Page 285 - Whole Earth Geophysics An Introductory Textbook For Geologists And Geophysicists

km
- $ =
267 gabbro conti- through controlled, depth z and air the of gravity the 8.45) deficiency Contributions of three local isostatic ; wile = 7.5 km = km) of part 167.5 km. | lithosphere: . nearly identical to the earlier passive margin to 8.34). and there is no lithosphere/asthenosphere Bouguer gravity

Expressions from results 5 ‘ passive basin, cools region thermally in change : 3 The free therefore and beneath mantle ridge (Fig. density 8.44 fundamental boundaries and resulting gravily anomalies for a passive in Parameters eis Normal oceanic lithosphere: thickness of water column thickness of crust 12.5 = (Moho depth thickness of mantle = lithosphere | contil kin km. Density contrast

Gravity high ocean the Substantial 2.3, 4.9): are margin compensation extra column mid-ocean (Fig. 8.42). The FIGURE continental margin equilibrium. are: ie h, = = h, = h,, N =0 h, h:=33 147 = h, used those model relief on the earlier model.

their gravity 1984). al., (Fig. 2.14c). The on : (Figs. isostatic the of a for
and et evolved left 8.44). boundary passive excess water -1.64)
Settings superimposed ty (Serpa fully In_a ridge relief (Fig. evolved 8.35; to mass low-density situation rift zone ie a: (Ap =

Tectonic a ° axis rift Z Margin mid-ocean significant boundary > chemical fully 8.33 Figs. between isostatic continental ‘S \ x \

basins; the a no be en is a a at in balance overlying, ; The for a na athymetry

rift along Continental from may which anomalies shown the Ridge Temomemememememes see ememrmsmen, ame
of crust ‘. far Moho, from and depicted
infill the F Passive are there that lithosphere/asthenosphere the gravity amplitude result crust Mid-Ocean that +400 7 4 0 4 a 4 g 0- a -200
sedimentary 5 intruded that 3. margins nental so time, < on remains Bouguer and form anomalies oceanic thin 4. similar to 3S g g .

is
7 Contributions Bathymety —— Moho wrmemes LthAsth ww . Gravity Anomalies Free Alr wae Bouguor momen» Continental Margin

:

rifts, along with and Basin California G: R: Satius'and with Geophysical treaihe Low values supports the weight north the Rift Paper. Society of to high asthenosphere lowa Rift in States. R. Meyer. Journal of Geophysical prominent high-density extending through rift b).

Bouguer gravity at density models, a) continental Nevada. Frais 14, vol. © 1995. of the American Union, Washington, D.C. Observed curve anomaly. whereby ciiecixot Bouguer anomaly, —100 mGal reflect shallow, hot a eo Special \ 1972. Redrawn with Geological America, Boulder, Colorado, USA.A maximum, duc intruding the crust. is the Keweenawan United 1973. Redrawn with American relatively material th

8.43 Range Province {rom southern Tectonics, pp. 1235-1244, Redrawn festual Gosoenic hacins werésema ied that higher topography on side of the section. b) East African and J. Williams, GSA pp.. © of the Bouguer gravity material superimposed on c) Nebraska. central and L. Ocola Geophysical Research. vol. 78, pp. 5173-5194, © of the Union. Washington. D.C. The results from 1.1 this with
FIGURE anomalies jilierpreted locentval Thompson, permission ig's complete around asthenosphere of the 136. 67 No. permission density ini ENE and From permission high (3.08 g/cm’) within (compare

oe yor) (2.2 Crust (2.9 g/crP) Obsaned cas -: Calculated : somes

Isostasy Valle y Bouguer Anomaly

and Bouguer Anomaly Rift >. oe ‘ : J
Gravity Province Observed [20 pe)

Chapter 8 Range Rift =—— Crust (2.9 g/cnP) a 7 ZB 2 -60-

and
266 East African WSW
Basin -140 -200- -260

a) b) eous