Search results for "Precambrian"
showing 5 items of 65 documents
Ca. 1318 Ma A-type granite on the northern margin of the North China Craton: Implications for intraplate extension of the Columbia supercontinent
2012
Abstract Identification of the Mesoproterozoic A-type Jining granite and granite porphyry, which with abundant coeval mafic dike sills and volcanic rocks on the northern margin of the Precambrian North China Craton (NCC), may suggest intraplate extension of Columbia supercontinent. Major and trace elements of the Jining granite show an affinity to A-type granites, and may reflect an intraplate rift setting (A 1 ‐type granite). High Rb, Y, Yb, and Ta contents also show features of within-plate granites. SHRIMP zircon dating yielded concordant weighted mean 207 Pb/ 206 Pb ages of 1318 ± 7 Ma and 1321 ± 15 Ma, which define a Mesoproterozoic magmatic event. The zircons have negative e Hf(t) of …
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…
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…
Age of Palaeozoic granites and metamorphism in the Tuvino-Mongolian Massif of the Central Asian Mobile Belt: loss of a Precambrian microcontinent
2001
Abstract The Tuvino-Mongolian Massif (TMM) was previously interpreted as a Precambrian block within the Central Asian Mobile Belt. According to this idea, it consists of tectonic slices composed of metamorphic rocks of pre-Mesoproterozoic basement that experienced two episodes of regional metamorphism, and Mesoproterozoic ‘cover rocks’ that were reworked together with the basement during high-grade metamorphism. Zircon U–Pb dating of granitoids from all metamorphic complexes demonstrates that the earliest metamorphic event occurred at 536±6 Ma, significantly later than the deposition of the cover rocks. Regional upper amphibolite-facies metamorphism, which affected all metasedimentary units…
Elements of the Archean thermal history and apparent polar wander of the eastern Kaapvaal Craton, Swaziland, from single grain dating and paleomagnet…
1989
Abstract Single grains of zircon, hornblende, biotite and feldspar have been dated to define the thermal history of the Archean Mbabane Pluton, Swaziland. Coincident207Pb/206Pb zircon and40Ar/39Ar hornblende ages suggest that the pluton underwent rapid cooling to about 450°C at the time of emplacement at ∼ 2690 Ma. Because the Mbabane Pluton is one of a suite of granites which represent the last major Archean intrusive event in the eastern Kaapvaal Craton, this time of emplacement marks the end of cratonization. Much younger biotite and feldspar ages indicate argon loss, perhaps due to several low-temperature events related to dike intrusion at 2000–2300 Ma. From such a thermal history, the…