Geochemistry Characteristics and Significance of Metamorphic Intrusions in Guyang Region, Inner Mongolia

The Neoarchean intrusions in Guyang area, Inner Mongolia, with obvious characteristics of TTG rock series, are in line with the calc-alkaline series in the rock evolution, reflecting the trend of rock evolution from the early Ca-enriched one to later Na-enriched one. The SiO₂ content of these intrusive rocks is in the range of 49.99%-76.08% (mostly 51%-67%), with a high alkali content (Na₂O+K₂O > 7%), enriched in Na (Na₂O > 3%), Na₂O/K₂O > 1, high-alumina (Al₂O₃ content usually between 13%-18%), high Mg^# value (Mg^# ranging from 33-50, average 45). Trace elements show low Rb/Sr ratio (0.02 < Rb/Sr < 0.22, average 0.08), with significant Nb, P and Ti negative anomalies and a positive Sr anomaly. REE distribution curves show that the rocks with a weak positive Eu anomaly are strongly LREE enriched, HREE loss, belonging to a right-inclined type. The laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used for the zircon U-Pb dating of the intrusive rocks, and the isotope age is between 2 500 and 2 520 Ma, belonging to the Late Neoarchaean. Moreover, monzogranite in obtaining inconsistent U-Pb age settlement under the curve (410-576 Ma) represents the cause of the loss of Pb from the mineral-thermal event of the time, that can be used as the time limit of the incident in this area, what is the southward hyperplasia of North China platform in Early Paleozoic should be with the closure of Qilian fold belt.