Collaborative Research: Lithospheric Weakening, Deep Crustal Flow and the Initiation of Orogenesis at a Noncollisional Convergent Margin in the Andes

合作研究：安第斯山脉非碰撞汇聚边缘的岩石圈弱化、深部地壳流和造山作用的启动

• 批准号: 0635923
• 负责人: Stuart Thomson
• 金额: $ 7.7万
• 依托单位: Yale University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-09-01 至 2011-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0635923&HistoricalAwards=false
• 关键词: Collaborative; Research; Lithospheric; Weakening; Deep

A fundamental problem in continental tectonics centers on how orogenesis initiates at noncollisional convergent margins. Field studies and the results of mechanical modeling show that the strength and rheology of the pre-orogenic overriding plate is a crucial factor that controls structural variability in these settings. In the Andes, the archetypal noncollisional orogen, a leading cause of pre-orogenic weakening involved the formation and destruction of large extensional basins during the Mesozoic. However, in most areas, the effects of the modern Andean orogen has obscured the geologic record of how these the transition from extension to contraction controlled the initial rise of the Cordillera from below sea level. Even fewer areas preserve a record of how the deep crust evolved through these changing tectonic regimes. The objective of this project is to determine how the high temperatures, thin crust, and rheological stratifications that result from intraplate extension affected the thermal and structural evolution of the deep crust during subsequent shortening. This observational approach is possible because the Darwin Complex in southernmost Chile preserves a nearly complete record of the thermal and structural evolution of the middle crust during the formation and destruction of a large extensional basin. Preliminary results indicate that basin closure in the southernmost Andes led to the large-scale underthrusting and/or partial subduction of continental lithosphere in a noncollisional, intraplate setting. The project utilizes structural geology, metamorphic petrology, U-Pb geochronology, and thermochronology to determine the ages of deformation as well as the nature of the tectonic and thermal evolution of Darwin Complex.This project is an intensive geological exploration of an important, yet poorly understood, region in southernmost South America. Here, crust that had been stretched in one tectonic event subsequently experienced contraction during a mountain building episode. As such, this region affords examination of how mechanical properties established in one tectonic cycle influence the mechanical behavior in later events. Results of this study should shed light on how narrow orogenic belts characterized by thick skinned tectonics are formed and how deeply buried continental rocks are subducted and exhumed. This project also involves a substantial collaborations among U.S., Chilean, and Australian institutions.

大陆构造学的一个基本问题是造山作用如何在非碰撞汇聚边缘开始。野外研究和力学模拟结果表明，造山前逆冲板块的强度和流变性是控制这些背景下构造变异性的关键因素。在安第斯山脉，典型的非碰撞造山带是造山前减弱的主要原因，涉及中生代大型伸展盆地的形成和破坏。然而，在大多数地区，现代安第斯造山带的影响掩盖了这些从伸展到收缩的转变如何控制科迪勒拉最初从海平面以下上升的地质记录。保存深部地壳如何通过这些不断变化的构造制度演化的记录的地区甚至更少。该项目的目标是确定板内伸展引起的高温、薄壳和流变层如何在随后的缩短过程中影响地壳深部的热和结构演化。这种观察方法是可能的，因为智利最南端的达尔文杂岩几乎完整地记录了大型伸展盆地形成和破坏期间中地壳的热和结构演化。初步结果表明，安第斯山脉最南端的盆地闭合导致了板块内非碰撞环境下大陆岩石圈的大规模俯冲和/或部分俯冲。该项目利用构造地质学、变质岩石学、U-Pb地质年代学和热年代学来确定达尔文杂岩的变形年龄以及构造和热演化的性质。该项目是对南美洲最南端一个重要但鲜为人知的地区的密集地质勘探。在这里，在一次构造事件中拉伸的地壳随后在一次造山事件中经历了收缩。因此，该区域提供了一个构造旋回中建立的力学性质如何影响后来事件中的力学行为的检验。这项研究的结果应该有助于揭示以厚皮构造为特征的狭窄造山带是如何形成的，以及埋藏在地下的大陆岩石是如何俯冲和折返的。该项目还涉及美国、智利和澳大利亚机构之间的大量合作。