Geology, geochemistry and mineralization of the silica-carbonate alteration (listwaenite) from Late Cretaceous ophiolitic melanges at Curek-Divrigi in Sivas Province and at Guvene, Karakuz-Hekimhan in Malatya Province, central east Turkey

摘要

The late Cretaceous (pre Maastrichtian) alteration of serpentinite bodies in the Divrigi and Kuluncak ophiolitic melanges has formed two distinct types of listwaenite. The earliest, type I, is silica-carbonate listwaenite, which is dominated by $rm silicasp+calcitesp+dolomitesp+ankeritepm$ magnesite. Later, type II listwaenite bodies are carbonate listwaenite characterized by $rm calcitesp+dolomitesp+ankeritepm magnesite,$ and lack any significant introduced silica. Accessory opaque minerals including pyrite, hematite, limonite, gerdorsffite, marcasite, carollite, langsite, and chromite are less abundant in type II listwaenite than they are in type I listwaenite. Type I and type II listwaenite bodies have been distinguished in the Guvenc and Karakuz areas, however, in Curek only type I has been recognized. The two listwaenite types are dissimilar in their major oxide, base-precious metal and trace-REE element contents.;Type I listwaenite has in order of relative abundance, SiO$sb2,$ CaCo$sb3,$ Fe$rmsb2Osb3$ and MgO, whereas type II listwaenite is dominated by CaCO$sb3,$ Fe$rmsb2Osb3$ and MgO. Aluminum, Ti, Mn, Na, K and P oxides are negligibly low in both listwaenite types in all study areas. Concentration of base and precious metals are much higher in type I listwaenite bodies than in type II listwaenite bodies but Au and Ag are present only in very low concentrations in both listwaenite types. Concentrations of Co, Ni, Pb, As, Sb, S and Ag are greater in listwaenite than in associated sperpentinite, and these elements have probably been leached from adjacent serpentinite by hydrothermal fluids.;Type I and type II listwaenite in the Karakuz and type I listwaenite in Guvenc area formed along thrust fault zones. However, the majority of type I in Curek and type II in Guvenc are not fault controlled. In clearly fault-related listwaenite bodies, thrust fault(s) acted as path ways for mineralizing and altering fluids. In non fault-related listwaenite bodies, hydrothermal fluids moved along highly serpentinized microfractured, stockworked and porous ultramafic rocks. The hydrothermal fluids involved in the formation of listwaenite, differed from those that formed type I listwaenite, which were enriched in SiO$sb2$, as well as CO$sb2,$ Ca and $rm Hsb2O,$ whereas those that formed type II listwaenite were SiO$sb2$ deficient, and enriched only in CO$sb2,$ Ca and $rm Hsb2O.$.;The rare-earth and trace element concentration of serpentinite, listwaenite and scapolite in the Divrigi and Kuluncak ophiolitic melanges indicate that all of the ultramafics and their alteration products were derived from MORB, which is depleted in certain elements and oxides. A comparison of the geochemistry of rocks in the Ankara melange with that of the Divrigi-Kuluncak melanges suggests that those melanges were derived from different oceanic environments. The results presented in this study support the idea that the Divrigi and Kuluncak ophiolitic melanges within Taurides ophiolite belt originated from a northern Tauride oceanic lithosphere (Poisson, 1986), instead of a northern branch of the Neo-Tethys (Sengor and Yilmaz, 1981).