Subduction polarity reversal facilitated by plate coupling during arc-continent collision: Evidence from the Western Kunlun orogenic belt, northwest Tibetan Plateau

Geology Pub Date : 2024-02-08 DOI:10.1130/g51847.1
Zaili Tao, Jiyuan Yin, Christopher J. Spencer, Min Sun, W. Xiao, Andrew C. Kerr, Tao Wang, Pengpeng Huangfu, Yunchuan Zeng, Wen Chen
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Abstract

Subduction polarity reversal usually involves the break off or tearing of the downgoing plate (DP) along the continent-ocean transition zone, in order to initiate subduction of the overriding plate (OP) with opposite polarity. We propose that subduction polarity reversal can also be caused by DP-OP coupling and can account for the early Paleozoic geological relationships in the Western Kunlun orogenic belt in the northwestern Tibetan Plateau. Our synthesis of elemental and isotopic data reveals transient (∼2 m.y.) changes in the sources of early Paleozoic arc magmatism in the southern Kunlun terrane. The early-stage (ca. 530−487 Ma) magmatic rocks display relatively high εNd(t) (+0.3 to +8.7), εHf(t) (−3.6 to +16.0), and intra-oceanic arc-like features. In contrast, the late-stage (485−430 Ma) magmatic rocks have predominantly negative εNd(t) (−4.5 to +0.3), εHf(t) (−8.8 to +0.9), and higher incompatible trace elements (e.g., Th), similar to the sub-continental lithospheric mantle beneath the Tarim craton. This abrupt temporal-spatial variation of arc magmatism, together with the detrital zircon evidence, indicate that subduction polarity reversal of the Proto-Tethys Ocean occurred in a period of ∼10 m.y., consistent with the time interval reflected by ophiolite age. This rapid polarity reversal corresponds with the absence of ultrahigh-pressure (UHP) metamorphic and post-collisional magmatic rocks, features normally characteristic of slab break-off or tearing. Numerical modeling shows that this polarity reversal was caused by plate coupling during arc-continent collision. This coupling modified the normal succession of arc-continent collision events, preventing slab break-off or tearing-induced buoyant rock rebound and asthenosphere upwelling. Our model successfully explains early Paleozoic orogenesis in the Western Kunlun orogenic belt and may be applied elsewhere where post-collisional magmatic and UHP rocks are absent.
弧-大陆碰撞过程中的板块耦合促进了俯冲极性逆转:来自青藏高原西北部西昆仑造山带的证据
俯冲极性反转通常是指下行板块(DP)沿大陆-海洋过渡带断裂或撕裂,从而引发极性相反的凌驾板块(OP)的俯冲。我们提出,俯冲极性反转也可由 DP-OP 耦合引起,并可解释青藏高原西北部西昆仑造山带的早古生代地质关系。我们对元素和同位素数据的综合分析揭示了南昆仑地层早古生代弧形岩浆活动来源的瞬时(∼2 m.y.)变化。早期(约530-487Ma)岩浆岩显示了相对较高的εNd(t)(+0.3至+8.7)、εHf(t)(-3.6至+16.0)和洋内弧样特征。相反,晚期(485-430 Ma)岩浆岩的εNd(t)(-4.5至+0.3)、εHf(t)(-8.8至+0.9)主要为负值,不相容微量元素(如Th)较高,与塔里木克拉通下的次大陆岩石圈地幔相似。弧岩浆作用的这种突然的时空变化,以及锆英石碎片的证据,表明原特提斯洋的俯冲极性逆转发生在 10 m.y.之间,与蛇绿岩年龄所反映的时间间隔一致。这种迅速的极性反转与没有超高压变质岩和碰撞后岩浆岩(通常是板块断裂或撕裂的特征)相对应。数值模拟显示,这种极性反转是由弧-大陆碰撞过程中的板块耦合造成的。这种耦合改变了弧-大陆碰撞事件的正常演替,阻止了板块断裂或撕裂引起的浮力岩石反弹和岩浆层上涌。我们的模型成功地解释了西昆仑造山带古生代早期的造山运动,并可应用于其他缺乏碰撞后岩浆岩和超高压岩石的地区。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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