Geofísica Internacional ISSN: 0016-7169 [email protected] Universidad Nacional Autónoma de México México Carciumaru, Dana; Ortega, Roberto On the origin of low angle normal faulting in the Southern Rio Grande Rift Geofísica Internacional, vol. 50, núm. 2, junio, 2011, pp. 177-190 Universidad Nacional Autónoma de México Distrito Federal, México Available in: http://www.redalyc.org/articulo.oa?id=56819976004 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative GEOFÍSICA INTERNACIONAL (2011) 50­2: 177­190 ORIGINAL PAPER On the origin of low angle normal faulting in the Southern Rio Grande Rift Dana Carciumaru and Roberto Ortega ,'4'-A'*V#W)1'#XXO#XYY>T#"44'$&'*V#Q'M%)"%7#6O#XY66T#$)M+-(H'*#/1#+-1'V#S"%4H#X>O#XY66 Resumen Abstract !"#$"%&'#()%#*'+#,-.&#,-/#0%"1*'#'(&2#*'31-*"#$/%# We reconstruct the stress regime in the East una serie de fallas normales de alto ángulo que Potrillo and Franklin Mountains. Using modern separan bloques elevados de grandes cuencas 1)B'%-4"+# &'4H1-D)'(# &H'# (&%'((# 3'+*# "1*# &H'# de depósitos del Cenozoico. Una serie de fallas tectonic history of this region is discussed normales de bajo ángulo se encuentran en los and extensional veins were compared with bloques elevados y sus relaciones con la cuenca y &H'# I'1'%"+# (&%'((# 3'+*C# JH'# B"K/%-&7# /.# .")+&(# con las estructuras montañosas es controversial. L'%'#%'"4&-A"&'*#*)%-1I#&H'#3%(&#,-/#0%"1*'#%-.&# Estudios preliminares concluyeron que las fallas extensional event and occurrence of extensive de bajo ángulo se formaron en una fase previa tilting and rotations occurred. In the East de extensión y después fueron inclinadas sobre Potrillo Mountains, back tilting by W25°SE and la orientación actual de fallas más recientes. W45°SE oriented along strikes of N30°W are Otros estudios concluyeron que estas fallas son el required in order to obtain two homogeneous resultado de un fallamiento reciente y son un factor (&%'((# 3'+*(C# JH'# 4/%%'4&'*# .")+&# $+"1'# (H/L(# clave en el desarrollo de las cuencas actuales y de "# (-I1-34"1&# /M+-D)'# 4/B$/1'1&# -1# M/&H# (&%'((# la topografía montañosa. Por esta razón, en esta 3'+*(C#JH'#3%(&#(&%'((#3'+*#4/%%'($/1*(#&/#"#.")+&# parte de la dorsal de Rift Rio Grande el análisis %'"4&-A"&-/1#L-&H#56#"1*#58#/%-'1&'*#9:;N<#"1*# de esfuerzos es una tarea difícil. FecHar la edad 9=>N<# %'($'4&-A'+7O# LH'%'"(# &H'# ('4/1*# (&%'((# geológica de las estructuras y el basculamiento 3'+*# -(# %'+"&'*# &/# &H'# 7/)1I'(&# .")+&# /%-'1&'*# extensivo del área son las principales fuentes de 9=?N@#"1*#9=6N<#%'($'4&-A'+7C#P1#&H'#Q%"1R+-1# error. En este artículo reconstruimos el régimen S/)1&"-1(O# &-+&-1I# -(# +'((# (-I1-34"1&T# H/L'A'%# de esfuerzos usando técnicas numéricas basadas &L/# (&%'((# 3'+*(# L-&H# (-B-+"%# /%-'1&"&-/1(# M)&# en estadística para dos montañas del Rift del *-..'%'1&# $H-# A"+)'(# "%'# %'4/I1-U'*C# JH'# $/(&# F# Rio Grande: East Potrillo Mountains y FranKlin Laramide stress history of the region is controlled Mountains. El campo de esfuerzos y la Historia M7# *-..'