首页|Petrology,geochemistry,and crystal size distribution of the basaltic andesite-dacite association at Mt.Sumbing,Central Java,Indonesia:Insights to magma reservoir dynamics and petrogenesis
Petrology,geochemistry,and crystal size distribution of the basaltic andesite-dacite association at Mt.Sumbing,Central Java,Indonesia:Insights to magma reservoir dynamics and petrogenesis
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Petrology,geochemistry,and crystal size distribution of the basaltic andesite-dacite association at Mt.Sumbing,Central Java,Indonesia:Insights to magma reservoir dynamics and petrogenesis
Ten rock samples consisting of one pyroclastic density current(PDC1)deposit,seven lava flows(LF1-7),and two summit lava domes(LD1,2)were studied to under-stand the petrogenesis and magma dynamics at Mt.Sumb-ing.The stratigraphy is arranged as LF1,PDC1,LF2,LF3,LF4,LF5,LF6,LF7,LD1,and LD2;furthermore,these rocks were divided into two types.Type Ⅰ,observed in the oldest(LF1)sample,has poor MgO and high Ba/Nb,Th/Yb and Sr.The remaining samples(PDC1-LD2)represent typeⅡ,characterized by high MgO and low Ba/Nb,Th/Yb and Sr values.We suggest that type Ⅰ is derived from AOC(altered oceanic crust)-rich melts that underwent significant crustal assimilation,while type Ⅱ originates from mantle-rich melts with less significant crustal assimilation.The early stage of type Ⅱ magma(PDC1-LF3)was considered a closed sys-tem,evolving basaltic andesite into andesite(55.0-60.2 wt％SiO2)with a progressively increasing phenocryst(0.30-0.48φPC)and decreasing crystal size distribution(CSD)slope(from-3.9 to-2.9).The evidence of fluctuating silica and phenocryst contents(between 55.9-59.7 wt％and 0.25-0.41φPC,respectively),coupled with the kinked and steep(from-5.0 to-3.3)CSD curves imply the interchanging condi-tion between open(i.e.,magma mixing)and closed mag-matic systems during the middle stage(LF4-LF6).Finally,it underwent to closed system again during the final stage(LF7-LD2)because the magma reached dacitic composition(at most 68.9 wt％SiO2)with abundant phenocryst(0.38-0.45 φPC)and gentle CSD slope(from-4.1 to-1.2).
SumbingWhole-rock geochemistryPetrogenesisFractionationMagma mixingCrystal size distribution
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