The Caltepec shear zone is a dextral transpressional tectonic boundary between the Oaxacan and Acatlán Complexes, which are crystalline basements of the Zapo-teco and Mixteco terranes in southern México, respectively. The terrane boundary (2–6 km wide) reveals protracted and polyphase tectonic activity from at least Early Permian to the present. The major tectonothermal event in the Caltepec fault zone was related to the oblique collision of the metamorphic complexes during the amalgamation of Pangea. An anatectic leucosome and the resulting syntectonic granite (Cozahuico Granite) in the fault zone yielded U-Pb zircon ages of 275.6 ± 1.0 Ma and 270.4 ± 2.6 Ma, respectively. The initial 87 Sr/ 86 Sr ratios (0.70435–0.70686) and Sm-Nd model ages (T DM ) (1.0–1.6 Ga) for the Cozahuico Granite and leucosome indicate a magmatic mixture that originated from melted Proterozoic crust and a component of depleted mantle. The Leonardian age of the cover (Matzitzi Formation) and a 40 Ar/ 39 Ar cooling age (muscovite) of 268.59 ± 1.27 Ma for mylonitic mica schist at the base of the thrust imply high cooling rates (∼180 °C/Ma) and uplift during the Permian. The adjacent sedimentological record indicates intense tectonic reactivation during Early Cretaceous, Paleogene, and Neogene along the long-lived Caltepec fault zone, alternating with periods of relative tectonic quiescence during Triassic, Jurassic, and Mid-Cretaceous times. The trend of the Caltepec fault zone parallel to the Oaxaca fault, 50 km to the east, is interpreted as part of a synchronous and dynamically coupled tectonic system that has been releasing tectonic stresses associated with the rupture of Pangea and the evolution of the Pacific margin of southern México from Jurassic to Holocene times.

Mesoproterozoic igneous protoliths that were metamorphosed to granulite facies during the Grenville orogeny are exposed south of the Ouachita suture in eastern and southern Mexico, and clasts of Mesoproterozoic granitoids occur in a Paleozoic conglomerate in northeastern Mexico. These rocks can be divided into two groups, based on crystallization ages. The older group has arc and backarc geochemical signatures and was emplaced between ca. 1235 Ma and ca. 1115 Ma. The younger group, an anorthosite-mangerite-charnockite-granite (AMCG) suite, is not well dated, but present data suggest that it was emplaced between ca. 1035 Ma and ca. 1010 Ma. The Mex-ican terrane was probably a trailing margin from ca. 1115 Ma until the Grenville orogeny at 990 ± 5 Ma that produced widespread granulite-facies metamorphism. There is no structural or metamorphic evidence in Mexico for a major, widespread orogenic event before the emplacement of the AMCG rocks; thus, the model relating the origin of AMCG suites to delamination or convective thinning of subcontinental lithosphere following collision and crustal thickening may not apply to the Mexican Grenville terrane. The Pb isotopic compositions of acid-leached potassium feldspars define a tight linear array on a 207 Pb/ 204 Pb versus 206 Pb/ 204 Pb diagram. This array is interpreted to reflect mixing between two end-member reservoirs. The radiogenic component was presumably continental in origin (perhaps subducted Paleoproterozic sediments), whereas the nonradiogenic end-member was most likely ca. 1200 Ma mantle. The Pb isotopic compositions of feldspars from eastern and southern Mexico are distinct from those of feldspars from Laurentia as represented by the Grenville Province and Grenville granites of Texas.

To better define the cooling history of the northern Oaxacan Complex, titanite and phlogopite from metasedimentary calc-silicate and biotite from a pegmatite were collected. All these rocks were involved in the granulite-facies Zapotecan orogeny between ca. 1004 and 978 ± 3 Ma, inferred to result from underthrusting the Oaxacan Complex beneath an arc or continent. Fragments of 2 × 5 cm 2 titanite crystals yielded a concordant U-Pb age of 968 ± 9 Ma, whereas 40 Ar/ 39 Ar analyses of phlogopite and biotite gave ages of 945 ± 10 Ma and 856 ± 10 Ma, respectively. These ages are inferred to date cooling through 660–700 °C, 450 °C, and 300–350 °C, respectively. When combined with published ages (Sm-Nd garnet, 40 Ar/ 39 Ar hornblende, Rb-Sr biotite and whole rock, and K-Ar biotite and K-feldspar) the data define a two-stage cooling curve: (1) 8 °C/m.y. between 978 and 945 Ma, cooling through 450 °C by which time the rocks had risen through a depth of 15 km; and (2) 2 °C/m.y., which, by extrapolation, brought the rocks to the surface between 710 and 760 Ma. The first stage of exhumation is interpreted in terms of tectonic switching between steep and flat slab subduction, a result of interactions of a ridge, a plume, or an oceanic plateau with the trench. The second stage may be related to thermal relaxation of the lithosphere, ending with the breakup of Rodinia, which brought the rocks to the surface.

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