近日，兰州大学翟新伟团队研究了古亚洲洋南部的初始开放：来自中国西北部中亚造山带南部北山地区新元古代岩浆活动的证据。2025年8月11日，《地球化学学报》杂志发表了这一成果。

北山地区（BA）位于中亚造山带南缘，是研究新元古代南部古亚洲洋（PAO）开口的关键区域。由于约束不足，目前对BA新元古代构造演化的理解仍然有限。

研究组对BA的辉长岩（765 Ma）、英安质凝灰岩（756 Ma），正长花岗岩（764 Ma）和二长花岗岩（770 Ma）进行了岩石学、全岩地球化学、Sr-Nd同位素、锆石U-Pb定年和Hf同位素分析。辉长岩显示出高MgO（8.06–8.31 wt%）和低K₂O（0.23–1.09 wt%）含量，高场强元素（Nb、Ta和Ti）耗尽，（⁸⁷Sr/⁸⁶Sr）i比值为0.7051–0.7057，ε_Nd（t）值为正（+2.55至 + 3.19）。 这些地球化学特征表明，其起源于俯冲板块衍生熔体交代的贫化地幔，与弧后裂谷环境中的形成一致。

英安质凝灰岩显示负ε_Nd（t）值（-16.38至-1.29）Zr-Hf富集，表明其起源于古代地壳熔融。正长花岗岩和二长花岗岩的特征是高达10000 Ga/Al和（Zr+Nb+Ce+Y）值，将其归类为A1型花岗岩。它们产生负ε_Nd（t）值（-6.66至-2.29) 以及可变ε_Hf（t）值（-3.7至 + 4.8），表明古元古代地壳物质部分熔融。基于这些发现和之前的研究，研究组提出，BA中南部PAO的初始开启不早于770 Ma，可能是由俯冲板块回滚和地幔柱上涌共同驱动的。

附：英文原文

Title: Initial opening of the southern Paleo-Asian Ocean: evidence from Neoproterozoic magmatism in the Beishan area, southern central Asia orogenic belt, NW China

Author: Wang, Erteng, Zhai, Xinwei, Wang, Ju, Tian, Xiao, Chen, Wanfeng, Zhao, Honggang, Zhao, Jiaolong, Wang, Jinrong

Issue&Volume: 2025-08-11

Abstract: The Beishan area (BA), located along the southern margin of the Central Asian orogenic belt, represents a key region for studying the opening of the southern Paleo-Asian Ocean (PAO) during the Neoproterozoic Era. Current understanding of BA’s Neoproterozoic tectonic evolution remains limited because of insufficient constraints. This study presents petrological, whole-rock geochemical, Sr–Nd isotopic, zircon U–Pb dating, and Hf isotopic analyses of gabbro (765 Ma), dacitic tuff (756 Ma), syenogranite (764 Ma), and monzogranite (770 Ma) from the BA. The gabbros show high MgO (8.06–8.31 wt%) and low K2O (0.23–1.09 wt%) contents, depletion of high-field-strength elements (Nb, Ta, and Ti), (87Sr/86Sr)i ratios of 0.7051–0.7057, and positive εNd(t) values (+2.55 to+3.19). These geochemical signatures suggest derivation from a depleted mantle metasomatized by subducted slab-derived melts, consistent with formation in a back-arc rift setting. The dacitic tuffs display negative εNd(t) values (16.38 to 1.29) and Zr-Hf enrichment, indicating an origin from ancient crustal melting. The syenogranites and monzogranites are characterized by high 10,000 Ga/Al and (Zr+Nb+Ce+Y) values, classifying them as A1-type granites. They yield negative εNd(t) values (6.66 to 2.29) and variable εHf(t) values (3.7 to+4.8), indicating partial melting of Paleoproterozoic crust material. Based on these findings and previous studies, we propose that the initial opening of the southern PAO in the BA occurred no earlier than 770 Ma, likely driven by combined subducted slab rollback and mantle plume upwelling.

DOI: 10.1007/s11631-025-00815-5

Source: https://link.springer.com/article/10.1007/s11631-025-00815-5