浙西早寒武世大陈岭组地震液化脉碳氧同位素特征研究

Research of carbon and oxygen isotopic characteristics from seismic liquefied vein of Early Cambrian Dachenling Formation in western Zhejiang

针对浙江西部裴岭脚地区早寒武世大陈岭组中发育两套地震事件沉积,通过自下而上共采取了14块含液化脉的样品,分别对脉体和其对应的围岩进行碳氧同位素研究。研究发现:δ^(13)C_(PDB)-w为+0.01‰^-1.09‰,δ^(13)C_(PDB)-v为-0.07‰^-1.51‰,数值均属于正常海相碳酸盐岩沉积区,但每一个样品均显示δ^(13)C_(PDB)-w>δ^(13)C_(PDB)-v,研究认为这是由于地震驱动造成的泄水构造产生的同位素分馏、后期蚀变和泄水过程中δ^(12)C优先于δ^(13)C从沉积物中迁移所致;脉体和围岩的氧同位素值均表现受强烈的蚀变作用,因为泄水构造在形成过程中伴有热蚀变作用,形成之后,是一个构造薄弱面,易受大气降水、后期热液等作用的影响。

Aiming at the development of two seismic events in Early Cambria Dachenling Formation in Peilingjiaojiao area,western Zhejiang,the authors collected 14 samples of dolomitic limestone with liquefied veins.For every sample,the authors analyzed C and O isotopic in vein material and surrounding rock（dolomitic limestone）respectively.The carbon isotopes（δ^（13）C_（PDB）-v）values of veins material,from-0.07‰to-1.51‰.And theδ^（13）C_（PDB）-w values of dolomitic limestone of surrounding rock rang from＋0.01‰to-1.09‰.The test data belongs to normal marine carbonate rocks.But all of the test result shows thatδ^（13）C_（PDB）-wδ^（13）C_（PDB）-v.It is because water-escape structure create isotope fractionation by earthquake,the later alteration and 12C prior to 13C remove from deposits during sluicing.Seismic action can cause the value of 13C occur negative drifts.Theδ^（18）O_（PDB）-w value varies from-13.47‰to-18.56‰in the veins material and surrounding rock（dolomitic limestone）,and theδ^（18）O_（PDB）-w value varies from-12.65‰to-18.09‰.That is because water-escape structure is a weak structure plane,more likely to be influenced by atmospheric precipitation,and later hydrothermal alteration.