Gravity evidence for shaping of the crustal structure of the Ameca graben (Jalisco block northern limit). Western Mexico
Por:
Alatorre-Zamora M.A., Campos-Enríquez J.O., Fregoso-Becerra E., Quintanar-Robles L., Toscano-Fletes R., Rosas-Elguera J.
Publicada:
1 mar 2018
Resumen:
The Ameca tectonic depression (ATD) is located at the NE of the Jalisco
Block along the southwestern fringe of the NW-SE trending Tepic-Zacoalco
Rift, in the west-central part of the Trans-Mexican Volcanic Belt,
western Mexico. To characterize its shallow crustal structure, we
conducted a gravity survey based on nine N-S gravity profiles across the
western half of the Ameca Valley. The Bouguer residual anomalies are
featured by a central low between two zones of positive gravity values
with marked gravity gradients. These anomalies have a general NW-SE
trend similar to the Tepic-Zacoalco Rift general trend. Basement
topography along these profiles was obtained by means of: 1) a Tsuboi's
type inverse modeling, and 2) forward modeling. Approximately northward
dipping 10 slopes are modeled in the southern half, with south tilted
down faulted blocks of the Cretaceous granitic basement and its
volcano-sedimentary cover along sub-vertical and intermediate normal
faults, whereas southward dipping slopes of almost 15 are observed at
the northern half. According to features of the obtained models, this
depression corresponds to a slight asymmetric graben. The Ameca Fault is
part of the master fault system along its northern limit. The
quantitative interpretation shows an approximately 500 to 1100 m thick
volcano-sedimentary infill capped by alluvial products. This study has
several implications concerning the limit between the Jalisco Block and
the Tepic-Zacoalco Rift. The established shallow crustal structure
points to the existence of a major listric fault with its detachment
surface beneath the Tepic-Zacoalco Rift. The Ameca Fault is interpreted
as a secondary listric fault. The models indicate the presence of
granitic bodies of the Jalisco Block beneath the TMVB volcanic products
of the Tepic-Zacoalco rift. This implies that the limit between these
two regional structures is not simple but involves a complex transition
zone. A generic model suggests that the extension related normal
faulting has been operating as a mechanism in the evolution of this
rift. Analysis of seismicity affecting the study area and neighborhood
indicates the inferred faults are active. (C) 2018 Elsevier Ltd. All
rights reserved.
Filiaciones:
Alatorre-Zamora M.A.:
Departamento de Ingeniería Civil, Universidad de Guadalajara, Guadalajara, Jalisco, Mexico
Campos-Enríquez J.O.:
Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico City, Mexico
Fregoso-Becerra E.:
Departmento de Matemáticas, Universidad de Guadalajara, Guadalajara, Jalisco, Mexico
Quintanar-Robles L.:
Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico City, Mexico
Toscano-Fletes R.:
Departmento de Física, Universidad de Guadalajara, Guadalajara, Jalisco, Mexico
Rosas-Elguera J.:
CU Valles, Universidad de Guadalajara, Guadalajara, Jalisco, Mexico
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