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The complex magmatic plumbing system of the Miocene Laleaua Albă composite dykes (East Carpathians, NW Romania) revealed by crystal chemistry

Marinel KOVACS1, Alexandru SZAKÁCS2, Ákos KŐVÁGÓ3

  • Affiliations:  1Technical University of Cluj-Napoca, North University Centre of Baia Mare, Baia Mare, Romania  2Institute of Geodynamics, Romanian Academy, Bucharest, Romania 3Eötvös Loránd University, Doctorate School of Earth Sciences, Budapest, Hungary

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 233

  • Programme No: 1.1.19

  • Theme 1 > Session 1

Abstract

The Laleaua Albă magmatic complex (8.5-8.0 Ma) in the Miocene Gutâi Volcanic Zone (East Carpathian, NW Romania) mainly comprises two sub-parallel composite dykes both composed of an external zone of aphyric andesite and an internal zone of macroporphyric dacite. Complex mineralogy characterizes both rock-types: sanidine macrocrysts (up to 5 cm), large-sized plagioclase, quartz and biotite phenocrysts and smaller-sized amphibole and pyroxene as xenocrysts in dacites and much smaller-sized xenocrysts of plagioclase, amphibole and pyroxene and phenocrysts of plagioclase, quartz and biotite in andesites. Abundant microgranular gabbroic enclaves of various sizes (up to 90 cm) occur in the dacites. Similar pressure values for the high-Al, high-Mg amphibole and high-Mg clinopyroxene were obtained in all three lithologies, suggesting similar deep crystallization levels of 23-33 km from the mafic magmas. High An (70-90) plagioclase (phenocrysts in the enclaves, xenocrysts in andesites and antecryst cores in dacites) are comagmatic with the amphibole and clinopyroxene. Large-sized low An (28-40) plagioclase, strongly Ba-zoned sanidine alongside quartz and biotite suggests an evolved magma source, stalled in upper crustal reservoirs (probably a felsic crystal mush). This interpretation is supported by the chemical composition of melt inclusions in the quartz crystals of dacite (72-76% wt SiO2) similar with the composition of the felsic enclaves (77% wt SiO2) in the same dacite. The assumed architecture of the magmatic plumbing system consisting of deep (lower crust) and shallow (upper crust) magma reservoirs is consistent with the observed magma-mingling and -mixing features involved in the petrogenesis of the Laleaua Albă magmatic complex.