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<title>Geology &amp; Geophysical Sciences</title>
<link>http://drs.nio.org/drs/handle/2264/5</link>
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<pubDate>Sun, 09 Jul 2017 18:05:38 GMT</pubDate>
<dc:date>2017-07-09T18:05:38Z</dc:date>
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<title>Geology &amp; Geophysical Sciences</title>
<url>http://drs.nio.org:80/drs/bitstream/id/14/god.gif</url>
<link>http://drs.nio.org/drs/handle/2264/5</link>
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<title>Pseudofaults and associated seamounts in the conjugate Arabian and Eastern Somali basins, NW Indian Ocean- New constraints from high-resolution satellite-derived gravity data</title>
<link>http://drs.nio.org/drs/handle/2264/5111</link>
<description>Pseudofaults and associated seamounts in the conjugate Arabian and Eastern Somali basins, NW Indian Ocean- New constraints from high-resolution satellite-derived gravity data
Sreejith, K.M.; Chaubey, A.K.; Mishra, A.; Kumar, S.; Rajawat, A.S.
Marine gravity data derived from satellite altimeters are effective tools in mapping fine-scale tectonic features of the ocean basins such as pseudofaults, fracture zones and seamounts, particularly when the ocean basins are carpeted with thick sediments. We use high-resolution satellite-generated gravity and seismic reflection data to map boundaries of pseudofaults and transferred crust related to the Paleocene spreading ridge propagation in the Arabian and its conjugate Eastern Somali basins. The study has provided refinement in the position of previously reported pseudofaults and their spatial extensions in the conjugate basins. It is observed that the transferred crustal block bounded by inner pseudofault and failed spreading ridge is characterized by a gravity low and rugged basement. The refined satellite gravity image of the Arabian Basin also revealed three seamounts in close proximity to the pseudofaults, which were not reported earlier. In the Eastern Somali Basin, seamounts are aligned along NE-SW direction forming ~300 km long seamount chain. Admittance analysis and Flexural model studies indicated that the seamount chain is isostatically compensated locally with Effective Elastic Thickness (T&lt;sub&gt;e&lt;/sub&gt;) of 3-4 km. Based on the present results and published plate tectonic models, we interpret that the seamounts in the Arabian Basin are formed by spreading ridge propagation and are associated with pseudofaults, whereas the seamount chain in the Eastern Somali Basin might have probably originated due to melting and upwelling of upper mantle heterogeneities in advance of migrating/propagating paleo Carlsberg Ridge.
</description>
<pubDate>Fri, 01 Jan 2016 00:00:00 GMT</pubDate>
<guid isPermaLink="false">http://drs.nio.org/drs/handle/2264/5111</guid>
<dc:date>2016-01-01T00:00:00Z</dc:date>
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<item>
<title>The origin and tectonic setting of precambrian greywacke of Ribandar-Chimbel, Goa, India: Petrological and geochemical evidence</title>
<link>http://drs.nio.org/drs/handle/2264/5110</link>
<description>The origin and tectonic setting of precambrian greywacke of Ribandar-Chimbel, Goa, India: Petrological and geochemical evidence
Fernandes, G.Q.; Iyer, S.D.; Kotha, M.
The Precambrian greywacke of Ribandar-Chimbel belonging to the Sanvordem Formation of the Goa Group, India, has been studied for petrography and analyzed for major trace elements. The greywacke is characterized by angular to sub-round grains of quartz, feldspar, biotite, chlorite and clay minerals. The abundance of clay in the matrix seems to have influenced the Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; content and the K&lt;sub&gt;2&lt;/sub&gt;O/Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; ratio. The variation diagrams indicate a decreasing trend of TiO&lt;sub&gt;2&lt;/sub&gt;, Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;, Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; and MgO; whereas Na&lt;sub&gt;2&lt;/sub&gt;O and CaO exhibit a scatter which could be a result of the variable presence of feldspar within the sediments. The immobile elements, vanadium (25 to 144 ppm), nickel (up to 107 ppm) and chromium (up to 184 ppm), reflect abundance of clay minerals. The greywacke shows strongly fractionated REE patterns with LaN/YbN = 8 to 26 and with higher total REE abundances (up to 245 ppm). The low REE enrichment and depletion in heavier REE with prominent negative Eu anomaly (Eu/Eu*= 0.54 to 0.79) suggest a derivation of the greywacke from an old upper continental crust composed chiefly of felsic components. Petrological evidence and geochemical data suggest that the deposition of the greywacke largely took place in a deep to shallow basin that progressively changed from that of a continental island arc to an active continental setting
</description>
<pubDate>Fri, 01 Jan 2016 00:00:00 GMT</pubDate>
<guid isPermaLink="false">http://drs.nio.org/drs/handle/2264/5110</guid>
<dc:date>2016-01-01T00:00:00Z</dc:date>
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<item>
<title>Distribution and fractionation of rare earth elements and Yttrium in suspended and bottom sediments of the Kali estuary, western India</title>
<link>http://drs.nio.org/drs/handle/2264/5107</link>
<description>Distribution and fractionation of rare earth elements and Yttrium in suspended and bottom sediments of the Kali estuary, western India
Suja, S.; Fernandes, L.L.; Rao, V.P.
