A layered basic intrusion, deformed and metamorphosed in granulite faciès of the Sri Lanka basement

1991 ◽  
Vol 80 (3) ◽  
pp. 779-800 ◽  
Author(s):  
R. Kleinschrodt ◽  
G. Voll ◽  
W. Kehelpannala
Keyword(s):  
Sri Lanka ◽  
Granulite Facies

Petrology and geochronology of cordierite bearing assemblages from the Wanni Complex – Sri Lanka

2020 ◽  
Author(s):  
Nikolaus Lechner ◽  
Christoph Hauzenberger ◽  
Marcel Masten ◽  
Dominik Sorger ◽  
G.W.A. Rohan Fernando
Keyword(s):  
Sri Lanka ◽  
Rock Type ◽  
Granulite Facies ◽  
Granulite Facies Metamorphism ◽  
Pan African ◽  
Basement Rocks ◽  
The Matrix ◽  
The Common ◽  
Group 2 ◽  
Uht Metamorphism

<p>Based on differences in metamorphic grade and isotope model ages, the basement rocks of Sri Lanka can be subdivided from NW to SE into the Wanni Complex (WC), the Highland Complex (HC) and the Vijayan Complex (VC) (Milisenda et al. 1994). The UHT conditions of the HC were studied extensively and are well constrained whereas data from the WC and VC are less abundant. Only few recent petrological and geochemical work has been done especially along the WC–HC boundary which is still ill-defined (Kitano et al. 2018; Wanniarachchi & Akasaka 2016). Due to the common occurrence of migmatites, pyroxene bearing gneisses, and cordierite bearing metapelites/paragneisses, the WC clearly experienced granulite facies metamorphism. However, PT conditions are lower compared to the HC. In this study, U-Th-Pb monazite dating combined with a petrological study including phase equilibria modelling and thermobarometry was conducted focusing on cordierite bearing migmatic biotite gneisses located at the WC–HC boundary in the West of Sri Lanka. The HC underwent UHT metamorphism at 580-570Ma (Sajeev et al. 2010), the main metamorphic phase of the VC is dated with 580Ma. (Kröner et al., 2013). With U-Th-Pb monazite ages of around 530 Ma, the cordierite bearing assemblages from the WC are significantly younger (Wanniarachchi & Akasaka 2016). The predominantly felsic but also mafic peraluminous migmatic ortho- and paragneisses comprising the mineral assemblage cordierite + garnet + biotite + plagioclase + k-feldspar + quartz + ilmenite + magnetite + spinel + sillimanite ± orthopyroxene and contain monazite (+ zircon ± xenotime) as garnet inclusions (Group1) and in the matrix (Group2). Group1 monazite ages cluster around 575±5 Ma and 561±5 Ma whereas ages of Group 2 cluster at 550±3 and 527±3. Based on ages and textural occurrence of monazite we suggest that two thermal events at ca. 550-575 Ma and ca. 530-550 Ma are recorded in this rock type indicating a complex evolution during the late stage of the Pan-African orogeny. PT conditions range from 700–900°C and from 5–8 kbar with a decreasing north-south gradient. Further geochronological investigations are needed to relate either to the older or the younger overprint to the main metamorphic phase of the WC.</p><p>Kitano, I., Osanai, Y., Nakano, N., Adachi, T., & Fitzsimons, I. C. W. (2018). Journal of Asian Earth Sciences, 156, 122–144.</p><p>Kröner, A., Rojas-Agramonte, Y., Kehelpannala, K. V. W., Zack, T., Hegner, E., Geng, H. Y., … Barth, M. (2013). Precambrian Research, 234, 288–321. </p><p>Milisenda, C. C., Liewa, T. C., Hofmanna, A. W., & Köhler, H. (1994). Precambrian Research, 66(1–4), 95–110.</p><p>Sajeev, K., Williams, I. S., & Osanai, Y. (2010). Geology, 38(11), 971–974.</p><p>Wanniarachchi, D. N. S., & Akasaka, M. (2016). Journal of Mineralogical and Petrological Sciences, 111(5), 351–362.</p>

Metamorphic evolution and geochronology of gneisses from the Wanni Complex, Sri Lanka

2020 ◽  
Author(s):  
Marcel Masten ◽  
Christoph A. Hauzenberger ◽  
Nikolaus Lechner ◽  
Daniela Gallhofer ◽  
G.W.A. Rohan Fernando
Keyword(s):  
Earth Sciences ◽  
Sri Lanka ◽  
Granulite Facies ◽  
Northwestern Part ◽  
Southwestern Part ◽  
Metamorphic Overprint ◽  
Icp Ms ◽  
Wide Range ◽  
History Of ◽  
Isotopic Model

