The north‐eastern part of the Chotanagpur Granite Gneiss Complex (CGGC) in the East Indian shield contains enclaves of migmatitic pelitic granulites (PG) within felsic orthogneiss (FOG). Field observations, petrology and geochronology (LA–MC–ICP–MS U–Pb dating of zircon and EPMA Th–U–total‐Pb dating of monazite) of the PG suggest two distinct metamorphic events. The earliest event M1, which is characterized by high‐temperature (>850°C) granulite facies metamorphism, occurred in the timespan of ~1680–1580 Ma. Extensive dehydration melting of biotite + sillimanite + quartz‐rich protoliths led to stabilization of the restitic assemblage (garnet + alkali‐feldspar + quartz + sillimanite + ferrian‐ilmenite) together with large volumes of felsic melts (leucosomes). Collisional tectonics followed by delamination and asthenospheric upwelling could have triggered the M1 event. Subsequently, at ~1470–1400 Ma, the igneous protolith of the host FOG intruded and hydrated the PG. Thereafter, a second metamorphic event, M2, accompanied by compressional structures, affected both the rock types. A clockwise P–T path that culminated at ≥10 kbar ~760–850°C and is followed by a steeply decompressive retrograde path characterizes this event. The P–T path and the inferred geothermal gradient (<27°C/km) are compatible with a continent–continent collisional setting. Geochronological findings suggest a protracted orogeny for the M2 event with its major pulse during ~970–950 Ma. When combined with the published information, this study supports the view that a large (if not the entire) portion of the Indian shield and the granulite terranes of east Antarctica share similar tectonothermal events that led to the formation of two supercontinents, Columbia and Rodinia.
The North Volcanic Zone of the Andes is the result of an overall uniform subduction of the Nazca Plate beneath the South American Plate in Ecuador and Colombia; however, age, composition, and thickness of the continental crust and the distance between the trench and arc, among other components of this subduction system, vary significantly along this segment of the Andes (Stern, 2004). Those changes are most likely responsible for differences in the geochemical characteristics of volcanic products in different parts of the Colombian arc as discussed in Monsalve (2020). Although several works related to the isotopic geochemistry of the volcanic products have been carried out in Ecuador (Bryan et al., 2006; Chiaradia et al., 2009, references therein), there are few records of the same type of data for Colombia and those available focus on the SW part of the arc (Marín-Cerón, 2007). This study seeks to fill the gap and use this new data to elucidate processes of magma generation and differentiation currently occurring under the northern Andes. Whole rock major elements, trace elements, and 176Hf/177Hf analyses from main volcanic centers along the Colombian arc are used to track lithospheric and crustal processes of mixing, assimilation, and fractional crystallization as well as the main source materials and contributions in magma generation in the subduction zone. From a broader view, this new data helps to discuss regional comparisons of the geochemical expressions in the Andean arcs caused by different tectono-magmatic processes.   Bryant, J.A., Yogodzinski, G.M., Hall, M.L., Lewicki, J.L. & Bailey, D.G. (2006). Geochemical constraints on the origin of volcanic rocks from the Andean Northern Volcanic Zone, Ecuador. Journal of Petrology, 47(6): 1147–1175. Chiaradia, M., Müntener, O., Beate, B., & Fontignie, D. (2009). Adakite-like volcanism of Ecuador: lower crust magmatic evolution and recycling. Contributions to Mineralogy and Petrology, 158, 563-588. Marín–Cerón, M.I. (2007). Major, trace element and multi–isotopic systematics of SW Colombian volcanic arc, northern Andes: Implication for the stability of carbonate–rich sediment at subduction zone and the genesis of andesite magma. Doctoral thesis, Okayama University, 140 p. Okayama, Japan. Monsalve–Bustamante, M.L. (2020). The volcanic front in Colombia: Segmentation and recent and historical activity. In: Gómez, J. & Pinilla–Pachon, A.O. (editors), The Geology of Colombia, 97–159. Stern, C.R. (2004). Active Andean volcanism: its geologic and tectonic setting. Revista geológica de Chile, 31(2), 161-206.
