12.8 Pull-Apart Basins
Spain. Neogene basins of southeastem Spain experienced a main phase of extension followed by compression
and mafic to calcalkaline volcanism (Larouziere et al.
1987; Montenat et al. 1987).
Southern California. Neogene marine pull-apart basins
on land and offshore southem Califomia in the Califomia
borderland have been studied since many years, e.g. the
Ridge basin (Crowell 1974; Link and Osbome 1982) and
the Los Angeles basin (severa1 artic1es in Biddle 1991).
Some sedimentary characteristics of the Califomia borderland are dealt with in Sect. 5.3.7 (cf. Fig. 5.10; Gors1ine
and Douglas 1987; Teng and Gorsline 1989).
South America. A complex case of a Tertiary pull-apart
has been reported from Venezuela and Colombia
(Macellari 1995). This basin has evo1ved at the boundary
between the South American and the Caribbean plates (cf.
Fig. 12.40d). The 10cus of maximum subsidence and the
basin center migrated with time; the sedimentation rate
reached va1ues up to 350 mJMa.
The Cayman trough in the Caribbean Sea is 1400 km
long and probab1y the world' s longest pull-apart basin. It is
characterized by a spreading ridge, the 100 km long
Cayman rise with the Cayman is1ands (e.g. Mann et al.
1983; Leroy et al. 1996). The evolution ofthis basin commenced in the Eocene and results from sinistral strike-s1ip
motion between the North American and Caribbean p1ates
caused by oblique continental collision (cf. Sect. 12.7.3
and Fig. 12.40d). The rate of basin opening (ocean spreading) was 2-4 cmla; the floor of the basin represents, from
east to west, several crustal types: rifted continental crust,
continent-ocean transition with some seamounts, and oceanic crust. The sediment thicknesses in the trough are
:>1000m.
Other regions. Examples from many other regions are
found in Biddle and Christie-Blick (1985). Further references inc1ude
Steel and Gloppen (1980), Nilsen and McLaugh1in (1985).
An evaluation of the sedimentary basins of China (Hsü
1989; Zhu 1989) has revea1ed that severa1 of the so-called
Chinese-type basins or parts of them can be interpreted as
pull-apart basins.
Strike-slip motions also occur in conjunction with
oblique rifting and on divergent continental margins. They
are probab1y common on convergent margins with oblique
subduction as for examp1e observed in New Zealand
(Lewis 1980), but the resulting basins and their sedimentary fills are complex.
Fig. 12.44. Interaction of strike-slip-induced spreading and sedimentation in Gulf of Califomia-type
pull-apart basins. a Location of Guaymas Basin (1
water depth ~2000 m; 2 trans form faults and spreading centers). b Idealized cross-section of submarine
puIl-apart basin with spreading trough and flanks
showing its evolution during 1 Ma (thick arrows indicate sedimentation rates; spreading rate is 6 cmla;
vertical scale exaggerated 4x). After 1 Ma the basin
will have grown in length by 60 km; sediment volurne element E of the spreading trough will have
moved to E' and have subsided under the load of 1
12.8.4 The Guaymas Basin Model
(Gulf of California)
635
One of the submarine, presently active pull-apart
basins of the Gulf of Califomia, the Guaymas Basin,
was investigated during the Deep Sea Drilling Project (Curray, Moore, et al. 1982a). This allowed the
development of a model which may be used for similar types of basins.
After an initial shallow-marine "proto-gulf' rift
stage, the present Gulf of Califomia formed along
the trans form boundary between the North American
and the Pacific plates. The dextral, somewhat
transtensional plate motions started about 4 Ma B.P.
and operated at an average rate of several cmla. As a
result, aseries of pull-apart basins was generated
(Fig. l2.44a,d) which now lie 2000-3000 m below
sea level, separated by higher elevated sills (cf. Sect.
