U–Pb Neoproterozoic–Ordovician protolith age constraints for high- to medium-pressure rocks thrust over low-grade metamorphic rocks in theIxcamilpa area, Acatlán Complex, southern Mexico

Abstract

High-grade and high-pressure rocks in Acatlán Complex (southern Mexico) are inferred to have been emplaced either during the convergence and collision between Laurentia and Gondwana or during subduction on the western margin of Pangea. In the Ixcamilpa area, such rocks occur in a synformal nappe and are subdivided into (1) the Neoproterozoic–Ordovician Piaxtla Suite (metapsammite, meta-pelite, and amphibolite) that passes structurally upwards from blueschist through eclogite to amphibolite facies; intruded by (2) Cambro-Ordovician megacrystic granitoids; both of which were thrust westwards over (3) the Carboniferous Zumpango Unit consisting of clastic and meta-volcanic rocks. Laser ablation – inductively coupled plasma – mass spectrometry (LA–ICP–MS) U–Pb zircon geochronology yielded age population peaks at (i) 435–490 Ma, probably derived from Acatlán granitoids; (ii) 500–700 Ma, likely derived from the Yucatan Peninsula and Brasiliano orogens; (iii) 800–900 Ma, with provenance in the Goiás arc of eastern Amazonia; and (iv) 950–1300 Ma, sourced either from Oaxaquia, Amazonia, or Laurentia: the younger ca. 310–360 Ma ages are limited to the Zumpango Unit and likely have a local provenance. The overall similarity of the Piaxtla rocks in the Ixcamilpa area and those in the Piaxtla-Mimilulco median belt suggests that Ixcamilpa nappe roots in the median belt, which is interpreted as an extrusion zone within the Acatlán Complex. Since neither high-pressure belt represents a closed ocean, deposition of the Neoproterozoic–Ordovician rocks is inferred to have taken place on the southern margin of Rheic Ocean adjacent to Oaxaquia–Amazonia, whereas the Carboniferous rocks were deposited on the western margin of Pangea synchronous with extrusion of the high-pressure rocks.

Permian-Carboniferous arc magmatism and basin evolution along the western margin of Pangea: Geochemical and geochronological evidence from the eastern Acatlan Complex, southern Mexico

“…2). To the west, the Acatlán Complex is thrust over Cretaceous platformal carbonates, located between the exposed Acatlán Complex and the emplaced Guerrero terrane (Centeno-García et al, 2008;Ramos-Arias and Keppie, 2011). To the north, the complex is unconformably overlain by Meso zoic rocks and the Cenozoic Trans-Mexican volcanic belt (Ferrari et al, 1999).…”

U–Pb geochronological constraints on the Triassic–Jurassic Ayú Complex, southern Mexico: Derivation from the western margin of Pangea-A

“…2;Caballero-Miranda et al, 1990;Morán-Zenteno et al, 1993;Centeno-García et al, 2009;Elías-Herrera et al, 2011;Rubio-Cisneros and Lawton, 2011;Silva-Romo et al, 2011), which mark the Early Mesozoic continental margin of southern Mexico. To the west, the Acatlán Complex is thrust over Cretaceous limestones of the Guerrero-Morelos platform along the Upper Cretaceous-Paleocene Papalutla Fault (Cerca et al, 2007;Ramos-Arias and Keppie, 2011;Fig. 2).…”

A Carboniferous high-pressure klippe in the western Acatlán Complex of southern México: implications for the tectonothermal development and palaeogeography of Pangea

“…The western part of the Acatlán Complex in the Olinalá and Ixcamilpa areas were initially studied by Hermanns (1994), Farfán-Panamá (1998), Ram´rez-Espinoza (2001), Torres de León (2001), and De la Cruz-Vargas (2004). Subsequently, Talavera-Mendoza et al (2005) and VegaGranillo et al (2007VegaGranillo et al ( , 2009) sampled the western Acatlán Complex for geochronology, and Ortega-Obregon et al (2009) and Ramos-Arias and Keppie (2011) have recently published detailed geological maps of the Olinalá and Ixcamilpa areas, respectively, accompanied by zircon U-Pb geochronological data. The rocks of the Piaxtla Suite in the Ixcamilpa area preserve metamorphic grades from blueschist through amphibolite eclogite to greenschist facies and were subdivided into a series of tectonic slices ( Figure 2) by Ramos-Arias and Keppie (2011).…”

“…Thus, incorporation of the most recent data led OrtegaObregon et al (2009OrtegaObregon et al ( , 2010 and Ramos-Arias and Keppie (2011) to derive the following geological history for the Ixcamilpa-Olinalá area:…”

“…Ramos-Arias and Keppie (2011) assigned the HP and associated rocks of Ixcamilpa area to the Piaxtla Suite and subdivided them into several tectonic slices ( Figure 2) (from bottom to top): (1) Coacalco Unit (glaucophane schist, amphibolite, and meta-sedimentary rocks); (2) Tlanipantla Unit (meta-psammites, metapelites, and a few amphibolites); (3) Cuatlaxtecoma Unit (amphibolite, metasedimentary rocks cut by granitic dikes); (4) Zacango Unit (paragneiss, meta-psammite, and metapelite); (5) Buenavista Unit (meta-psammite, metapelite, and a few amphibolites); and (6) Chicomala Unit (graphitic schist, meta-quartzite cut by pegmatite, and rare mafic dikes). Also within the high-grade rocks is the Ordovician megacrystic Tecolapa metagranitoid, which is cut by metaleucogranite dikes.…”