UPb geochronology of the Sri Lankan basement

Hölzl, Stefan; Hofmann, A. W.; Todt, W.; Köhler, Hermann

doi:10.1016/0301-9268(94)90048-5

Cited by 137 publications

(44 citation statements)

References 31 publications

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“…In most of the zircon, the overgrowths in age range 6 shows Th/U ratio less than 0.1, which is reasonable to interpret them as product of the final metamorphic event (range 6; 630-500 Ma). The age range 6 has been also suggested by previous studies and considered as either parts of a single event or discrete thermal events (Kröner et al, 1987;Hölzl et al, 1991;Hölzl et al, 1994;Sajeev et al, 2010;Santosh et al, 2014;Dharmapriya, et al, 2015;Takamura et al, 2015;He et al, 2016aHe et al, , 2016b. Such thermal events may contribute to form peripheral thin layers of overgrowths observed in zircon grains (Figs.…”

Section: Formation Of Overgrowthssupporting

confidence: 62%

“…The age range 5 (1900-1700 Ma) can be regarded as ages of a metamorphic event because of the Th/U ratio of less than 0.1. Baur et al (1991) and Hölzl et al (1994) also recognized zircon upper intercept ages around 1900-1700 Ma for orthogneisses in the CHC. They interpreted these as the crystallization ages of the protoliths in the Highland Complex.…”

Section: Formation Of Overgrowthsmentioning

confidence: 93%

“…Baur et al (1991) and Hölzl et al (1994) obtained zircon upper intercept ages around 1900-1800 Ma for orthogneisses, which were interpreted as crystallization ages of the protoliths. On the other hand, Kröner et al (1987Kröner et al ( , 2003 identified lead loss and zircon growth events at 1100-750 Ma.…”

Section: Introductionmentioning

confidence: 95%

“…According to studies by U-Pb zircon dating (Kröner et al, 1987;Santosh et al, 2014;Dharmapriya et al, 2015;Takamura et al, 2015;He et al, 2016aHe et al, , 2016b, Nd model ages (Milisenda et al, 1988(Milisenda et al, , 1994Pram and Pohl, 1994) and Sr model ages (Crawford and Oliver, 1969), the detritus of the metasediments in the CHC were derived from unidentified Archean to Proterozoic source terrains of 3.2-2.0 Ga in age, and peak metamorphism occurred around 610-550 Ma (Hölzl et al, 1991;Hölzl et al, 1994;Sajeev et al, 2010;Santosh et al, 2014;Dharmapriya et al, 2015;Takamura et al, 2015;He et al, 2016aHe et al, , 2016b. Baur et al (1991) and Hölzl et al (1994) obtained zircon upper intercept ages around 1900-1800 Ma for orthogneisses, which were interpreted as crystallization ages of the protoliths.…”

Section: Introductionmentioning

confidence: 99%

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Internal textures and U–Pb geochronology of zircons in metamorphic rocks from the Southwestern Highland Complex, Sri Lanka

Wanniarachchi

Akasaka

Hayasaka

et al. 2016

Journal of Mineralogical and Petrological Sciences

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Internal textures and U-Pb ages of zircons in garnet-biotite gneiss of the Southwestern Highland Complex (SWHC), Sri Lanka, were studied to clarify the repeated thermal events in the study area. The zircons from garnet-biotite gneiss consist of the detrital cores and overgrowths with two to five growth stages. The detrital zircon cores are rounded or euhedral to subhedral in shape, and show transgressive internal textures or oscillatory zoning.The rounded or subhedral to euhedral detrital core morphology suggests several major Archaean to Proterozoic sources of detritus zircons in the SWHC. Ages of the detrital cores are in a range of 3.3-1.7 Ga, and can be categorized into five ranges of 3380-3220, 2730-2660, 2550-2490, 2220-2170, and 1900-1700 Ma, implying the source rock ages. The detrital cores in the 3380-2170 Ma have Th/U-ratios of more than 0.3, suggesting igneous origin. The detrital cores in the range 1900-1700 Ma have Th/U of >0.3 or 0.3-0.1, suggesting an igneous or metamorphic origin. Some overgrowths with the ages in the ranges of 1900-1700 and 630-500 Ma have Th/U-ratios less than 0.1 implying that zircon growth corresponds to the thermal events. Zircons lacking detrital cores and having growth zones with characteristic metamorphic internal textures gave ages in a range of 630-500 Ma, implying the generation at the final granulite grade metamorphic event.

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Section: Formation Of Overgrowthssupporting

confidence: 62%

Section: Formation Of Overgrowthsmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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Internal textures and U–Pb geochronology of zircons in metamorphic rocks from the Southwestern Highland Complex, Sri Lanka

Wanniarachchi

Akasaka

Hayasaka

et al. 2016

Journal of Mineralogical and Petrological Sciences

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“…1). This area phism in the Kerala Khondalite Belt (Buhl, 1987;Choudary et al, 1992;Kö hler et al, 1993) and the Sri has become well known through the occurrence of lenses of sapphirine granulites at Ganguvarpatti Lankan basement (Hö lzl et al, 1994). No isotope data are available for the sapphirine-bearing granulites.…”

mentioning

confidence: 99%

Ultra‐high‐temperature metamorphism and multistage decompressional evolution of sapphirine granulites from the Palni Hill Ranges, southern India

