Magmatic and tectonic evolution of the Chaval Granite at the end of the Neoproterozoic, northwestern border of the Borborema Province

Abstract

The northwestern region of Borborema Province is represented by the Ceara Central and Northwest Ceara crustal blocks connected by an extensive transcurrent shear zone that represents the northern portion of the Transbrasiliano Lineament in a complex geological context, which brings together geological units of nature, origin, and ages of the Archean to the Paleozoic. In this scenario, there is a large amount of granitic bodies, with different natures, age and tectonic environment, but predominantly representing a more intense granitogenesis in the Paleozoic Neoproterozoic and early Paleozoic, with plutons emplaced in different stages of the Brazilian Orogeny. In this context, the Chaval Granite corresponds to an isolated body in the extreme northwest of Borborema Province, located near the Atlantic coast, in the northern states of Ceará and Piauí. It is an intrusive batholith housed in Siderian orthogneisses (Granja Complex) and in Neoproterozoic supracrustal rocks (Martinopole Group), but is partly covered by sedimentary rocks from the Parnaíba Paleozoic Basin (Serra Grande Group), and coastal Cenozoic deposits. Field data and petrographic studies highlight the porphyritic texture with microcline megacrystals involved in coarce matrix as a remarkable feature. The predominant petrographic types are granodiorites, with variations for monzogranites and tonalites. The predominant primary mineral constituents are pertitic microcline, oligoclase, and quartz; biotite and rarely hornblende as qualified minerals and additionally titanite, apatite, zircon, alanite, and opaque minerals. Another peculiar characteristic is the deformational features related to the installation of the Santa Rosa Transcurrent Shear Zone along its eastern flank. The effects of the transcurrent shear deformation led to the modification of the original magmatic fabrics in much of the eastern half of the batolith, generating various types of mylonites. Thus, the typically igneous textures preserved in the western half of the pluton were gradually replaced by tectonic fabrics, which initially evolved into proto-mylonites in the central portion of the body, grading to mylonites eastward, highlighting strongly stretching, comminution associated with dynamic recrystallization, highlighting the formation of microcline and plagioclase porphyroclasts in a mylonitic matrix, which are involved by mylonitic foliation. Geochemical studies reveal compositional similarities, compatible with petrographic classifications, in which they mostly present granodioritic composition, followed by monzogranites and tonalites, classified as I-type granites, peraluminous with compatible with the calcium-alkaline series. The geochemical signatures of the Chaval Granite indicate the character of the tectonic magmatic arc environment. U-Pb zircon analysis by Mass Spectrometry (LA-ICP-MS) indicates crystallization age of 633 Ma, placing it in the Neoproterozoic, late Cryogenic-Early Ediacaran period, being one of the oldest granitoids in northwestern Borborema Province, correl...

The Borborema Strike-Slip Shear Zone System (NE Brazil): Large-Scale Intracontinental Strain Localization in a Heterogeneous Plate

“…The Granja shear zone bounds the southeastern border of a prekinematic granite, which was emplaced at ca. 633 Ma (U-Pb zircon age; [107]) and deformed in strike-slip shearing at ca. 591 Ma (U-Pb monazite age; [46]).…”

Geology, geochronology Pb-Pb, U-Pb-Hf zircon and Sm-Nd TDM of the Uruburetama batholith, Northern Borborema Province: contextualization in the Santa Quitéria Magmatic Arc

“…In the case of granites controlled by mega-transcurrent shear zones, there is the case of the Quixadá-Quixeramobim batholith, with U-Pb in zircon (ID-TIMS) ages at ca 587 ± 5 Ma (Nogueira 2004). Chaval Granite had also been included in this category (U-Pb age in monazite of 591 Ma, Fetter et al 2003), but Aragão et al (2020) obtained new U-Pb zircon data dating in 633 ± 11 Ma, correlating it to the SQMA; • Supersuite III (Post-orogenic): these granites correspond to the magmatism associated with the dismantling of the Brasiliano orogen, and are well represented by the plutons Tauá, Taperuaba, Morrinhos, São Paulo, and the Meruoca Granitic Suite: plutons Meruoca -523 ± 5 Ma, Archanjo et al (2009); Mucambo -532 ± 7 Ma, Fetter et al (2003);…”