Caldera formation and progressive batholith construction: Geochronological, petrographic and stratigraphic constraints from the Coxcatlan-Tilzapotla area, Sierra Madre del Sur, Mexico
Por:
Martiny, BM, Moran-Zenteno, DJ, Solari, L, Loopez-Martinez, M, de Silva, SL, Flores-Huertas, D, Zuniga-Lagunes, L, Luna-Gonzalez, L
Publicada:
1 ago 2013
Categoría:
Geology
Resumen:
A feature of great interest in the late Eocene-early Oligocene volcanic
province of the Sierra Madre del Sur is an elliptical NW-SE oriented
dome structure (52 x 30 km) in the Coxcatlan-Tilzapotla region. The
elliptical structure encompasses the Tilzapotla collapse caldera,
rhyolitic domes, large volumes of ignimbrites, as well as the Buenavista
intrusive body, and the Coxcatlan and Chautle plutons located west and
east of the structural margin of the caldera, respectively. Previous
geochronological studies carried out on the silicic and intermediate
magmatic rocks intercalated with pre-caldera tilted terrestrial
sediments, as well as the occurrence of an angular unconformity
separating fine-grained and coarse-grained beds, constrain uplift in the
dome area to the late Eocene (similar to 38-34 Ma). This suggests that
doming was related to emplacement of magmas into the crust prior to
collapse of the Tilzapotla caldera at 34.3 Ma.
New LA-ICPMS zircon U-Pb and Ar-40-Ar-39 mineral ages for the key
magmatic units combined with field observations, petrographic studies
and geochemical analyses reveal the geochronology of magma emplacement
and development of the volcano-plutonic complex, and its connection with
the dome. Zircon Pb-206/U-238 ages of the Coxcatlan pluton ranging from
39.5 +/- 0.6 to 35.2 +/- 0.2 Ma suggest that the Coxcatlan pluton was
constructed gradually over similar to 4 m.y. and overlapped in time with
the beginning of the development of the Tilzapotla ignimbrite (36.6 +/-
0.4 to 33.3 +/- 0.5 Ma). Significant overlap of the population density
distributions is found indicating temporal continuity of the zircon
crystallization record. Zircons from the mafic Chautle pluton (34.37 +/-
0.26 Ma) yield the same weighted mean age within uncertainty as zircon
from the Tilzapotla ignimbrite. These data are best reconciled with a
continuous but incremental assembly of a volcano-plutonic system that
climaxed with the caldera collapse and the eruption of the Tilzapotla
ignimbrite. The evidence of mafic inputs throughout the history
indicates that recharge provided the thermal engine for the prolonged
history of the system. Mutual intrusionrelationships observed between
mafic enclaves and granodiorite facies indicate magma mingling within
the magma chamber when both host and enclaves were not completely
crystallized.
Development of the Coxcatlan-Tilzapotla system resulted in updoming of
the surface, extending the ``roof' above the melt-rich part of the
system in the southeast. The spatial and temporal relationship between
the crystal-rich Tilzapotla ignimbrite and the less differentiated
Chautle intrusion suggests that mafic magma injection might have
disrupted crystal mushes in the chamber, and destabilized the
``perched'' magma reservoir and thereby triggering the eruption in the
southeastern part of the dome.
Filiaciones:
Martiny, BM:
Univ Nacl Autonoma Mexico, Inst Geol, Dept Geoquim, Mexico City 04510, DF, Mexico
Moran-Zenteno, DJ:
Univ Nacl Autonoma Mexico, Inst Geol, Dept Geoquim, Mexico City 04510, DF, Mexico
Solari, L:
Univ Nacl Autonoma Mexico, Ctr Geociencias, Queretaro 76230, Mexico
Zuniga-Lagunes, L:
Univ Nacl Autonoma Mexico, Fac Ingn, Mexico City 04510, DF, Mexico
Luna-Gonzalez, L:
Univ Nacl Autonoma Mexico, Inst Geol, Dept Geol Reg, Mexico City 04510, DF, Mexico
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