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Transformations to granular zircon revealed; twinning, reidite, and ZrO (sub 2) in shocked zircon from Meteor Crater (Arizona, USA)

Aaron J. Cavosie, Nicholas E. Timms, Timmons M. Erickson, Justin J. Hagerty and Friedrich Hoerz
Transformations to granular zircon revealed; twinning, reidite, and ZrO (sub 2) in shocked zircon from Meteor Crater (Arizona, USA)
Geology (Boulder) (September 2016) 44 (9): 703-706


Granular zircon in impact environments has long been recognized but remains poorly understood due to lack of experimental data to identify mechanisms involved in its genesis. Meteor Crater in Arizona (USA) contains abundant evidence of shock metamorphism, including shocked quartz, the high-pressure polymorphs coesite and stishovite, diaplectic SiO (sub 2) glass, and lechatelierite (fused SiO (sub 2) ). Here we report the presence of granular zircon, a new shocked-mineral discovery at Meteor Crater, that preserve critical orientation evidence of specific transformations that occurred during formation at extreme impact conditions. The zircon grains occur as aggregates of sub-micrometer neoblasts in highly shocked Coconino Sandstone (CS) comprised of lechatelierite. Electron backscatter diffraction shows that each grain consists of multiple domains, some with boundaries disoriented by 65 degrees around <110>, a known {112} shock-twin orientation. Other domains have {001} in alignment with {110} of neighboring domains, consistent with the former presence of the high-pressure ZrSiO (sub 4) polymorph reidite. Additionally, nearly all zircon preserve ZrO (sub 2) + SiO (sub 2) , providing evidence of partial dissociation. The genesis of CS granular zircon started with detrital zircon that experienced shock twinning and reidite formation at pressures from 20 to 30 GPa, ultimately yielding a phase that retained crystallographic memory; this phase subsequently recrystallized to systematically oriented zircon neoblasts, and in some areas partially dissociated to ZrO (sub 2) The lechatelierite matrix, experimentally constrained to form at >2000 degrees C, provided the ultrahigh-temperature environment for zircon dissociation ( approximately 1670 degrees C) and neoblast formation. The capacity of granular zircon to preserve a cumulative pressure-temperature record has not been recognized previously, and provides a new method for investigating histories of impact-related mineral transformations in the crust at conditions far beyond those at which most rocks melt.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 44
Serial Issue: 9
Title: Transformations to granular zircon revealed; twinning, reidite, and ZrO (sub 2) in shocked zircon from Meteor Crater (Arizona, USA)
Affiliation: Curtin University, Department of Applied Geology, Perth, West. Aust., Australia
Pages: 703-706
Published: 201609
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 32
Accession Number: 2016-083462
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2016228
Illustration Description: illus. incl. sketch map
N35°01'00" - N35°01'60", W111°01'60" - W111°00'00"
Secondary Affiliation: U. S. Geological Survey, USA, United StatesNASA Johnson Space Center, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201640
Program Name: USGSOPNon-USGS publications with USGS authors
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