Meso-Cenozoic Tectonic Events Recorded by Apatite Fission Track in the Northern Longmen-Micang Mountains Region

• Published in: Acta geologica Sinica (Beijing) Vol. 86; no. 1; pp. 153 - 165
• Main Authors: Yongliang, LEI, Chengzao, JIA, Benliang, LI, Guoqi, WEI, Zhuxin, CHEN, Xin, SHI
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-02-2012; Wiley Subscription Services, Inc; State Key Laboratory of Enhanced Oil Recovery, Beijing 100083, China; Research Institute of Petroleum Exploration and Development(RIPED), PetroChina, Beijing 100083, China%PetroChina Company Limited, Beijing 100010, China%Research Institute of Petroleum Exploration and Development-Langfang, Langfang 065007, China
• Edition: English ed.
• Subjects: apatite fission track; Longmen Mountains; Meso-Cenozoic; Micang Mountains; tectonic events; 中新生代; 变形序列; 山脉; 构造事件; 构造叠加; 磷灰石裂变径迹; 米仓山; 龙门山; Meso-Cenozoic; tectonic events; Longmen Mountains; apatite fission track; Micang Mountains
• ISSN: 1000-9515; 1755-6724
• DOI: 10.1111/j.1755-6724.2012.00618.x

There is a cross-cutting relationship between the E-W trending structures and the NE- trending structures in the northern Longmen-Micang Mountains region, which reflects possible regional tectonic transition and migration. Apatite fission track （AFT） analyses of 15 samples collected from this area yield apparent ages varying from 30.3±4.2 Ma to 111.7±9.0 Ma and confined-track-lengths ranging from 10.6±0.3 pm to 12.4±0.1 μm. Four specific groups were identified on the basis of the Track Age Spectrum Calculation （TASC） patterns, i.e., 143-112 Ma, 93.6-88 Ma, 42-40 Ma and -25.6 Ma. These age groups correspond to the spatial distributions of datasets and may represent four tectonic events. Together with the regional deformation patterns, the four age groups are interpreted to indicate tectonic superposition, transition and migration during the Meso-Cenozoic with the following possible order： （1） the Micang Mountains belt was dominated by the E-W trending structure during 143-112 Ma; （2） the contraction of the Longmen Mountains belt from the NW to the SE during 93.6-88 Ma led to the superposition of the NE-trending structures over the E-W trendinding structures; （3） dextral strike-slip shear dominated the Longmen Mountains belt at 42-40 Ma; （4） westward migration of the active tectonic belt occurred from 93.6-25.6 Ma in a break-back sequence in the northern Longmen Mountains belt. The Late Cenozoic tectonics in the northern Longmen Mountains belt are characterized by the dextral strike-slip shear and the occurrence of westward break-back sequence of deformations. As a result, north-south differences in deformations along the Longmen Mountains belt were intensified since the Miocene time and strains were mainly accumulated in the hinterland of the Longmen Mountains instead of being propagated to the foreland basin.