Drouin, Marion; Godard, Marguerite; Ildefonse, Benoit; Bruguier, Olivier; Garrido, Carlos J (2009): Geochemistry of the gabbroic lithosphere in IODP Holes 304-U1309D and 305-U1309D. PANGAEA, https://doi.org/10.1594/PANGAEA.780694, Supplement to: Drouin, M et al. (2009): Geochemical and petrographic evidence for magmatic impregnation in the oceanic lithosphere at Atlantis Massif, Mid-Atlantic Ridge (IODP Hole U1309D, 30°N). Chemical Geology, 264(1-4), 71-88, https://doi.org/10.1016/j.chemgeo.2009.02.013
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IODP Hole U1309D (Atlantis Massif, Mid-Atlantic Ridge 30°N) is the second deepest hole drilled into slow spread gabbroic lithosphere. It comprises 5.4% of olivine-rich troctolites (~ > 70% olivine), possibly the most primitive gabbroic rocks ever drilled at mid-ocean ridges. We present the result of an in situ trace element study carried out on a series of olivine-rich troctolites, and neighbouring troctolites and gabbros, from olivine-rich intervals in Hole U1309D. Olivine-rich troctolites display poikilitic textures; coarse-grained subhedral to medium-grained rounded olivine crystals are included into large undeformed clinopyroxene and plagioclase poikiloblasts. In contrast, gabbros and troctolites have irregularly seriate textures, with highly variable grain sizes, and locally poikilitic clinopyroxene oikocrysts in troctolites. Clinopyroxene is high Mg# augite (Mg# 87 in olivine-rich troctolites to 82 in gabbros), and plagioclase has anorthite contents ranging from 77 in olivine-rich troctolites to 68 in gabbros. Olivine has high forsterite contents (82-88 in olivine-rich troctolites, to 78-83 in gabbros) and is in Mg-Fe equilibrium with clinopyroxene. Clinopyroxene cores and plagioclase are depleted in trace elements (e.g., Ybcpx ~ 5-11 * Chondrite), they are in equilibrium with the same MORB-type melt in all studied rock-types. These compositions are not consistent with the progressively more trace element enriched (evolved) compositions expected from olivine rich primitive products to gabbros in a MORB cumulate sequence. They indicate that clinopyroxene and plagioclase crystallized concurrently, after melts having the same trace element composition, consistent with crystallization in an open system with a buffered magma composition. The slight trace element enrichments and lower Cr contents observed in clinopyroxene rims and interstitial grains results from crystallization of late-stage differentiated melts, probably indicating the closure of the magmatic system. In contrast to clinopyroxene and plagioclase, olivine is not in equilibrium with MORB, but with a highly fractionated depleted melt, similar to that in equilibrium with refractory oceanic peridotites, thus possibly indicating a mantle origin. In addition, textural relationships suggest that olivine was in part assimilated by the basaltic melts after which clinopyroxene and plagioclase crystallized (impregnation). These observations suggest a complex crystallization history in an open system involving impregnation by MORB-type melt(s) of an olivine-rich rock or mush. The documented magmatic processes suggest that olivine-rich troctolites were formed in a zone with large magmatic transfer and accumulation, similar to the mantle-crust transition zone documented in ophiolites and at fast spreading ridges.
Median Latitude: 30.085158 * Median Longitude: -42.059500 * South-bound Latitude: 30.001667 * West-bound Longitude: -42.119000 * North-bound Latitude: 30.168650 * East-bound Longitude: -42.000000
304-U1309D * Latitude: 30.168650 * Longitude: -42.119000 * Elevation: -1644.9 m * Recovery: 243.69 m * Campaign: Exp304 (Oceanic Core Complex Formation, Atlantis Massive 1) * Basis: Joides Resolution * Device: Drilling/drill rig (DRILL) * Comment: 77 cores; 380.7 m cored; 64 % recovered; 20.5 m drilled; 401.3 m penetrated
305-U1309D * Latitude: 30.001667 * Longitude: -42.000000 * Elevation: -1644.9 m * Recovery: 799.65 m * Campaign: Exp305 (Oceanic Core Complex Formation, Atlantis Massive 2) * Basis: Joides Resolution * Device: Drilling/drill rig (DRILL) * Comment: 216 cores; 1014.2 m cored; 78.8 % recovered; 0 m drilled; 1415.5 m penetrated
Datasets listed in this Collection
- Drouin, M; Godard, M; Ildefonse, B et al. (2009): (Table A1) General characteristics of studied samples from IODP Holes 204-U1309D and 305-U1309D. https://doi.org/10.1594/PANGAEA.780632
- Drouin, M; Godard, M; Ildefonse, B et al. (2009): (Table A2) Whole rock major elements from IODP Holes 204-U1309D and 305-U1309D. https://doi.org/10.1594/PANGAEA.780633
- Drouin, M; Godard, M; Ildefonse, B et al. (2009): (Table A3) Whole rock trace elements from IODP Holes 204-U1309D and 305-U1309D. https://doi.org/10.1594/PANGAEA.780638
- Drouin, M; Godard, M; Ildefonse, B et al. (2009): (Table A4, Table 1) Major and trace element analyses of clinopyroxenes of IODP Holes 204-U1309D and 305-U1309D. https://doi.org/10.1594/PANGAEA.780656
- Drouin, M; Godard, M; Ildefonse, B et al. (2009): (Table A5, Table 2) Major and trace element analyses of plagioclases of IODP Holes 204-U1309D and 305-U1309D. https://doi.org/10.1594/PANGAEA.780686
- Drouin, M; Godard, M; Ildefonse, B et al. (2009): (Table A6) Major element analyses of plagioclase of IODP Holes 204-U1309D and 305-U1309D. https://doi.org/10.1594/PANGAEA.780691
- Drouin, M; Godard, M; Ildefonse, B et al. (2009): (Table A7, Table 3) Major element analyses of olivine of IODP Holes 204-U1309D and 305-U1309D. https://doi.org/10.1594/PANGAEA.780692
- Drouin, M; Godard, M; Ildefonse, B et al. (2009): (Table A8) Major element analyses of spinel of IODP Holes 204-U1309D and 305-U1309D. https://doi.org/10.1594/PANGAEA.780693