ABSTRACT The gold and silver deposits of the Vetas-California mining district are hosted in Paleozoic gneisses and Mesozoic granites of the Santander massif in the Eastern Cordillera of Colombia, far from the northern Andean volcanic arc. In the California area, there is ambiguity in defining the epithermal-type metallogenic model with high to intermediate sulfidation due to the presence of Late Triassic-Early Jurassic and Miocene magmatism. The best-known hydrothermal episodes comprise two early porphyritic-style phases: a) characterized by a propylitic alteration with molybdenite of the ∼10.1 Ma-old La Mascota breccia, related to granodiorite porphyries and smaller-volume rhyodacitic dykes; and b) attributed to a magmatic-hydrothermal system due to phyllic alteration associated with quartz-pyrite veins with hydrothermal sericite dated at ∼3.4 Ma. These two hydrothermal episodes were followed by four epithermal phases related to the development of multiphase hydrothermal breccias and quartz-alunite alteration, defined by bornite, covellite, and chalcopyrite, alongside wolframite, enargite, and sphalerite, with gold and silver mineralization between ∼2.6 and ∼ 1.6 Ma. To understand the relationship of the emplacement of the porphyries and the subsequent auro-argentiferous enrichments to the deformation front observed in the Pamplona buttress, to the east of the Santander Massif, a 4D structural model of the mineralization is formulated here. This model is based on the spatial analysis of the stresses responsible for the La Baja-Angostura dextral fault in terms of the regional kinematics of the Bucaramanga sinistral fault. It is considered that the SW sector of the deposit area corresponds to a well-defined, tabular, sub-vertical body of the La Mascota breccia. On the other hand, the NE sector in the La Baja-Angostura fault is expressed as a topographically elevated right horsetail splay, which controls the more disseminated distribution of the mineralization by means of veinlet swarms arranged in an ∼E-W direction. The disseminated mineralization of Vetas-California was probably favored by late thermal expansion-contraction events in the gneissic sockets, which allowed the accumulation and precipitation of boiling solutions rich in volatiles and elements of economic interest.

RESUMEN Los depósitos auroargentíferos del distrito minero Vetas-California están alojados en gneises paleozoicos y rocas ígneas mesozoicas del Macizo de Santander en la cordillera Oriental de Colombia, a cientos de kilómetros del volcanismo septentrional Norandino. En el área de California, existe ambigüedad en la definición del modelo metalogénico de tipo epitermal con sulfuración alta a intermedia debido a la presencia de magmatismo del Triásico tardío-Jurásico temprano y Mioceno. Los episodios hidrotermales mejor conocidos comprenden dos fases tempranas de estilo porfirítico: a) una caracterizada por una alteración propilítica con molibdenita de la Brecha La Mascota, de edad ∼10,1 Ma, relacionada con pórfidos de granodiorita y diques riodacíticos de menor volumen; b) otra atribuida a un sistema magmático-hidrotermal con alteración fílica asociada a filones y vetas de cuarzo-pirita con sericita hidrotermal de edad ∼3,4 Ma. A estos episodios le suceden cuatro fases de estilo epitermal relacionadas con el desarrollo de brechas hidrotermales multifásicas y con alteración de cuarzo-alunita, definidas por bornita, covelina y calcopirita, además de wolframita, enargita y esfalerita, con mineralización de oro y plata entre los ∼2,6 y ∼1,6 Ma. En la presente contribución se formula una hipótesis del modelo 4D del control estructural de las mineralizaciones para comprender la relación del emplazamiento de los pórfidos y los subsecuentes enriquecimientos auroargentíferos con respecto al frente de deformación reconocido en el Contrafuerte de Pamplona, al oriente del Macizo de Santander. Para ello, se analizan los esfuerzos responsables de la falla dextral La Baja-Angostura a partir de la cinemática regional de la falla sinistral de Bucaramanga. Se establece que el sector SO del área de mineralización corresponde a un cuerpo bien definido, tabular, subvertical, de la Brecha La Mascota. En el sector NE, en cambio, la Falla La Baja-Angostura se expresa como una cola de caballo (horsetail) derecha, topográficamente más elevada, la que controla la distribución diseminada de la mineralización mediante enjambres de vetillas subordinadas dispuestas en dirección principal ∼E-O. La mineralización diseminada de las Vetas-California fue favorecida probablemente por fenómenos tardíos de dilatación-contracción térmica de los encajantes gnéisicos, que permitieron la acumulación y precipitación de soluciones en ebullición ricas tanto en volátiles como en sustancias de interés económico.

