Volcano-sedimentary Units Research Articles

Stratigraphy and geochronology of the Eocene volcanosedimentary units in the Hekimhan-Darende (Malatya) region: implications for the development of the Gürün Curl

Stratigraphy and geochronology of the Eocene volcanosedimentary units in the Hekimhan-Darende (Malatya) region: implications for the development of the Gürün Curl

Carboniferous–Early Permian volcano-sedimentary units from the northern margin of the North China Craton recorded subduction initiation in the Paleo-Asian Ocean

The precise timing of subduction initiation of the Paleo-Asian Ocean (PAO) in the northern margin of the North China Craton (NCC) remains controversial. In this study, we have conducted zircon UPb dating, whole-rock major and trace elements, and zircon Hf isotope analyses on metadacites and metamorphic greywackes from the Changde volcano-sedimentary rocks, feldspar quartz sandstones and argillaceous siltstones from the Luquantun Formation and the Sidao sedimentary rocks in central-eastern Jilin Province (NE China), to constrain the initial closure of the PAO. We obtained Early Carboniferous zircon UPb ages (345 ± 2 Ma and 351 ± 7 Ma) from the Changde volcano-sedimentary rocks. The metadacites are characterized by the enrichment in light rare earth elements and large ion lithophile elements, depletion in heavy rare earth elements and high field strength elements, and rare earth element ratios similar to those of the continental crust, indicating that these rocks originated from crustal melting. The metadacites exhibit affinity with the peraluminous A-type granite, with high zircon εHf(t) values (+3.46 − +12.21) and TDM2 of 1132–571 Ma, suggesting that they formed in a post-collisional extensional setting. Detrital zircon UPb ages from the Luquantun Formation and Sidao sedimentary rocks constrain their maximum depositional ages to the Late Carboniferous (319 ± 5 Ma) and Early Permian (284 ± 4 Ma), respectively. Most detrital zircons have age peaks at 1800 Ma with negative zircon εHf(t) values, and 2500 Ma with positive zircon εHf(t) values, suggesting that the Carboniferous–Early Permian sediments from these two formations were mainly sourced from the NCC. Moreover, the chemical index of alteration, index of compositional variability, and plagioclase index of alteration values suggest that the sediments of the Changde volcano-sedimentary rocks originated from a mafic igneous source with a low degree of weathering and a sedimentary recycling history, while the samples from the Luquantun Formation and Sidao sedimentary rocks were sourced from an intermediate-felsic igneous rock with a moderate to intense degree of weathering and mainly influenced by source composition. The crystallization age curves and summary plots of detrital zircons indicate that the Early Carboniferous metamorphic greywackes from the Changde Formation were mainly deposited in a passive margin, while the Carboniferous–Early Permian sediments of the Luquantun Formation and Sidao sedimentary rocks were mainly deposited in an active margin. We suggest that the tectonic transition from passive to active margin occurred at ∼333 Ma, marking subduction initiation in the PAO close to the northern margin of the NCC.

Geochronology and chemostratigraphy of the 2.47–1.96 Ga rift-related volcano-sedimentary succession in the Karasjok Greenstone Belt, northern Norway, and its regional correlation within the Fennoscandian Shield

