Fluid-driven resetting of titanite following ultrahigh-temperature metamorphism in southern Madagascar
48
Citation
67
Reference
10
Related Paper
Citation Trend
Keywords:
Titanite
Coesite
Geochronology
Trace element
Recent discoveries of diamond and coesite in the upper crustal rocks of the Earth have drastically changed scientists' ideas concerning the limits of crustal metamorphism. This book provides detailed accounts of the discoveries of diamond and coesite in crustal rocks and provides insights regarding their formation at very high pressures. The formation of these minerals is related to subduction and continental collision and the tectonics, petrological and mineralogical conditions of diamond and coesite formation are each discussed. Written by the leading workers in this exciting field, this book attempts to define an entirely new field of metamorphism - ultrahigh pressure metamorphism (UHPM). In doing so, it explains the formation of ultrahigh pressure minerals and explores new ideas regarding the tectonic setting of this style of metamorphism. This book will be of particular interest to researchers and graduate students of metamorphic petrology and global tectonics.
Coesite
Cite
Citations (516)
Geochronology
Titanite
Rutile
Cite
Citations (0)
Titanites previously reported from high-pressure rocks commonly contain high Al and F contents. This finding has led previous workers to conclude that high Al and F in titanite can expand its stability field to high-pressure and ultrahigh-pressure (UHP) conditions. In this study, a coesite inclusion was identified in titanite of aragonite- and jadeite-bearing gneiss from the Dabieshan UHP metamorphic terrane of eastern China. We also found UHP titanite in carbonate-bearing garnet clinopyroxenite from the Sulu UHP terrane. Interestingly, both types of the UHP titanite mentioned above contain low Al and F contents. Therefore, our data indicate that the high-Al and F contents are not necessary criteria for stabilizing titanite to UHP conditions. It is inferred that the UHP titanite formed via the reaction TiO2 + CaCO3 + SiO2 = CaTiSiO5 + CO2, and that the presence of the UHP assemblage aragonite + rutile + clinopyroxene + coesite in the host rock and a very low XCO₂ value in the coexisting fluid are crucial conditions for the formation of these UHP titanites
Titanite
Coesite
Cite
Citations (34)
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.
Titanite
Coesite
Diopside
Rutile
Cite
Citations (4)
The field of ultra‐high pressure metamorphism (UHPM) emerged only 12 years ago when microscopic relics of coesite were found in crustal rocks that had been metamorphosed during subduction related to continental collision. Coesite‐bearing metamorphic rocks were soon found elsewhere, and then metamorphic microdiamonds were discovered. Suddenly, the pressure axis for orogenic metamorphism had expanded from 1.5–2.0 to 3.0–4.0 GPa!
Coesite
Cite
Citations (3)
Coesite exsolved from supersilicic titanite was discovered in an impure calcite marble at Kumdykol in the Kokchetav UHP (ultrahigh-pressure) metamorphic terrane, northern Kazakhstan. This impure marble consists mainly of calcite, K-feldspar, diopside, and symplectites of diopside + zoisite, with minor amount of titanite, phengite, and garnet. No diamond was found in the marble. Coesite and quartz, which have needle or platy shapes measuring about 20-60 mm in length, occur as major exsolved phases in the cores and mantles of titanite crystals with minor calcite and apatite. The strongest Raman band for the coesite needles and plates was confirmed at about 524 cm-1 with a weak band at about 271 cm-1. To estimate the initial composition of the titanite before coesite exsolution, exsolved phases were reintegrated by measuring their area fractions on digital images. The highest excess Si in titanite was thus determined to be 0.145 atoms per formula unit (apfu). This composition requires a pressure higher than 6 GPa on the basis of phase relations in the system CaTiSiO5-CaSi2O5. This pressure is consistent with other evidence of high pressure in the same marble, such as 1.4-1.8 wt% K2O and over 1000 ppm H2O in diopside. Supersilicic titanite and coesite exsolution also indicate that SiO2 exsolution occurred in the coesite stability field during exhumation of the UHP metamorphic unit.
Titanite
Coesite
Diopside
Phengite
Cite
Citations (121)