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Published August 15, 2015 | public
Journal Article

Mineralogical anatomy and implications of a Ti–Sc-rich ultrarefractory inclusion from Sayh al Uhaymir 290 CH3 chondrite

Abstract

Titanium-rich minerals are common in Ca–Al-rich inclusions from primitive chondrites. They are important not only for testing the condensation models for a gas with a solar composition, but also for constraining the redox conditions of the early solar nebula. In this study, we report the detailed mineralogical features and its oxygen isotope compositions of a Ti–Sc-rich ultrarefractory inclusion A0031 from a CH3 chondrite Sayh al Uhaymir 290. The A0031 inclusion has a compact and layered texture with the interior consisting of panguite, Sc-rich anosovite, Ti-rich davisite, and anorthite. A few hexaferrum, perovskite, and spinel crystals are present as inclusions in these minerals. Outside of Ti-rich davisite are a layer of Al–Ti-rich diopside and two grains of enstatite. This texture strongly suggests that A0031 has a condensation origin. Panguite is its third occurrence in nature and similar in composition to the type panguite from the Allende meteorite. Sc-rich anosovite in A0031 has a chemical formula of (Ti^(4+),Ti^(3+),Mg,Sc,Al)_3O_5 with the pseudobrookite structure. This is the second report of Ti_3O_5 in nature, but is the first description of anosovite formed in the solar nebula as an ultrarefractory phase. The discovery of Sc-rich anosovite in A0031 reveals the stability of Ti_3O_5 in the early solar nebula and supports the prediction of previous equilibrium condensation calculations. The panguite, Sc-rich anosovite, and Ti-rich davisite in A0031 show a large variation in Ti^(3+)/Ti^(tot). The primitive nature of A0031 implies that the variations in Ti^(3+)/Ti^(tot) among different Ti-rich minerals are primary features. We propose that the distribution of Ti^(3+) and Ti^(4+) could be controlled mainly by their various competition abilities of incorporating into these Ti–Sc–Al-rich minerals. Similarity of Ti^(3+)/Ti^(tot) value between Ti-rich davisite from A0031 and those in other carbonaceous chondrites indicates that most refractory inclusions might have formed in highly reducing nebular settings. The ^(16)O-depleted isotope compositions of A0031 confirm the existence of diverse oxygen reservoirs for CH Ca–Al-rich inclusions in the solar nebula.

Additional Information

© 2015 Elsevier Ltd. Received 8 November 2014, Accepted 30 April 2015, Available online 6 May 2015. Associate editor: Alexander N. Krot We thank Mr. Rainer Bartoschewitz for providing the SaU 290 thin section. We are grateful to Prof. Andrew M. Davis, Prof. Makoto Kimura, and Associate Editor Dr. Alexander N. Krot for critical and helpful comments. This research was supported by the NSF – China grants (40703015, 41073052, 41373065) to Z.A.C. and NFS – China grants (41173076, 41273079) and the Minor Planet Foundation of Purple Mountain Observatory to H.W.B. SEM, EBSD and EPMA analyses were carried out at the Caltech GPS Division Analytical Facility, which is supported, in part, by NSF –United States grants EAR-0318518 and DMR-0080065.

Additional details

Created:
August 20, 2023
Modified:
October 23, 2023