Search results for "Metamorphism"
showing 10 items of 174 documents
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…
Age and evolution of a late Archean to Paleoproterozoic upper to lower crustal section in the Wutaishan/Hengshan/Fuping terrain of northern China
2005
Abstract The Taihangshan–Wutaishan area forms part of the central North China Craton and consists of three main components: the Hengshan and Fuping complexes, containing predominantly ductilely deformed late Archean to Paleoproterozoic high-grade granitoid orthogneisses, intruded by mafic dykes of gabbroic composition, and the low-grade late Archean Wutai greenstone belt, developed between the high-grade terrains and consisting of bimodal volcanic rocks and metasediments, associated with coeval granitoids. Zircon dating shows that both the Hengshan and Fuping complexes were intruded by major granitoid bodies between 2.52 and 2.48 Ga, with rare occurrences of 2.7 Ga gneisses. Wutai granitoid…
Palaeoproterozoic crustal accretion and collision in the southern Capricorn Orogen: the Glenburgh Orogeny
2004
Abstract The Capricorn Orogen in central Western Australia records the Palaeoproterozoic collision of the Archaean Pilbara and Yilgarn Cratons. Until recently only one orogenic event was thought to be the cause of this collision, the 1830–1780 Ma Capricorn Orogeny. However, recent work has uncovered an older event, the Glenburgh Orogeny that occurred between 2000 and 1960 Ma. The Glenburgh Orogeny reflects the collision of a late Archaean to Palaeoproterozoic microcontinent (the Glenburgh Terrane) with the Archaean Yilgarn Craton and is therefore tectonically distinct as well as significantly older than the widespread 1900–1800 Ma tectonothermal events recorded in northern Australia. The Gl…
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…
Single zircon ages from high-grade rocks of the Jianping Complex, Liaoning Province, NE China
1998
Abstract The high-grade rocks of the Jianping Complex in Liaoning Provi nce, NE China, belong to the late Archaean to earliest Proterozoic granulite belt of the North China craton. Single zircon ages obtained by the Pb–Pb evaporation method and SHRIMP analyses document an evolutionary history that began with deposition of a cratonic supracrustal sequence some 2522–2551 Ma ago, followed by intrusion of granitoid rocks beginning at 2522 Ma and reaching a peak at about 2500 Ma. This was followed by high-grade metamorphism, transforming the existing rocks into granulites, charnockites and enderbites some 2485–2490 Ma ago. The intrusion of post-tectonic granites at 2472 Ma is associated with wid…
Mesoproterozoic (Grenville-age) terranes in the Kyrgyz North Tianshan: Zircon ages and Nd–Hf isotopic constraints on the origin and evolution of base…
2013
Abstract The North Tianshan orogenic belt in Kyrgyzstan consists predominantly of Neoproterozoic to early Paleozoic assemblages and tectonically interlayered older Precambrian crystalline complexes and formed during early Paleozoic accretionary and collisional events. One of the oldest continental fragments of late Mesoproterozoic (Grenvillian) age occurs within the southern part of the Kyrgyz North Tianshan. Using SHRIMP zircon ages, we document two magmatic events at ~ 1.1 and ~ 1.3 Ga. The younger event is characterized by voluminous granitoid magmatism between 1150 and 1050 Ma and is associated with deformation and metamorphism. The older event is documented by ~ 1.3 Ga felsic volcanism…
Zircon evaporation ages and geochemistry of metamorphosed volcanic rocks from the Vinjamuru domain, Krishna Province: evidence for 1.78 Ga convergent…
2012
Palaeoproterozoic intermediate to potassic felsic volcanism in volcano-sedimentary sequences could either have occurred in continental rift or at convergent magmatic arc tectonic settings. The Vinjamuru domain of the Krishna Province in Andhra Pradesh, SE India, contains such felsic and intermediate metavolcanic rocks, whose geochemistry constrains their probable tectonic setting and which were dated by the zircon Pb evaporation method in order to constrain their time of formation. These rocks consist of interlayered quartz–garnet–biotite schist, quartz–hematite–baryte–sericite schist as well as cherty quartzite, and represent a calc-alkaline volcanic sequence of andesitic to rhyolitic rock…
Geochronology of the Hout River Shear Zone and the metamorphism in the Southern Marginal Zone of the Limpopo Belt, Southern Africa
2001
Abstract In this paper monazite U–Pb and zircon evaporation dates, stepleaching Pb/Pb results on garnet, staurolite and kyanite, and hornblende Ar/Ar data are presented which constrain the timing of granulite facies metamorphism in the Southern Marginal Zone of the Limpopo Belt and its thrusting onto the Kaapvaal Craton. The Southern Marginal Zone of the Limpopo Belt is considered to be a lower crustal equivalent of the northern Kaapvaal Craton. Granulite exhumation is associated with southward thrusting along the Hout River Shear Zone which is a set of thrust and strike slip shear zones. Zircon ages for the Matok Intrusive Complex which was emplaced within the zone during this thrusting (c…
Pan-African high-pressure metamorphism in the Precambrian basement of the Menderes Massif, western Anatolia, Turkey
2001
The Menderes Massif is made up of Pan-African basement and a Paleozoic to Early Tertiary cover sequence imbricated by Late Alpine deformation. The Precambrian basement comprises primarily medium- to high-grade schists, paragneisses, migmatites, orthogneisses, metagranites, charnockites, and metagabbros. High-pressure relies in the Pan-African basement are divided into two groups: eclogites and eclogitic metagabbros. The mineral assemblage in the eclogites is omphacite (Jd 44)-garnet-clinozoisite-rutile. The eclogites occur as pods and boudinaged layers in the basement schists and paragneisses. Inclusions found in the cores of the garnets indicate a medium-pressure protolith. The eclogitic m…
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…