U-Pb Geochronology Zircon (LA-ICP-MS) data of the Gneissic-Migmatitic Complex of Salvador-Esplanada-Boquim Belt, São Francisco Craton, Brazil/Geocronologia U-Pb (LA-ICP-MS) em zircões do Complexo Gnáissico-Migmatítico do Cinturão Salvador-Esplanada-Boquim, Cráton do São Francisco, Brasil

The Salvador-Esplanada-Boquim Belt (SEBB) is considered a branch of the São Francisco Craton, located in its northeastern portion, in the Brazilian states of Bahia and Sergipe. This paper analyzed the U-Pb (LA-ICP-MS) geochronology on the Gneissic-Migmatitic Complex (GMC) zircons in the rocks of the SEBB. Six analyses were made on the rocks of GMC and two on granitic dykes. The obtained data allowed concluding that the GMC rocks were formed between 2150 ± 19 – 2188 ± 30 Ma, while the dykes had their crystallization in line with the process of regional metamorphism in 2073 Ma. These metamorphic evens are interpreted as products of the collision with the Serrinha Block, provoking deformation, compression and uplifting of these rocks. After eroded, the granulitic roots of SEBB were exhumed, stabilizing on the way it is today with the GMC rocks, located on east and west of the Esplanada-Boquim Granulitic Complex

GEOQUIMICA Y GEOCRONOLOGIA U–Pb LA-ICP-MS DE UNIDADES VOLCÁNICAS Y PLUTÓNICAS DEL JURÁSICO EN LA REGIÓN DEL PUTUMAYO (SUR DE COLOMBIA): IMPLICACIONES TECTONICAS Y CORRELACIONES REGIONALES

Nuevos datos de campo, análisis geoquímicos y U-Pb LA-ICP MS en circón fueron obtenidos en rocas plutónicas y volcánicas en el Batolito de Mocoa y la Formación Saldaña, en el departamento de Putumayo en el sur de Colombia. Los resultados sugieren que el volcanismo y plutonismo que compartieron la misma historia de evolución magmática. Esta asociación vulcano-plutónica muestra enriquecimientos de LILE y LREE acompañado de anomalías negativas de Nb y Ti característico de arcos continentales. Rocas volcánicas y plutónicas de este arco continental cristalizaron entre 180 y 186 Ma como lo indica la geocronología U-Pb en circón. La actividad magmática esta temporal y geoquímicamente correlacionada con otro arco magmático expuesto en Colombia y Ecuador. Estas unidades pueden representar los remanentes de un solo cinturón que incluye varias unidades entre los 4°N en Colombia y 5°S en Ecuador. Este arco está relacionado a un cinturón magmático Jurásico fragmentado, que caracterizo las márgenes continentales de las Américas luego de la ruptura del súper continente Pangea.New field data, geochemical analyses and zircon U-Pb LA-ICP MS data were obtained on plutonic and volcanic rocks of the Mocoa Batholith and Saldaña Formation in southern Colombia Putumayo region. Results suggest that the plutonic and volcanic activities are closely related to a common magmatic history. This volcano-plutonic association presents a well-defined LILE and LREE enrichment and negative Nb and Ti negative anomalies characteristic of continental magmatic arcs. Volcanic and plutonic rocks crystallized between 180-186 Ma as revealed by U-Pb zircon geochronology. The magmatic activity is temporally and chemically correlatable with other magmatic arc exposures in Colombia and Ecuador. These units may represent the remnants of a single belt which includes several units from 4°N in Colombia and 5°S in Ecuador. This arc is related to the widespread Jurassic continental magmatic arc setting that characterized the continental margins of the Americas after Pangea break-up

U-Pb LA-ICP-MS GEOCHRONOLOGY AND REGIONAL CORRELATION OF MIDDLE JURASSIC INTRUSIVE ROCKS FROM THE GARZON MASSIF, UPPER MAGDALENA VALLEY AND CENTRAL CORDILLERA, SOUTHERN COLOMBIA

