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

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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.