Reactions and textures in grossular–wollastonite–scapolite calc–silicate granulites from Maligawila, Sri Lanka: evidence for high-temperature isobaric cooling in the meta-sediments of the Highland Complex

Mathavan, V.; Fernando, G.W.A.R.

doi:10.1016/s0024-4937(01)00057-3

Cited by 48 publications

(18 citation statements)

References 36 publications

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“…Baker et al, 1991;Carmichael, 1991;Connolly & Trommsdorff, 1991) allow prediction of the changes in both fluid and mineral compositions as a function of pressure and temperature. This approach has been widely applied in the five-and six-component systems CMS-HC (Skippen, 1971(Skippen, , 1974Skippen & Hutcheon, 1974;Baker et al, 1991), CAS-HC (Harley & Buick, 1992;Dasgupta, 1993;Fitzsimons & Harley, 1994;Bhowmik et al, 1995;Cartwright et al, 1997;Sengupta et al, 1997;Stephenson & Cook, 1997;Mathavan & Fernando, 2001), CMAS-HC (Carmichael, 1991;Connolly & Trommsdorff, 1991;Schm€ adicke et al, 2001;Castelli et al, 2007;Groppo et al, 2007), CFAS-C (Robinson, 1991;Sengupta & Raith, 2002) and CFAS-HC (Groppo et al, 2013b), whereas systems with more than six components have been very little investigated so far (Omori Moreover, in previous calculations the effects of Na-Ca substitution were mostly neglected, although Na-Ca solid solutions (plagioclase and scapolite) are often common in calc-silicate rocks. Owing to the lack of an appropriate solid solution model for scapolite, when 10 considered, the effects of Na-Ca substitution have been generally approximated either using activity-modified end-members (e.g.…”

Section: Novelty Of the Proposed 'Phase Diagram' 5 Approachmentioning

confidence: 99%

Metamorphic CO2 Production in Collisional Orogens: Petrological Constraints from Phase Diagram Modeling of Himalayan, Scapolite-bearing, Calc-silicate Rocks in the NKC(F)MAS(T)-HC system

Groppo

Rolfo

Castelli

et al. 2017

Journal of Petrology

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A reliable quantitative estimate of the metamorphic CO 2 flux from collisional orogens is fundamental to our understanding of the deep carbon cycle, but it is still far from being constrained. Among major uncertainties are the poor knowledge of the nature of metamorphic CO 2-producing processes and the amount of CO 2 potentially released through these reactions. Previous studies of metamorphic decarbonation reactions in metacarbonate rocks mainly used simple model reactions between end-members in simplified model systems. However, fully quantitative modelling of calcsilicate rocks requires an investigation of very complex systems with more than six components. Moreover, scapolite solid solution has been rarely included in previous studies, although this mineral is often a major constituent of calc-silicate rocks. This study focuses on (1) the CO 2-producing processes occurring in scapolite-bearing calc-silicate rocks and (2) the discussion of a methodological approach suitable to understand and quantify these processes. In this framework, phase relations and devolatilization reactions in the Na 2 O-K 2 O-CaO-(FeO)-MgO-Al 2 O 3-SiO 2-(TiO 2)-H 2 O-CO 2 [NKC(F)MAS(T)-HC] system are considered, with application to high-grade clinopyroxene þ calcite þ K-feldspar þ scapolite þ plagioclase þ zoisite calc-silicate rocks from the Himalaya. The NKC(F)MAS(T)-HC equilibria involving scapolite and plagioclase solid solutions are investigated using (1) isobaric T-X(CO 2) phase diagram sections and pseudosections and (2) mixed-volatile P-T phase diagram projections. This phase diagram approach allowed us to identify scapolite-bearing, CO 2-producing, univariant (i.e. isobaric invariant) equilibria that have never been recognized before, and that could not be detected without considering Na-Ca solid solutions in the calculations. It is demonstrated that the investigated calc-silicate rocks behaved as a nearly closed, internally buffered, system during prograde metamorphism and that most of the observed key microstructures correspond to isobaric univariant or invariant assemblages. In such a nearly closed system, the fluid was mostly produced during prograde heating at the isobaric invariant points, where abrupt changes in mineral modes also occurred. The proposed phase diagram approach further allows quantitative estimation of the amount and composition of the fluid produced at such isobaric invariant points. On average, 2Á5 mol of CO 2 (110 g) per 1000 cm 3 of reacting rock were produced during prograde metamorphism of this calc-silicate rock-type. Because similar scapolitebearing calc-silicate rocks are abundant in the Himalayan orogen, it is suggested that this calc-silicate rock-type might have produced large amounts of CO 2-rich fluids during Himalayan metamorphism. A preliminary estimate of these amounts at the scale of the whole orogen suggests a total metamorphic CO 2 production of $(2-7) Â 10 17 mol, corresponding to (1-3) Â 10 10 Mt of CO 2. Integrated over $20 Myr (i.e. the maximum duration of prograde metamorphism),...

