Editing Rio Grande rift (section)

==Geology==
The Rio Grande rift represents the easternmost manifestation of widespread extension in the western U.S. during the past 35 million years. The rift consists of three major basins and many smaller basins, less than {{convert|100|km2|sqmi}}. The three major basins (from northernmost to southernmost) are the [[San Luis basin|San Luis]], [[Espanola basin|Española]], and [[Albuquerque basin|Albuquerque]] basins. The rift's northern extent is delineated by the upper Arkansas River basin between [[Leadville, Colorado|Leadville]] and [[Salida, Colorado]]. Further south, the rift is defined by a network of smaller, less topographically distinct alternating basins and ranges. The distinction between these smaller basins and those of the [[Basin and Range Province]] becomes blurred in northern [[Mexico]].<ref name=russell1994>{{Cite book|last1=Russell |first1=L.|last2=Snelson |first2=S. |date=1994|chapter=Structure and tectonics of the Albuquerque basin segment of the Rio Grande Rift: Insights from reflection seismic data|title=Basins of the Rio Grande Rift: Structure, statigraphy, and tectonic setting|editor-last1=Keller|editor-first1=G. Randy|editor-last2=Cather|editor-first2=Steven M.|series=Geological Society of America Special Paper No. 291|location=Boulder, Colo.|publisher=Geological Society of America |pages=83–112|isbn=0-8137-2291-8}}</ref><ref name= Keller1999>{{Cite journal |last1=Keller|first1=G. Randy |last2=Baldridge |first2=W. Scot |year=1999 |title=The Rio Grande Rift: a geological and geophysical overview |journal=Rocky Mountain Geology |pages=121–130 |volume=34 |number=1 |doi=10.2113/34.1.121|bibcode=1999RMGeo..34..121K }}</ref>

Basin size generally decreases to the north in the rift, though the Española covers approximately {{convert|120|km|mi}} north–south and {{convert|40|km|mi}} east–west, and the San Luis is roughly {{convert|120|by|80|km|mi}}. These basins may contain smaller units within them, such as the [[Alamosa]] basin within the San Luis, which is bounded by the San Juan and Tusas mountains on the west and the [[Sangre de Cristo Mountains]] in the east.<ref name=brister1994>{{Cite book |last1=Brister |first1=B. |last2=Gries |first2=R. |date=1994 |chapter=Tertiary stratigraphy and development of the Alamosa basin (northern San Luis basin), Rio Grande Rift, south-central Colorado |title=Basins of the Rio Grande Rift: Structure, statigraphy, and tectonic setting|editor-last1=Keller|editor-first1=G. Randy|editor-last2=Cather|editor-first2=Steven M.|series=Geological Society of America Special Paper No. 291|location=Boulder, Colo.|publisher=Geological Society of America|pages=39–58 |isbn=0-8137-2291-8}}</ref> The Albuquerque basin is the largest of the three basins, spanning {{convert|160|km|mi}} north–south and {{convert|86|km|mi}} east–west at its widest points. It is the oldest of the three major basins, and contains {{convert|7,350|m|ft}} of [[Paleogene]] clastic [[sediments]] deposited on [[Precambrian]] basement. The southernmost Albuquerque basin contains pre-rift [[volcanic rock|volcanic deposits]], while the central and northern portions contain volcanics erupted during rifting.<ref name=russell1994 /> 
[[File:Riogranderift albuquerquebasin.png|thumb|upright=2|alt=Generalized cross section of the Albuquerque basin|A generalized cross section of the Albuquerque basin from east to west. Note the [[half-graben]] geometry, [[paleozoic]] and [[mesozoic]] sediments that existed pre-rift, and the large (up to 28%) amount of extension.<ref name=russell1994 />]]
[[File:Riogranderift sanluisbasin.png|thumb|upright=2|alt=Generalized cross section of the San Luis basin|A generalized cross section of the San Luis basin from east to west. Being further north, this basin has experienced less extension (up to 12%).<ref name=chapin1994 /> Also note the lack of pre-rift sediments and thinner profile.<ref name=brister1994 />]]
In cross-section, the geometry of the basins within the rift are asymmetrical [[half-graben]]s, with major [[fault (geology)|fault]] boundaries on one side and a downward hinge on the other. Which side of the basin has the major fault or the hinge alternates along the rift. The alternation between these half-grabens occurs along transfer faults, which trend across the rift to connect the major basin-bounding faults and occur between basins or, in places, within basins. The Precambrian basement changes relief sharply in this area, from {{convert|8700|m|ft}} below sea level at the bottom of the Albuquerque basin to {{convert|3300|m|ft}} above sea level in the nearby [[Sandia Mountains]], which flanks the Albuquerque basin to the east. Flanking mountains are generally taller along the east side of the rift (although some of this relief may be [[Laramide orogeny|Laramide]] in origin).<ref name=chapin1994 />  The thickness of the [[continental crust|crust]] increases to the north beneath the rift, where it may be as much as {{convert|5|km|mi}} thicker than it is in the south. The crustal thickness underneath the rift is on average {{convert|30|–|35|km|mi}}, thinner by {{convert|10|–|15|km|mi}} than the Colorado Plateau on the west and the Great Plains to the east.<ref name=perry1987>{{Cite journal |last1=Perry |first1=Frank |last2=Baldridge |first2=W. |last3=DePaolo |first3=D. |title=Role of Asthenosphere and Lithosphere in the Genesis of Late Cenozoic Basaltic rocks from the Rio Grande rift and adjacent regions of the Southwestern United States |journal=Journal of Geophysical Research |volume=92 |issue=B9 |pages=9193–9213 |date=10 August 1987|bibcode = 1987JGR....92.9193P |doi = 10.1029/JB092iB09p09193 |url=https://zenodo.org/record/1231416 }}</ref>

