东南沿海燕山期火山活动旋回划分及其成矿规律

Classification of Yanshanian volcanic cycle and the related mineralization in the coast area of southeastern China

中国东南部中生代受古太平洋板块俯冲的影响,火山作用强烈,在东南沿海地区形成巨型火山-侵入杂岩带。根据火山岩组合特征、火山岩时空分布规律、区域不整合、构造背景及其成矿作用类型,分为4个旋回:第Ⅰ旋回(200~165 Ma),为一套近EW向的拉斑玄武岩-流纹质火山岩构成的双峰式火山岩,其中的玄武岩主要起源于软流圈地幔,形成于印支造山后板内伸展环境,该时期成矿作用较微弱。第Ⅱ旋回(165~145 Ma),处于陆缘弧由俯冲挤压高峰期向挤压后的伸展过渡时期,零星分布钙碱性系列英安质-安山质岩石组合,伴生浅成低温热液型金矿和叶腊石等非金属矿产。第Ⅲ旋回((145~115 Ma),华南进入古太平洋板块俯冲挤压后的伸展阶段,发生遍及全区的强烈火山活动,形成诸多大型火山机构和大面积高钾钙碱性系列流纹质-安山质火山岩组合,是中生代活动最强、影响范围最大的一期火山活动,伴生有丰富的金属、非金属、稀土矿产,矿床类型以浅成低温热液型为主。第Ⅳ旋回(115~85 Ma),火山活动相对微弱,并向东迁移至沿海地区,与A型花岗岩带共生,为一套后造山环境下的双峰式火山岩、过碱性流纹岩,晚期往往伴随大规模碎斑熔岩侵出,此阶段形成丰富的金属和明矾石、叶腊石等非金属矿产,以浅成低温热液型为主,斑岩型次之。

Subduction of the Paleo-Pacific plate in Late Mesozoic resulted in intense volcanism and the formation of giant volcano-intrusive complex in the coastal area of southeastern China.Based on the rock association,time-space distribution,regional unconformity,tectonic background and mineralization type,the volcanic activities can be classified into four cycles. The first cycle( 200 ~ 165 Ma) is represented by a set of nearly EW-trending bimodal volcanic rocks consisting of tholeiitic basalt and rhyolite. The basalt was mainly originated from asthenospheric mantle under the Indosinain post-tectonic plate extensional environment. During this period, the mineralization was weak.The second cycle( 165 ~ 145 Ma) is the transition from peak compression to extension of epicontinental arc because of subduction,represented by the scattered calc-alkaline series andesitic dacite with association of low-temperature hydrothermal gold deposits and other non-metallic deposits,such as pyrophyllite.The third cycle( 145 ~ 115 Ma) reflects extension stage of South China after subduction of paleo-Pacific plate,in which large areas of volcanic rocks consisting of high potassium calc-alkaline series rhyolite and dacite were formed in Mesozoic due to intensive volcanism.It was associated with abundant metallic,nonmetallic and rare earth minerals,dominated by hydrothermal type. In the fourth cycle( 115 ~ 85 Ma),volcanism weakened and migrated toward east to the coastal area,dominated by the central eruption accompanied by A-type granite.It is a set of bimodal volcanic rocks with peralkaline rhyolite in the post-orogenic environment and developed porphyroclastic lava in the late period.In this stage,abundant metals and non-metallic minerals such as alunite and phyllite were formed,and the epithermal hydrothermal type was dominant,followed by porphyry type.