Collaborative Research: Preserving Evidence of Extreme Metamorphism in the Rhodope Complex

地球上的板块构造过程控制着主要火山爆发和地震的位置和时间，并在更长的时间尺度上控制着山带的位置。一些最活跃的构造区域发生在板块汇聚的地方，通常是一个板块在另一个板块下移动（“俯冲”），比如印度-澳大利亚板块目前在喜马拉雅山脉俯冲到欧亚板块下。俯冲带是混合的重要区域。例如，地表物质和流体通常被拉或拖进地球的深部地幔，而地幔物质可以被带到地表。为了更好地了解发生在俯冲带的关键过程的机制，认识和研究古代俯冲带是很重要的。特别重要的是，要认识到存在于地球表面的岩石和流体，它们被带到数百公里外的地幔中，然后又被带回地表。这项研究的目标是开发工具来识别和描述曾经被带到俯冲带深处的岩石和流体（或熔体），并最终将这些遥远的材料用作今天主要俯冲带发生的过程的记录仪或指示器。该项目由岩石地球化学和EPSCoR（刺激竞争性研究的实验项目）项目共同资助，代表了缅因州鲍登学院和马萨诸塞大学之间的合作。这项研究将为鲍登学院的本科生和麻省大学的研究生提供一个互动的机会，并为两所大学的学生提供一个使用现代分析仪器进行高水平研究的机会。虽然人们普遍认为，在许多板块构造碰撞中，特别是显生宙（距今5亿年），地表物质被俯冲到高压和超高压下，但超高压变质作用的实际证据通常被较年轻的事件所掩盖。提出的研究的主要目的是确定哪些因素有利于保存极端变质作用的证据。最终目标是揭开超高压岩石叠印的影响，深入了解超高压构造作用的机制，并有可能开发出新的方法来识别在超高压条件下变质的岩石，但现在几乎没有这种转变的证据。这一发现可能会提高我们在更古老的构造环境中识别超高压变质作用证据的能力。在保加利亚和希腊的Rhodope变质岩复合体内，选择了五个相对容易到达的地点进行详细研究。这五个地方都经历了超高压变质作用，但地质证据已经重叠，并在不同程度上模糊不清。通过实地考察，为期10周的暑期研究，以及未来两年的合作研究，来自鲍登学院和马萨诸塞大学的学生和教师研究人员将描述高压和超高压变质作用的岩石学、微观结构和地质年代学证据，并强调重叠和模糊这一记录的结构和岩石学过程。

Plate tectonic processes on Earth control the location and timing of major volcanic eruptions and earthquakes, and over longer time scales, the location of mountain belts. Some of the most active tectonic regions occur where plates converge, typically with one plate moving ('subducting') under another, such as the Himalayan Mountains where the Indo-Australian Plate is currently subducting under the Eurasian plate. Subduction zones are important regions of mixing. For example, surface materials and fluids are commonly pulled or dragged into Earth's deep mantle and mantle materials can be brought to the surface. In order to better understand the mechanics of critical processes that occur at subduction zones, it is important to recognize and investigate ancient subduction zones. In particular, it is essential to recognize rocks and fluids that were present at the Earth's surface, were carried hundreds of kilometers into the mantle, and then were returned to the surface. The goal of this research is to develop tools to identify and characterize rocks and fluids (or melts) that were once brought to great depth in subduction zones, and to ultimately use these far-traveled materials as recorders or indicators of the processes that occur in major subduction zones today. This project is co-funded by the Petrology & Geochemistry and the EPSCoR (Experimental Program to Stimulate Competitive Research) programs and represents a collaboration between Bowdoin College, Maine and the University of Massachusetts. The study will provide an opportunity for undergraduate students from Bowdoin College to interact with graduate students from UMass and for students from both institutions to carry out high-level research using modern analytical instruments. Although it is widely accepted that surface materials were subducted to high- and ultrahigh- pressures in many plate tectonic collisions, especially in Phanerozoic time ( 500 million years before present), the actual evidence of ultrahigh-pressure metamorphism ('UHP metamorphism') is commonly obscured by younger events. The primary objective of the proposed research is to determine what factors favor the preservation of evidence of extreme metamorphism. The ultimate goal is to unravel the effects of overprinting on UHP rocks, gain insight about the mechanics of UHP tectonism, and potentially develop new methods to identify rocks that were metamorphosed at UHP conditions, but now retain little to no evidence of this transformation. This insight may improve our ability to identify evidence of UHP metamorphism in older tectonic settings. Five relatively accessible localities within the Rhodope Metamorphic Complex, Bulgaria and Greece, have been chosen for detailed study. The five localities have all experienced UHP metamorphism, but the geologic evidence has been overprinted and obscured to varying degrees. Through fieldwork, a 10-week summer research institute, and collaborative research over the next two years, student and faculty researchers from Bowdoin College and UMass will characterize the petrologic, microstructural, and geochronological evidence for high- and ultrahigh-pressure metamorphism and highlight the structural and petrologic processes that overprint and obscure this record.