Jyotiranjan Ray | Physical Research Laboratory (original) (raw)
Papers by Jyotiranjan Ray
40Ar-39Ar analyses of three fresh alkaline rock samples and a phlogopite separate from a carbonat... more 40Ar-39Ar analyses of three fresh alkaline rock samples and a phlogopite separate from a carbonatite from
Amba Dongar carbonatite-alkaline complex of the Deccan Flood Basalt Province, India, yield
indistinguishable precise plateau ages of 64.80.6, 64.70.5, 65.50.8 and 65.30.6 Ma, giving a
mean plateau age of 65.00.3 Ma, which is the age of emplacement of this complex. This age implies
contemporaneity of Amba Dongar with several other carbonatite-alkaline activities of Chhota Udaipur
subprovince and is consistent with their Reunion-Deccan plume origin hypothesis. The emplacement of
these complexes at 65 Ma makes them very significant in the ongoing debate on the K/T extinctions
owing to their capacity to rapidly inject a substantial amount of CO2 and SO2 into the atmosphere.
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Study of the Nd-Pb-Sr isotopic, trace element, and major element characteristics of lavas from th... more Study of the Nd-Pb-Sr isotopic, trace element, and major element characteristics of lavas from the Nazca Ridge and Easter Seamount Chain east of Salas y Gomez (SYG) Island provides insight into the nature of the Easter-SYG hotspot source through the last 30 Myr. Samples were dredged during the DRIFT expedition, Leg 6, of the R/V Revelle (Nov. 5-Dec. 14, 2001). Major element analyses of glasses and whole-rocks from seamounts located between 17^o 15.64'S, 78^o 10.01'W and 19^o 9.72'S, 79^o 38.99'W reveal that most are moderately evolved, transitional to moderately alkalic basalts (MgO = 4-7 wt%, TiO_2=2-4 wt%, K_2O=0.5-1.65 wt%). However, tholeiitic, alkali-rich (Na_2O+K_2O>5.5 wt%), and more siliceous (SiO_2>54 wt%) lavas also are present. Incompatible element concentrations cover a wide range, from normal mid-ocean-ridge type (N-MORB, e.g., [La/Sm]_n = 0.58) to alkalic ocean-island type (OIB, [La/Sm]_n = 7.5). Most of the seamounts we sampled are composed of OIB-type lavas, indicating a normal hotspot style of magmatism. Two anomalously young (4-5 Myr, neighboring 23-25 Myr volcanoes) seamounts on the Nazca Ridge are isotopically distinct, but initial Sr, Nd and Pb isotopic ratios for all the rest of the lavas define two categories: (1) N-MORB-like and transitional basalts (206Pb/204Pb= 18.709, 87Sr/86Sr= 0.70267, ɛNd= +8.6) and (2) incompatible- element-enriched MORB-like to strongly alkalic OIB (206Pb/204Pb= 19.402-20.012, 87Sr/86Sr= 0.70320-0.70389, ɛNd= +2.8 to +5.8). The Pb, Nd, and Sr isotope arrays are co-linear with those for southern East Pacific Rise MORB (e.g., Hanan & Schilling, JGR, 94, 1989; Mahoney et al., EPSL, 121, 1994) and OIB from relatively recent products of the Easter-SYG hotspot (e.g., Haase et al., Nature, 382, 1996; Kingsley &Schilling, JGR, 103, 1998; Cheng et al., CMP, 135, 1999), indicating that the same end-members have been involved for the last 30 Myr: a high ɛNd, low 87Sr/86Sr, low 206Pb/204Pb MORB source and a low ɛNd, high 87Sr/86Sr, high 206Pb/204Pb hotspot source. The hotspot end-member is isotopically similar to the "C" component (Hanan &Graham, Science, 272, 1996). East of SYG, the lack of any geochemical gradient along the chain indicates that there has been no systematic change over time in the proportions of the end-members involved.
