Eastern Indian Ocean DSDP sites; correlations between petrography, geochemistry and tectonic setting

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doi: 10.1029/SP009p0189
Author(s): Frey, F. A.; Dickey, J. S., Jr.; Thompson, G.; Bryan, W. B.
Author Affiliation(s): Primary:
Mass. Inst. Technol., Dep. Earth and Planet. Sci., Cambridge, Mass., United States
Woods Hole Oceanogr. Inst., United States
Volume Title: Indian Ocean geology and biostratigraphy; studies following Deep-Sea Drilling legs 22-29
Volume Author(s): Heirtzler, J. R., editor; Bolli, H. M.; Davies, T. A.; Saunders, J. B.; Sclater, J. G.
Source: Indian Ocean geology and biostratigraphy; studies following Deep-Sea Drilling legs 22-29, edited by J. R. Heirtzler, H. M. Bolli, T. A. Davies, J. B. Saunders and J. G. Sclater, p.189-257. Publisher: Am. Geophys. Union, Washington, D.C., United States. ISBN: 978-1-118-66491-9
Note: In English. 103 refs.; illus. incl. tables, sketch maps
Summary: At 10 of 13 Deep Sea Drilling Project (DSDP) sites in the eastern Indian Ocean there is a correlation between inferred tectonic history and the petrographic and geochemical nature of basement basalts. Compositions of unaltered glasses and phenocrysts, in addition to abundances of Ti, Zr, and rare-earths in crystalline rocks, are used to determine the geochemical characteristics of magmas erupted at each site. At sites 212, 213, 257, 259, 260 and 261 the basalts are within the compositional range of large ion lithophile(LIL) element-depleted tholeiites dredged from spreading ridge axes, such as the Mid-Indian Ocean Ridge. These results are consistent with tectonic models indicating a seafloor spreading origin for basement basalt at these sites. In contrast, the alkali-olivine basalts at site 211 are probably related to volcanism creating the nearby Cocos, Keeling and Christmas Islands. Rocks from the aseismic Ninetyeast Ridge (sites 214, 216 and 254) are LIL element-enriched tholeiites, ferrotholeiites and oceanic andesites. Similar suites occur on oceanic islands such as Iceland, Galapagos, Faeroes and the St. Pauls-Amsterdam complex in the Indian Ocean. The geochemical features of these Ninetyeast Ridge rocks therefore imply a petrogenesis similar to that of tholeiitic island sequences. This conclusion is consistent with tectonic models relating portions of the Ninetyeast Ridge to a hot spot trace. Inconsistencies between tectonic models and magma geochemistry occur at sites 215, 253 and 256. The occurrence of LIL element-depleted tholeiite at site 253 on the Ninetyeast Ridge is anomalous and unexplained. Equally surprising are the high LIL element abundances in tholeiitic basalts at site 215. These basalts are similar in composition to a basalt dredged from a seamount flank in the north-east Indian Ocean, but they are distinctly different from Ninetyeast Ridge basalts. There are no anomalous bathymetric features at site 215, but the unexpectedly young, inferred basement age and the atypical composition imply that site 215 basalts were not formed at a spreading ridge axis. At site 256, LIL element-enriched ferrotholeiites are also unlike basalts formed at spreading ridge axes. These basalts may be related to the volcanism creating the north-easterly trend of topographic highs extending from Broken Ridge through site 256. Abstract Copyright (1977), by the American Geophysical Union.
Year of Publication: 1977
Research Program: DSDP Deep Sea Drilling Project
Key Words: 07 Marine Geology and Oceanography; Basalts; Chemical composition; Deep Sea Drilling Project; East Indian Ocean; Evolution; Geochemistry; Hot spots; Igneous rocks; Indian Ocean; Magmas; Metals; Mid-ocean ridges; Mineral composition; Models; Ninetyeast Ridge; Petrography; Petrology; Plate tectonics; Rare earths; Sea-floor spreading; Tectonophysics; Tholeiite; Titanium; Trace elements; Volcanic rocks; Zirconium
Record ID: 1978039305
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.

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