Se presentan nuevas edades U-Pb en circones de cuatro unidades graníticas muestreadas a lo largo de una transecta SE-NW entre el Macizo de Garzón y la Serranía de las Minas (Cordillera Central), las cuales registran una actividad magmática en el Jurásico Medio en dos dominios espaciales y temporales diferentes: 189 Ma y 180 a 173 Ma. Estos cuatro granitoides tiene características mineralógicas y geoquímicas afines con un ambiente de arcomagmático continental. Los nuevos resultados sugieren que la margen continental al sur de Colombia incluye remanentes de elementos tectono-magmáticos formados por la subducción de la placa Farallón bajo la margen continental suramericana. Este magmatismo de arco del Jurásico medio es parte de la provincia de arco que se presenta a lo largo de los Andes, y es importante para el entendimiento de la dinámica tectónica y la paleogeografía que caracterizó el Mesozoico de los Andes del Norte. Palabras clave: Geocronología U-Pb, Colombia, Jurásico, Rocas intrusivas, Macizo de Garzón, CordilleraCentral.    New U-Pb zircon geochronology from four granitic units sampled along a southeast-northwest transect between the Garzón Massif and the Serranía de las Minas (Central Cordillera), records a Middle Jurassic magmatic activity with two different spatio-temporal domains at ca. 189 Ma and 180-173 Ma. Reconnaissance data suggest that the four granitoids are characterized by mineralogical and geochemical characteristics akin to acontinental magmatic arc setting. The new results suggest that the southern Colombian continental margin includes remnants of tectonomagmatic elements formed by the subduction of the Farallon plate under the South American continental margin. This Middle Jurassic arc magmatism is part of the broader Andean scale arc province, and is significant for understanding the tectonic and paleogeographic scenario that characterized the Mesozoic tectonic evolution of the Northern Andes. Key words: U-Pb geochronology, Colombia, Jurassic, Intrusive rocks, Garzón Massif, Central Cordillera. &nbsp

The missing Rheic Ocean magmatic arcs: Provenance analysis of Late Paleozoic

Early Carboniferous turbiditic sedimentary rocks in synorogenic basins located on both sides of the Rheic suture in SW Iberiawere studied for provenance analysis. An enigmatic feature of this suture, which resulted from closure of the Rheic Ocean with the amalgamation of Pangea in the Late Carboniferous, is that there are no recognizable mid- to Late Devonian subduction-related magmatic rocks,which should have been generated during the process of subduction, on either side of it. U–Pb LA–ICP-MS geochronology of detrital zircons from Early Carboniferous turbidites in the vicinity of the Rheic suture in SW Iberia, where it separates the Ossa–Morena Zone (with Gondwana continental basement) to the north from the South Portuguese Zone (with unknown/Meguma? continental basement) to the south, reveals the abundance of mid- to Late Devonian (51–81%) and Early Carboniferous (13–25%) ages. The Cabrela andMértola turbidites of the Ossa–Morena and South Portuguese zones, respectively, are largely devoid of older zircons, differing from the age spectra of detrital zircons in the oldest (Late Devonian) strata in the underlying South Portuguese Zone, which contain abundant Cambrian and Neoproterozoic ages. Mid- to Late Devonian zircons in the Cabrela Formation (age cluster at c. 391 Ma, Eifelian–Givetian transition) and Mértola Formation (age clusters at c. 369 Ma and at c. 387 Ma, Famennian and Givetian respectively) are attributable to a source terrane made up of magmatic rocks with a simple geological history lacking both multiple tectonic events and older continental basement. The terrane capa- ble of sourcing sediments dispersed on both sides of the suture is interpreted to have been completely re- moved by erosion in SW Iberia. Given that closure of the Rheic Ocean required subduction of its oceanic lithosphere and the absence of significant arc magmatism on either side of the Rheic suture, we suggest: 1) the source of the zircons in the SW Iberia basins was a short-lived Rheic ocean magmatic arc, and 2) given the lack of older zircons in the SW Iberia basins, this short-lived arc was probably developed in an intra-oceanic environment

Two-Stage Late Jurassic to Early Cretaceous Hydrothermal Activity in the Sakar Unit of Southeastern Bulgaria

Southeastern Bulgaria is composed of a variety of rocks from pre-Variscan (ca. 0.3 Ga) to pre-Alpine sensu lato (ca. 0.15 Ga) time. The Sakar Unit in this region comprises a series of granitoids and gneisses formed ormetamorphosed during these events. It is cut by a series of post-Variscan hydrothermal veins, yet lacks pervasiveAlpine deformation. It thus represents a key unit for detecting potential tectonism associatedwiththe enigmaticCimmerianOrogenic episode, but limitedgeochronologyhasbeenundertaken on this unit. Here we report age constraints on hydrothermal activity in the Sakar Pluton. The investigated veins containmainly albite–actinolite–chlorite–apatite–titanite–quartz–tourmaline–epidote and accessory minerals. The most common accessory minerals are rutile and molybdenite. Apatite and titanite from the same vein were dated by U–Pb LA–ICP-MS geochronology. These dates are interpreted as crystallization ages and are 149 7Ma on apatite and 114 1Ma on titanite, respectively. These crystallization ages are the first to document two stages of hydrothermal activity during the late Jurassic to early Cretaceous, using U–Pb geochronology, and its association with the Cimmerian orogenesis. The Cimmerian tectono-thermal episode is well-documented further to the east in the Eastern Strandja Massif granitoids. However, these are the first documented ages from the western parts of the Strandja Massif, in the Sakar Unit. These ages also temporally overlap with previously published Ar–Ar and K–Ar cooling ages, and firmly establish that the Cimmerian orogeny in the studied area included both tectonic and hydrothermal activity. Such hydrothermal activity likely accounted for the intense albitization found in the Sakar Unit

