Is ash layer of ∼8 Ma at ODP-758 from Bay of Bengal and Fe-Mn oxide coated pumice from Central Indian Ocean Basin are from same eruption?

Author(s): Pattan, J. N.; Jumaila, C.; Ahmad, S. M.; Khedekar, V.; Parthiban, G.; Padmakumari, V.
Author Affiliation(s): Primary:
CSIR, National Institute of Oceanography, Dona Paula, India
Cochin University of Science and Technology, India
CSIR, National Geophysical Research Institute, India
Volume Title: AGU 2013 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2013; American Geophysical Union 2013 fall meeting, San Francisco, CA, Dec. 9-13, 2013. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: An ash layer of F Ma old is recovered from the Bay of Bengal ODP 758 site. Glass shards from this ash layer have been studied for their morphology and chemical composition to trace its source. Earlier, in the Central Indian Ocean Basin occurrence of uncoated and Fe-Mn oxide coated pumice which are of younger (few thousand years) and older (few Ma) in age were reported. Glass grains were separated from the Fe-Mn oxide coated pumice and a studied for morphology and chemical composition. In the present study, an attempt has been made to compare both ash layer and glass from the pumice to trace their source and relation between them if any. Glass shards from the ash layer exhibit bubble wall type morphology and presence of pumice shards while, glass from pumice have pumice shards, suggesting magmatic type of eruption. Electron Probe Micro Analysis of glass shards and glass shows has high content of SiO2 (79%) and total alkalies (6%) indicating rhyolite nature and rich in K- cal-alkaline series. Potassium content in pumice is relatively low as compared to glass shards probably suggest leaching of K by the sea water interaction. Other major oxide contents (Al2O3, TiO2, FeO, MnO and MgO) are nearly similar in both shard and pumice glass. Total rare earth element (ΣREE) of glass shard (147 ppm) and glass (158 ppm) are nearly same, enriched in light REE, with a pronounced negative Eu-anomaly and exhibit flat heavy REE distribution. Tectnomagmatic and triangular plots suggest that both glass shards and glass are of arc type origin. The nearest Indonesian Arc is most probably acting as the source for both of them. Pumice in the present study has 3-4 mm thick Fe-Mn oxide coatings. In Central Indian Ocean Basin earlier report suggested that Fe-Mn oxide accumulates at ∼2 mm/Ma. This indicates that pumice are of ∼6-8 Ma old which is nearly similar in age (∼8 Ma) of ash layer encountered at ODP site 758. Therefore, the present study suggest that ash layer of ∼8 Ma old and Fe-Mn oxide coated pumice may probably correspond to a single eruption from Indonesian Arc Volcanism. However, precise dating of these pumice needs to be carried out for further confirmation.
Year of Publication: 2013
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Bay of Bengal; Cenozoic; Chemical composition; Igneous rocks; Indian Ocean; Iron oxides; Leg 121; Manganese oxides; Miocene; Neogene; Ninetyeast Ridge; ODP Site 758; Ocean Drilling Program; Oxides; Pumice; Pyroclastics; Tertiary; Volcanic ash; Volcanic rocks
Coordinates: N052302 N052303 E0902141 E0902140
Record ID: 2015006425
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