北秦岭老君山和秦岭梁环斑结构花岗岩及构造环境——一种可能的造山带型环斑花岗岩  

Laojunshan and Qinlingliang rapakivi-textured granitoids in North Qinling and their tectonic setting;A possible orogenic-type rapakivi granitoids.

作　　者：王晓霞[1] 王涛[2] 卢欣祥 肖庆辉[4] 

机构地区：[1]长安大学地球科学与资源学院 [2]中国地质科学院地质研究所,北京100037 [3]河南地质科学研究所,郑州450053 [4]国土资源部信息研究院,北京100037

出　　处：《岩石学报》2003年第4期650-660,共11页Acta Petrologica Sinica

基　　金：国家自然科学基金(40072065);中国地质调查局"中国花岗岩重大地质问题研究"(200113900018);西北大学大陆动力学教育部重点实验室资助项目

摘　　要：老君山和秦岭梁岩体产于秦岭造山带商丹缝合带北侧,其岩石普遍发育环斑结构,表现为碱性长石巨晶多为卵球状,有些发育斜长石外壳,有些不发育。这不同于一般花岗岩局部出现的具斜长石外壳自形碱性长石巨晶结构。在地球化学上,该岩石显示I-A型花岗岩过渡特点。区域背景、构造被动定位特点和地球化学综合分析表明,它们可能定位于后碰撞或后造山环境。这些特征与典型的元古代克拉通非造山环境中的环斑花岗岩既有相似之处,也有一定差异,而与巴西造山带中环斑花岗岩较为相似。本文认为,它们不是一般的斑状花岗岩,而是最近注意研究的环斑结构花岗岩,有可能是一种造山带型环斑花岗岩,即产于造山带中的非典型环斑花岗岩。The Laojunshan and Qinlingliang rapakivi-textured granitoids occur along the north side of the Shangdan suture in Qinling orogenic belt. Their texture is characterized by rapakivi texture, showing ovoid alkali feldspar megacrystal surrounded by one or occasionally, two plagioclase mantles. Some of them remain unmantled. This texture is different from that of euhedral alkali feldspar mantled by plagioclase. Geochemically, they show transition features from I to A type granites. Integration analysis of their geochemistry, passive-emplacement structural pattern and regional tectonic setting suggests that the plutons were emplaced in postorogenic or post-collision setting. All those characteristics show both similarities and differences compared with typical Proterozoic nonorogenic rapakivi granites, and are similar to some rapakivi granitoids in the orogenic belt in Brazil. Therefore, this paper suggests that they are not common porphyritic granitoids, but rapakivi-textured granitoids, and could be a kind of orogenic-type rapakivi granites, i.e., untypical rapakivi granites, which occur in orogenic belt.

关 键 词：环斑结构 I-A过渡型花岗岩 后碰撞 秦岭 

分 类 号：P588.121[天文地球—岩石学]