碰撞带热结构与碰撞成矿系统

Thermal regime and metallogenesis of collisional orogens

造山带热结构对大陆碰撞带的形态大小、构造式样、岩浆活动和变质作用具有重要控制作用。然而,热结构对碰撞成矿作用的控制还不清楚。本文概述比利牛斯、阿尔卑斯、加里东、扎格罗斯、青藏高原和华力西等全球主要碰撞带的热结构与成矿系统发育特征,对比各个造山带内不同矿床类型成矿温度变化,探讨热结构对碰撞成矿的控制作用。研究表明,碰撞带主要发育盆地流体有关的密西西比河谷型铅锌矿床、变质流体有关的造山型金矿床和岩浆热液有关矿床(斑岩铜矿床、云英岩型钨锡矿床和岩浆热液有关的铌钽锂铍矿床等)。其中,前两者在大多数碰撞带内均有发育,代表了大陆碰撞成矿作用的基本类型。这些矿床的成矿温度在热碰撞带比较高而在冷碰撞带则偏低。岩浆热液有关矿床一般只出现在比较热的碰撞带内,这些热碰撞带的温度压力条件有很大区域在湿固相线以内,热扰动能够造就地壳发生部分熔融形成含矿岩浆。

Previous studies have shown that the thermal regime of continental collisional orogen has important controls on the shape, size, tectonic pattern, magmatism and metamorphism of collision zones. However, the relationship between the thermal regime and metallogenesis of continental collisional orogen is unclear. Here, we compared the Pyrenean, Alpine, Caledonian, Zagros-Iranian, Himalayan-Tibetan and Variscan orogens in terms of their thermal regimes and mineral deposits, focusing especially on the relationship between the thermal regime and ore-forming temperatures. We found three types of deposits in these continental collisional orogenic belts: basin brine(e.g., Mississippi Valley-type Pb-Zn deposits), metamorphic fluids(e.g., orogenic Au deposits) and magmatic hydrothermal(e.g., porphyry Cu-Mo-Au deposits and greisen W-Sn deposits) deposits. Among them, the Mississippi Valley-type Pb-Zn deposits and orogenic Au deposits can occur in all types of collisional orogens. The ore-forming temperatures in these deposits are relatively high in hot collisional orogen and low in cold collisional orogen. However, magmatic hydrothermal deposits only occur in hot collisional orogens as the pressure-temperature conditions for hot collisional orogen overlap largely with that for wet granite solidus in the p-T diagram. The thermal structure of collisional orogens is affected easily by thermal disturbance conducive to crustal partial melting and forming ore-bearing magmas.