ABSTRACT The Andean intra-arc is characterized by large-scale continuous lineaments, often the direct surface expression of tectonic structures. In this study, we analyze the main lineaments around the Laguna del Maule Volcanic Complex, Central Chile (∼36° S), to shed light on the main tectonic processes. We show that the lineament directions are consistent with structures based on a theoretical Riedel model and suggest the occurrence of two conjugate Riedel shears crossing Laguna del Maule. This structural arrangement can accommodate deformation related to either a transtensional regime, having a WNW-oriented master fault (Laguna Fea Fault), or a transpressional regime, characterized by NNE-oriented master faults (e.g., Melado Fault). In this context, the NE-striking Troncoso Fault would be a long-lived dextral fault compatible with both regimes. According to the Riedel model, ENE-oriented lineaments are predicted to be tensional structures, whilst NW-oriented structures (e.g., Los Cóndores Fault) would correspond to P-type structures accommodating compressional deformation. This tectonic architecture, characterized by the most intense deformation just at the intersection between shears, has likely promoted magma accumulation and would explain the compositional variability at Laguna del Maule. This study therefore demonstrates the usefulness of oriented lineament maps in interpreting regional tectonics for volcanically active areas.

RESUMEN El intrarco andino está caracterizado por la presencia de lineamientos continuos de carácter regional, los que frecuentemente son la expresión superficial directa de estructuras tectónicas mayores. En este estudio se presenta un análisis de los principales lineamientos en torno al Complejo Volcánico Laguna del Maule, ubicado en Chile Central (∼36° S), para proveer inferencias sobre los principales procesos tectónicos en la zona. Los resultados obtenidos indican que las direcciones de los lineamientos principales pueden ser explicados por un modelo teórico de deformación Riedel. La distribución espacial de ellos sugiere la ocurrencia de dos bandas de cizalla conjugadas, las que dividen la Laguna del Maule. Esta disposición estructural puede acomodar la deformación asociada tanto a un régimen transtensional, caracterizado por una falla maestra orientada ONO (Falla Laguna Fea), como a un régimen transpresional, caracterizado por fallas maestras orientadas al NNE (e.g., Falla Melado). En este contexto, la Falla Troncoso, de orientación NE, sería de tipo dextral transcurrente bajo cualquiera de los dos regímenes. Los lineamientos ENE, en tanto, corresponderían a estructuras tensionales, mientras que los lineamientos NO (e.g., Falla Los Cóndores) serían estructuras tipo P, acomodando la deformación compresional. Este marco tectono-estructural, caracterizado por una deformación más intensa donde las bandas de cizalla se cortan, facilitaría la acumulación de magma en profundidad y explicaría la variación composicional de los productos volcánicos del Complejo Volcánico Laguna del Maule. Este estudio, en consecuencia, demuestra que los mapas de lineamientos orientados pueden ser de gran utilidad para interpretar la tectónica regional en áreas volcánicas activas.

Abstract Net erosion recorded in lithological columns of hundreds of wells from the proximal domain of the Sergipe–Alagoas Basin was quantified through palaeoburial indicators: transit time sonic logs (DT) and vitrinite reflectance profiles (VRe). The preferred determinations with DT logs of pelitic rocks compound a large database and are less subject to variations in sampling and laboratory procedures. The sonic log profiles of 485 wells have been used for the calculation of the net erosion grid, while just 60 VRe profiles have been used for this purpose. Net erosion varies typically from 100 to 700 m in the Sergipe Sub-basin to the south, probably as a result of isostatic compensation to the sedimentary loads of the post-rift stratigraphic sequences. The Alagoas Sub-basin to the north stands as the most eroded. The average net erosion in the Alagoas SB is around 750 m but reaches more than 1,200 m in the north. The main cause of the erosion of the syn-rift strata in the Alagoas SB is probably the long-time sub-aerial exposure of uplifted rift flanks. Late Albian tectonic inversion, focused on northern Alagoas SB, enhanced erosion as evidenced in seismic sections, especially those parallel to the coast. SergipeAlagoas indicators (DT VRe. . (VRe) procedures 48 grid 6 purpose 10 70 Subbasin Sub basin south postrift post sequences eroded 75 1200 1 200 1,20 synrift syn longtime long subaerial sub aerial flanks inversion sections coast (VRe 4 7 120 20 1,2 12 2 1,

Abstract The lithostratigraphic units that conform the Sorocayense Group and fill the Sorocayense-Hilario sub-basin represent an alluvial-fluvial-lacustrine succession with significant volcanic supply during its deposition. They are namely the Cerro Colorado del Cementerio, Agua de los Pajaritos, Monina, Hilario and El Alcázar formations and present several carbonate levels. The genesis, diagenesis, and main controlling factors on continental carbonates present a means to understand basin evolution through the study of their petrography and chemical elemental composition through cathodoluminescence techniques. We have identified six microfacies: a) homogeneous micrite, b) bioclastic micrite, c) dolomicrite, d) laminated micrite, e) oncolitic packstone, and f) sparitic carbonate. Among these microfacies, six cementation and alteration phases have been identified: a) micritization, b) mechanical compaction, c) calcitic cementation, d) sparitic cementation, e) microsparitic cementation, and f) chemical compaction. This analysis allowed establishing a chronology of the diagenetic modifications undergone by the carbonates. Results support diagenesis was controlled mainly by tectonics showing major impact in carbonate facies identified at the flexural margin of the rift. The effect would have been linked to exertion of a paleohydrological effect favoring lateral meteoric water migration through faulting. The presence of dolomite in some of the microfacies is linked to the presence of montmorillonite as the dominant Mg-rich-phyllosilicate in clay assemblages most likely acting as the potential source. In turn, Mg is more likely to be replaced by Mn leading to luminescent carbonate microfacies.