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Journal of Earth System Science, 2001
40Ar-39Ar analyses of one alkali pyroxenite whole rock and two phlogopite separates of calcite ca... more 40Ar-39Ar analyses of one alkali pyroxenite whole rock and two phlogopite separates of calcite carbonatites from the Sung Valley carbonatite-alkaline complex, which is believed to be a part of the Rajmahal-Bengal-Sylhet (RBS) flood basalt province, yielded indistinguishable plateau ages of 108.8 ± 2.0Ma, 106.4 ± 1.3Ma and 107.5 ± 1.4Ma, respectively. The weighted mean of these ages, 107.2 ± 0.8 Ma, is the time of emplacement of this complex. This implies that Sung Valley complex and probably other such complexes in the Assam-Meghalaya Plateau postdate the main flood basalt event (i.e., the eruption of tholeiites) in the RBS province by ∼10Ma.
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Journal of Asian Earth Sciences, 2000
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Precambrian Research, 2004
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Contributions To Mineralogy and Petrology, 2009
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Geophysical Research Letters, 1999
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Gondwana Research, 2008
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Barren Island, Andaman Sea, is India's only active volcano and is built of lava flows an... more Barren Island, Andaman Sea, is India's only active volcano and is built of lava flows and volcani-clastic deposits of prehistoric through recent ages that are mainly of basalt and basaltic andesite compositions. Historic eruptions occurred during 17871832, and it erupted ...
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We report for the first time 40Ar-39Ar plateau ages for the Sylhet Traps of eastern India. Our re... more We report for the first time 40Ar-39Ar plateau ages for the Sylhet Traps of eastern India. Our results provide concordant ages for two samples, vertically separated by ~200 m, from a tholeiite lava flow sequence. The ages are indistinguishable at 2σ confidence level indicating a rapid emplacement of these lavas. The weighted mean of the plateau ages associated with least errors, 116.0 +/- 3.5 Ma, most likely represents the age of eruption. Clearly, the Sylhet Traps are contemporaneous with the Kerguelen plume generated Rajmahal and Bengal Traps. Our results in conjunction with the existing age data in the Rajmahal-Bengal-Sylhet igneous province suggest that the latter experienced widespread, and rapid emplacement of flood basalts at ~118 +/- 2 Ma. Such a large-scale volcanism would have required a direct involvement of the Kerguelen plume, suggesting that the Kerguelen hotspot was located close to the eastern Indian margin during its initiation.
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Journal of Earth System Science, 2006
The Vindhyan Supergroup of India is one of the largest and thickest sedimentary successions of th... more The Vindhyan Supergroup of India is one of the largest and thickest sedimentary successions of the world. Deposited in an intra-cratonic basin, it is composed mostly of shallow marine deposits. It is believed to have recorded a substantial portion of Proterozoic time and therefore, likely to contain valuable information on the evolution of the atmosphere, climate, and life on our planet. It also contains some of the most disputed fossils of earliest animal life. Despite their importance, the absolute age of these rocks had remained unknown until recently. In this work I evaluate all the recent chronological information and discuss their implications. From the present findings it appears that the issues surrounding the age of the Lower Vindhyans in the Son valley are now resolved, whereas problems with the age of the Upper Vindhyans and that with the stratigraphic correlations remain to be answered.
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Journal of Earth System Science, 2004
Carbonatites are believed to have crystallized either from mantle-derived primary carbonate magma... more Carbonatites are believed to have crystallized either from mantle-derived primary carbonate magmas or from secondary melts derived from carbonated silicate magmas through liquid immiscibility or from residual melts of fractional crystallization of silicate magmas. Although the observed coexistence of carbonatites and alkaline silicate rocks in most complexes, their coeval emplacement in many, and overlapping initial87Sr/86Sr and143Nd/144Nd ratios are supportive of their cogenesis; there have been few efforts to devise a quantitative method to identify the magmatic processes. In the present study we have made an attempt to accomplish this by modeling the trace element contents of carbonatites and coeval alkaline silicate rocks of Amba Dongar complex, India. Trace element data suggest that the carbonatites and alkaline silicate rocks of this complex are products of fractional crystallization of two separate parental melts. Using the available silicate melt-carbonate melt partition coefficients for various trace elements, and the observed data from carbonatites, we have tried to simulate trace element distribution pattern for the parental silicate melt. The results of the modeling not only support the hypothesis of silicate-carbonate melt immiscibility for the evolution of Amba Dongar but also establish a procedure to test the above hypothesis in such complexes.
