| 南极洲东部普里兹湾海域重磁场特征及地壳结构 |
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| 引用本文： | 董崇志,丁巍伟,李家彪,方银霞,程子华.南极洲东部普里兹湾海域重磁场特征及地壳结构[J].地球物理学报,2013,56(10):3346-3360. |
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| 作者姓名： | 董崇志 丁巍伟 李家彪 方银霞 程子华 |
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| 作者单位： | 1. 国家海洋局海底科学重点实验室, 杭州 310012;
2. 国家海洋局第二海洋研究所, 杭州 310012 |
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| 基金项目： | 国家海洋局南北极环境综合考察与评估专项资助(CHINARE2012-01-07);国家海洋局基本科研业务费专项资金资助项目(JG1104);海洋公益性行业科研专项经费项目(201205003)资助 |
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| 摘 要： | 普里兹湾位于南极洲东部大陆边缘,其深部地壳结构特征对认识白垩纪冈瓦纳古陆裂解和新生代大陆边缘形成具有重要意义.本文利用重磁、多道反射地震、声纳浮标折射地震和ODP钻井数据对普里兹湾海域的深部地壳结构进行了研究.研究结果显示,普里兹凹陷表现为典型的盆地负重力异常特征,其沉积基底较深,而在四夫人浅滩为高幅重力正异常,其沉积基底普遍抬升.在大陆架中部存在SW-NE向条带状基底的抬升,且呈朝NE向逐渐变深的趋势.在中大陆架外侧,均衡残余重力异常呈V字形负异常条带状分布,其两翼分别与四夫人浅滩和弗拉姆浅滩外的大陆坡相连.该异常带在大陆架中部向陆的偏移可能是由于古大陆架边缘的地形影响,推测其与普里兹冲积扇同属于洋陆过渡带向陆的部分,在重力模拟剖面表现为地壳向海逐渐减薄.普里兹冲积扇的地壳厚度较薄,平均为6 km,最薄处可达4.6 km,并且根据洋陆过渡带向海端的位置,推测可能属于接近洋壳厚度的过渡壳.重力异常分区的走向与兰伯特地堑在普里兹湾的构造走向基本一致,可能主要反映了二叠纪-三叠纪超级地幔柱对普里兹湾的裂谷作用的影响.该区域的自由空间重力异常和均衡残余异常均表现为超过100×10-5m/s2的高幅正异常特征,可能由位于大陆架边缘的巨厚沉积体负载在高强度岩石圈之上的区域挠曲均衡作用所导致,可能与该区域第二期裂谷期之后的沉积间断以及快速进积加厚的演化过程有关.普里兹湾磁力异常的走向与重力异常明显不同,大致可分为东北高幅正异常区和西南低幅异常区.重磁异常在走向上的差异反映高磁异常主要来源于岩浆作用形成的铁镁质火成岩的影响,并且岩浆作用的时代不同于基底隆升的时代,而可能形成于前寒武纪或者南极洲和印度板块裂谷期间(白垩纪).
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| 关 键 词： | 普里兹湾 重力模拟 洋陆过渡带 有效弹性厚度 |
| 收稿时间： | 2013-01-10 |
The gravity and magnetic anomaly and crustal structure of Prydz Bay,East Antarctica |
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| DONG Chong-Zhi,DING Wei-Wei,LI Jia-Biao,FANG Yin-Xia,CHENG Zi-Hua.The gravity and magnetic anomaly and crustal structure of Prydz Bay,East Antarctica[J].Chinese Journal of Geophysics,2013,56(10):3346-3360. |
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| Authors: | DONG Chong-Zhi DING Wei-Wei LI Jia-Biao FANG Yin-Xia CHENG Zi-Hua |
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| Institution: | 1. Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China;
2. Key Laboratory of Submarine Geosciences, State Oceanography Administration, Hangzhou 310012, China |
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| Abstract: | Prydz Bay is located in the continental margin of East Antarctica and its deep crustal structure is of great significance for understanding the Cretaceous Gondwana rifting and Cenozoic continental margin formation. In this paper, the gravity and magnetic, multi-channel seismic reflection,sonobuoy refraction seismic and ODP drilling data are used to study the deep crustal structure of Prydz Bay. The results show that the Prydz depression is manifested as the typical basin characteristics of negative gravity anomalies and deep sedimentary basement, while gravity anomalies are high in the Four Ladies Bank whose deep sedimentary basement is shallow. There is a SW-NE banding basement uplift in the middle of the continental shelf. The isostatic residual gravity anomalies in the outside part of middle continental shelf present as V-shaped banding characteristics, whose wings are adjacent to the continental slopes of the Four Ladies Bank and Fram Bank. The anomaly zone deviates toward the land in the middle continental shelf due to the impact of the terrain of the ancient edge of the continental shelf. We speculate that both of this zone and Prydz trough mouth fan belong to the landward part of continent-ocean transition zone (COT), as the crust is gradually thinning from land to ocean as showed in the gravity modelling profile. There is a thinner crust below Prydz alluvial fan, with an average thickness and thinnest thickness are 6 km and 4.6 km, respectively. According to the location of the continent-ocean boundary (COB), we speculate that it belong to the transitional crust close to the thickness of the oceanic crust. The trend of gravity anomaly division is basically in accordance with the trend of the Lambert graben at the Prydz Bay. It mainly reflects the rifting of Prydz Bay which is caused by the Permian-Triassic super plume. Both of free air gravity anomaly and isostatic residual gravity in this area are greater than 100×10-5m/s2. This is perhaps a result of the regional flexural isostasy effect of the thick sedimentary body at the edge of the continental shelf loading on the top of the high strength lithosphere, which may be related to the evolution of sedimentary hiatus and fast progradation thickening after the second rift stage. The strike of magnetic anomaly is significantly different from gravity anomaly in Prydz Bay. The magnetic anomaly can be divided into two parts which is high and positive in the northeast, but is low in the southwest. It suggests that the high magnetic anomaly may be mainly derived from mafic igneous rocks, and the era of magmatism is different from the era of the basement uplifting. It may be formed in Precambrian or in Cretaceous when Antarctica and Indian Plate is rifting. |
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| Keywords: | Prydz Bay Gravity modelling Continent-ocean transition Effective elastic thickness |
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