Interplay between oceanic subduction and continental collision in building continental crust

Abstract

Generation of continental crust in collision zones reflect the interplay between oceanic subduction and continental collision. The Gangdese continental crust in southern Tibet developed during subduction of the Neo-Tethyan oceanic slab in the Mesozoic prior to reworking during the India-Asia collision in the Cenozoic. Here we show that continental arc magmatism started with fractional crystallization to form cumulates and associated medium-K calc-alkaline suites. This was followed by a period commencing at ~70 Ma dominated by remelting of pre-existing lower crust, producing more potassic compositions. The increased importance of remelting coincides with an acceleration in the convergence rate between India and Asia leading to higher basaltic flow into the Asian lithosphere, followed by convergence deceleration due to slab breakoff, enabling high heat flow and melting of the base of the arc. This two-stage process of accumulation and remelting leads to the chemical maturation of juvenile continental crust in collision zones, strengthening crustal stratification.

Secular Evolution of Continents and the Earth System

“…For accretionary orogens, this is generally invoked to involve fluxing of fluid and sediment derived from recycled dense oceanic lithosphere driving melting in the mantle and magmatism in the overlying lithosphere (Marschall & Schumacher, 2012). For recent collisional orogens, heat input to the lithosphere, perhaps facilitated by an increase in the rate of convergence or slab break‐off, drives melting of the lower crust (D. C. Zhu et al., 2022a), whereas during the Earth's early history, high mantle potential temperatures would likely lead to decompression melting during inferred delamination and lithospheric peel‐back in the zone of convergence (Chowdhury et al., 2020; Perchuk et al., 2018). The termination of convergence in collisional orogens results in continental growth and reworking through the assembly of largely preexisting lithosphere.…”

Paleogeographic Reconstruction of Precambrian Terranes Reworked by Phanerozoic Orogens: An Example Based on Detrital Zircon REE From Lhasa Terrane in Southern Tibet

“…The partly decoupled $$\overline{{\mathrm{L}\mathrm{R}\mathrm{E}\mathrm{E}}_{\mathrm{N}}}/\overline{{\mathrm{H}\mathrm{R}\mathrm{E}\mathrm{E}}_{\mathrm{N}}}$$ period from ca. 72.5 to 67.5 Ma is possibly due to the rising asthenosphere triggered by coeval roll‐back of oceanic slab (Zhu, Wang, et al., 2022) that modified the redox conditions or water content of the magmatic system. This roll‐back event is further supported by the subsequent crustal thinning process from ca.…”

Petrogenesis of the Quxu intrusive complex: Implications for Eocene magmatism in the southern Lhasa Terrane, Tibet

“…The widespread Eocene rocks crop as batholiths within the Gangdese Batholith and contain abundant MMEs and dykes of similar age (Figure 8; Ji et al, 2009;Zhu et al, 2011Zhu et al, , 2013Zhu et al, , 2015. This phase of magmatism is characterized by small amounts of hornblendites and cumulate hornblende gabbros, with compositional diversity from mafic to high-K felsic rocks (Zhu et al, 2019(Zhu et al, , 2022. The Eocene intrusive rocks exposed in the Gangdese Batholith include gabbro, diorite, granodiorite and granite (Ma et al, 2017;Mo et al, 2005;Wang et al, 2019).…”

“…The Gangdese magmatic belt in the southern Lhasa Terrane is part of the India-Asia collisional orogen, in which the magmatic records from growth of the continental arc crust during the Mesozoic to its reworking during the Cenozoic are well-preserved (Chung, et al, 2005;Ji et al, 2009;Yin et al, 2000;Zhu et al, 2015Zhu et al, , 2019Zhu et al, , 2022.…”

“…The Gangdese magmatism can be divided into three stages: precollision (>60 Ma), co-collision (60-45 Ma) and post-collision (45-10 Ma) (Zhu et al, 2022), and the Quxu magmatic activity of ca. 50 Ma in this paper corresponds exactly to the co-collision stage.…”