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The potential of phosphorus in clinopyroxene as a geospeedometer: examples from mantle xenoliths

Baziotis, I. and Xydous, S. and Asimow, P. D. and Mavrogonatos, C. and Flemetakis, S. and Klemme, S. and Berndt, J. (2019) The potential of phosphorus in clinopyroxene as a geospeedometer: examples from mantle xenoliths. Geochimica et Cosmochimica Acta, 266 . pp. 307-331. ISSN 0016-7037. https://resolver.caltech.edu/CaltechAUTHORS:20190509-151839952

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Abstract

We investigate the potential to use concentrations and zoning patterns of phosphorus (P) in clinopyroxene as indicators of the rates of igneous and metasomatic processes, comparable to recent applications of P in olivine but applicable to more evolved rocks and lower temperatures of crystallization. Few high-P pyroxenes have been previously reported, and none have been analyzed in detail for the mechanism of P enrichment or the implications for mineral growth kinetics. Here, we report the discovery and characteristics of exotic phosphorus-rich secondary clinopyroxene in glassy pockets and veins in composite mantle xenoliths from the Cima Volcanic Field (California, USA) and the Middle Atlas Mountains (Morocco, West Africa). These glass-bearing xenoliths preserve evidence of melt infiltration events and the contrasting behavior of P in their pyroxene crystals constrains the different rates of reaction and extents of equilibration that characterized infiltration in each setting. We report optical petrography and chemical analysis of glasses and minerals for major elements by electron microprobe microanalyzer and trace elements by laser-ablation Inductively Coupled Plasma Mass Spectrometry. The Cima Volcanic Field specimen shows one end-member behavior, with unzoned P-rich clinopyroxene in a melt pocket. We attribute this occurrence to a slow crystallization process that occurred after the melt temperature reached near-equilibrium with the host rock and during which the P concentration in the melt was buffered by apatite saturation. In the Morocco xenolith, by contrast, clinopyroxene exhibits zonation with P increasing all the way to the rim, in contact with the glass. We ascribe this feature to a rapid growth process in which excess P was incorporated into the growing clinopyroxene from a diffusive boundary layer. We demonstrate quantitative agreement between the enrichment of P and other trace elements and their expected diffusion and partitioning behavior during rapid growth. We suggest that P has not been widely reported in clinopyroxene in large part because it has rarely been looked for and that its analysis offers considerable promise as a kinetic indicator both in xenoliths and volcanic rocks.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.gca.2019.04.024DOIArticle
ORCID:
AuthorORCID
Baziotis, I.0000-0003-0185-5847
Asimow, P. D.0000-0001-6025-8925
Mavrogonatos, C.0000-0002-3099-5219
Additional Information:© 2019 Elsevier Ltd. Received 8 December 2018, Revised 24 April 2019, Accepted 24 April 2019, Available online 9 May 2019. We thank the constructive comments raised by Dr. Anne Peslier, Dr. Emily J. Chin and an anonymous reviewer. Also, we are grateful to the associate editor Dr. James Day for his editorial handling and fruitful review. I.B. obtained funds for this research from the Action «Supporting Postdoctoral Researchers» of the Operational Program “Education and Lifelong Learning” of the General Secretariat for Research and Technology, co-financed by the European Social Fund (ESF) and the Greek State. I.B. and S.K. acknowledge the IKYDA academic exchange program between the Greek State Foundation and the Deutscher Akademischer Austauschdienst – DAAD. PDA is supported by the US NSF through award GI-1550934. I.B. would like to thank Theo Ntaflos for support with the electron probe microanalyses. This paper is dedicated to Larry Augustus Taylor, with deep respect from all the authors for his many long-lasting contributions to the study of terrestrial, lunar, and martian rocks. I.B. wishes to express what a great honor and inspiration it was to work with Larry as a postdoc and to have learned meteoritics and mantle xenolith studies from such a distinguished scientist.
Funders:
Funding AgencyGrant Number
General Secretariat for Research and Technology (GSRT)UNSPECIFIED
European Social FundUNSPECIFIED
Greek State FoundationUNSPECIFIED
Deutscher Akademischer Austauschdienst (DAAD)UNSPECIFIED
NSFGI-1550934
Subject Keywords:phosphorus content; phosphorus-rich pyroxene; diffusive relaxation; mantle xenolith; metasomatism
Record Number:CaltechAUTHORS:20190509-151839952
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190509-151839952
Official Citation:I. Baziotis, S. Xydous, P.D. Asimow, C. Mavrogonatos, S. Flemetakis, S. Klemme, J. Berndt, The potential of phosphorus in clinopyroxene as a geospeedometer: Examples from mantle xenoliths, Geochimica et Cosmochimica Acta, Volume 266, 2019, Pages 307-331, ISSN 0016-7037, https://doi.org/10.1016/j.gca.2019.04.024. (http://www.sciencedirect.com/science/article/pii/S0016703719302509)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95382
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:09 May 2019 22:24
Last Modified:24 Oct 2019 14:54

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