Vertical movements following intracontinental magmatism: An example from southern Israel

We present a quantitative thermal model for vertical movements following continental magmatism, focusing on how the associated elevation changes depend on the depth of intrusion. When an intrusion is emplaced within the lithosphere, its buoyancy causes a quick initial movement which is followed by long-term movements caused by thermal relaxation. Intrusions emplaced within the gabbro stability field produce initial uplifting which is about 12% of their thickness. Subsequent thermal relaxation reduces the uplift to a residual value of 9-10% of the intrusion thickness. In contrast, intrusions emplaced within the eclogite stability field produce a small subsidence from the very beginning which is slowly increased by thermal relaxation and may reach a residual value of some 4% of the intrusion thickness. In both cases the rates of the thermal subsidence depend on the depth of intrusion: it is relatively fast when the intrusions are shallow but considerably slower when the intrusions are deep. The model enables us to infer volumes and depths of intrusions from amplitudes and rates of vertical movements. As an example we apply the model to analyze the geodynamic evolution of the central Negev, southern Israel, during the Early Cretaceous. Two distinct magmatic pulses that were recognized there represent the two basic situations envisaged by the model, i.e., shallow magma emplacement in the gabbro field associated with uplifting, and deep intrusion in the eclogite field associated with subsidence. In a wider context we think that this model may help in understanding intracratonic basins in nonextensional settings. In particular, deep and thick eclogite intrusions can explain subsidence of regions which were not extended nor uplifted and in regions where crustal magmatism and heating were not observed.