Oligocene HP metamorphism and anatexis of the Higher Himalayan Crystalline Sequence in Yadong region, east-central Himalaya

The Fuping Complex is one of the important basement terranes within the central segment of the Trans‐North China Orogen (TNCO) where mafic granulites are exposed as boudins within tonalite–trondhjemite–granodiorite (TTG) gneisses. Garnet in these granulites shows compositional zoning with homogeneous cores formed in the peak metamorphic stage, surrounded by thin rims with an increase in almandine and decrease in grossular contents suggesting retrograde decompression and cooling. Petrological and phase equilibria studies including pseudosection calculation using thermocalc define a clockwise P–T path. The peak mineral assemblages comprise garnet+clinopyroxene+amphibole+quartz+plagioclase+K‐feldspar+ilmenite±orthopyroxene±magnetite, with metamorphic P–T conditions estimated at 8.2–9.2 kbar, 870–882 °C (15FP‐02), 9.6–11.3 kbar, 855–870 °C (15FP‐03) and 9.7–10.5 kbar, 880–900 °C (15FP‐06) respectively. The pseudosections for the subsequent retrograde stages based on relatively higher H2O contents from P/T–M(H2O) diagrams define the retrograde P–T conditions of <6.1 kbar, <795 °C (15FP‐02), 5.6–5.8 kbar, <795 °C (15FP‐03), and <9 kbar, <865 °C (15FP‐06) respectively. Data from LA‐ICP‐MS zircon U–Pb dating show that the mafic dyke protoliths of the granulite were emplaced at c. 2327 Ma. The metamorphic zircon shows two groups of ages at 1.96–1.90 Ga (peak at 1.93–1.92 Ga) and 1.89–1.80 Ga (peak at 1.86–1.83 Ga), consistent with the two metamorphic events widely reported from different segments of the TNCO. The 1.93–1.92 Ga ages are considered to date the peak granulite facies metamorphism, whereas the 1.86–1.83 Ga ages are correlated with the retrograde event. Thus, the collisional assembly of the major crustal blocks in the North China Craton (NCC) might have occurred during 1.93–1.90 Ga, marking the final cratonization of the NCC.

Section: Discussionmentioning

confidence: 97%

Petrology, phase equilibria modelling and zircon U–Pb geochronology of Paleoproterozoic mafic granulites from the Fuping Complex, North China Craton

Tang

Santosh

Tsunogae

et al. 2017

“…A common approach consists in considering the probable melt productivity of the model protolith composition reconstructed by melt‐reintegration method (e.g. Cai et al., ; Diener et al., ; Guilmette et al., ; Hasalová et al., ; Indares et al., ; Nicoli et al., ; Taylor et al., ; White et al., ; Zhang et al., ). These amounts of melt are a maximum, because melt loss would reduce rock fertility at higher temperature (Korhonen et al., ; Yakymchuk & Brown, ).…”

Section: Discussionmentioning

confidence: 99%

“…In some works, the simplest case of melt loss, and therefore of melt‐reintegration, was assumed to occur in one step (e.g. Guilmette et al., ; Hallet & Spear, ; Indares et al., ; Lasalle & Indares, ; Tian et al., ; Zhang et al., ; Zou et al., ). Melt compositions were calculated and reintegrated in different ways, such as at the intersection of the solidus for the residual composition with a presumed prograde P–T path (Indares et al., ), at the peak P–T conditions (Groppo et al., ) or at the hypothetical conditions at which melt was lost (Groppo et al., ).…”

Section: Melt‐reintegration Procedures Proposed In the Literaturementioning

confidence: 99%

“…This issue was circumvented by reintegrating a certain amount of melt to the residuum composition and by performing phase equilibria modelling of the new model protolith composition to reconstruct the probable prograde history (see White, Powell, & Halpin, ). The melt‐reintegration approach has become an increasingly routine method among metamorphic petrologists and various ways of calculating and reintegrating the extracted melt have been developed and applied (Anderson, Kelsey, Hand, & Collins, ; Boger, White, & Schulte, ; Cai et al., , ; Chen, Ye, Liu, & Sun, ; Diener, White, & Hudson, ; Diener, White, Link, Dreyer, & Moodley, ; Diener, White, & Powell, ; Dumond, Goncalves, Williams, & Jercinovic, ; Fitzherbert, ; Groppo, Rolfo, & Indares, ; Groppo, Rolfo, & Mosca, ; Groppo, Rubatto, Rolfo, & Lombardo, ; Guilmette, Indares, & Hébert, ; Hallett & Spear, ; Hasalová et al., ; Jiang et al., ; Kelsey & Hand, ; Kohn, ; Korhonen, Brown, Clark, & Bhattacharya, ; Indares, White, & Powell, ; Lasalle & Indares, ; McGee, Giles, Kelsey, & Collins, ; Morrissey, Hand, Kelsey, & Wade, ; Nahodilová, Faryad, Dolejš, Tropper, & Konzett, ; Nicoli, Stevens, Moyen, & Frei, ; Palin et al., ; Redler, White, & Johnson, ; Shrestha, Larson, Guilmette, & Smit, ; Skrzypek, Štípská, & Cocherie, ; Štípská, Schulmann, & Powell, ; Taylor, Nicoli, Stevens, Frei, & Moyen, ; Tian, Zhang, & Dong, ; Tucker, Hand, Kelsey, & Dutch, ; Wang & Guo, ; White et al., ; Yakymchuk et al., ; Yin et al., ; Zhang et al., ; Zou et al., ). Furthermore, the reconstruction of a plausible protolith composition is essential to assess the likely melt productivity of rocks (White et al., ) which, in turn, allows the potential role of loss and redistribution of melt in the evolution of the deeper crust to be explored (Diener & Fagereng, ; Diener et al., ; Korhonen, Saito, Brown, & Siddoway, ; Korhonen et al.,…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Phase equilibria modelling of residual migmatites and granulites: An evaluation of the melt‐reintegration approach

