Petrochemical Comparison of 3.5 Ga Old Mafic Amphibolite Inclusions from Eastern Hebei Province with Archean Mafic—ultramafic Supracrustals of Uncertain Antiquity,Southern Jilin Eastern Liaoning Prov

New major element data for coexisting minerals and bulk-rock REE analyses,combined with previously obtained petrologic/geologic information,allow comparison of Archean mafic-ultramafic meta-igneous rocks from adjacent portions of northeastern Sino-Korean shield .Isotope data published by previous workers document an Early Archean age of formation for metabasaltic rocks now occurring as mafic amphibolite inclusions in tonalitic gneisses west of Bohai Bay(area).Mafic-ultramafic mineral assemblages developed in tonalitic gneisses west of Bohai Bay(areaA).Mafic-ultramafic mineral assemblages developed in amphibolite facies Archean supracrustals east of Bohai Bay(areaB)are chemically similar ,but pre-existing phase associations have been overprinted by the effects of several later metamorphic events.Non0peridotitic area B protoliths appear to be more magnesian ,averaging-12wt.%MgO(versus-7wt.%for area A),and are slightly less fractionated in REE concentrations relative to chondrites(La-Lu=30-8X versus 37-14X for area A),thus perhaps being more mantle-like than area A metabasaltic analogues.The basaltic-komatiitic series east of Bohai Bay probably represents the most ancient crust of that region,being invaded by Archean tonalities,which were subsequently converted to orthogneisses.These observations are compatible with the hypothesis that ,similar to area A metabasaltic rocks now found as amphibolitic inclusions in orthogneisses,are B mafic supracrustals were formed during Early of Middle Archean time ,prior to widespread isofacial amphibolite facies metamorphism(600-700℃,5-7kb,low αH2O).

Petrochemical comparison of 3.5 Ga old mafic amphibolite inclusions from eastern Hebei province with Archean mafic — ultramafic supracrustals of uncertain antiquity,southern Jilin eastern Liaoning provinces,China

New major element data for coexisting minerals and bulk-rock REE analyses, combined with previously obtained petrologic/geologic information, allow comparison of Archean mafic-ultramafic meta-igneous rocks from adjacent portions of northeastern Sino-Korean shield. Isotope data published by previous workers document an Early Archean age of formation for metabasaltic rocks now occurring as mafic amphibolite inclusions in tonalitic gneisses west of Bohai Bay (area A). Mafic-ultramafic mineral assemblages developed in amphibolite fades Archean supracrustals east of Bohai Bay (area B) are chemically similar, but pre-existing phase associations have been overprinted by the effects of several later metamorphic events. Non-peridotitic area B protoliths appear to be more magnesian, averaging ∼ 12 wt. % MgO (versus ∼ 7 wt. % for area A), and are slightly less fractionated in REE concentrations relative to chondrites (La-Lu=30-8X versus 37-14X for area A), thus perhaps being more mantle-like than area A metabasaltic analogues. The basaltic-komatiitic series east of Bohai Bay probably represents the most ancient crust of that region, being invaded by Archean tonalites, which were subsequently converted to orthogneisses. These observations are compatible with the hypothesis that, similar to area A metabasaltic rocks now found as amphibolitic inclusions in orthogneisses, area B mafic supracrustals were formed during Early or Middle Archean time, prior to widespread isofacial amphibolite facies metamorphism (600–700°C, 5–7 kb, low αH₂O). Institute of Geophysics and Planetary Physics Publication No. 3032.