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Palaeomagnetic studies in the Malani Igneous Suite (ca. 770-750 Ma) of the Marwar Crustal Block, NW India, provide essential constraints on palaeogeographic reconstructions of the Rodinia Supercontinent. The Malani Igneous Suite is intrusive into megacrystic granite and granite-gneissic enclaves of the Marwar Crustal Block. A crustal-scale NE-SW ductile transpressional shear zone with a southeasterly dip known as the Phulad Shear Zone (820-810 Ma) separates this Marwar Crustal Block from the rocks farther east. The pre-shearing tectonic evolution of the Marwar Crustal Block is poorly understood. Three phases of ductile deformations (D1, D2, and D3, with associated fabrics S1, S2, and S3) were identified in the Marwar Crustal Block. The D1 deformation is restricted to enclave gneisses. The megacrystic granite was emplaced syn-tectonically during D2 deformation. The S2 magmatic foliation (NNW-SSE) in the megacrystic granite is oblique to the Phulad Shear Zone. The D3 deformation in the megacrystic granite is synchronous with the Phulad Shear Zone mylonites. Another porphyritic granite (Phulad granite, ca. 820 Ma) emplaced syn-tectonically during D3 deformation along and across the Phulad Shear Zone. U-Pb zircon dates in the Marwar Crustal Block document ca. 890 Ma and ca. 860 Ma magmatic dates. U-Pb-Th monazite dates in the Marwar Crustal Block show a strong peak at ca. 820 Ma. By integrating critical field relations, deformational patterns, and geochronology, we argue that the Marwar Crustal Block shows distinct geological evolution prior to its accretion with the remaining parts of India. We propose that the accretion of the Marwar Crustal Block must be younger than ca. 860 Ma and culminated during ca. 820-810 Ma to form the Greater India landmass along the Phulad Shear Zone. [ABSTRACT FROM AUTHOR]

Contrasting models for internal versus external locations of the South China Craton (SCC) in the supercontinent Rodinia and associated mantle plume or ocean subduction dominated tectonic processes can be resolved by detrital zircon U-Pb dating and Lu-Hf isotopic analyses on the Cryogenian Nanhua Supergroup in the central SCC. Our results show that samples from the lower Liantuo, Tiesi'ao, and Datangpo formations of the Nanhua Supergroup show three age peaks at 2.50 Ga, 2.05 Ga, and 0.85 Ga, and those of the upper Nantuo Formation yield four peaks at 2.50 Ga, 2.05 Ga, 0.85 Ga, and 0.65 Ga. The Archean and Paleoproterozoic (1.80-2.10 Ga) zircons have εHf(t) values of -16.3 to +4.7 and -23.0 to +4.2, and may be sourced from the Kongling and Douling complexes and Paleoproterozoic intrusions in the northern Yangtze Block, respectively. Early Neoproterozoic (0.70-0.96 Ga) zircon grains show variable εHf(t) values of -20.0 to +15.0. In combination with the absence of Mesoproterozoic detrital zircons in the Nanhua Supergroup, huge volumes of Neoproterozoic granitic intrusions in the northern Yangtze Block are the potential sources for the 0.70-0.96 Ga detrital zircons. Only the siltstone of the Nantuo Formation has late Neoproterozoic (0.63-0.69 Ga) detrital zircons with high and positive εHf(t) values (+7.9 to +9.4). Several granitoid intrusions (0.63-0.68 Ga) in the Wudang and Ankang uplift of the South Qinling belt in the northern Yangtze Block provide the late Neoproterozoic detrital zircons of the Nantuo Formation. These provenance analyses of the Nanhua Supergroup indicate an interior source from the SCC, rather than an exterior source from the Laurentia and Australia cratons. The Neoproterozoic rift basins and magmatic rocks in the SCC were produced by secular episodic subductions and back-arc extensions, rather than a Neoproterozoic super-mantle plume. The SCC occupied a peripheral position adjacent to northern India in Rodinia during the Neoproterozoic. These conclusions will promote our understanding of genetic mechanism and distribution prediction of the several Cryogenian-Cambrian black-shale layers and excellent source rocks in the SCC. [ABSTRACT FROM AUTHOR]

We present zircon and monazite U-Pb data from ultrahigh-temperature (UHT) metamorphosed orthogneisses and paragneisses collected from key areas of the Eastern Ghats Belt, India. The results show contrasting tectono thermal histories in different isotopic domains of the Eastern Ghats Belt that were identified by previous workers. Of particular importance is the discovery of a ca. 1760 Ma event (concordia age) in the southern domain 1A, which is interpreted to be the age of an early UHT metamorphism event. This was followed by a second granulite-facies metamorphism event and partial melting at ca. 1600 Ma. This domain was presumably cratonized with India at around 1600 Ma. The record of the ca. 1760--1600 Ma events in domain 1A of the Eastern Ghats Belt allows us to speculate on modeling the Paleoproterozoic--Mesoproterozoic transcontinental correlation. The accretionary orogenic processes in the supercontinent Columbia encompassed Australia, Antarctica, Laurentia, and parts of India. The central part of Eastern Ghats Belt (isotopic domain 2), on the other hand, contains zircons showing inherited ages of ca. 1880--1700 Ma, with a concordant age group of ca. 1760 Ma. Moderately to strongly discordant ages in the time span of ca. 1600--1100 Ma in domain 2 are interpreted to be mixing ages as a result of strong overprint of a ca. 1030--900 Ma tectonothermal event(s) that affected this domain. An early UHT metamorphism event in this domain is inferred to have occurred at ca. 1030--990 Ma (chemical dating of included monazite grains). Zircon records the most pervasive tectonothermal event in this domain at ca. 980--900 Ma, which is correlative with the Rayner orogeny in East Antarctica as a part of the formation of Rodinia. [ABSTRACT FROM AUTHOR]