Geoscience Reference
In-Depth Information
(a)
Thermal Doming (Diapirism)
(b)
Graben Formation and Continental Rifting
M
CRUSTAL EXTENSION
Flood basalts
Mafic volcano
CONTINENTAL
CRUST
Feeder dykes
Magma chamber
(c)
Sea-floor Spreading
(d)
Basin-range Structures: Asymmetrical Rifting
CRUSTAL SUBSIDENCE
ASYMMETRICAL EXTENSION
Graben
Horst
Embryonic mid-ocean
Marine flooding
Structural
basin
Ridge
Large
DIAPIR
Asthenosphere
Figure 10.7
Rift formation and development. Thermal doming or diapirism (a) causes crustal extension and graben formation
(b). Continuing subsidence of new, denser basaltic crust leads eventually to marine flooding and the birth of a new ocean (c).
Asymmetrical extension frequently leads to basin-range structures (d) with terrestrial sediments collecting in graben. Faulting is
indicated by split arrows on downthrow side.
Plate 10.1
Cinder cones and a 3 km long basalt lava flow in the Cima volcanic field, products of Quaternary crustal extension
in south-east California.
Photo: Ken Addison