From the Late Cretaceous to the Quaternary, the northeastern end of the Eurasian margin experienced a complicated tectono-magmatic history including the subduction of the Izanagi-Pacific ridge in the Eocene time, the opening of the Japan and Kuril basins and the associated trench migration in the Oligocene to Miocene time, the possible collision of the Eurasian plate and the North American (Okhotsk) plate around the Oligocene to Miocene time, and subduction zone magmatism in all periods. In central Hokkaido (Japan), Eocene-Miocene plutonic bodies are distributed along the north-south orientated Hidaka Magmatic Zone (HMZ). We report new zircon U-Pb ages and geochemical data from plutonic rocks in the HMZ, which reveal Miocene compositionally bimodal magmatism; the felsic magmatism present is characterized by island-arc geochemical signatures. Trace element compositions of the Miocene mafic-intermediate plutonic rocks of the HMZ appear as a mixture between typical N-MORB and island-arc compositions. Trace element profiles from HMZ plutonic rocks are similar, albeit with less pronounced arc signatures, to the Miocene volcanic rocks formed along the Paleo-Japan Trench. Together, these data suggest the coexistence and mixing of N-MORB-type primitive magma, with the parental magmas of the HMZ mafic rocks, implying petrogenesis of a different nature than typical subduction zone magmatism. The cause of the north-south orientation of the Miocene plutono-volcanic rocks from central Hokkaido to its northern extension into Russia (Sakhalin) is probably along some kind of tectonic/structural boundary. However, the inferred paleo-position of the HMZ is very close to the trench and far from the volcanic front at that time and the existence of N-MORB-type primitive magma cannot be explained by subduction magmatism. The newly proposed possible geodynamic setting in this study that can reasonably explain the distribution and geochemical signature of these rocks is the simultaneous opening of the Japan and Kuril basins at different rates. In the Japan Trench, the Pacific plate was subducted at a relatively shallow angle and the magmatic arc forcibly moved eastward due to the opening of the Japan Basin. In the Kuril Trench, the rollback corresponding to the steep subduction of the plate and the associated opening of the Kuril Trench occurred simultaneously in a short period of time. If the Paleo-Kuril Trench retreated rapidly relative to that of the Paleo-Japan Trench, a horizontal propagating tear that cuts the slab horizontally is estimated to have occurred at the bend of both trenches, together with a (vertical) slab tearing and blocky opening of the subducting oceanic plate on the Paleo-Japan Trench side. At the western margin of the Kuril Basin, the N-MORB magma and hot asthenosphere inflow induced remelting of the mantle already contaminated to various degrees at the subduction zone.
The Cenozoic stratigraphic infill of hinterland and foreland basins in central Colombia holds the record of basin development during tectonic inversion of rift in the context of subduction orogenesis. A comprehensive review of detrital U–Pb geochronologic and thermochronologic data reveals that activation of interconnected fault systems in the hinterland Magdalena Valley and the Eastern Cordillera occurred coevally since Paleocene time. Longitudinal basins were fed by detritus shed from the Central Cordillera carried along axial drainage systems in open basins in times where slow deformation rates prevailed. Faster deformation since Oligocene resulted in the transient formation of internally drained basins. Differential along-strike exhumation and subsidence patterns in the Eastern Cordillera and the foredeep, respectively, document tectonic acceleration since late Miocene, which we attribute to superimposed collision of the Panama arc leading to oroclinal bending in the Cordillera. Our data documents that the inherited structural grain led to the formation of longitudinal drainage patterns, even in closed basins, which seem to be a general feature of early stages of inversion. We hypothesize that the presence of more humid climatic conditions and faster tectonic rates along the range’s eastern margin favoured the development of internally drained basins, as has also been shown in the Central Andes.
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