板内造山作用与成矿

中国大陆广泛分布强烈的板内变形和造山作用,传统的板块构造理论常常将其解释为板块边缘汇聚力的远程效应。然而,中国大陆的板内造山作用与汇聚板块边界之间缺乏可预期的动力学联系,不能简单地解释为大陆碰撞或板块俯冲的远程效应。本文提出另一种可供选择的解释,认为板内变形主要取决于岩石圈不均一性。相邻的板块拼合在一起形成统一板块之后,区域地质演化进入板内阶段。板块碰撞导致的岩石圈不均一性和重力不稳定性可以触发强烈的板内变形甚至造山作用,其延迟时间的长短取决于岩石圈不稳定性的程度和地球深部的热扰动。与板缘造山带相比,板内造山作用缺少板块俯冲-碰撞过程,板内造山带的演化历史相对简单,通常是以岩石圈拆沉作用开始,以地壳的垂向增生为特征,最后以岩石圈拆沉作用结束或形成重力不稳定岩石圈。因此,板内造山作用一般沿着古造山带发育。古造山带岩石圈结构低成熟度的特点不仅是岩石圈不稳定性的主要原因之一,而且由于挥发分和含矿元素的富集在活化过程中具有很强的成矿潜力。板内造山带的成矿作用依赖于深埋在岩石圈-软流圈系统不同深度水平上含矿流体的突然释放,主要发生在造山作用初始阶段和造山后伸展阶段。

lntraplate orogenesis and its implications in metallogenesis

The broadly intensive intraplate deformation and orogenesis in the China continent are usually considered as the distant effects of the force from plate convergent boundaries in traditional plate tectonics.However,there are not expected geodynamie relations between the intraplate orogenesis in the China continent and any convergent boundary.The intraplate orogenesis can not be simply explained as the distant effects of continental collision or plate subduction.This paper proposed an alternative interpretation attributing the intraplate deformation to the local lithospheric heterogeneity or discontinuity.Since formation of an integrated plate by plate suture, the geological evolution in a region is in the intraplate stage.The lithospheric heterogeneity and gravitational instability induced by plate collisions may trigger intensive intraplate deformation and even orogenesis.The time interval between the plate integration and the orogenic reactivation is decided by the levels of the lithospheric instability and the thermal disturbance from the Earth's depths. Distinguished from the orogenesis at the plate boundaries,the intraplate orogenesis lacks the processes of plate subduction and collision.The intraplate orogen has relatively simple history commonly initiated by lithospheric delamination and characterized by vertical accretion of the orogenic crust.The intraplate orogenesis will be completed by the other delamination event or the formation of a new lithosphere with light gravitational instability.Therefore,the intraplate orogenesis develops commonly along a ancient orogen. The feature of lower matured lithospheric structure in an ancient orogenic belt is not only one of the primary factors causing the lithospheric gravitational instability.A lower matured lithosphere contains huge volatiles and ore-forming elements and hence has higher potential ability to form ore deposits.Metallogenesis in an intraplate orogen is dependent to if sudden releasing ore-bearing fluids from various depths of the lithosphere-asthenosphere system.Consequently,the metallogenesis occurs mainly in the initial stage and the post-orogenic extension stage.