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

合作研究：危地马拉莫塔瓜断裂带蛇纹岩中硬玉和其他高压岩石的岩石成因

• 批准号: 0309320
• 负责人: George Harlow
• 金额: --
• 依托单位: American Museum Natural History
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-01-15 至 2009-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0309320&HistoricalAwards=false
• 关键词: Collaborative; Research; Petrogenesis; Jadeitite; Other

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.

硬玉岩是一种罕见的材料，在世界各地约有十个地方发现，但在危地马拉中部有两个不同的来源，在莫塔瓜断层带（MFZ）的两侧-分开北美和加勒比板块的板块边界带。 硬玉岩来源于蛇纹岩，与榴辉岩和蓝片岩共生，是俯冲带的标志。 硬玉岩似乎代表高压/低温（HP/LT）结晶流体来自俯冲洋壳，没有保存的原岩残余。 硬玉岩的成因是一个重要的地质过程，但我们缺乏深入的了解硬玉岩，他们的关系榴辉岩，蓝片岩，和主机蛇纹橄榄岩，以及他们是如何被挖出。 最近对高压/低温岩石中云母的测年表明，两次碰撞的残余物，一次是125-113 Ma的MFZ南侧的Aptian碰撞，另一次是77-65 Ma的Maastrichtian碰撞。 这不仅是一对独特的碰撞带，而且是两个含硬玉岩的岩石的配对。 此外，MFZ南部存在丰富的硬柱石榴辉岩，表明与MFZ北部更温和的蓝片岩条件形成对比的是非常高的压力、低温、潮湿的过程。 这些不同的岩石提供了一个非凡的机会，调查碰撞环境和过程，生产和发掘硬玉岩，其他HP/LT岩石，和他们的主机蛇纹岩。 预计新的数据将使流体结晶假说的严格测试，以及流体和溶质的来源进行评估，结晶硬玉岩，改变蓝片岩和榴辉岩，并产生蛇纹岩和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）进行更多的实地研究，对危地马拉新发现的高P/T岩石矿点的当地地质进行取样和研究;（2）进行结构/构造研究，了解构造就位的分布和机制;（3）对高P/T岩石的矿物学和岩石学特征进行鉴定，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）用U/Pb、Sm/Nd、Rb/Sr、Ar/Ar和裂变径迹方法限制岩石历史;（6）用TIMS研究分离物的Nd、Sr、Pb和S同位素系统，并用微束技术推断原岩，研究高P/T下的流体来源、分配和分馏。 这些信息将被整合到危地马拉古俯冲带的演变和形成，特别是硬玉岩的构造和岩石成因模型。 这项研究的更广泛的影响包括大学和博物馆的研究人员的合作，学生的参与，与中美洲翡翠（硬玉岩）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，文章和博物馆网站向媒体和公众宣传，并计划举办一个展览，展示玉石与文化和采购的科学关系。