New geochronological data for the amphibolite-facies volcano-sedimentary Karasjok Greenstone Belt in northwestern Fennoscandia bracket its age between 2.47 and 1.96 Ga. The volcano-sedimentary units were deposited on the 3005 ± 24 to 2776 ± 69 Ma crystalline basement rocks of the Jergul Gneiss Complex. The lowermost Vuomegielas Formation contains rhyodacites dated at 2469 ± 12 Ma that were deposited in an intracratonic rift setting related to the Matachewan mantle plume event. The overlying Skuvanvárri Formation, correlative with the early Jatulian (c. 2.2 Ga) units on the Fennoscandian Shield, consists of siliciclastic sedimentary rocks deposited in coastal deltaic and shallow-marine settings. The overlying mid-Jatulian Gollebáiki Formation contains 2151 ± 5 Ma mafic intrusions and tholeiitic basalts related to a rifting event and breakup of the Superia supercraton that resulted in voluminous volcanic and shallow-marine deposits. The Ni-Cu-PGE-mineralized Porsvann intrusion, hosted by the Gollebáiki Formation, yielded an age of 2056 ± 10 Ma, which corresponds with other Ni-Cu-PGE-bearing intrusions on the Fennoscandian Shield. The uppermost Báhkilvárre Formation consists of basalts, komatiites, and andesitic lavas. A synvolcanic gabbro within the komatiites in the lower part of the formation yielded an age of 1984 ± 16 Ma. Andesites in the upper part of the same formation were dated at 1961 ± 1 Ma. They represent the final Paleoproterozoic magmatic event that affected large areas of the Fennoscandian Shield prior to the Lapland-Kola and Svecofennian orogenies. Carbon isotope values for carbonates of the Skuvanvárri and Gollebáiki formations range up to highly positive (+12.4 ‰) values, corresponding to the c. 2.22–2.06 Ga Lomagundi carbon isotope excursion. In contrast, carbonates from the Báhkilvárre Formation do not yield elevated δ13C values, indicating that it was deposited in the aftermath of the Lomagundi carbon isotope excursion. New geochronologic and chemostratigraphic data for the Karasjok Greenstone Belt support correlation with the early Paleoproterozoic sedimentary successions deposited on the eastern margin of the Superior craton and position the northern-northwestern margin of the Karelia-Kola craton against the eastern margin of the Superior craton between c. 2.5 and 2.05 Ga.

Cadomian Iron ore bodies in the Bafq-Saghand metallogenic province, Iran: genetic constraints from field observations and laser ablation ICP-MS mineral studies

ABSTRACT The volcano-sedimentary unit in the Bafq-Saghand metallogenic province (BSMP) of Central Iran hosts various types of iron ore bodies including Fe-oxides with jaspilite beds, Mn-dominated iron lenses, magnetite-apatite lenses, and massive magnetite-apatite deposits. The Fe-oxides with jaspilite beds and Mn-dominated iron lenses have limited outcrops and show volcano-sedimentary features in the field. The main features are the presence of syngenetic submarine rhyolite-hosted magnetite, lamination and bedding of iron ore body, jaspilite and dropstone. Volcano-sedimentary origin is testified by magnetite composition showing affinity to BIF and positive Eu and negative Ce anomaly. Magnetite-apatite lenses and massive magnetite-apatite deposits that having spatio-temporal correlation form the main economically important deposits. They have magmatic to high-temperature hydrothermal field characteristics (lava flow-like ore bodies, the presence of degassing tubes in ore bodies, occurrence of brecciated texture and developed Na-Ca metasomatism). Mineral composition (enrichment of LREE, magnetite and apatite negative Eu anomaly and Co/Ni < 1 in pyrites) is in agreement with magmatic and high temperature hydrothermal origin. We propose a hydrous and oxidizing mantle derived iron-rich basic magma that formed in an extensional post-collisional setting for origin of Kiruna-type IOA ore bodies of the BSMP. Fe-oxides with jaspilite beds and Mn-dominated iron lenses resulted from degassing or eruption of iron-rich magma during Ediacaran in a submarine environment. However, magnetite-apatite lenses and massive magnetite-apatite deposits formed from an Early Cambrian magmatic-hydrothermal transition system from a magnetite-crystal mush zone.

Tectonic inversion of the Abanico basin eastern border and the structuring of the Aconcagua thrust-fold belt, southern Central Andes at 32°-33°S

Previous geologic studies and structural interpretations of the Meso-Cenozoic units in the Andean Principal Cordillera, between 32°- 33°S, have faced many difficulties due to the strong variability in volcanic deposits' thickness, the structural complexity that affects the involved units, and the scarcity of geochronological data that prevents defining a clear boundary between them. Structural-lithologic work carried out between 32°45′-33°S allowed us to recognize and define 4 different lithologic units along the Aconcagua-Juncal river valleys: one marine sedimentary unit assigned to the Cretaceous Mendoza Group and Late Jurassic exposures from the Río Damas/Tordillo Formation, and 3 volcano-sedimentary units mainly associated with Cenozoic volcanism represented by the Farellones, Abanico, and Cristo Redentor formations. The stratigraphic-structural model proposed in this work also allows for defining 3 structural domains throughout the study area: a western domain close to the Pocuro Fault Zone, a central domain, and an eastern domain close to the Alto del Juncal Fault Zone, next to the Chile-Argentina international border. The western and central domains show folds with larger wavelengths than the eastern domain, while the eastern domain shows intense deformation related to the emplacement and evolution of the Aconcagua fold and thrust belt. This deformation results from tectonic events which mainly occurred between the Upper Oligocene and Miocene. In the study region, these events caused a minimum shortening of ∼30 km in the Principal Cordillera. Based on the collected information, the Alto del Juncal Fault is also interpreted as the eastern Abanico basin bounding fault in which the Aconcagua fold-thrust belt is rooted.

