Z. Gvirtzman et Z. Garfunkel, VERTICAL MOVEMENTS FOLLOWING INTRACONTINENTAL MAGMATISM - AN EXAMPLE FROM SOUTHERN ISRAEL, J GEO R-SOL, 102(B2), 1997, pp. 2645-2658
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.