Post-peak metamorphic evolution of the Sumdo eclogite from the Lhasa terrane of southeast Tibet

Cao, Dongliang; Hao, Changchun; Zhang, Lingmin; Wang, Ke

doi:10.1016/j.jseaes.2017.04.020

Cited by 17 publications

(10 citation statements)

References 60 publications

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“…8), we infer that the PT1 path would be the most reliable scenario for the metamorphic evolution of the schist, which shares the same evolution with the eclogite. The newly reported heating with decompression P-T path of the phengite eclogite in the Sumdo area also demonstrates the possibility of a thermal relaxation process during the exhumation of the Sumdo Complex (Cao et al 2017).…”

Section: A Metamorphic Evolution Of the Garnet-bearing Mica Schistmentioning

confidence: 58%

“…SHRIMP and LA-ICP-MS U-Pb zircon dating as well as whole-rock mineral Sm-Nd and Lu-Hf isotopic dating methods have been performed on the eclogite and yielded 260-274 Ma eclogite-facies metamorphic ages in the Sumdo and Jilang areas (Yang et al 2009;Cheng et al 2012;Weller et al 2016;Cao et al 2017) and an age of c. 230 Ma in the Bailang area for the Sumdo Complex, respectively (Cheng et al 2015). No metamorphic ages were obtained from the country rocks of the eclogite until now because of the sedimentary origin of the zircons.…”

Section: B Age Constrains and Tectonic Significancementioning

confidence: 99%

“…The dichotomy of the Lhasa terrane has been accepted since the discovery of UHP eclogite in the Sumdo Complex (Yang et al 2006(Yang et al , 2009. Geochemical and isotopic data show that the eclogites were derived from either a mid-ocean ridge basalt (MORB) or an oceanic island basalt (OIB) protolith and experienced eclogitefacies metamorphism during Late Permian to Early Triassic times (Yang et al 2009;Cheng et al 2012Cheng et al , 2015Cao et al 2017;Zhang et al 2018). P-T conditions of the eclogite from the Sumdo Complex have been reported by several researchers, ranging from 450-800°C and 2.5-3.9 GPa (Yang et al 2009(Yang et al , 2014Zhang, Zhang & Zhao, 2011;Cheng et al 2012Cheng et al , 2015Zhang et al 2018).…”

Section: Introductionmentioning

confidence: 99%

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Metamorphic evolution and age constraints of the garnet-bearing mica schist from the Xindaduo area of the Sumdo (U)HP metamorphic belt, Tibet

et al. 2018

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As one of the major components of the Himalayan–Tibetan Orogeny, the Lhasa terrane plays a key role in understanding the origin and evolution of this giant orogenic belt and the opening and closure of the Tethys oceans. The eclogite-bearing Sumdo Complex in the central Lhasa terrane was recognized as the main suture of the Palaeo-Tethys Ocean between the north and south Lhasa sub-terranes. Despite the eclogite having been studied for a long time, no attempts have been applied to studying the country rocks, causing confusion in understanding the relationship between the eclogite and the adjacent schist. Petrological investigations and phase equilibrium calculations on the garnet-bearing mica schist of the Sumdo Complex have been performed to constrain its metamorphic evolution. The P–T conditions for three metamorphic stages are constrained as P1 (480–500°C, 2.6–2.7 GPa), P2 (580–600°C, 1.3–1.4 GPa) and R (530°C, 0.9 GPa), which represent the prograde, temperature peak and retrograde stages. Two possible P–T paths were constructed, which experienced isothermal decompression (PT1) or heating with a decompression process (PT2), corresponding to the growth and extinction of garnet porphyroblasts in the matrix. The LA-MC-ICP-MS U–Pb dating method yielded a metamorphic age of 229.7±3.5 Ma, which was interpreted as the age of amphibolite-facies metamorphism at c. 600°C, 1.2–1.4 GPa during the closure of the Palaeo-Tethys Ocean, resulting in the aggregation of the north and south Lhasa sub-terranes. The close relationship between the eclogite and garnet-bearing mica schist, and their similar P–T–t paths indicate an in situ tectonic evolution rather than tectonic juxtaposition during exhumation.

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Section: A Metamorphic Evolution Of the Garnet-bearing Mica Schistmentioning

confidence: 58%

Section: B Age Constrains and Tectonic Significancementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Metamorphic evolution and age constraints of the garnet-bearing mica schist from the Xindaduo area of the Sumdo (U)HP metamorphic belt, Tibet

et al. 2018

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“…For instance, SHRIMP U-Pb dating on zircon grains from the Sumdo eclogite yielded a relatively large scatter in apparent 206 Pb/ 238 U ages from ~292 Ma to ~242 Ma with a weighted mean age of 262 ± 5 Ma (Yang et al, 2009), in contrast to a garnet-omphacite-whole rock Sm-Nd isochron age of 239.0 ± 3.5 Ma (Zeng et al, 2009). Recently, a lower intercept zircon U-Pb age of 273.6 ± 2.8 Ma (Weller et al, 2016) and a garnet-whole rock Lu-Hf isochron age of 266.6 ± 0.7 Ma (Cao et al, 2017) were reported. In addition, samples to the northeast of the Sumdo eclogite yielded a garnet-omphacite-whole rock Lu-Hf isochron age of 265.9 ± 1.1 Ma for the Jilang eclogite (Cheng et al, 2012), whereas a zircon U-Pb age of 227.4 ± 6.4 Ma was obtained for the Bailang eclogite (Cheng et al, 2015).…”

