中南大学李欢教授团队报道了大神山I-型花岗岩成因与地球动力学，及其对华南地块三叠纪构造演化的意义。相关论文发表在2024年12月12日出版的《地球化学学报》杂志上。

据了解，关于华南地块（SCB）在中生代早期的构造特征及其演化的认识存在着重大争议。争论的焦点之一是三叠纪的构造-岩浆活动及其动力机制。然而，研究人员对关键地区花岗岩岩体的详细年代学和构造背景的研究仍然不足，限制了人们对三叠纪期间SCB内部构造-岩浆动力学机制的认识。

研究人员提供了华南西北部湘中地区大神山岩体的全岩主微量元素数据、Sr-Nd同位素数据、LA-ICP-MS锆石U-Pb年龄和Lu-Hf同位素数据。数据分析显示，大神山花岗岩的侵位年龄为208.4-212.5Ma，具有SiO₂、Na₂O和K₂O含量高，MgO和CaO含量低的特征。大神山花岗岩富集轻稀土元素，具有显著的负Eu异常（平均δEu=0.42）。还具有Rb、K、Th富集，Nb、Ta、Ti明显亏缺的特点，将其归为过铝钙碱性花岗岩，属于I型。锆石εHf(t)值在-8.39到-4.4之间，平均为-5.82， Sr-Nd同位素相对富集[εNd(t)=-9.31到-6.8]。

综合以上的地球化学特征，研究人员认为，大神山花岗岩是由中低温条件下中上部变质基底物质部分熔融形成的，幔源物质的贡献可能较小。此外，它还经历了分离结晶，包括斜长石分化。结合华南板块三叠纪的区域构造演化特征可知，湘中地区晚三叠世构造环境由同碰撞挤压向碰撞后伸展过渡。大神山岩体形成于碰撞后的伸展环境，是中上部地壳岩石减压熔融作用的结果。软流圈的上涌和向上的热传递，可能对大神山花岗质岩浆的形成起了重要作用。

附：英文原文

Title: Petrogenesis and geodynamics of the Dashenshan I-type granite and its implications for the Triassic tectonic evolution of the South China Block

Author: Xi, Zhen, Zhang, Yang, Liu, Zhennan, Li, Huan, Liu, Fenliang

Issue&Volume: 2024-12-12

Abstract: There is significant debate concerning the tectonic characteristics and evolutionary understanding of the South China Block (SCB) during the Early Mesozoic. One of the key points of contention is the tectonic–magmatic activity during the Triassic and its dynamic mechanisms. However, research on the detailed chronology and tectonic settings of granite plutons in key regions remains insufficient, limiting the understanding of the tectonic–magmatic dynamic mechanisms in the interior of SCB during the Triassic. In this contribution, we present whole-rock major and trace elemental data, Sr–Nd isotope data, LA-ICP-MS zircon U–Pb age dating, and Lu–Hf isotope data for granites of Dashenshan pluton in the Xiangzhong, northwest part of SCB. The results indicate that the Dashenshan granite has an emplacement age of 208.4–212.5 Ma, characterized by high SiO₂, Na₂O, and K₂O contents and low MgO and CaO. The Dashenshan granite is enriched in light rare-earth elements with a significant negative Eu anomaly (average δEu = 0.42). It is also enriched in Rb, K, and Th and shows pronounced depletion in Nb, Ta, and Ti, classifying it as peraluminous calc-alkaline granite, specifically of the I-type. The zircon εHf(t) values range from -8.39 to -4.4, with an average of -5.82, and the Sr–Nd isotopes are relatively enriched [εNd(t) = -9.31 to -6.8]. Combining these geochemical characteristics, it is revealed that the Dashenshan granite was derived from the partial melting of middle to upper crustal metamorphic basement materials under medium- to low-temperature conditions, with possible minor contributions from mantle-derived materials. Furthermore, it underwent fractional crystallization, including plagioclase differentiation. By integrating the geochemical features and spatial distribution of Triassic granites in SCB, this study suggests that the regional tectonic evolution of SCB during the Triassic was primarily controlled by the collision of the SCB with the Indochina Block and the North China Block. In Xiangzhong, the tectonic setting transitioned from syn-collisional compression to post-collisional extension during the Late Triassic. The Dashenshan pluton formed in a post-collisional extensional setting, resulting from the decompression melting of middle-to-upper crustal rocks. The upwelling of the asthenosphere and upward heat transfer likely played a significant role in the formation of the Dashenshan granitic magma.

DOI: 10.1007/s11631-024-00748-5

Source: https://link.springer.com/article/10.1007/s11631-024-00748-5