<p>The Wanni Complex is found in the northwestern part of Sri Lanka. The boundary to the Highland complex occurring to the south is partly ill defined. Differences in isotopic model ages were used to seperate both units (Kitano et al. 2018; Milisenda et al. 1994). While the Highland Complex has gained a lot of attention due to the UHT metamorphic overprint (up to 1150°C and 8-12kbar)(Sajeev and Osanai 2004) detailed petrological and geochronological work in the Wanni Complex is missing. Only a few studies focus on the border area between the Wanni Complex and the Highland Complex (Kitano et al. 2018; Wanniarachchi and Akasaka 2016).</p><p>Large areas of the Wanni Complex are covered by biotite gneisses, mostly migmatic, partly with occurrences of arrested charnockites or displaying potassium metasomatism (Cooray 1994; Kröner et al. 2003). However, charnockitic gneisses, garnet bearing gneisses and in the southwestern part cordierite bearing gneisses and metapelites occur which can be used for obtaining the PTt history of this complex. PT conditions of the Wanni Complex obtained from garnet bearing rocks place the metamorphic overprint clearly into the granulite facies and partly into the UHT field. Compared to the Highland Complex, temperatures are somewhat lower at 800-1000°C at 7-9kbar.</p><p>LA-ICP-MS U/Pb dating was performed on zircons from different locations of the Wanni Complex and shows igneous protolith ages of 855-963Ma. The ages were obtained from felsic hornblende-biotite gneisses and charnockitic gneisses. The wide range of ages could be a result of resetting shortly after magmatic crystallisation. CL images of some zircons show dark zones separated from oscillatory zoned cores by thin bright fronts. Taken together with core/rim dating of these zircons, this could be a sign of transgressive recrystallization (Hoskin and Black 2000).</p><p> </p><p> </p><p>Cooray, P.G. 1994. Precambrian Research 66(1–4):3–18.</p><p>Hoskin, P.W. and Black L.P. 2000. Journal of Metamorphic Geology 18:423–39.</p><p>Kitano, I., Osanai, Y., Nakano, N., Adachi, T. and Fitzsimons, I.C.W. 2018. Journal of Asian Earth Sciences 156:122–44.</p><p>Kröner, A., Kehelpannala, K.V.W. and Hegner, E. 2003. Journal of Asian Earth Sciences 22(3):279–300.</p><p>Milisenda, C.C., Liew, T.C., Hofmann, A.W. and Köhler, H. 1994. Precambrian Research 66:95–110.</p><p>Sajeev, K. and Osanai, Y. 2004. Journal of Petrology 45(9):1821–44.</p><p>Wanniarachchi, D.N.S. and Akasaka, M. 2016. Journal of Mineralogical and Petrological Sciences 111(5):351–62.</p>

Fluid and mineral inclusions in corundum from gem gravels in Sri Lanka

1989 ◽  
Vol 53 (373) ◽  
pp. 539-545 ◽  
Author(s):  
A. A. de Maesschalck ◽  
I. S. Oen
Keyword(s):  
Sri Lanka ◽  
Fluid Inclusions ◽  
Granulite Facies ◽  
Granulite Facies Metamorphism ◽  
Source Areas ◽  
Mineral Inclusions ◽  
Primary Fluid ◽  
Facies Metamorphism ◽  
Secondary Fluid

AbstractMineral and fluid inclusions were studied in seven gem corundums from gravels of three areas in Sri Lanka. All fluid inclusions are pure CO2. Microthermometry results on primary fluid inclusions suggest formation of corundum under granulite facies metamorphism (>630°C, 5.5 kbar). Secondary fluid inclusions indicate different retrograde events of post-metamorphic cooling and uplift for different source areas.

Geothermometry and geobarometry of high-grade rocks: a case study on garnet-pyroxene granulites in southern Sri Lanka

1991 ◽  
Vol 55 (378) ◽  
pp. 33-56 ◽  
Author(s):  
S. Faulhaber ◽  
M. Raith
Keyword(s):  
Sri Lanka ◽  
Large Scale ◽  
Equilibrium Constants ◽  
Granulite Facies ◽  
Mineral Chemistry ◽  
Compositional Variation ◽  
Data Set ◽  
Rock Types ◽  
Ideal Mixing ◽  
Granulite Belt

AbstractIn the central granulite belt of Sri Lanka, garnet-pyroxene granulites of granitic and gabbro-noritic composition are the most abundant rock types. The micro-structures and mineral chemistry data prove complete attainment of textural and large-scale chemical equilibrium during and following a phase of extreme penetrative deformation at conditions of the granulite facies (800–850 °C, 5 to 9 kbar). On a local scale, especially along the intergranular system, continued cation exchange decoupling from the early ceasing net-transfer reactions destroyed the near-peak metamorphic equilibrium. The extreme compositional variation of the coexisting ferro-magnesian phases (Fe/(Fe + Mg): gar 0.98−0.65, opx 0.92−0.40, cpx 0.88−0.28) and the near-isothermal conditions of equilibration throughout the studied area enabled examination of the effects of non-ideal mixing in garnet and pyroxenes on the equilibrium constants of reactions used in geothermobarometry, and tests on the quality of commonly applied thermometers/barometers and the validity of activity models adopted in the calibrations. The Sri Lankan data set reveals more or less pronounced compositional dependences for all of the tested gar-opx/gar-cpx Fe-Mg exchange thermometers and the opx + plg ⇌ gar + qtz barometers. Evidently the recommended solution models do not adequately describe the mixing properties of the involved ferro-magnesium mineral phases (garnet, orthopyroxene and clinopyroxene).

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