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International Geology Review, 2002
A petrologically diverse suite of Deccan Trap rocks, comprising basalts, trachytes, rhyolites, an... more A petrologically diverse suite of Deccan Trap rocks, comprising basalts, trachytes, rhyolites, and various alkaline rocks, was studied in the Bombay area along the western Indian rifted continental margin. A previous petrogenetic study of these trachytes and rhyolites suggested derivation through fractional crystallization of basaltic magmas, or partial melting of basaltic material at depth, without involvement of continental crust. A Rb-Sr isochron age for the rhyolites was also calculated, but this isochron in our view is fictitious and represents a mixing line instead. Although some of the evolved liquids may have formed by fractional crystallization of basaltic magmas or partial melting of earlyformed basalts, we show that Rb/Sr-87Sr/86Sr variations in the Bombay trachyte-rhyolite suite are consistent with a combined assimilation-fractional crystallization (AFC) process involving a parental trachyte magma (Sr 225 ppm, 87Sr/86Sr = 0.7040) and an Archaean basement gneiss (Sr 145 ppm, 87Sr/86Sr = 0.7690). Although the required amount of crustal contamination is small (0.27-3.15%), the effects are sufficiently large to make any isochron age determination unviable. The role of simple or complex mixing/contamination processes must be evaluated and rejected before age significance is ascribed to linear arrays in parent-daughter isotopic ratio plots.
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Precambrian Research, 2003
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40Ar-39Ar analyses of three fresh alkaline rock samples and a phlogopite separate from a carbonat... more 40Ar-39Ar analyses of three fresh alkaline rock samples and a phlogopite separate from a carbonatite from
Amba Dongar carbonatite-alkaline complex of the Deccan Flood Basalt Province, India, yield
indistinguishable precise plateau ages of 64.80.6, 64.70.5, 65.50.8 and 65.30.6 Ma, giving a
mean plateau age of 65.00.3 Ma, which is the age of emplacement of this complex. This age implies
contemporaneity of Amba Dongar with several other carbonatite-alkaline activities of Chhota Udaipur
subprovince and is consistent with their Reunion-Deccan plume origin hypothesis. The emplacement of
these complexes at 65 Ma makes them very significant in the ongoing debate on the K/T extinctions
owing to their capacity to rapidly inject a substantial amount of CO2 and SO2 into the atmosphere.
Bookmarks Related papers MentionsView impact
Study of the Nd-Pb-Sr isotopic, trace element, and major element characteristics of lavas from th... more Study of the Nd-Pb-Sr isotopic, trace element, and major element characteristics of lavas from the Nazca Ridge and Easter Seamount Chain east of Salas y Gomez (SYG) Island provides insight into the nature of the Easter-SYG hotspot source through the last 30 Myr. Samples were dredged during the DRIFT expedition, Leg 6, of the R/V Revelle (Nov. 5-Dec. 14, 2001). Major element analyses of glasses and whole-rocks from seamounts located between 17^o 15.64'S, 78^o 10.01'W and 19^o 9.72'S, 79^o 38.99'W reveal that most are moderately evolved, transitional to moderately alkalic basalts (MgO = 4-7 wt%, TiO_2=2-4 wt%, K_2O=0.5-1.65 wt%). However, tholeiitic, alkali-rich (Na_2O+K_2O>5.5 wt%), and more siliceous (SiO_2>54 wt%) lavas also are present. Incompatible element concentrations cover a wide range, from normal mid-ocean-ridge type (N-MORB, e.g., [La/Sm]_n = 0.58) to alkalic ocean-island type (OIB, [La/Sm]_n = 7.5). Most of the seamounts we sampled are composed of OIB-type lavas, indicating a normal hotspot style of magmatism. Two anomalously young (4-5 Myr, neighboring 23-25 Myr volcanoes) seamounts on the Nazca Ridge are isotopically distinct, but initial Sr, Nd and Pb isotopic ratios for all the rest of the lavas define two categories: (1) N-MORB-like and transitional basalts (206Pb/204Pb= 18.709, 87Sr/86Sr= 0.70267, ɛNd= +8.6) and (2) incompatible- element-enriched MORB-like to