Section: Geological Setting and Sample Descriptionsmentioning

confidence: 99%

Rutile to Titanite Transformation in Eclogites and its Geochemical Consequences: An Example from the Sumdo Eclogite, Tibet

Zhao

Zeng

Gao

et al. 2023

Acta Geologica Sinica (Eng)

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The formation of titanite coronae after rutile is common in retrograde high‐ to ultrahigh‐pressure meta‐mafic rocks, which provides a good opportunity to address the geochemical behavior of HFSE in crustal environments. In the Sumdo eclogite, titanite occurs either as a corona around rutile grains or as semi‐continuous veins cross‐cutting the major foliation, whereas rutile grains occur either as inclusions in garnet or omphacite or as a relict core surrounded by titanite. Textural relationships and trace elements characteristics of rutile and titanite with different occurrences indicate that both minerals preferentially incorporate Nb and Hf over Ta and Zr in aqueous fluid. Moreover, the breakdown of omphacite and epidote could release substantial amounts of aqueous fluids enriched in Ca, Si, Fe and REE, which would react with rutile to form titanite coronae and veins. During this process, water‐insoluble elements, like HFSE and HREE, behave like mobile elements, but they do not migrate substantially out of the system, instead, tending to react in situ. This suggests that the aqueous fluids released during the retrograde metamorphic reactions in mafic rocks could not substantially transfer fluid‐immobile elements into the overlying mantle wedge in subduction environments.

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“…Published radiometric dates of the Sumdo eclogite showed large variance. Three groups of zircon U–Pb dates from the Sumdo eclogite define a weighted mean of 262 ± 5 Ma ( n = 15, MSWD = 1.08; Yang et al., ) and two lower intercept dates of 261 ± 15 Ma ( n = 18; MSWD = 1.0; Cao, Cheng, Zhang, & Wang, ) and 273 ± 2.8 Ma ( n = 25, MSWD = 1.5; Weller et al., ). The first two dates were interpreted to reflect the peak metamorphism, and the last to reflect a prograde timing according to pseudosection modelling results and inclusions in zircon.…”

Section: Geological Settingmentioning

confidence: 99%

Pseudosection modelling and garnet Lu–Hf geochronology of HP amphibole schists constrain the closure of an ocean basin between the northern and southern Lhasa blocks, central Tibet

Cao

Hao

Zhang

2017

Journal Metamorphic Geology

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The P-T-t path of high-P metamorphic rocks in subduction zones may reveal valuable information regarding the tectonic processes along convergent plate boundaries. Herein, we present a detailed petrological, pseudosection modelling and radiometric dating study of several amphibole schists of oceanic affinity from the Lhasa Block, Tibet. The amphibole schists experienced an overall clockwise P-T path that was marked by post-P max heating-decompression and subsequent isothermal decompression following the attainment of peak high-P and low-T conditions (~490°C and 1.6 GPa). Pseudosection modelling shows that the amphibole schists underwent water-unsaturated conditions during prograde metamorphism, and the stability field of the assemblage extends to lower temperatures and higher pressures within the water-unsaturated condition relative to water-saturated model along the prograde path. The high-P amphibole schists were highly reduced during retrograde metamorphism. Precise evaluation of the ferric iron conditions determined from the different compositions of epidote inclusions in garnet and matrix epidote is crucial for a true P-T estimate by garnet isopleth thermobarometry. Lu-Hf isotope analyses on garnet size separates from a garnet-bearing amphibole schist yield four two-point garnet-whole-rock isochron ages from 228.2 AE 1.2 Ma to 224.3 AE 1.2 Ma. These Lu-Hf dates are interpreted to constrain the period of garnet growth and approximate the timing of prograde metamorphism because of the low peak metamorphic temperature of the rock and the well-preserved Mn/Lu growth zoning in garnet. The majority of zircon U-Pb dates provide no constraints on the timing of metamorphism; however, two concordant U-Pb dates of 222.4 AE 3.9 Ma and 223.3 AE 4.2 Ma were obtained from narrow and uncommon metamorphic rims. Coexistence of zircon and sphene in the samples implies that the metamorphic zircon growth was likely assisted by retrogression of rutile to sphene during exhumation. The near coincident radiometric dates of zircon U-Pb and garnet Lu-Hf indicate rapid burial and exhumation of the amphibole schists, suggesting a closure time of c. 224-223 Ma for the fossil ocean basin between the northern and southern Lhasa blocks.

show abstract

Post-peak metamorphic evolution of the Sumdo eclogite from the Lhasa terrane of southeast Tibet

Cited by 17 publications

References 60 publications

Metamorphic evolution and age constraints of the garnet-bearing mica schist from the Xindaduo area of the Sumdo (U)HP metamorphic belt, Tibet

Metamorphic evolution and age constraints of the garnet-bearing mica schist from the Xindaduo area of the Sumdo (U)HP metamorphic belt, Tibet

Rutile to Titanite Transformation in Eclogites and its Geochemical Consequences: An Example from the Sumdo Eclogite, Tibet

Pseudosection modelling and garnet Lu–Hf geochronology of HP amphibole schists constrain the closure of an ocean basin between the northern and southern Lhasa blocks, central Tibet

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