Terrane

About: Terrane is a research topic. Over the lifetime, 11025 publications have been published within this topic receiving 442596 citations. The topic is also known as: tectonostratigraphic terrane.

Late Paleozoic to Triassic evolution of the Gondwana margin: Evidence from Chilean Frontal Cordilleran batholiths (28°S to 31°S)

Abstract: Upper Paleozoic to Triassic Chilean granitoids in the Andean Frontal Cordillera between 28°S and 31°S record crustal and mantle conditions at the Gondwana margin during the final assembly and initial breakup of the Pangea supercontinent. This period overlaps the end of Paleozoic terrane accretion and precedes Andean subduction. Integration of new trace-element and isotopic data with other information on the granitoids and the regional geology leads to a tectonic model that has implications for other parts of the Gondwana margin. In the model, the Carboniferous to Early Permian is a period of oblique convergence. Associated Elqui complex granitoids are diverse. Those in the Guanta and Montosa units are predominantly related to subduction processes, whereas those in the Cochiguas and El Volcan units are dominated by melting of the subduction complex and older crust. Progressive oblique collision of the last pre-Pangea terrane (Equis) along the margin resulted in crustal thickening associated with shortening deformation of foreland basinal sedimentary rocks and uplift of the Elqui complex. Subsequent gravitational collapse of the inactive slab and lithospheric delamination resulted in the production of large amounts of basalt, which intruded and melted the crust, producing the post-collisional Ingaguas complex. The Los Carricitos granitoids formed in thickened crust, whereas the Chollay, El Colorado, and El Leon units formed in thinner crust. The Ingaguas complex is part of the Choiyoi granite-rhyolite province, whose formation, similar to that of other Gondwana silicic provinces, was probably accentuated by anomalously hot upper mantle associated with the Pangea supercontinent.

Late Caledonian (Acadian) transpression in north-west England: timing, geometry and geotectonic significance

Abstract: SUMMARY The late Caledonian structure of the Lower Palaeozoic slate belts which lie to the south of the Iapetus suture in Britain is not ‘Caledonoid’ (NE-SW) but characterised by arcuate trends. The significance of the major cleavage arc of northern England is the subject of this paper. Its exposed part, in the Lake District and adjacent inliers, is described and its regional extent inferred from the control exerted by Caledonian basement trends on early Carboniferous sedimentation patterns. The arc is shown to be a major feature of the orogen, marking a change from a NE-SW ‘Appalachian’ trend to the ESE-WNW ‘Tornquist’ trend of northern Germany and Poland. Evidence for the age of deformation in the British slate belts is reviewed. It is shown that the deformation was not ‘end-Silurian’ as previously supposed, but of early Devonian age, climaxing in the Emsian and approximately synchronous with the Acadian orogeny of Canada. The systematic variation in cleavage/fold transection angles around the arc is described and interpreted in terms of transpressive strains associated with the northward movement of a basement block, the Midlands Massif, which acted as a rigid indenter during accretion of the southern British terrane (Eastern Avalonia) onto the Laurentian margin. These new data on the timing and geometry of the Acadian accretion event in Britain go some way to resolving the current controversy concerning late Ordovician vs. Devonian closure of Iapetus.

Seismic polarization anisotropy beneath the central Tibetan Plateau

Abstract: SKS and SKKS shear waves recorded on the INDEPTH III seismic array deployed in central Tibet during 1998–1999 have been analyzed for the direction and extent of seismic polarization anisotropy. The 400-km-long NNW trending array extended south to north, from the central Lhasa terrane, across the Karakoram-Jiali fault system and Banggong-Nujiang suture to the central Qiangtang terrane. Substantial splitting with delay times from 1 to 2 s, and fast directions varying from E-W to NE-SW, was observed for stations in the Qiangtang terrane and northernmost Lhasa terrane. No detectable splitting was observed for stations located farther south in the central Lhasa terrane. The change in shear wave splitting characteristics occurs at 32°N, approximately coincident with the transcurrent Karakoram-Jiali fault system but ∼40 km south of the surface trace of the Banggong-Nujiang suture. This location is also near the southernmost edge of a region of high Sn attenuation and low upper mantle velocities found in previous studies. The transition between no measured splitting and strong anisotropy (2.2 s delay time) is exceptionally sharp (≤15 km), suggesting a large crustal contribution to the measured splitting. The E-W to NE-SW fast directions are broadly similar to the fast directions observed farther east along the Yadong-Golmud highway, suggesting that no large-scale change in anisotropic properties occurs in the east-west direction. However, in detail, fast directions and delay times vary over lateral distances of ∼100 km in both the N-S and E-W direction by as much as 40° and 0.5–1 s, respectively. The onset of measurable splitting at 32°N most likely marks the northern limit of the underthrusting Indian lithosphere, which is characterized by negligible polarization anisotropy. Taken in conjunction with decades of geophysical and geological observations in Tibet, the new anisotropy measurements are consistent with a model where hot and weak upper mantle beneath northern Tibet is being squeezed and sheared between the advancing Indian lithosphere to the south and the Tsaidam and Tarim lithospheres to the north and west, resulting in eastward flow and possibly thickening and subsequent detachment due to gravitational instability. In northern Tibet, crustal deformation clearly follows this large-scale deformation pattern.