Field-based Analysis of Diapiric and Channel Flow of Partially Molten Crust

造山作用的特点是地壳增厚、大量部分熔融和大陆高原的形成。地球动力学模型表明，部分熔融的地壳通过在通道中横向流动或在底辟中垂直流动，在造山带内重新分配质量和热量。尽管河道流和底辟流是控制造山带演化的一级机制，但这些模型的野外试验滞后。该项目集中于两个出土的混合岩区的地质研究，即Okanogan-Kettle穹顶(北美科迪莱拉)和纳克索斯穹隆(爱琴海变质核杂岩)。在这些地体中，混合岩结构和组构保存了对水道/底辟流的记忆，以及在水道和穹隆折返之前和期间部分熔融的地壳与上地壳相互作用的程度。该项目的方法包括使用磁场测绘和磁化率各向异性分析来确定混合岩中流动的几何和运动学。变质组合的温压和结构分析重建了混合岩的压力和温度历史，这两种历史在河道和底辟流动方面是不同的。地质年代学分析，使用已知与变形有关的白体中结晶的锆石颗粒的原位测年(SHRIMP设备)，确定了部分熔融地壳的流动时间。此外，独居石与变质组合的已知关系的测年为压力-温度路径提供了时间上的限制。用Ar和裂变径迹年代学方法研究了这些岩石的冷却时间，评估了河道/底辟流与折返作用之间的成因关系。这一综合方法应用于两个第三系造山段，评估了部分熔融地壳在造山作用中的作用，以及地壳流动与板块地球动力学之间的关系。

Mountain building processes (orogenesis) are characterized by crustal thickening, abundant partial melting, and the formation of continental plateaus. Geodynamic models show that partially molten crust redistributes mass and heat in the orogen by flowing laterally in a channel or vertically in diapirs. Although channel flow and diapiric flow are first-order mechanisms controlling the evolution of orogens, field-testing of these models is lagging. This project is concentrating on geologic studies of two exhumed migmatite terrains, the Okanogan-Kettle dome (North American Cordillera), and the Naxos dome (Aegean metamorphic core complex). In these terrains, migmatite structures and fabrics have preserved the memory of channel/diapiric flow and the extent to which the partially molten crust interacts with the upper crust prior to and during exhumation of the channel and the domes. The project's methodology includes the determination of the geometry and kinematics of flow in migmatites using both field mapping and the analysis of anisotropy of magnetic susceptibility. Thermobarometric and textural analyses of metamorphic assemblages reconstructs the pressure and temperature histories of migmatites, which are distinct for channel and diapiric flow. Geochronologic analyses, using in-situ dating (SHRIMP facilty) of zircon grains crystallized in leucosomes of known relationship to deformation, date the flow of partially molten crust. In addition, dating of monazite of known relationship to metamorphic assemblages offers temporal constraints on the pressure-temperature path. The timing of cooling of these rocks, approached by argon and fission-track geochronologic methods, evaluates the genetic relationship between channel/diapiric flow and exhumation. This integrated methodology applied to two Tertiary orogenic segments evaluates the role of the partially molten crust during orogeny and the relationship between crustal flow and plate geodynamics.