NOVILLO METAMORPHIC COMPLEX, HUIZACHAL-PEREGRINA ANTICLINORIUM, TAMAULIPAS, MEXICO: CHARACTERIZATION AND DEVELOPMENT BASED ON WHOLE-ROCK GEOCHEMISTRY AND ND-ISOTOPIC RATIOS

The Precambrian metamorphic basement exposed in the eroded core of the Huizachal-Peregrina Anticlinorium (Cd. Victoria, Mexico) is described in this contribution as Novillo Metamorphic Complex (NMC). Based on field relations, modal content, whole rock geochemistry and Nd-isotopic ratios is possible to recognize two major units: (a) Metaigneous Unit (MIU) and (b) Metasedimentary Unit (MSU). The MIU is subdivided into the Old Suite, constituted by (a) felsic gneisses from Novillo canyon, (b) felsic gneisses from Peregrina canyon, (c) metagranites, (d) mafic gneisses, and (d) migmatites; and the AMCG Suite, composed by (a) meta-anorthosites, (b) metagranite-gabbro intercalations, (c) metacharnockites, (d) garnet-rich metaferrodiorite dykes, and (e) metanelsonites. The MSU is represented by (a) meta-arkose – amphibolite intercalations and (b) calcsilicate marbles. Tectonic discrimination diagrams based on linear discriminant analysis of natural logarithm transformed ratios of elements show an island arc tectonic setting for the MIU. Nd isotopic ratios show crustal residence T_DM ages of 1.49 – 1.44 Ga for the Old Suite and 1.63 – 1.33 Ga for the AMCG Suite. The MSU have T_DM ages between 1.39 a 1.25 Ga that support the interpretation that the protoliths were possibly deposited in a basin with sediment input from the younger MIU members.

The proposed event succession for the NMC starts with the intrusion of the Old Suite rocks as an island that later collided against Gondwana after having reached a degree of maturity enough to generate a large volume of felsic magma. After the collision of the arc against Gondwana and the breakup of the subducted slab, the AMCG Suite magma was generated and intruded into the former arc. The MSU metasediments were derived from the exposed igneous units and later thrusted over MIU rather than intruded, and together metamorphosed under granulite facies conditions by the ca. 1.0 Ga Zapotecan orogeny. However, since the metaferrodioritic bodies of the AMCG Suite cut discordantly the meta-anorthosites fabric, they represent a younger tectonothermal event, not yet described for the NMC.