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

3.0Ga左右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，这段时间被认为是发生向现代板块构造样式转变的时期。这被认为是生热和散热之间平衡转移的结果；在3.0Ga之前，生热被认为是主导散热的。然而，这种转变本身被认为是快速的(在0.5Ga内)，目前还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紧密间隔(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。我们发展了序列动力学模拟方法(模拟矿物成分分阶段分带的扩散改造)，并成功地将其应用于现代火山系统和超高温变质系统。在这个项目中，我们希望使用这个工具来研究印度西部达瓦尔克拉通和南印度库格地块的一组岩石的热演化(加热/冷却和埋藏/折返历史)，以表征它们的构造风格。这些岩石在3.3年间的关键时期经历了几次热变质作用。和2.5Ga，并含有可应用顺序动力学模拟的矿物组合。我们在这个项目中的目标是(A)获得同一时期具有对比特征的两个相邻地块的高分辨率热历史，以及(B)利用这些例子开发出在太古宙岩石中普遍使用的工具，以便它可以用于其他太古宙地体以及后来的项目，以量化地球历史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.