Raith

Karmakar²,

Brown

1997

Journal Metamorphic Geology

208

159

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Sapphirine granulites from a new locality in the Palni Hill Ranges, southern India, occur in a small enclave of migmatitic, highly magnesian metapelites (mg=85-72) within massive enderbitic orthogneiss. They show a variety of multiphase reaction textures that partially overprint a coarse-grained high-pressure assemblage of Bt+Opx+Ky+Grt+Pl+Qtz. The sequence of reactions as deduced from the corona and symplectite assemblages, together with petrogenetic grid considerations, records a clockwise P-T evolution with four distinct stages. (1) Equilibration of the initial high-P assemblage in deep overthickened crust (12 kbar/800-900°C) was followed by a stage of near-isobaric heating, presumably as a consequence of input of extra heat provided by the voluminous enderbitic intrusives. During heating, kyanite was converted to sillimanite, and biotite was involved in a series of vapour-phase-absent melting reactions, which resulted in the ultra-high-temperature assemblage Opx+Crd+Kfs+Spr±Sil, Grt, Qtz, Bt, coexisting with melt (equilibration at c. 950-1000°C/11-10 kbar). (2) Subsequently, as a result of decompression of the order of 4 kbar at ultra-high temperature, a sequence of symplectite assemblages (Opx+Sil+Spr/ Spr+Crd Opx+Spr+Crd Opx+Crd Opx+Crd+Spl/Crd+Spl) developed at the expense of garnet, orthopyroxene and sillimanite. This stage of near-isothermal decompression implies rapid ascent of the granulites into mid-crustal levels, possibly due to extensional collapse and erosion of the overthickened crust. (3) Development of late biotite through back-reaction of melt with residual garnet indicates a stage of near-isobaric cooling to c. 875°C at 7-8 kbar, i.e. relaxation of the rapidly ascended crust to the stable geotherm. (4) A second period of near-isothermal exhumation up to c. 6-5 kbar/850°C is indicated by the partial breakdown of late biotite through volatile phase-absent melting reactions. Available isotope data suggest that the early part of the evolutionary history (stages 1-3) is presumably coeval with the early Proterozoic metamorphism in the extended granulite terrane of the Nilgiri, Biligirirangan and Shevaroy Hills to the north, while the exhumation of the granulites from mid-crustal levels (stage 4) occurred only during the Pan-African thermotectonic event, which led to the accretion of the Kerala Khondalite Belt to the south.

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Prolonged Neoproterozoic high‐grade metamorphism of the Wanni Complex, Sri Lanka: New insights from petrology, phase equilibria modelling, and zircon U–Pb geochronology of partially melted cordierite gneiss from Walpita

et al. 2020

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We report new petrological and geochronological data of garnet‐cordierite (Grt‐Crd) gneiss as well as two types of leucocratic rocks (garnet‐bearing and cordierite‐bearing leucosomes) crystallized during prograde and near‐peak metamorphisms of the Wanni Complex (WC) in Sri Lanka, and investigate the pressure–temperature–time evolution of granulite‐facies metamorphism for unravelling the timing and tectonics of the Neoproterozoic collisional processes related to Gondwana amalgamation. Grt‐Crd gneiss, garnet‐biotite (Grt‐Bt) gneiss, garnet‐bearing leucocratic rock (Grt‐L), and cordierite‐bearing leucocratic rock (Crd‐L) discussed in this study were collected from Walpita in the margin of the WC along the boundary with the Highland Complex (HC). Grt‐L occurs as thin layers parallel to the foliation of matrix Grt‐Bt and Grt‐Crd gneisses. The occurrences of porphyroblastic garnet in quartzo‐feldspathic matrix and crystallised melt inclusions within the garnet suggest that the Grt‐L could have formed by partial melting of host Grt‐Bt gneiss during prograde to peak metamorphism. Crd‐L is coarse‐grained and massive, lacks obvious foliation, and crosscuts the foliation of host Grt‐Bt gneiss. These observations suggest that the Crd‐L could have intruded after the crystallization of the Grt‐L. Application of phase equilibria modelling in the system NCKFMASHTO for the rocks yielded three discrete thermal events: 600–800°C/4.0–6.0 kbar (Stage 1 from Grt‐L), 700–840°C/5.5–7.0 kbar (Stage 2 from Grt‐Crd gneiss), and 840–880°C/4.5–5.5 kbar (Stage 3 from Crd‐L), suggesting a clockwise P–T evolution. LA‐ICP‐MS zircon U–Pb dating of the leucosomes yielded several metamorphic events: >577 Ma (partial melting of Grt‐L), ~562 Ma (crystallization of Grt‐L), 537 ± 14 Ma (peak metamorphism and crystallization of Crd‐L), and 507–503 Ma (post‐peak cooling event). The results of this study therefore confirmed prolonged (>70 Myr) high‐grade metamorphism of the WC, although the duration might be shorter than that of the HC (>100 Ma). The continuous heat supply necessary for such long‐lived high‐grade metamorphism is explained by a recent tectonic model of Sri Lanka. The model suggests double‐sided subduction and continent‐continent collision, which could have given rise to subsequent slab delamination and differential heating of lower to middle crust. Such complex subduction–collision processes possibly controlled the difference in the style of P–T path and the duration of high‐grade metamorphism between the HC and the WC.

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UPb geochronology of the Sri Lankan basement

Cited by 137 publications

References 31 publications

Internal textures and U–Pb geochronology of zircons in metamorphic rocks from the Southwestern Highland Complex, Sri Lanka

Internal textures and U–Pb geochronology of zircons in metamorphic rocks from the Southwestern Highland Complex, Sri Lanka

Ultra‐high‐temperature metamorphism and multistage decompressional evolution of sapphirine granulites from the Palni Hill Ranges, southern India

Prolonged Neoproterozoic high‐grade metamorphism of the Wanni Complex, Sri Lanka: New insights from petrology, phase equilibria modelling, and zircon U–Pb geochronology of partially melted cordierite gneiss from Walpita

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