中国大陆科学钻探(CCSD)UHP岩石石英脉中磷灰石团块独居石出溶物的U-Th-Pb化学定年  

U-Th-Pb Chemical dating of monazite exsolutions in apatite aggregates in quartz veins of UHP rocks from the Chinese Continental Scientific Drilling (CCSD) Project.

作　　者：汤倩[1] 孙晓明[1] 徐莉[1] 翟伟[1] 梁金龙[1] 梁业恒[1] 沈昆 

机构地区：[1]中山大学地球科学系,广州510275 [2]山东省地质科学研究院,济南250013

出　　处：《岩石学报》2006年第7期1927-1932,共6页Acta Petrologica Sinica

基　　金：本文由国家自然科学基金(编号:40399142);中国科学院同位素年代学和地球化学实验室合作基金(GIGIso-0504);国家重点基础研究发展规划项目(973项目)(编号:2003CB716501);中国地质大学地质过程与矿产资源国家重点实验室开放基金(编号:2003015)联合资助.

摘　　要：CCSD主孔榴辉岩等UHP岩石石英脉中存在团块状到不规则脉体状的磷灰石集合体,显微镜下观察发现其中存在四种出溶物:磁铁矿和赤铁矿的连生体、赤铁矿、独居石和锶重晶石;出溶物的长轴和生长方向均基本平行于磷灰石之C轴,显示它们可能是基本同时出溶的。其中独居石出溶体多为菱形到板状自形晶体,宽约6—10μm,长约50～75μm。运用CHIME化学定年方法对CCSD磷灰石团块中的独居石出溶物进行了年代学研究,获得其Th-Pb等时线年龄为202±28．3Ma,表明磷灰石团块形成于榴辉岩在折返过程中的重结晶和退变质,时代为晚三叠世。该年龄可能也代表了CCSD中UHP岩石中包裹磷灰石团块的石英脉的形成时代。Massive to irregular veins of apatite aggregates were recognized in quartz veins of CCSD UHP rocks, within which four types of exsolutions were found ： magnetite and hematite intergrowths, hematite, monazite and strontium barite. The long axis of all the exsolutions are nearly parallel with the C axis of the apatite, suggesting that they were probably expelled synchronously. The monazite exsolutions are in the form of rhombus to platy idiomorphism, with a width of 6 - 10μm and a length of about 50 -75μm. Th-U-Pb chemical dating of the monazite exsolutions by electron probe show their U-Pb isochrone age is 202 ± 28.3Ma, implying that the apatite aggregates were probably formed during recrystallization and retrograde metamorphism of the exhumated UHP rocks such as eclogites in the late Triassic Epoch. Besides, it＇ s believed that the age may represent the forming age of quartz veins which wrap the apatite aggregates in the CCSD UHP rocks.

关 键 词：化学定年 独居石出溶物 磷灰石 石英脉 榴辉岩 板块折返 中国大陆科学钻探(CCSD) 

分 类 号：P597.3[天文地球—地球化学] P588.348[天文地球—地质学]