CAJ | 학술논문

本文报道出露于越南西北部的Posen花岗岩岩体锆石U-Pb年龄和Hf同位素组成特征,讨论岩石成因和该地区新元古代岩浆作用的大地构造意义.分析3个花岗岩样品获得723Ma至760Ma的锆石U-Pb年龄,表明花岗岩形成于新元古代.该花岗岩的锆石Hf同位素组成有较大的变化范围,ε_(Hf)(t)值变化范围为-16.1至+3.4,单阶段Hf模式年龄为1186～1945Ma,暗示Posen花岗岩有着复杂的源区物源组成.在误差范围内,锆石两阶段Hf同位素模式年龄值主要集中在2.0～2.1Ga,与两阶段Nd同位素模式年龄值2.1～2.2Ga一致,说明花岗岩体主要由古元古代地壳物质部分熔融形成的.部分锆石颗粒具有正ε_(Hf)(t)值,可能指示花岗岩岩浆形成过程中存在壳-幔混合相互作用.在越南西北部发育新元古代岩浆作用可能与扬子板块广泛发育的、伴随Rodinia超大陆裂解过程的岩浆活动存在成因的联系,也揭示越南西北部地体可能与扬子板块具有亲缘关系,因此,可以推断马江断裂带应该代表印支板块和华南板块之间的古特提斯缝合带在越南西北部的延伸.
본문보도출로우월남서북부적Posen화강암암체고석U-Pb년령화Hf동위소조성특정,토론암석성인화해지구신원고대암장작용적대지구조의의.분석3개화강암양품획득723Ma지760Ma적고석U-Pb년령,표명화강암형성우신원고대.해화강암적고석Hf동위소조성유교대적변화범위,ε_(Hf)(t)치변화범위위-16.1지+3.4,단계단Hf모식년령위1186～1945Ma,암시Posen화강암유착복잡적원구물원조성.재오차범위내,고석량계단Hf동위소모식년령치주요집중재2.0～2.1Ga,여량계단Nd동위소모식년령치2.1～2.2Ga일치,설명화강암체주요유고원고대지각물질부분용융형성적.부분고석과립구유정ε_(Hf)(t)치,가능지시화강암암장형성과정중존재각-만혼합상호작용.재월남서북부발육신원고대암장작용가능여양자판괴엄범발육적、반수Rodinia초대륙렬해과정적암장활동존재성인적련계,야게시월남서북부지체가능여양자판괴구유친연관계,인차,가이추단마강단렬대응해대표인지판괴화화남판괴지간적고특제사봉합대재월남서북부적연신.
This study presents zircon U-Pb ages and Hf isotopic composition of the Posen granite exposing in northwestern Vietnam and discusses its petrogenesis and tectonic significances of the study area in Neoproterozoic. Zircons from three samples of the Posen granite were analyzed and yield U-Pb ages of 723Ma to 760Ma, suggesting that the granite formed in Neoproterozoic. Zircon grains from this granite exhibit variable Hf isotopic compositions, their ε_(Hf)(t) values range from -16.1 to +3.4, single-stage Hf modal age values from 1186Ma to 1945Ma, implying complex material sources for the magma of this granite. Two-stage modal Hf age values of zircons are within analytical errors similar to two-stage Nd modal ages of whole-rocks, suggesting Paleoproterozoic crustal rocks as the major source material of the magma. A small part of zircon grains have positive ε_(Hf)(t) values, probably indicating existence of the mixture between crust and mantle material during the formation of the magma. In genetically, Neoproterozoic magmatism in northwestern Vietnam is probably similar to the magmatic activities widely distributed in the Yangtze block, which are related to the break-up of the Rodinia suppercontinent and likely reveals an affinity between the Yangtze block and the northwestern Vietnam. Hence, it is proposed that the Song Ma fault zone can represent the prolongation of the Paleo-Tethyan suture of the Indochina and South China blocks.