Resumen Diagénesis de los carbonatos continentales del margen flexural de la subcuenca Sorocayense-Hilario, Argentina. Las unidades litoestratigráficas que conforman el Grupo Sorocayense y que constituyen el relleno de la subcuenca Sorocayense-Hilario representan sistemas aluviales-fluviales-lacustres con aporte volcánico significativo durante su depositación. Estas unidades corresponden a las formaciones: Cerro Colorado del Cementerio, Agua de los Pajaritos, Monina, Hilario y El Alcázar y cada una de ellas contiene niveles carbonáticos. Estos carbonatos continentales constituyen un medio útil para entender la evolución de la subcuenca a través del estudio petrográfico complementado con técnicas de catodoluminiscencia. Estos estudios han permitido entender la génesis y diagénesis carbonática e inferir qué factores principales la controlaron. Se identificaron seis microfacies: a) micrita homogénea, b) micrita bioclástica, c) dolomicrita, d) micrita laminada, e) packstone oncolítico, y f) carbonato esparítico. En tales microfacies, se identificaron seis fases de cementación y alteración: a) micritización, b) compactación mecánica, c) cementación calcítica, d) cementación esparítica, e) cementación microesparítica, y f) compactación química. Estos análisis permitieron establecer una cronología diagenética y apoyan la hipótesis de que la diagénesis fue controlada por la tectónica, con mayor impacto en las facies carbonáticas asociadas al margen flexural de la subcuenca. El principal efecto habría sido por medio de la acción paleohidrológica, lo que favoreció la migración lateral de agua meteórica a través de los fallamientos. La presencia de dolomita en algunas microfacies se vincula con la composición predominantemente montmorillonítica de los ensambles de arcillas que habría aportado el Mg. A su vez, en los carbonatos, el Mg tiende a ser fácilmente reemplazado por Mn, lo que causa incremento de la luminiscencia.

Abstract The hydrological basins can be considered sources of relevant information about the evolution of the Earth’s crust since the relief forms that define the hydrographic channels are the resultant of the interaction between tectonics, pedogenics, intemperics and thermals processes. The geothermal field of Muriaé watershed was evaluated using eight (8) thermal logs and twenty-two (22) geochemical logs. The structural lineaments evidenced on the surface were interpreted jointly with the identification of sixty-five (65) magnetic lineaments from airborne magnetic data interpretation. The depths of these structures were range from the surface up to 4.5 km. The interpreted data allowed identification of regional tectonics features in the NE-SW direction, where the identified magnetic lineaments show a spatial correlation with accentuated topographic structures. The differences in the depths of the magnetic bodies found in conjunction with the heat flow distribution, evidence two distinct thermostructural zones: A1 (east part) presenting heat flow values within the average (approximately 60$\frac{mW Earths Earth s pedogenics processes 8 (8 twentytwo twenty 22 (22 sixtyfive sixty five 65 (65 interpretation 45 4 5 4. km NESW NE SW direction distribution zones A east part approximately 60$\fracmW 60fracmW fracmW 60$\frac mW 60 frac ( 2 (2 6 (6 60frac

