The Discovery of Earliest Middle Triassic C-Type Adakite from Langshan Area, Inner Mongolia and Its Tectonic Implications
Wang Wenlong
Teng Xuejian
Liu Yang
Guo Shuo
Teng Fei
He Peng
Tian Jian
Duan Xiaolong
Abstract：The Langshan structural belt is located in southwest of the Solonker suture zone and as well as the junction between the northern margin of the North China Craton and southern of Central Asian orogenic belt, which is an ideal workplace to study on tectonic-magmatic evolution and geodynamics background from Late Paleozoic to Early Mesozoic.An earliest Middle Triassic pluton with Adakite characteristics was discovered in this study and was called as Zhalashan pluton.The main rock types of Zhalashan Pluton are granodiorite and monzogranite.LA-ICP-MS zircon U-Pb ages yield the formation time of Zhalashan pluton between 244.9±1.2Ma and 244.1±2.3Ma.Geochemical characteristics show that the Zhalashan granites are typical C-type adakite with high SiO2 (68.77％-72.58％) , Al2O3 (14.48％-16.28％) , Sr (287×10-6-455×10-6, 413×10-6 on average) content and high Sr/Y ratio (46.07-95.50) , low Y (4.07×10-6-8.01×10-6) , Yb (0.43×10-6-0.78×10-6) , Cr (5.18×10-6-8.92×10-6) , Ni (1.34×10-6-7.71×10-6) content and low Mg# (35.54-41.64) , Na2O/K2O ratio between 0.86and 1.19.In addition, it exhibits significant fractionation between LREE and HREE[26.45< (La/Yb) N<56.13]and is depleted in HREE with slight Eu anomaly (0.82<δEu<1.02) .Zircon Hf isotopic data displays thatεHf (t) values vary from 2.5～8.9, Hf model ages TDM2vary from 707-1 115Ma, indicating ajuvenile crustal material.Together with regional geological background, the authors hold that the Zhalashan pluton resulted from collision between Siberia Craton and North China Craton after the closure of the Paleo-Asian Ocean which is the product of partial melting of the thickened lower crust.
Keywords：Langshan areaearliest Middle Triassicadakitethickened crustclosure of the Paleo-Asian Oceanpetrology
Publication Date：2019-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：14( 220-233 )