Abstract

Late Jurassic–Cretaceous arc-related volcaniclastic rocks from the southern Guerrero and western Mixteca terranes of Mexico were analyzed by U-Pb detrital zircon geochronology(laserablation-multicollector–inductively coupled plasma–mass spectroscopy) to place constraints on the depositional history and provenance of the rocks. Pre–Middle Jurassic basement rocks and sandstone from the Upper Cretaceous Mexcala Formation were also analyzed to define the origin and provenance of the prevolcanic substratum, and the time of accretion of Guerrero composite terrane sequences.

Data from the Taxco-Taxco Viejo, Teloloapan, and Arcelia assemblages indicate that the youngest (129–141 Ma) zircon fraction in each sequence was derived from local volcanic sources, whereas older populations (ca. 247–317, 365–459, 530–617, 712–878, 947–964, 1112–1188, 1350–1420, 1842–1929, 2126–2439, and 2709–3438 Ma) show sediment influx from varied sources, most likely through grain recycling. The major zircon clusters in these sequences match the populations recorded in the nearby Acatlán Complex. In contrast, the Huetamo sample is dominated by Lower Cretaceous (ca. 126 Ma) zircons of local volcanic provenance, and the Zihuatanejo sample contains zircon clusters (ca. 259, ca. 579, and ca. 947–1162 Ma) comparable to major populations recorded in the underlying Arteaga Complex.

A sample from the Middle Triassic–Middle Jurassic Arteaga Complex at Tzitzio contains zircon clusters (ca. 202–247, ca. 424, ca. 600, ca. 971, and ca. 2877 Ma) consistent with an ultimate derivation from both North American and South American sources. The sample from the Las Ollas suite contains comparable zircon populations (ca. 376–475, ca. 575, ca. 988–1141, and ca. 2642–2724 Ma), and it is interpreted to be part of the prevolcanic basement. In contrast, the youngest zircon cluster (ca. 105 Ma) in the Mexcala Formation coincides with the major volcanic events in the Taxco-Taxco Viejo, Teloloapan, and Arcelia assemblages, whereas the older clusters (ca. 600, ca. 953, ca. 1215, ca. 1913, and ca. 2656–2859 Ma) broadly match the major populations recorded in rocks from the Acatlán Complex.

These new data combined with available geochemical and isotopic data indicate that the Taxco-Taxco Viejo arc assemblage developed on continental crust. The Acatlán Complex is the most plausible candidate. The Teloloapan and Arcelia arc assemblages were developed on oceanic crust as offshore arcs facing the Acatlán Complex. The Zihuatanejo terrane assemblages were developed on the Arteaga Complex, and evidence no influence from the Acatlán Complex. This suggests that these assemblages were formed farther away or in a restricted basin.

The Guerrero composite and Mixteca arc successions are coeval with the Alisitos arc of northern Mexico and in part with the Nevada and Klamath ranges of the southwestern United States, and with the arc series from the Greater and Lesser Antilles and northern South America. Data indicate that during late Mesozoic time, southwestern North America was a site of intensive volcanism in a complex arc-trench system similar to that of the east Pacific. Our data are consistent with a diachronic accretion of the Guerrero composite terrane sequences, beginning during late Cenomanian time with the amalgamation of the Teloloapan and probably the Arcelia assemblages, and finishing at the end of Cretaceous time with the accretion of the Zihuatanejo terrane assemblages.

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