Near-primary melt inclusions in anorthite phenocrysts from the Galapagos Platfrom

Composition and Crystallization Temperatures of Primary Melts from Hole 896A Basalts: Evidence from Melt Inclusion Studies

“…Plagioclases of similar composition have been reported from a variety of midocean ridge basalts (MORB); the Mid-Atlantic Ridge (Deep Sea Drilling Project Leg 37, Aumento, Melson, et al, 1977;Donaldson and Brown, 1977;FAMOUS, Stakes et al, 1984), the South East Indian Ridge (Price et al, 1986), the East Pacific Rise (Siqueiros Fracture Zone; Natland, 1989), and the Galapagos Platform (Sinton et al, 1993), and are commonly associated with megacrysts of Cr-rich magnesian diopside, forsteritic (Fo 88 _ 9l ) olivine, and Cr-Al spinel.…”

“…In an ideal fluid-saturated system the composition of the inclusion at the moment of homogenization is equal to that of the trapped melt, and the temperature of homogenization matches the temperature of trapping. Two techniques are employed; heating in a 1-atm furnace, under controlled oxygen fugacity (Sinton et al, 1993;Johnson et al, 1995), or in a visually controlled heating stage with a pure He atmosphere (Sobolev et al, 1980).…”

Composition of the Oceanic Crust

“…Thus, to the extent that the phenocrysts crystallized from a less evolved or less well-mixed melt, the melt inclusions record the nature of more primitive melt compositions. Studies of melt inclusions have revealed that, although they are broadly similar in major element composition to their host lavas, they tend to extend to more primitive (higher MgO) compositions, suggesting that they indeed record an earlier point in the evolutionary history of the magma (e.g., Nielsen et al, 1995;Shimizu, 1998;Sinton et al, 1993;Sobolev and Shimizu, 1993;Sours-Page et al, 1999Zhang et al, 2010). Maclennan (2008) found that melt inclusions in Icelandic lavas were more heterogeneous than whole-rock samples of the same flow.…”

Late Cretaceous crustal growth in the Gangdese area, southern Tibet: Petrological and Sr–Nd–Hf–O isotopic evidence from Zhengga diorite–gabbro

“…Previous studies indicate that anorthite mainly occurs in rocks from arc-related settings, such as high-Al basalts in island-arcs (Arculus and Wills, 1980;Brophy, 1986;Stolz et al, 1988;Beard and Borgia, 1989), boninitic lavas and gabbros from intraoceanic forearcs (Thy et al, 1989;Falloon and Crawford, 1991) and gabbros from active continental margins (Beard, 1986;Wilson, 1989;Zhou et al, 1994). Less commonly, anorthitic plagioclase has been reported in anhydrous mid-ocean ridge basalts (MORBs) (Donaldson and Brown, 1977;Wilkinson, 1982;Autio and Rhodes, 1984;Fisk, 1984;Stakes et al, 1984;Koyagnchi, 1986;Price et al, 1986;Sinton et al, 1993). Experimental studies indicate, however, that anorthite generated under these conditions requires refractory melts with high CaO/Na 2 O (12-15), or melts with exceptionally high Al 2 O 3 (>18 wt.%) (Panjasawatwong et al, 1995).…”