Insights into orogenic processes from drab schists and minor intrusions: Southern São Francisco Craton, Brazil

Minor altered intrusions and drab retrogressed schists can easily be overlooked in geological studies but this contribution explores these rocks within the Archaean and Palaeoproterozoic southern S?o Francisco Craton (SSFC), Brazil using geological relationships and accessory mineral in situ analyses in the context of cratonic assembly. Three magmatic pulses are documented: i) Archaean and ii) Palaeoproterozoic felsic intrusions, both hosted by Archaean protoliths, and iii) Palaeoproterozoic felsic intrusions in Palaeoproterozoic supracrustal sequences. Archaean felsic intrusions confirm the Palaeoarchaean age of the mafic/ultramafic sequence of the Rio das Velhas Greenstone Belt and Rhyacian intrusions mark the collisional stage of the Mineiro Belt with the SFC at c. 2130?Ma. Greenstone belt schists show a wide distribution of rounded ?soccer ball? Archaean detrital and metamorphic zircon grains ranging in age from 3200 to 2750?Ma with an interpreted overprinting high-grade metamorphic event at c. 2700 to 2680?Ma. Most high-grade metamorphic rims have Th/U?>?0.1, negative ?Hf(t) values and REE pattern consistent with eclogite/granulite metamorphic facies, reinforcing the hypothesis of a dehydrated-refractory crust formed during the stabilization of the SSFC, even though no such protoliths are preserved. This event links crustal thickening and partial melting of Archaean lower crust. Archaean rutile crystals from the greenstone belt schist were reset during the Palaeoproterozoic event but still preserve the early Archaean high-grade metamorphic signature. The presence of unstable ilmenite replaced by rutile in the schist, associated to felsic intrusions with the same age at c. 2130?Ma suggest high pressure, low temperature prograde metamorphism during the collisional stage of the Palaeoproterozoic orogen. Elongate and prismatic zircon grains from the Rhyacian intrusions have low ?Hf(t) signature and crystallised from partial melting of sedimentary protoliths. Accretionary events produced thicker and more differentiated crust by the end of Rhyacian time. Easily overlooked rocks in this study, when studied, have revealed a rich multi-event history of cratonic evolution

Evolution of Siderian juvenile crust to Rhyacian high Ba-Sr magmatism in the Mineiro Belt, southern São Francisco Craton

Plutonic rocks from the Mineiro Belt, Brazil record a delayed onset of the transition from TTG to sanukitoid-type magmatism (high Ba-Sr), starting during the Siderian magmatic lull when little juvenile magma was added to the continental crust. Rocks mostly belong to the calc-alkaline series, meta- to peraluminous and originally “I-type”, meaning that oxidized magmas were formed by partial melting of subducted material. The temporal distribution and apparent secular changes of the magmas are consistent with the onset of subduction-driven plate tectonics due to an increase of the subduction angle and opening of the mantle wedge. New isotopic analyses (Sm-Nd whole rock and Lu-Hf in zircon) corroborate the restricted juvenile nature of the Mineiro Belt and confirm the genetic link between the Lagoa Dourada Suite, a rare ca. 2350 Ma high-Al tonalite-trondhjemite magmatic event, and the sanukitoid-type ca. 2130 Ma Alto Maranhão Suite. U-Pb dating of zircon and titanite constrain the crystallisation history of plutonic bodies; coupled with major and trace element analyses of the host rocks, they distinguish evolutionary trends in the Mineiro Belt. Several plutons in the region have ages close to 2130 Ma but are distinguished by the lower concentration of compatible elements in the juvenile high Ba-Sr suite. Keywords: São Francisco Craton, Magmatic lull, TTG-Sanukitoid transition, Zircon U-Pb-Hf, Titanite U-Pb, Whole rock Nd isotope

U–Pb ages and Hf-isotope data of detrital zircons from the late Neoarchean-Paleoproterozoic Minas Basin, SE Brazil

