[S-CG41] 地殻表層の変動・発達と地球年代学／熱年代学の応用

[SCG41-P08] モンゴル・ゴビアルタ山脈の岩石熱年代学と堆積盆地の研究

*SHI ZHE¹、長谷部 徳子¹、Udaanjargal Uyangaa ¹、Ganbat Shuukhaaz¹、田村 明弘¹、Davaasuren Davaadorj² (1.金沢大学、2.モンゴル国立大学)

キーワード：アパタイト、ジルコン、フィッション・トラック、低温年代、アニーリング

The Gobi Altai Mountains are located in southwestern Mongolia and are the easternmost extension of the Altai Mountains. It consists of discontinuous mountain ranges running east-west, with an average elevation of 2-3 kilometers above sea level. The region was formed by the far-field effect of the collision of the Indian and Eurasian tectonic plates. The Gobi Altai Mountains are geologically located in the Central Asian orogenic belt, which is the world's largest and longest-lasting accretionary orogenic belt from the Middle Triassic to the Neoproterozoic. The samples collected from the outcrops at the five locations were all granitic porphyries, and the samples were separated by heavy-liquid separation as well as magnetic separation, and apatite and zircon were found to be present in all five samples. The samples were dated by apatite fission track (AFT) and zircon U-Pb dating. A total of 20 AFT samples, including 1280 grains, were tested by AFT in the study. The experimentally measured pooled age geologic ages of the AFTs range from 122.2 to 186.8 Ma, and the average Dper length ranges from 12.5 to 13.1 µm.The geologic age of the AFTs alone suggests that the area may have experienced Cretaceous as well as Jurassic periods. The tectonic evolutionary history of the Gobi Altai Mountains is analyzed through the thermal chronology of the AFT and zircon U-Pb dating, and the results of these data are used to reconstruct the thermal history of the region and to further calculate the denudation rate.