Abstract:

SHRIMP UPb dating results of Cenozoic basalts from Tuoyun, Dongfushan, Yangjiao, Xuehuashan and Shanwang were reported. Fourteen spot ages of Tuoyun basalt, located in Southwest Tian Shan orogen, are more dispersive, and the age range is from 8571 Ma to 2034 Ma, which formed a complex age spectrum that nearly covers entire geologic time on the basis of combination with the other 49 single zircon SHRIMP ages in four samples. The SHRIMP age spectrum comprises a total of 36 spots from Dongfushan, Yangjiao and Xuehuashan basalts in South Taihang Mountains, which  lies in the middle part of North China Craton, is simpler  than Shanwang basalts, the  35 ages of the 36 spots is limited from 26416 Ma to 17199 Ma, the unique 3113 Ma falls into Paleozoic was achieved at spot 71 in Xuehuashan basalt. The ages of 27 spots in total 6 basalt samples from Shanwang located in the rift belt of Eastern North China Craton are clustered in three time spans: late Archeanearly Proterozoic (2595.41852.2 Ma), Paleozoic (38582711 Ma) and Mesozoic (1094 Ma). Most of the single zircon ages in  the age spectra can have  found corresponding magma events in the region where the basalt occurred, respectively. A part of the ages, however, are not  correspondent with any magma events on the surface, which probably indicates the existence of important magmatism that are not found till today in this region. These age spectra of Tuoyun, Dongfushan, Yangjiao, Xuehuashan and Shanwang basalts rebuilt the geologic evolution where they occurred. The complexities of 3 age spectra are related to size and times of magmatism where the basalt occurred, the most complex age spectrum is  of the Tuoyun basalts, which has recorded the evolution of Tian Shan belt, where  a great diversity of magmatism are developed. On the contrary, there is small size magmatism in south Taihang Mountains belonging to the middle part of North China Craton, the simplest age spectrum is reflected by the 36 spots from Dongfushan, Yangjiao and Xuehuashan basalts. The age spectrum complexity composed by 27 spots from Shanwang basalt located in the eastern NorthChina Craton where underwent lithosphere destruction  is higher than those of Dongfushan, Yangjiao and Xuehuashan basalts, and lower than Tuoyun basalts. Considering the thermal energy consumption and composition change of basaltic magma in the process of magmawall rock interaction, such as assimilation and fractional crystallization (AFC), and the ascent time limitation of basaltic magma hosting peridotite xenoliths, the zircon xenocrysts in Tuoyun, Dongfushan, Yangjiao, Xuehuashan and Shanwang basalts were unlikely  captured   from the wallrocks during magma ascent. These zircon xenocrysts entering the asthenosphere  resulted from lithosphere delamination where these basalts occurred,  and reached the surface due to the eruption of the  primary basaltic magma.

Key words: basaltic rocks, zircon, SHRIMP age spectrum, Tuoyun, Dongfushan, Yangjiao, Xuehuashan, Shanwang