The analyzed samples are metamorphic clasts and serpentine muds collected onboard the JOIDES Resolution during Legs 125 (Site 778 and 779, Conical Seamount) and 195 (Site 1200, South Chamorro Seamount). Examination of several impregnated serpentinite mud thin sections under cross-polarized light and smear slide analysis reveals that the muds contain abundant mineral grains, different from serpentine, and, less commonly, entire lithic fragments containing more than one mineral. Onboard X-ray diffraction analysis, as well as onshore electron microprobe analysis (Gharib et al., 2002) of the serpentinite muds confirms that Leg 195 muds contain mostly serpentine but also minerals like brucite, chlorite, amphiboles, micas, spinel, carbonates, pyroxene, talc, and epidote (Salisbury, Shinohara, Richter, et al., 2002; Fryer et al., submitted [N1]). A detailed description of the Leg 125 serpentine mud mineralogy is given by Fryer and Mottl (1992), Lagabrielle et al. (1992), and Benton (1997). The similarities (and differences) between the Leg 125 and Leg 195 muds is discussed by Fryer (this volume).
A quantity of wash-core material was recovered from Hole 1200B. We wet-sieved a portion of this material using 60-µm mesh sieves and dried the sample in an oven for several hours at 100°C. Then the material was further sieved to separate the >0.1-cm fraction. The largest fraction included lithic material, mineral fragments, and crystals (mostly fibrous serpentine vein filling material) that ranged from 0.1 to ~2 cm in size (grit). The discovered metamorphic clasts are usually sub-rounded and millimeter size to a few centimeters in diameter (Fig. F2A, F2B). The grit was inspected under a binocular microscope and handpicked for discrete lithologies. Material processed for whole-rock analysis was 0.5–2 cm in diameter.
Mineralogical investigation of the larger clasts from Leg 125 shows that they are metabasalts, recording prehnite-pumpellyite to greenschist facies metamorphism (Johnson, 1992). Leg 195 metabasic lithologies include a mineralogically diverse suite of schists: chlorite/serpentine schist, sodic-amphibole/mica schist (Fig. F2C), tremolite/chlorite schist (Fig. F2B), and less common talc (Fig. F2A) and chlorite-pyroxene schists (Salisbury, Shinohara, Richter, et al., 2002; Gharib et al., 2002). Recent study of the Leg 195 metabasic clasts, as well as previous studies on Leg 125 metabasic clasts (Maekawa et al., 1992, 1993; Fryer et al., 1999), discovered high-pressure/low-temperature (HP/LT) mineral phases (Gharib et al., 2002; Fryer et al., submitted [N1]). The schists with Na amphibole composed ~1 vol% of the muds, and the proportion of metabasic grit in relation to the remaining, mostly serpentine, material is ~6 vol%. The coarse mica-schists are less abundant in Holes 1200D, 1200E, and 1200F. A predominance of chlorite-containing schists was observed in all of the holes.
According to Johnson (1992), the non-serpentinite clasts from Leg 125 are metabasalts and metadiabases. Secondary textures usually associated with these metabasalts and metadiabases involve abundant serpentine, chlorite, carbonates, prehnite-pumpellyite, epidote, and hydrogarnets, all overprinting primary igneous textures, and less common talc, lawsonite, quartz, and Fe oxides (Johnson, 1992). In the Leg 195 metamorphic clasts, all of the primary minerals are entirely replaced by low-temperature assemblages and the primary textures of the clasts are impossible to identify. The analytical work reported in this paper is on single metamorphic (metabasic) clasts, which represent very limited amounts of sample powder. However, we have not attempted to combine or group metamorphic schists based on their similar visual appearances.