Based on geologic, seismic and drilling data of basins in China, the basic types of "truncation and onlap" unconformities are examined and their temporal and spatial variation and geologic significances are explored. The "truncation and onlap" unconformities and superimposing styles of overlying and underlying strata vary under different tectonic settings. Under extensional settings, there are three basic superimposing styles and unconformities, such as parallel superimposing style and unconformity with breaking outward, parallel superimposing style and unconformity with breaking inward, as well as superimposing and unconformity style with rotation. Under compressional settings, there are four basic types, such as overlap superimposing style and unconformity on fold, syn-depositional fold superimposing style and unconformity, anticline-syncline superimposing style and unconformity, as well as superimposing style and unconformity in overlap-filling incised valley on top of folds. "Truncation and onlap" unconformities always superimposed each other in space, and exhibit three kinds of superimposed unconformities, i.e., superimposed unconformities formed under continuous uplifting, under transition of uplifting, and under propagation of deposition center. They may also change with time too, i.e., tilting, rotating, folding, and migration. Controlled by the migration of basin depocenters, it is shown that there are unconformities formed under the transition of paleogeomorphy or subsidence center, under the migration of fault-sag, and under the slipping of detachment fault. "Truncation and onlap" unconformities are important positions for traps and significant pathways for hydrocarbon migration, and they are favorable sites for ore deposit and resources occurrence.
New whole-rock major and trace elements,and zircon U-Pb and Hf-Nd isotope compositions are reported for the Karamay dikes,enclaves,and host granites in the West Junggar,NW China.Zircon U-Pb dating of the Karamay pluton yields an age of 300.7 ± 2.3 Ma for the enclave and 300.0 ± 2.6 Ma for the host granite,which was intruded by dike with an age of 298 Ma.The host granites exhibit relatively low SiO_2 contents and A/CNK and Ga/Al ratios,low initial ^(87)Sr/^(86)Sr ratios(0.703421—0.703526) and positive εHf(t)(5.5—14.1) and εNd(t)(7.3—8.1) values with a young model age,suggesting that they are I-type granites and were mainly derived from a juvenile lower crustal source.The enclaves and dikes belong to an andesitic calc-alkaline series and have high MgO concentrations at low silica content and positive εNf(t)(7.6-13.2,14.2-14.9) and εNd(t)(6.8-8.3,~6.9) values.They are enriched in LILEs(Rb,Ba and U) and LREE and depleted in HFSEs(Nb and Ta) with insignificant negative Eu anomalies,indicating that the melts were derived from an enriched lithospheric mantle modified by subducted oceanic crust-derived melts and minor fluids,followed by fractional crystallization.The Karamay host granites and enclaves are of mixed origin and are most probably formed by the interaction between the lower crust- and lithospheric mantle-derived magmas,and were intruded by the unmixed dikes subsequently.The upwelling mantle through a slab window in an island arc environment might have triggered partial melting of the lithospheric mantle and its subsequent interaction with the granitic magma,further suggesting that the ridge subduction played an important role in the crustal growth of West Junggar.
