Sulfides in Leg 37 drill core from the Mid-Atlantic Ridge

Abstract

Sulfides in 27 samples of drill core from four Leg 37 drill holes have been studied. Pynte is the most abundant sulfide, averaging 0.39 % 0.51% of basalt samples. Also present in basalt are sparse (0.0001%) and small ((8 p n ) magmatic globules of finely intergrown pyrrhotite, pentland~t e , and chalcopyrite4ss, as well as a few globules composed of only one of these minerals. Larger and more abundant magmatic globules are present in gabbro and peridotite; pyrite is a minor phase in these rocks.Fe. Ni. Cu, and S are the major elements. and Co a minor element in rhe globuIes. A v e n g e d NilCtr ratios Fur globules are: 3.3 (peridatitel, 1.0 (gabbro), and 0.4(basalt), the decrease in ralio indicaring less normi~tivcolivine in the respective parent magmas when the globules were formed.Sulfides in globules in peridotite. and to a lesser extent in gahhro. form distinci grains free of inclusions. and appear to have equilibrated to below 3110'C. In basalt rhe minenils are finely inrergmwn and ind~cate quenching above abour hOOCC, w i~h local equilibratian at lower tempemtures.Three analyses of sulfur in basalt glass ranged from 930 to 1160 ppm, in good agreement with other analyses of deep-ocean basalts.On a etudie les sulfures dans 27 echantillons de carottes provenant de quatre forages de la bordee 37, DSDP. La pyrite est la forme de sulfure la plus abondante avec en moyenne 0.39 4 0.51% des echantillons de basalte. I1 y a aussi dans le basalte de rares (0.0001%) et petits (<8 ~m ) globules magmatiques ou on observe la fine intercroissance de pyrrhotite, de pentlandite et de chalcopyrite, aussi bien que quelques globules comprenant seulement un de ces mineraux. Des globules magmatiques plus gros et plus abondants sont presents dans le gabbro et la peridotite, mais la pyrite dans ces roches est une phase mineure.Fe, Cu, Ni et S sont les elements majeurs et Co est un Clement mineur dans les globules. Les rapports moyens de Ni/Cu pour les globules sont: 3.3 (peridotite), 1.0 (gabbro) et 0.4 (basalte), la diminution du rapport indiquant moins d'olivine normative dans les magmas parents respectifs au moment de la formation des globules.Les sulfures dans les globules de la peridotite, et jusqu'i un certain point dans le gabbro, forment des grains distincts sans inclusions et paraissent avoir atteint l'equilibre en dessous de 300°C. Dans le basalte, les mineraux presentent une fine intercroissance, ce qui indique un refroidissement rapide au dessus d'environ 600°C avec equilibration localisee a plus basses temperatures.Trois analyses de soufre dans le verre basaltique donnent des valeurs de 930 a 1160 ppm, en accord avec d'autres analyses de basaltes des fonds oceaniques.[Traduit par le journal]Can.

Immiscible sulfide melts in primitive oceanic magmas: Evidence and implications from picrite lavas (Eastern Kamchatka, Russia)

“…Our data are consistent with the records of omnipresent sulfide globules in the Atlantic and Pacific basalts and glasses (e.g., Czamanske and Moore, 1977;Kanehira et al, 1973;MacLean, 1977;Mathez, 1976;Moore and Calc, 1971) and reconfirm sulfide saturation of common MORB melts during crystallization (e.g., Haughton et al, 1974;Mathez, 1976).…”

“…Even in the case of rare high-Mg rocks with primitive olivine in some large igneous provinces on continents (see review in Kamenetsky et al, 2017), a record of the early sulfide immiscibility is yet to be discovered. In contrast to continental magmas, sulfide globules in phenocrysts and glasses at mid-ocean ridge basalts (MORB) have been documented since the underwater samples became available in the 1960's (e.g., Czamanske and Moore, 1977;Francis, 1990;Kanehira et al, 1973;MacLean, 1977;Mathez, 1976;Moore and Calc, 1971;Peach et al, 1990). These studies provided first insights into occurrence of silicate-sulfide unmixing in shallow plumbing systems during crystallization and eruption, but lacked specific details about the liquidus assemblage and compositions at the onset of immiscibility.…”

Magmatic fluids immiscible with silicate melts: examples from inclusions in phenocrysts and glasses, and implications for magma evolution and metal transport

“…Desborough et al. 1968; Mathez 1976; Mathez & Yeats 1976; Czamanske & Moore 1977; MaClean 1977; Gurenko et al. 1987; Chaussidon et al.…”

“…The occurrence and compositions of sulphide globules in glasses and olivine phenocrysts in basalts from mid-ocean rifts, backarc basins and oceanic seamounts and islands, documented by numerous studies (e.g. Desborough et al 1968;Mathez 1976;Czamanske & Moore 1977;MaClean 1977;Gurenko et al 1987;Chaussidon et al 1989;Francis 1990;Peach et al 1990;Stone & Fleet 1991;Ackermand et al 1998;Roy-Barman et al 1998) have been used to put constraints on the process of sulphide immiscibility and partitioning of sulphur and metals, however, application of studies of tiny sulphide melt samples (usually <100 lm) is still problematic. In part, this relates to the fact that droplets of formerly homogeneous sulphide melt are composed of several phases at room temperature (Fig.…”

EVIDENCE FOR OPEN-SYSTEM BEHAVIOR IN IMMISCIBLE Fe S O LIQUIDS IN SILICATE MAGMAS: IMPLICATIONS FOR CONTRIBUTIONS OF METALS AND SULFUR TO ORE-FORMING FLUIDS

“…Although support for the hypothesis is not universal (e.g., Fleet et al 1977, Stone et al 1989, the importance of immiscibility of sulfide liquids in ultramafic melts in forming Ni-Cu sulfide ores is well known. In addition, immiscible globules of sulfide are common in intrusive and extrusive mafic rocks from a variety of tectonic settings (e.g., Desborough et al 1968, Mathez 1976, MacLean 1977, Groves et al 1986, Naldrett 1992. It is also widely recognized that an Fe-sulfide phase is commonly formed at some stage during evolution of more silicic magmas (e.g., Whitney & Stormer 1983, Whitney 1984, 1988, Candela 1989, Imai 1994.…”