Subduction-driven mantle melting controls the magmatic evolution of the early Permian Tianshan orogen

Abstract

<p>Mantle-derived <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/magma" title="Learn more about magmas from ScienceDirect's AI-generated Topic Pages">magmas</a> provide a window into deep <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/geodynamics" title="Learn more about geodynamic from ScienceDirect's AI-generated Topic Pages">geodynamic</a> processes and the evolution of <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/continental-lithosphere" title="Learn more about continental lithosphere from ScienceDirect's AI-generated Topic Pages">continental lithosphere</a>. Late Paleozoic overlap of <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/mantle-plume" title="Learn more about mantle plume from ScienceDirect's AI-generated Topic Pages">mantle plume</a> activity beneath the Tarim <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/craton" title="Learn more about craton from ScienceDirect's AI-generated Topic Pages">craton</a> and collisional <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/orogeny" title="Learn more about orogenesis from ScienceDirect's AI-generated Topic Pages">orogenesis</a> in the adjacent Tianshan orogen presents a rare opportunity to explore their interplay during convergent tectonics. Here, we present a comprehensive dataset on mafic dykes from the eastern Tianshan, <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/central-asia" title="Learn more about Central Asia from ScienceDirect's AI-generated Topic Pages">Central Asia</a>. <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/zircon" title="Learn more about Zircon from ScienceDirect's AI-generated Topic Pages">Zircon</a> U-Pb dating indicates that these dykes were emplaced at ca. 293 Ma, contemporaneous with the early eruption of the Tarim <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/large-igneous-province" title="Learn more about large igneous province from ScienceDirect's AI-generated Topic Pages">large igneous province</a> (LIP; ca. 290 Ma). However, their arc-like major and trace element signatures point to water-fluxed melting in the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/mantle-source" title="Learn more about mantle source from ScienceDirect's AI-generated Topic Pages">mantle source</a>, rather than melting induced by plume-related heating and decompression. Trace element modeling suggests an equivalent degree of partial melting, which could account for the formation of both the dykes and the LIP-related <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/basalt" title="Learn more about basalts from ScienceDirect's AI-generated Topic Pages">basalts</a>, but this does not explain their distinct geochemical compositions. <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/zircon" title="Learn more about Zircon from ScienceDirect's AI-generated Topic Pages">Zircon</a> H₂O contents (102–1190 ppm) from mafic dykes demonstrate a hydrous lithospheric mantle origin, contrasting with the characteristics of typical plume <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/magmatism" title="Learn more about magmatism from ScienceDirect's AI-generated Topic Pages">magmatism</a>. Furthermore, elevated zircon ε_Hf(t) and δ¹⁸O values (1.5–11.0 and 5.0–7.9 ‰, respectively) reveal a juvenile lithospheric <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/mantle-source" title="Learn more about mantle source from ScienceDirect's AI-generated Topic Pages">mantle source</a> with contributions from fluids derived from a subducted slab. These findings support a model involving melting within subduction-modified lithospheric mantle triggered by slab break-off, demonstrating that the Tarim plume head had minimal influence on the Tianshan orogen during the early <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/permian" title="Learn more about Permian from ScienceDirect's AI-generated Topic Pages">Permian</a>. Such processes are consistent with the spatial and <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/temporal-distribution" title="Learn more about temporal distribution from ScienceDirect's AI-generated Topic Pages">temporal distribution</a> of post-collisional mafic <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/magma" title="Learn more about magmas from ScienceDirect's AI-generated Topic Pages">magmas</a> throughout Earth's orogenic cycles. Although often overlooked due to limited surface exposure, these magmas provide stable, incremental additions to the <a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/continental-lithosphere" title="Learn more about continental lithosphere from ScienceDirect's AI-generated Topic Pages">continental lithosphere</a> and are key drivers of long-term crustal growth.</p>