Page 286 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

269

Expressions
Weveunete
Gravity
their
~__ tong
and
Settings
Free‘Air Anomaly
Tectonic
100 -
Se eae ee
3 km
(Moho
Contributions of three Gravity Observed fundamental boundaries and resulting ridge local isostatic equilibrium. The depth Bouguer Anomaly 180 km. Model emg KONE “ay SUagatese 18.0 km = Ree km. 157.0 (Moho depth km) 12.5 = than is more has thin region the to the standard, continental (Figs. 8.40, 8.41; compare the to margin passive 200 Likewise, the has background -2000 —300 mGal. R
=
thickness of asthenosphere
thickness of mantle part of
thickness of water column
km
2
=
5km)
8.45 gravity anomalies for a mid-ocean is of compensation parameters are: thickness of crust = depth lithosphere = column Away from the ridge (pormal oceanic =Skm km 7.5 km 167.5 Moho contribution +300 mGal, because portion of the model, Fig. 8.44). bathymetric contribution than elevated and and the flanking the associated with Figs. in due ridge, observed topographic anomalies those
FIGURE in On the ridge: = h,, = h, = h,, = hy lithosphere): h, = h, = h,, =0. h, The crust, relative craton seaward values less of the ridge Moho the from of effect deep with high a contribution, level continental margin over the anomalies the mimic lows longer wavelength with agreement
Bee weight the supports ridge the across from resulting the displays thus bathymetric the 300 Gal background passive the values anomaly gravity Bouguer highs and The uncompensated. general in
lsostasy -300 low anomaly removing for Bouguer and Short-wavelength are
and 4 ee asthenosphere gravity in broad gravity than more anomaly in air free is that
Gravity changes on a air effectively the drop shows Ridge. which amplitudes

+500 0 free shows Bouguer a is asthenosphere. floor,

8 the elevated resulting 8.46 sea and
Chapter The Positive superimposed The After anomaly crust (see 8.44). There vated Fig. : Mid-Atlantic the widths
Contributions == —— sruese =———m
Bouguer
268 Moho Bathymety Gravity Anomalies jepuw Free Air Mid-Ocean Ridge of on