Search results for "Mafic"

A layered basic intrusion, deformed and metamorphosed in granulite faciès of the Sri Lanka basement

1991

A layered basic intrusion has been found in the Central Granulite Belt of the Sri Lanka continental basement. It intruded parallel to bedding, before all or early during deformation of neighbouring metasediments. Deformation, affecting metasediments and the intrusion alike, includes flattening to c. 1/20 of the original thickness and NNW-stretching to c. 20 times the original length. The intrusion is now 170–300 m thick. Most of the deformation was acquired under granulite facies metamorphism. The intrusion was then folded, still at high T, by a large F4-synform with an axis parallel to str1 and a steep axial plane. A steep axial plane cleavage and minor folds are related to this big fold. …

Geochemistry and origin of ultramafic enclaves and their basanitic host rock from Kula Volcano, Turkey

2013

Abstract The Quaternary Kula Volcanic Province is located in western Anatolia, Turkey. This Na-alkaline anorogenic volcanism includes exposures of around 80 cinder cones, lava flows, and tuffs, representing one of the youngest volcanic activities in this region (1.9–0.026 Ma). The magmatism is related to an extensional regime and is interpreted as being derived predominantly from the asthenospheric mantle. The lava flows are mostly of a basanitic composition and host rare comagmatic enclaves. The enclaves are composed of two dominant lithologies: amphibolites and clinopyroxenites with and without olivine. Amphibole is usually resorbed and replaced by a rhoenite-rich breakdown corona. The mi…

Internal Differentiation of the Archean Continental Crust: Fluid-Controlled Partial Melting of Granulites and TTG-Amphibolite Associations in Central…

2009

Fault bound blocks of granulite and enderbite occur within upper amphibolite-facies migmatitic tonalitic-trondhjemitic-granodioritic (TTG) gneisses of the Iisalmi block of Central Finland. These units record reworking and partial melting of different levels of the Archean crust during a major tectonothermal event at 2·6-2·7 Ga. Anhydrous mineral assemblages and tonalitic melts in the granulites formed as a result of hydrous phase breakdown melting reactions involving amphibole at peak metamorphic conditions of 8-11 kbar and 750-900°C. A nominally fluid-absent melting regime in the granulites is supported by the presence of carbonic fluid inclusions. The geochemical signature of light rare e…

Geochemistry, zircon ages and whole-rock Nd isotopic systematics for Palaeoproterozoic A-type granitoids in the northern part of the Delhi belt, Raja…

2006

Determination of zircon ages as well as geochemical and Sm–Nd isotope systematics of granitoids in the Khetri Copper Belt of the Aravalli mountains, NW India, constrain the late Palaeoproterozoic crustal evolution of the Aravalli craton. The plutons are typical A-type within-plate granites, derived from melts generated in an extensional tectonic environment. They display REE and multi-element patterns characterized by steep LREE-enriched and almost flat HREE profiles and distinct negative anomalies for Sr, P and Ti. Initial εNd values range from −1.3 to −6.2 and correspond to crustal sources with mean crustal residence ages of 2.5 to 2.1 Ga. A lower mafic crustal anatectic origin is envisag…

RELATIONSHIPS BETWEEN MAFIC AND FELSIC MAGMATISM AT PANTELLERIA: A PETROLOGICAL STUDY ON INTERMEDIATE TRACHYTE MAGMAS

2011

Plume — Lid interactions during the Archean and implications for the generation of early continental terranes

2020

Abstract Many Archean terranes are interpreted to have a tectonic and metamorphic evolution that indicates intra-crustal reorganization driven by lithospheric-scale gravitational instabilities. These processes are associated with the production of a significant amount of felsic and mafic crust, and are widely regarded to be a consequence of plume-lithosphere interactions. The juvenile Archean felsic crust is made predominantly of rocks of the tonalite–trondhjemite–granodiorite (TTG) suite, which are the result of partial melting of hydrous metabasalts. The geodynamic processes that have assisted the production of juvenile felsic crust, are still not well understood. Here, we perform 2D and …

Evolution of the middle Paleozoic magmatism in the Chinese Altai: Constraints on the crustal differentiation at shallow depth in the accretionary oro…

2019

Abstract The Chinese Altai underwent intensive mafic and felsic magmatism in the middle Paleozoic, which was the most important magmatic event in the region. It is still unclear for the role of the event in formation of the crust that is thick (∼56 km) and has structure of three-layer stratification. In this study, the data for the middle Paleozoic mafic rocks and granites are comprehensively compiled and integrated with new geochronological, petrological, geochemical and Sr-Nd-Pb isotopic data for gabbroic rocks from Keketuohai area and tonalite and biotite granites from Habahe area. The middle Paleozoic mafic rocks exhibit two evolutionary trends, which can be defined as high-Al and low-A…

Roots of an Archean volcanic arc complex: the Lac des Iles area in Ontario, Canada

1997

Abstract The Lac des Iles area is located in the Wabigoon Subprovince, an Archean granite-greenstone terrain in the Superior Province in Ontario, Canada. The area consists of several unmetamorphosed plutons of biotite- and hornblende-tonalite and mafic and ultramafic intrusions which are emplaced into an older tonalitic gneiss. The mafic/ultramafic bodies are concentric in shape and consist of periodotite, pyroxenite, gabbro and hornblende gabbro cumulates and diorite. The largest intrusion, the Lac des Iles complex, consists of several mafic and ultramafic centers. An internal SmNd isochron from the southern ultramafic complex gives an intrusion age of 2736 ± 28 Ma (MSWD = 1.5; ϵNd(t) = 1…

Zircon ages for high pressure granulites from South Bohemia, Czech Republic, and their connection to Carboniferous high temperature processes

2000

Petrological and isotopic investigations were undertaken on high pressure granulites of granitic to mafic composition from the Prachatice and Blanský les granulite complexes of southern Bohemia, Czech Republic. The predominant felsic granulites are quartz + ternary feldspar (now mesoperthite)-rich rocks containing minor garnet, kyanite and rutile, and most show a characteristic mylonitic fabric formed during retrogression along the exhumation path. Three high temperature reaction stages at distinctly different pressures are recognized. Rare layers of intermediate to mafic composition, containing clinopyroxene, best record a primary high pressure–high temperature stage (>15 kbar, >900 °C), a…

Geochemical characteristics of Archaean and Late Proterozoic to Palaeozoic fine-grained sediments from Southern Africa and significance for the evolu…

1985

Chemical data for pelitic rocks (shallow-marine platform sediments) of the ∼ 2.9 Ga old Pongola Supergroup, South Africa, and the 550–700 Ma old Nama Group, Namibia, revealed clearly different compositions in both groups. A comparison of the Pongola and Nama data with literature values for sedimentary rocks shows a trend for Cr/TiO2 and Cr/Zn ratios as well as the absolute Cr and Ni concentrations to lower values with decreasing age, whereas the Cr/Ni ratios seem to remain broadly constant through time. REE patterns of Pongola and Nama sediments show no significant difference, thus giving the impression of a post-Archaean origin for the demonstrably Archaean Pongola sediments. However, a pl…