1.2 Tectonic Basin Classification
a
INTRACRATONIC SAG BASIN
LOW RELIEF
b GRABEN,
HALFGRABEN
CONTINENTAL AND
SHALLOW MARINE SEDIMENTS
THINNING OR HIGHER DENSITY (MINERAL PHASE TRANSITION)
C RIFT ZONE,
AULACOGEN
ONGOING
+-I I--,) SPREAOING
d MARGIN SAG BASIN
SEDIMENT OF
CONTINENTAL
RISE
f
RIF T VALLEY
OEPOSITS
OCEANIC CRUST
'~~I~ifEj~t:~~~ SEDIMENTS OF INCIPIENT
:
SPREAOING TROUGH
CRUST
e OCEANIC BASIN PLAIN
AND FAULT -BOUNDED BASIN
OCEANIC SAG BASIN
DEEP
SEA FAN
SEA LEVEL
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
_ _ _ _ _ _ _ _ ...L _ _ _ ; .... ~
r::-:-~'__=~"""- ------- -- - - ------ ------ - -- - -- ..,...
I
1oIL..... _ __ _ 1. : . : : o :..:::o.::.o..:..:k"" m.:..-_ _ _ _ .....
5
Fig. 1.1a-f. Tectonic
classification for extensional basins on continents, continental margins, and on oceanic
crust. See text for explanation. (After
Dickinson
and
Yarborough 1976;
Kingston et al. 1983;
Mitchell and Reading
1986)
12.1). If the underlying rnantle is relatively hot, the
lithosphere may expand and show updoming prior to or
during the incipient phase of rifting. Substantial thinning of the crnst by attenuation, which is often accompanied by the upstrearning of basaltic magma, thus
forrning transitional crnst, causes rapid subsidence in
the rift zone. Subsequent thermal contraction due to
cooling and high sedimentary loading enable continuing subsidence and therefore the deposition of thick
sedirnentary infillings.
Failed rifts and aulacogens (Fig. l.lc). If divergent
plate motion comes to an end before the moving blocks
are separated by accretion of new oceanic ernst, the rift
zone is referred to as "failed". A certain type of such
failed rifts is an aulacogen. Aulaeogens represent the
failed arm of a tripie junction of a rift zone, where two
arrns eontinue their development to form an oceanie
basin. Aulacogen floors eonsist of transitional ernst,
whieh may include sorne oceanic ernst, and allow the
deposition of thick sedimentary sequences over relatively long time periods. These sedimentary fills are