走滑汇聚是华南广西运动的成因?【“华南古大陆演化及其资源环境效应”专辑】
- 收稿日期:
2023-07-20
- 网络出版日期:
2023-12-18
摘要: 【目的】华南东南部在早古生代发生了大规模的褶皱造山运动——广西运动。该期造山运动的属性仍然存在较大争议。为了确定华南广西运动的动力学机制,尝试利用碎屑多矿物U-Pb年代学恢复早古生代扬子地块和华夏地块的古地理位置以及相对位移。【方法】重新评估了扬子地块和华夏地块下古生界碎屑锆石/独居石U-Pb年代学和Hf同位素数据,并与潜在源区进行对比。【结果】结果显示:(1)扬子西缘寒武系-奥陶系碎屑锆石具有850-750 Ma 和550-500 Ma两期主要的特征年龄峰,以及1 000-900 Ma、1 900-1 800 Ma和2 550-2 400 Ma三个次要年龄峰。扬子西缘550-500 Ma碎屑锆石的εHf(t)值多为正值,指示岩浆源区中大量新生地壳物质的参与,其源区可能为伊朗-土耳其Cadomian岩浆弧。新元古代碎屑锆石主要来自于扬子西缘岩浆岩和下伏新元古界沉积岩的再循环;(2)华夏板块寒武系-奥陶系碎屑锆石/独居石具有1 000-900 Ma和550-500 Ma两期主要的年龄峰,前者对应于印度东北部的East Ghats造山带和东南极洲板块的Rayner造山带,而后者对应于印度东北缘的Kuunga造山带;(3)扬子东南缘志留系碎屑锆石460-410 Ma的年龄峰与华夏地区过铝质花岗岩浆活动的年龄相吻合,大于440 Ma峰值年龄的碎屑锆石则具有与该地区前志留纪样品相似的年龄峰。【结论】物源分析结果表明寒武纪至奥陶纪期间华夏地块和扬子地块分别位于印度东北缘和伊朗东北缘,两者的古地理位置沿冈瓦纳大陆北缘斜列分布。晚奥陶世(~460 Ma)响应于冈瓦纳大陆的最终聚合发生斜向走滑汇聚,形成武夷-云开陆内造山带(460-420 Ma)。
Is the strike-slip convergence the cause of the Kwangsian Orogeny in South China?
- Received Date:
2023-07-20
- Available Online:
2023-12-18
Abstract: [Objective] The southeastern part of South China underwent a strong orogenic process, known as the Kwangsian Orogeny, during the Early Paleozoic period. However, there is still considerable controversy surrounding the nature of Kwangsian Orogeny. In order to understand the geodynamic mechanism of the Early Paleozoic Kwangsian Orogeny of South China, the detrital multi-minerals U-Pb geochronology is used to reconstruct the paleogeographic position of the Yangtze and Cathaysia blocks in Early Paleozoic and restore the relative displacement of terranes. [Methods] U-Pb geochronology and hafnium isotopic data of detrital zircon and detrital monazite from Early Paleozoic strata of South China are revisited to trace the potential sources. [Results and Discussions] The results show that: (1) Detrital zircons from the Cambrian to Ordovician strata in Western Yangtze yield predominantly age peaks at 850-750 Ma and 550-500 Ma, with minor age peaks at 1 000-900 Ma, 1 900-1 800 Ma and 2 550-2 400 Ma. In combination with the regional lithofacies evolution, provenance analysis demonstrates that the abundant 550-500 Ma detrital zircons with positive εHf(t) values reflecting a large involvement of juvenile crustal materials, were probably derived exotically from the Cadomian arc belt along the Iran-Turkey margin. The Neoproterozoic detrital zircons preserved in the Cambrian to Ordovician strata of the western margin of the Yangtze Block are mainly derived from the Neoproterozoic igneous rock in the western Yangtze Block and the recycled materials from the underlying Neoproterozoic strata in Western Yangtze. Provenance analysis reveals that the Yangtze Block and Iran have a close provenance linkage; (2) U-Pb ages of detrital zircon and detrital monazite from the Cambrian to Ordovician strata in the Cathaysia Block exhibit predominantly age peaks at 1 000-900 Ma and 550-500 Ma. The former aligns with the age of the magmatic and metamorphic zircon/monazite in the East Ghats belt of NE India and Rayner belt in East Antarctic, while the latter corresponds to the U-Pb ages of the zircon and monazite from the Kuunga Orogen in NE India, and (3) In the age spectra of the Silurian succession of southeastern Yangtze, the peaks older than 440 Ma are identical to those of the pre-Silurian strata, indicating that the provenance of detritus of those ages is mainly the recycled materials from the underlying Cambrian to Ordovician strata. The age peak of 460-410 Ma coincides with the timing of the massive 440?400 Ma Syn-orogenic granites in Cathaysia Block. [Conclusions] The result of provenance analysis favors an oblique distribution of the Yangtze and Cathaysia blocks along the northeastern margin of East Gondwana. The Yangtze Block, specifically, was situated in the northeast of Iran, while Cathaysia occupied the northeastern margin of India during the Cambrian to Ordovician period, respectively. It is crucial to note that the Kwangsian Orogeny is an oblique strike-slip convergence triggered by the final assembly of the supercontinent Gondwana during the late Neoproterozoic to Cambrian period. The oblique strike-slip convergence of the Yangtze and Cathaysia blocks after the late Ordovician (~460 Ma) resulted in the formation of the Wuyi-Yunkai Orogenic Belt (460-420 Ma).