Mineralogy of MARK peridotites: replacement through magma channeling examined from Hole 920D, MARK area

Abstract

Peridotites drilled at Site 920 of Ocean Drilling Program Leg 153 in the Mid-Atlantic Ridge near the Kane Transform (MARK) area were examined to understand the mode of magma channeling and modification of the upper mantle peridotites. This paper presents mineralogical data from a slow-spreading ocean ridge for peridotites that have been modified by magma channeling and for those that are free from the modification.The chemical compositions of primary minerals in spinel harzburgite and lherzolite are highly uniform. Olivine core compositions concentrate around Fo = 91.0 and NiO = 0.37 wt%. Spinel cores also have a small compositional range of Mg# = 70-75 and Cr# = 27-31. Orthopyroxenes with Mg# = 90.5-91.6 have A1 2 O 3 contents of 3.17 to 4.77 wt%. TiO 2 and Na 2 O contents in primary clinopyroxenes are extremely low, less than 0.15 and 0.11 wt%, respectively. These results suggest that the MARK peridotites represent moderately depleted upper mantle peridotite. The chemical compositions of primary minerals are modified where the peridotites are crosscut by gabbro and pyroxenite dikes and veins. Such peridotites are enriched in FeO* and TiO 2 , and depleted in MgO, NiO, and A1 2 O 3 .Spatial variations in chemical composition of minerals were examined across channels in Samples 153-920D-10R-2 (Piece 4, 35-41 cm) and 153-920D-13R-2 (Piece 7, 136-143 cm). Primary minerals in spinel harzburgite are enriched in FeO* and TiO 2 within narrow replacement bands next to websterite veins. No evidence for melt extractions was detected in the harzburgite wall, indicating that the replacement occurred as a one-way modification process by melt addition from the channeling magma. The Fo-NiO systematics for the modified olivines support a model of open-system reaction between the wall harzburgite and the infiltration melt with a highly evolved composition. All of the results emphasize that the final magma channeling occurred in "cold" peridotites at a shallow level of the upper mantle.

The Lithium, Boron and Beryllium content of serpentinized peridotites from ODP Leg 209 (Sites 1272A and 1274A): Implications for lithium and boron budgets of oceanic lithosphere

“…(Kelemen et al, 2004b, core description). Such small gabbroic pockets were also identified in the MARK area (Niida, 1997). In the following, this olivine will be termed 'magmatic'.…”

Water in Abyssal Peridotite: Why Are Melt‐Depleted Rocks so Water Rich?

“…The composition of the intrusive rocks is close to the depleted extreme of Atlantic MORB (Barling et al, 1997). The peridotite is predominantly harzburgite, with minor lherzolite and dunite and has a porphyroclastic texture with orthopyroxene, olivine, and, more rarely, clinopyroxene porphyroclasts that occur in a fine-grained recrystallized matrix (e.g., Niida, 1997;Will et al, 2010).…”

Revisiting the electron microprobe method of spinel-olivine-orthopyroxene oxybarometry applied to spinel peridotitesk

“…3), and we use it to calculate precision in our corrected measurements of Fe 3+ /ΣFe ratios of unknown spinel samples. Deviations of each session average (Supplementary 1 Table S2) from their respective multisession means (Table 4) (2016): (Prinz et al 1976;Hamlyn and Bonatti 1980;Dick and Bullen 1984;Michael and Bonatti 1985;Shibata and Thompson 1986;Dick 1989;Bryndzia and Wood 1990;Johnson et al 1990;Juteau et al 1990;Komor et al 1990;Bonatti et al 1992Bonatti et al , 1993Cannat et al 1992;Johnson and Dick 1992;Snow 1993;Constantin et al 1995;Arai and Matsukage 1996;Dick and Natland 1996;Ghose et al 1996;Jaroslow et al 1996;Niida 1997;Ross and Elthon 1997;Stephens 1997;Hellebrand et al 2002aHellebrand et al , 2002bBrunelli et al 2003;Hellebrand and Snow 2003;Seyler et al 2003Seyler et al , 2007Coogan et al 2004;Workman and Hart 2005;Morishita et al 2007;Cipriani et al 2009;Warren et al 2009;Brunelli and Seyler 2010;Dick et al 2010;Warren and Shimizu 2010;…”