Melt-induced Buoyancy: The Driving Force for Fast UHP Exhumation?

熔化引起的浮力：快速超高压折返的驱动力？

• 批准号: 1019709
• 负责人: Stacia Gordon
• 金额: $ 28.55万
• 依托单位: Board of Regents, NSHE, obo University of Nevada, Reno
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1019709&HistoricalAwards=false
• 关键词: Melt; induced; Buoyancy; Driving; Force

In ultrahigh-pressure terranes, buoyancy is a commonly evoked model for driving the exhumation of subducted material from mantle depths to the mid-crust, where neutral buoyancy is obtained. This model is adequate for ultrahigh-pressure terranes that do not contain significant evidence for the former presence of melt; however, in melt-rich ultrahigh-pressure terranes, such as in Papua New Guinea, a new model needs to be evaluated in which the rapid exhumation of ultrahigh rocks is driven by the buoyancy generated during two-stage partial melting of continental material, first at ultrahigh-pressure conditions and then during decompression and return of the ultrahigh-pressure body to Earth?s surface. In this project, high-precision zircon dating of variably deformed samples of rock collected in Papua New Guinea that represent former melt and are in a variety of different textural relationships to the ultrahigh-pressure rocks is being carried out. Trace elements are measured from zircon and garnet to determine if the zircon grew in the presence of garnet and/or plagioclase, tying the zircon date to the pressure-temperature conditions, and thus to determine whether the melt was present at ultrahigh-pressure conditions or later during ascent of the ultrahigh-pressure rocks back to the surface. Mapping of the different rock units in the field will determine the volume of each melt generation, and the combined mapping and analytical data is being used to quantify the buoyancy of the melt.Low-density rocks from the continental crust can be subducted to 100-150 kilometers into the Earth's mantle where they are recyrstallized in high pressure or ultrahigh pressure mineral assemblages. These high pressure/ultrahigh pressure rocks are exhumed and found at the Earth's surface. The mechanisms by which these high density rocks are exhumed are poorly understood. In particular it is not clear how they rise through the low density crust. This project explores a novel model in which ultrahigh pressure rocks partially melt, which reduces their density, decreases their bulk viscosity and allows them to rise into to the crust.

在超高压的地面中，浮力是一种通常诱发的模型，用于将俯冲材料从地幔深度驱动到中壳中，并获得中性浮力。该模型足以适用于不包含以前熔体存在的重要证据的超高压底层。然而，在诸如巴布亚新几内亚等富含融化的超高压台中，需要评估一种新模型，在该模型中，在两阶段的大陆材料中产生的浮力驱动了超高岩石的快速发掘，首先是在Ultrahigh Pressure条件下，首先在超高压力条件下，然后在压缩和返回紫外线的体现上。在这个项目中，在巴布亚新几内亚收集的可变岩石样品的高精度锆石预期代表了以前的熔体，并且正在与超高压岩石进行各种不同的质地关系。痕量元素是从锆石和石榴石中测量的，以确定在石榴石和/或斜长石存在下锆石是否生长，将锆石的日期绑定到压力温度的条件，从而确定熔体在超紧强度条件下是否存在于超压力岩石的静态条件下，或者是在超紧压岩的播放过程中。田间不同岩石单元的映射将决定每种熔体的体积，并且正在使用合并的映射和分析数据来量化熔体的浮力。大陆壳的高密度岩石可以俯冲到100-150公里的地球上，以在高压或超压力或Ultrulultraigh压力矿物组装中恢复到地面。这些高压/超高压力岩石被挖掘出来并在地球表面发现。这些高密度岩石被挖掘出的机制知之甚少。特别是尚不清楚它们如何通过低密度外壳上升。该项目探索了一个新型模型，其中超高压力部分融化，从而降低了它们的密度，降低了它们的散装粘度，并使它们可以升入外壳。