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• Four metamorphic stages (M 1 –M 4) of the Helanshan pelitic granulites are recorded by the mineral inclusions and reaction textures of garnets. • A complete clockwise P–T path of the Helanshan pelitic granulites is defined for the first time. • The prograde geothermal gradient of the Helanshan pelitic granulites (14 ± 1 °C/km) is similar to that the pelitic schists in the Himalayan Orogen (13 ± 2 °C/km). Granulite-facies metamorphic rocks are widely exposed in Paleoproterozoic orogens, and their prograde metamorphic evolution is critical for a better understanding of the Paleoproterozoic collisional orogenic and geodynamic processes. In this paper, we present the results of petrology, trace element geochemistry of garnet, P–T conditions calculated by phase equilibrium modeling and garnet trace element geothermobarometry, for the pelitic granulites of the Helanshan Complex in the western Khondalite Belt of the North China Craton (NCC). These results are used for determination of their metamorphic evolution and tectonic implications. Petrographic observations show that the metamorphic evolution of the pelitic granulites can be divided into four stages (M 1 –M 4), and these metamorphic stages are recorded by the mineral inclusions and reaction textures of garnets. Compared with the nearly flat major-element zoning, the zoning of yttrium (Y) and heavy rare earth elements (HREEs) in the garnet cores and mantles show bell-shaped distributions as well as inner-rim troughs and increases on the outer-rims. Different garnets have the same REE patterns in the same textural domain. The bell-shaped distributions of trace elements (Y and HREEs) in the garnets were controlled mainly by Rayleigh fractionation processes under subsolidus conditions, whereas the increases in these elements in the garnet rims were related to the breakdown of major and accessory phases under suprasolidus conditions. By combination of phase equilibrium modeling and garnet trace element geothermobarometry, a complete clockwise P–T path is constructed for the pelitic granulites. This P–T path is characterized by the heating as pressure rising during evolution from early metamorphic stage (M 1 : 4.2 ± 0.3 kbar/524 ± 17 °C) to peak metamorphic stage (M 2-1 ; 9.8–10.6 kbar /794–815 °C), which is followed by a isothermal decompression (ITD) to the condition of 5.8–6.5 kbar/808–833 °C and later near isobaric cooling (IBC) to subsolidus. As a result, the pelitic granulites revealed that the formation of the Khondalite Belt experienced initially crustal thickening and post collisional extensional uplift. Integrated with previously reported results, the prograde geothermal gradient of the Helanshan pelitic granulites (14 ± 1 °C/km) is similar to that the pelitic schists in the Himalayan Orogen (13 ± 2 °C/km), which suggests that the Paleoproterozoic and present-day orogens have similar geothermal gradient during crustal thickening. [ABSTRACT FROM AUTHOR]

• The quartz monzodiorites are contemporaneous with the UHT pelitic granulites. • The quartz monzodiorites formed by differentiation of mantle-derived magma. • Crust–mantle interaction at ca. 1.93 Ga in the Helanshan Complex. Insights into crust–mantle interaction in continental collisional orogens is key to understanding high- and ultrahigh-temperature (HT–UHT) metamorphism, continental crustal growth, and the tectonic evolution of such orogens. Here, we present whole-rock major- and trace-element and Nd isotope geochemistry, as well as zircon U–Pb geochronology and Hf isotope data, for quartz monzodiorites from the Helanshan Complex to constrain their petrogenesis and draw implications regarding crust–mantle interaction during formation of the Khondalite Belt in the North China Craton. LA–ICP–MS zircon U–Pb dating yields crystallization ages of 1938–1931 Ma for three samples, contemporaneous with spinel-bearing UHT pelitic granulites from the Helanshan Complex. The quartz monzodiorite samples have variable whole-rock compositions, with relatively low SiO 2 (low to 51.41 wt.%) but high MgO (up to 5.05 wt.%) and Cr (up to 80.9 ppm) contents, as well as high Mg# values (up to 0.50), which suggest their derivation from the mantle. These samples exhibit a narrow range of ε Nd (t) values of −0.3 to + 1.0, with no decrease as decreasing whole-rock MgO content, and variable zircon ε Hf (t) values of −2.4 to + 5.8. In addition, Mg# values of hornblende and biotite, and X an values of plagioclase decrease gradually with increasing whole-rock SiO 2 content. All of these geochemical data indicate that the studied quartz monzodiorites were produced by fractional crystallization of mantle-derived magma, with assimilation of crustal material. On the basis of previously published data in the Khondalite Belt, the Helanshan quartz monzodiorites formed in the post-collisional setting, and record a tectonic transition from compression to extension during the period ca. 1.95–1.93 Ga. The emplacement of mantle-derived magma that formed the quartz monzodiorites through differentiation at ca. 1.93 Ga, was possibly responsible for the formation of ca. 1.93 Ga UHT rocks in the Helanshan Complex. [ABSTRACT FROM AUTHOR]