[[File:Canones fault.jpg|thumb|Cañones Fault on southeastern margin of Colorado Plateau, near Abiquiú, New Mexico]]
Formation of the rift began with significant deformation and faulting with offsets of many kilometers starting about 35&nbsp;Ma.<ref>{{cite journal |last1=Grauch |first1=V.J.S. |last2=Hudson |first2=Mark R. |title=Guides to understanding the aeromagnetic expression of faults in sedimentary basins: Lessons learned from the central Rio Grande rift, New Mexico |journal=Geosphere |date=2007 |volume=3 |issue=6 |pages=596 |doi=10.1130/GES00128.1|doi-access=free |bibcode=2007Geosp...3..596G }}</ref>  The largest-scale manifestation of rifting involves a pure-shear rifting mechanism, in which both sides of the rift pull apart evenly and slowly, with the lower crust and [[upper mantle (Earth)|upper mantle]] (the [[lithosphere]]) stretching like [[Taffy (candy)|taffy]].<ref name=wilson2005 /><ref>{{Cite journal |last=Fleck |first=John |title=Study Sheds Light on 30 Million Years of Rio Grande Valley Stretching |journal=Albuquerque Journal |date=24 February 2005 }}</ref><ref>{{Cite journal |last=Hill |first=Karl |date=25 February 2005 |title=The Rio Grande Rift: a continent "stretched like taffy" |journal=NMSU News Release }}</ref>  This extension is associated with very low seismic velocities in the upper mantle above approximately {{convert|400|km|mi}} depth associated with relatively hot mantle and low degrees of partial melting.<ref>{{Cite journal |last1=Gao |first1=W. |last2=Grand |first2=S. |last3=Baldridge |first3=S. |last4=Wilson |first4=D.|last5=West |first5=M. |last6=Ni |first6=J. |last7=Aster |first7=R. |title=Upper mantle convection beneath the central Rio Grande rift imaged by P and S wave tomography |journal=J. Geophys. Res. |volume=109 |issue=B3 |pages=B03305 |doi=10.1029/2003JB002743 |year=2004 |bibcode = 2004JGRB..109.3305G }}</ref> This intrusion of the [[asthenosphere]] into the [[lithosphere]] and [[continental crust]] is thought to be responsible for nearly all of the volcanism associated with the Rio Grande rift.

