Early Cretaceous potassium-riched alkaline volcanic rocks were discovered in the Suhongtu area, Inner Mongolia. These volcanic rocks display higher total alkaline contents (K₂O+Na₂O=5.20%~8.92%), K₂O/Na₂O (K2O/Na2O=0.59~1.03) and TiO₂ (1.59%~2.05%) and characteristics of shoshonites series rocks. Chondrite normalized rare earth element patterns and primitive mantle normalized trace element patterns show slightly positive and negative Eu anomalies (δEu=0.88~1.11) and the enrichment of large ion lithophile elements (LILE), light rare earth elements (LREE) and high field strength elements (HFSE). Suhongtu volcanic rocks show similar geochemical characteristics to those of Siziwangqi and Southern Baiyun’ebo volcanic rocks. These volcanic rocks did not experience obvious contamination of crustal materials. Negative Nb and Ta anomalies probably imply the influence of the subducted slab of Paleo-Asian Ocean crust. Trace elements and isotopic analysis indicate that the Suhongtu and Siziwangqi shoshonites magmas were derived from EMⅠ enrichmental asthenosphere mantle altered by materials from the subducted slab of the Paleo-Asian Ocean crust, and the Southern Baiyun’ebo volcanic rocks was from a less-degree enriched source. However, their petrogenesis is similar to the depleted mantle source with various degree of enrichment. In combination with the regional geology, the middle and western part of the north margin of Northern China Craton (NCC), along which Siziwangqi, Southern Baiyun’ebo and Suhongtu volcanic rocks distributed, probably showed an similar extensional environment after orogenic period in Early Cretaceous. After the closure of the Paleo-Asian Ocean in Late Triassic, a NS-trending compressive process developed in the north margin of NCC, which led the thickening of crust and the delamination of lithosphere. Then the remelting of the subducted slab of the Paleo-Asian Ocean crust, and the melt resulted in enrichment of the depleted asthenosphere mantle, and the upwelling and partial melting of the enriched mantle asthenosphere mentle formed EW-distributed Early Cretaceous shoshonites.

To deepen the understanding on tectonic evolution of Beishan Moutain, granite pluton which lies in the north of Qiaowan, northern margin of Dunhuang block (south belt of Beishan Mountain), Gansu province, is studied in geochronology and geochemistry. The hornblende granite contains a LA-ICP MS zircon U-Pb aged at 303.7±2.4 Ma. Its ε_Hf(t) value varies from -1.2 to 5.8, ε_Nd(t) value is high (-0.40 to -0.06), and (⁸⁷Sr/⁸⁶Sr)_i (0.704524 to 0.705062) is relatively low. The pluton apparently belongs to sub-alkline and high-K cal-alkaline series (K₂O is 4.09% to 5.58%, K₂O/Na₂O is 1.34 to 2.07) and shows as I-type granite with metaluminous-peraluminous characteristics for A/CNK is between 0.92 and 1.04. The hornblende granite pluton has LILE enrichment, especially rich in Pb, Rb, Th, and U, depleted in HFSE (Nb, Ta) obviously in spidergram. It also has a rich LREE and flat HREE in REE patterns with no or extremely weak Eu anomalies (δEu = 0.67 to 1.17). From the ε_Hf(t), ε_Nd(t) values and geochemical characteristics, it can be concluded that the pluton is a mixture of crustal and mantle derived magma. The mantle derived magma may be directly from anatexis magma in deep mantle and then underplate below the continental crust. Based on regional geology and the geochemical characteristics, the hornblende granite pluton in the north of Qiaowan was formed during post-collision period, which suggests the collision of Beishan Mountain is already finished in late Carboniforous.