Using apatite to resolve the age and protoliths of mid-crustal shear zones: A case study from the Taxaquara Shear Zone, SE Brazil

From microanalysis to supercontinents: Insights from the Rio Apa Terrane into the Mesoproterozoic SW Amazonian Craton evolution during Rodinia assembly

“…The 44069 monazite yielded an average 206 Pb/ 238 U age of 422 ± 2 Ma (MSWD = 0.3, N = 100), Madagascar apatite yielded an 207 Pb‐corrected age (using the in‐built Stacey and Kramers, 1975, correction in IsoplotR) of 490 ± 6 Ma (MSWD = 0.6, N = 32), OLT titanite yielded a concordia age of 1,009 ± 7 Ma (MSWD = 2.7, N = 13), and R632 rutile yielded a concordia age of 497 ± 5 Ma (MSWD = 1.1, N = 7). All secondary standards yielded ages in agreement with reference values for each standard and to the long‐term reproducibility of the Isotopia Lab results (e.g., Ribeiro, Lagoeiro, et al, 2020; Ribeiro, Mulder, et al, 2020; Zoleikhaei et al, 2021).…”

“…Apatite from the Porto Murtinho and Caracol complexes have different trace element chemistries and U–Pb ages. In general, the higher REE content, negative Sr and Eu anomalies, and enrichment of LREE–MREE characteristics of apatite from the Porto Murtinho Complex are akin to igneous apatite (Belousova et al, 2001; Ribeiro, Mulder, et al, 2020; Sha & Chappell, 1999). However, when the compositions are plotted in the apatite classification diagram, only apatite from sample FMR101 plots in the sections that correspond to I‐type and mafic igneous rocks (O'Sullivan et al, 2020), whereas those from samples FMR104 and FMR109 plot as high‐grade metamorphic apatite (Figure 12a).…”

“…U and Pb isotopes were measured using a Thermo Scientific iCAP triple quadrupole TQ‐ICP‐MS, and trace element concentrations were measured using an iCAP Q‐ICP‐MS. The analytical routines for apatite, titanite, and rutile are detailed described elsewhere (see Ribeiro, Mulder, et al, 2020; Zoleikhaei et al, 2021). Data reduction was performed in Iolite4 using the built‐in data reduction schemes for U–Pb (no common‐Pb correction considered) and trace elements (Paton et al, 2010, 2011).…”

“…200 Ma younger than the average crystallization age of the Porto Murtinho Complex. Since these samples are granitic mylonites and apatite has otherwise retained its igneous chemistry, we interpret that the apatite U-Pb system was reset via volume diffusion in response to a medium-grade mylonitization process (Jepson et al, 2021;Odlum and Stockli, 2020;Ribeiro et al, 2020c). Thus, the ca.…”

Geological-structural mapping and geocronology of shear zones: A methodological proposal

“…adjacent to shear zones Given the different geological processes (deformation, metamorphism, and fluid-rock interaction) related to the evolution of a shear zone, it is necessary to integrate geochronological and thermochronological studies of syntectonic elements of the structure, in order to constrain the age of deformation in shear zones (Fossen and Tikoff, 1997;Xypolias and Kokkalas, 2006;Vitale and Mazzoli, 2008;Carreras et al, 2013;Pennacchioni and Zucchi, 2013;Ribeiro et al, 2020b). These studies include: a) Intrusive synkinematic (Table 3), which correspond to igneous bodies emplaced during reactivation episodes of fault systems, in which magmatic units are transported through the crust by shear zones that behave as channels connecting magma generation areas with the upper crust (D' Lemos et al, 1992;Reavy, 1989;Clemens and Mawer, 1992;Rosenberg, 2004).…”