The sedimentary fill of the basins consists largely of [[alluvial fan]] and [[mafic]] volcanic flows. The most [[alkalic]] lavas erupted outside the rift.<ref name=baldridge1984>{{Cite book |last1=Baldridge |first1=W. |last2=Olsen |first2=K. |last3=Callender |first3=J. |year=1984 |chapter=Rio Grande Rift: Problems and Perspectives |title=New Mexico Geological Society Guidebook, 35th field conference |pages=1–11}}</ref> The sediments that were deposited during rifting are commonly known as the [[Santa Fe Group (geology)|Santa Fe Group]]. This group contains [[sandstone]]s, [[Conglomerate (geology)|conglomerates]], and volcanics. [[Aeolian processes|Aeolian deposits]] are also present in some basins.<ref name=chapin1994 /><ref name=kluth1994 />

The Rio Grande rift is intersected in northern New Mexico by the NE-SW trending [[Jemez Lineament]] which extends well into [[Arizona]]. The lineament is defined by aligned volcanic fields and several [[calderas]] in the area, including the [[Valles Caldera National Preserve]] in the [[Jemez Mountains]]. The Jemez Lineament is thought to be a hydrous subduction zone scar, separating [[Precambrian]] [[basement rock]] of the [[Yavapai orogeny|Yavapai]]-[[Mazatzal orogeny|Mazatzal]] transition zone from the Mazaztl Province proper.<ref name="aldrich1986">{{cite journal|last=Aldrich Jr.|first=M. J.|title=Tectonics of the Jemez Lineament in the Jemez Mountains and Rio Grande Rift|journal=Journal of Geophysical Research|year=1986|volume=91|issue=B2|pages=1753–1762|doi=10.1029/JB091iB02p01753|bibcode = 1986JGR....91.1753A |url=https://zenodo.org/record/1231400}}</ref><ref name="wk2007">{{cite journal |last1=Whitmeyer |first1=Steven |last2=Karlstrom |first2=Karl E. |journal=Geosphere |date=2007 |volume=3 |issue=4 |pages=220 |doi=10.1130/GES00055.1 |title=Tectonic model for the Proterozoic growth of North America|doi-access=free }}</ref> Also on the Colorado Plateau but further north lies the [[San Juan volcanic field]] in the [[San Juan Mountains]] of Colorado.

