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

硬玉岩是一种稀有的材料，在世界上大约有10个地方发现，但在危地马拉中部，在莫塔瓜断裂带（MFZ）的两侧有两个不同的来源，莫塔瓜断裂带是分隔北美和加勒比板块的板块边界地带。翡翠岩来源于蛇纹岩，并与榴辉岩和蓝片岩伴生，是俯冲带的标志。硬玉岩似乎代表了源自俯冲洋壳的流体的高压/低温结晶，而没有保留原岩的残余。翡翠岩的形成是一个重要的地质过程，但我们对翡翠岩、翡翠岩与榴辉岩、蓝片岩和寄主蛇纹橄榄岩的关系以及它们是如何被发掘出来的缺乏深入的了解。最近对HP/LT岩石中的云母进行的年代测定表明，这是两次碰撞的残留物，一次是MFZ南侧的125-113 Ma Aptian碰撞，另一次是77-65 Ma Maastrichtian碰撞。这不仅是一对奇特的碰撞带，而且是一对含硬玉的地体。此外，MFZ南部丰富的榴辉岩的存在表明高压、低温、潮湿的过程，与MFZ北部较为温和的蓝片岩条件形成对比。这些不同的地形为研究碰撞环境以及产生和挖掘翡翠岩、其他高压/低温岩石及其寄主蛇纹岩的过程提供了绝佳的机会。预计新的数据将能够严格检验流体结晶假说，并评估使硬玉岩、蚀变蓝片岩和榴辉岩结晶并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的结果将包括：(1)进一步的实地研究，对危地马拉新发现的高p /T岩石产地的当地地质进行取样和研究；(2)构造/构造研究，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，包括地温、地球化学研究；(4)流体/岩石相互作用建模；(5)利用U/Pb、Sm/Nd、Rb/Sr、Ar/Ar和裂变径迹等方法对岩石历史进行约束；(6)利用分离物的TIMS和微束技术研究Nd、Sr、Pb和S同位素系统，以推断原岩，并研究高P/T下流体的来源、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。这项研究的广泛影响包括大学和博物馆研究人员的合作、学生的参与、中美洲翡翠考古研究的联系、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的联系，以及计划举办一个展览，将翡翠的科学维度与文化和采购联系起来。

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.