Bartoli

2017

Suprasolidus continental crust is prone to loss and redistribution of anatectic melt to shallow crustal levels. These processes ultimately lead to differentiation of the continental crust. The majority of granulite facies rocks worldwide has experienced melt loss and the reintegration of melt is becoming an increasingly popular approach to reconstruct the prograde history of melt‐depleted rocks by means of phase equilibria modelling. It involves the stepwise down‐temperature reintegration of a certain amount of melt into the residual bulk composition along an inferred P–T path, and various ways of calculating and reintegrating melt compositions have been developed and applied. Here different melt‐reintegration approaches are tested using El Hoyazo granulitic enclaves (SE Spain), and Mt. Stafford residual migmatites (central Australia). Various sets of P–T pseudosections were constructed progressing step by step, to lower temperatures along the inferred P–T paths. Melt‐reintegration was done following one‐step and multi‐step procedures proposed in the literature. For El Hoyazo granulites, modelling was also performed reintegrating the measured melt inclusions and matrix glass compositions and considering the melt amounts inferred by mass–balance calculations. The overall topology of phase diagrams is pretty similar, suggesting that, in spite of the different methods adopted, reintegrating a certain amount of melt can be sufficient to reconstruct a plausible prograde history (i.e. melting conditions and reactions, and melt productivity) of residual migmatites and granulites. However, significant underestimations of melt productivity may occur and have to be taken into account when a melt‐reintegration approach is applied to highly residual (SiO2 <55 wt%) rocks, or to rocks for which H2O retention from subsolidus conditions is high (such as in the case of rapid crustal melting triggered by mafic magma underplating).

“…In comparison, recent studies across the central and eastern Himalaya have revealed evidence that upper structural levels of the GH achieved granulite, and possibly earlier eclogite facies conditions prior to exhumation (e.g. Groppo et al ., ; Grujic et al ., ; Guilmette et al ., ; Warren et al ., ; Ambrose et al ., ; Zhang et al ., ). The upper‐GH samples from central and eastern Bhutan in this study do not contain orthopyroxene or abundant K‐feldspar and muscovite, observed in nearly all samples (the exception being BU12‐212B), are interpreted to be part of the peak assemblage (Figs ).…”

Section: Discussionmentioning

confidence: 99%

Pressure–temperature–structural distance relationships within Greater Himalayan rocks in eastern Bhutan: implications for emplacement models

Agustsson

Gordon

Long

et al. 2016

In the Himalayan orogen, Greater Himalayan (GH) rocks were buried to mid-to lower-crustal levels and are now exposed across the strike of the orogen. Within the eastern Himalaya, in the Kingdom of Bhutan, the GH is divided into structurally lower (lower-GH) and upper (upper-GH) levels by the Kakhtang thrust (KT). Pressure-temperature estimates from lower-and upper-GH rocks collected on two transects across the KT yield similar P-T-structural distance trends across each transect. In the eastern transect, temperatures are similar (from 730 to 650°C) over a structural thickness of~11 km, but peak pressures decrease from~10 to 6 kbar with increasing structural level. In comparison, peak temperatures in the central Bhutan transect are similar (from 730 to 600°C), but pressures decrease from 10 to 6.5 kbar with increasing structural level over a structural thickness of~6 km. The structurally highest sample reveals slightly higher pressures of 8.0 kbar in comparison to pressures of 6.5 kbar for samples collected from within the KT zone,~4 km below. Within each transect, there are increases in pressure AE temperature within the overall upright P-T gradient that may demarcate intra-GH shear zone(s). These P-T results combined with evidence that the timing of initial melt crystallization becomes older with increasing structural level suggest that the intra-GH shear zones emplaced deeper GH rocks via progressive ductile underplating. These shear zones, including the KT, likely aided in the initial emplacement and construction of the GH as a composite tectonic unit during the Late Oligocene to Early Miocene, from c. 27 to 16 Ma.