Early Triassic roll-back of subducted Paleo-Tethys oceanic lithosphere: Insights from A2-type silicic igneous rocks in the Pingxiang area, southwest China

IF 1.7 3区地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY

Geosphere Pub Date : 2023-07-27 DOI:10.1130/ges02617.1

Wenlong Huang, Xijun Liu, Lei Liu, Zhenglin Li, Xinyu Liu, Hao Wu

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引用次数: 1

Abstract

A suite of subduction-related early Triassic igneous rocks crops out in the Pingxiang area of the Dian-Qiong suture (DQS) in southwest China; this suite represents an important geological record of subduction and closure of the Paleo-Tethys Ocean. In this study, we report geochronological, geochemical, and Nd-Hf isotope data for newly discovered rhyolites and biotite granites in the Pingxiang area. We use these data to constrain their emplacement ages, origins, and geodynamic implications. Zircon U-Pb dating indicates that the rhyolites and biotite granites were emplaced at 251–250 Ma and 249 Ma (early Triassic), respectively. The rhyolites and biotite granites have elevated FeOT/(FeOT + MgO) (0.78–0.89) and 10,000 × Ga/Al (2.83–4.11) ratios, with geochemical affinities to A2-type granites. These rocks are enriched in some large-ion lithophile elements (e.g., Rb, Th, and Ba) and depleted in high-field-strength elements (e.g., Nb, Ta, and Ti), indicating their formation in a subduction-related arc. The rhyolites and biotite granites have negative whole-rock εNd(t) (−11.5 to −9.7) and zircon εHf(t) (−14.5 to −6.2) values, suggesting that these magmas were derived from an ancient crust-dominated source. Geochemical and Nd isotope data reveal that the peraluminous A2-type rhyolites and biotite granites were derived by partial melting of felsic crustal rocks under low-pressure and high-temperature conditions. By integrating all the available data with the regional tectonic evolution of the southwestern Youjiang Basin and adjacent regions, we attribute the generation of the peraluminous A2-type rhyolites and biotite granites to the extensional setting that existed during oceanic subduction, which was induced by roll-back of the Paleo-Tethys oceanic lithosphere at 251–249 Ma. This study indicates that subduction-related magmatism related to Paleo-Tethys oceanic lithosphere was still active in the early Triassic.

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俯冲古特提斯洋岩石圈的早三叠世回滚:萍乡地区a2型硅质火成岩的启示

滇琼缝合带萍乡地区发育一套与俯冲作用有关的早三叠世火成岩；该套代表了古特提斯洋俯冲和闭合的重要地质记录。本研究报告了萍乡地区新发现的流纹岩和黑云母花岗岩的地质年代、地球化学和Nd-Hf同位素数据。我们使用这些数据来限制它们的侵位年龄、起源和地球动力学意义。锆石U-Pb定年表明，流纹岩和黑云母花岗岩分别侵位于251–250 Ma和249 Ma（三叠纪早期）。流纹岩和黑云母花岗岩具有较高的FeOT/（FeOT+MgO）（0.78–0.89）和10000×Ga/Al（2.83–4.11）比率，与A2型花岗岩具有地球化学亲和力。这些岩石富含一些大离子亲石元素（如Rb、Th和Ba），并贫含高场强元素（如Nb、Ta和Ti），表明它们是在俯冲相关弧中形成的。流纹岩和黑云母花岗岩具有负的全岩εNd（t）（−11.5至−9.7）和锆石εHf（t）值（−14.5至−6.2），表明这些岩浆来源于古代地壳为主的岩浆源。地球化学和Nd同位素数据表明，过铝质A2型流纹岩和黑云母花岗岩是由长英质地壳岩石在低压和高温条件下部分熔融形成的。通过将所有可用的数据与右江盆地西南部及邻近地区的区域构造演化相结合，我们将过铝质A2型流纹岩和黑云母花岗岩的产生归因于海洋俯冲过程中存在的伸展环境，该环境是由251–249 Ma的古特提斯海洋岩石圈回滚引起的。该研究表明，与古特提斯洋岩石圈有关的俯冲相关岩浆活动在三叠纪早期仍然活跃。

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来源期刊

Geosphere 地学-地球科学综合

CiteScore

4.40

自引率

12.00%

发文量

审稿时长

6-12 weeks

期刊介绍： Geosphere is GSA''s ambitious, online-only publication that addresses the growing need for timely publication of research results, data, software, and educational developments in ways that cannot be addressed by traditional formats. The journal''s rigorously peer-reviewed, high-quality research papers target an international audience in all geoscience fields. Its innovative format encourages extensive use of color, animations, interactivity, and oversize figures (maps, cross sections, etc.), and provides easy access to resources such as GIS databases, data archives, and modeling results. Geosphere''s broad scope and variety of contributions is a refreshing addition to traditional journals.