Determination of high resolution thermal and tectonic history of Archean terranes: Development of a tool through a case study from the Western Dharwar Craton and the Coorg block in S. India

大约3.0 Ga的时间段是地球历史上的一个关键时期，因为在许多模型中，它被认为是发生向现代板块构造样式过渡的时期。这被认为是热产生和热损失之间的平衡发生变化的结果;在3.0 Ga之前，热产生被认为占主导地位。然而，这种转变本身被认为是快速的（在< 0.5 Ga内），并且不清楚它是否是全球性的和同步的。同位素钟的分辨率并不总是足以分辨这些古老岩石中各种间隔很近（在时间上）的事件。因此，有必要开发新的工具来更好地量化和理解这种热过程。我们已经开发了顺序动力学建模的方法（模拟矿物成分分阶段分区的扩散修改），并成功地将其应用于当今的火山系统，以及在低温变质系统。在这个项目中，我们希望使用这个工具来研究的热演化（加热/冷却和埋葬/剥露历史）的一套岩石从西达尔瓦尔盆地和Coorg块在印度南部的构造风格的特点。这些岩石在3.3 ~ 3.5 ℃的关键期内经历了多次热变质作用。和2.5 Ga，并包含矿物组合，其中顺序动力学模型可以应用。我们在这个项目中的目标是（a）获得两个相邻区块的高分辨率热历史，具有来自同一时期的对比特征，（B）使用这些例子来开发在太古代岩石中普遍使用的工具，以便它可以用于其他太古代岩石以及在以后的项目中量化地球历史的这一关键时期的全球热演化。

The time period around 3.0 Ga is a critical period in the history of the Earth because in many models it is thought to be the period when a transition occurred to present day plate tectonic styles. This is considered to be the result of a shift in the balance between heat generation and heat loss; heat generation was thought to have dominated over heat loss before 3.0 Ga. However, the transition itself is thought to have been rapid (within < 0.5 Ga), and it is not clear if it was global and synchronous. The resolution of isotopic clocks do not always suffice to resolve the various closely spaced (in time) events in these ancient rocks. Therefore, it is necessary to develop new tools to quantify and understand such thermal processes better. We have developed the approach of sequential kinetic modelling (modelling the diffusive modification of compositional zoning in minerals in stages) and applied it successfully to present day volcanic systems as well as in ultrahigh temperature metamorphic systems. In this project we wish to use this tool to study the thermal evolution (heating/cooling and burial/exhumation histories) of a set of rocks from the Western Dharwar Craton and the Coorg Block in South India to characterize their tectonic style. These rocks experienced several episodes of thermal metamorphism in the critical period between 3.3. and 2.5 Ga, and contain mineral assemblages in which sequential kinetic modelling can be applied. Our objective in this project is to (a) obtain high resolution thermal histories of two adjacent blocks with contrasting signatures from the same time period, and (b) use these examples to develop the tool for general use in Archean rocks, so that it may be used in other Archean terranes as well in later projects to quantify the global thermal evolution during this critical period of the history of the Earth.