粤西龙修地区大理岩的Pb-Pb年龄及其地质意义

Pb Pb DATING OF MARBLES FROM LONGXIU AREA WITHIN YUNKAI COMPLEX AND ITS GEOLOGICAL IMPLICATION

粤西龙修地区大理岩的Ｐｂ同位素分析结果给出了一个新元古代末期的等时线年龄（５５５±６８）Ｍａ。结合野外和岩相学研究结果，大理岩的Ｐｂ同位素记录了大理岩碳酸盐矿物后变形静态重结晶之后等压冷却事件，（５５５±６８）Ｍａ大致反映了云开地区新元古代末期热水沉积事件之后的一次变质变形事件的年龄，从而确立了新元古代末期热构造事件的存在，这对揭示云开地区前寒武纪地质演化历史具有十分重要的意义。

b isotopic analyses about marble samples from the Longxiu area in Gaozhou county of western Guangdong within Yunkai complex give a late Neo Proterozoic isochron age of(555±68)Ma ( MSWD =19). It is the age of the isobaric cooling event of static recrystallized carbonate minerals in marble post deformation, reflecting approximately the age of metamorphism and deformation after the hydrothermal deposition in late Neo Proterozoic in the Yunkai area. This is very important for our understanding the Precambrian geological evolution in the Yunkai complex. Our study provides an example that demonstrates the great potential of employing the U Pb systems of marbles for dating thermal tectonic event.