Collaborative Research: Petrogenesis of Jadeitite and Other High-Pressure Rocks in Serpentinites, Motagua Fault Zone, Guatemala

翡翠岩是一种罕见的物质，在世界各地约有10个地点发现，但在危地马拉中部，Motawa断裂带(MFZ)两侧有两个不同的来源-分隔北美和加勒比海板块的板块边界带。翡翠岩来源于蛇纹岩，与俯冲带标志榴辉岩和蓝片岩共生。翡翠岩似乎代表了来自俯冲洋壳的流体的高压/低温(HP/LT)结晶，没有保存原始岩石的残留物。翡翠岩成岩作用是一个重要的地质过程，但我们对翡翠岩、它们与榴辉岩、蓝片岩、寄主蛇纹岩橄榄岩的关系以及它们是如何折返的缺乏深入的了解。最近对HP/LT岩石中云母的测年表明，两次碰撞的残留物是125-113 Ma的阿普提亚碰撞和77-65 Ma的马斯特里赫特碰撞。这不仅是一对独特的碰撞带，而且是两个含有翡翠岩的地体的配对。此外，MFZ以南丰富的劳钠铝石榴辉岩的存在表明了非常高的压力、低温和潮湿的过程，这与MFZ以北更温和、主要是蓝片岩的条件形成了鲜明的对比。这些不同的地体为研究碰撞环境和产生和剥离翡翠岩、其他HP/LT岩石及其寄主蛇纹岩的过程提供了一个非同寻常的机会。预计新的数据将能够对流体结晶假说进行严格的测试，并评估使翡翠岩结晶、蚀变蓝片岩和榴辉岩以及产生蛇纹岩的流体和溶质的来源以及这些多阶段过程发生的条件。这项为期三年的调查结果将包括：(1)对危地马拉新发现的高P/T岩石产状进行更多的实地研究，以采样和研究当地地质；(2)构造/构造研究，以了解构造侵位的分布和机制；(3)高P/T岩石的矿物学和岩石学特征，包括地质温压和地球化学研究；(4)模拟流体/岩石相互作用；(5)使用U/Pb、Sm/ND、Rb/SR、Ar/Ar和裂变径迹方法约束岩石历史；(6)利用TIMS分离岩系和微束技术研究高P/T时的原岩和流体的来源、分配和分馏。这些信息将被整合到危地马拉古俯冲带演化的构造和岩石成因模型中，特别是翡翠岩的形成。这项研究的更广泛影响包括大学和博物馆的研究人员的合作，学生的参与，与美洲中部翡翠玉的考古研究的联系，危地马拉和美国研究人员之间的联系，通过采访、文章和博物馆网站与媒体和公众进行接触，以及策划一个展览，展示玉石与文化和采购有关的科学层面。

Jadeitite-jadeite rock-is a rare material found at about ten locations worldwide, but in central Guatemala there are two distinct sources, on either side of the Motagua Fault Zone (MFZ) - the plate boundary zone separating North American and Caribbean plates. Jadeitite is sourced from serpentinites and associated with eclogite and blueschist, the markers of subduction zones. Jadeitites appear to represent high-pressure / low-temperature (HP/LT) crystallization of fluid derived from subducted ocean crust, without preservation of remnants of a protolith. Jadeitite petrogenesis represents an important geological process, but we lack a deep understanding of jadeitites, of their relationship to eclogites, blueschists, and host serpentinized peridotite, and of how they are exhumed. Recent dating of micas in HP/LT rocks show that remnants of two collisions, an 125-113 Ma Aptian one on the south side of the MFZ and a 77-65 Ma Maastrichtian. Not only is this a singular pairing of collisional belts, but the pairing of two jadeitite-bearing terranes. Moreover, the presence of abundant lawsonite eclogite south of the MFZ indicates very high pressure, low-temperature, wet processes that contrast with the more moderate mostly blueschist conditions north of the MFZ. These differing terranes offer an extraordinary opportunity to investigate the collisional environments and the processes that produce and exhume jadeitites, other HP/LT rocks, and their host serpentinites. It is anticipated that new data will enable a rigorous testing of the fluid crystallization hypothesis as well as assessment of the sources of fluid and solutes that crystallized jadeitite, altered blueschists and eclogites, and produced serpentinite and the conditions at which these multistage processes occurred. The results of this three-year investigation will include (1) additional field studies to sample and study the local geology of the newly discovered high-P/T rock occurrences in Guatemala; (2) structural/tectonic studies to understand the distribution and mechanisms of tectonic emplacement; (3) characterization of the mineralogy and petrology of the high-P/T rocks including geothermobarometric and geochemical studies; (4) modeling fluid/rock interactions; (5) constraining the rock histories using U/Pb, Sm/Nd, Rb/Sr, Ar/Ar, and fission-track methods; and (6) investigation of Nd, Sr, Pb, and S isotope systematics by TIMS on separates and by microbeam techniques to infer protoliths and to investigate fluid sourcing, partitioning, and fractionation at high P/T. This information will be integrated into both tectonic and petrogenetic models for the evolution of the Guatemalan paleosubduction zones and the formation, in particular, of jadeitites. The broader impacts of this study include the collaboration of researchers at universities and museums, involvement of students, links with archaeological studies on Middle-American jade which is jadeitite, connections between Guatemalan and U.S. researchers, outreach to both the media and the public via interviews, articles and a Museum web-site, and planning for an exhibition that will feature the scientific dimensions of jade in relation to culture and procurement.