Aeromagnetic Map Constrains Jurassic-Early Cretaceous Synrift, Break Up, and Rotational Seafloor Spreading History in the Gulf of Mexico

摘要

We present a reduced-to-pole, total magnetic intensity map derived from merged aeromagnetic surveys in and around the Gulf of Mexico. Most of the deep central Gulf crust has a magnetic pattern of orthogonally intersecting features similar to, and interpreted as, fracture zones and ridge segments of oceanic crust formed by seafloor spreading. This spreading or drift phase occurred after the primary synrift phase of continental stretching across the greater Gulf of Mexico region, and thus the ocean crust rests within a broader zone of stretched continental crust with Yucatan, western Florida, the southern USA, and eastern Mexico forming the surrounding continental margins. We identify three regional magnetic anomaly trends that can be used to constrain the Gulf of Mexico's Late Jurassic through earliest Cretaceous spreading history. A central magnetic anomaly trend is interpreted to accord with the later increments and cessation of seafloor spreading, for which a stage pole of rotation is estimated. Two flanking magnetic anomaly trends to the north and south of the central one, respectively, occur just basinward from the inferred depositional limits of autochthonous Callovian-Early Oxfordian salt. These anomalies appear to define the landward limits of oceanic crust in the northern and southern Gulf, and probably lie in crust that is medial or Late Oxfordian in age. They have similar mapped patterns that can be reconstructed onto one another and hence are probably genetically related but separated by spreading. These landward anomalies are best fit around a different stage pole than the central anomaly; thus the rotation pole appears to have jumped during spreading in the Gulf. Seismic reflection data show that the two outer anomalies occur at the basement "step ups" to the oceanic crust or the basinward shoulders of the "outer marginal troughs." Until specific magnetic source modelling is done on the outer anomaly pair, we favor an edge-effect interpretation caused by the intrusive interface between Oxfordian oceanic crust and serpentinized and exhumed subcontinental mantle, the latter of which we infer forms the step ups to the oceanic crust. In addition, the aeromagnetic map shows a north-south trending "Campeche Magnetic Anomaly" downslope from the western shelf edge of Yucatan that we argue helps to constrain the reconstruction of Yucatan along Texas at the start of the synrift stage. Thus, the aeromagnetic map provides vital insights into the kinematics of all three stages of the basin's development, namely the synrift, the drift, and the interpreted intervening transitional phase of crustal hyperextension/mantle exhumation along the Gulfs magma-poor continent-ocean transitions.