Because of its world-class iron ore deposits and promising Au and U mineralizations, the late Neoarchean to Paleoproterozoic Minas Basin (Minas Supergroup, SE of Brazil) is one of the best-studied basins in South America. However, the lack of datable interlayered volcanic rocks prevented discourse over ages of the strata, the sources and the nature of its ore deposits. In this paper, we present detrital zircon U–Pb age patterns coupled with Lu–Hf data for 18 samples, representing different stages of the Minas Basin evolution (∼2000 analyzed zircons). Age spectra for the main basal unit (Moeda Formation) show a classic rift-related detrital zircon pattern, characterized by multiple autochthonous sources, which in turn are much older than the age of deposition. Maximum age for the rifting event is constrained at ca. 2600 Ma. Detritus accumulated at the base of the Minas Supergroup were derived from Archean source rocks and their sedimentation was marked by differential uplift of the Archean crust, shortly after the 2730–2600 Ma high-K calc-alkaline magmatism (Mamona Event). The age of the BIF deposits is younger than 2600 Ma, most likely coinciding with the great oxygenation event between 2400 and 2200 Ma and the precipitation of banded iron deposits worldwide. Detrital zircons from the topmost units of the Minas strata suggest that tectonic inversion and closure of the basin took place at ca. 2120 Ma with the deposition of the synorogenic Sabará Group. Rhyacian zircon supply showing juvenile Hf signatures gives evidence of a late Rhyacian amalgamation between the Mineiro Belt and the craton. The εHf signatures support the hypothesis that the Archean crystalline crust of the craton was mostly built by crust–mantle mixing processes, with a successive decrease of εHf values in zircons crystallized after 3250 Ma and minor mantle-like additions after Paleoarchean times. Regionally, our dataset supports previous interpretations of a long-lived evolution of the southern São Francisco Craton comprising a succession of convergent island arcs, small microplate collisions, and development of Archean convergent and divergent basins that evolved between Archean and Paleoproterozoic times.Fil: Martínez Dopico, Carmen Irene. Universidade Federal de Ouro Preto; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lana, Cristiano. Universidade Federal de Ouro Preto; BrasilFil: Moreira, Hugo S.. University of Portsmouth; Reino UnidoFil: Cassino, Lucas F.. Universidade Federal de Ouro Preto; BrasilFil: Alkmim, Fernando F.. Universidade Federal de Ouro Preto; Brasi

Attosecond electron-spin dynamics in Xe 4d photoionization

The photoionization of xenon atoms in the 70-100 eV range reveals several fascinating physical phenomena such as a giant resonance induced by the dynamic rearrangement of the electron cloud after photon absorption, an anomalous branching ratio between intermediate Xe$^+$ states separated by the spin-orbit interaction and multiple Auger decay processes. These phenomena have been studied in the past, using in particular synchrotron radiation, but without access to real-time dynamics. Here, we study the dynamics of Xe 4d photoionization on its natural time scale combining attosecond interferometry and coincidence spectroscopy. A time-frequency analysis of the involved transitions allows us to identify two interfering ionization mechanisms: the broad giant dipole resonance with a fast decay time less than 50 as and a narrow resonance at threshold induced by spin-flip transitions, with much longer decay times of several hundred as. Our results provide new insight into the complex electron-spin dynamics of photo-induced phenomena

Metamorphism and exhumation of basement gneiss domes in the Quadrilátero Ferrífero: two stage dome-and-keel evolution?