Abstract This article discusses the geochemical and petrological evolution of the São José do Campestre granite complex (SJCgr), the last Neoarchean plutonic event so far described in the São José do Campestre massif in NE Brazil. We report field, petrographic, zircon U-Pb dating, and whole rock and mineral chemistry for representative SJCgr samples. Laser ablation zircon U-Pb data indicate that the granite emplacement took place at 2664 ± 13 Ma. The rocks comprising the SJCgr have relatively well-preserved primary textures and fabrics and compositions varying from gabbro to syenogranite. Major and trace element contents reveal a metaluminous, calc-alkaline through transitional to alkaline signature, and LILE- and LREE-enriched series analogous to late Archean sanukitoid and modern arc granitoid. The evolution of the SJCgr is envisaged as follows: (1st) partial melting of a metasomatized mantle (2.5–3.0 GPa, ~85–102 km, 1,000–1,200°C), generating a basaltic to basaltic andesitic magma; (2nd) fractional crystallization (FC) of olivine at mantle or lower crustal depth, leading to the parental magmas of the magmatic series; and (3rd) 40–15% FC of olivine gabbro-norite and olivine monzonite cumulates (400–600 MPa, 15–23 km). The SJCgr shares similarities with post-collisional granitoids and, thus, would represent the last Neoarchean episode of mantle-derived magma in Northeastern Brazil. SJCgr, , (SJCgr) Brazil field petrographic UPb U Pb dating samples 266 1 Ma wellpreserved well preserved syenogranite metaluminous calcalkaline calc signature LILE LREEenriched LREE enriched granitoid follows 1st st (1st 2.5–3.0 2530 2 5 3 0 (2.5–3. GPa 85102 85 102 ~85–10 km 1,000–1,200°C, 10001200C C 1,000–1,200°C 000 200 1,000–1,200°C) 2nd nd (2nd (FC depth 3rd rd (3rd 4015 40 15 40–15 gabbronorite norite 400–600 400600 400 600 (400–60 MPa 1523 23 15–2 km. . km) postcollisional post collisional thus mantlederived derived (SJCgr 26 2.5–3. 253 (2.5–3 8510 8 10 ~85–1 00 20 401 4 40–1 400–60 40060 60 (400–6 152 15– 2.5–3 25 (2.5– 851 ~85– 40– 400–6 4006 6 (400– 2.5– (2.5 ~85 400– (400 2.5 (2. ~8 (40 2. (2 ~ (4 (

Abstract The Bonsucesso zinc-lead (Zn-Pb) sulfide deposit is hosted in carbonate rocks from the Vazante Group (transition of the Mesoproterozoic to the Neoproterozoic time), northwest of Minas Gerais State, Brazil. Regional deformation is associated with the thin-skinned tectonics that led to the formation of the foreland zone of the Brasília Orogen during the Neoproterozoic. These orogenic processes are the trigger of Zn-Pb mineralization in many base-metal deposits in the Vazante Group. Here, we describe the ore textures and the structures of the deposit to define its structural controls in deposit scale and formulate hypotheses about its forming process in the context of other Vazante Zn-Pb deposits. Mineralization distribution is controlled by a high-angle fault zone striking NNW and dipping 60° to WSW. Fault-related fractures functioned as pathways for Zn-Pb-rich fluids to be redistributed and crystallize where chemical conditions were adequate. Mineralization was likely formed in an extensional setting in breccia zones controlled by flexurally induced normal faults related to development of the foreland basin of Brasília Orogen. Later, the entire Vazante sequence underwent an inversion process and extensional structures were reactivated or obliterated. Finally, an understanding of local controls may be of good use to target exploration for new orebodies in the district scale. zinclead zinc lead ZnPb Zn Pb (Zn-Pb transition time, time , time) State Brazil thinskinned thin skinned basemetal base metal Here highangle high angle 60 WSW Faultrelated Fault ZnPbrich rich adequate Later obliterated Finally 6

RESUMEN Las secuencias sedimentarias con niveles evaporíticos presentan estructuras tridimensionales complejas debido a movimientos halocinéticos (tectónica salina). En el Anticlinal de Zipaquirá, ubicado en la Cordillera Oriental de Colombia, se reportan niveles salinos en las unidades del Cretácico Temprano. Este trabajo analizó estructuralmente el Anticlinal de Zipaquirá, basado en modelos análogos que simulan la relación entre la tectónica salina y las zonas trasversales que limitan y segmentan esta estructura. Los modelos se realizaron en una mesa de deformación tipo seducción con velocidad constante de desplazamiento. Los mismos simulan anisotropías de basamento mediante un bloque rígido de madera constituido por dos rampas frontales de 30° de inclinación conectadas por una rampa lateral. Adyacente, se dispone una capa de fluido no-newtoniano y capas de arena cuarzosa fina de color variable. Se efectuaron tres configuraciones con diferentes distribuciones de la capa de fluido no-newtoniano: A) continua delgada, B) discontinua y C) continua espesa. Para cada configuración se llevaron a cabo al menos 15 experimentos. Los resultados del modelamiento análogo mostraron un cuerpo salino en el núcleo del anticlinal que es cortado por fallas inversas, formando una estructura de lámina de sal paralela a la estratificación. Las estructuras observadas, como almohadas de sal, glaciares de sal, láminas de sal y lenguas de sal, indican estilos estructurales compresivos de madurez intermedia a alta. El modelo discontinuo resultó ser el más coherente, ya que la rampa lateral no presentaba niveles evaporíticos, lo cual coincide con la observación en la naturaleza. La Falla transversal del Neusa se representó en el modelo como la rampa lateral, explicando la localización de los niveles salinos en la zona sur del Anticlinal de Zipaquirá. Por último, la evolución de los modelos mostró rotaciones horarias cercanas a la rampa lateral, consistentes con los patrones de rotaciones horarias reportados en la zona axial de la Cordillera Oriental.