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Section: Novelty Of the Proposed 'Phase Diagram' 5 Approachmentioning

confidence: 99%

Metamorphic CO2 Production in Collisional Orogens: Petrological Constraints from Phase Diagram Modeling of Himalayan, Scapolite-bearing, Calc-silicate Rocks in the NKC(F)MAS(T)-HC system

Groppo

Rolfo

Castelli

et al. 2017

Journal of Petrology

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“…comm.). Calc-silicate rocks from the KKB and the Buttala Klippe, an outlier of the HC in SE Sri Lanka, record temperatures of> 837~ and 875-900~ at pressures of< 6.6kbar and c. 9kbar, respectively (Satish-Kumar & Harley 1998;Mathavan & Fernando 2001). Reaction textures indicate isobaric cooling from peak metamorphic temperatures followed by near-isothermal decompression (Schumacher et aI.…”

Section: Correlation Between the Southern Granulite Terrain (Sgt) Andmentioning

confidence: 99%

Proterozoic crustal evolution of southernmost India and Sri Lanka

Braun

Kriegsman

2003

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The Southern Granulite Terrain of India comprises four Proterozoic domains (from north to south): the Madurai Block, and the Achankovil, Ponmudi and Nagercoil Units. All but the Achankovil Unit share similarities with the Highland Complex of Sri Lanka: (1) evidence for Palaeoproterozoic crust formation (from U-Pb ages and 2.0–3.0 Ga Nd model ages); and (2) Pan-African ultrahigh-temperature metamorphism between 610 and 550 Ma. More specifically, the Ponmudi Unit and the Madurai Block share lithological and petrological characteristics with the low-P and high-P domains of the Highland Complex, respectively. The Achankovil Unit is correlated with the Wanni Complex of Sri Lanka on the basis of lithologies and Nd model ages (1.0–2.0Ga). These domains and the Vijayan and Kadugannawa Complexes of Sri Lanka represent Late Mesoproterozoic-Early Neoproterozoic crustal domains.Similarities in tectonic style, degree of metamorphism and Neoproterozoic U-Pb ages, suggest a common Pan-African tectonothermal evolution for the lower crustal domains of southern India, Sri Lanka and the Lützow-Holm Bay of Eastern Antarctica. Sri Lanka may have been located at the junction between the Mozambique Belt and a second belt partly involving areas that underwent a Grenvillian high-grade event during the formation of Rodinia. Madagascar shows a similar Pan-African metamorphic overprint, but is located in a different position and lacks the influence of the second belt. Alternative views are discussed.

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“…The presumable source area belongs to the Highland Complex (Cooray , Kröner et al . , Mathavan and Fernando ), which is dominated by Proterozoic rocks that have experienced high‐grade (partially ultrahigh‐temperature) metamorphism during the Pan‐African event at ca . 550 Ma (Sajeev et al .…”

Section: Samples and Preparationmentioning

confidence: 99%

“…Both originated from placer deposits in the Ratnapura district, Sri Lanka (Dahanayake andRanasinghe 1985, Zoysa 2014). The presumable source area belongs to the Highland Complex (Cooray 1994, Kr€ oner et al 1994, Mathavan and Fernando 2001, which is dominated by Proterozoic rocks that have experienced high-grade (partially ultrahigh-temperature) metamorphism during the Pan-African event at ca. 550 Ma (Sajeev et al 2010, Dharmapriya et al 2017, andreferences therein).…”

Section: Samples and Preparation General Descriptionmentioning

confidence: 99%

GZ7 and GZ8 – Two Zircon Reference Materials for SIMS U‐Pb Geochronology

Nasdala

Corfú

Schoene

et al. 2018

Geostandard Geoanalytic Res

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Here, we document a detailed characterisation of two zircon gemstones, GZ7 and GZ8. Both stones had the same mass at 19.2 carats (3.84 g) each; both came from placer deposits in the Ratnapura district, Sri Lanka. The U‐Pb data are in both cases concordant within the uncertainties of decay constants and yield weighted mean 206Pb/238U ages (95% confidence uncertainty) of 530.26 Ma ± 0.05 Ma (GZ7) and 543.92 Ma ± 0.06 Ma (GZ8). Neither GZ7 nor GZ8 have been subjected to any gem enhancement by heating. Structure‐related parameters correspond well with the calculated alpha doses of 1.48 × 1018 g−1 (GZ7) and 2.53 × 1018 g−1 (GZ8), respectively, and the (U‐Th)/He ages of 438 Ma ± 3 Ma (2s) for GZ7 and 426 Ma ± 9 Ma (2s) for GZ8 are typical of unheated zircon from Sri Lanka. The mean U mass fractions are 680 μg g−1 (GZ7) and 1305 μg g−1 (GZ8). The two zircon samples are proposed as reference materials for SIMS (secondary ion mass spectrometry) U‐Pb geochronology. In addition, GZ7 (Ti mass fractions 25.08 μg g−1 ± 0.18 μg g−1; 95% confidence uncertainty) may prove useful as reference material for Ti‐in‐zircon temperature estimates.

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Reactions and textures in grossular–wollastonite–scapolite calc–silicate granulites from Maligawila, Sri Lanka: evidence for high-temperature isobaric cooling in the meta-sediments of the Highland Complex

Cited by 48 publications

References 36 publications

Metamorphic CO2 Production in Collisional Orogens: Petrological Constraints from Phase Diagram Modeling of Himalayan, Scapolite-bearing, Calc-silicate Rocks in the NKC(F)MAS(T)-HC system

Metamorphic CO2 Production in Collisional Orogens: Petrological Constraints from Phase Diagram Modeling of Himalayan, Scapolite-bearing, Calc-silicate Rocks in the NKC(F)MAS(T)-HC system

Proterozoic crustal evolution of southernmost India and Sri Lanka

GZ7 and GZ8 – Two Zircon Reference Materials for SIMS U‐Pb Geochronology

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