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

变质矿物的莫氏氧同位素分析为地壳的热演化和流体流动提供了关键的制约因素。区域变质岩中矿物的氧同位素系统学研究主要是基于成斑岩和基质相之间的同位素分馏来评估随着变质程度的增加而达到的同位素平衡程度。然而，很少有研究明确考虑区域变质岩的变形历史，即断续的组构发展(顺序面理/褶皱发展)和不连续的斑岩成核和生长对矿物间同位素平衡程度的影响。本研究将探讨两个区域变质地体的变形分配和点状组构发育对矿物氧同位素系统学的影响。具体地说，所有组构元素中的所有矿物都处于氧同位素平衡的假设将得到检验。这将需要毫米量级的空间分辨率和对毫克量材料的分析。这样的分辨率将通过激光加热氟化少量矿物(包括难熔的斑岩)来获得，这些矿物从多重变形的岩石中的不同区域分离出来。在这项研究中，氧同位素分析将有助于将变质岩的地球化学(同位素和常量元素平衡)、热(基于同位素分馏)和物理(矿物反应和变形历史)演化联系起来。除了氧同位素平衡外，稳定同位素分析还提供了变质组合中哪些矿物可能处于主元素平衡的洞察。这对常规地温压法重建古造山带P-T-t轨迹中变质矿物之间的平衡具有重要意义。

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.