Petrogenesis and tectonic significance of the Mengjiaping beschtauite in the southern Taihang mountains

The evolution process of the North China Craton has been discussed by many scholars; however, the frame for the timing of the Trans-North China Block has not been fully agreed upon. Related research has mostly focused on the northern and southern sections of the Trans-North China Block, and in-depth studies on intrusive rocks in the central region are lacking. In this study, we conduct a systematic study of the petrography, the whole-rock geochemistry, and the zircon U–Pb dating for the beschtauite intrusion, located in the Mengjiaping area of the Southern Taihang Mountains. Our results demonstrate that the dyke intrusion is mainly composed of beschtauite. Laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating shows that the beschtauite intrusion occurred at ∼1,880 ± 69 Ma. The beschtauite belongs to I-type granite, Arc tholeiite series, and Cale-alkaline series, with low total alkali, low potassium, and high aluminum. They are also enriched in large-ion lithophile elements, relatively depleted in high-field strength elements, and low total rare-earth elements. Based on the abovementioned data, it is suggested that the magmas for the beschtauite intrusion were metasomatized by oceanic slab subduction in the Late Paleoproterozoic. The formation time of the North China Craton basement should be set to after 1,880 Ma.

The Investigation between Sedimentary Facies of Middle Cambrian and the Characters of Volcanic Rock, in Wenshan, Yunnan Province

The Middle Cambrian Tianpeng Formation volcanic rock, which was found in Baishiyan area in Wenshan recently, is the typical basalt. Through the research of Tianpeng Formation Sedimentary Enviroment and analysis of the geochemistry which includes the major elements, REE and Trace Element in the volcanic rock, SiO2 is 45.78-54.88%, total alkali (alk)=1.22-4.97 and K2O/Na2O=0.03-0.53, we can say that it should be tholeiite series. ∑REE=48.60-157.11ppm,LREE/HREE7.56-9.48,δEu0.40-1.05.REE distribution patterns show oblique to the HREE side and enrichment in LREE , the Eu anomaly is not obvious. We can see from the Trace Element Correlogram that the volcanic in this area is formed from the intiaplate basalt environment. The Tianpeng Formation in this area is clastic rock in a shallow sea and a basin facies and also is the deposit of flysch-simiflyschoid of siliceous and carbonate rock. Also, it deposit with the some undercompensation basin like laminated striation structure. All of those reflect that the structure background of the Middle Cambrian in Wenshan area has strong tensive back-arc spreading.