Oxygen Isotope Systematics in Polymetamorphic Rocks: The Effects of Multiple Periods of Deformation and Mineral Growth

多变质岩中的氧同位素系统学：变形和矿物生长的多个时期的影响

• 批准号: 9814991
• 负责人: David Moecher
• 金额: $ 9.8万
• 依托单位: University of Kentucky Research Foundation
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-05-01 至 2002-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9814991&HistoricalAwards=false
• 关键词: Oxygen; Isotope; Systematics; Polymetamorphic; Rocks

9814991MoecherOxygen isotope analyses of metamorphic minerals provide critical constraints on the thermal evolution of, and fluid flow in, the crust. Studies of the oxygen isotope systematics of minerals in regional metamorphic rocks have mainly assessed the extent of isotopic equilibrium with increasing metamorphic grade based on isotopic fractionations among porphyroblasts and matrix phases. However, few studies explicitly consider the deformation history of regional metamorphic rocks in terms of what effect punctuated fabric development (sequential foliation/crenulation development) and discontinuous porphyroblast nucleation and growth may have on the extent of isotopic equilibrium among minerals. The current research will investigate the effects of deformation partitioning and punctuated fabric development on oxygen isotope systematics in minerals from two regional metamorphic terranes. Specifically, the hypothesis that all minerals in all fabric elements are in oxygen isotopic equilibrium will be tested. This will require spatial resolution on the order of millimeters and analysis of milligram quantities of material. Such resolution will be obtained using laser heating fluorination of small volumes of minerals (including refractory porphyroblasts) separated from distinct domains within a multiply deformed rock. In the context of this study, oxygen isotope analysis will serve to link the geochemical (isotopic and major element equilibrium), thermal (based on isotopic fractionations) and physical (mineral reactions and deformation history) evolution of metamorphic rocks. In addition to oxygen isotope equilibrium, stable isotope analysis provides insight into which minerals in a metamorphic assemblage are likely to be in major element equilibrium. This has important implications regarding equilibrium among metamorphic minerals used in conventional geothermobarometry to reconstruct P-T-t paths in ancient orogens.

[98149991] moecher变质矿物的氧同位素分析为地壳的热演化和流体流动提供了关键约束。区域变质岩中矿物氧同位素系统的研究主要是根据斑岩母岩和基质相之间的同位素分馏来评价随变质等级增加而达到的同位素平衡程度。然而，很少有研究明确考虑到区域变质岩的变形历史，即间断的组构发育（序贯叶理/粒化发育）和间断的斑岩成核和生长对矿物间同位素平衡程度的影响。本研究将探讨变形分配和断续构造发育对两个区域变质地体矿物氧同位素系统的影响。具体来说，所有织物元素中的所有矿物质都处于氧同位素平衡的假设将被检验。这将需要毫米级的空间分辨率和毫克级的材料分析。这种分辨率将通过激光加热氟化从多重变形岩石内的不同区域分离出的小体积矿物（包括难熔卟卟母细胞）来获得。在本研究的背景下，氧同位素分析将有助于联系变质岩的地球化学（同位素和主元素平衡）、热（基于同位素分馏）和物理（矿物反应和变形历史）演化。除了氧同位素平衡外，稳定同位素分析还有助于了解变质岩组合中哪些矿物可能处于主元素平衡状态。这对于用于重建古代造山带P-T-t路径的常规地温测量中变质矿物之间的平衡具有重要意义。