江苏东海县幔源橄榄岩包体及其深部构造意义  

Mantle-derived Xenoliths of Peridotite from Pingmingshan, Donghai County, Jiangsu Province and Their Implications for Deep Structures

作　　者：金振民[1] 余日东[2] 杨文采[3] 欧新功[1] 

机构地区：[1]中国地质大学,武汉430074 [2]中国地质大学研究生院,武汉430074 [3]中国地质科学院地质研究所,北京100037

出　　处：《地质学报》2003年第4期451-462,共12页Acta Geologica Sinica

基　　金：中国大陆科学钻探工程项目;国家自然科学基金(编号 40172068)

摘　　要：东海县境内仅有两个碱性玄武岩火山口(平明山和安峰山)形成于晚新生代,K-Ar同位素年龄测定,平明山为4.02～6.38Ma,安峰山为7.3～12.3Ma。岩石学和地球化学特征揭示包体寄主岩为碧玄岩,岩浆没有经历明显分异和同化混杂作用。平明山碧玄岩含有丰富幔源包体,包括尖晶石二辉橄榄岩、方辉橄榄岩和二辉岩。采用Bertrand等(1985)和Kohler等(1990)的温度-压力计估算了包体平衡温度和压力分别为830～900℃和1.5～1.7GPa。根据温压资料构建的古地温曲线,对应于大陆热流值75mW/m^2和岩石圈厚度55km。氧化缀饰法揭示本区橄榄岩包体经历了高温低应变速率塑性流动变形,形成各种类型的位错构造。高温高压实验测定,二辉橄榄岩Vp速度为8.0～8.2km/s,Vs速度为4.50～4.77km/s。中国大陆科学钻(CCSD)附近幔源橄榄岩包体的发现对东海地区岩石圈厚度、物质组成、热结构和底侵作用动力过程提供了重要约束。The only two volcanic craters (Pingmingshan and Anfengshan) found in Donghai County, Jiangsu Province were formed in the late Cenozoic. Their petrological and geochemical characters suggest that the host rock of the xenoliths is basanite, and the magma has not experienced obvious differentiation and assimilatory contamination. The isotopic ages of the Pingmingshan basanite are 4. 02 to 6. 38 Ma determined with the K-Ar method. By using the geothermobarometer of Bertrand and Mercier (1985) and Kohler (1990) the equilibrium temperature and pressure of the xenoliths are estimated to be 830~900℃ and 1. 5~1. 7 GPa, respectively. The paleotemperature curve constructed on the basis of the p-t data of xenoliths corresponds to a continental thermal flow value of 75 mW/m2 and a lithospheric thickness of 55 km in this area. As revealed by the method of oxidation decoration, the peridotite xenoliths have undergone plastic flow deformation of high temperature and low strain rate, resulting in dislocation structures of different types. Based on experimental measurements at high temperatures and high pressures, the Vp and Vs values of the peridotite xenoliths are estimated to be 8. 0~8. 2 km/s and 4. 50~4. 77 km/s, respectively. The discovery of the mantle-derived xenoliths in the area adjacent to the site of the CCSD (Chinese Continental Scientific Drilling) provides an important constraint for understanding the composition, thickness and thermal structure of the lithosphere as well as the underplating process in the Donghai area.

关 键 词：碧玄岩 橄榄岩包体 热结构 岩石圈 底侵作用 深部构造 

分 类 号：P588.1[天文地球—岩石学]