The presence of dome-and-keel provinces in Archean cratons has been connected with the initiation of plate tectonics on Earth as these features are most commonly observed in Archean rocks. The Quadril\ue1tero Ferr\uedfero in Brazil has been identified as a Paleoproterozoic dome-and-keel province for more than three decades. The prevailing model suggests that it formed during the Rhyacian Transamazonian orogeny, making it unique among dome-and-keel provinces. However, a lack of appropriate lithologies, datable minerals and the metamorphic overprint of later orogenesis has resulted in a cryptic metamorphic record for the formation of this dome-and-keel province. A clinopyroxene-bearing migmatite from the core of the Ba\ue7\ue3o dome has peak P\u2013T conditions of 5\u20137 kbar and 700\u2013750 \ub0C and a published age of ca. 2730 Ma based on U\u2013Pb ages of zircon from leucosomes, suggesting that this age represents the migmatisation event. A fine-grained epidote-albite-titanite assemblage overprints the coarse-grained clinopyroxene and amphibole, giving P\u2013T conditions of 8\u20139 kbar and 550 \ub0C with an associated titanite age of ca. 2050 Ma. A garnet-bearing amphibolite sample also from the core of the dome has peak P\u2013T conditions of 7\u20138 kbar and 650\u2013700 \ub0C, and texturally late titanite from this sample produces an age of ca. 2060 Ma. Three additional samples were collected from the edges of the dome. A garnet-gedrite bearing felsic schist produces peak P\u2013T conditions of 8\u20139 kbar and 650\u2013700 \ub0C on a clockwise P\u2013T evolution. This sample has a U\u2013Pb zircon age of ca. 2775 Ma, which could date metamorphism or be the age of its volcaniclastic protolith. Texturally unconstrained titanite from the sample gives an age of ca. 2040 Ma. A garnet-bearing amphibolite that occurs as a boudin within the felsic schist gives both zircon and titanite ages of ca. 2050 Ma and has peak P\u2013T conditions of 5\u20136 kbar and 650\u2013700 \ub0C on a near isobaric P\u2013T path. An amphibolite dike, observed to cross-cut the felsic schist produces a zircon U\u2013Pb age of ca. 2760 Ma. Altogether this data suggests that the samples were metamorphosed in the Archean (ca. 2775\u20132730 Ma) and again during the Transamazonian event. The most plausible explanation for this data is that dome-and-keel formation occurred in the Archean with migmatisation and high-temperature metamorphism occurring at this time. The Paleoproterozoic event is interpreted as a reactivation of the dome-and-keel formation structures, with Paleoproterozoic keels crosscutting Archean keels and producing metamorphic aureoles. The high radiogenic heat production and the presence of dense sedimentary successions in Archean terranes make dome-and-keel provinces a uniquely Archean feature, but they are susceptible to reworking, resulting in an enigmatic record of formation

Paleoproterozoic juvenile magmatism within the northeastern sector of the São Francisco paleocontinent: insights from the shoshonitic high Ba-Sr Montezuma granitoids

New, integrated petrographic, mineral chemistry, whole rock geochemical, zircon and titanite U?Pb geochronology, and zircon Hf isotopic data from the Montezuma granitoids, as well as new geochemical results for its host rocks represented by the Corrego Tingui Complex, provides new insights into the late- to post-collisional evolution of the northeastern S~ao Francisco paleocontinent. U?Pb zircon dates from the Montezuma granitoids spread along the Concordia between ca. 2.2 Ga to 1.8 Ga and comprise distinct groups. Group I have crystallization ages between ca. 2.15 Ga and 2.05 Ga and are interpreted as inherited grains. Group II zircon dates vary from 2.04 Ga to 1.9 Ga and corresponds to the crystallization of the Montezuma granitoids, which were constrained at ca. 2.03 Ga by the titanite U?Pb age. Inverse age zoning is common within the ca. 1.8 Ga Group III zircon ages, being related to fluid isotopic re-setting during the Espinhaco rifiting event. Zircon ?Hf(t) analysis show dominantly positive values for both Group I ( 4 to ?9) and II ( 3 to ?8) zircons and TDM2 model ages of 2.7?2.1 Ga and 2.5?1.95 Ga, respectively. Geochemically, the Montezuma granitoids are weakly peraluminous to metaluminous magnesian granitoids, enriched in LILES and LREE, with high to moderate Mg# and depleted in some of the HFSE. Their lithochemical signature, added to the juvenile signature of both inherited and crystallized zircons, allowed its classification as a shoshonitic high Ba?Sr granitoid related to a late- to post-collisional lithosphere delamination followed by asthenospheric upwelling. In this scenario, the partial melting of the lithospheric mantle interacted with the roots of an accreted juvenile intra-oceanic arc, being these hybrid magma interpreted as the source of the Montezuma granitoids. The Corrego Tingu? Complex host rocks are akin to a syn- to late-collisional volcanic arc granitoids originated from the partial melting of ancient crustal rocks. The results presented in this study have revealed the occurrence of juvenile rocks, probably related to an island arc environment, that are exotic in relation to the Paleo- to Neoarchean crust from the S~ao Francisco paleocontinent?s core

