoshonitic. We collectively term them the Yao'an Shoshonite Complex (YSC). The YSC is located in the (south)easternmost part of the ENE—WSW‐trending, ∼500‐km‐long and ∼250‐km‐wide Cenozoic magmatic zone, which separates the orthogonal and oblique collision belts of the India–Eurasia collision orogen. Previously published geochronological and thermochronological data revealed that the rocks of YSC were emplaced over a short period of 34–32 Ma. Previously published data and our new data suggest that primary magma of the YSC likely were formed by partial melting of an ancient continental lithospheric mantle beneath the Yangtze block. This part of continental lithospheric mantle likely has not been modified by any oceanic subduction. Fractionation crystallization of a Mg‐ and Ca‐bearing mineral and Ti‐Fe oxides during the magmatic evolution probably account for variable lithologies of the YSC.

Present‐day Upper‐crustal Strain Rate Field in Southeastern Tibet and its Geodynamic Implications: Constraints from GPS Measurements with ABIC Method

“…The southeastern part of the Tibet Plateau occupies a significant position within the transition zone between the uplifted plateau and the Yangtze Plate. This region is characterized by intense volcanic and magmatic activity (e.g., Dong et al, 2023;Yang et al, 2023), fragmented crust, deep and extensive fractures, as well as frequent and strong seismic events. It is widely accepted that the intricate tectonic patterns of crustal shortening, plateau uplift, and block slip in this area are intimately associated with the collision and compression between the Indian and Eurasian plates.…”

Petrogenesis and Tectonic Implications of the Oligocene Dalongtan Shoshonitic Syenite Porphyry in Central Yunnan, Southeastern Tibetan Plateau: Constraints from Geochronology, Geochemistry and Sr-Nd-Hf Isotopes

“…In southeastern Tibet, Eocene-Oligocene potassic magmatic suites (including felsic shoshonitic rocks) commonly occur in the Ailaoshan-Red River shear zone (ARSZ), documenting the post-collisional processes of the India-Asia collision and providing significant magmatic evidence of crustal and mantle evolution [17,18]. Although numerous studies have been carried out on these felsic shoshonitic rocks [7,15,[19][20][21][22][23], their petrogenesis and tectonic mechanisms remain controversial. The continued debate primarily revolves around two key aspects: (1) Which component, the thickened mafic lower crust or the lithospheric mantle, is responsible for the source region?…”