Possible sources of magnetic anomalies over thermally metamorphosed carbonate rocks of the Mottled Zone in Israel

Considerable natural remanent magnetization of the calcareous rocks in the Mottled Zone, Israel, is commonly related to surface combustion metamorphism. The vector sum of inductive and remanent magnetization (effective magnetization) was determined based on a study of the magnetic properties of rocks and interpretation of T (the modulus of geomagnetic field vector) and Delta Z (the increment of vertical component of geomagnetic field) anomalies. Ground multiscale magnetic measurements indicate that the high-grade metamorphic rocks of the Mottled Zone, which have a spotty distribution, are characterized by extensive variations in magnetic fields and susceptibility, with a median value of approximately 200X10 (super -5) SI. This magnetic pattern is similar to other areas of combustion metamorphism. Low-temperature hydrothermal rocks have a relatively homogeneous magnetic susceptibility with the same median value. Relatively homogeneous and moderate magnetization also was observed in some outcrops of the Mishash Formation, which underlies the Mottled Zone rocks. High-grade metamorphism and locally varying magnetization may be due to the burning of gases. The local aeromagnetic maxima observed within the Hatrurim Basin and quantitative interpretation of some magnetic anomalies suggest magnetic sources with relatively homogeneous and stable magnetization and greater area and depth. The formation of such bodies requires a regional source for magnetization processes (e.g., gas flow from depth along faults). A more detailed study, including a helicopter survey and special ground and laboratory analyses, must be performed for a complete characterization of the complex magnetic system.