Geochemistry of Serpentine Muds and Metamorphic Rocks from the Mariana Forearc, ODP Sites 1200 and 778 -779, South Chamorro and Conical seamounts

摘要: New geochemical data on serpentinite muds and metamorphic clasts recovered during Ocean Drilling Program Legs 195 (Holes 1200A– 1200E) 125 778A 779A) provide insights into the proportions of rock types various sources that compose mudflows fluid-rock interactions predominate in these muds. We interpret fragments as derivatives mostly metamorphosed mafic rocks from descending Pacific oceanic crust. Based their mid-ocean-ridge basalt (MORB)-like Al2O3, TiO2, CaO, Si/Mg, rare earth element (REE) systematics, are classified metabasalts/metagabbros and, therefore, ~30-km depths represent an active subduction zone setting. The Holes 1200A 1200E have slightly lower REE when compared to Hole 1200D, but overall abundance levels range between 0.1–1 × chondrite (CI) levels. chondrite-normalized patterns [La/Sm]N ~ 2.3 [Sm/Yb]N 2. With exception one sample, analyzed show flat depleted light with 1.0–15 CI levels, resembling MORBs. Visually, ~6 vol% serpentinized composed “exotic” materials 1Savov, I.P., Guggino, S., Ryan, J.G., Fryer, P., Mottl, M.J., 2005. Geochemistry Mariana forearc, ODP Sites 1200 778–779, South Chamorro Conical Seamounts. In Shinohara, M., Salisbury, M.H., Richter, C. (Eds.), Proc. ODP, Sci. Results, 195, 1–49 [Online]. Available World Wide Web: . [Cited YYYYMM-DD] 2Department Geology, University Florida—Tampa, 4202 East Fowler Avenue, SCA 528, Tampa FL 33620-5201, USA. Correspondence author: savovi@si.edu 3Hawaii Institute Geophysics Planetology, School Earth Science Technology, Hawaii at Manoa, 1680 East-West Road, POST 602B, Honolulu HI 96822, 4Department Oceanography, 1000 Pope Marine Sciences Building, Initial receipt: 10 January 2004 Acceptance: 12 July Web publication: 24 February 2005 Ms 195SR-103 I.P. SAVOV ET AL. SERPENTINITE MUD AND METAMORPHIC ROCK GEOCHEMISTRY 2 (metamorphic [schists]). Our mixing calculations confirm this result produced by additions ~5% metamafic (with up levels) peridotite clast material very low abundances U-shaped patterns). preferential incorporation B, Cs, Rb, Li, As, Sb, Ba structure H2O-bearing sheet silicates (different than serpentine) Leg (chlorite, amphibole, micas) little effect fluid-mobile (FME) enrichments (average B = ~13 ppm; average Cs ~0.05 As ~1.25 ppm). extent FME enrichment is similar described for peridotites, both recording interaction fluids rich originating subducting slab.