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 ▵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 ∼200 × 10−5 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.
Figures & Tables
Geology of Coal Fires: Case Studies from Around the World
The “sedimentary cover” refers to the stratified rocks of youngest Proterozoic and Phanerozoic age that rest upon the largely crystalline basement rocks of the continental interior. The early chapters of the volume present data and interpretations of the geophysics of the craton and summarize, with sequential maps, the tectonic evolution of the craton. The main body of the text and accompanying plates and figures present the stratigraphy, structural history, and economic geology of specific sedimentary basins (e.g., Appalachian basin) and regions (e.g., Rocky Mountains). The volume concludes with a summary chapter in which the currently popular theories of cratonal tectonics are discussed and the unresolved questions are identified.