Petrology of Basalt Drilled from the Galapagos Spreading Center, Deep Sea Drilling Project Leg 54

Abstract

Basalt recovered from Site 424, 22 km south of the Galapagos spreading center, East Pacific Ocean, is FeO*-and TiO 2 -rich (-13.3 and 1.85 wt. %, respectively, FeO* expressing the total Fe content) oceanic tholeiite containing groundmass clinopyroxene (Fs 16 _ 35 ), plagioclase (An 60 _ 70 ), titaniferous magnetite, pyrrhotite, and interstitial material, much of which is altered but SiO 2 -rich where fresh. Trace-element abundances in these ferrobasalts (FeOVMgÕ 2.1) show low Ni contents (30 to 90 ppm), a depletion in light REE, and a negative Eu anomaly. Basalt recovered from Site 425, 62 km north of the spreading center, is high-SiO 2 (51.5 wt %) and lowNa 2 O (-2.0 wt °/o) oceanic tholeiite and is composed of phases similar to those of Site 424 ferrobasalt, except that clinopyroxene is richer in MgO (Fs lo _ 3O ). Basalts at both sites are relatively fresh and free of notable hydrothermal alteration.The ferrobasalts are compositionally similar to those previously reported from the region of the Galapagos spreading center, and are characteristic of a "normal" mid-oceanic ridge environment where substantial clinopyroxene and plagioclase (and minor olivine) fractionation occurred in light REE and LIL element-depleted parental magma. The Site 425 basalt, although fractionated, is substantially closer to primitive oceanic tholeiite than ferrobasalt and is probably the product of largely plagioclase and lesser olivine fractionation from primitive oceanic tholeiite magma.

Petrographical and Chemical Study of Basement Basalts from the Galapagos Spreading Center, Leg 70

“…They can, therefore, be classified as ferrobasalts (Melson et al, 1976) and are similar to other ferrobasalts already dredged from the area of the Galapagos Spreading Center (Anderson et al, 1975;Schilling et al, 1976;Clague and Bunch, 1976;Fodor et al, 1980). The medium content of Ni (118-148 ppm) and Co (61-103 ppm) and the high FeOVMgO (1.77 to 1.97) ratio indicate a substantial fractionation of Fo-rich olivine from the parental magma.…”

“…For Clague and Bunch (1976) these ferrobasalts are formed by fractionation of Plagioclase, clinopyroxene, and olivine in the proportions 9.3:7.7:1 (differentiate 3). The calculated proportions given by Fodor et al (1980) are respectively 11.3:12.8:1 and 50% of crystallized magma for the same ferrobasalts.…”

“…Site 425 basalts represent moderately fractionated oceanic tholeiites by mainly Plagioclase plus olivine fractionation in the proportion 3:1 (crystallized: 28%, Fodor et al, 1980). Basalts from Sites 507, 508, and 424 are close to differentiate 3 (Clague and Bunch, 1976).…”

“…However they are slightly poorer in TiO 2 (1.56-1.78 wt.%), wt.%), V (347-375 ppm), and Cr (176-190 ppm) than the latter. Normative quartz is Fodor et al (1980) described basalts from Sites 424 and 425, which were drilled during Leg 54 in the area of the Galapagos Spreading Center. Site 424 is located near Sites 506, 507, and 508, whereas Site 425 is located near Site 510 (Fig.…”

Constraints on the source of Cu in a submarine magmatic-hydrothermal system, Brothers volcano, Kermadec island arc

“…The presented dataset was supplemented by previously published magmatic sulphide data from Brothers volcano (n = 128; Keith et al 2017) and from mid-ocean ridges of the Atlantic (Kanehira et al 1973;MacLean 1977;Mathez 1980;Petersen 1984;Patten et al 2012Patten et al , 2013Marchesi et al 2013), Pacific (Mathez and Yeats 1976;Foder et al 1980;Distler et al 1983;Schrader and Stow 1983;Francis 1990;Ackermand et al 2007;Patten et al 2012) and Indian Ocean (Francis 1990;Yang et al 2014). …”