View Full Document


Unformatted text preview:

Winterer E L Sager W W Firth J V and Sinton J M Eds 1995 Proceedings of the Ocean Drilling Program Scientific Results Vol 143 15 PETROLOGY AND GEOCHEMISTRY OF IGNEOUS ROCKS FROM ALLISON AND RESOLUTION GUYOTS SITES 865 AND 8661 P E Baker 2 P R Castillo 3 and E Condliffe2 ABSTRACT At Site 866 Resolution Guyot the volcanic basement 1620 mbsf and 128 Ma consists of a series of subaerial lava flows separated by scoriaceous rubbly and clay iron rich smectite intervals The lavas may be divided into three main groups on petrographic and geochemical grounds Because of alteration the geochemical evidence depends mainly on relatively immobile elements such as Ti Zr Nb and the rare earth elements The lowest group 1727 mbsf is picritic and alkalic high Nb Ti and Nb Zr The middle group 1673 1727 mbsf with megacrysts and phenocrysts of Plagioclase olivine and clinopyroxene is more markedly alkalic e g steep mid ocean ridge basalt normalized light rare earth element enriched patterns The upper group above 1673 mbsf includes basalts rich in Plagioclase megacrysts overlain by picrites and is more tholeiitic lower Nb Ti Zr Ti and flatter rare earth element patterns At Site 865 Allison Guyot altered basaltic sills are intrusive into Albian clayey dolomitic limestones between 830 and 870 mbsf Several lines of evidence indicate that the sediment was unconsolidated at the time of invasion by the basalt lll Ma Salitic clinopyroxenes abundances and ratios of the less mobile incompatible elements and pronounced light rare earth element enrichment all point to a decidedly more alkalic affinity than was seen at Site 866 Resolution and Allison guyots probably originated within the region of intense hotspot volcanism referred to as the South Pacific isotopic and thermal anomaly or SOPITA The two guyots probably followed a similar tectonic pathway and may have passed over more than one hotspot Geochemical evidence e g Nb Zr and Zr Ti suggests that they have more in common with the Society Austral

Access the best Study Guides, Lecture Notes and Practice Exams

Loading Unlocking...

Join to view sr143_15 and access 3M+ class-specific study document.

We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view sr143_15 and access 3M+ class-specific study document.


By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?