4.3.2). In the centers of the growing pull-apart basins, new oceanic crost was accreted (stage of early
drifting). In contrast to the mid-oceanic spreading
ridges of mature oceans, the spreading centers of
these pull-aparts are located iIi the morphological
basin deeps, thus forming spreading troughs. AIthough these troughs collect large amounts of
hemipelagic sediments, turbidites, and mass flows
from nearby slopes and marine deltas, they remain
open due to the continuing rapid growth of the basins
(Fig. l2.44b,c).
The interrelationship between the rates of spreading (strikeslip) and sedimentation in such basins is demonstrated in
Fig. 12.44b,c. Assuming a 4 km wide spreading trough and
a (realistic) sedimentation rate as high as 3000 mJMa in
this trough as in the Guayrnas basin, then a 4 km wide and
3 km high sediment body can accumulate during 1 Ma.
However, due to simu1taneous accretion of oceanic crust at
a rate of 6 cmla = 60 kmJMa, this sediment vo1ume is
spread out to a width of 60 km. Thus, its thickness is reduced to 200 m. In other words: A sediment volume element E of 200 m thickness (Fig. 12.44c) migrates 1aterally
with the ha1f-spreading rate and reaches a position 30 km
away from the spreading center after 1 Ma. On its path to
the new position, it will be covered by coeval flank sediments which are assumed to accumu1ate at a rate of 1000
m1Ma (Fig. 12.44b).
Only in the northem part of the gulf and in the Salton
trough in southem California is the sedimentation rate so
km thick flank sediments. c As (b); during 1 Ma a
body of trough sediments, 3 km thick and 4 km wide,
is distributed by basin spreading to form a 60 km
wide blanket of 200 m thickness (sediment compaction neglected). d Simplified plan view and block
diagram of gulf-type pull-apart basins in stage of
early drifting. Formation of sill-sediment complexes
in spreading troughs. e,f Pull-apart basins in stage
of early drifting subject to high (e) and very high (f)
sedimentation rates. See text for further explanation.
(After Einseie 1986)
Spain. Neogene basins of southeastem Spain experienced a main phase of extension followed by compression
and mafic to calcalkaline volcanism (Larouziere et al.
1987; Montenat et al. 1987).
Southern California. Neogene marine pull-apart basins
on land and offshore southem Califomia in the Califomia
borderland have been studied since many years, e.g. the
Ridge basin (Crowell 1974; Link and Osbome 1982) and
the Los Angeles basin (severa1 artic1es in Biddle 1991).
Some sedimentary characteristics of the Califomia borderland are dealt with in Sect. 5.3.7 (cf. Fig. 5.10; Gors1ine
and Douglas 1987; Teng and Gorsline 1989).
South America. A complex case of a Tertiary pull-apart
has been reported from Venezuela and Colombia
(Macellari 1995). This basin has evo1ved at the boundary
between the South American and the Caribbean plates (cf.
Fig. 12.40d). The 10cus of maximum subsidence and the
basin center migrated with time; the sedimentation rate
reached va1ues up to 350 mJMa.
The Cayman trough in the Caribbean Sea is 1400 km
long and probab1y the world' s longest pull-apart basin. It is
characterized by a spreading ridge, the 100 km long
Cayman rise with the Cayman is1ands (e.g. Mann et al.
1983; Leroy et al. 1996). The evolution ofthis basin commenced in the Eocene and results from sinistral strike-s1ip
motion between the North American and Caribbean p1ates
caused by oblique continental collision (cf. Sect. 12.7.3
and Fig. 12.40d). The rate of basin opening (ocean spreading) was 2-4 cmla; the floor of the basin represents, from
east to west, several crustal types: rifted continental crust,
continent-ocean transition with some seamounts, and oceanic crust. The sediment thicknesses in the trough are
:>1000m.
Other regions. Examples from many other regions are
found in Biddle and Christie-Blick (1985). Further references inc1ude
Steel and Gloppen (1980), Nilsen and McLaugh1in (1985).