ABSTRACT Sedimentary sequences containing evaporitic levels exhibit complex three-dimensional structures due to halokinetic movements known as salt tectonics. In the Anticlinal de Zipaquirá, located in the Cordillera Oriental of Colombia, saline levels are reported within the Lower Cretaceous units. This study conducted a structural analysis of the evolution of the Anticlinal de Zipaquirá, based on analogue models that simulate the relationship between salt tectonics and the transverse zones that bound and segment this structure. The models were constructed on a sandbox-type deformation table, maintaining a constant displacement velocity. The models simulate basement anisotropies using a rigid wooden block consisting of two frontal ramps inclined at 30° connected by a lateral ramp. Adjacent to this block, a layer of non-newtonian fluid and variable-colored fine quartz sand layers were arranged. Three configurations were implemented with different distributions of the non-newtonian fluid layer: A) thin continuous, B) discontinuous, and C) thick continuous. At least 15 experiments were conducted for each configuration. The results of the analogue modeling showed that the salt body in the core of the anticline is cut by reverse faults, forming a parallel salt sheet structure to the stratification. The observed structures, such as salt pillows, salt glaciers, salt sheets, and salt tongues, indicate compressive structural styles of intermediate to high maturity. The discontinuous model proved to be the most coherent since the lateral ramp did not exhibit evaporitic levels, aligning with observations in nature. The Neusa transverse Fault was represented by the lateral ramp in the model, explaining the localization of saline levels in the southern zone of the Anticlinal de Zipaquirá. Finally, the evolution of the models revealed clockwise rotations near the lateral ramp, consistent with the reported patterns of clockwise rotations in the axial zone of the Cordillera Oriental.

RESUMEN La Formación La Quinta es una unidad volcano-sedimentaria del Triásico-Jurásico que aflora en ambos flancos de la serranía del Perijá y en la parte occidental de Los Andes de Mérida, en Colombia y Venezuela. Está conformada por capas de lodolita y arenisca rojiza intercaladas con lavas basálticas a riolíticas e ignimbritas. Esta sucesión está localmente intruida por cuerpos hipoabisales riolíticos-dacíticos, diques félsicos y stocks monzodioríticos. El volcanismo registrado en la Formación La Quinta abarca un rango composicional amplio en la serie subalcalina que incluye: basalto alcalino-andesita basáltica (plagioclasa+augita), andesita-traquiandesita-dacita (plagioclasa+augita+cuarzo+anfíbol) y riolita-riolita alcalina (cuarzo+sanidina+plagioclasa+biotita). Los minerales accesorios son magnetita, ilmenita, hema-tita, circón y apatito, lo que sugiere condiciones oxidantes en los magmas (desde +1.2 Ni-NiO hasta el campo de hema-tita-magnetita). Análisis de geotermobarometría en clinopiroxeno (~1120 °C y 4.6 kbar) indican que su cristalización ocurrió en la porción media de una corteza continental normal a engrosada (26-49 km), y precedió al fraccionamiento de ilmenita-magnetita (~720 °C). Adicionalmente, las rocas exhiben alteración de calcisilicatos (grosularia-andradita hidratada, epidota y ceolitas), en asociación con posibles depósitos cupríferos estrato-ligados. Las evidencias mineralógicas y geoquímicas halladas sugieren que estas rocas pertenecen a una suite comagmática donde los procesos de diferenciación estuvieron gobernados por la cristalización fraccionada a baja presión y la asimilación parcial de la corteza media. Asimismo, estas rocas se formaron a partir de grados de fusión parcial bajos en una lherzolita de espinela (o una fuente enriquecida) dentro de un ajuste tectónico suprasubducción de naturaleza híbrida entre un arco y un rift. De tal modo, en este artículo se propone un escenario tectónico mixto en el cual la placa Farallón subducía bajo la placa Suramericana al mismo tiempo que se generaban cuencas transtensionales ligadas al rompimiento de Pangea. De allí la existencia de la actividad volcánica con firma de arco en La Quinta, que estaba ubicada detrás del arco principal.