Concentrations of rare earth elements (REE) and yttrium (Y), and major metals (Al, Fe and Mn) were measured in suspended particulate matter (SPM) and bottom sediments of the Kali estuary, western India, for their distribution and fractionation. The contents of SPM and metals in it were more uniform along the longitudinal transect during the monsoon. During the post- and pre-monsoons, low SPM in the upper/middle estuary coincided with high Fe and Mn and total REE (ƩREE). But in the lower estuary SPM and its ƩREE content increased seaward, while Fe and Mn decreased. The Y/Ho ratios decreased seaward during the monsoon but increased during the post-monsoon. Sm/Nd ratios were more uniform along the transect during monsoon but decreased marginally seaward in other seasons. The Post-Archean Average Australian Shale (PAAS)-normalized REE patterns exhibited middle REE and heavy REE enrichment with positive Ce ( Ce/Ce*Ce/Ce* ), Eu ( Eu/Eu*Eu/Eu* ) and Y anomalies. The Ce/Ce*Ce/Ce* increased but Eu/Eu*Eu/Eu* decreased marginally seaward. The fine-grained sediments showed higher ƩREE and lower Y/Ho ratios than in coarse-grained sediments. The PAAS-normalized REE patterns of sediment were similar to that of SPM. The results revealed two processes, colloidal flocculation and coagulation of metals in the low-salinity zone and an estuarine turbidity maximum in the high salinity zone. Rare earths and yttrium (REY) in SPM and sediments primarily reflected the source rock composition than that of chemical weathering. Apart from physico-chemical processes, the mineralogy and grain size of sediments controlled the distribution and fractionation of REY in the estuary
</description>
<pubDate>Sun, 01 Jan 2017 00:00:00 GMT</pubDate>
<guid isPermaLink="false">http://drs.nio.org/drs/handle/2264/5107</guid>
<dc:date>2017-01-01T00:00:00Z</dc:date>
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<item>
<title>First evidence of denitrification vis-a-vis monsoon in the Arabian Sea since late Miocene</title>
<link>http://drs.nio.org/drs/handle/2264/5106</link>
<description>First evidence of denitrification vis-a-vis monsoon in the Arabian Sea since late Miocene
Tripathi, S.; Tiwari, M.; Lee, J.; Khim, B.-K.; Pandey, D.K.; Clift, P.D.; Kulhanek, D.K.; Ando, S.; Bendle, J.A.P.; Aharonovich, S.; Griffith, E.M.; Gurumurthy, G.P.; Hahn, A.; Iwai, M.; Kumar, A.; Kumar, A.G.; Liddy, H.M.; Lu, H.; Lyle, M.W.; Mishra, R.; Radhakrishna, T.; Routledge, C.M.; Saraswat, R.; Saxena, R.; Scardia, G.; Sharma, G.K.; Singh, A.D.; Steinke, S.; Suzuki, K.; Tauxe, L.; Xu, Z.; Yu, Z.
In the Arabian Sea, South Asian monsoon (SAM)-induced high surface water productivity coupled with poor ventilation of intermediate water results in strong denitrification within the oxygen minimum zone (OMZ). Despite the significance of denitrification in the Arabian Sea, we have no long-term record of its evolution spanning the past several million years. Here, we present the first record of denitrification evolution since Late Miocene (~10.2?Ma) in the Eastern Arabian Sea, where the SAM generates moderate surface water productivity, based on the samples retrieved during the International Ocean Discovery Program (IODP) Expedition 355. We find that (i) the SAM was persistently weaker from ~10.2 to 3.1 Ma; it did not intensify at ~8 Ma in contrast to a few previous studies, (ii) on tectonic timescale, both the SAM and the East Asian Monsoon (EAM) varied synchronously, (iii) the first evidence of denitrification and productivity/SAM intensification was at ~3.2–2.8 Ma that coincided with Mid-Pliocene Warm Period (MPWP), and (iv) the modern strength of the OMZ where denitrification is a permanent feature was attained at ~1.0 Ma
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<pubDate>Sun, 01 Jan 2017 00:00:00 GMT</pubDate>
<guid isPermaLink="false">http://drs.nio.org/drs/handle/2264/5106</guid>
<dc:date>2017-01-01T00:00:00Z</dc:date>
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