Stability of fluorite and titanite in a calc‐silicate rock from the Vizianagaram area, Eastern Ghats Belt, India

Abstract

In the Vizianagaram area (E 83°29.442¢; N 18°5.418¢) of the Eastern Ghats Belt, India, a suite of graphite-bearing calc-silicate granulites, veined by syenitic rocks, developed wollastonite-rich veins at 6-7 kbar and > 850°C. During subsequent near-isobaric cooling wollastonite was replaced by calcite + quartz and a graphic intergrowth of fluorite + quartz ± clinopyroxene. Titanite with variable Al and F contents is present throughout the rock. Combining the compositional variation of titanite and recent experimental data, it is demonstrated that the mineral assemblage, the composition of coexisting fluids and the mobility of Al exert a far greater control on the composition of titanite than pressure, temperature or the whole rock composition. Thermodynamically computed isothermalisobaric logf O 2 -logf CO 2 and logf F 2 -logf O 2 grids in the systems Ca-Fe-Si-O-F (CISOF; calcite-free) and Ca-Fe-Si-O-F-C-H (CISOFV; calcite-present) demonstrate the influence of bulk rock and fluid compositions on the stability of the fluorite-bearing assemblages in diverse geological environments and resolve the problem of the stability of titanite in fayalite + fluorite-bearing rocks in the Adirondacks. The mineralogy of the studied rocks and the topological constraints tightly fix the logf O 2 , logf F 2 and logf CO 2 at )15.8, )30.6 and 4.1, respectively, at 6.5 kbar and c. 730°C. Because of the similarity in the P-T conditions, the compositions of pore fluids in the fluorite-bearing assemblages of the Adirondacks and the Eastern Ghats Belt have been compared.

Complexly zoned niobian titanite from hedenbergite skarn at Písek, Czech Republic, constrained by substitutions Al(Nb,Ta)Ti—2, Al(F,OH)(TiO)—1 and SnTi—1

“…Chakhmouradian, 2004), hence, niobian titanite is typically a low-T mineral. Concerning Al,F-rich but Nb(Ta)-free titanite, it is stable over a very wide range of P-T conditions from high-grade metamorphic rocks of eclogite facies (Markl and Piazolo, 1999;Castelli and Rubatto, 2002;Sengupta et al, 2004) to lowgrade metasediments (Enami et al, 1993).…”

Experimental determination of CePO4 and YPO4 solubilities in H2O–NaF at 800°C and 1 GPa: implications for rare earth element transport in high‐grade metamorphic fluids

“…Increased fluorine concentrations are indicated by F-bearing minerals in a wide variety of deep metamorphic settings (Bohlen & Essene 1978;Zhu & Sverjensky 1992;Pradeepkumar & Krishnanath 1996;Markl & Piazolo 1998;Tsunogae et al 2003;Sengupta et al 2004). Increased fluorine concentrations are indicated by F-bearing minerals in a wide variety of deep metamorphic settings (Bohlen & Essene 1978;Zhu & Sverjensky 1992;Pradeepkumar & Krishnanath 1996;Markl & Piazolo 1998;Tsunogae et al 2003;Sengupta et al 2004).…”

“…Fluorine plays an important role in metal complexing during fluid-rock interaction at high pressure (P) and temperature (T). Increased fluorine concentrations are indicated by F-bearing minerals in a wide variety of deep metamorphic settings (Bohlen & Essene 1978;Zhu & Sverjensky 1992;Pradeepkumar & Krishnanath 1996;Markl & Piazolo 1998;Tsunogae et al 2003;Sengupta et al 2004). Fluorine-rich fluids can strongly influence the distribution of Ti and other high field-strength elements (HFSE), rare earth elements (REE; light rare earth elements, LREE; heavy rare earth elements, HREE), and U and Th during metamorphism and partial melting (Oreskes & Einaudi 1990;Peterson et al 1991;Pan & Fleet 1996;Rudnick et al 2000;Klemme 2004;Jiang et al 2005;Rapp et al 2010).…”

A new occurrence of garnetiferous skarn rocks in Saudi Arabia: a case study from Bahrah area, Jeddah–Makkah Al Mukaramah highway

“…Titanite in the calc-silicates of these workers contains 2.58 wt.% Al 2 O 3 and 0.56 wt.% FeO t , and our Bahrah titanite contains up to 3.25 and 1.77 wt.%, respectively. Sengupta et al (2004) concluded that chemistry of titanite in calc-silicate rocks is controlled by the coexisting fluids and mobility of Al 3+ rather than by pressure, temperature, and whole-rock composition. However, role of Al 3+ in titanite from calcsilicates, either formed by regional metamorphism under high pressure or by a metasomatic thermal effect, is not well understood as titanite in both cases has low Al content (Ye et al 2002).…”