Titanite Stability in UHP Metacarbonate Rocks from the Kokchetav Massif, Northern Kazakhstan

Content Provider	Semantic Scholar
Author	Ogasawara, Yoshihide
Copyright Year	2014
Abstract	Stability relations of Ti-bearing mineral assemblages in the ultrahigh-pressure metacarbonate rocks from the Kokchetav Massif, northern Kazakhstan were analyzed by thermochemical calculations in the model system CaO-MgO-SiO2-TiO2-CO2-H2O. Each of three carbonate rocks has a distinct Ti-bearing mineral: rutile in diamond-bearing dolomite marble, titanite in calcite (after aragonite) marble and Ti-clinohumite in dolomitic marble (diamond-free). P-T-XCO2 relations in the system CaO-MgO-SiO2-TiO2-CO2-H2O were calculated using the published internally consistent dataset. Three reactions among 8 minerals (aragonite/calcite, coesite/quartz, diopside, dolomite, rutile, and titanite) are possible in this system: (1) dolomite + SiO2 (coesite/quartz) ＝ diopside + CO2, (2) CaCO3 (aragonite/calcite) + rutile + SiO2 (coesite/quartz) ＝ titanite + CO2, (3) dolomite + titanite ＝ CaCO3 (aragonite/calcite) + diopside + rutile. Schreinemakers’ analysis was employed to determine the stable configuration of the univariant curves. Reaction (3), a solid-solid reaction, indicates that titanite-dolomite pair was unstable at ultrahigh-pressure conditions and at medium to high XCO2. Dolomite-free ultrahigh-pressure carbonate rocks can contain titanite because the stability of aragonite + dolomite + rutile divides the bulk composition space into titanite-bearing compositions and dolomite-bearing compositions. This can explain the lack of titanite in natural ultrahigh-pressure dolomite-bearing metacarbonate rocks. In the Kokchetav UHP calcite marble, diopside formation preceded titanite formation at high- to ultrahigh-pressure conditions and stabilized diopside-rutile-aragonite assemblage as a compositional divide. At ultrahigh-pressure conditions, titanite formation from aragonite + coesite + rutile required extremely low XCO2 as 0.02 or lower. Such extremely low-XCO2 condition might have also controlled the stability of diamond in the Kokchetav UHP calcite marble. A simple model “Intraslab UHP Metasomatism” based on aqueous fluid infiltration and circulation in subducting slabs has been introduced to understand the role of fluid during deep continental subductions like the Kokchetav Massif.
Starting Page	11
Ending Page	31
Page Count	21
File Format	PDF HTM / HTML
Volume Number	62
Alternate Webpage(s)	https://core.ac.uk/download/pdf/144441030.pdf
Language	English
Access Restriction	Open
Content Type	Text
Resource Type	Article