ABSTRACT The La Quinta Formation is a Triassic-Jurassic volcano-sedimentary unit exposed in Colombia and Venezuela, that crops out along both flanks of the Serranía del Perijá and in western Mérida Andes. It is composed of reddish mudsto-nes and sandstones interbedded with basaltic-to-rhyolitic lava flows and ignimbrites. This succession is locally intruded by dacitic-rhyolitic hypabyssal bodies, felsic dikes and small monzodioritic intrusions. The volcanism recorded in La Quinta comprises the whole subalkaline compositional spectrum from basaltic andesites-alkali basalts (plagioclase-au-gite), though andesites-trachyandesites-dacites (plagioclase-augite-ß quartz-amphibole) and rhyolites-alkali rhyolites (ß quartz-sanidine-plagioclase-biotite). Magnetite, ilmenite, hematite, zircon and apatite are recurrent accessory phases and suggest dominant oxidized conditions (+1.2 Ni-NiO to hematite-magnetite buffers) in the magmas. Clinopyroxene and ilmenite-magnetite geothermobarometry suggest an early crystallization of the former (ca. 1120 °C and 4.6 kbar) in the middle portion of a normal-to-thickened continental crust (26-49 km), and later fractionation of the Fe oxides (ca. 720 °C). In addition, some samples exhibit calc-silicate alteration formed of hydrated grossular-andradite, epidote and zeolites in association with possible sediment-hosted stratiform copper occurrences. According to mineralogical and geochemical evidence, these rocks belong to a single comagmatic suite in which differentiation processes were driven by low-pressure fractional crystallization and middle-crustal assimilation. Moreover, these rocks exhibit geochemical features indicative of low degrees of partial melting of a spinel lherzolite (or an enriched source) in a hybrid setting between subduction-related arc and intracontinental rifting. Thus, we propose a mixed tectonic scenario in which subduction of the Farallon plate beneath western South America combined with transtensional tectonics resulting from the break-up of Pangea, generated volcanic activity with an inherited arc-signature behind (landward) the arc axis.

Abstract The main purpose of the present study is to assess the role of active tectonics on soil radon emanation level across two tectonically active structures of the Northern Dead Sea Fault (NDSF) northwestern Syria: namely, the Qastoon and the Al-Harif fault segments. Radon measurements were basically directed by the results drawn from earlier archaeoseismic and paleoseismic studies in Al-Harif, besides integrated geophysical and morphotectonic survey at the Qastoon site. A total of 80 soil radon gas measurements were performed at 75 cm sampling depth, using AlphaGUARD PQ 2000Pro radon detector. The background range of normal radon emission from local soil was determined in an area located far from the influence of the tectonic disturbances. The obtained radon data were statistically analyzed and the mean values were standardized in terms of magnitude probability which enhances the comparison process facilitating the separation of normal radon variations from other anomalous or geotectonic related values. The overall results revealed remarkable occurrences of fault-associated radon anomalies with maximum peak values of ~6 to 7 times above the background, trending in accordance with the predicted traces of the fault ruptures at the Qastoon and Al-Harif, respectively.

Resumen El objetivo principal del presente estudio es evaluar el papel de la tectónica activa en el nivel de emanación de radón del suelo en dos estructuras tectónicamente activas de la Falla del Mar Muerto del Norte (NDSF, por sus siglas en inglés, al noroeste de Siria, es decir, los segmentos de falla Qastoon y Al-Harif. Las mediciones de radón se basaro básicamente en los resultados extraídos de estudios arqueosísmicos y paleosísmicos anteriores en Al-Harif, además del estudio geofísico y morfotectónico integrado en el sitio de Qastoon. Se realizaron un total de 80 mediciones de gas radón en el suelo, a una profundidad de muestreo de 75 cm; se utilizó el detector de radón AlphaGUARD PQ 2000Pro. El rango de fondo de la emisión normal de radón del suelo local se determinó en un área ubicada lejos de la influencia de las perturbaciones tectónicas. Los datos de radón obtenidos se analizaron estadísticamente y los valores medios se estandarizaron en términos de probabilidad de magnitud, lo ciual mejora el proceso de comparación y facilita la separación de las variaciones normales del radón de otros valores anómalos o relacionados con la geotectónica. Los resultados generales revelaron ocurrencias notables de anomalías de radón asociadas con fallas con valores pico máximos de ~6 a 7 veces por encima del fondo, con una tendencia de acuerdo con los rastros previstos de rupturas de fallas en Qastoon y Al-Harif, respectivamente.

RESUMEN El análisis morfotectónico es un método útil, económico y ahorrador de tiempo para evaluar la actividad tectónica, especialmente en regiones grandes. En este artículo, el estudio morfotectónico se realizó en la ciudad de Kerman, en el sudeste de Irán, y que es parte de la zona estructural de Centro Irán. Si bien han ocurrido numerosos terremotos históricos o de detección instrumental en Kerman, hay una brecha en los registros de estos movimientos que oscurecen el estatus sísmico. El objetivo de este estudio es identificar las fallas activas y el riesgo sísmico asociado para la ciudad de Kerman. Para este propósito se examinaron siete índices geomórficos (índice del gradiente del perfil longitudinal, SL; asimetría de cuenca, Af; integral hipsométrica, Hi; relación de la parte baja del valle con la altura del valle, Vf; índice de la forma de cuenca, Bs; índice de sinuosidad de frentes montañosos, Smf, y factor de simetría topográfica transversal, T) en 51 cuencas en el área de estudio con Modelos de Elevación Digital (DEM) y mapas geológicos en un ambiente de Sistemas de Información Geográfica. Luego se calcularon dos clases de índices de actividad tectónica relativa para cada cuenca, por ejemplo Iat e Iat_T, desde la combinación de estos índices. El índice Iat_T fue elegido porque sus resultados muestran concordancia con la geología estructural y los registros sísmicos de la región. Finalmente, el área de estudio se dividió en tres regiones, de acuerdo con los valores Iat_T. Los análisis morfotectónicos indican que el sistema de fallas de Kuhbanan, especialmente en su extensión al sur, tiene el potencial de producir riesgos sísmicos serios a la ciudad de Kerman en el futuro; los pliegues relacionados con la falla Mahan-Jupar, la punta sur de la falla Jorjafk, la posible falla de Zangi-Abad, el sistema de fallas de Rafsanjan-Zarand, y la falla de Gowk se consideran como otras amenazas a Kerman. Además, este estudio muestra que el análisis morfotectónico es una herramienta confiable para evaluar la capacidad de las fallas y para determinar los tipos de falla y, además, para estimar el riesgo sismotectónico.

