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In this paper, U-Pb zircon geochronology, Lu-Hf and Sm-Nd isotope systematics, geochemistry and geothermobarometry of metaigneous basement rocks exposed in the southeastern Chiapas Massif Complex are presented. Geologic mapping of the newly defined “El Triunfo Complex” located at the southeastern edge of the Chiapas Massif reveals (1) partial melting of a metamorphic basement mainly constituted by mafic metaigneous rocks (Candelaria unit), (2) an Ediacaran metasedimentary sequence (Jocote unit), and (3) occurrence of massif-type anorthosite. All these units are intruded by undeformed Ordovician plutonic rocks of the Motozintla suite. Pressure and temperature estimates using Ca-amphiboles, plagioclase and phengite revealed prograde metamorphism that reached peak conditions at ~ 650 °C and ~ 6 kbar, sufficient for partial melting under water saturated conditions. Relict rutile in titanite and clinopyroxene in amphibolite further indicate a previous metamorphic event at higher P-T conditions. U-Pb zircon ages from felsic orthogneiss boudins hosted in deformed amphibolite and migmatite yield crystallization ages of ~ 1.0 Ga, indicating that dry granitic protoliths represent remnants of Rodinia-type basement. Additionally, a mid-Tonian (~ 920 Ma) metamorphic overprint is suggested by recrystallized zircon from a banded gneiss. Zircon from folded amphibolite samples yield mainly Ordovician ages ranging from ~ 457 to ~ 444 Ma that are indistinguishable from the age of the undeformed Motozintla plutonic suite. Similar ages between igneous- and metamorphic- zircon suggest a coeval formation during a high-grade metamorphic event, in which textural discrepancies are explained in terms of differing zircon formation mechanisms such as sub-solidus recrystallization and precipitation from anatectic melts. In addition, some amphibolite samples contain inherited zircon yielding Stenian-Tonian ages around 1.0 Ga. Lu-Hf and Sm-Nd isotopes and geochemical data indicate that the protoliths of the amphibolite have E-MORB characteristics and were derived from a depleted mantle source younger than the Rodinia-type basement. Inasmuch as similar amphibolites also occur in the Ediacaran metasedimentary rocks as dykes or lenses, Late Neoproterozoic magmatism in a rift setting is suggested. Hence, the geologic record of the El Triunfo Complex includes evidences for Rodinia assemblage, Tonian circum-Rodinia subduction, and breakup during the Late Neoproterozoic. Metamorphism, and partial melting are interpreted in terms of a convergent margin setting during the Ordovician. The results place the southern Chiapas Massif along with Oaxaquia and similar Northern Andes terranes on the NW margin of Gondwana interpreted as the extension of the Famatinian orogen that evolved during the closure of the Iapetus Ocean.

Two meta-anorthosite inliers (∼20 km 2 each) were discovered on each side of the Polochic-Tonala fault system within the Chiapas Massif Complex (CMC) in southeastern Mexico. The anorthosites occur commonly associated to subordinate hornblendite, rutile-bearing ilmenitite, oxide-apatite-rich amphibolite and nelsonite. An absolute crystallization age for the anorthosite could not be precisely constrained due to the paucity and apparent resetting of the magmatic zircon. However, they are interpreted as remnants of a Proterozoic massif-type anorthosite complex older than 909 ± 27 Ma as suggested by U-Pb data and the striking geochemical similitudes (major, trace and REE, Sr-Nd isotopes; T DM = 1.39–1.45 Ga) to Stenian-Tonian massif-type anorthosites found elsewhere. A complex tectono-thermal history for the anorthosite suite is inferred from the discovery of abundant metamorphic zircon in all samples. Ubiquitous petrographic evidence suggests formation of secondary zircon from reactions involving baddeleyite and srilankite (ZrTi2O 6 ) breakdown at different stages of the anorthosite suite evolution. Two generations of baddeleyite are recognized: (1) exsolution from igneous ilmenite and hogbomite ([Mg,Fe 2+ ] 2 [Al,Ti] 5 O 10 ) during cooling, and (2) exsolution product from metamorphic rutile and hogbomite during retrogression. U-Pb zircon data (LA-MC-ICPMS) of three comagmatic rocks, including one anorthosite sample, reflect the complex polymetamorphic nature observed in the petrographical evidence; concordant to sub-concordant ages spread in a range from ∼909 Ma to ∼242 Ma. Most U-Pb ages cluster around known regional metamorphic events at ≃450 Ma and ≃250 Ma. In addition, an age cluster at ∼600 Ma suggests a Neoproterozoic event, interpreted in terms of reheating of anorthosite during mafic intrusions associated to intra-plate rifting.

Metasedimentary rocks from the El Triunfo Complex (Jocote Unit) in the southern Chiapas Massif (SE Mexico) are constituted mainly by sillimanite-rich micaschist, locally intercalated with marble and calc-silicate rocks. Mafic rocks (now amphibolite) intruded the sequence prior to deformation and folding. Peak metamorphic conditions are estimated by geothermobaromerty at ~6.0 kbar and ~650oC. The timing of the metamorphic event is dated by LA-MC-ICPMS analysis on zircon rims at 438+23/–12 Ma. Furthermore, detrital zircon grains yield mainly Stenian–Tonian and minor early Mesoproterozoic ages, indicating provenance from Grenville-type orogens (such as Oaxaquia) and some older cratonic sources. The 87Sr/86Sr values of 0.70775–0.70777 and the δ13C values from +1.9‰ to +2.7‰ in associated calcite marble define the time of deposition between 600 and 580 Ma. Geochemical markers from metapelite samples (such as La/Th > 3.94, La/Sc > 3.72, Th/U > 8.19, Th/Co > 0.42 and CIA = 74 to 83), as well as Sm–Nd iso...

El Macizo de Chiapas, en el sur de México, tiene como basamento una secuencia compuesta por anfibolitas deformadas y migmatizadas intercaladas con rocas calcisilicatadas y gneises félsicos, denominada Unidad Candelaria. In the Chiapas Massif of southern Mexico basement exposures referred to as the Candelaria Unit are composed of deformed and migmatized amphibolites interlayered calcsilicates rocks and felsic gneisses.