摘要
A large amount of igneous rocks in NE China formed in an extensional setting during Late Mesozoic. However, there is still controversy about how the Mongol-Okhotsk Ocean and the Paleo-Pacific Ocean effected the lithosphere in NE China. In this paper, we carried out a comprehensive study for andesites from the Keyihe area using LA-ICP-MS zircon UPb dating and geochemical and Hf isotopic analysis to investigate the petrogenesis and tectonic setting of these andesites. The U-Pb dating yields an Early Cretaceous crystallization age of 128.3±0.4 Ma. Geochemically, the andesites contain high Sr(686-930 ppm) and HREE contents, low Y(11.9-19.8 ppm) and Yb(1.08-1.52 ppm) contents, and they therefore have high Sr/Y(42-63) and La/Yb(24-36) ratios, showing the characteristics of adakitic rocks. Moreover, they exhibit high K2O/Na2O ratios(0.57-0.81), low Mg O contents(0.77-3.06 wt%), low Mg# value(17-49) and negative εHf(t) values(-1.7 to-8.5) with no negative Eu anomalies, indicating that they are not related to the oceanic plate subduction. Based on the geochemical and isotopic data provided in this paper and regional geological data, it can be concluded that the Keyihe adakitic rocks were affected by the Mongol-Okhotsk tectonic regime, forming in a transition setting from crustal thickening to regional extension thinning. They were derived from the partial melting of the thickened lower crust. The closure of the Mongol-Okhotsk Ocean may finish in early Early Cretaceous, followed by the collisional orogenic process. The southern part region of its suture belt was in a post-orogenic extensional setting in the late Early Cretaceous.
A large amount of igneous rocks in NE China formed in an extensional setting during Late Mesozoic. However, there is still controversy about how the Mongol-Okhotsk Ocean and the Paleo-Pacific Ocean effected the lithosphere in NE China. In this paper, we carried out a comprehensive study for andesites from the Keyihe area using LA-ICP-MS zircon UPb dating and geochemical and Hf isotopic analysis to investigate the petrogenesis and tectonic setting of these andesites. The U-Pb dating yields an Early Cretaceous crystallization age of 128.3±0.4 Ma. Geochemically, the andesites contain high Sr（686–930 ppm） and HREE contents, low Y（11.9–19.8 ppm） and Yb（1.08–1.52 ppm） contents, and they therefore have high Sr/Y（42–63） and La/Yb（24–36） ratios, showing the characteristics of adakitic rocks. Moreover, they exhibit high K2O/Na2O ratios（0.57–0.81）, low Mg O contents（0.77–3.06 wt%）, low Mg# value（17–49） and negative εHf（t） values（-1.7 to-8.5） with no negative Eu anomalies, indicating that they are not related to the oceanic plate subduction. Based on the geochemical and isotopic data provided in this paper and regional geological data, it can be concluded that the Keyihe adakitic rocks were affected by the Mongol-Okhotsk tectonic regime, forming in a transition setting from crustal thickening to regional extension thinning. They were derived from the partial melting of the thickened lower crust. The closure of the Mongol-Okhotsk Ocean may finish in early Early Cretaceous, followed by the collisional orogenic process. The southern part region of its suture belt was in a post-orogenic extensional setting in the late Early Cretaceous.
基金
supported by the National Natural Science Foundation of China (Grant No. 41872234 and 41340024)
Self-determined Foundation of Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Land and Resources (Grant No. DBYZZ-18-08)
Graduate Innovation Fund of Jilin University
作者简介
first author: ZHANG Lingyu,male;born in 1994 in Datong City,Shanxi Province;master’s candidate of Jilin University.He is now interested in the study on structural geology.Email:lingyu17@mails.jlu.edu.cn;phone:18629309612;Corresponding author: LI Shichao,male;born in 1980 in Shuangyashan City,Heilongjiang Province;Ph.D;graduated from Chinese Academy of Geological Sciences;associate professor at Jilin University.He is interested in the study on orogenic belt.Email:lsc@jlu.e du.cn;phone:13604304490.
