RT Journal Article
T1 Geochemistry of mafic phenocrysts from alkaline lamprophyres of theSpanish Central System: implications on crystal fractionation, magmamixing and xenoliths entrapment within deep magma chambers
A1 Orejana García, David
A1 Villaseca González, Carlos
A1 Paterson, Bruce A.
AB The Permian alkaline lamprophyres from the Spanish Central System (SCS) are highly porphyritic rocks which carrya heterogeneous population of clinopyroxene and kaersutite zoned phernocrysts. Clinopyroxene phenocrysts may show 1) normalzoning (Cpx-I), 2) reverse zoning with Fe-rich green cores (Cpx-II), and 3) reverse zoning with colourless Al-poor, silica-rich cores(Cpx-III). Kaersutite phenocrysts also show a slight reverse zoning. Major and trace element composition of Cpx-I suggests thattheir compositional variation is related to a crystal fractionation process from melts similar to the host lamprophyres. The Cpx-IIcores represent crystallization from highly evolved melts (low Mg-Cr contents and incompatible element enrichment), geneticallyrelated with the SCS alkaline magmatism, and the growth or surrounding Mg-rich inner rims points to a magma mixing process.The major and trace element composition of Cpx-III cores supports derivation from a magma which has fractionated plagioclase.This characteristic, together with their similarities when compared to clinopyroxenes from charnockite xenoliths, suggests thatthey might be xenocrysts from deep calc-alkaline cumulates. The composition of melts in equilibrium with clinopyroxene andamphibole phenocrysts supports a model in which Cpx-II and Cpx-III cores would have been incorporated into a more primitivelamprophyric magma stagnated at lower crustal levels. The low pressure composition of all phenocryst outer rims indicates thatthey crystallised directly from the host alkaline magma at their subvolcanic emplacement levels.
PB E. Schweizerbart'sche Verlagsbuchhandlung
SN 0935-1221
YR 2007
FD 2007
LK https://hdl.handle.net/20.500.14352/49618
UL https://hdl.handle.net/20.500.14352/49618
LA eng
DS Docta Complutense
RD 1 sept 2024