The Role of Fluid Flow in the Cooling of Metamorphic Core Complexes

流体流动在变质核杂岩冷却历史中的作用明尼苏达大学Mark Person印第安纳大学的Christian Teyssier这个项目的目的是利用结合地壳变形运动学的热液模型来量化在折返过程中流体对变质核杂岩热史的影响。数值模型受到基于不列颠哥伦比亚省Shuswap变质核杂岩的大量构造、变质和热年代学数据的现场研究的限制。该模型允许将热传递与Shuswap系统内的岩石热年代学和流体-岩石同位素交换进行定量比较。该模拟有助于测试流体流动对上地壳(地垒和地堡、多米诺骨牌式块体、里氏体系)的断层几何、运动学和渗透性的敏感性，以及下地壳的韧性流动和参与热平流的敏感性。模拟还评估了流体流动对拆离带下的热分布和地温梯度的影响，这对于理解核杂岩中的变质分带具有重要意义。定量结果正在与我们在不列颠哥伦比亚省Shuswap变质核杂岩中开发的大型热年代学数据库进行比较；这种通用模拟类型可以直接输出到其他变质核杂岩和裂谷带。研究还有助于揭示Shuswap变质核杂岩拆离带中流体-岩石相互作用和热历史的系统学。为此，我们基于裂变径迹和(U-Th)/He方法对两个横跨哥伦比亚河拆离和断裂系统的断面进行了详细的热年代学研究，这两个断面位于东部变质核杂岩的边界。在同一地区，我们正在通过分析稳定的同位素特征和矿脉、断层岩和未破裂岩石中的流体包裹体来研究流体-岩石相互作用。这一部分的研究制约着流体的性质、流体路径的范围、地表流体穿透变质壳的程度、流体的古温度，以及可能的流体通量。我们正在构建一套数值实验，在这个较小的框架内表示同位素流体-岩石相互作用以及热年代学数据，以便更好地了解拆离/正断层系统中的流体流动。详细的野外工作和化探结果也是对模拟结果进行检验的基本事实。对流体流动作为主要传热机制的定量分析将有助于改进地质学家使用冷却速率来确定折返速率的方法。

The role of fluid flow in the cooling history of metamorphic core complexesChristian Teyssier, University of MinnesotaMark Person, Indiana UniversityThe aim of this project is to quantify the effects of fluid flow on the thermal history of metamorphic core complexes during exhumation using a hydrothermal model that incorporates the kinematics of crustal deformation. The numerical model is constrained by field studies based on extensive structural, metamorphic, and thermochronologic data for the Shuswap metamorphic core complex, British Columbia. The modeling allows for quantitative comparison of heat transfer with rock thermochronology and fluid-rock isotopic exchange within the Shuswap system. The modeling helps to test the sensitivity of fluid flow to fault geometry, kinematics, and permeability in the upper crust (horst and graben, domino-style blocks, listric systems), as well as ductile flow and attending heat advection in the lower crust. The modeling also evaluates the effect that fluid flow has on heat distribution and geothermal gradients below the detachment zone, which has implications for the understanding of metamorphic zoning in core complexes. Quantitative results are being compared to the large-scale thermochronology database we developed in the Shuswap metamorphic core complex, British Columbia; this type of generic modeling is directly exportable to other metamorphic core complexes as well as rift zones.The research also sheds light on the systematics of fluid-rock interactions and thermal history in the detachment zones of the Shuswap metamorphic core complex. Towards this end, we are conducting a detailed thermochronologic study based on the fission-track and (U-Th)/He methods on two transects across the Columbia River detachment and fault system that bounds the metamorphic core complex to the east. In the same regions, we are examining fluid-rock interaction by analyzing the stable isotope signature and fluid inclusions within veins, fault rocks, and unfractured rock. This part of the study constrains the nature of the fluids, the extent of fluid pathways, the degree to which surficial fluids penetrate the metamorphic crust, the fluids paleo-temperatures, and possibly also fluid fluxes. We are constructing a suite of numerical experiments to represent isotopic fluid-rock interactions as well as thermochronologic data within this smaller-scale framework in order to better understand fluid flow in detachment/normal fault systems. The detailed field work and geochemical results also serve as ground truth against which the modeling results are tested. The quantitative analysis of fluid flow as a major heat transfer mechanism will help to refine the method in which geologists use cooling rates to determine exhumation rates.