Identification, classification, and interpretation of boninites from Anthropocene to Eoarchean using Si-Mg-Ti systematics

Julian A. Pearce; Mark K. Reagan

doi:10.1130/GES01661.1

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Identification, classification, and interpretation of boninites from Anthropocene to Eoarchean using Si-Mg-Ti systematics

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Identification, classification, and interpretation of boninites from Anthropocene to Eoarchean using Si-Mg-Ti systematics

Julian A. Pearce and Mark K. Reagan

Geosphere, Vol.15, pp.1008-1037

06/07/2019

DOI: 10.1130/GES01661.1

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Published (Version of record)Geosphere, v. 15 (7 June 2019), p.1–30,

Abstract

<p>Boninites are rare, high-Si, high-Mg, low-Ti lavas that have considerable tectonic significance, especially for recognizing and interpreting episodes of subduction initiation in the geologic record. Formal identification and classification of boninites may be carried out using MgO-SiO2 and MgO-TiO2 diagrams to find compositions that satisfy modified International Union of Geological Sciences (IUGS) criteria of Si8 > 52 and Ti8 < 0.5, where Si8 and Ti8 refer to concentrations of the oxides at 8 wt% MgO. However, screening of highly metasomatized rocks and accurate classification require precautions, including normalization to a 100% volatile-free basis. The MgO-SiO2 diagram can also be used for subdivision into low-Si boninites (Si8 < 57) and high-Si boninites (Si8 > 57). Satisfying one but not both of the boninite criteria are rocks with Si8 > 52 but Ti8 ≥ 0.5 (siliceous high-magnesium basalts) and rocks with Si8 ≤ 52 but Ti8 < 0.5 (low-Ti basalts). We tested the classification methodologies using ~100 low-Ti lava suites dating from the present-day back to the Eoarchean. We conclude that, of those classifying as “boninite series,” Izu-Bonin-Mariana arc–type subduction initiation terranes provide the dominant setting only back as far as ca. 2 Ga, which marks the maximum age of extensive clinopyroxene-undersaturated melting and eruption of high-Si boninites. From 2 to 3 Ga, most boninites formed in intraplate settings by melting of refertilized, depleted cratonic roots. Prior to 3 Ga, hot, depleted mantle plumes provided the main boninite sources. Nonetheless, arc-basin boninites, though rare, do extend back to 3.8 Ga, and, together with the inherited subduction component in intracratonic boninites, they provide evidence for some form of subduction during the Archean.</p>

Geochemistry

Geology

Earth Sciences

Tectonics and Structure

Details

Title: Subtitle: Identification, classification, and interpretation of boninites from Anthropocene to Eoarchean using Si-Mg-Ti systematics
Creators: Julian A. Pearce - Cardiff University
Mark K. Reagan - University of Iowa
Resource Type: Journal article
Publication Details: Geosphere, Vol.15, pp.1008-1037
DOI: 10.1130/GES01661.1
ISSN: 1553-040X
Number of pages: 30 pages
Language: English
Date published: 06/07/2019
Academic Unit: Earth and Environmental Sciences
Record Identifier: 9983557656702771

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