Paper No. 31-13
Presentation Time: 8:30 AM-5:30 PM
EARLY CRETACEOUS PROTOLITH AGES FOR
METAVOLCANIC ROCKS FROM TAXCO AND
TAXCO VIEJO IN SOUTHERN MEXICO
CAMPA URANGA, Maria Fernanda, ERCT, Universidad Autonoma de
Guerrero, Ex-hacienda de San Juan Bautista, Taxco Viejo, Taxco, 40200,
Mexico, mfernanda@data.net.mx and IRIONDO, Alexander, Geological
Sciences, Univ of Colorado at Boulder, Boulder, CO 80309
A metamorphosed vulcanosedimentary sequence from Taxco and Taxco Viejo
outcrops near an isolated areas inside the Taxco synclinorium. This structural
feature is part of the southern section of the Guerrero-Morelos platform. The
protolith ages for the Taxco schist and Taxco Viejo greenstone were interpreted
as Paleozoic and Triassic, respectively (Fries C, 1960). Using TIMS U-Pb
zircon geochronology we analyzed three zircon fractions from a greenstone
Taxco and obtained a weighted average age (206Pb/238U) of
130 ± 2.6 Ma that we interpret as the crystallization age for the volcanic
sample from
protolith. In addition, we analyzed another three zircon fractions from a
porphytitic sample from Taxco
Viejo. One of these zircon fractions is
concordant with a weighted average age (206Pb/238U) at 131.7 ± 0.85
Ma that we interpret as a crystallization age for the volcanic protolith. The
other two fractions are discordant, yielding Precambrian upper intercepts that
we interpret as representing zircon inheritance from the nearby basement of the
Oaxaca-Mixteca terranes (Campa, 2002). Within limits of analytical error, the
protoliths for these two metavolcanic samples from Taxco and Taxco Viejo are
the same age and perhaps similar to those arc volcanic deposits from the
Guerrero terrane, Chiautla arc, and Juarez terrane. We interpret that the
vulcanosedimentary sequences of the central section of the Guerrero-Morelos
platform could have been deposited during the Early Cretaceous time in an
environment typical of the Mexican Pacific arcs in the western margin of a
Precambrian continent. In addition, preliminary Ar/Ar geochronology of
metamorphosed volcanic rocks from Chapolapa-Izcuinatoyac formations at the
southern end of the platform indicates the possibility that deformation and
metamorphism recorded in the vulcanosedimentary sequence occurred during
the Late Cretaceous Early Tertiary time.
Cordilleran Section - 99th Annual (April 1–3, 2003)
General Information for this Meeting
Session No. 31--Booth# 13
Tectonics and Structural Geology (Posters)
Hotel NH Krystal: La Capilla
8:30 AM-5:30 PM, Thursday, April 3, 2003
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