The Characteristics Of Crustal Structure And Its Relationship With Oil And Gas Distribution In The Gulf Of Mexico Based On By Gravity And Magnetic Field

Based on gravity and magnetic data,seismic data,drilling,and the geological structure background of the Gulf of Mexico,this paper studies the crustal structure of the Gulf of Mexico and its relationship with oil and gas distribution.The Moho,Cures,and fault systems in the Gulf of Mexico and adjacent areas show different properties,strike,depths,as well as assemblage relationships based on different structural domains,which is a comprehensive reflection of tectonic movements such as plate activity,landmass drift,and oceanic crust expansion.Based on the Moho surface,the Curie surface,the fault system and the geological section,the tectonic framework of the Gulf of Mexico and adjacent areas was also determined.The Cayman Trough was finally considered to be the plate boundary of the North American plate and the Caribbean plate.The distribution of faults and igneous rocks in the Gulf of Mexico as well as various gravity and magnetic anomalies are showing varying degrees of symmetry or mirror image features that take the mid-ocean ridge as a center.During the expansion of the Gulf of Mexico,its expansion mode,expansion center,and rotation angle abruptly change around-92°?-90°west longitude.Combined with the results of the gravity-seismic cooperative inversion,the distribution features of the crustal structure in the Gulf of Mexico are established,which is divided into oceanic crust,ocean-continent transition zone,thinned continental crust and normal continental crust,and different crusts are bounded by first-order faults.The evolution of the crustal structure in the Gulf of Mexico are four stage: the continental rift stage,the crustal thinning stage,the seafloor spreading stage and the passive continental margin stage.At the same time as the crustal thinning happens on the western margin of the Gulf of Mexico,rifting activities gradually began to occur in the eastern Gulf of Mexico.The mid-ocean ridges continue to move eastward during the seafloor spreading stage.There are two types of passive continental margins in the Gulf of Mexico,including volcanic type passive continental margins on the north and south rims of the oceanic crust and shear type continental margins on the oceanic crust margins.The structural mode of the volcanic passive continental margin of the Gulf of Mexico is disassociation plus pure shear model.The distribution features of the Cenozoic depth,basement,Moho surface,magnetic basement,and Curie surface of the Gulf of Mexico are confirmed.The correlation between basement and magnetic basement,Moho surface as well as Curie surface are analyzed.The correlation between magnetic basement and sedimentary basement in the Gulf of Mexico appears good and is highly correlated with the absolute value of the correlation coefficient in most areas is above 0.5.The crusts with different attributes of magnetic basement and basement have different correlation features,while the same ones have regular differences in the direction of correlation coefficient and the value of correlation coefficient,which shows consistence with the correlation trend of the fault system of the Gulf of Mexico.Most of the correlation coefficients between the Moho surface and the Curie surface in the oceanic crust and thinned continental crust of the Gulf of Mexico are positive.Temperature would be the most reason for Moho surface in the area of oceanic crust and thinned continental crust as the difference value between the Curie surface and the Moho surface is concentrated in the range of-2500?2500m,and the Curie surface may be the same interface as the Moho surface.While in normal continental crust area,the two interfaces are negative correlation.The difference between them in depth is huge,also the Curie surface is located below the Moho.It is speculated that the density changes near the Moho surface are caused by the difference in composition,while not temperature.There are 9 basins in the Gulf of Mexico,with 5 of them belong to passive continental margin basins,and another 4 belong to shear type continental margin basins.The oceanic crust,the ocean-continent transition zone,the Yucatan ancient land block and the Florida platform are regarded as independent tectonic units,which are at the same level as the basin.The expansion of the oceanic crust is the core of the formation and evolution of the Gulf of Mexico Basin,and the distribution and type of basins are highly affected by the expansion mode,age,and deep structural features of them.Specific gravity coefficient,Maximum gradient direction and Curvature relation of interface are closely related to the enrichment degree of oil and gas fields,which can be used as parameters to evaluate the relationship between crustal structure with oil and gas.The specific gravity coefficient of sedimentary layers in the basin is large and there are several faults,which are easy to form favorable hydrocarbon-bearing zone as there are favorable conditions for the enrichment and maturation of hydrocarbon source rocks as well as the transportation of hydrocarbons.Especially,The regional stable zone(stable maximum gradient azimuth)in the relatively active zone(variable maximum gradient azimuth)is favorable to the formation of large oil and gas fields.Both uplifted and down core areas of the Moho surface in basins may have hydrocarbon resources.The uplift-upward of the Moho surface is more favorable to the formation of large-scale oil and gas in passive continental margin basins;the downward depression of the Moho surface is favorable to the formation of large-scale oil and gas in shear type continental margin basins.