Gondwana

About: Gondwana is a research topic. Over the lifetime, 6078 publications have been published within this topic receiving 263050 citations. The topic is also known as: Gondwanaland.

Geologic framework, tectonic evolution, and displacement history of the Alexander Terrane

Abstract: The Alexander terrane consists of upper Proterozoic(?)-Cambrian through Middle(?) Jurassic rocks that underlie much of southeastern (SE) Alaska and parts of eastern Alaska, western British Columbia, and southwestern Yukon Territory. A variety of geologic, paleomagnetic, and paleontologic evidence indicates that these rocks have been displaced considerable distances from their sites of origin and were not accreted to western North America until Late Cretaceous-early Tertiary time. Our geologic and U-Pb geochronologic studies in southern SE Alaska and the work of others to the north indicate that the terrane evolved through three distinct tectonic phases. During the initial phase, from late Proterozoic(?)-Cambrian through Early Devonian time, the terrane probably evolved along a convergent plate margin. Arc-type(?) volcanism and plutonism occurred during late Proterozoic(?)-Cambrian and Ordovician-Early Silurian time, with orogenic events during the Middle Cambrian-Early Ordovician (Wales orogeny) and the middle Silurian-earliest Devonian (Klakas orogeny). The second phase is marked by Middle Devonian through Lower Permian strata which accumulated in tectonically stable marine environments. Devonian and Lower Permian volcanic rocks and upper Pennsylvanian-Lower Permian syenitic to dioritic intrusive bodies occur locally but do not appear to represent major magmatic systems. The third phase is marked by Triassic volcanic and sedimentary rocks which are interpreted to have formed in a rift environment. Previous syntheses of the displacement history of the terrane emphasized apparent similarities with rocks in the Sierra-Klamath region and suggested that the Alexander terrane evolved in proximity to the California continental margin during Paleozoic time. Our studies indicate, however, that the geologic record of the Alexander terrane is quite different from that in the Sierra-Klamath region, and we conclude that the two regions were not closely associated during Paleozoic time. The available geologic, paleomagnetic, and paleontologic data are more consistent with a scenario involving (1) early Paleozoic origin and evolution of the Alexander terrane along the paleo-Pacific margin of Gondwana, (2) rifting from this margin during Devonian time, (3) late Paleozoic migration across the paleo-Pacific basin in low southerly paleolatitudes, (4) residence in proximity to the paleo-Pacific margin of South America during latest Paleozoic(?)-Triassic time, and (5) Late Permian(?)-Triassic rifting followed by northward displacement along the eastern margin of the Pacific basin.

Tectonic evolution of the Brasília Belt, Central Brazil, and early assembly of Gondwana

Abstract: Abstract The Brasília Belt comprises terranes and thrust-sheets that were tectonically transported towards the western passive margin of the São Francisco–Congo palaeocontinent during an orogenic episode resulting from collision of the Paranapanema and Goiás blocks and the Goiás magmatic arc against São Francisco–Congo at 0.64–0.61 Ga. The tectonic zones of the belt are, from east to west: a foreland zone with Archaean–Palaeoproterozoic granite–greenstone basement covered by Neoproterozoic anchimetamorphic sedimentary rocks (Bambuí Group); a low metamorphic grade thrust-fold belt of proximal shelf successions, mostly siliciclastic, containing rare basement slivers; metamorphic nappes in upper greenschist to granulite facies of distal shelf and slope metasediments and subordinate tholeiitic metabasalts; the Goiás massif, possibly a microcontinent; and the Goiás magmatic arc. The accretion of these terranes against the western margin of the São Francisco–Congo palaeocontinent took place during an early phase of Gondwana supercontinent amalgamation, when terranes accreted around São Francisco–Congo to create a proto-West Gondwana landmass, around which subsequent collisional and accretionary events followed, such as those in the Borborema–Trans-Saharan province (c. 0.62–0.60 Ga); in the Ribeira–Araçuaí belt (c. 0.58 Ga); along the Araguaia and Paraguay belts (collision of Amazonia, c. 0.54–0.52 Ga); and the accretion of Cabo Frio terrane in the Ribeira Belt (c. 0.53–0.50 Ga).

Pacific subduction coeval with the Karoo mantle plume: the Early Jurasssic Subcordilleran belt of northwestern Patagonia

Abstract: The Early Mesozoic magmatism of southwestern Gondwana is reviewed in the light of new U-Pb SHRIMP zircon ages (181 ± 2 Ma, 181 ± 3 Ma, 185 ± 2 Ma, and 182 ± 2 Ma) that establish an Early Jurassic age for the granites of the Subcordilleran plutonic belt in northwestern Argentine Patagonia. New geochemical and isotopic data confirm that this belt represents an early subduction-related magmatic arc along the proto-Pacific margin of Gondwana. Thus, subduction was synchronous with the initial phase of Chon Aike rhyolite volcanism ascribed to the thermal effects of the Karoo mantle plume and heralding rifting of this part of the supercontinent. Overall, there is clear evidence that successive episodes of calc-alkaline arc magmatism from Late Triassic times until establishment of the Andean Patagonian batholith in the Late Jurassic involved westerly migration and clockwise rotation of the arc. This indicates a changing geodynamic regime during Gondwana break-up and suggests differential rollback of the subducted slab, with accretion of new crustal material and/or asymmetrical ‘scissor-like’ opening of back-arc basins. This almost certainly entailed dextral displacement of continental domains in Patagonia.