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Mineral Chemistry of Mildly Alkalic Basalts from the 25 Ma Mont Crozier Section, Kerguelen Archipelago: Constraints on Phenocryst Crystallization Environments |
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| Authors: | DAMASCENO DIMITRI; SCOATES JAMES S; WEIS DOMINIQUE; FREY FREDERICK A; GIRET ANDRE |
| Institution: | 1DEPARTMENT OF EARTH AND ENVIRONMENTAL SCIENCES, UNIVERSITÉ LIBRE DE BRUXELLES CP 160/02, AVENUE F. D. ROOSEVELT 50, B-1050, BRUSSELS, BELGIUM 2DEPARTMENT OF EARTH, ATMOSPHERIC AND PLANETARY SCIENCES, MASSACHUSETTS INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MA 02139, USA 3LABORATOIRE DE GÉOLOGIE–PÉTROLOGIE, UNIVERSITÉ JEAN MONNET, CNRS–UMR 6524, SAINT-ÉTIENNE, FRANCE |
| Abstract: | Phenocryst compositions and mineral–melt equilibria inthe mildly alkalic basalts from the 25 Ma Mont Crozier sectionon the Kerguelen Archipelago are used to estimate the depthsat which magmas stalled and crystallized and to constrain therole of crustal structure in the evolution of magmas producedby the Kerguelen mantle plume. The Crozier section, of nearly1000 m height, consists of variably porphyritic flows (up to21 vol. % phenocrysts), dominated by plagioclase ± clinopyroxene± olivine ± Fe–Ti oxides. Feldspars showan extreme range of compositions from high-Ca plagioclase (An88)to sanidine and variable textures that are related to extensivefractionation, degassing, and mixing in relatively low-pressure(sub-volcanic) magma chambers. Although clinopyroxene is a minorphenocryst type (0–3 vol. %), its non-quadrilateral components,principally Al (1·9–8·6 wt % Al2O3), varywidely. The results of clinopyroxene–liquid thermobarometryand clinopyroxene structural barometry indicate that the Croziermagmas crystallized at pressures ranging from |
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