A complex magma mixing origin for rocks erupted in 1915, Lassen Peak, California

被引:229
作者
Clynne, MA [1 ]
机构
[1] US Geol Survey, Menlo Pk, CA 94025 USA
关键词
magma mixing; undercooled inclusions; disequilibrium phenocryst populations; banded pumice; Larsen;
D O I
10.1093/petrology/40.1.105
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
The eruption of Lassen Peak in May 1915 produced four volcanic rock types within 3 days, and in the following order: (1) hybrid black dacite lava containing (2) undercooled andesitic inclusions, (3) compositionally banded pumice with dark andesite and light dacite bands, and (4) unbanded light dacite. All types represent stages of a complex mixing process between basaltic andesite and dacite that was interrupted by the eruption. They contain disequilibrium phenocryst assemblages characterized by the co-existence of magnesian olivine and quartz and by reacted and unreacted phenocrysts derived from the dacite. The petrography and crystal chemistry of the phenocrysts and the variation in rock compositions indicate that basaltic andesite intruded dacite magma and partially hybridized with it. Phenocrysts from the dacite magma were reacted. Cooling, crystallization, and vesiculation ofthe hybrid andesite magma converted it to a layer of magic foam. The decreased density of the andesite magma destabilized and disrupted the foam. Blobs of foam rose into and were further cooled by the overlying dacite mar;ma, forming the andesitic inclusions. Disaggregation of andesitic inclusions in the host dacite produced the black dacite and light dacite magmas. Formation of foam was a dynamic process. Removal of foam propagated the foam layer downward into the hybrid andesite magna. Eventually the thermal and compositional contrasts between the hybrid andesite and black dacite magmas were reduced. Then, they mixed directly, forming the dark andesite magma. About 40-50% andesitic inclusions were disaggregated into the host dacite to produce the hybrid black dacite. Thus, disaggregation of inclusions into small fragments and individual crystals can be an efficient magma-mixing process. Disaggregation of under-cooled inclusions carrying reacted host-magma phenocrysts produces co-existing reacted and unreacted phenocryst populations.
引用
收藏
页码:105 / 132
页数:28
相关论文
共 61 条
[41]   MAGMATIC INCLUSIONS IN THE HOLOCENE RHYOLITES OF NEWBERRY VOLCANO, CENTRAL OREGON [J].
LINNEMAN, SR ;
MYERS, JD .
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH AND PLANETS, 1990, 95 (B11) :17677-17691
[42]   JORULLO VOLCANO, MICHOACAN, MEXICO (1759-1774) - THE EARLIEST STAGES OF FRACTIONATION IN CALC-ALKALINE MAGMAS [J].
LUHR, JF ;
CARMICHAEL, ISE .
CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, 1985, 90 (2-3) :142-161
[43]  
MACDONAL.GA, 1965, GEOL SOC AM BULL, V76, P475, DOI 10.1130/0016-7606(1965)76[475:EOLPCR]2.0.CO
[44]  
2
[46]   SUB-SOLIDUS DEHYDRATION OF AMPHIBOLES IN AN ANDESITIC MAGMA [J].
MAZZONE, P ;
STEWART, DC ;
HUGHES, JM .
CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, 1987, 97 (02) :292-296
[47]  
MORIMOTO N, 1988, AM MINERAL, V73, P1123
[48]  
PAPIKE JJ, 1974, GEOL SOC AM ABSTR, V6, P1053
[49]   MAGMA ASCENT RATES FROM AMPHIBOLE BREAKDOWN - AN EXPERIMENTAL-STUDY APPLIED TO THE 1980-1986 MOUNT ST-HELENS ERUPTIONS [J].
RUTHERFORD, MJ ;
HILL, PM .
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH, 1993, 98 (B11) :19667-19685
[50]  
SAKUYAMA M, 1984, B VOLCANOL, V47, P685