构造体制转换的温度场效应及其耦合成矿动力学数值模拟

运用FLAC方法 ,再现了湖南中生代岩石圈构造体制由挤压增厚转换为伸展减薄过程中 ,区域构造应力场和地温场的可能的演化历程 ,探讨了其耦合成矿效应和深部动力学制约。结果表明 :(1)剪切应变带在地壳中纵横交错的分布格局为印支燕山期岩浆底侵和地壳物质部分熔融、成矿物质运移和定位提供了有利条件 ;(2 )构造热体制转换可驱动深部流体活动 (大规模侧向运移或向上运动 ) ,导致壳幔物质活化 ,控制流体循环和水岩作用过程 ,形成热液矿床 ;(3)矿床 (体 )往往赋存于剪切应变、体积应变和温度由极大向极小转换的构造部位 (或时段 ) ,而其极大值和极小值区域 (或时段 )均不利于成矿 ;(4 )由于不同构造部位剪切应变、体积应变和温度场扰动的差异 ,其成矿效应明显不同 ,从而形成金属矿床的韵律性分带结构 ;(5 )这种空间上的分带结构可能反映了其成矿作用时间结构、构造物理化学条件和剥蚀程度的差异 ,印支期W Pb Zn或Sn和Cu矿的形成与中地壳片麻岩类岩石部分熔融关系密切 ,而燕山期Cu Au矿的形成主要与基性岩浆底侵和下地壳物质部分熔融有关 ,并直接受控于该区中生代早期的岩石圈伸展减薄作用。这一认识可为成矿预测提供依据。

NUMERICAL MODELING OF THE TEMPERATURE EFFECTS OF TECTONIC REGIMES TRANSFORMATION AND THEIR ORE-FORMING DYNAMICS

Using the numerical scheme of Fast Lagrangian Analysis of Continua (FLAC), the authors have stimulated the possible process of the stress field and temperature field in Hunan, China and its adjacent area, during the process of the transformation of tectonic regimes of lithosphere from compression and thickening to extension and thinning in Mesozoic. With the above mentioned results, the authors discuss the relationship between the two kinds of tectonic regimes, and their coupling effects of ore forming, and the possible dynamic constraints in deep. The results show the following: (1) The shear strain belts is interlaced in the crust, and this distribution pattern redounds to magma underplating, partial melting of materials in crust, flowing and depositing of metallogenic materials during Indosinian and Yanshan epochs. (2) The transition of tectono thermal regimes can drive the fluid to flow in deep (for example, flow sideward, and upward), thus results in crust mantle materials becoming activation, and controls the processes of fluid circulation and fluid rock interaction, finally, the hydrothermal deposits formed. (3) The ore deposits are usually located in these places (or stages), where (or when) the shear strain, volume strain and temperature transfer from maximum to minimum; while those places (or stages), whose values are maximum or minimum, are not in favor of ore forming. (4) The zoning of ore deposits is resulted from the variety of shear strain, volume strain, temperature perturbation, and ore forming effects in different structural places. (5) The spatial zoning can imply the diversity of metallogenic temporal texture, tectonic physicochemistry condition and the degree of denudation. The formation of W Pb Zn ores, or Sn and Cu ores is closely related to partial melting of the rocks of gneiss in middle crust in Indosinian Epoch, while the formation of Cu Au ores is mainly related to underplating of basic magma and the partial melting of rocks in lower crust in Yanshan Epoch, and is controlled by the process of extending and thinning of lithosphere in the early Mesozoic. These results can be propitious to metallogenic prognosis.