TY - JOUR
T1 - Silicic magmatism associated with Late Cretaceousrifting in the Arctic Basin – petrogenesis of the Kap Kane sequence, the Kap Washington Group volcanics, North Greenland
AU - Þórarinsson, Sigurjón Böðvar
AU - Holm, Paul Martin
AU - Duprat, Helene Inga
AU - Tegner, Christian
PY - 2011/7
Y1 - 2011/7
N2 - The bimodal, Late Cretaceous-Palaeocene (71-61Ma) Kap Washington Group volcanic sequence on the north coast of Greenland was erupted in a continental rift setting during the opening of the Arctic Ocean. On Kap Kane ca. 70Ma silicic lavas and ignimbrites dominate over mildly alkaline basalts. Intermediate rocks are scarce (SiO2=57-62wt.%) and cognate mafic inclusions, resorbed crystals, and highly variable clinopyroxene compositions indicate that they formed by magma mixing. Silicic lavas (66-74wt.% SiO2) on Kap Kane show geochemical features typical of A-type granitoids and form two chemically and mineralogically distinct suites: (i) one-feldspar, peralkaline trachytes and rhyolites with elevated contents of high field strength elements (HFSE); and (ii) two-feldspar, weakly peraluminous, HFSE-poor trachytes and rhyolites. The peralkaline lavas have Sr-Nd-Pb isotopic compositions which overlap with the compositions of mildly alkaline Kap Kane basalts. The peralkaline lavas are inferred to have originated from an evolved basaltic parent by ca. 90% fractional crystallisation of an assemblage consisting of plagioclase, alkali feldspar, clinopyroxene, Fe-Ti oxide, olivine, kaersutite and apatite. The peraluminous lavas have mixed mantle-crust Sr-Nd-Pb isotopic signatures and it is proposed that they were formed by partial melting of hybridised mafic crust with >70% contribution from juvenile, mantle-derived material in the form of lower crustal gabbros. Feldspar phenocrysts have near pure end-member compositions and many crystals display a patch antiperthite texture characterised by patches of Or98-99 in a host of Ab99, reflecting low-temperature dissolution-reprecipitation reactions during hydrothermal alteration. Leaching experiments, moreover, indicate that the Sr isotopic system of Sr-poor peralkaline lavas has been disturbed by interaction with a fluid with relatively low Rb/Sr and 87Sr/86Sr. The Nd and Pb isotopic systems do not appear significantly affected by this process.
AB - The bimodal, Late Cretaceous-Palaeocene (71-61Ma) Kap Washington Group volcanic sequence on the north coast of Greenland was erupted in a continental rift setting during the opening of the Arctic Ocean. On Kap Kane ca. 70Ma silicic lavas and ignimbrites dominate over mildly alkaline basalts. Intermediate rocks are scarce (SiO2=57-62wt.%) and cognate mafic inclusions, resorbed crystals, and highly variable clinopyroxene compositions indicate that they formed by magma mixing. Silicic lavas (66-74wt.% SiO2) on Kap Kane show geochemical features typical of A-type granitoids and form two chemically and mineralogically distinct suites: (i) one-feldspar, peralkaline trachytes and rhyolites with elevated contents of high field strength elements (HFSE); and (ii) two-feldspar, weakly peraluminous, HFSE-poor trachytes and rhyolites. The peralkaline lavas have Sr-Nd-Pb isotopic compositions which overlap with the compositions of mildly alkaline Kap Kane basalts. The peralkaline lavas are inferred to have originated from an evolved basaltic parent by ca. 90% fractional crystallisation of an assemblage consisting of plagioclase, alkali feldspar, clinopyroxene, Fe-Ti oxide, olivine, kaersutite and apatite. The peraluminous lavas have mixed mantle-crust Sr-Nd-Pb isotopic signatures and it is proposed that they were formed by partial melting of hybridised mafic crust with >70% contribution from juvenile, mantle-derived material in the form of lower crustal gabbros. Feldspar phenocrysts have near pure end-member compositions and many crystals display a patch antiperthite texture characterised by patches of Or98-99 in a host of Ab99, reflecting low-temperature dissolution-reprecipitation reactions during hydrothermal alteration. Leaching experiments, moreover, indicate that the Sr isotopic system of Sr-poor peralkaline lavas has been disturbed by interaction with a fluid with relatively low Rb/Sr and 87Sr/86Sr. The Nd and Pb isotopic systems do not appear significantly affected by this process.
U2 - 10.1016/j.lithos.2011.01.013
DO - 10.1016/j.lithos.2011.01.013
M3 - Journal article
SN - 0024-4937
VL - 125
SP - 65
EP - 85
JO - Lithos
JF - Lithos
IS - 1-2
ER -