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New clues from Earth's most elusive impact crater; evidence of reidite in Australasian tektites from Thailand

Aaron J. Cavosie, Nicholas E. Timms, Timmons M. Erickson and Christian Koeberl
New clues from Earth's most elusive impact crater; evidence of reidite in Australasian tektites from Thailand
Geology (Boulder) (March 2018) 46 (3): 203-206


Australasian tektites are enigmatic drops of siliceous impact melt found in an approximately 8000 X approximately 13,000 km strewn field over Southeast Asia and Australia, including sites in both the Indian and Pacific oceans. These tektites formed only 790,000 yr ago from an impact crater estimated to be 40-100 km in diameter; yet remarkably, the young and presumably large structure remains undiscovered. Here we report new evidence of a rare high-pressure phase in Australasian tektites that further constrains the location of the source crater. The former presence of reidite, a high-pressure polymorph of zircon, was detected in granular zircon grains within Muong Nong-type tektites from Thailand. The zircon grains are surrounded by tektite glass and are composed of micrometer-sized neoblasts that contain inclusions of ZrO (sub 2) . Each grain consists of neoblasts in three distinct crystallographic orientations as measured by electron backscatter diffraction, where all [001] directions are orthogonal and aligned with one <110> direction from the other two orientations. The systematic orientation relationships among zircon neoblasts are a hallmark of the high-pressure polymorphic transformation to reidite and subsequent reversion to zircon. The preserved microstructures and dissociation of zircon to ZrO (sub 2) and SiO (sub 2) require a pressure >30 GPa and a temperature >1673 degrees C, which represent the most extreme conditions thus far reported for Australasian Muong Nong-type tektites. The data presented here place further constraints on the distribution of high-pressure phases in Australasian tektites, including coesite and now reidite, to an area centered over Southeast Asia, which appears to be the most likely location of the source crater.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 46
Serial Issue: 3
Title: New clues from Earth's most elusive impact crater; evidence of reidite in Australasian tektites from Thailand
Affiliation: Curtin University, Department of Applied Geology, Perth, West. Aust., Australia
Pages: 203-206
Published: 201803
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 32
Accession Number: 2018-041973
Categories: Petrology of meteorites and tektites
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2018049
Illustration Description: illus. incl. geol. sketch map
N05°45'00" - N20°30'00", E96°30'00" - E106°00'00"
Secondary Affiliation: Lunar and Planetary Institute, USA, United StatesNatural History Museum, AUT, Austria
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, 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: 201810
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