CRYSTAL-CHEMISTRY AND INTRACRYSTALLINE RELATIONSHIPS OF ORTHO-PYROXENE IN A SUITE OF HIGH-PRESSURE ULTRAMAFIC NODULES FROM THE NEWER VOLCANICS OF VICTORIA, AUSTRALIA
| Autor: | Marilena Stimpfl, Gian Mario Molin |
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| Jazyk: | angličtina |
| Rok vydání: | 1994 |
| Předmět: |
Peridotite
010504 meteorology & atmospheric sciences Crystal chemistry orthopyroxene Mineralogy Structural formula 010502 geochemistry & geophysics 01 natural sciences Mantle (geology) Basanite Crystallography Geochemistry and Petrology Ultramafic rock spinel lhertzolite Formula unit Xenolith crystal chemistry Geology 0105 earth and related environmental sciences |
| Popis: | A suite of orthopyroxenes from spinel Iherzolite xenoliths associated with basanites occurring in the Victorian (Australia) post-Pliocene ‘Newer Volcanics’ province was investigated by means of a crystal chemical methodology which provides accurate site occupancy and site configuration parameters.The M1 configuration is essentially constrained by AlVI rather than Fe2+. In addition, Fe3+, Cr3+ and Ti4+ are confined to M1 (Molin, 1989) and AlIV to TB. M2 is controlled by FeM22+ ⇌ MgM2, constrained by (Fe2+ + Ca)M2 > 0.14 atoms per formula unit (p.f.u.). Cation substitution in TB and M2 constrains the sum of the volumes of the respective polyhedra VTB+VM2 to remain essentially constant. Therefore, M2 favours the retention of the large Fe2+ up to melting-point, causing non-ideality of this iron-depleted orthopyroxene. As a consequence, the investigated orthopyroxene can be considered an ultimate Fe2+ carrier during partial mantle melting. |
| Databáze: | OpenAIRE |
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