Sulfate in plagiogranites from the Troodos ophiolite, Cyprus.

Abstract

Plagiogranites occur locally in the interface between the sheeted dike complex and the uppermost level of gabbros, containing a high proportion of sulfate with a &34S value of 13.0%0 on average. Strontium and sulfur isotopic compositions of the plagiogranites suggest that magmatic or magmatic-hydrothermal sulfate constitutes the major fraction of the sulfate in the plagiogranites with high &`i4S values and that seawater derived Sr might have been incorporated in the latest stage of crystallization.

Diversity of Felsic Rocks in Oceanic Crust: Implications From the Neoproterozoic Plagiogranites Within the Northeast Jiangxi Ophiolite, Southern China

“…The decreasing La N and (La/Yb) N indicate increasing differentiation by fractional crystallization. Similar geochemical trends have also been observed in plagiogranites from Troodos and Oman (Coleman & Peterman, 1975;Mukasa & Ludden, 1987;Kawahata et al, 1997;Stakes & Taylor, 2003;Amri et al, 2006;Rollinson, 2009;Anenburg et al, 2015;Haase et al, 2016), but these plagiogranites show overall low (La/ Yb) N ratios, indicating low-pressure partial melting or fractional crystallization of basaltic magmas (Freund et al, 2014). In addition, the La concentrations are not as low as those of the NJO suite, which arose fractional crystallization of basaltic magma as a dominant mechanism for the formation of plagiogranites within such oceanic crust (Coleman & Peterman, 1975;Pallister & Knight, 1981;Haase et al, 2006;Whattam et al, 2016).…”

“…Figure 13. La N -(La/Yb) N plot for typical plagiogranites worldwide (Coleman & Peterman, 1975;Pedersen & Malpas, 1984;Mukasa & Ludden, 1987;Li et al, 1994Li et al, , 1997Kawahata et al, 1997;Stakes & Taylor, 2003;Amri et al, 1996;Xu et al, 2006;Tang et al, 2007;Li et al, 2008;Rollinson, 2009;Fan et al, 2010;Freund et al, 2014;Anenburg et al, 2015;Haase et al, 2016). The dashed circles indicate the two groups of NJO plagiogranites.…”

“…Therefore, Figure 6. Chondrite-normalized whole-rock REE (Sun and McDonough, 1989) patterns of the NJO samples compared with typical plagiogranites worldwide (Coleman & Peterman, 1975;Mukasa & Ludden, 1987;Kawahata et al, 1997;Stakes & Taylor, 2003;Amri et al, 1996;Rollinson, 2009;Anenburg et al, 2015;Haase et al, 2016). only the analyses with concordant U-Th-Pb dates (−10% < discordance <10%) close to the crystallization age (ca.…”

A missing link between ancient and active mafic-hosted seafloor hydrothermal systems – Magmatic volatile influx in the exceptionally preserved Mala VMS deposit, Troodos, Cyprus

“…Secondary veins of gypsum that cross-cut massive sulfide at the Skouriotissa VMS deposit in Troodos average +6.6‰, a δ 34 S value that is indistinguishable from hypogene sulfide minerals (Parvaz, 2004). Furthermore, measured δ 34 S values from gypsum at Mala are indistinguishable from values for magmatic sulfate analysed in Troodos plagiogranites at +12.3‰ (Kawahata et al, 1997). Additional sulfur sources, such as sediment interaction and Miocene evaporites, can be discounted as the Troodos ophiolite formed in a sediment-free environment and gypsum formation during later uplift and exposure related fluid flow (e.g., Miocene evaporites) would lead to an enrichment in δ 34 S to approximately +22‰ (Alt, 1994) and this is not observed (Figure 6).…”

Discovery of lanthanide tetrad effect in an oceanic plagiogranite from an Ocean Core Complex at the Central Indian Ridge 25.DEG.S

“…This leads us to propose that the external fluids, probably derived from seawater, were incorporated into the oceanic plagiogranite magma and played a significant role in the formation of the tetrad REE pattern during the final stage of magma evolution. In fact, incorporation of seawater-derived fluid into plagiogranite magma has previously been pointed out by many researchers based on isotopic studies, e.g., Sr (Lanphere and Coleman, 1981;Kawahata et al, 1997;Bosch et al, 2004). Anatexis of amphibolites that were altered by seawater-derived hydrothermal fluid (Gillis and Coogan, 2002) is also likely to generate such fluid-rich oceanic plagiogranite magma.…”