Peculiar characteristics of the Bjerkreim-Sokndal intrusion (Rogaland anorthosite province, S. Norway) and implications for the layering formation

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Mapeamento geológico de rochas ígneas: Um estudo de caso na região de Garzón, Cordilheira Oriental dos Andes Colombianos

Granitos Jurássicos (sensu lato) e rochas relacionadas são as rochas mais comuns que afloram na Cordilheira Oriental da Colômbia no norte dos Andes. Apresenta-se um mapa e uma caracterização detalhada da diversidade petrográfica dos granitos jurássicos e rochas subvulcânicas relacionadas que afloram na região de Garzón, extremo sul da Cordilheira Oriental. Elaboraram-se novos mapas geológicos para os Maciços Plutônicos de Algeciras e Altamira, baseados nos conceitos descritivos de fácies e associações de fácies petrográficas, petrografia detalhada e caracterização mineralógica dos tipos de granitos observados. Oito fácies petrográficas ou associações de fácies plutônicas e três subvulcânicas foram reconhecidas e mapeadas no Maciço Plutônico de Algeciras e outras cinco no Maciço Plutônico de Altamira. Hornblenda biotita granitos (sieno- e monzogranitos) predominam no primeiro maciço, enquanto leucogranitos são predominantes no segundo. Um padrão zonado de distribuição de fácies foi mapeado no Maciço Plutônico de Algeciras. Corpos menores e/ou diques de pórfiros félsicos (dacitos e riolitos) e diques máficos-intermediários sin-plutônicos (principalmente microdioritos) cortam as principais rochas plutônicas nos dois maciços. Características geológicas e petrográficas (e.g. texturas micrográficas) sugerem níveis de colocação relativamente rasos para as rochas plutônicas e soerguimento e erosão levemente mais acentuados na região norte da área estudada. Estruturas planares de deformação em estado sólido e a orientação dos diques mapeados são compatíveis com movimentações dextrais do Sistema de Falhas de Algeciras, orientado SSW-NNE, em um regime transpressivo, associado com importante compressão e convergência oblíqua durante o Jurássico.Jurassic granites (sensu lato) and related rocks are the most abundant rocks cropping out in the Eastern Cordillera of Colombia in the northern Andes. We present an attempt to map and characterize in detail the petrographic diversity of the Jurassic granites and related subvolcanic rocks emplaced in the Garzón region, southernmost the Eastern Cordillera. We also provide new geological maps for the Algeciras and Altamira Plutonic Massifs based on descriptive concepts of the petrographic facies and facies associations and detailed petrographic and mineralogical characterizations of the observed granite types. Eight plutonic and three subvolcanic petrographic facies or facies associations were mapped in the Algeciras Plutonic Massif, and another five in the Altamira Plutonic Massif. Hornblende biotite granites (syeno- and monzogranites) are the main plutonic types constituting the first massif, while leucogranites prevail in the second massif; a zoned facies distribution was mapped in the Algeciras Plutonic Massif. Felsic porphyries (dacite and rhyolite) crop out as minor irregular intrusive bodies or dikes and mafic-intermediate syn-plutonic dikes (mostly microdiorites) cross cut the main plutonic rocks in both massifs. Geological and petrographic characteristics (e.g. micrographic textures) suggest relatively shallow emplacement levels for the plutonic rocks as well as slightly high uplift and erosion rates at the north of the studied area. Local penetrative solid-state planar structures and dike orientations conform with dextral strike-slip movements along the SSW-NNE trending Algeciras Fault System in a transpressional regime associated with a major compressive and oblique convergence in Jurassic ages

Timing of magmatic-hydrothermal activity in the Variscan Orogenic Belt: LA-ICP-MS U–Pb geochronology of skarn-related garnet from the Schwarzenberg District, Erzgebirge

