小兴安岭晚石炭世花岗岩岩浆混合作用的岩相学证据及其地质意义

Petrographic evidence of magma mixing of Late Carboniferous granite in the Xiao Hinggan Mountains, China and its geological implications

小兴安岭晚石炭世花岗岩具有明显的岩浆混合特征。岩体中暗色岩浆包体发育,主要为细粒闪长质岩浆包体,包体形态多样、大小不一,与寄主岩石呈截然、模糊或过渡关系。包体的矿物组合明显不平衡,如出现了寄主岩石中的碱性长石捕虏晶,有时可见其具暗色矿物镶边,发育针状磷灰石。这表明小兴安岭晚石炭世花岗岩的岩浆混合表现为基性岩浆和酸性岩浆的混合。这为探讨这些花岗岩的成因提供了岩石学依据,同时也暗示晚古生代佳木斯—松嫩古陆可能发生过地壳的垂向生长。

Late Carboniferous granite in the Xiao Hinggan Mountains shows magma-mixing characteristics. In the granite mafic magmatic enclaves are well developed. They are mosdy fine-grained dioritic magmatic enclaves. The enclaves are highly varied in shape and size and have clear-cut, vague or transitional relationships with host rocks. It is evident that the mineral assemblage of enclaves is not in balance. For example, xenocrysts of alkali feldspar appear in the host rocks, sometimes rims of dark-colored minerals may be observed, and there also appears acicular apatite, which suggests that the magma mixing of the Late Carboniferous granite in the Xiao Hinggan Mountains is marked by mixing of basic magma and acid magma. This prorides petrographic evidence for the study of the genesis of the granites and also implies that vertical crustal growth probably took place in the Late Paleozoic Jiamusi-Songnen craton.