Dreyer, Brian; Chavagnac, Valerie M. C.; Morris, Julie D.; Font, Laura (2006): Source and petrogenesis of the igneous complex cored during ODP Leg 205; implications for off-axis plume-ridge interaction on the Cocos Plate. Texas A&M University, Ocean Drilling Program, College Station, TX, United States, In: Morris, Julie D., Villinger, Heinrich W., Klaus, Adam, Cardace, Dawn M., Chavagnac, Valerie M. C., Clift, Peter D., Haeckel, Matthias, Hisamitsu, Toshio, Kastner, Miriam, Pfender, Marion, Saffer, Demian M., Santelli, Cara, Schramm, Burkhard, Screaton, Elizabeth J., Solomon, Evan A., Strasser, Michael, Moe, Kyaw Thu, Vannucchi, Paola, Proceedings of the Ocean Drilling Program; scientific results; fluid flow and subduction fluxes across the Costa Rica convergent margin; implications for the seismogenic zone and subduction factory; covering Leg 205 of the cruises of the Drilling Vessel JOIDES Resolution; Victoria, Canada, to Balboa, Panama; Sites 1253-1255; 2 September-6 November 2002, 205, georefid:2007-025138

New major and trace element analyses of Ocean Drilling Program Leg 170 and 205 mafic igneous samples are presented along with Sr and Nd isotopic results. Samples were cored from a sill unit (Subunit 4A) and a lower igneous unit (Subunit 4B) whose lower boundary was not drilled. The samples are dominantly microcrystalline to medium-grained glomerocrystic plagioclase-clinopyroxene gabbro in a nearly holocrystalline groundmass. Samples are dominantly low-K subalkaline tholeiites with trace element systematics that correlate with unit stratigraphy. Using isotopic data, trace element ratios little affected by fractionation, and abundance data from the least fractionated samples, it is possible to model their mantle sources and subsequent igneous processing. Melting models suggest that small differences in degrees of partial melting can generate the two geochemical groups identified within the igneous complex. Crystal fractionation and accumulation have further modified the melt compositions, particularly within the lower stratigraphic unit. Mixing models indicate that these units are derived from a mantle source that is 50%-70% enriched compared to depleted mid-ocean ridge source mantle. In the context of the complex regional tectonic and volcanic history of the Cocos plate, this igneous complex likely represents melts of depleted upper mantle that were previously enriched during transit near the Galapagos hotspot. A postenrichment change in the local-regional tectonic stress regime may have triggered decompression melting and emplacement of the igneous complex far from any active spreading center or plume. Preexisting plate fractures, ridge jumps, and abandoned spreading centers may have facilitated distal reach of plume-overprinted material.
West: -86.1200 East: -86.1000 North: 9.4000 South: 9.3800
Expedition: 205
Supplemental Information:
Available only on CD-ROM in PDF format and on the Web in PDF or HTML
Data access:
Provider: SEDIS Publication Catalogue
Data set link: http://sedis.iodp.org/pub-catalogue/index.php?id=10.2973/odp.proc.sr.205.212.2006 (c.f. for more detailed metadata)
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