%'1&# 'G&'1(-/1"+# 'A'1&(# &H"&# -1E)'14'*# tectónica también se discuten. Las direcciones the preexisting structures and generated other de las venas extensionales fueron comparadas young fault systems. con el campo general de esfuerzos. Se encontró que la mayoría de las fallas fueron reactivadas Key words: stress inversion, low angle normal en la primera etapa de extensión de Rio Grande, faults, back tilting, Rio Grande rift. además con la ocurrencia de un basculamiento extensivo con rotaciones. En Potrillo Mountains se requiere un proceso de corrección angular por basculamiento de W25 SE y W45 SE orientado N30W para obtener dos campos de esfuerzos Homogéneos. El plano de falla corregido muestra un componente oblicuo en estos dos campos de esfuerzos; el primero corresponde a la reactivación *'#+"(#."++"(#4/1#'+#56#7#58#/%-'1&"*/(#9:;<#7#9=><# respectivamente mientras el segundo campo de esfuerzos es relacionado con las fallas más actuales 7#'(#/%-'1&"*/#9=?@#7#9=6<#%'($'4&-A"B'1&'C#<1# FranKlin Mountains el basculamiento es menos D. Carciumaru importante sin embargo dos campos de esfuerzos Orbis Consultores en Geología y Geofísica SC con orientaciones similares pero valores de pHi ,'&/%1/#Z"+"3"#6XYO#Z/+C#Z"+"3"O diferentes fueron detectados (reconocidos). La La Paz, BCS, 23054, Historia de esfuerzos post – Laramidica de la región México es controlada de diferentes eventos exensiónales Corresponding author: [email protected] D)'#-1E)'14-"%/1#+"(#'(&%)4&)%"(#$%'#F#'G-(&'1&'(# R. Ortega y también generaron un sistema de falla nueva. CICESE !"#["UO#S-%"E/%'(#88? Palabras clave: inversión de esfuerzos, falla Fracc. Bella Vista normal de bajo ángulo, correccion angular por La Paz, BCS, 23050 basculamiento, rift del Rio Grande. México 177 D. Carciumaru and R. Ortega Introduction classical stress inversion method of Angelier ]6>>?_#(/#&H"&#"#+"%I'#1)BM'%#/.#/$&-B"+#(&%'(('(# JH'# (/)&H'%1# ,-/# 0%"1*'# %-.&# -(# *'31'*# M7# "# is computed and analysed as a point in stress series of high angle normal faults which separate ($"4'C#a-I1-34"1&#(&%'(('(#"%'#&H)(#%'$%'('1&'*# uplifted blocks of bedrock from large basins M7#4+)(&'%(#/.#$/-1&(C#`'%'#L'#"1"+7('#B)+&-$+'# L-&H# *''$# Z'1/U/-4# 3++C# 9)B'%/)(# +/L# "1I+'# inverse method results by the stress difference normal faults occur within the uplifted blocks technique proposed by Orife and Lisle (2003). whose relationship to the current basin and range structure has been controversial. Several Once the data set is corrected, we apply the previous studies have concluded that the low classical stress inversion technique of Michael angle faults were formed during an early phase ]6>;?_#-1#/%*'%#&/#%'4/1(&%)4&#&H'#&'4&/1-4#H-(&/%7# of extension and were tilted into their present /.#&H'#%'I-/1C#JL/#%'I-/1(O#&H'#<"(&#[/&%-++/#"1*# orientation by younger faults. Other studies have Franklin Mountains in the southern Rio Grande concluded that the faults are the result of recent rift are studied. Results in the East Potrillo faulting and are a Key factor in the development Mountains suggest that a substantial tilting of the modern basin and range topography. For correction is needed. In the Franklin Mountains this reason in this part of the Rio Grande rift, &H'# &-+&-1I# 4/%%'4&-/1# -(# +'((# (-I1-34"1&# "1*# &L/# $"+'/(&%'((# "1"+7(-(# -(# "# *-.34)+&# &"(RC# \"&-1I# (&%'((# 3'+*(# L-&H# (-B-+"%# (&%'((# /%-'1&"&-/1# M)&# uncertainties of the geological structures and different stress ratio (phi value) were obtained. extensive tilting during periods of late Cenozoic JH-(# ()II'(&(# &H"&# &H'# %'I-/1# H"(# M''1# )1*'%# extension are the main sources of error. continuous deformation. In the southern Rio Grande rift, a Key Geological setting problem is determining if normal faults formed in response to different stress regimes or to a JH'#!"