T237 Tick Tock in the Rock: Elucidating the Time Scales of Geologic Processes and Honoring the Contributions of Bruce Watson, 2018 Roebling Medalist

Wednesday, 7 November 2018
8:00 AM - 12:00 PM
Room 240-241

TIMESCALES AND RATES OF SUBDUCTION CHANNEL PROCESSES: INSIGHTS FROM THE (U)HP TERRANE OF SOUTHEAST PAPUA NEW GUINEA

Paper number: T237-9
Program: Technical Sessions
Time: 10:00 AM – 10:15 AM

Authors

Abstract

Documenting pressure-temperature-time histories of rocks subducted to mantle depths and returned to the surface is particularly challenging because protoliths (re)crystallize throughout their evolution and mineral assemblages rarely chemically and isotopically equilibrate. Bruce Watson’s legacy of pioneering research on the redistribution of chemical elements and their isotopes in the solid Earth has inspired multimethod thermochronologic and trace element thermobarometric studies that reveal the timescales of metamorphic and magmatic processes in the (ultra)high pressure ((U)HP) terrane of Papua New Guinea (PNG). The timing of UHP metamorphism is 7–8 Ma, known from concordant ages obtained on cogenetic metamorphic zircon (U-Pb SIMS), garnet (Lu-Hf), and phengite (40Ar/39Ar) from coesite eclogite. Both phengite and omphacite yielded atmospheric 38Ar/36Ar and 20Ne/22Ne, trapped during crystallization at mantle depths. There is no evidence that phengite contains excess Ar, an interpretation often used to dismiss the validity of 40Ar/39Ar data from (U)HP terranes. Zircon U-Pb and trace element SIMS depth profiles from the coesite eclogite host gneiss document intragrain age and geochemical heterogeneities indicating chemical and isotopic disequilibrium during zircon growth following (ca. 4 m.y.) UHP metamorphism. Many aspects of Bruce Watson’s legacy remain to be applied to the (U)HP PNG terrane. For example, modelling the rates of zircon dissolution and growth during subduction and exhumation can constrain transport through the rock cycle. Additionally, partial melts crystallized during rapid (cm/yr) exhumation provide targets to assess cold magma storage and transport. These highlighted results, together with future research targets, indicate that the (U)HP terrane is a natural laboratory to determine the flux of recycled materials, including atmospheric gases, that are subducted to, and exhumed from mantle depths.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-323219

© Copyright 2018 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.