strongly alkalic OIB (206Pb/204Pb= 19.402-20.012, 87Sr/86Sr= 0.70320-0.70389, ɛNd= +2.8 to +5.8). The Pb, Nd, and Sr isotope arrays are co-linear with those for southern East Pacific Rise MORB (e.g., Hanan & Schilling, JGR, 94, 1989; Mahoney et al., EPSL, 121, 1994) and OIB from relatively recent products of the Easter-SYG hotspot (e.g., Haase et al., Nature, 382, 1996; Kingsley &Schilling, JGR, 103, 1998; Cheng et al., CMP, 135, 1999), indicating that the same end-members have been involved for the last 30 Myr: a high ɛNd, low 87Sr/86Sr, low 206Pb/204Pb MORB source and a low ɛNd, high 87Sr/86Sr, high 206Pb/204Pb hotspot source. The hotspot end-member is isotopically similar to the "C" component (Hanan &Graham, Science, 272, 1996). East of SYG, the lack of any geochemical gradient along the chain indicates that there has been no systematic change over time in the proportions of the end-members involved.
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Journal of Earth System Science, 2001
40Ar-39Ar analyses of one alkali pyroxenite whole rock and two phlogopite separates of calcite ca... more 40Ar-39Ar analyses of one alkali pyroxenite whole rock and two phlogopite separates of calcite carbonatites from the Sung Valley carbonatite-alkaline complex, which is believed to be a part of the Rajmahal-Bengal-Sylhet (RBS) flood basalt province, yielded indistinguishable plateau ages of 108.8 ± 2.0Ma, 106.4 ± 1.3Ma and 107.5 ± 1.4Ma, respectively. The weighted mean of these ages, 107.2 ± 0.8 Ma, is the time of emplacement of this complex. This implies that Sung Valley complex and probably other such complexes in the Assam-Meghalaya Plateau postdate the main flood basalt event (i.e., the eruption of tholeiites) in the RBS province by ∼10Ma.
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Journal of Asian Earth Sciences, 2000
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International Geology Review, 2009
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Precambrian Research, 2004
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Contributions To Mineralogy and Petrology, 2009
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Geophysical Research Letters, 1999
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Gondwana Research, 2008
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Geophysical Research Letters, 2005
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Earth and Planetary Science Letters, 1999
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Barren Island, Andaman Sea, is India's only active volcano and is built of lava flows an... more Barren Island, Andaman Sea, is India's only active volcano and is built of lava flows and volcani-clastic deposits of prehistoric through recent ages that are mainly of basalt and basaltic andesite compositions. Historic eruptions occurred during 17871832, and it erupted ...
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Geophysical Research Letters, 2005
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Geophysical Research Letters, 2005
We report for the first time 40Ar-39Ar plateau ages for the Sylhet Traps of eastern India. Our re... more We report for the first time 40Ar-39Ar plateau ages for the Sylhet Traps of eastern India. Our results provide concordant ages for two samples, vertically separated by ~200 m, from a tholeiite lava flow sequence. The ages are indistinguishable at 2σ confidence level indicating a rapid emplacement of these lavas. The weighted mean of the plateau ages associated with least errors, 116.0 +/- 3.5 Ma, most likely represents the age of eruption. Clearly, the Sylhet Traps are contemporaneous with the Kerguelen plume generated Rajmahal and Bengal Traps. Our results in conjunction with the existing age data in the Rajmahal-Bengal-Sylhet igneous province suggest that the latter experienced widespread, and rapid emplacement of flood basalts at ~118 +/- 2 Ma. Such a large-scale volcanism would have required a direct involvement of the Kerguelen plume, suggesting that the Kerguelen hotspot was located close to the eastern Indian margin during its initiation.
