First Identification of Mafic Igneous Enclaves in Miocene Lavas of Southern Tibet With Implications for Indian Continental Subduction

Abstract

The history of Indian continental subduction beneath Asian plate remains unclear. Miocene ultrapotassic rocks in southern Tibet, with extremely enriched isotopes, have often been used to trace mantle metasomatism and geodynamic processes associated with Indian continental subduction. These rocks, however, may have been contaminated by Lhasa ancient crust. Uncertainties on primary ultrapotassic magmas obscure their mantle sources. Here we report on first mafic igneous enclaves in Cenozoic lavas of southern Tibet. They consist principally of clinopyroxene, phlogopite, and sanidine and have a zircon U‐Pb age of 21.5 ± 0.3 Ma. Mineral and bulk‐rock geochemical characteristics indicate their crystallization from primary ultrapotassic magmas. Bulk‐rock Sr‐Nd, clinopyroxene Sr, and zircon O isotopes demonstrate their isotopically enriched character. Combined with precollisional basalts, we suggest that the mantle source of the enclaves was enriched by the subducted Indian continent. This study implies that the Indian continent had subducted beneath central Lhasa no later than early Miocene.

Petrofabrics and Seismic Properties of Himalayan Amphibolites: Implications for a Thick Anisotropic Deep Crust Beneath Southern Tibet

“…Miocene lavas of the Lasha Block (Hao et al, 2018). A thick layer of amphibolite in the middle-lower crust of southern Tibet is also consistent with the observed high heat flows (~90 mW m −2 ) in the Himalaya Orogen and the Lasha Block because the radiogenic heat production in amphibolite is much higher than those in mafic granulite or eclogite (Jiang et al, 2019).…”

“…Based on these similarities, we propose a relatively thick layer of subducting amphibolitic Indian crust in middle‐lower crust beneath southern Tibet. Such an interpretation is also supported by geochemical evidence showing the contribution of Indian continental subduction to the formation of mafic igneous enclaves in Miocene lavas of the Lasha Block (Hao et al, 2018). A thick layer of amphibolite in the middle‐lower crust of southern Tibet is also consistent with the observed high heat flows (~90 mW m −2 ) in the Himalaya Orogen and the Lasha Block because the radiogenic heat production in amphibolite is much higher than those in mafic granulite or eclogite (Jiang et al, 2019).…”

Tectonic Control Over Shallow Crustal Exhumation Across the India‐Asia Convergent Margin

“…The stranded, weak, and permeable Indian crust (Klemperer et al., 2013; the pale yellow and orange block), cut by the lithosphere‐scale KF, is shown just below the Asian/Tibetan upper crust. Rapid uplift of the SE Karakoram range induced by delamination of the lithosphere above the mantle wedge ultrapotassic volcanism at places (Cheng & Guo, 2017; Hao et al., 2018) (shown by orange triangles). Blue curves indicate the evident flow of mantle sourced He to the surface in the SE Karakoram range (Klemperer et al., 2013) and southwestern Tibet (Hoke et al., 2000).…”

“…Subsurface structures are based on: (a) Rolland et al., 2009. (b) Longitudinal variation in compiled ultra potassic and adakitic magmatism ages from the Tibet (Data from: Arnaud et al., 1992; Chen et al., 2011, 2012; Cheng & Guo, 2017; Ding et al., 2003; Guo et al., 2013; Hao et al., 2018; Kapp et al., 2003; D. Liu et al., 2014; Z. C. Liu et al., 2014; Liu et al., 2017; Miller et al., 1999; Williams et al., 2001, 2004; Zhang et al., 2017). (c) Longitudinal variation in compiled thermochronological data from the Tibet and Karakoram range (Data from Carrapa et al., 2014; Copeland et al., 1995; Dai et al., 2013; Gourbet et al., 2016; Sanchez et al., 2013; Shen et al., 2016 and this study).…”

“…Subsurface structures are based on: (a) Rolland et al, 2009. (b) Longitudinal variation in compiled ultra potassic and adakitic magmatism ages from the Tibet (Data from: Arnaud et al, 1992;Chen et al, 2011Chen et al, , 2012Ding et al, 2003;Guo et al, 2013;Hao et al, 2018;Kapp et al, 2003;D. Liu et al, 2014;Liu et al, 2017;Miller et al, 1999;Williams et al, 2001Williams et al, , 2004Zhang et al, 2017).…”