Early Miocene shortening in the lower Comondu Group in Baja California Sur (Mexico)
Por:
Bonini M., Cerca M., Moratti G., López-Martínez M., Corti G., Gracia-Marroquín D.
Publicada:
13 nov 2017
Resumen:
The Late Oligocene-Early Miocene volcaniclastic deposits of Baja
California Sur form most of the exposed western margin of the Gulf of
California rift. In some places these deposits, collectively referred to
as Comondu Group, show complex deformation patterns given by the
coexistence of tectonic and gravitational features. The area north of La
Paz is characterized by the occurrence of several slump bodies, which
are displaced by normal faults connected with the rift opening. In some
places we have identified 100's m scale thrust-related folds and reverse
faults that we have interpreted as shortening features. The latter
displace the slump layers and are offset by the normal faults. If
confirmed, this would represent the first report of a shortening event
in the Early Miocene volcaniclastic deposits of Baja California Sur. The
observed shortening has modest magnitude (ca 3-5% bulk shortening), and
has been detected in a sector extending over similar to 100 km north
from La Paz. New Ar-40-Ar-39* ages, integrated with existing
radiometric age datasets, constrain the timing of this shortening
episode. The rocks affected by shortening have ages between similar to
24 and 21 Ma, and are capped by undeformed volcanic rocks with ages
spanning between similar to 19.4 and similar to 17.2 Ma. These
relationships define an intra-Early Miocene unconformity, which we
interpret to be related to the shortening deformation. The available
timing constraints allow us to infer that a main ENE-to-ESE-trending
shortening was short-lived, possibly ca. 19.4-21 Ma. The account of this
shortening event may shed some light on the complex subduction and
microplate processes that preceded the continental rifting of the Gulf
of California. (C) 2017 Elsevier B.V. All rights reserved.
Filiaciones:
Bonini M.:
UOS Firenze, CNR, Ist Geosci & Georisorse, Via G La Pira 4, I-50121 Florence, Italy
CNR, Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse, UOS Firenze, via G. La Pira 4, Firenze, 50121, Italy
Cerca M.:
Univ Nacl Autonoma Mexico, Ctr Geociencias, Lab Mecan Geosistemas, Blvd Juriquilla 3000, Col Juriquilla 76230, Queretaro, Mexico
Lab. de Mecánica de Geosistemas, Centro de Geociencias, Universidad Nacional Autónoma de México, Blvd. Juriquilla 3000, col. Juriquilla, Queretaro 76230, Mexico
Moratti G.:
UOS Firenze, CNR, Ist Geosci & Georisorse, Via G La Pira 4, I-50121 Florence, Italy
CNR, Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse, UOS Firenze, via G. La Pira 4, Firenze, 50121, Italy
López-Martínez M.:
Ctr Invest Cient & Educ Super Ensenada, Dept Geol, Lab Geocronol, Ensenada, Baja California, Mexico
Lab. de Geocronología, Dep. de Geología, Centro de Investigación Científica y de Educación Superior de Ensenada, Mexico
Corti G.:
UOS Firenze, CNR, Ist Geosci & Georisorse, Via G La Pira 4, I-50121 Florence, Italy
CNR, Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse, UOS Firenze, via G. La Pira 4, Firenze, 50121, Italy
Gracia-Marroquín D.:
Univ Nacl Autonoma Mexico, Ctr Geociencias, Lab Mecan Geosistemas, Blvd Juriquilla 3000, Col Juriquilla 76230, Queretaro, Mexico
Lab. de Mecánica de Geosistemas, Centro de Geociencias, Universidad Nacional Autónoma de México, Blvd. Juriquilla 3000, col. Juriquilla, Queretaro 76230, Mexico
|