Formation of high-Al komatiites from the Mesoarchean Quebra Osso Group, Minas Gerais, Brazil

Author(s)

D van Acken, J.E. Hoffmann, J.H.D. Schorscher, Toni Schulz, David Heuser, Ambre Luguet

Abstract

We report highly siderophile element data combined with Re-Os isotopes and major and trace elements of the ca. 2.7-3.0 Ga komatiites from the Quebra Osso Group, Minas Gerais, Brazil. These komatiites resemble the rare high Al-type, characterized by high Al

₂O

₃/TiO

₂ ratios (26.7-59.8). These geochemical similarities are shared with the 3.33 Ga Commondale and 3.26 GaWeltevreden komatiites fromthe eastern Kaapvaal Craton pointing to a similar origin of these suites. While anhydrous melting in an unusually hot mantle was inferred for the Weltevreden komatiites, the Commondale komatiites were suggested to have formed by hydrous, multi-stage melting. Significant depletion in LREE is coupled with subchondritic Re/Os, unradiogenic to radiogenic

¹⁸⁷Os/

¹⁸⁸Os and fractionated HSE, with enrichments in Ru, Pt, and Pd over Os and Ir. The combination of these signatures suggests minor late-stage crustal influence. Potential late-stage alteration overprint, assimilation of ambient mantle material during magma ascent and complex phase relationships of HSE-hosting phases make it difficult to estimate the composition of the source of the Quebra Osso komatiites and to place constraints on the nature of the late Archean mantle. However, the Quebra Osso komatiites are unlikely to have formed in a single-stage plume setting or in a supra-subduction zone setting. Insteadwe suggest amulti-stage melting history of the komatiite source to explain the origin of their peculiar geochemical characteristics, as has been suggested for other high-Al

₂O

₃/TiO

₂ komatiite suites.

Organisation(s)

Department of Lithospheric Research

External organisation(s)

Rheinische Friedrich-Wilhelms-Universität Bonn, Universität zu Köln, Instituto Oceanográfico, Freie Universität Berlin (FU)

Journal

Chemical Geology

Volume

422

Pages

108-121

No. of pages

14

ISSN

0009-2541

DOI

https://doi.org/10.1016/j.chemgeo.2015.12.015

Publication date

03-2016

Peer reviewed

Yes

Austrian Fields of Science 2012

105105 Geochemistry

Keywords

ASJC Scopus subject areas

Geochemistry and Petrology, Geology

Portal url

https://ucrisportal.univie.ac.at/en/publications/bec3d0e7-1467-4622-af0e-181551723fa0