Papers
1757AD Felsic volcanism off Pondicherry Coast - Fact or Fiction?
Longhinos Biju and Nambiar C.G., published in ECO-CHRONICLE, Vol. 3, No. 3. September 2008 , pp: 201-204
A subtle submarine volcanic eruption was reported in 1757AD off Pondicherry coast in southeast India (location between 11.750 - 120 N, 800 - 810 E ). Various scientific journals and maps of 18th, 19th and early 20th centuries had mentioned the volcano (Dodsley (1759), Berghaus(1840),Darwin (1842), Buist (1852), Jameson (1852) Bidwell (1861), Hartwig (1871), Hartwig andHartwig (1887) and Global Volcanism Programme (2002) .In later half of 20th century, the geological diagonosis of east coast of India based on plate tectonic concepts and non recurrance of eruption, negated the eighteenth century report on submarine volcanism. In 1959, the Geological Survey of India asserted 'uncertain' status to the report. Geographical plotting of the continental and the oceanic tectonic units (including the Indra-Indrayani faults and Gulf of Mannar Pamban lineament) and their extension towards each other is seen to be intersecting at a point closer to the coast of Pondicherry ( Figure 1), expressing transform fault- continent intraction tectonics. It calls for exploring the geophysical characterestics of the coast.
The geographical coincidences of ocean-land tectonic junctions, epicenter of recurring minor earthqukes, aberrancies in bathymetric, gravimetric and total field magnetic anomalies and the report of pumice catches from sea bottom account the mariner's claim. A detailed and pointed analysis of hydroacoustical and geophysical characters of subsuface terrain could bring out further picture.
LikeDoes Gold mineralization in Wynad owe to Buried Batholith?
Jishnu, B.K. and Longhinos, B. (accepted to be published in Eco _Chronicle, September 2009)
Abstract
The Proterozoic granulites of Wynad, host gold bearing quartz veins. But granulites seldom form the source of gold. Recent studies on geochemistry of the mineralization point that the sulphides associated to gold bear magmatic character. Since no igneous intrusions are seen in the vicinity, their presence as hidden bodies is scrutinized from the available geophysical data in and around the region.
The δ34S of Au in WGF and found that its values fall in the range -1.4% to 4.8% CDT, which is one among the indicatives of igneous characteristics. The ionic chemophilic re-equilibriation in pyrites of in the region has striking differences in geochemistry and established that there are two phases of pyrites mineralization in the region. The pyrite associated to the gold bearing quartz veins have Co:Ni ratio, LREE : HREE ratio, Ce- anomaly and Eu-anomaly, which are characteristics of igneous intrusions. On contrary, the La: Yb ratio in these pyrites neither suite to range exhibited by magmatic source nor a range shown by metamorphic/ metasomatic source. Further Jishnu (2009) holds the view that country rock had no role in mobilizing gold ions for mineralization . The concentration of Cu is higher and that of Zr is lower in pyrites of gold bearing quartz veins which points to their source different from the country rock.
The geochemical parameters of auriferous veins in WGF favour magma related gold metallogenesis in WGF. The evaluation of the available geophysical data in and around WGF was done to verify possibility of an igneous intrusion in the vicinity.The WPGL is a typical bouguer anomaly characteristics of granitic batholiths. The clustering of magnetic anomalies indicate that the region bears an intrusion which is capable enough to impart Curie temperature to the magnetic minerals. The high heat flow further substantiates the presence of heat delivering body in the region.
The geochemistry, geophysical characters and regional geology favour the presence of a granitic body within WGF. A detail study is therefore proposed to authenticate its presence.
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