Rb–Sr Isotopic Age of the Kunavaram Series — A Group of Alkaline Rocks from India

1971 ◽  
Vol 8 (12) ◽  
pp. 1597-1602 ◽  
Author(s):  
G. S. Clark ◽  
K. V. Subbarao
Keyword(s):  
Nepheline Syenite ◽  
South India ◽  
Country Rock ◽  
Sedimentary Rocks ◽  
Eastern Ghats ◽  
Initial Ratio ◽  
Isotopic Age ◽  
Biotite Gneiss ◽  
Alkaline Rocks ◽  
Eastern Ghats Belt

A Rb–Sr isochron age of 1265 ± 85 m.y. has been obtained for a group of alkaline rocks (Kunavaram series) which intrude highly folded, metamorphosed igneous and sedimentary rocks of the Eastern Ghats belt of South India. The initial 87Sr/86Sr ratio is 0.7051 ± 0.0013. This age is believed to be the time of intrusion of these rocks. Assuming an initial ratio of 0.710, two mica samples from the nepheline syenite (a biotite and a muscovite) gave an age of 620 m.y. One sample of the country rock (garnet–biotite gneiss) gave an age of 2100 m.y., which agrees with prior estimates for the age of the principal orogenic activity in the Eastern Ghats belt.

Zircon geochronology of deformed alkaline rocks along the Eastern Ghats Belt margin: India–Antarctica connection and the Enderbia continent

2018 ◽  
Vol 310 ◽  
pp. 407-424 ◽  
Author(s):  
Sameer Ranjan ◽  
Dewashish Upadhyay ◽  
Kumar Abhinay ◽  
Kamal L. Pruseth ◽  
Jayanta K. Nanda
Keyword(s):  
Eastern Ghats ◽  
Zircon Geochronology ◽  
Alkaline Rocks ◽  
Eastern Ghats Belt

Aluminous sapphirine granulites from the Eastern Ghats Belt (India): Phase relations and relevance to counterclockwise P-T history

2006 ◽  
Vol 18 (1) ◽  
pp. 35-48 ◽  
Author(s):  
Suman Das ◽  
Abhijit Bhattacharya ◽  
Michael M. Raith ◽  
Subhadip Bhadra ◽  
Manua Banerjee
Keyword(s):  
Phase Relations ◽  
Eastern Ghats ◽  
Eastern Ghats Belt

The Eastern Ghats Belt, India, in the context of supercontinent assembly

2017 ◽  
Vol 457 (1) ◽  
pp. 87-104 ◽  
Author(s):  
Somnath Dasgupta ◽  
Sankar Bose ◽  
Santanu Kumar Bhowmik ◽  
Pulak Sengupta
Keyword(s):  
Eastern Ghats ◽  
Eastern Ghats Belt

scholarly journals The Tikiusaaq carbonatite: a new Mesozoic intrusive complex in southern West Greenland

2006 ◽  
Vol 10 ◽  
pp. 41-44 ◽  
Author(s):  
Agnete Steenfelt ◽  
Julie A. Hollis ◽  
Karsten Secher
Keyword(s):  
Lithospheric Mantle ◽  
Chemical Elements ◽  
Country Rock ◽  
Alkaline Rock ◽  
Geological Mapping ◽  
Carbonatite Complex ◽  
West Greenland ◽  
Alkaline Rocks ◽  
Kimberlite Indicator Minerals ◽  
Indicator Minerals

Ultrabasic alkaline magmatic rocks are products of melts generated deep within or at the base of the lithospheric mantle. The magmas may reach the surface to form lavas and pyroclastic deposits; alternatively they crystallise at depth to form dykes or central complexes. The rocks are chemically distinct and may contain high concentrations of economically interesting minerals and chemical elements, such as diamonds, niobium, tantalum, rare earth elements, phosphorus, iron, uranium, thorium, and zirconium. Ultrabasic alkaline rocks are known from several provinces in Greenland, but extrusive facies have only been preserved at a few places; e.g. at Qassiarsuk in South Greenland where pyroclastic rocks occur, and in the Maniitsoq region, where a small volcanic breccia (‘Fossilik’) contains fragments of Palaeozoic limestone. Ultramafic lamprophyre and kimberlite are mainly emplaced as dykes, whereas carbonatite forms large intrusive bodies as well as dykes. The ultrabasic alkaline magmas that have been emplaced at certain times during the geological evolution of Greenland can be related to major episodes of continental break-up (Larsen & Rex 1992). The oldest are Archaean and the youngest dated so far are Palaeogene. Figure 1 shows the distribution of known ultrabasic alkaline rocks in West Greenland. The large and well-exposed bodies of alkaline rocks and carbonatites in the Gardar Province were discovered already in the early 1800s (Ussing 1912), while less conspicuous bodies were discovered much later during geological mapping and mineral exploration. Many alkaline rock bodies, particularly dykes, are difficult to identify in the field because they weather more extensively than the country rock gneisses and form vegetated depressions in the landscape. However, their distinct chemistry and mineralogy render alkaline rocks identifiable in geochemical and geophysical survey data. Thus, the Sarfartôq carbonatite complex was discovered during regional airborne gamma-spectrometric surveying owing to its elevated uranium and thorium contents (Secher 1986). The use of kimberlite indicator minerals has led to the discovery of alkaline rocks such as kimberlites and ultramafic lamprophyres that carry fragments of deep lithospheric mantle. Such rocks may also contain diamonds. Kimberlite indicator minerals are high-pressure varieties of minerals, such as garnet, clinopyroxene, chromite and ilmenite that were formed in the lithospheric mantle. Exploration companies have processed thousands of till samples from southern West Greenland for kimberlite indicator minerals and found many new dykes.

Metamorphic chronology of the Precambrian provinces of South India

1968 ◽  
Vol 5 (3) ◽  
pp. 591-600 ◽  
Author(s):  
U. Aswathanarayana
Keyword(s):  
South India ◽  
Regional Metamorphism ◽  
Southern India ◽  
Eastern Ghats ◽  
Cuddapah Basin ◽  
Upper Limit

There are three Precambrian provinces in southern India — the Dharwars (metavolcanics, metasediments, charnockites and granites), the Eastern Ghats (metasediments, charnockites and granites), and the Cuddapahs (essentially flat-lying continental sediments disturbed at the margins) — with chronostratigraphic histories dovetailing into one another. The Dharwars bear the impress of three episodes (about 3000 m.y., 2600–2300 m.y., and about 2000 m.y.) of folding, metamorphism, and emplacement of granites, the second being the most important. The pelitic sediments deposited in the Eastern Ghats geosyncline during the post-Dharwar times (upper limit, 2600 m.y.) were later folded and metamorphosed about 1600 m.y. ago into garnet-sillimanite-graphite gneisses (khondalites). Important deposits of mica pegmatites developed during this episode. Charnockites and granites associated with the Eastern Ghats were emplaced 1520–1300 m.y. ago. The Eastern Ghats rocks were subsequently cross-folded and metamorphosed about 500 m.y. ago. The sedimentation in the Cuddapah Basin was initiated sometime after the Eastern Ghats orogeny (1600 m.y. ago) but before 1160 m.y. ago. The Cuddapahs were subjected to regional metamorphism about 500 m.y. ago.

Sign in / Sign up

Export Citation Format

Share Document