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Tranquillityite; the last lunar mineral comes down to Earth

Birger Rasmussen, Ian R. Fletcher, Courtney J. Gregory, Janet R. Muhling and Alexandra A. Suvorova
Tranquillityite; the last lunar mineral comes down to Earth
Geology (Boulder) (November 2011) 40 (1): 83-86


Tranquillityite [Fe (super 2+) (sub 8) (ZrY) (sub 2) Ti (sub 3) Si (sub 3) O (sub 24) ] was first discovered in mare basalts collected during the Apollo 11 lunar mission to the Sea of Tranquillity. The mineral has since been found exclusively in returned lunar samples and lunar meteorites, with no terrestrial counterpart. We have now identified tranquillityite in six dolerite dikes and sills from Western Australia. Terrestrial tranquillityite commonly occurs as clusters of fox-red laths closely associated with baddeleyite and zirconolite in quartz and K-feldspar intergrowths in late-stage interstices between plagioclase and pyroxene. Its composition is relatively uniform, comprising mostly Si, Zr, Ti, and Fe, with minor Al, Mg, Mn, Ca, Nb, Hf, Y, and rare earth elements. Its habit and chemistry are consistent with tranquillityite in lunar basalts, and it has a face-centered-cubic subcell, similar to that of annealed lunar tranquillityite. Unlike coexisting baddeleyite and zirconolite, it is commonly altered to a secondary intergrowth of submicron phases comprising mainly Si, Ti, and Ca, with minor Zr. In situ sensitive high-resolution ion microprobe (SHRIMP) U-Pb geochronology of tranquillityite from sills intruding the Eel Creek Formation, northeastern Pilbara Craton, yields a (super 207) Pb/ (super 206) Pb age of 1064+ or -14 Ma. This age indicates that the previously undated sills belong to the ca. 1070 Ma Warakurna large igneous province, extending the geographic range of this mafic complex. The date also provides a new minimum age (>1.05 Ga) for the intruded sedimentary rocks, which were previously thought to be Neoproterozoic. Examination of dolerite from Western Australia suggests that tranquillityite is a relatively widespread, albeit volumetrically minor, accessory mineral and, where sufficiently coarse, it represents an exceptional new U-Pb geochronometer.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 40
Serial Issue: 1
Title: Tranquillityite; the last lunar mineral comes down to Earth
Affiliation: Curtin University, Department of Applied Geology, Bentley, West. Aust., Australia
Pages: 83-86
Published: 20111123
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 17
Accession Number: 2012-016324
Categories: Mineralogy of silicates
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2012028
Illustration Description: illus. incl. 2 tables
S22°30'00" - S20°19'60", E117°00'00" - E121°30'00"
Secondary Affiliation: University of Western Australia, AUS, Australia
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: 201209
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