Detrital Zircon Geochronology And Detrital Component Studies Of The Wawukuang Formation,Laiyang Sag And Their Geological Implications

At Early Cretaceous times,the North China Craton(NCC)had experienced destruction and reached a peak at?125 Ma,triggering extensive magmatism,mineralization and faulting witnessed in the Jiaodong Peninsula where the Jiaobei terrane experienced a rapid uplift in the Early Cretaceous,however,the timing of uplift and association with the craton destruction were poorly constrained.Moreover,there have been some debates about whether the Sulu orogenic belt exhumated into surface in the Early Cretaceous.The Jiaolai Basin has been a potential candidate in documenting the uplift and erosion processes of the Jiaobei terrane and Sulu orogenic belt.In this study,we have therefore carried out detrital zircon U-Pb and Hf isotope,detrital framework component feature analyses,and made elaborate discussion on deposition timing of the Laiyang Group,provenance characteristics and tectonic evolution of adjacent units of basin in the Early Cretaceous.We collected three sandstones from different stratigraphic levels at the Wawukuang Formation of the Laiyang Group for detrital zircon U-Pb and Hf isotope analyses and fourteen sandstones for detrital framework component analysis.The detrital zircon age spectrum of three sandstones show different age peaks suggesting diverse source regions.Sandstone W-1 from the base of the Wawukuang Formation has a wide age range of detrital zircon between 114?3580 Ma with three main age peaks of?125 Ma,?750 Ma and two secondary age peaks of?2500 Ma and?1800 Ma and ?Hf(t)spans from-28.81 to+0.88.Sandstone W-5 was collected from middle stratigraphic sequence of the Wawukuang Formation and its detrital zircon age ranges from 126?2899 Ma with two major age peaks of?130 Ma and?1850 Ma,and three secondary age peaks of?245 Ma,?715 Ma and?2437 Ma in the age distribution.The ?Hf(t)values of detrital zircon range from-27.01 to+6.04.Noticeably,the detrital zircon spectrum of the sandstone W-9 from upper stratigraphic level of the Wawukuang Formation has a restricted age range from 1790 to 2121 Ma showing only one prominent peak of?1850 Ma with ?Hf(t)values spanning from-8.15 to-2.83.Detrital component of sandstones commonly exhibits a decrease in the amount of quartz and an increase in feldspar contents along upward stratigraphic sequence.Lithic fragments include metamorphic lithics and a little amount of sedimentary lithics.To integrate total amount of quartz,feldspar and lithics into 100%,basal sandstones have variable components in amount with quartz of 55.65-75.53%,feldspar of 8.7-31.25%,lithics dominant by metamorphic lithics of 0.39-29.84%.Detrital components of middle sandstones have relatively homogenous amount with quartz of 54.37-59.37%,feldspar of 30.07-31.55%and metamorphic lithics of 5.51-8.02%.Upper sandstones have detrital components in terms of quartz of 40.87-57.34%,feldspar of 33.45-47.75,metamorphic lithics of 2.63-6.02%.The results of detrital zircon U-Pb age and Hf isotopes suggest that basal detritus were mostly sourced from the Sulu orogenic belt.Upward along sequence,primary source regions gradually switched to the Jiaobei terrane.In addition,the detrital component features of sandstones fall into the region from recycled orogeny to continental basement uplift suggesting provenance switched from the original Sulu orogenic belt into the Jiaobei terrane.The presence of the Sulun orogenic belt fingerprints in the basal sandstones indicates that the Sulu orogenic belt has been exhumated into the surface prior to?125 Ma and served as a main source region for the surrounding basin.The transition of provenance indicates a rapid uplift of the Jiaobei terrane at?125 Ma associated closely to removal of the craton lithosphere mantle of NCC.