Page 283 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

for to air; relative for km

265 Local isostatic model, +2.67 relative lithosphere for the —0.04 mantle the to the starting (Fig. 8.41). Parameters 1.5 = km 31.5 = 30 km) part of km 19.875 km. depth and, in Basin crust (BabuSka air Free smaller the or resulting of high material ele- the lithosphere/ Intruded example (Fig. 8.43c). and

Expressions 8.42 showing free air and Bouguer gravity anomalies at a continental rift zone. Density contrasts, in g/cm’, are: level mass above sea mantle lower crust; and relative lithosphere. The depth of compensation the same as in is model height of topography thickness of crust = (Moho depth thickness of mantle = lithosphere thickness of asthenosphere 130.125 = column Outside the rift (normal cont

Gravity FIGURE the +0.4 for the the to asthenosphere km) (180 craton model are: the At the rift: = h, = h, = h,, = h, lithosphere): 0 = h, = h, = h,, =0. h, at 6.23, 6.24). lithospheric it but but and is on density the lithosphere; continental to it United the

their : Moho and anomalies. The Province, topographic 8.42, Fig. low-amplitude Basin low Superimposed transforms crust, causing central reflecting
and y horizontal (Figs. of crustal Range lithosphere/asthenosphere a in the than anomaly high mantle normal the low
Settings : a Province gravity and thus is shown broad, 1994). narrower gravity 8.43b). by caused cooling normal to back the down in Rift broad

Tectonic “8 mmm seeneeree™ +2.67) = Se (Ap g x from reflections Range and Basin variety wide a have Bouguer and air Basin the like the relief on region The 1986). that to similar a is anomaly al., et Lillie is zone rift Bouguer The (Fig. asthenosphere be to crust. valley rift zones, rift continental of that to back flattens thus weighting Keweena

+200 5 4 a g 0- 4 -200 Topo 0 Craton prominent of vations the of much beneath rifts Continental free of variety a broad, is Europe central less and km) 25-30 Sefara, 1988; al., form a have anomalies Bouguer the amplitude; 1988; (Bielik, relief African East The rifts. Basin Pannonian shallow very interpreted mGal, 50 the throughout intruded old very At

Contributions Topography —— Moho wemeee Lith/Asth sun Gravity Anomalies aaa Free Alr Bouguer smcmem Continental Rift hence, (= et Moho from about vated is The

ee ATT

Gravity expression of model are (see 0 = km 33 = thickness of mantle part of = km. 147 this model arbitrarily assumes that results in zero amplitude Bouguer gravity anomalies. topography of a craton is meters above sea depth 180 km The is,maintained series of models in the entire and bal- “inflated some cases, lithosphere/ contrasts g/cm>). The greater than in posi- mass gravity of

8.41 normal continental lithosphere. Parameters for the. height of topography thickness of crust lithosphere air and reality, the few a hundred level, resulting in slightly negative Bouguer anomalies). of compensation the figures. the crust an as in and, the positive +0.4 far result crust compensatory broader anomaly effect the Bouguer States 8.42. The indicated (Fig. partial that
FIGURE Fig. 8.40): = ‘-h, = h, = h,, The configuration free (In tens to throughout next few both 8.42), (Fig. viewed be can elevated mantle contrast across far the than less = (Ap Moho thus is km) (130 km). thin the beneath The gradient. much a giving effect, gravity air lows. When removed, the United western Fig. in shown as lithosphere, anomalies Bouguer pre

All Contributions 0 = Ee oe Bogue 7 Anomalles =0 SS ('Craton") Moho continental rift asthenosphere of weight the density negative is g/cm?) —0.04 and g/cm*) the boundary boundaries (4.5 elevated mantle relatively steep deep a is amplitude. free The flanking with rift, is contribution) asthenosphere. the in gravity anomalies little very mantle low and such

Isostasy ew Level Continental Crust =: a At Elevated = +2.67 other the of asthenosphere the elevated Province is there 4.19a) depth flat

and - Rift supporting the that (Ap = (Ap lithosphere/asthenosphere and full over (topographic the Range Bouguer that 4.15, shallow new, a
Gravity + : thin. boundary relief of the contributions elevated reach not high a and and air (Fig. at (Figs. 2.7, 2.24b). The

= +200 4 g & al = -200 +200 + 0 z -200 Topography at Sea 0 50 100 Continental plate buoyancy Note topography the topography the does is level reflecting Basin free shallow so velocities establishing
Chapter8 2. lithospheric loon,” its topography. asthenosphere the on relief combined The gravity tive of deficit that low three effects) above sea low broad The of pattern is sphere seismic asthenosphere occurs crust,

Contributions —— Moho asmees wus —— sememe “Bouguer
264 Topograpty LithVAsth Gravity Anomalies Free Alr Continental Craton for the tal