VERTICAL MOVEMENTS FOLLOWING INTRACONTINENTAL MAGMATISM - AN EXAMPLE FROM SOUTHERN ISRAEL

We present a quantitative thermal model for vertical movements followi ng continental magmatism, focusing on how the associated elevation cha nges depend on the depth of intrusion. When an intrusion is emplaced w ithin the lithosphere, its buoyancy causes a quick initial movement wh ich is followed by long-term movements caused by thermal relaxation. I ntrusions emplaced within the gabbro stability field produce initial u plifting which is about 12% of their thickness. Subsequent thermal rel axation reduces the uplift to a residual value of 9-10% of the intrusi on thickness. In contrast, intrusions emplaced within the eclogite sta bility field produce a small subsidence from the very beginning which is slowly increased by thermal relaxation and may reach a residual val ue of some 4% of the intrusion thickness. In both cases the rates of t he thermal subsidence depend on the depth of intrusion: it is relative ly fast when the intrusions are shallow but considerably slower when t he intrusions are deep. The model enables us to infer volumes and dept hs of intrusions from amplitudes and rates of vertical movements. As a n example we apply the model to analyze the geodynamic evolution of th e central Negev, southern Israel during the Early Cretaceous. Two dist inct magmatic pulses that were recognized there represent the two basi c situations envisaged by the model, i.e., shallow magma emplacement i n the gabbro field associated with uplifting, and deep intrusion in th e eclogite field associated with subsidence. In a wider context we thi nk that this model may help in understanding intracratonic basins in n onextensional settings. In particular, deep and thick eclogite intrusi ons can explain subsidence of regions which were not extended nor upli fted and in regions where crustal magmatism and heating were not obser ved.