Mineral Transformations in Low Grade Rocks

通过对细粒碎屑沉积物和火成岩的黑云母级变质作用进行成岩作用的研究，重点介绍了透射电子显微镜和其他电子微束技术。重点放在粘土矿物的特征上，高分辨率技术允许直接进行结构、化学和结构表征。对涵盖给定工艺范围的表征样本进行比较，可以确定转变机制。这项研究强调了温度、水岩比和应力的变化在促进亚稳相反应中的平行效应，在亚稳相中，向通常在绿片岩相条件下达到的平衡状态的转变是可预测的Ostwald阶跃规则变化。具体项目包括：(1)墨西哥湾沿岸泥质沉积物，重点是伊利石/蒙皂石关系；(2)伊利石结晶度变化原因的定量研究；(3)通过黑云母级变质作用的成岩作用，重点是导致新西兰南部岩石结构变化的过程。以灰岩为主；(4)浅变质作用，叠加接触变质作用；(5)海相玄武岩的蚀变作用，着重于540B岩芯中的三八面体粘土矿物。这些研究有助于更好地了解富粘土岩石的成岩作用，对油气勘探具有重要意义。

Transmission electron microscope and other electron microbeam techniques are being emphasized in studies of diagenesis through biotite-grade metamorphism of fine-grained clastic sediments and igneous rocks. The focus is on charac- terization of clay minerals, for which the high resolution techniques permit direct structural, chemical and textural characterization. Comparison of characterized samples that cover the range of a given process permit mechanisms of transitions to be defined. This research emphasizes the parallel effects of changing temperature, water/rock ratio and stress in promoting reactions in metastable phases, for which transitions are in predictable Ostwald-step-rule-like changes toward the equilibrium state generally reached at greenschist facies conditions. Specific projects include: (1) Gulf Coast argillaceous sediments, with emphasis on illite/smectite relations (2) quanti- tative studies of the causes of variation in illite crystallinity (3) diagenesis through biotite-grade metamorphism, with emphasis on processes causing textural changes in southern New Zealand rocks, principally greywackes (4) low grade metamorphism with contact metamorphic overprint in Welsh pelites (5) alteration of marine basalts, emphasizing trioctahedral clay minerals in DSDP core 540B. Such studies lead to a better understanding of diagenesis in clay-rich rocks which will have important implications to oil and gas exploration.