Terminology of Extensional Tectonics


Geometry of normal mistake arrays, inwards cross section. (a) Parallel rotational faults.
Before faulting (top), the faults are parallel as well as non curved. After faulting (bottom), mistake blocks are tilted. In reality, crushing as well as small-scale faulting at the base of operations of the blocks fill upward the gaps. (b) Listric faults as well as associated unfaulted rollover. Before faulting (top), the faults shallow amongst depth and merge amongst a detachment. After faulting (bottom), the blocks convey moved. The block to the right curves downwards to hold contact amongst the footwall, forming a rollover anticline.

Accommodation zones Normal mistake systems are non continuous along the length of a rift. Rather, rifts are divided intosegments, whose axes may move kickoff from i another. Further, the faults of i segment may dip inwards the contrary direction to the faults of some other segment. An accommodation zone is the percentage of complex construction that links the ends of ii rift segments. Accommodation zones typically include strike-slip faults.

Active margin H5N1 continental margin that coincides amongst either a strike-slip or convergent plate boundary, andthus is seismically active.

Aulacogen An unsuccessful rift that cuts across a continental margin at a high angle to the margin. Typically, aulacogens transect the grain of an orogen that borders the margin. Aulacogens may stand upward for failed arms of three-armed rifts, or they may exactly move older rifts (formed long before the evolution of the continental margin, during an before episode of rifting at a unlike orientation) that were cutting off when the margin formed .

Axis (of rift or MOR) The middle trouble along the length of a rift or a mid-ocean ridge (MOR). The tendency of the axis is the overall tendency of the rift.

Breakaway fault The normal mistake that forms the border of the rift. (A breakaway mistake forms the boundary betwixt stretched as well as unstretched crust).

Graben A narrow, symmetric trough or basin, bounded on both sides past times normal faults that dip toward
the middle of the trough.

Half graben An asymmetric basin formed on the dorsum of a tilted mistake block; i border of the basin is a normal fault.

Horst An elongate, symmetric crustal block bordered on both sides past times normal faults; both faults dip
away from the middle of the horst.

Listric normal fault H5N1 normal mistake whose dip decreases amongst depth, thereby making the mistake surface concave upward.

Midocean ridge The elongate submarine mount arrive at that is the bathymetric manifestation of a divergent plate boundary. Though some midocean ridges (e.g., the Mid-Atlantic Ridge) make prevarication inwards the middle of bounding main basins, some (e.g., the East Pacific Rise) make not. Therefore, some geologists role the
term “oceanic ridge” inwards house of “mid-ocean ridge” for these features.

Oblique rifting Rifting that occurs where the stretching direction is at an needlelike angle to the rift axis.
Passive margin H5N1 continental margin that is non a plate boundary and, therefore, is non seismically active. It is underlain past times the relict of a successful rift. The rift relict subsides as well as is buried past times a thick wedge of sediment.

Planar normal fault H5N1 normal mistake whose dip remains constant amongst depth.
Nonrotational normal mistake H5N1 normal mistake on which skid does non effect inwards rotation of the hanging-wall block.

Rift (rift system) H5N1 belt of continental lithosphere that is undergoing, or has undergone, extensional deformation (i.e., stretching); every bit good called a continental rift.

Rift–drift transition The fourth dimension at which active rift faulting ceases as well as seafloor spreading begins (i.e., the fourth dimension at which a mid-ocean ridge initiates, as well as the relicts of a rift perish the foundation of a passive margin).

Rifting The procedure past times which continental lithosphere undergoes extensional deformation (stretching)
past times the formation as well as action of normal faults.
Rotational normal mistake H5N1 normal mistake whose hanging wall block rotates approximately a horizontal axis during slip.

Subsidence The sinking of the surface of the lithosphere. Subsidence produces sedimentary basins. For example, the relict of a successful rift subsides to cast a passive-margin basin.
Successful rift H5N1 rift inwards which stretching has proceeded until the continent cutting past times the rift ruptures to cast ii pieces separated past times a novel mid-ocean ridge.

Transfer fault H5N1 dominantly strike-slip mistake that links ii normal faults that are non coplanar; some transfer faults serve every bit accommodation zones.

Unsuccessful rift H5N1 rift inwards which extensional deformation ceased prior to rupture of the continent that was cutting past times the rift.

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