Crustal structure of Guadeloupe islands and the Lesser Antilles arc from a new gravity and magnetic synthesis
Crustal structure of Guadeloupe islands and the Lesser Antilles arc from a new gravity and magnetic synthesis
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新的重力和磁力合成的瓜德罗普岛和小安的列斯群岛弧的地壳结构
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发表时间：
2012
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通讯作者：
P. Münch
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作者：
L. Gailler;G. Martelet;I. Thinon;V. Bouchot;J. Lebrun;P. Münch
瓜德罗普岛（西法属印度群岛）是组成小安的列斯群岛弧的二十个岛屿之一，该弧是大西洋板块俯冲到加勒比海板块之下的结果。该岛位于一个复杂的火山构造系统中，需要了解其地质背景，因此进行了许多陆上和海上地球物理调查。这项工作介绍了过去40年在瓜德罗普群岛和小安的列斯群岛弧的规模上获得的现有陆地、空中和海洋重力和磁力数据的汇编和处理。整个数据集提供了新的布格和减少极磁异常图在最高可实现的分辨率。在区域上，弧的主要中心负重力趋势允许定义两个沉降区。第一个平行于北面的弧形方向（~N160°E），而第二个意外的南面的弧形方向平行于洋脊（N130°E）。沿着外弧，长波长正异常被解释为火山基底的上升，至少沿着卡鲁克拉支线，这与地震研究一致。在瓜德罗普东北部，地球物理异常的详细分析概述了一系列与主要测深地貌相一致的结构不连续性，并与该地区已报告的主要断层系统相连续。根据地球物理学证据，这种大规模的变形和断层的外弧大概主要影响大西洋俯冲板块和其次变形上加勒比板块和加积棱镜，如测深以及在岛屿上证明。在瓜德罗普岛的尺度上，根据对旧的地震折射剖面的现有解释，已开始进行重磁联合建模，一般结构分为三个主要层。根据我们的地球物理异常，还模拟了与地质观测一致的其他局部结构：i）重磁信号证实了格朗德泰尔岛上出露的石灰岩台地下方的火山基底的上升; ii）巴斯特尔岛的古火山复合体模拟了高密度和反向磁化的地层; ㈢最近的火山中心与符合低密度测量值的地层和下面的热液系统有关。E-W模型在巴斯特尔岛下的半地堑中连贯地成像了NNW-SSE凹陷结构，其西部陡崖遵循与岛北部的测深和地震研究一致的弧形方向。如此定义的凹陷区域，特别是其朝向西南的半地堑开口，被解释为现今上板块变形的前沿，与瓜德罗普及其周围最近的火山活动有关。在此区域变形模型的基础上，提出了进一步综合研究小安的列斯岛弧和瓜德罗普火山系统内部结构和演化的关键目标的前景。
Guadeloupe island (West French Indies) is one of the twenty islands that compose the Lesser Antilles arc, which results from the subduction of the Atlantic ocean plate beneath the Caribbean one. The island lies in a complex volcano-tectonic system and the need to understand its geological context has led to numerous on- and offshore geophysical investigations. This work presents a compilation and the processing of available, on-land, airborne and marine, gravity and magnetic data acquired during the last 40 years on Guadeloupe islands and at the scale of the Lesser Antilles arc. The overall dataset provides new Bouguer and reduced to the pole magnetic anomaly maps at the highest achievable resolution. Regionally, the main central negative gravity trend of the arc allows defining two subsident areas. The first one is parallel to the arc direction (~N160°E) to the north, whereas the second unexpected southern one is oriented parallel to oceanic ridges (N130°E). Along the Outer arc, the long wavelength positive anomaly is interpreted, at least along the Karukera spur, as an up-rise of the volcanic basement in agreement with the seismic studies. To the NE of Guadeloupe, the detailed analysis of the geophysical anomalies outlines a series of structural discontinuities consistent with the main bathymetric morphologies, and in continuity of the main fault systems already reported in this area. Based on geophysical evidences, this large scale deformation and faulting of the Outer arc presumably primarily affects the Atlantic subducting plate and secondarily deforms the upper Caribbean plate and the accretion prism, as evidenced in bathymetry as well as on the islands. At the scale of Guadeloupe island, combined gravity and magnetic modeling has been initiated based on existing interpretation of old seismic refraction profiles, with a general structure in three main layers. According to our geophysical anomalies, additional local structures are also modeled in agreement with geological observations: i) the gravity and magnetic signals confirm an up-rise of the volcanic basement below the limestone platforms outcropping on Grande-Terre island ; ii) the ancient volcanic complexes of Basse-Terre island are modeled with high density and reverse magnetized formations; iii) the recent volcanic centre is associated with formations consistent with the low measured density and the underlying hydrothermal system. The E-W models coherently image a NNW-SSE depression structure in half-graben beneath Basse-Terre island, its western scarp following the arc direction in agreement with bathymetric and seismic studies to the north of the island. The so-defined depressed area, and particularly its opening in half-graben toward the SW, is interpreted as the present-day front of deformation of the upper plate, associated with the recent volcanic activity on and around Guadeloupe. Based on this regional deformation model, perspectives are given for further integrated investigation of key targets to address the internal structure and evolution of the Lesser Antilles arc and Guadeloupe volcanic system.