The youngest eruptions in the rift region are in the [[Carrizozo Malpais|Valley of Fires]], New Mexico, and are approximately 5,400&nbsp;years old.<ref>{{Cite web |last=Aber |first=James S. |title=Rio Grande Rift |url=http://academic.emporia.edu/aberjame/struc_geo/rio/rio.htm |access-date=8 February 2006 |archive-url=https://web.archive.org/web/20060129141006/http://academic.emporia.edu/aberjame/struc_geo/rio/rio.htm |archive-date=29 January 2006 |url-status=dead |work=GO 568 Structural Geology }}</ref><ref>{{Cite web |last=Veatch |first=Steven Wade |title=The Rio Grande Rift |date=20 March 1998 |url=http://home.att.net/~sgeoveatch/rio_grande_rift.htm |access-date=8 February 2006 |url-status=dead |archive-url=https://web.archive.org/web/20051220215216/http://home.att.net/~sgeoveatch/rio_grande_rift.htm |archive-date=20 December 2005 }}</ref>  The [[Socorro, New Mexico]], region of the central rift hosts an inflating mid-crustal sill-like magma body at a depth of 19&nbsp;km that is responsible for anomalously high earthquake activity in the vicinity, including the largest rift-associated earthquakes in historic times (two events of approximately magnitude 5.8) in July and November 1906.<ref>{{Cite journal |last=Reid |first=H.G. |title=Remarkable earthquakes in central New Mexico in 1906 and 1907 |journal=Bull. Seismol. Soc. Am. |volume=1 |pages=10–16 |year=1911 |issue=1 |doi=10.1785/BSSA0010010010 |bibcode=1911BuSSA...1...10R }}</ref><ref>{{Cite journal |last1=Sanford |first1=A.R. |first2=R.S. |last2=Balch |first3=K.W. |last3=Lin |title=A seismic anomaly in the Rio Grande Rift near Socorro, New Mexico |volume=78 |place=Socorro, NM |pages=17 |publisher=New Mexico Institute of Mining and Technology Geophysics Open-File Report |year=1995 }} Abstract at: {{Cite journal|doi=10.1785/gssrl.66.2.15 |title=Annual Meeting |journal=Seismological Research Letters |date=1995 |volume=66 |issue=2 |at=page 44 of 15–61}}
</ref><ref>{{Cite journal |last1=Schlue |first1=J. |last2=Aster |first2=R. |last3=Meyer |first3=R. |title=A lower-crustal extension to a mid-crustal magma body in the Rio Grande Rift, New Mexico |journal=J. Geophys. Res. |volume=101 |issue=B11 |pages=25,283–25,291 |year=1996 |doi=10.1029/96JB02464 |bibcode = 1996JGR...10125283S }}</ref>  Earth and space-based geodetic measurements indicate ongoing surface uplift above the Socorro magma body<ref>{{Cite web |url=http://www.ees.nmt.edu/Geop/Museum_Posters/NMseismology.html |title=Socorro Magma Body |url-status=dead |archive-url=https://web.archive.org/web/20100615041810/http://www.ees.nmt.edu/Geop/Museum_Posters/NMseismology.html |archive-date=15 June 2010 }}</ref> at approximately 2&nbsp;mm/year.<ref>{{Cite journal |last1=Fialko |first1=Yuri |last2=Simons |first2=Mark |year=2001 |title=Evidence for on-going inflation of the Socorro magma body, New Mexico, from interferometric synthetic aperture radar imaging |journal=Geophysical Research Letters  |volume=28 |issue=18 |pages=3549–3552 |doi=10.1029/2001GL013318 |bibcode=2001GeoRL..28.3549F |doi-access=free }} <small style="color:blue;"> (Doi fails redirect.)</small></ref>

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File:Riogranderift deepXsection.png|alt=Generalized cross section of the Rio Grande Rift, showing lithospheric and asthenospheric structure.|A generalized cross section of the Rio Grande Rift, showing [[Lithosphere|lithospheric]] and [[Asthenosphere|asthenospheric]] structure. Note the magma lenses and volcanics caused by the welling up of the asthenosphere into the crust, and the thinning of the lithosphere<ref name=baldridge1984 />

Image:RioGrande Rift RISTRA Seismic Image.jpg|Deep seismic image of the Rio Grande rift compiled from the seismic transect shown in the previous figure, showing inferred mantle flow and imaged crust-mantle ([[Mohorovičić discontinuity|Moho]]) topography (after Wilson et al.)(2005).<ref name=wilson2005 >{{Cite journal|last1=Wilson|first1=David|first2=Richard|last2=Aster|first3=Michael|last3=West|first4=James|last4=Ni|first5=Steve|last5=Grand|first6=Wei|last6=Gao|first7=W. Scott|last7=Baldridge|first8=Steve|last8=Semken|first9=Paresh|last9=Pate|title=Lithospheric structure of the Rio Grande rift|journal=Nature|volume=433|issue=7028|pages=851–855|date=24 February 2005|pmid=15729338|doi=10.1038/nature03297|bibcode = 2005Natur.433..851W  |s2cid=4387908}}</ref>\

File:Riogranderift timeline.png|alt=Timeline for extension and volcanism in the area of the Rio Grande rift.|A brief timeline showing extension and volcanism in the Rio Grande rift area. The end of the Laramide orogeny was followed by volcanism and then extension. Changes in lava chemistry are also found, resulting from changes in magmatic sources.<ref name=morgan1984>{{Cite book|last1=Morgan|first1=P.|last2=Golombek|first2=M.|year=1984|chapter=Factors controlling the phases and styles of extension in the northern Rio Grande rift|title=New Mexico Geological Society Guidebook, 35th field conference|pages=13–20}}</ref>
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