Mr. Jun Wang Department of earth sciences, HKU
Early Cretaceous sedimentary and igneous rocks in East Shandong, North China, provide essential evidence to decipher sedimentary environment and tectonic history of this area. U-Pb age distributions of detrital zircon populations for Early Cretaceous terrestrial sandstones and turbidites that distributed in the Jiaolai basin and central Sulu orogenic belt show different characteristics, indicating different depositional ages and sedimentary provenances.
Geochronological analyses of different igneous rocks from the central Sulu orogenic belt identified a relatively restricted population of ages ranging from 123±2 Ma to 120±2 Ma. Geochemical data suggest different magma sources for these rocks. Assimilation and fractionation processes did not contribute to lamprophyre formation, but did play an important role in generating andesitic porphyrites, syenogranites and rhyolites. Lithospheric thinning was likely caused by an abrupt change in the direction of the subducting Pacific plate.
Marine turbidites with syn-sedimentary deformations in the central Sulu orogenic belt have been recognized recently. New detrital zircon U-Pb age data allow a correlation of these turbidites. The Laoshan granites emplaced to the margin of the marine facies with a sharp contact, implying a subsidence of the latter since the former were formed deeply in the crust. We propose a transpessional tectonic setting of East Shandong at 122-121 Ma. The transpression was ceased by the emplacement of the Laoshan granites, which were formed in an extensional setting at 111 Ma. Therefore, the turbidites subsided at a high velocity during this period.