Pb–Pb age of earliest megascopic, eukaryotic alga bearing Rohtas Formation, Vindhyan Supergroup, India: implications for Precambrian atmospheric oxygen evolution

Sarangi, Sanat; Gopalan, K.; Kumar, Sanjeev

doi:10.1016/j.precamres.2004.02.006

Cited by 167 publications

(51 citation statements)

References 41 publications

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“…1). The Kajrahat Limestone, which occurs below the Porcellanite Formation, has been dated at 1729 5 110 Ma by Pb-Pb methods (Sarangi et al 2004). Taken together, these results suggest that the Vindhyan basin opened ca.…”

Section: Discussionmentioning

confidence: 84%

U-Pb Age and Hf Isotopic Compositions of Magmatic Zircons from a Rhyolite Flow in the Porcellanite Formation in the Vindhyan Supergroup, Son Valley (India): Implications for Its Tectonic Significance

Bickford

Mishra

Mueller

et al. 2017

The Journal of Geology

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The Porcellanite Formation in the basal Semri Group of the Proterozoic Vindhyan Supergroup, exposed along the Son River Valley, India, primarily consists of intercalated silicified felsic tuff beds (porcellanite), rhyolitic breccia, and shale. Lensoid patches of very coarse-grained rhyolite occur in a stretch of about 10 km near the eastern end of the valley. These are newly interpreted as rhyolite flows, with flow structures including aligned volcanic fragments and phenocrysts, a few of which are ∼10-cm-long feldspars. Microphenocrysts consist of fragments of patchy perthite and quartz, with subordinate Fe-oxide minerals set in a very fine-grained groundmass of quartz and feldspar. Volcanic rock fragments and fiamme are common. Bulk chemical compositions of nine samples also identify them as rhyolite (SiO 2 p 75.24%; Na 2 O 1 K 2 O p 7.06%, CaO p 1.66%). Rare earth element distribution is typical of granitic rocks, with a negative Eu anomaly of 0.57. The samples are enriched in U, Th, La, and Rb and depleted in Cr and Ni relative to upper continental crust and total crust. New U-Pb isotopic analyses of magmatic zircons in the rhyolitic flow give a concordia intercept age of 1640 5 4 Ma and a weighted-mean 207 Pb/ 206 Pb average age of 1642 5 7 Ma. These are essentially identical with those determined previously from zircons in porcellanite outcrops to the west. Lu-Hf isotopic compositions show that all but one ε Hf value at 1640 Ma are less than chondrite uniform reservoir values, indicating a significant contribution from older, felsic crust. Crustal models suggest derivation from about 2.5 Ga middle to lower crust. The new data do not support Semri sedimentation in an active arc setting or derivation of the rhyolite magma from a putative and now-concealed subduction zone with contribution from the mantle. We suggest that far-field effects of one or more of the ca. 1650 Ma collisions of continental blocks caused crustal fracturing as the basin subsided, which induced melting and the consequent rhyolitic volcanism.

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Section: Discussionmentioning

confidence: 84%

U-Pb Age and Hf Isotopic Compositions of Magmatic Zircons from a Rhyolite Flow in the Porcellanite Formation in the Vindhyan Supergroup, Son Valley (India): Implications for Its Tectonic Significance

Bickford

Mishra

Mueller

et al. 2017

The Journal of Geology

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“…The age of the Lower Vindhyan rocks (silicified tuffs bounding the Chorhat Sandstone, Semri Group) as determined by SHRIMP U-Pb zircon chronology is bracketed between >1700 Ma and 1601 ± 130 Ma (Ray et al 2003). The oldest age of a Vindhyan Supergroup component reported so far is 1721 ± 90 Ma (Pb-Pb isochron method; Sarangi et al 2004; Kajrahat limestone, Son valley).…”

Section: The Age Of the Dhala Structurementioning

confidence: 99%

The Dhala structure, Bundelkhand craton, Central India—Eroded remnant of a large Paleoproterozoic impact structure

Pati

Reimold

Koeberl

et al. 2008

Meteorit & Planetary Scien

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Abstract-The newly discovered Dhala structure, Madhya Pradesh State, India, is the eroded remnant of an impact structure with an estimated present-day apparent diameter of about 11 km. It is located in the northwestern part of the Archean Bundelkhand craton. The pre-impact country rocks are predominantly granitoids of ∼2.5 Ga age, with minor 2.0-2.15 Ga mafic intrusive rocks, and they are overlain by post-impact sediments of the presumably >1.7 Ga Vindhyan Supergroup. Thus, the age for this impact event is currently bracketed by these two sequences. The Dhala structure is asymmetrically disposed with respect to a central elevated area (CEA) of Vindhyan sediments. The CEA is surrounded by two prominent morphological rings comprising pre-Vindhyan arenaceousargillaceous and partially rudaceous metasediments and monomict granitoid breccia, respectively. There are also scattered outcrops of impact melt breccia exposed towards the inner edge of the monomict breccia zone, occurring over a nearly 6 km long trend and with a maximum outcrop width of ∼170 m. Many lithic and mineral clasts within the melt breccia exhibit diagnostic shock metamorphic features, including multiple sets of planar deformation features (PDFs) in quartz and feldspar, ballen-textured quartz, occurrences of coesite, and feldspar with checkerboard texture. In addition, various thermal alteration textures have been found in clasts of initially superheated impact melt. The impact melt breccia also contains numerous fragments composed of partially devitrified impact melt that is mixed with unshocked as well as shock deformed quartz and feldspar clasts. The chemical compositions of the impact melt rock and the regionally occurring granitoids are similar. The Ir contents of various impact melt breccia samples are close to the detection limit (1-1.5 ppb) and do not provide evidence for the presence of a meteoritic component in the melt breccia. The presence of diagnostic shock features in mineral and lithic clasts in impact melt breccia confirm Dhala as an impact structure. At 11 km, Dhala is the largest impact structure currently known in the region between the Mediterranean and southeast Asia.

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“…Rasmussen et al (2002) and Ray et al (2002) determined the age of the Porcellanite Formation to be 1630 Ma by the U/Pb SHRIMP dating technique. Recently, Sarangi et al (2004) obtained an age of 1600 Ma for the Rohtas Limestone (topmost formation of the Semri Group) in the Semri Group. Based on these dates, the Kajrahat Limestone seems to be older than 1630 Ma.…”

Section: Geological Backgroundmentioning

confidence: 99%

Carbon and oxygen isotopic variations in peritidal stromatolite cycles, Paleoproterozoic Kajrahat Limestone, Vindhyan basin of central India

Banerjee

Bhattacharya

Sarkar

2007

Journal of Asian Earth Sciences

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Pb–Pb age of earliest megascopic, eukaryotic alga bearing Rohtas Formation, Vindhyan Supergroup, India: implications for Precambrian atmospheric oxygen evolution

Cited by 167 publications

References 41 publications

U-Pb Age and Hf Isotopic Compositions of Magmatic Zircons from a Rhyolite Flow in the Porcellanite Formation in the Vindhyan Supergroup, Son Valley (India): Implications for Its Tectonic Significance

U-Pb Age and Hf Isotopic Compositions of Magmatic Zircons from a Rhyolite Flow in the Porcellanite Formation in the Vindhyan Supergroup, Son Valley (India): Implications for Its Tectonic Significance

The Dhala structure, Bundelkhand craton, Central India—Eroded remnant of a large Paleoproterozoic impact structure

Carbon and oxygen isotopic variations in peritidal stromatolite cycles, Paleoproterozoic Kajrahat Limestone, Vindhyan basin of central India

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