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Shock-produced high-pressure (La, Ce, Th)PO (sub 4) polymorph revealed by microstructural phase heritage of monazite

Timmons M. Erickson, Nicholas E. Timms, Mark A. Pearce, Cyril Cayron, Alex Deutsch, Lindsay P. Keller and David A. Kring
Shock-produced high-pressure (La, Ce, Th)PO (sub 4) polymorph revealed by microstructural phase heritage of monazite
Geology (Boulder) (April 2019) Pre-Issue Publication

Abstract

The responses of uranium-bearing accessory minerals to shock metamorphism have received growing interest, because under extreme pressure and temperature conditions, these phases can form unique microstructures and/or polymorphs and their radiometric ages can be partially to wholly reset. This study presents new, high-resolution electron backscatter diffraction microstructural analyses of shock-deformed monazite, (La, Ce, Th)PO (sub 4) , from the Haughton Dome, Nunavut, Canada, and the Nordlinger-Ries Crater, southern Germany. At each locality, shocked monazite grains contain distinctive lamellae comprising interlocking laths in four systematic crystallographic orientations. Modelling of orientation relationships among these lath-textured microstructures reveals that they were produced by reversion from lamellae of a previously undescribed high-pressure polymorph with a tetragonal symmetry. This is the first report of polymorphism found in natural (La, Ce, Th)PO (sub 4) . The orientation relationships, lamellar forms, and ready reversion to monazite at low pressures are consistent with a deviatoric transformation. The former presence of this new (La, Ce, Th)PO (sub 4) polymorph is detected in moderately to highly shocked rocks, suggesting that it may be common at other impact craters.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: Pre-Issue Publication
Title: Shock-produced high-pressure (La, Ce, Th)PO (sub 4) polymorph revealed by microstructural phase heritage of monazite
Affiliation: NASA, Johnson Space Center, Houston, TX, United States
Published: 20190416
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 24
Accession Number: 2019-038018
Categories: Mineralogy of non-silicatesIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2019186
Illustration Description: illus. incl. geol. sketch maps
N74°30'00" - N76°30'00", W97°00'00" - W79°30'00"
N48°46'00" - N49°00'00", E10°22'60" - E10°45'00"
Secondary Affiliation: Curtin University, AUS, AustraliaCSIRO Mineral Resources, AUS, AustraliaEcole Polytechnique Federale de Lausanne, CHE, SwitzerlandWestfaelische Wilhelms-Universitaet Muenster, DEU, GermanyUniversities Space Research Association, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, 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: 2019
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