Granitoid gneisses dominated by tonalitic–trondhjemitic–granodioritic (TTG) compositions, with metamorphic supracrustal rocks consisting of sedimentary and volcanic rocks, are widely exposed in the Eastern Hebei terrane, North China Craton (NCC). This study presents systematic zircon U–Pb geochronological and whole-rock geochemical data of the Neoarchean granitoid gneisses and supracrustal rocks in Eastern Hebei. Zircon U–Pb isotopic dating for the representative samples reveals that magmatic precursors of granitoid gneisses were emplaced between 2524 ± 7 and 2503 ± 12 Ma, and the protoliths of the pelitic granulites were deposited in the Late Neoarchean era. Both of them have been subjected to granulite facies metamorphism during 2508 ± 10 to 2468 ± 33 Ma, coeval with the intrusion of syenogranitic pegmatite (2488 ± 5 Ma). Zircon ages of 2.45–2.01 Ga obtained from the analyzed samples were considered mixed data from 2.53–2.48 Ga and 1.9–1.8 Ga and were chronologically meaningless. Paleoproterozoic metamorphic zircon ages of 1.9–1.8 Ga were usually neglected because of hardly being obtained from TTG gneisses and supracrustal rocks. The tectonic regime during the Neoarchean era was considered to be dominated by vertical tectonism in the Eastern Hebei terrane.

Protolith

Anatexis

10.3390/min12070863

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Phase relations in metabasic rocks: constraints from the results of experiments, phase modelling and ACF analysis

Geological Society London Special Publications (2018)

Chunjing Wei Zhanzhan Duan

Abstract Phase relations in metabasic rocks are documented from the results of phase modelling, experiments and ACF analysis. A P–T pseudosection for a mid-ocean-ridge basalt (MORB) composition was calculated in the P–T range of 1–32 kbar and 400–1100°C using THERMOCALC 3.45. Phase relations in this pseudosection are mostly consistent with the results from experiments but complicated. ACF analyses suggest that the complicated phase relations can be simplified into 10 invariant assemblages involving orthopyroxene, clinopyroxene, hornblende, glaucophane, actinolite, garnet, chlorite, epidote, lawsonite, kyanite and plagioclase, assuming quartz, NaAlO 2 and H 2 O/melt being are excess. Phase relation analyses in the P–T projections that are constructed according to Schreinemakers’ rules and qualitative P–T pseudosections that are obtained for a MORB composition indicate that 22 subfacies assemblages are recognized for metabasic rocks. A four-fold classification of metamorphism is proposed on the basis of the phase relations for metabasic rocks, including low-, medium-, high- and very-high- P / T types, with apparent geothermal gradients >110°C/kbar, between 110 and 55°C/kbar, between 55 and 28°C/kbar, and <28°C/kbar, respectively. This four-fold classification of metamorphism is better able to match various tectonic settings.

10.1144/sp474.10

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Formation mechanism of salt piercement structures in a compressive environment: An example from the Kuqa depression, western China

Journal of Structural Geology (2023)

Keji Yang Jiafu Qi Fangle Shen Tong Sun Zhanzhan Duan

Basement

10.1016/j.jsg.2023.105005

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Metamorphic P–T paths for the Archean Caozhuang supracrustal sequence, eastern Hebei Province, North China Craton: Implications for a sagduction regime

Precambrian Research (2019)