Search results for "Facies"
showing 10 items of 232 documents
Extensive magmatism and metamorphism at ca. 3.2 Ga in the eastern Kaapvaal Craton
2020
Abstract The timing of the emergence of modern-style plate tectonics on Earth is of fundamental importance in understanding the thermal and compositional history of the planet. Although the magmatism and metamorphism in the eastern Kaapvaal Craton was thought by some as geological records for mid-Archean subduction at 3.2 Ga, their petrogenesis was fiercely debated. To reveal the nature of the 3.2 Ga magmatism and metamorphism in the eastern Kaapvaal Craton, here we provide a comprehensive zircon and monazite U-Pb geochronological investigation, coupled with in situ trace element and Hf-O isotopic analyses, for the magmatic and metamorphic rocks from the Barberton granitoid-greenstone terra…
Pathways and fate of REE in the shallow hydrothermal aquifer of Vulcano island (Italy)
2019
Abstract We investigated the geochemical behaviour of major and Rare Earth Elements (REE), together with oxygen and deuterium isotopic composition in the aquifer of Vulcano, the southernmost island of the Aeolian archipelago (Italy). Studied wells, located at different distances from the crater, are characterised by different contributions of the rising volcanic fluids. In particular, those located in the proximity of La Fossa crater are affected by a strong interaction with volcanic-hydrothermal fluids and show REE behaviour similar to that of fresh rocks, suggesting a congruent dissolution of the solid matrix. Samples from the other wells, located in an area where the volcanic deposits ar…
Zircon geochronology and metamorphic evolution of mafic dykes in the Hengshan Complex of northern China: Evidence for late Palaeoproterozoic extensio…
2006
Abstract Magmatic and metamorphic zircons have been dated from ductilely deformed gabbroic dykes defining a dyke swarm and signifying crustal extension in the northern part of the Hengshan Complex of the North China Craton. These dykes now occur as boudins and deformed sheets within migmatitic tonalitic, trondhjemitic, granodioritic and granitic gneisses and are conspicuous due to relics of high-pressure granulite or even former eclogite facies garnet + pyroxene-bearing assemblages. SHRIMP ages for magmatic zircons from two dykes reflect the time of dyke emplacement at ∼1915 Ma, whereas metamorphic zircons dated by both SHRIMP and evaporation techniques are consistently in the range 1848–18…
Birth and Early evolution of a Jurassic Escarpment: Monte Kumeta, Western Sicily
2002
The accurate reconstruction of the facies architecture in the Jurassic succession of Monte Kumeta, coupled with a detailed biostratigraphy, allow to define dynamics and genetic factors controlling the conversion of a Bahamian-type carbonate platform to a pelagic escarpment. A change from tidalites to oolites i.e. from the restricted, interior lagoon to a more open-marine sandy depositional environment, records the establishment of a basin south of the Monte Kumeta sector in late Hettangian-Sinemurian times. The oolitic limestones are overlain by earliest Carixian bioclastic grainstones and packstones with micritized grains and by wackestones with radiolarians and sponge spicules, organized …
A ∼700 Ma Sm–Nd garnet–whole rock age from the granulite facies Central Kaoko Zone (Namibia): Evidence for a cryptic high-grade polymetamorphic histo…
2007
Continental collision of the Kalahari and the Congo craton in Africa and the Rio de la Plata Craton in South America resulted in a structurally complex Neoproterozoic belt system, the Kaoko–Dom Feliciano–Ribeira belt. It is uncertain whether these three cratons collided more or less simultaneously during one single orogenic event at ∼580–550 Ma or whether the belt owe its structural and metamorphic features to several so far poorly constrained events. The Kaoko Belt (NW Nambia), representing the belt system between the southern Congo Craton and the Rio de la Plata Craton, is an ideal object to study these complexities. Within this belt, high-grade meta-igneous and metasedimentary rocks of t…
