Igneous-related Metallogenesis of the Great Basin

提出了大盆地科迪勒兰造地槽显生宙岩体火成岩成矿作用的双重研究：(1)区域性研究与白垩纪花岗岩类相关的晚期岩浆成矿作用和成矿作用，集中研究与二云母花岗岩相关的亲石元素成矿作用（LEM）；(2)新生代地槽中侏罗系、白垩系和第三系侵入岩的岩浆作用和成矿作用对比研究。这项建议建立在美国国家科学基金会正在支持的关于LEM及其区域背景的研究结果的基础上。这种方法的理由包括：(1)登月舱是一种在美国西部很少研究的类型，但它与世界其他地方的重要矿床有许多共同特征；(2)在一个单一的、地质均匀的（在大范围内）地区检查与火成岩有关的成矿作用，名义上消除了作为变异原因的横向地壳非均质性，使同一类型系统的多个例子能够进行比较，并研究其他因素，如地壳热结构的长期时间变化。LEM系统的评价包括完成局部地区的研究，并深入研究一个地区（加利福尼亚州的Birch Creek），该地区含有一个暴露良好的双云母花岗岩，具有相关的变形、变质和热液蚀变作用。该方法将详细的实地工作与地球化学和岩石学研究相结合。这些将由协作的地质年代学和地球物理测量加以补充。主要目的是完善对大盆地型LEM的描述和成因认识，并与其他地区进行比较。现有资料表明，大盆地显生宙的成岩作用与成矿作用相互关联，并随时间系统变化；它们似乎反映了地壳热结构的变化（Barton, in press）。火成岩和矿床资料不足，妨碍了定量解释。建议对侏罗纪和第三纪注入物进行地球化学侦察（全岩和矿物学、同位素和元素分析），以补充正在进行的白垩纪花岗岩类系统变化研究。这项调查连同继续汇编已公布的数据，将成为更好地查明和解释区域时间趋势的基础。

A two-fold study of igneous-related metallogenesis of Phanerozoic plutons in the Cordilleran miogeocline of the Great Basin is proposed: (1) district-scale studies of late-stage magmatic and mineralizing processes related to Cretaceous granitoids, concentrating lithophile-element mineralization (LEM) associated with two-mica granites; (2) a comparative investigation of the magmatism and metallogeny of Jurassic, Cretaceous, and Tertiary intrusions in the miogeocline. This proposal builds on the results of ongoing NSF supported studies of LEM and its regional context. Justifications for this approach include: (1) the LEM is of a type that has been little studied in the western United States, yet it shares many characteristics with important deposits elsewhere in the world; (2) examination of igneous-related metallogeny in a single, geologically uniform (at a large scale) area nominally eliminates lateral crustal heterogeneities as a cause for variation, enabling comparison of multiple examples of the same type of system and investigation of other factors such as long-term temporal changes in crustal thermal structure. Evaluation of LEM systems involves completing studies of local areas, and intensively studying one area (Birch Creek, CA), which contains a well exposed two-mica granite with related deformation, metamorphism and hydrothermal alteration. The approach combines detailed field work with geochemical and petrological studies. These will be complemented by collaborative geochronological and geophysical measurements. The main goals are to refine the descriptive and genetic understanding of Great Basin-type LEM and to compare it with other areas. Available data demonstrate the Great Basin Phanerozoic petrogeny and metallogeny correlate, and that they change systematically with time; they appear to reflect changes in crustal thermal structure (Barton, in press). Quantitative interpretation is hindered by insufficient data on the igneous rocks and ore deposits. Geochemical reconnaissance (whole rock and mineralogical, isotopic and elemental analyses ) of Jurassic and Tertiary intusions is proposed to complement ongoing studies of systematic variations in Cretaceous granitoids. This survey, along with continuing compilation of published data, will form the basis for better indentifying and interpreting regional temporal trends.