ABSTRACT
This paper describes the first discovery of eclogite-facies rocks in the Paleozoic Chuacús basement complex of north-central Guatemala. In this area, the complex comprises a thick, polyde-formed sequence of high-Al metapelite, amphibolite, and quartzofeldspathic banded gneisses and schists characterized by garnet, phengite, and kyanite. Detailed petrographic, electronprobe microanalyses, and a late Carboniferous U-Pb zircon apparent age indicate that this deeply rooted orogenic terrane may be related to the Alleghenian suturing between Gondwana and Laurentia. Eclogite-facies metamorphism is established by assemblages with omphacite-garnet-rutile ± phengite ± zoisite in mafic rocks, which are consistent with garnet-kyanite-zoisite-rutile-quartz-phengite ± staurolite ± chloritoid assemblages in pelitic rocks, and amphibole-calcite/dolomite/aragonite?-rutile-quartz-zoisite ± clinochlore ± diopside in marbles. Moreover, various textural and mineralogical features (such as radial cracks in garnet and kyanite around quartz inclusions; palisade-like coronas of a silica mineral around quartz in some carbonates; lamellar inclusions of a titaniferous phase in garnet, zoisite, and phengite; and plagioclase or white mica in some omphacite; as well as the relatively high Na2O content of garnet [up to 0.12 wt%]), suggest relict ultrahigh-pressure metamorphism (UHPM). These conditions predated high-temperature–high-pressure hydration and decompression melting that occurred between 18 and 23 kbar and 700–770°C. This decompressional melting event of eclogitic rocks is dated as late Carboniferous by U-Pb on discordant zircons from a leucocratic neosome, and may be associated with the initial closure of Pangea. K-Ar ages of ~70–75 Ma on micas and amphibole, stable at 14 kbar and 597°C, are interpreted to record the Cretaceous obduction of Caribbean ophiolites and arc assemblages onto the Chuacús complex and the southern edge of the Maya block, along the paleo-Motagua fault zone.