%"B-*'#&'4&/1-4(#/.#(/)&H'%1#9'L#S'G-4/# single progressive deformation. Dating geological remains controversial (Seager, 2004). Models structures in this region by means of crosscutting include thin ­ skinned tectonics (Corbitt and relations, mineral associations or stratigraphy is @//*L"%*O# 6>:8T# @//*L"%*# "1*# \)# ZH'1'O# *-.34)+&#M'4")('#B"17#1/%B"+#.")+&(#"%'#7/)1I# 6>;6_T# 4/)$+'*# L-&H# M"('B'1&# d# -1A/+A'*# /%# %'"4&-A"&'*# /+*'%# .")+&(C# JH'%'./%'O# +/L# "1*# ./%'+"1*# )$+-.&# ]\%'L'(O# 6>:;O# 6>;6O# 6>;;_O# high angle normal faulting in the Rio Grande rift L-&H# M"('B'1&# M+/4R# )$+-.&(# ]a'"I'%O# 6>;8T# -(# 4/1&%/A'%(-"+# ]!'L-(# "1*# ^"+*%-*I'O# 6>>?_C# a'"I'%#"1*#S"4RO#6>;c_#"1*#-1A'%(-/1#&'4&/1-4(# Extensive faulting and tilting may have occurred ]^"7/1"O#6>>;T#!"L&/1O#6>>=T#!"L&/1O#XYYY_C during two distinct extensional phases in the Rio Grande rift (Aldrich et alCO# 6>;=T# `'1%7# Outcrops of Laramide structures are mostly "1*# [%-4'O# 6>;?T# S/%I"1# et alCO# 6>;=T# a'"I'%# uplifted bed rock blocks. Most of the early et alCO# 6>;?_C# JH'%'./%'O# M"4R# &-+&-1I# .%/B# "# J'%&-"%7# *'./%B"&-/1# L"(# %'(&%-4&'*# &/# 1"%%/L# single correction factor is unlikely and rotation north ­ west trending fault zones that resulted in corrections are needed in order to reconstruct a series of northwest trending uplifts and basins %'+-"M+'#$"+'/(&%'((#3'+*(C ]a'"I'%O# XYY?_C# JH'# M"(-1(# "%'# "(7BB'&%-4"+T# they deepen to the south toward a thrust or Classical stress inversion is based on the idea reverse fault and they are generally associated /.# -131-&'(-B"+# (&%"-1C# b# *'31-&-/1# /.# (&%'((# ./%# with uplifts along their southwestern margins. &H'#4"('#/.#*'./%B"&-/1#L-&H#31-&'#%/&"&-/1(#-(#1/&# )1-D)'# ]Q)1IO# 6>=c_C# JH'%'./%'# -&# -(# 1'4'(("%7## JH'#$/(&#d#!"%"B-*'#(&%'((#%'I-B'#-(#L-*'+7# reconsider the analysis of deformation without recognized (Aldrich et alCO# 6>;=T# ^"+*%-*I'# et "#%'(&%-4&-/1#/.#-131-&'(-B"+#*-($+"4'B'1&(C#JH'# alCO#6>;YT#S/%I"1#"1*#0/+/BM'RO#6>;?T#S/%I"1# I'1'%"+-U"&-/1# .%/B# -131-&'(-B"+# (&%"-1# &H'/%7# et alCO#6>;=_C#JH'#,-/#0%"1*'#%-.&#/$'1'*#-1#&L/# &/# 31-&'# *'./%B"&-/1# -1A/+A'(# &%'B'1*/)(# stages associated with different stress regimes. complexity of the normal equations. Nonlinear JH'#3%(&#$H"('#/.#*'./%B"&-/1#/44)%%'*#.%/B#8Y# 3'+*# &H'/%7# -(# M'7/1*# &H'# (4/$'# /.# &H-(# $"$'%O# &/#6;#S"O#LH'1#(H"++/L#M"(-1(#M/)1*'*#M7#+/L# but another possible approach is to consider "1I+'# 1/%B"+# .")+&(# L'%'# ./%B'*C# JH-(# $'%-/*# mechanical or kinematic constraints. A likely is associated with volcanism and is attributed kinematic assumption is that tilted blocks are to a thinning of hot lithosphere with a shallow produced from an identical normalized stress brittle ­ ductile transition (Baldridge et alCO#6>>cT# tensor that conserves similar relations before Keller et alC#6>>6T#S/%I"1#"1*#0/+/BM'RO#6>;?_C# tilting, as successfully tested by Yamaji et al.