Ultra high performance liquid chromatography–tandem mass spectrometry method for cyclosporine a quantification in biological samples and lipid nanosystems

Cyclosporine A (CyA) is an immunosuppressant cyclic undecapeptide used for the prevention of organ transplant rejection and in the treatment of several autoimmune disorders. An ultra high performance liquid chromatography–tandem mass spectrometry method (UHPLC–MS/MS) to quantify CyA in lipid nanosystems and mouse biological matrices (whole blood, kidneys, lungs, spleen, liver, heart, brain, stomach and intestine) was developed and fully validated. Chromatographic separation was performed on an Acquity UPLC® BEH C18 column with a gradient elution consisting of methanol and 2 mM ammonium acetate aqueous solution containing 0.1% formic acid at a flow rate of 0.6 mL/min. Amiodarone was used as internal standard (IS). Retention times of IS and CyA were 0.69 min and 1.09 min, respectively. Mass spectrometer operated in electrospray ionization positive mode (ESI+) and multiple reaction monitoring (MRM) transitions were detected, m/z 1220.69 → 1203.7 for CyA and m/z 646 → 58 for IS. The extraction method from biological samples consisted of a simple protein precipitation with 10% trichloroacetic acid aqueous solution and acetonitrile and 5 μL of supernatant were directly injected into the UHPLC–MS/MS system. Linearity was observed between 0.001 μg/mL–2.5 μg/mL (r ≥ 0.99) in all matrices. The precision expressed in coefficient of variation (CV) was below 11.44% and accuracy in bias ranged from −12.78% to 7.99% including methanol and biological matrices. Recovery in all cases was above 70.54% and some matrix effect was observed. CyA was found to be stable in post-extraction whole blood and liver homogenate samples exposed for 6 h at room temperature and 72 h at 4 °C. The present method was successfully applied for quality control of lipid nanocarriers as well as in vivo studies in BALB/c mice

Evaluation of 3D printed gelatin-based scaffolds with varying pore size for MSC-based adipose tissue engineering

Adipose tissue engineering aims to provide solutions to patients who require tissue reconstruction following mastectomies or other soft tissue trauma. Mesenchymal stromal cells (MSCs) robustly differentiate into the adipogenic lineage and are attractive candidates for adipose tissue engineering. This work investigates whether pore size modulates adipogenic differentiation of MSCs toward identifying optimal scaffold pore size and whether pore size modulates spatial infiltration of adipogenically differentiated cells. To assess this, extrusion-based 3D printing is used to fabricate photo-crosslinkable gelatin-based scaffolds with pore sizes in the range of 200-600 mu m. The adipogenic differentiation of MSCs seeded onto these scaffolds is evaluated and robust lipid droplet formation is observed across all scaffold groups as early as after day 6 of culture. Expression of adipogenic genes on scaffolds increases significantly over time, compared to TCP controls. Furthermore, it is found that the spatial distribution of cells is dependent on the scaffold pore size, with larger pores leading to a more uniform spatial distribution of adipogenically differentiated cells. Overall, these data provide first insights into the role of scaffold pore size on MSC-based adipogenic differentiation and contribute toward the rational design of biomaterials for adipose tissue engineering in 3D volumetric spaces