ABSTRACT The morphotectonic analysis is a useful time-saving and cost-effective method to assess tectonic activity, especially in large regions. In this paper, the morphotectonic study was carried out in Kerman city which is in the southeast of Iran and is a part of the Central Iran structural zone. Despite the occurrence of numerous historical and instrumental earthquakes around Kerman city, there is a gap in earthquake records of this city that has obscured its seismicity status. The aim of this study is to identify active faults and the associated seismic hazard to Kerman city. For this purpose, seven geomorphic indices namely stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), index of mountain front sinuosity (Smf) and Transverse Topographic Symmetry Factor (T) were examined for 51 basins of the study area, using digital elevation model (DEM) and geological maps in a GIS environment. Then, two kinds of relative tectonic activity indices were calculated for each basin, i.e., Iat and Iat_T, from the combination of these indices. The Iat_T was chosen because its results show better agreement with the structural geology and seismic records of this region. Finally, the study area was divided into three regions according to the Iat_T values. The morphotectonic analyses indicate that the Kuhbanan fault system, especially its southern splays, has the potential to produce serious seismic hazards to Kerman city in the future; the Mahan-Jupar fault-related folds, the southern tip of the Jorjafk fault, the probable fault of Zangi-Abad, the Rafsanjan-Zarand fault system, and Gowk fault are considered as other threats to Kerman city. Furthermore, this study reveals that morphotectonic analysis is a reliable tool to evaluate fault capability and to determine the fault types, and therefore to estimate seismotectonic hazard.

Abstract The Itataia phosphate-uranium deposit is located in the northwest segment of the Borborema Province in the Ceará Central Domain. The ore mineral is uranium-enriched microcrystalline collophanite apatite that occurs in massive bodies and lenses, stockworks, as well as hydrothermal and karst breccias associated with marble, calc-silicate rocks and gneisses of the Itataia Group. The deformational history of the deposit includes ductile structures developed in the final stages of thrust tectonics linked to the Brasilian orogeny and later brittle phases related to extensional tectonics, which influenced phosphorus and uranium remobilization and the formation of ore bodies. The main uranium anomaly coincides with the upper part of the Serrote da Igreja hill, bordered to the north by an E-W trending subvertical fault scarp that controls a wide valley. Geometric modeling of the geological data of the deposit provides a three-dimensional view of the geometry of ore bodies, distribution of host rock and faults that propagate beneath the surface and control mineralization, as well as the upper and lower limits of surface weathering. The three-dimensional geometric model using the GoCAD software served as a powerful tool for the analysis of the geology of the Itataia deposit, highlighting the geometry of rocks and ore bodies and the processes involved in the genesis of phosphate-uranium mineralization.

