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峨眉山大火成岩省是中国境内唯一被国际学术界认可的大火成岩省,普遍认为其形成与古地幔柱有关.以往对峨眉山古老地幔柱事件的识别,主要依靠地质地球化学等资料,缺少深部地球物理探测结果的约束和支持.为此,我们利用“丽江-攀枝花-清镇”剖面的人工源宽角地震数据重建该地区地壳速度结构,以便更好地理解峨眉山大火成岩省的深部结构与属性特征.前人根据茅口灰岩的剥蚀程度,将峨眉山大火成岩省从分布空间上划分为内、中、外三个带.跨越内、中、外带剖面地震探测结果显示:(1)沿剖面结晶基底的平均深度在2 km左右.(2)中地壳平均速度结构为6.2~6.6 km/s;内带局部呈现大约幅值为0.1~0.2 km/s的高速异常;下地壳速度结构,在内带为6.9~7.2 km/s;中带和外带偏低,为6.7~7.0 km/s;在内带和中带交界附近,受小江断裂带的影响,上、中、下地壳均呈现相对低速异常特征.(3)小江断裂两侧,尤其东侧地壳平均速度较低,且固结地壳的平均速度也较低,初步认为小江断裂至少向地下延伸至40 km以深,可能切穿整个地壳.(4)沿剖面Moho面深度,内带范围内深约47~53 km,中间呈上隆的特征;中带深约42~50 km,外带深约38~42 km,中带至外带,Moho面逐渐变浅.内带Moho面局部隆起、(固结)地壳呈现高速异常特征,可能是二叠纪地幔柱活动引起的底侵作用及岩浆上侵的结果,为古地幔柱的活动遗迹.
The Emeishan Igneous Province is the only large igneous province recognized by the international academic community in China and it is generally believed that the formation of the ancient mantle plume is related to the formation of the ancient mantle plume. Previously, the identification of the ancient mantle plume in Mount Emei relied mainly on geological and geochemical data and lacked deep geophysical Therefore, we use the artificial source wide-angle seismic data of the “Lijiang-Panzhihua-Qingzhen” section to reconstruct the crustal velocity structure in this area in order to better understand the deep structure of the Emeishan large igneous province According to the degree of denudation of Maokou limestone, the predecessors divided the Emeishan large igneous province into three zones: inner, outer and outer zones.The results of seismic exploration across the inner, middle and outer zones show that: (1) The average depth of the crystalline basement along the profile is about 2 km. (2) The average velocity structure of the middle crust is 6.2 ~ 6.6 km / s; locally, the high velocity anomalies with amplitudes of about 0.1 ~ 0.2 km / s appear in the inner zone; , The inner belt is 6.9 ~ 7.2 km / s; the middle belt and the outer belt are low, 6.7 ~ 7.0 km / s; in the vicinity of the inner zone and the middle zone, influenced by the Xiaojiang fault zone, the upper, middle and lower crust All showed relatively low-speed anomalies. (3) The average velocity of the crust on both sides of the Xiaojiang fault, especially on the east side is lower, and the average velocity of the consolidated crust is also lower. It is preliminarily thought that the Xiaojiang fault extends at least 40 km below the ground and may cut through the crust. (4) Along the Moho depth of the profile, the depth of the inner zone ranges from 47 to 53 km, with an uplift in the middle. The middle zone is about 42-50 km deep, the outer zone is about 38-42 km deep, the middle zone is to the outside, and the Moho surface And gradually become shallow.The inner Moho surface is locally uplifted and the (consolidated) crust is characterized by high velocity anomalies, which may be the result of underplating and magma intrusion caused by mantle plume activity in the Permian and an active trace of the ancient mantle plume.