Chemical characteristics of chromian spinel in plutonic rocks; implications for deep magma processes and discrimination of tectonic setting

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doi: 10.1111/j.1440-1738.2010.00747.x
Author(s): Arai, Shoji; Okamura, Hidenobu; Kadoshima, Kazuyuki; Tanaka, Chima; Suzuki, Kenji; Ishimaru, Satoko
Author Affiliation(s): Primary:
Kanazawa University, Department of Earth Sciences, Kanazawa, Japan
Volume Title: Island Arc
Source: Island Arc, 20(1), p.125-137. Publisher: Wiley Blackwell on behalf of Geological Society of Japan, Tsukuba, Japan. ISSN: 1038-4871
Note: In English. 92 refs.; illus.
Summary: We summarize chemical characteristics of chromian spinels from ultramafic to mafic plutonic rocks (lherzolites, harzburgites, dunites, wehrlites, troctolites, olivine gabbros) with regard to three tectonic settings (mid-ocean ridge, arc, oceanic hotspot). The chemical range of spinels is distinguishable between the three settings in terms of Cr# (=Cr/(Cr+Al) atomic ratio) and Ti content. The relationships are almost parallel with those of chromian spinels in volcanic rocks, but the Ti content is slightly lower in plutonics than in volcanics at a given tectonic environment. The Cr# of spinels in plutonic rocks is highly diverse; its ranges overlap between the three settings, but extend to higher values (up to 0.8) in arc and oceanic hotspot environments. The Ti content of spinels in plutonics increases, for a given lithology, from the arc to oceanic hotspot settings by mid-ocean ridge on average. This chemical diversity is consistent with that of erupted magmas from the three settings. If we systematically know the chemistry of chromian spinels from a series of plutonic rocks, we can estimate their tectonic environments of formation. The spinel chemistry is especially useful in dunitic rocks, in which chromian spinel is the only discriminating mineral. Applying this, discordant dunites cutting mantle peridotites were possibly precipitated from arc-related magmas in the Oman ophiolite, and from an intraplate tholeiite in the Lizard ophiolite, Cornwall. Abstract Copyright (2011), Blackwell Publishing Asia Pty Ltd.
Year of Publication: 2011
Key Words: 05 Petrology, Igneous and Metamorphic; 16 Structural Geology; Alkaline earth metals; Alteration; Aluminum; Arabian Peninsula; Asia; Chrome spinel; Chromitite; Chromium; Cornwall England; Crust; Dunite; England; Europe; Ferric iron; Ferrous iron; Gabbros; Great Britain; Harzburgite; Hot spots; Igneous rocks; Iron; Island arcs; Lherzolite; Lizard Ophiolite; Mafic composition; Magmatism; Magnesium; Metals; Mid-ocean ridges; Mineral composition; Ocean floors; Oceanic crust; Olivine gabbro; Oman; Ophiolite; Oxides; Peridotites; Petrology; Plate tectonics; Plutonic rocks; Semail Ophiolite; Tectonics; Titanium; Troctolite; Ultramafics; United Kingdom; Wehrlite; Western Europe
Record ID: 2014029019
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from John Wiley & Sons, Chichester, United Kingdom

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