Zircon U-Pb age of the altered syenogranite in Fengyu area of southern Taihang Mountain and its significance

An altered syenogranite pluton was found in Fengyu area, southern Taihang Mountain of central-eastern North China Craton, which unconformably underlies the Changcheng System. The rock type is biotite granite, which has undergone obvious Kfeldspar alteration and sericitization. The rocks are characterized by low SiO₂ (SiO₂=67.46%-68.89%) and high K₂O + Na₂O (K₂O + Na₂O=8.09-9.62, K₂O/Na₂O >> 1) content, with aluminum index A/CNK being 1.20-1.57, showing features of peraluminous, calc-alkaline A-type granite. The pluton is also characterized by enrichment of LILE and depletion of Ba, Nb, Ta, Sr, P, Ti, as well as high ∑REE values (192-774 μg/g, 483 ug/g om average). LA-ICP-MS zircon U-Pb dating of Fengyu altered syenogranite pluton yielded an ²⁰⁷Pb/²⁰⁶Pb age of(1790±22) Ma (n=22, MSWD=0.80), which is by far the most direct control of the lower limit age of Changcheng System in southern Taihang Mountain. Petrochemistry, rare earth elements, trace element geochemistry and isotopic geochronology all prove that Fengyu altered syenogranite pluton was formed in an intraplate extensional environment in the Paleoproterozoic period, thus providing an important magmatism evidence for the existence of northeast Xiongerrian trident continental rift; they also show that the Taihang Mountain area where Fengyu altered syenogranite pluton was formed and the western Henan Province where Xiong'er Group volcanic rocks were developed constitute part of the Xiongerrian trident continental rift, which thus provides an important support for the stratigraphic correlation of the Changcheng System between Taihang Mountain area and western Henan Province.