An Early Cretaceous garnet pressure–temperature pa

Authors: Eric D Kelly Thomas D Hoisch Michael L Wells Jeffrey D Vervoort Mengesha A Beyene

Publish Date: 2015/08/05

Volume: 170, Issue: 2, Pages: 20-

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Abstract

Rocks may undergo complex pressure–temperature P–T histories during orogenesis in response to alternating episodes of synconvergent burial and exhumation In this study chemical zoning in garnets combined with textural and chemical evidence from the schist of Willow Creek in the Albion Mountains of southcentral Idaho USA reveals a complex P–T path during the early stages of Sevier orogenesis The distribution of quartz inclusions combined with internal resorption features establishes a hiatus in garnet growth Chemical zoning was simulated using a Gminimization approach to yield a P–T path consisting of three distinct pressure changes during increasing temperature defining an “N” shape Lu–Hf isochron ages from multiple garnet fractions and wholerock analyses in two samples are 1321 ± 24 and 1387 ± 35 Ma The samples were collected from the hanging wall of the BasinElba thrust fault and yielded results similar to those previously obtained from the footwall This leads to several conclusions 1 Both the hanging wall and footwall experienced the same metamorphic event 2 the paths document a previously unrecognized crustal thickening and synorogenic extension cycle that fills an important time gap in the shortening history of the Sevier retroarc suggesting progressive eastward growth of the orogen rather than a twostage history and 3 episodes of extensional exhumation during protracted convergent orogenesis are increasingly well recognized and highlight the dynamic behavior of orogenic beltsWe thank J Wittke for assistance in collecting EPMA data at NAU and D Wilford for assistance with the Lu–Hf garnet dating at WSU We also thank W Carlson and his research group for constructive discussions that significantly improved the interpretation of the garnet growth history Two anonymous reviewers are thanked for providing helpful comments This work was funded by a Geological Society of America grant to EDK and by National Science Foundation grant EAR9805076 to TDH EAR061009 to MLW and EAR0609856 to JDV

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