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Generation of Porphyritic and Equigranular Mafic Enclaves During Magma Recharge Events at Unzen Volcano, Japan |
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| Authors: | BROWNE BRANDON L; EICHELBERGER JOHN C; PATINO LINA C; VOGEL THOMAS A; DEHN JONATHAN; UTO KOZO; HOSHIZUMI HIDEO |
| Institution: | 1 UNIVERSITY OF ALASKA FAIRBANKS, GEOPHYSICAL INSTITUTE, FAIRBANKS, AK 99775, USA 2 MICHIGAN STATE UNIVERSITY, DEPARTMENT OF GEOLOGICAL SCIENCES, EAST LANSING, MI 48824, USA 3 GEOLOGICAL SURVEY OF JAPAN, HIGASHI 1-1-3, TSUKUBA, IBARAKI 305-8567, JAPAN |
| Abstract: | Mafic to intermediate enclaves are evenly distributed throughoutthe dacitic 1991–1995 lava sequence of Unzen volcano,Japan, representing hundreds of mafic recharge events over thelife of the volcano. This study documents the morphological,textural, chemical, and petrological characteristics of theenclaves and coexisting silicic host lavas. The eruptive productsdescribed in this study appear to be general products of magmamingling, as the same textural types are seen at many othervolcanoes. Two types of magmatic enclaves, referred to as Porphyriticand Equigranular, are easily distinguished texturally. Porphyriticenclaves display a wide range in composition from basalt toandesite, are glass-rich, spherical and porphyritic, and containlarge, resorbed, plagioclase phenocrysts in a matrix of acicularcrystals and glass. Equigranular enclaves are andesitic, non-porphyritic,and consist of tabular, medium-grained microphenocrysts in amatrix glass that is in equilibrium with the host dacite magma.Porphyritic enclaves are produced when intruding basaltic magmaengulfs melt and phenocrysts of resident silicic magma at theirmutual interface. Equigranular enclaves are a product of a moreprolonged mixing and gradual crystallization at a slower coolingrate within the interior of the mafic intrusion. KEY WORDS: mafic enclaves; quenched mafic inclusions; magma mingling; Unzen volcano; Unzen Scientific Drilling Project; resorbed plagioclase |
| Keywords: | : mafic enclaves quenched mafic inclusions magma mingling Unzen volcano Unzen Scientific Drilling Project resorbed plagioclase |
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