HIBRIDIZAÇÃO MAGMÁTICA NO PLÚTON QUIXABA NW DO DOMÍNIO RIO PIRANHAS-SERIDÓ: UM ESTUDO TEXTURAL QUANTITATIVO E QUALITATIVO

The Quixaba Pluton is an Ediacaran age batholith outcropping more than 100 km2 in a NE-SW trend, located within the Rio Piranhas-Seridó Domain (Setentrional portion of the Borborema Province). This pluton is composed by two main facies, Quixaba and Umari. The predominant facies is the Quixaba composed by coarse equigranular pink monzonitic rocks. The Umari facies is composed by the equigranular dioritic rocks in the central part of the Quixaba Pluton as a semi-circular intrusion with main axis E-W trending. This dioritic rocks presents two pyroxenes, ferrossilite and diopside, and subsolidus amphibole of grunerite and hornblende composition. Rocks of hybrid composition between both facies, as well the presence of mafic magmatic enclaves, like rapakivi texture, quartz ocelli, mixed apatites, synneusis and mafic clots indicate coexistence and local mixture processes between the monzonitic magma dioritic magmas.

Magma Mushes of the Fogo Island Batholith: a Study of Magmatic Processes at Multiple Scales

This field, petrographic, and geochemical study examines mingling of compositionally similar rocks at multiple scales. Evidence of complex magma interaction in a multi-component crystal mush reservoir is preserved within the Wild Unit, located along the northeast shoreline of Fogo Island, Newfoundland and Labrador, Canada. The irregular contacts and lack of chilled margins between units, the back-intrusion of younger units by older units, the similar composition of units, and an overlap in U-Pb zircon ages suggest all units interacted as viscous crystal mushes at similar temperatures in the shallow crust. Abundant rounded to ellipsoidal magmatic enclaves, of which there are at least three populations based on composition and crystallinity, appear to represent separate magmas that were entrained either as earlier mush material or crystal-poor intrusions that experienced break-up. Evidence of changes in liquid environment at deeper levels is preserved both in the field and at the mineral-scale, where it is highlighted by abrupt compositional spikes in traverses across early forming plagioclase and pyroxene crystals. Heterogeneity in textures and composition of both major minerals (plagioclase and pyroxene) and an accessory mineral (zircon) point to processes such as crystal exchange and capture affecting tonalite crystal mushes, magmatic enclaves, and other intrusions in the study area earlier in their histories at deeper levels.

The sulfide enclave cargo: Insights into magmatic-hydrothermal ore systems

<p>The study of magmatic enclaves can provide a vertical understanding of the variable levels at which magmatic differentiation occurs, allowing us to quantify the conditions under which processes like sulfide saturation take place. Recent studies have confirmed the importance of lower crustal hornblende-rich enclaves (Chang and Audétat, 2018) and deep pyroxene-rich cumulates, as fertile sources in post-subduction and collisional settings, by sequestrating most of the Cu extracted from the mantle (Chen et al., 2019). Moreover, studies of sulfides in the host rock (Keith et al., 2017, Georgatou et al., 2018, 2020) and in enclaves (Du et al., 2014; Georgatou et al., 2018) have shown that sulfide saturation appears to be a multi-stage process starting with Fe,Ni-rich sulfides, switching to Ni-poor, Cu-rich sulfides and finally to only Cu-rich sulfides. Bracketing the P-T range in which sulfide saturation occurs relative to the sulfide occurrence and composition for diverse geodynamic settings in both mineralised and barren systems would permit us to assess the effect of sulfide saturation on the mineralization potential of the ascending residual melt.</p><p>Here, we investigate sulfide-bearing magmatic enclaves from: (i) the Miocene volcano-plutonic complexes of Konya (hosting the Doganbey Cu-Mo-W porphyry and Inlice Au-epithermal) and Usak (hosting the Kisladag giant Au-porphyry), in Western Turkey (post-subduction settings), (ii) the Kula Plio-Quaternary volcano, in the Usak basin, also in Turkey (intraplate OIB-like signature volcano in post-subduction setting). We compare results from the above areas with those of previously studied enclaves (Georgatou et al., 2018) and of new enclaves of the Quaternary Ecuadorian volcanic arc, hosting, among others, the Cascabel Cu-Au Miocene porphyry deposits (subduction setting).</p><p>Our results confirm previous conclusions (Georgatou et al., 2018) that mafic enclaves and cumulates carry a greater amount of sulfides compared to the more felsic host rock and that sulfides are generally Cu-poorer compared to the ones found in the host rock. Preliminary thermobarometry data on sulfide bearing amphibole cores found in the host rock yield P(GPa)/T(<sup>o</sup>C) (Ridolfi et al., 2010) of 0.39-0.53/1060-1093 for Kula, 0.46-0.11/1015-819 for Konya, 0.20-0.33/917-969 for Usak and 0.2-0.38/902-987 for Ecuador. Estimates on amphibole occuring in hornblende-rich enclaves of Kula and Ecuador indicate P/T values of 0.22-0.57/988-1097 and 0.24-0.4/900-1013, respectively. Crossrefencing with Mutch et al., 2016 shows similar temperatures but significantly higher pressures, indicating for the case of Kula 0.69-0.83 GPa in the host rock and 0.53-0.86 GPa in the enclaves. These data suggest widespread sulfide saturation occurring at mid- to upper crustal depths with the highest P-T values corresponding to the onset of early Fe,Ni-rich sulfide saturation. Future investigation of sulfide-rich enclaves found in other areas and crossreferencing with multiple thermobarometers will further constrain the P-T conditions for later stages of sulfide saturation.</p><p> </p><p><em>Chang and Audétat 2018, J.Petrol. 59(10):1869-1898</em></p><p><em>Chen et al., 2019, Earth Planet.Sci.Lett. 531, 115971</em></p><p><em>Du et al., 2014, Geosci.Front. 5,237-248</em></p><p><em>Georgatou et al., 2019, Lithos 296-299,580-599</em></p><p><em>Georgatou and Chiaradia, 2020, Solid Earth 11(1):1-21</em></p><p><em>Keith et al., 2017, Chem.Geol. 451:67–77</em></p><p><em>Ridolfi et al., 2010, Contrib.Mineral.Petrol. 160,45-66</em></p><p><em>Mutch et al., 2016, Contrib.Mineral.Petrol. 171,85</em></p>