Page 373 - Global Tectonics

356 CHAPTER 11

sedimentary rock that are deformed by thrust faults and dome-and-keel province with a history spanning 3.72–
strike-slip shear zones (e.g. Figs 10.13, 10.19). Another 2.83 Ga (Collins et al., 1998; Van Kranendonk et al.,
pattern, commonly referred to as a dome-and-keel 2002, 2007). The craton exposes nine granitoid domes
architecture, occurs exclusively in Archean crust. This with diameters ranging from 35 km to 120 km. Studies
latter structural style forms the focus of the discussion of seismic refraction data and gravity and magnetic
in this section. anomalies (Wellman, 2000) indicate that the margins
Dome-and-keel provinces consist of trough-shaped of the domes are generally steep and extend to mid-
or synclinal keels composed of greenstone that sur- crustal depths of ∼14 km. Despite their simple out-
round ellipsoidal and ovoid-shaped domes composed lines, the internal structure of the domes is complex.
of gneiss, granitoid, and migmatite (Section 9.8). The Each contains remnants of 3.50–3.43 Ga TTG suite
contacts between domes and keels commonly are granitoids (Section 11.3.2) that are intruded by
high-grade ductile shear zones. Marshak et al. (1997) younger (3.33–2.83 Ga) more potassic igneous suites
distinguished between two types of these provinces. (Fig. 11.9a). The domes display compositional zona-
One type has keels composed of greenstones and tions and variable degrees of deformation. In many
their associated metasedimentary strata (Section cases, the youngest bodies are located in the cores of
11.3.2) and domes composed of granitoid rock that the domes with older, more deformed granitoids at
is similar in age or slightly younger than the green- the margins. This internal structure indicates that
stones. The other type has domes of mostly gneissic each dome was constructed through the emplace-
and migmatitic basement rock and keels composed ment of many intrusions over hundreds of millions
of greenstones that are younger than the dome of years and that deformation accompanied the
rocks. magmatism.
The Eastern Pilbara craton of northwestern Aus- Between the granitoid domes are synclinal tracts of
tralia (Fig. 11.8) is one of the oldest and best pre- greenstone composed of dipping volcanic and sedimen-
served examples of a granite-greenstone belt and tary sequences up to 23 km thick (Van Kranendonk

N
Indian Ocean Port Hedland
Western Pilbara
Roebourne Eastern Pilbara
Scholl Shear Zone

21 S
ME

Permian-Mesozoic rocks
Late Archean Hamersley Basin CD
Middle Archean greenstones
S
Early Archean greenstones
Lalla Rookh – Western Shaw Australia
structural corridor
Granitoid rocks and gneiss
22 S Syncline Fault or shear zone 0 50
Anticline Thrust fault km
117 E 118 E 119 E 120 E

Fig. 11.8 Geologic map of the Pilbara granite-greenstone belt (modified from Zegers & van Keken, 2001, with
permission from the Geological Society of America, with additional structural information from Van Kranendonk et al.,
2007) showing the typical ovoid pattern of TTG suite granitoids surrounded by greenstones belts. ME, Mt. Edgar Dome;
CD, Corunna Downs Dome; S, Shaw Dome. Black box shows location of Fig. 11.9.