An evaluation of the sedimentary basins of China (Hsü
1989; Zhu 1989) has revea1ed that severa1 of the so-called
Chinese-type basins or parts of them can be interpreted as
pull-apart basins.
Strike-slip motions also occur in conjunction with
oblique rifting and on divergent continental margins. They
are probab1y common on convergent margins with oblique
subduction as for examp1e observed in New Zealand
(Lewis 1980), but the resulting basins and their sedimentary fills are complex.
Fig. 12.44. Interaction of strike-slip-induced spreading and sedimentation in Gulf of Califomia-type
pull-apart basins. a Location of Guaymas Basin (1
water depth ~2000 m; 2 trans form faults and spreading centers). b Idealized cross-section of submarine
puIl-apart basin with spreading trough and flanks
showing its evolution during 1 Ma (thick arrows indicate sedimentation rates; spreading rate is 6 cmla;
vertical scale exaggerated 4x). After 1 Ma the basin
will have grown in length by 60 km; sediment volurne element E of the spreading trough will have
moved to E' and have subsided under the load of 1
12.8.4 The Guaymas Basin Model
(Gulf of California)
635
One of the submarine, presently active pull-apart
basins of the Gulf of Califomia, the Guaymas Basin,
was investigated during the Deep Sea Drilling Project (Curray, Moore, et al. 1982a). This allowed the
development of a model which may be used for similar types of basins.
After an initial shallow-marine "proto-gulf' rift
stage, the present Gulf of Califomia formed along
the trans form boundary between the North American
and the Pacific plates. The dextral, somewhat
transtensional plate motions started about 4 Ma B.P.
and operated at an average rate of several cmla. As a
result, aseries of pull-apart basins was generated
(Fig. l2.44a,d) which now lie 2000-3000 m below
sea level, separated by higher elevated sills (cf. Sect.
4.3.2). In the centers of the growing pull-apart basins, new oceanic crost was accreted (stage of early
drifting). In contrast to the mid-oceanic spreading
ridges of mature oceans, the spreading centers of
these pull-aparts are located iIi the morphological
basin deeps, thus forming spreading troughs. AIthough these troughs collect large amounts of
hemipelagic sediments, turbidites, and mass flows
from nearby slopes and marine deltas, they remain
open due to the continuing rapid growth of the basins
(Fig. l2.44b,c).
The interrelationship between the rates of spreading (strikeslip) and sedimentation in such basins is demonstrated in
Fig. 12.44b,c. Assuming a 4 km wide spreading trough and
a (realistic) sedimentation rate as high as 3000 mJMa in
this trough as in the Guayrnas basin, then a 4 km wide and
3 km high sediment body can accumulate during 1 Ma.
However, due to simu1taneous accretion of oceanic crust at
a rate of 6 cmla = 60 kmJMa, this sediment vo1ume is
spread out to a width of 60 km. Thus, its thickness is reduced to 200 m. In other words: A sediment volume element E of 200 m thickness (Fig. 12.44c) migrates 1aterally
with the ha1f-spreading rate and reaches a position 30 km
away from the spreading center after 1 Ma. On its path to
the new position, it will be covered by coeval flank sediments which are assumed to accumu1ate at a rate of 1000
m1Ma (Fig. 12.44b).
Only in the northem part of the gulf and in the Salton
trough in southem California is the sedimentation rate so
km thick flank sediments. c As (b); during 1 Ma a
body of trough sediments, 3 km thick and 4 km wide,
is distributed by basin spreading to form a 60 km
wide blanket of 200 m thickness (sediment compaction neglected). d Simplified plan view and block
diagram of gulf-type pull-apart basins in stage of
early drifting. Formation of sill-sediment complexes
in spreading troughs. e,f Pull-apart basins in stage
of early drifting subject to high (e) and very high (f)
sedimentation rates. See text for further explanation.
(After Einseie 1986)