摘要
扬子与华夏古板块均存在太古宙—中元古代古老基底,在构造演化历程中响应全球超大陆聚合-裂解过程,并最终碰撞拼贴形成钦-杭结合带,且经历构造运动之后,其总体演化格架为＂两开三合一转折＂。结合带内存在元古宙洋壳,以蛇绿岩套与镁铁质-超镁铁质岩石为特征,并以此推断结合带形成于新元古代。钦-杭结合带是斑岩成矿带,斑岩铜矿时空分布具有三段划分特征,且处于170~150 Ma和100 Ma左右两个成矿期。与成矿有关的斑岩主要为钙碱性岩浆系列的中酸性岩,岩石类型主要为花岗闪长斑岩、花岗斑岩和二长花岗斑岩等。钦-杭结合带燕山期的斑岩具岛弧岩浆作用特点,指示了华南地区中生代构造转折事件发生以前的地质演化及太平洋板块俯冲作用,即古俯冲带物质在中生代活化成矿。中侏罗世岩石圈减薄及太平洋板块俯冲的扰动导致上涌软流圈地幔带来大量的热量,这些热量加热上覆元古宙岛弧底部玄武质岩石导致它们发生重熔形成了含矿岩浆,本质上该类矿床带有岛弧俯冲环境的基因。而100 Ma左右斑岩铜矿的形成,则与太平洋俯冲换向所扰动有关。
South China was formed by amalgamation of the Yangtze and Cathaysia blocks, both of which have basement built from the Archean to the Mesoproterozoic. Based on the Proterozoic oceanic crust, evidenced by ophiolite and mafic-ultramafic rocks, it was believed that the final amalgamation happened during the Neoproterozoic. The formation of the juncture, called Qinzhou-Hangzhou suture zone （QHSZ）, and intracontinental magmatism afterwards have relevance to the assemblage and break-up of supercontinent. The geological evolution of the suture zone is described as ＂twice opening, triple closure and once turning＂. The QHSZ is an important porphyry copper deposit （PCD） belt. The PCDs are well distributed in the north, the middle and the south segment of the suture zone. They are mainly formed in the Yanshanian period, by two eras of 170- 150 Ma and 100 Ma or so. The associated porphyries are mainly granodiorite porphyry, granite porphyry and monzonitie granite-porphyry, which belong to the calc-alkaline magma series of acidic rock. Geodynamic of Mesozoic porphyry petrogenesis and mineralization in QHSZ was closely relative to the subduction of Paleo-Pacific plate; materials for ore formation might have been derived from remobilizing of arc magma by ancient subduction. Triggered by dynamic mechanism of lithospheric thinning and subduction of Paleo-Pacific Plate, the upwelling of asthenospheric mantle brought massive heat, heating the overlying Proterozoie arc basaltic rocks and led to the formation of ore magma. It is concluded that such acidic porphyries of the QHSZ resulted from the partial melting of the Proterozoic island arc basaltic rocks triggered by the subduction, including the direction changing of the Paleo-Pacific Plate during the Mesozoic period, and that the associated PCDs have the gene of island arc subduction environment.
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2015年第2期144-159,共16页
Earth Science Frontiers
基金
中国地质调查局项目(1212011085412)
关键词
钦-杭结合带
斑岩铜矿
中、新元古代板块俯冲
岩浆弧
超大陆裂解
古洋壳深熔
构造体系转换
Qin-Hang suture zone
porphyry copper deposits
Meso- to Neoproterozoic plate subduction
rnagma arc
supercontinent breakup
ancient oceanic crust anatexis
structural system conversion
