Open AccessReaction between picrite magma and continental crust: early Tertiary silicic basalts and magnesian andesites from Disko, West Greenland
Author(s) -
Asger Ken Pedersen
Publication year - 1985
Publication title -
bulletin
Language(s) - English
Resource type - Journals
eISSN - 2597-2936
pISSN - 0105-3507
DOI - 10.34194/bullggu.v152.6694
Subject(s) - geology , geochemistry , silicic , basalt , igneous rock , andesites , fractional crystallization (geology) , magma , olivine , mineral redox buffer , rhyolite , lava , phenocryst , volcanic rock , volcano , mantle (geology) , andesite
The Kûgánguaq Member is a lava and tuff sequence comprising about 7.S km3 of magnesian silicic basalts (92%), magnesian andesites (7%) and feldspar-phyric silicic basalts ( 18%) through reaction with crustal rocks, presumably Cretaceous sand or siltstones. The reaction led to sulphide fractionation and to magma modification which cannot be explained in terms of crystal fractionation or by simple mixing between magma and contaminants. The transition element (Fe, Ti, Vand Cr) concentrations in rocks, glasses and minerals indicate that the Kûgánguaq Member rocks equilibrated at oxygen fugacities several orders of magnitude below the FMQ buffer, but above the IW-buffer. The partitioning of vanadium between olivine and glass and between chromite and glass show particularly large variations and appears to be the most sensitive recorder of fo2 variations in the range between the FMQ and IW buffers at high igneous temperatures.