[EN] Here, we present in situ U-Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) ages of andradite-grossular garnet from four magmatic-hydrothermal polymetallic skarn prospects in the Schwarzenberg District, Erzgebirge (Germany), located in the internal zone of the Variscan Orogenic Belt. Within the geochronological framework of igneous rocks and hydrothermal mineralization in the Erzgebirge, the obtained garnet ages define three distinct episodes of Variscan skarn formation: (I) early late-collisional mineralization (338-331 Ma) recording the onset of magmatic-hydrothermal fluid flow shortly after the peak metamorphic event, (II) late-collisional mineralization (similar to 327-310 Ma) related to the emplacement of large peraluminous granites following large-scale extension caused by orogenic collapse and (III) post-collisional mineralization (similar to 310-295 Ma) contemporaneous with widespread volcanism associated with Permian crustal reorganization. Our results demonstrate that the formation of skarns in the Schwarzenberg District occurred episodically in all sub-stages of the Variscan orogenic cycle over a time range of at least 40 Ma. This observation is consistent with the age range of available geochronological data related to magmatic-hydrothermal ore deposits from other internal zones of the Variscan Orogenic Belt in central and western Europe. In analogy to the time-space relationship of major porphyry-Cu belts in South America, the congruent magmatic-hydrothermal evolution in the internal zones and the distinctly later (by similar to 30 Ma) occurrence of magmatic-hydrothermal ore deposits in the external zones of the Variscan Orogenic Belt may be interpreted as a function of their tectonic position relative to the Variscan collisional front.Open Access funding enabled and organized by Projekt DEAL. This study was funded by the Federal State of Saxony and the European Social Fund (Grant no. 100339454 received by M. Burisch

Reinvestigating the relationships between the Badenoch Group, Dalradian Supergroup and the Grampian Shear Zone

In situ monazite and titanite U-Pb LA-ICP-MS geochronology and combined petrological and microstructural analysis has revealed both Neoproterozoic and Ordovician deformation within the Grampian Shear Zone (GSZ), central Scotland. The Grampian Shear Zone has been posited to separate the Dalradian Supergroup from the Badenoch Group, representing either, a structural break, an orogenic unconformity or a shear zone that predominantly affects the top of the Glen Banchor Subgroup. New monazite U-Pb data gave Neoproterozoic ages which provide a youngest age of deformation/monazite growth within the GSZ at 824 ± 2.73Ma, with subsequent Neoproterozoic resetting of the monazite at 751.81 ± 3.56Ma and a further resetting during the Early Ordovician/Late Cambrian at 485.85 ± 2.63Ma, from within sample RG1716. Monazite U-Pb data from sample RG1718 Ruthven Semipelite of the Corrieyairack Sub-Group (Grampian Group, of the Dalradian Supergroup) produced two distinct populations of monazite, one population of monazite growth associated with the Grampian Orogeny at 475.03 ± 1.11Ma, the other population from a detrital domain within the monazite produced lower intercept age of 475.51 ± 2.84Ma and an upper intercept age of 3004.7 ± 58Ma, revealing that the Ruthven Semipelite shows a distinct lack of Neoproterozoic deformation. The titanite U-Pb data collected produced an age of 467.45 ± 1.84Ma from Sample RG1703 a sheared garnet amphibolite from within the GSZ and 469 ± 0.3Ma from sample RG1710 a Badenoch Group lithology. The titanites dated within the Garnet amphibolite are from a titanite population within the garnet cores and must date or predate the onset of garnet growth. These garnets subsequently developed large strain shadows indicating a reactivation of the GSZ after the garnet growth. Sample RG1710s titanite population contains rare rutile cores, biotite quartz intergrowth textures and, cordierite pseudomorphs indicating a higher grade mineralogy predating the titanites. This mineralogy may be related to eclogite deformation within the Badenoch Group which predates migmitization of the Dava Sub-Group

Final Inversion of the Midcontinent Rift During the Rigolet Phase of the Grenvillian Orogeny

Despite being a prominent continental-scale feature, the late Mesoproterozoic North American Midcontinent Rift did not result in the break-up of Laurentia, and subsequently underwent structural inversion. The timing of inversion is critical for constraining far-field effects of orogenesis and processes associated with the rift\u27s failure. The Keweenaw fault in northern Michigan (USA) is a major thrust structure associated with rift inversion; it places ca. 1093 Ma rift volcanic rocks atop the post-rift Jacobsville Formation, which is folded in its footwall. Previous detrital zircon (DZ) U-Pb geochronology conducted by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) assigned a ca. 950 Ma maximum age to the Jacobsville Formation and led researchers to interpret its deposition and deformation as postdating the ca. 1090–980 Ma Grenvillian Orogeny. In this study, we reproduced similar DZ dates using LA-ICP-MS and then dated 19 of the youngest DZ grains using high-precision chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS). The youngest DZ dated by CA-ID-TIMS at 992.51 ± 0.64 Ma (2σ) redefines the maximum depositional age of the Jacobsville Formation and overlaps with a U-Pb LA-ICP-MS date of 985.5 ± 35.8 Ma (2σ) for late-kinematic calcite veins within the brecciated Keweenaw fault zone. Collectively, these data are interpreted to constrain deposition of the Jacobsville Formation and final rift inversion to have occurred during the 1010–980 Ma Rigolet Phase of the Grenvillian Orogeny, following an earlier phase of Ottawan inversion. Far-field deformation propagated \u3e500 km into the continental interior during the Ottawan and Rigolet phases of the Grenvillian Orogeny