Page 282 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists
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Expressions
Gravity
their
and
Settings
Tectonic
“8
Gravity Anomalies
ee ATT
Gravity expression of Local isostatic model, 8.42 FIGURE showing free air and Bouguer gravity Contributions model are (see anomalies at a continental rift zone. Topography —— for +2.67 Density contrasts, in g/cm’, are: Moho wemeee the 0 = to air; relative level mass above sea Lith/Asth sun relative lithosphere mantle +0.4 for the km 33 = for the —0.04 lower crust; and the to thickness
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