藏南活动断裂带第四纪CO_(2)释放初探:来自钙华年代学与地球化学的约束  

Preliminary study on hydrothermal CO_(2) flux from active fault zones in southern Tibet:Constraints from travertine geochronology and geochemistry

作　　者：曹晨晞 张茂亮 王立胜[2] 王学锋 段武辉[2] 徐胜 CAO Chenxi;ZHANG Maoliang;WANG Lisheng;WANG Xuefeng;DUAN Wuhui;XU Sheng(School of Earth System Science,Tianjin University,Tianjin 300072,China;State Key Laboratory of Lithospheric and Environmental Coevolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]天津大学地球系统科学学院,天津300072 [2]中国科学院地质与地球物理研究所,岩石圈演化与环境演变全国重点实验室,北京100029

出　　处：《地学前缘》2025年第3期334-349,共16页Earth Science Frontiers

基　　金：国家自然科学基金项目(41930642);国家重点研发计划项目(2020YFA0607700)。

摘　　要：青藏高原南部构造运动活跃,为深源含碳流体的形成和释放创造了有利条件,使其成为现今全球最重要的深部碳释放地区之一。如何估算地质历史时期构造运动导致的深部碳释放通量是探索青藏高原生长动力学过程对深部碳释放影响的重要科学问题,也是重建印度-亚洲大陆碰撞造山带地质碳循环的关键环节。活动断裂带内广泛出露的钙华沉积物为回溯地质碳排放提供了理想对象。本研究对青藏高原南部活动断裂带的44个钙华样品进行了铀系年代学、矿物学、元素和同位素地球化学分析,结果显示:(1)钙华U-Th年龄为267.3~1.8 kyr B.P.,形成于中更新世至全新世,沉积速率约为0.02~1.49 mm·yr-1;(2)钙华主要由方解石组成,个别具有方解石和文石混合特征,CaCO3平均含量为94.2%;(3)碳-氧同位素组成(δ13C_(V-PDB)=-3.1‰~+8.6‰;δ18O_(V-SMOW)=-0.5‰~+15.0‰)显示钙华具有热成因性质,沉积过程中受到不同程度的CO_(2)脱气、泉水沸腾及蒸发作用的影响;深部碳是钙华中总碳的最主要来源。基于钙华体积、孔隙度、CaCO_(3)含量以及沉积时间,估算得到研究区伴随钙华沉淀释放的CO_(2)通量处于104~106 mol·km^(-2)·yr^(-1)数量级,与意大利中西部构造活跃区的部分钙华沉积区相当。本研究为理解藏南活动断裂带中钙华的形成年代、成因机制以及CO_(2)释放通量提供了新视角,对于全面认识印度-亚洲大陆碰撞造山带的深部碳循环特征具有重要意义。Active tectonics in southern Tibetan Plateau create favorable pathways for the formation and release of deeply-sourced CO_(2)-rich fluids,making it a globally significant carbon source at present.However,in the case of southern Tibetan Plateau,estimating the deep carbon outgassing flux for tectonic degassing in the geological past remains challenging but is crucial for reconstructing the geological carbon cycle that operates in the India-Asia continental collision zone.Here,we report,for the first time to our knowledge,the hydrothermal CO_(2) fluxes during the Quaternary period for representative active faults in southern Tibetan Plateau based on an integrated dataset of U-Th ages,mineralogical,elemental,and C-O isotopic compositions of travertine deposits.The U-series dating results show that the travertines were formed during the Middle Pleistocene to Holocene periods(267.3-1.8 kyr B.P.),with the deposition rates ranging approximately from 0.02 to 1.49 mm·yr^(-1).These Quaternary travertines,primarily composed of calcite with rare samples exhibiting mixed calcite and aragonite in mineral assemblage,have an average CaCO_(3) content of 94.2 wt.%.Carbon and oxygen isotopic compositions(δ13C_(V-PDB)=-3.1‰to+8.6‰;δ18O_(V-SMOW)=-0.5‰to+15.0‰)suggest a thermogenic origin influenced by varying degrees of CO_(2) degassing,spring boiling,and evaporation,with deep metamorphic CO_(2) being the primary carbon source of the travertines.Based on the volume,porosity,CaCO3 content,and deposition ages of the travertines,the CO_(2) outgassing fluxes accompanied with travertine deposition are estimated to be in the magnitude of 104 to 106 mol·km-2·yr^(-1) for the study areas,comparable to some travertine deposits in tectonically active regions of the central and western Italy.Our results provide new insights into the deposition ages,genesis,and CO_(2) outgassing fluxes of Quaternary travertines in southern Tibetan Plateau and would contribute to our understanding of geological carbon cycle in the India-Asia continenta

关 键 词：钙华沉积物 铀系年代学 碳同位素地球化学 深部碳释放 青藏高原南部 

分 类 号：P597[天文地球—地球化学] P578.6[天文地球—地质学] P512.2