y Cenozoic magmatism and extension in western Mexico: Linking the Sierra Madre Occidental silicic large igneous province and the Comondu Group with the Gulf of California rift
Por:
Ferrari, Luca, Orozco-Esquivel, Teresa, Bryan, Scott E., Lopez-Martinez, Margarita, Silva-Fragoso, Argelia
Publicada:
1 ago 2018
Categoría:
Earth and planetary sciences (miscellaneous)
Resumen:
A new view on the genesis of, and links between, the Sierra Madre
Occidental silicic large igneous province, the Comonclii Group of Baja
California, and the Gulf of California rift has been emerging over the
past decade. Underpinning this has been a wealth of new data from both
margins of the Gulf of California including offshore sampling and marine
geophysical data, in part seeded by the NSF Margins program where the
Gulf of California was a principal focus site. Previously, the Sierra
Madre Occidental silicic large igneous province and Comondd Group had
been widely regarded as supra-subduction volcanism, with the Comondd
Group in particular defining the location of the early to mid-Miocene
supra-subduction zone volcanic arc and therefore acting as both a
spatial and temporal barrier to when the rifting of the Gulf of
California could begin. More broadly, this continental magmatism
occurring during the last phase of subduction of the Farallon Plate
between the late Eocene and the middle Miocene shows little to no
petrogenetic connection to the active plate boundary and is more
strongly linked to the progressive thinning of the upper plate and
establishment of a shallow asthenospheric mantle beneath western Mexico.
A database developed for this study of 4255 ages and chemical analyses
for igneous rocks from 100 to 5 Ma from across western Mexico reveals a
significant transition period between 50 and 40 Ma where relatively low
volume magmatism was established across a broad area up to 800 km wide
and extended up to 1000 km in the board of the paleotrench. Since 40 Ma,
magma fluxes greatly increased across this broad belt, and compositions
were initially silicic-dominated but quickly became bimodal by similar
to 30 Ma. The space-time pattern of crustal extension is constrained in
39 areas, for which the approximate age of extension can be established
on the basis of geologic relations or thermochronology. The onset of
continental extension is constrained to the Eocene when extensional
basins developed across the Central Plateau and the easternmost part of
the Sierra Madre Occidental, approximately 500 km inboard of the
paleo-plate boundary. By the end of Oligocene, crustal extension had
affected a wide region (250 km width) from the eastern Sierra Madre
Occidental to the site of the future Gulf of California (wide rift
mode). Concomitant with this extension was (1) a widespread invasion of
the mid- to upper crust by mafic magmas with lithospheric signatures
[the Southern Cordillera Orogenic Basaltic Andesite (SCORBA) suite)
and lesser erupted volumes of uncontaminated asthenosphere-derived
within-plate lavas and (2) crustal melting producing voluminous pulses
of silicic ignimbrite eruptions (the SMO SLIP) with a ferroan (dry) and
transitional within-plate signature. At similar to 19 Ma, orthogonal
extension became focused between the western side of the SMO and eastern
Baja California in a similar to 80-100-km-wide belt. Consequences of
this switch to a narrow rift mode were a general abandonment of
volcanism across much of the wide rift zone and volcanism becoming more
effusive and intermediate in composition (the Comondu Group), being
concentrated within rapidly extending but narrow tectonic depressions
along the future site of the Gulf of California. By similar to 12 Ma,
the crust had thinned to half its original thickness along the axis of
the Gulf. Since the late Miocene, right-lateral transtensional
deformation associated with the dragging of Baja California by the
Pacific Plate was then able to quickly complete lithospheric rupture to
form the modern Gulf of California.
The tectono-magmatic evolution of western Mexico and, by extension,
southwestern USA can be interpreted in the frame of recent plate
reconstructions and seismic tomography models. The removal of the
subducted slab began in the early Eocene with the separation of the
Vancouver plate from the rest of the Farallon plate, whose diffuse plate
boundary intersected Mexico at the latitude of the Sonora-Sinaloa border
and moved progressively North. Since then, a slab window/slab-free area
began to grow by rollback and slab fragmentation and detachment
promoting the melting of the ascending asthenosphere, the mantle
lithosphere, and crust, which are variably observed in the igneous
records of the SMO and Comonclii Group. The ascent of buoyant and hot
mantle also favored crustal extension in a broad area that progressively
focused in the Gulf of California region.
Filiaciones:
Ferrari, Luca:
Univ Nacl Autonoma Mexico, Ctr Geociencias, Campus Juriquilla, Queretaro, Qro, Mexico
Orozco-Esquivel, Teresa:
Univ Nacl Autonoma Mexico, Ctr Geociencias, Campus Juriquilla, Queretaro, Qro, Mexico
Bryan, Scott E.:
Queensland Univ Technol, Sch Earth Environm & Biol Sci, Brisbane, Qld 4001, Australia
Lopez-Martinez, Margarita:
CICESE, Dept Geol, Carretera Ensenada Tijuana 3918, Ensenada 22860, Baja California, Mexico
Silva-Fragoso, Argelia:
Univ Nacl Autonoma Mexico, Ctr Geociencias, Campus Juriquilla, Queretaro, Qro, Mexico
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