Search

[Display omitted] • (1) Trachydacites have zircon U-Pb ages of 116 Ma and were coeval with the most extensive thinning of the North China Craton. • (2) 116 Ma trachydacites were related to subduction of Yangtze Craton and Paleo-Pacific plate. • (3) The mantle source underneath the southeastern North China Craton was modified by the subduction of the Yangtze Craton. The North China Craton has witnessed a large-scale lithospheric thinning event in the Mesozoic. The volcanic rocks of the Qingshan Group formed during the destruction of the North China Craton, therefore retaining important information to the deep processes in this region. Zircon U-Pb dating and geochemical analyses have been carried out on volcanic rocks of the Qingshan Group collected from southeastern margin of the Jiaolai Basin. In combination with previously published data on the volcanic rocks of the Qingshan Group, the newly acquired data show that: (1) the volcanic rocks of Qingshan Group in Mashan have SiO 2 content of 62.82 ∼ 66.3 wt% and total alkali content (K 2 O + Na 2 O) of 7.64 ∼ 9.34 wt%. According to TAS diagram, they belong to trachydacite which experienced strong fractionation between LREEs and HREEs with depletion of HFSEs and enrichment of LILEs. (2) The crystallization age of trachydacite in Mashan is 116.4 ± 2.3 Ma (MSWD = 1.9, n = 9). The magma originated from the partial melting of the ancient lower crust and the enriched lithospheric mantle metasomatized by the fluids/melts released from the subducted slab of the Yangtze Craton. (3) The formation age of magmatic rocks in western Shandong is generally earlier than that in eastern Shandong, while the lower crust delamination in western Shandong preceded that in eastern Shandong. The occurrence of magmatism in eastern Shandong is probably attributed to the delamination process in western Shandong as well as the ongoing tectonic activities along the Tan-Lu fault zone. The lithospheric thinning of the North China Craton was mainly controlled by the change of the subduction angle of the Paleo-Pacific plate, and is probably influenced by the continuous activity of the Tan-Lu fault zone in eastern Shandong. [ABSTRACT FROM AUTHOR]

The Cambrian SPICE (Steptoean Positive Carbon Isotope Excursion) event is widely reported from the late Miaolingian to the early Furongian, but recent studies imply that the synchroneity and magnitude of the SPICE may be controversial. In order to test the spatial variation of the SPICE, here we present 367 carbonate δ13C data from six outcrop sections across a ~700 km transect along the eastern North China Platform. The SPICE is present in all the studied sections, but showing different features regarding the duration and magnitude. An abrupt increase in δ13C from ~1.5‰ to 3.5‰ occurs in three Shandong sections, with maximum value present only in a thin (0.5–1.2 m thick) transgressive lag deposit (crudely wave stratified, bioclastic grainstone). In contrast, the δ13C record of the Baijiashan and Shashan sections in the Liaoning region displays a gradual increase (~20 m thick) from ~1.5‰ to the maximum value of 4.7‰. Both facies analysis and trilobite collections suggest that the spatial variation of the SPICE in the North China Platform most likely resulted from missing of sedimentary record (with high δ13C values) in the Shandong sections as a result of erosion and non-deposition during sea-level lowstand, a possible coeval hiatus prior to the Sauk III transgression in the Laurentian basins. Further high-resolution, integrated studies of sedimentology, biostratigraphy, and sedimentary geochemistry on the SPICE event are required to better understand its nature. • Six outcrop sections from the eastern North China Platform were studied for SPICE. • A complete SPICE (with max. value of ~4.7‰) was recorded in northeastern NCP. • Spatial variation in SPICE resulted from stratigraphic missing in Shandong region. [ABSTRACT FROM AUTHOR]