Geochronology, mineralogy and geochemistry of alkali-feldspar granite and albite granite association from the Changyi area of Jiao-Liao-Ji Belt: Implications for Paleoproterozoic rifting of eastern North China Craton

• Unusual association of alkali-feldspar granite and albite granite is newly identified in the Jiao-Liao-Ji Belt.
• Both the granites are A-type and were emplaced during 2171 and 2193 Ma.
• The alkali-feldspar granite was derived from melting of Archean granodioritic rocks.
• The albite granite originated from reworking of plagioclase-rich layers after extraction of A-type melts.
• The A-type association indicates a Paleoproterozoic continental rifting in eastern North China Craton.

Paleoproterozoic granites, divided into alkali-feldspar granite and albite granite, were newly discovered in the Changyi area of the Jiao-Liao-Ji Belt from the Eastern Block of the North China Craton. LA–ICP-MS zircon U–Pb dating shows that the alkali-feldspar granite was emplaced at 2193 Ma, whereas the albite granite intruded at 2171 Ma. These granites have high SiO2, Na2O + K2O, Zr, Nb, Ga, Y and HREE contents and show remarkably low CaO, Eu, Ba and Sr concentrations, strongly suggesting their A-type affinities. Zircon saturation thermometry and AlT-in-biotite geobarometer indicate that the alkali-feldspar granite crystallized at temperatures of 823–856 °C (averaging at 839 °C) and pressures of 1.54–2.73 kbar (averaging at 2.05 kbar) while the albite granite was cooled at the temperatures of 851–853 °C and the pressures of 2.34–2.64 kbar (averaging at 2.45 kbar). Combined with such high temperatures and low pressures, the crustal-like Nd–Hf isotopic compositions (ɛNd(t) = −5.3 to −4.4, ɛHf(t) = −7.0 to −3.8.) support their derivation from the shallow melting of Archean crustal rocks under high heat flow. However, the contrasted K2O and Na2O compositions between the alkali-feldspar granite (K2O = 4.76–5.14 wt.%, Na2O = 4.76–5.14 wt.%) and the albite granite (K2O = 0.29–0.44 wt.%, Na2O = 6.15–6.56 wt.%) imply that they may have been derived from distinct source rocks or have undergone different magmatic processes. Genetic modeling suggests that the alkali-feldspar granite was originated from melting of granodioritic rocks. The albite granite, however, was most likely derived from the reworking of plagioclase-rich layers after the extraction of A-type melts. Coupled with other studies on sedimentary and volcanic successions in the Jiao-Liao-Ji Belt, the unusual association of the A-type alkali-feldspar granite and albite granite indicates that the southern segment of the Jiao-Liao-Ji Belt experienced continental rifting during 2.1–2.2 Ga.