Bookmarks Related papers MentionsView impact
Journal of Earth System Science, 2006
The Vindhyan Supergroup of India is one of the largest and thickest sedimentary successions of th... more The Vindhyan Supergroup of India is one of the largest and thickest sedimentary successions of the world. Deposited in an intra-cratonic basin, it is composed mostly of shallow marine deposits. It is believed to have recorded a substantial portion of Proterozoic time and therefore, likely to contain valuable information on the evolution of the atmosphere, climate, and life on our planet. It also contains some of the most disputed fossils of earliest animal life. Despite their importance, the absolute age of these rocks had remained unknown until recently. In this work I evaluate all the recent chronological information and discuss their implications. From the present findings it appears that the issues surrounding the age of the Lower Vindhyans in the Son valley are now resolved, whereas problems with the age of the Upper Vindhyans and that with the stratigraphic correlations remain to be answered.
Bookmarks Related papers MentionsView impact
Journal of Earth System Science, 2004
Carbonatites are believed to have crystallized either from mantle-derived primary carbonate magma... more Carbonatites are believed to have crystallized either from mantle-derived primary carbonate magmas or from secondary melts derived from carbonated silicate magmas through liquid immiscibility or from residual melts of fractional crystallization of silicate magmas. Although the observed coexistence of carbonatites and alkaline silicate rocks in most complexes, their coeval emplacement in many, and overlapping initial87Sr/86Sr and143Nd/144Nd ratios are supportive of their cogenesis; there have been few efforts to devise a quantitative method to identify the magmatic processes. In the present study we have made an attempt to accomplish this by modeling the trace element contents of carbonatites and coeval alkaline silicate rocks of Amba Dongar complex, India. Trace element data suggest that the carbonatites and alkaline silicate rocks of this complex are products of fractional crystallization of two separate parental melts. Using the available silicate melt-carbonate melt partition coefficients for various trace elements, and the observed data from carbonatites, we have tried to simulate trace element distribution pattern for the parental silicate melt. The results of the modeling not only support the hypothesis of silicate-carbonate melt immiscibility for the evolution of Amba Dongar but also establish a procedure to test the above hypothesis in such complexes.
Bookmarks Related papers MentionsView impact
International Geology Review, 2002
A petrologically diverse suite of Deccan Trap rocks, comprising basalts, trachytes, rhyolites, an... more A petrologically diverse suite of Deccan Trap rocks, comprising basalts, trachytes, rhyolites, and various alkaline rocks, was studied in the Bombay area along the western Indian rifted continental margin. A previous petrogenetic study of these trachytes and rhyolites suggested derivation through fractional crystallization of basaltic magmas, or partial melting of basaltic material at depth, without involvement of continental crust. A Rb-Sr isochron age for the rhyolites was also calculated, but this isochron in our view is fictitious and represents a mixing line instead. Although some of the evolved liquids may have formed by fractional crystallization of basaltic magmas or partial melting of earlyformed basalts, we show that Rb/Sr-87Sr/86Sr variations in the Bombay trachyte-rhyolite suite are consistent with a combined assimilation-fractional crystallization (AFC) process involving a parental trachyte magma (Sr 225 ppm, 87Sr/86Sr = 0.7040) and an Archaean basement gneiss (Sr 145 ppm, 87Sr/86Sr = 0.7690). Although the required amount of crustal contamination is small (0.27-3.15%), the effects are sufficiently large to make any isochron age determination unviable. The role of simple or complex mixing/contamination processes must be evaluated and rejected before age significance is ascribed to linear arrays in parent-daughter isotopic ratio plots.
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Precambrian Research, 2003
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Journal of Earth System Science, 2000
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