MESOPROTEROZOIC TO LATE PALEOZOIC SUPERCONTINENT COLLISIONS AND FRAGMENTATION - THE RECORD FROM SOUTH-CENTRAL LAURENTIA AND INSIGHTS FROM ZIRCON U/PB DATA

Structures and strata of south-central Laurentia record supercontinent interactions from Grenvillian orogenesis and assembly of Rodinia, to its fragmentation by rifting, to the amalgamation of Pangaea. Emerging zircon U/Pb data from the Llano and Devils River Uplifts (Texas) and from Cuyania (southern Laurentia-derived terrane, Argentina) provide insight to Grenvillian tectonism, magmatism and metamorphism. Grains from Mesoproterozoic felsic gneisses of the DRU (LA-ICPMS) yield uniform U-Pb crystallization ages of ~1230 +/- 5 Ma [cf. protolith ages of 1238 - 232 Ma for Grenvillian granitic orthogneisses in Llano Uplift]. In Cuyania detrital zircons dated from 1228 to 1240 Ma have been recovered from schists and metasandstones in the Neoproterozoic to Lower Cambrian Caucete Group, Sierra Pie de Palo. Younger Grenvillian grains, including volcanic zircons (1070-1030 Ma), predominate in upper Mid- to Upper Cambrian metamorphic and sedimentary rocks of the DRU. An analogous population (youngest peak ages 1081 to 1038 Ma) is dominant in metasiliciclastics of the Western Sierras Pampeanas.

Pangaea assembly during Early Carboniferous to Early Permian time resulted in both plate-margin and intraplate deformation in the region, expressed in the thin-skinned Ouachita-Marathon fold-thrust belt and in basement-cored Ancestral Rocky Mt. uplifts (Florida-Moyotes, Placer de Guadalupe–Carrizalillo, Ojinaga–Tascotal and Hueco Mts. blocks, the Diablo and Central Basin Platforms). During collision, igneous and metamorphic rocks were exhumed in the Marathon belt – rocks that provide critical geochronologic data on pre-Pangaean events.

Between supercontinent collisions there were Cryogenian (700-780 Ma) and Eocambrian (600-500 Ma) episodes of intraplate magmatism in southern Laurentia, related to rifting of Rodinia and opening of Iapetus. Zircon U/Pb data from unmetamorphosed volcanic boulders in Ordovician debris flows in the Marathon Basin (SHRIMP), from Lower to Mid-Cambrian metasediments/ metavolcanics on Devils River Uplift (LA-ICPMS), and from metamorphic rocks of like composition in Cuyania (LA-ICPMS) attest to their shared early history. By 450 Ma the rifted Cuyania terrane had been accreted to the proto-Andean margin.

Structures and strata of south-central Laurentia record supercontinent interactions from Grenvillian orogenesis and assembly of Rodinia, to its fragmentation by rifting, to the amalgamation of Pangaea. Emerging zircon U/Pb data from the Llano and Devils River Uplifts (Texas) and from Cuyania (southern Laurentia-derived terrane, Argentina) provide insight to Grenvillian tectonism, magmatism and metamorphism. Grains from Mesoproterozoic felsic gneisses of the DRU (LA-ICPMS) yield uniform U-Pb crystallization ages of ~1230 +/- 5 Ma [cf. protolith ages of 1238 - 232 Ma for Grenvillian granitic orthogneisses in Llano Uplift]. In Cuyania detrital zircons dated from 1228 to 1240 Ma have been recovered from schists and metasandstones in the Neoproterozoic to Lower Cambrian Caucete Group, Sierra Pie de Palo. Younger Grenvillian grains, including volcanic zircons (1070-1030 Ma), predominate in upper Mid- to Upper Cambrian metamorphic and sedimentary rocks of the DRU. An analogous population (youngest peak ages 1081 to 1038 Ma) is dominant in metasiliciclastics of the Western Sierras Pampeanas.

Pangaea assembly during Early Carboniferous to Early Permian time resulted in both plate-margin and intraplate deformation in the region, expressed in the thin-skinned Ouachita-Marathon fold-thrust belt and in basement-cored Ancestral Rocky Mt. uplifts (Florida-Moyotes, Placer de Guadalupe–Carrizalillo, Ojinaga–Tascotal and Hueco Mts. blocks, the Diablo and Central Basin Platforms). During collision, igneous and metamorphic rocks were exhumed in the Marathon belt – rocks that provide critical geochronologic data on pre-Pangaean events.

Between supercontinent collisions there were Cryogenian (700-780 Ma) and Eocambrian (600-500 Ma) episodes of intraplate magmatism in southern Laurentia, related to rifting of Rodinia and opening of Iapetus. Zircon U/Pb data from unmetamorphosed volcanic boulders in Ordovician debris flows in the Marathon Basin (SHRIMP), from Lower to Mid-Cambrian metasediments/ metavolcanics on Devils River Uplift (LA-ICPMS), and from metamorphic rocks of like composition in Cuyania (LA-ICPMS) attest to their shared early history. By 450 Ma the rifted Cuyania terrane had been accreted to the proto-Andean margin.