Structural and Thermochronological Constraints on the Role of Partial Melting During Late-Orogenic Extension

;​R o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o4 @ -。/ 0 1 2 3 4 5 6 7 F Microsoft Word 6.0 Document MSWordDoc。6;​[9526915 . Teyssier]拟建项目的目的是研究地壳部分熔融在晚造山伸展过程中所起的作用。造山演化通常涉及地壳的缩短和增厚，这具有重要的热影响。特别是，预计在大约2000 - 3000万年的特征时间后，热松弛将导致中下地壳的部分熔融。造山演化的晚期以地壳伸展为主要特征。因此，地壳部分熔融导致的机械弱化与增厚的地壳在自身重量作用下重力坍缩产生的晚造山伸展之间存在着根本联系。所提出的工作假设包括刚性上地壳的伸展，由韧性流动和下地壳的混杂岩丘发育所调节。该测试将在不列颠哥伦比亚省的Shuswap变质岩心综合体中进行，该岩心综合体显示了目前暴露水平的不同地壳水平的横截面，从高级变质岩和混杂岩到未变质沉积岩。初步工作和已发表的资料表明，该杂岩体核心的部分熔融与上覆地壳古近系伸展构造的发育是同时发生的。此外，现有的同位素资料表明，古近纪时期地形冷却迅速（30-50(C/.yr)）。因此，认为地形的快速冷却和掘出与中下地壳的部分熔融同时发生，与部分熔融相关的机械弱化是造山带重力塌陷的主要原因。基于构造和变质地质学以及同位素测年方法的综合方法将检验提出的假设。;Oh +' 0 $ H l D H R:\WWUSER\TEMPLATE\NORMAL。如果你是我的朋友，我就会去找你，我就会去找你。9526915 Felicia Smith@ @ @ @ f# Microsoft Word 6.0；e = e ' ' j j j j j j j j j j S 1 5 T 5 S j S j j j j提出的项目的目的是研究地壳部分熔融在晚造山伸展中的作用。造山演化通常涉及地壳的缩短和增厚，这具有重要的热影响。特别是，预计在大约2000 - 3000万年的特征时间后，热松弛将导致中下地壳的部分熔融。造山演化的晚期以地壳伸展为主要特征。因此，地壳部分熔融导致的机械弱化与增厚的地壳在自身重量作用下重力坍缩产生的晚造山伸展之间存在着根本联系。所提出的工作假设包括刚性上地壳的伸展，由韧性流动和下地壳的混杂岩丘发育所调节。测试将在不列颠哥伦比亚省的Shuswap变质岩心综合体中进行，在目前的暴露水平下，它显示了不同水平的c

; R o o t E n t r y F 4p C o m p O b j b W o r d D o c u m e n t O b j e c t P o o l 4p 4p 4 @ - . / 0 1 2 3 4 5 6 7 F Microsoft Word 6.0 Document MSWordDoc Word.Document.6 ; 9526915 Teyssier The goal of the proposed project is to investigate the role that partial melting of crust plays during late-orogenic extension. Orogenic evolution typically involves crustal shortening and thickening which have important thermal consequences. In particular, thermal relaxation is expected to lead to partial melting of the mid-to lower crust after a characteristic time of approximately 20-30 million years. The late stages of orogenic evolution are commonly characterized by crustal extension. Therefore, it is proposed that a fundamental link exists between partial melting of crust, which results in mechanical weakening, and late-orogenic extension produced by gravitational collapse of the thickened crust under its own weight. The proposed working hypothesis involves extension of the rigid upper crust accommodated by ductile flow and migmatite-dome development in the lower crust. The test will be conducted in the Shuswap metamorphic core complex, British Columbia, which displays, at present exposure level, a cross section of various levels of the crust, from high-grade metamorph ic rocks and migmatites to unmetamorphosed sedimentary rocks. Preliminary work as well as published data suggest that partial melting in the core of this complex was coeval with development of Paleogene extensional fabric in the overlying crustal layers. In addition, existing isotopic data suggest that terrain cooled rapidly (30-50(C/.yr) during Paleogene time. Therefore, it is proposed that rapid cooling and exhumation of the terrain was coeval with partial melting of the mid-to lower crust, and that the mechanical weakening associated with partial melting was responsible for gravitational collapse of the orogen. An integrated approach based upon the methods of structural and metamorphic geology as well as isotopic dating will test the proposed hypothesis. ; Oh +' 0 $ H l D h R:\WWUSER\TEMPLATE\NORMAL.DOT S u m m a r y I n f o r m a t i o n ( , 9526915 Felicia Smith Felicia Smith @ @ @ @ F # Microsoft Word 6.0 1 ; e = e ` ` j j j j j j j S 1 5 T 5 S j S j j j j ~ j j j j @ 9526915 Teyssier The goal of the proposed project is to investigate the role that partial melting of crust plays during late-orogenic extension. Orogenic evolution typically involves crustal shortening and thickening which have important thermal consequences. In particular, thermal relaxation is expected to lead to partial melting of the mid-to lower crust after a characteristic time of approximately 20-30 million years. The late stages of orogenic evolution are commonly characterized by crustal extension. Therefore, it is proposed that a fundamental link exists between partial melting of crust, which results in mechanical weakening, and late-orogenic extension produced by gravitational collapse of the thickened crust under its own weight. The proposed working hypothesis involves extension of the rigid upper crust accommodated by ductile flow and migmatite-dome development in the lower crust. The test will be conducted in the Shuswap metamorphic core complex, British Columbia, which displays, at present exposure level, a cross section of various levels of the c