Editing Alpine Fault (section)

== Fault zone geology ==
The fault zone is exposed at numerous locations along the West Coast,<ref>{{cite web |title=Alpine Fault virtual field trip |url=https://www.otago.ac.nz/geology/research/alpine-fault/virtual-af.html |publisher=University of Otago department of geology |access-date=5 July 2021}}</ref> and typically consists of a 10 to 50 m wide [[fault gouge]] zone<ref name="Howarth2018"/> with pervasive hydrothermal alteration. This last is because water penetrates down to up to {{convert|6|km|abbr=on}} through hot rock associated with the fault. The water then can arise in hot springs with temperatures of over {{convert|50|C|abbr=on}} in the fault valley,<ref name="Koons1987">{{cite journal|last1=Koons |first1= P. O. |year=1987 |title= Some thermal and mechanical consequences of rapid uplift: an example from the Southern Alps, New Zealand. |journal= Earth and Planetary Science Letters |volume=86 |issue= 2–4 |pages= 307–319 |doi=10.1016/0012-821X(87)90228-7 |bibcode= 1987E&PSL..86..307K }}</ref> although the temperature of the water at depth is much more extreme.<ref name="Sutherland2017">{{cite journal|last1=Sutherland|first1=R.|last2=Townend|first2=J.|last3=Toy|first3=V.|last4=Upton|first4=P. and sixty two others|date=1 June 2017|title=Extreme hydrothermal conditions at an active plate-bounding fault|journal=Nature|volume=546|issue=7656|pages=137–140|doi=10.1038/nature22355|pmid=28514440|url=http://www.escholarship.org/uc/item/5345t6p6|bibcode=2017Natur.546..137S|hdl=1874/351355 |s2cid=205256017|hdl-access=free}}</ref> Most of the movement along the fault occurs in this zone.{{sfn|Graham|2015|p=|pp=120}} In outcrop, the fault zone is overlain by [[mylonite]]s which formed at depth and have been uplifted by the fault.{{sfn|Graham|2015|p=|pp=120–121}}

A structural study<ref name=":0">{{Cite journal |last1=Barnes |first1=Philip M. |last2=Sutherland |first2=Rupert |last3=Davy |first3=Bryan |last4=Delteil |first4=Jean |date=2001 |title=Rapid creation and destruction of sedimentary basins on mature strike-slip faults: an example from the offshore Alpine Fault, New Zealand |url=http://dx.doi.org/10.1016/s0191-8141(01)00044-x |journal=Journal of Structural Geology |volume=23 |issue=11 |pages=1727–1739 |doi=10.1016/s0191-8141(01)00044-x |bibcode=2001JSG....23.1727B |issn=0191-8141|url-access=subscription }}</ref> of a segment of the Alpine Fault to the southwest of [[Fiordland]] examined the Dagg Basin, an offshore [[sedimentary basin]] at {{convert|3000|m|abbr=on}} depth. Basin sediments are primarily from [[Pleistocene]] [[Glacier|glaciation]], and structures within them reveal a past complexity that is no longer present in the basin. The current structure is a [[pull-apart basin]] along a releasing bend in the Alpine Fault, with a segment of inverted basin along the southern edge due to [[transpression]]. The study discussed the short-lived nature of the releasing bend (on the order of 10{{Superscript|5}} to 10{{Superscript|6}} years), during which there were 450 – 1650 m of dextral displacement. The nature of the displacement served as an example of the kinds of ephemeral structures that can develop along a mature strike-slip fault system.<ref name=":0" />