Abstract Microbialites are the most abundant life evidence in Precambrian sedimentary rocks. They are produced by microbial interaction activity and sedimentary processes reflecting paleoenvironmental conditions. The Ediacaran-Cambrian carbonate and siliciclastic successions in the Southern Amazon Craton in Central Brazil, provide a key opportunity to understand how the metazoan life coexisted with the microbial communities. The spatial and temporal distribution of microbialites as well as morphological and paleoenvironmental changes have been assessed, reinterpreting previous works and including new data from the Araras-Alto Paraguai and Corumbá basins. The deposition was controlled by subsidence and sea-level changes that affected these basins, considered extensions of epicontinental seas during the Gondwana assembly. The stromatolites are restricted to coastal deposits and experienced thriving flourishment intervals after the Marinoan Glaciation (635 Ma). Post-glacial transgression was marked by microbial colonization in shallow platforms represented by stratiform and giant domical stromatolites in the Araras-Alto Paraguai Basin. The continuity of the transgression generated a moderately deep aragonite sea at about 622 Ma. A progressive sea-level fall caused the implantation of coastal environments under greenhouse conditions with tidal flat and sabkha settings colonized by centimetric-scale stromatolites. The sea retreat was accompanied by progressive uplift, causing a moderate inversion of the basin and erosion of the succession until ~560 Ma with the deposition of the last preserved tidal flat deposits with the occurrence of thrombolites. The subsiding Corumbá Basin was the site of microbially-induced deposition of carbonates in a shallow platform connected to an offshore setting with the proliferation of metazoan straddling the Ediacaran-Cambrian boundary. Microbial communities were restricted to lagoon deposits during the Lower Cambrian transgression in the Araras-Alto Paraguai Basin and the last phase refers to the sea retreat towards southeast, developing a fluvial system connected with the arid and evaporitic tidal flats colonized by microbialites that lasted until the upper Cambrian. Except for the post-glacial stromatolites, the columnar and domal microbialite indicate that the coastal settings dominated the Ediacaran-Cambrian transition. The preservation of microbialites in the post-glacial intervals can be associated with the Mg-Ca-CO3 oversaturation in dolomitic platforms. The rapid calcification and ability to resist the dissolution and replacement have increased the stromatolites’ preservation potential reported here, where its well-preserved occurrence in tidal flats and sabkha occurs due to intense early diagenetic silicification. The change from carbonate accumulation to siliciclastic-rich environments contributed to the demise of microbially-induced strata. In general, the scarce coexistence between coastal stromatolite and metazoan-bearing marine deposits makes it challenging to establish a competitive relationship between these organisms, as previously postulated.

Abstract Tectonic rejuvenation has been widely described in ancient rifting areas of intraplate settings, despite extensive active tectonics being discontinued long ago. Various models have been invoked to justify such tectonic rejuvenation, suggesting that the long-term deformation in intraplate interiors may be more complex than once supposed. Inherited weakness zones, e.g., pre-existing faults are stress concentrators. However, not all weakness zones in plate interiors show tectonic rejuvenation and recognizing intraplate fault reactivation remains puzzling. Bedrock channels play an essential role in tectonically unstable landscapes and therefore they may unveil which pre-existing structures have been rejuvenated. Here we explore the Cinzas Catchment in order to investigate the interactions between tectonic rejuvenation, bedrock inheritance and geomorphic river signatures in an important Brazilian rifting feature, the Ponta Grossa Arch. We perform a geomorphic analysis combined with fieldwork, dating techniques and existing data to evaluate whether the geomorphic responses of the major rivers show perturbations related to the bedrock inheritance and post-rift rejuvenation. We also show that the interactions between river signatures and the bedrock fault zones are responses to post-rifting rejuvenation coupled with bedrock inheritance. This post-rifting rejuvenation is consistent with a mosaic of superimposed mechanisms which have been invoked by previous studies.

Abstract Sanukitoid rocks make up a complete magmatic series with distinct geochemical characteristics of TTG suites and granitoids from modern magmatic arcs and are regarded as markers of the transition from typically Archean geodynamics to modern plate tectonics. Although most known sanukitoid suites formed during the Neoarchean and Mesoarchean, numerous papers have characterized Paleoproterozoic magmatic arc granitoid rocks showing affinity with the sanukitoid series. This work presents new data from field, lithogeochemistry, zircon U-Pb geochronology, and Sm-Nd and Sr isotopic studies on granodioritic granulites with sanukitoid signatures from the Juiz de Fora Complex (JFC), one of the Paleoproterozoic tectonic components of the Minas-Bahia Orogenic System (MBOS), southern São Francisco Paleocontinent (southeastern Brazil). These rocks crystallized at ~2175 Ma and present values of εNdt between −4.0 and +0.5, TDM between 2.57 and 2.12 Ga, and 87Sr/86Sri between 0.6937 and 0.7137. We interpret these rocks as the result of crystallization of magmas from a hybrid mantle source extensively contaminated by crustal material during protracted subduction. In southeastern São Francisco Paleocontinent, the association of sanukitoid rocks with other magmatic arc rocks points to a complex and prolonged Rhyacian accretionary system similar to modern plate tectonics. tectonics Mesoarchean field lithogeochemistry UPb U Pb geochronology SmNd Sm Nd JFC, JFC , (JFC) MinasBahia Minas Bahia MBOS, MBOS (MBOS) Brazil. Brazil . Brazil) 2175 ~217 40 4 0 −4. 05 5 +0.5 257 2 57 2.5 212 12 2.1 Ga 87Sr86Sri SrSri 87Sr 86Sri Sri 06937 6937 0.693 07137 7137 0.7137 subduction (JFC (MBOS 217 ~21 −4 +0. 25 2. 21 1 0693 693 0.69 0713 713 0.713 ~2 − +0 069 69 0.6 071 71 0.71 ~ + 06 6 0. 07 7 0.7