Geology of the Bozdag area, central Menderes massif, SW Turkey: Pan-African basement and Alpine deformation
1998
The Menderes massif consists of a Precambrian Core Series that preserves evidence for a polymetamorphic history and a Paleozoic/Mesozoic Cover Series that experienced only the Alpine tectonometamorphic evolution. Structural, petrographic, and geochronologic investigations in the central Menderes massif demonstrate that (a) part of the metamorphic and structural evolution of the Precambrian basement is older than the undeformed 551+/-1.4-Ma-old Birgi metagranite, and (b) inferred Alpine fabrics overprinting the Cover Series largely have the same attitudes as the old structures in the much older Core Series. The inferred Alpine fabrics include both contractional and extensional structures. Co…
Structural and thermal history of poly-orogenic basement: U-Pb geochronology of granitoid rocks in the southern Menderes Massif, Western Turkey
2004
Ion microprobe U-Pb dating of granitoid rocks from key structural outcrops of the Menderes Massif in western Turkey provides an important constraint to the thermal and deformational history of a structurally complex metamorphic belt within the Alpine chain. Crystallization ages of two granite protoliths, derived from the weighted means of rim ages and the ages of homogeneous prismatic zircon grains, are 541 +/- 14 Ma and 566 +/- 9 Ma, whereas the cores of zoned pyramidal and short-prismatic zircon grains range from Palaeoproterozoic to Neoproterozoic in age. These ages indicate that amphibolite- to gramilite-facies metamorphic rocks in much of the Menderes Massif were deformed, metamorphose…
Aspects of the kinematic history and mechanisms of superposition of the proterozoic mobile belts of eastern Central Africa (northern Malawi and south…
1993
Abstract Commonly the Proterozoic tectonic evolution of the Central African basement is subdivided into three major events: (1) the Ubendian (∼2300−1800 Ma), (2) the Irumide (∼1350−950 Ma), and (3) the Pan-African (∼900−450 Ma) orogenic cycles. Relics of the Ubendian event are granite intrusions and, possibly, an amphibolite- to granulite-facies metamorphism. The Ubendian orogeny was followed by deposition of clastic sediments (Muva supergroup). In northern Malawi these sediments and the underlying basement were then thrust to the east-southeast/southeast during the Irumide orogeny. Horizontal shearing along subvertical zones (i.e. the Ubendian belt) was associated with subhorizontal crusta…
Inner vs. outer wedge-top depozone “sequences” in the Late Miocene (late Tortonian–early Messinian) Sicilian Foreland Basin System; new data from the…
2012
Abstract The wedge-top depozone belongs to the innermost portion of a Foreland Basin System (FBS) ( DeCelles and Giles, 1996 ) and includes all sediments, typically coarse-grained proximal facies, that bury the active frontal part of a fold and thrust belt. The Terravecchia Formation ( Flores, 1959 , Schmidt Di Friedberg, 1962 , Schmidt Di Friedberg, 1964 , Catalano, 1979 ) is a composite lithostratigraphic unit widespread in Sicily (southern Italy) which has been recently considered ( Gugliotta, 2010 ) as a part of the stratigraphic record of the Late Miocene (late Tortonian to early Messinian) Sicilian wedge-top depozone and represent the main object of this paper. Two end-member wedge-to…
Resorption, growth, solid state recrystallisation, and annealing of granulite facies zircon—a case study from the Central Erzgebirge, Bohemian Massif
2005
Zircon crystals have been investigated from a gneiss area in the Central Erzgebirge, Bohemian Massif, where small occurrences/lenses of granulites (and sometimes eclogites) are located within amphibolite facies gneisses. Geological relationships indicate that leucocratic quartzofeldspathic rocks within the granulite boudins represent melts, whereas garnet-rich melanocratic rocks are considered restites, derived through multiple extraction of the leucocratic melts. The morphology of zircon crystals is quite different in these two types of granulites, with rounding pointing to higher zircon resorption in garnet-rich rocks due to multiple interaction with melts. Extensive new zircon growth can…