Generation of Porphyritic and Equigranular Mafic Enclaves During Magma Recharge Events at Unzen Volcano, Japan
Open Access
- 28 September 2005
- journal article
- research article
- Published by Oxford University Press (OUP) in Journal of Petrology
- Vol. 47 (2), 301-328
- https://doi.org/10.1093/petrology/egi076
Abstract
Mafic to intermediate enclaves are evenly distributed throughout the dacitic 1991–1995 lava sequence of Unzen volcano, Japan, representing hundreds of mafic recharge events over the life of the volcano. This study documents the morphological, textural, chemical, and petrological characteristics of the enclaves and coexisting silicic host lavas. The eruptive products described in this study appear to be general products of magma mingling, as the same textural types are seen at many other volcanoes. Two types of magmatic enclaves, referred to as Porphyritic and Equigranular, are easily distinguished texturally. Porphyritic enclaves display a wide range in composition from basalt to andesite, are glass-rich, spherical and porphyritic, and contain large, resorbed, plagioclase phenocrysts in a matrix of acicular crystals and glass. Equigranular enclaves are andesitic, non-porphyritic, and consist of tabular, medium-grained microphenocrysts in a matrix glass that is in equilibrium with the host dacite magma. Porphyritic enclaves are produced when intruding basaltic magma engulfs melt and phenocrysts of resident silicic magma at their mutual interface. Equigranular enclaves are a product of a more prolonged mixing and gradual crystallization at a slower cooling rate within the interior of the mafic intrusion.This publication has 45 references indexed in Scilit:
- Experimental and textural constraints on mafic enclave formation in volcanic rocksJournal of Volcanology and Geothermal Research, 2003
- Mafic injections, in situ hybridization, and crystal accumulation in the Pyramid Peak granite, CaliforniaGSA Bulletin, 2002
- Magma recharge, contamination and residence times revealed by in situ laser ablation isotopic analysis of feldspar in volcanic rocksEarth and Planetary Science Letters, 2001
- Magmas in collision: Rethinking chemical zonation in silicic magmasGeology, 2000
- Depositional features and stratigraphic sections in granitic plutons: implications for the emplacement and crystallization of granitic magmaJournal of Structural Geology, 1998
- Thermal and mechanical constraints on mixing between mafic and silicic magmasJournal of Volcanology and Geothermal Research, 1986
- Segregation Vesicles, Gas Filter-Pressing, and Igneous DifferentiationThe Journal of Geology, 1984
- Magmatic inclusions in rhyolites, contaminated basalts, and compositional zonation beneath the Coso volcanic field, CaliforniaBeiträge zur Mineralogie und Petrographie, 1984
- Melting kinetics of a plagioclase feldsparBeiträge zur Mineralogie und Petrographie, 1983
- Effects of volatiles on mixing in calc-alkaline magma systemsNature, 1982