Characterization of volcanic reservoirs; insights from the Badejo and Linguado oil field, Campos Basin, Brazil

The Badejo and Linguado oil fields are hosted within non-conventional volcanic reservoirs which produced commercial hydrocarbons from the Lower Cretaceous Cabiúnas Formation, Campos Basin, offshore Brazil. Despite over 30 years of production, limited characterization of the nature and reservoir properties of the volcanic reservoirs have been presented to date. A comprehensive reappraisal of the Cabiúnas Formation volcanic reservoirs is presented in this study incorporating extensive existing and new data including core descriptions, laboratory petrophysical analyses, petrography, QEMSCAN, SEM, wireline, and microtomography results from five cored intervals of wells spanning the main reservoirs of the Badejo and Linguado fields. Volcanic facies analyses of the sequences reveal a predominance of subaerial effusive basic volcanic rocks interbedded with sediment and in several cases comprising peperites revealing intricate lava-sediment interaction products. Four volcano-sedimentary units are identified, showing alternations between low (compound pahoehoe lava dominated Units 1 and 3) and high (tabular rubbly pahoehoe lava dominated Units 2 and 4) effusion rates. Paleoenvironmental conditions also varied between units with extensive oxidation present in Unit 1 inferred to relate to extended periods of subaerial exposure and weathering in an arid environment. Overlying Units 2–4 reveal an increase in humidity evidenced by an increase in the presence of well sorted fine-grained sediment interlayers, peperites, and non-marine ostracods. Both original facies and alteration reveal key controls on reservoir properties. Extensive weathering and alteration of Unit 1 caused pervasive filling of original porosity (vesicles and fractures) and resulted in reservoir degradation. Lesser weathering of overlying Units 2, 3 and 4, resulted in improved reservoir properties which can be clearly linked to volcanic intra-facies including vesiculated and autobrecciated lava flow tops which commonly reveal extensive oil staining. This study reveals the intricate interplay between primary volcanic facies and subsequent alteration history in dictating volcanic reservoir properties in a successful offshore oil field development.

Petrogenetic constraints of the La Quinta Formation igneous rocks, Serranía del Perijá, northern Colombian Andes

La Quinta Formation is a Triassic-Jurassic volcano-sedimentary unit that crops out along both flanks of the Serranía de Perijá, in Cesar and La Guajira departments of Colombia, and Zulia state in Venezuela. It is mainly composed of red clastic sedimentary rocks (siltstones, sandstones, and minor conglomerates), interbedded with volcanic rocks and cut by small stocks. The volcanic horizons are mainly formed by rhyolitic tuffs and lava flows (basalts and andesites).&#x0D; &#x0D; Andesites and basalts are constituted by plagioclase, clinopyroxene, biotite, magnetite, apatite, and zircon, whereas rhyolites and tuffs are formed by plagioclase, ß quartz, biotite, and sanidine. EMPA analyses revealed that plagioclase display varying compositions from labradorite-andesine in intermediate and basic rocks to oligoclase in rhyolites. Besides, clinopyroxene from basalts was classified as augite, and several hydrothermal mineral phases were also recognized, such as epidote, Ca-zeolites, and andradite-grossular. Using ILMAT (ilmenite-magnetite) geothermometer, temperature and oxygen fugacity conditions of 700-730°C and +1.2 ∆NNO were determined for dolerite.&#x0D; &#x0D; Whole-rock geochemistry results evidence that La Quinta Formation volcanic rocks belong to the sub-alkaline (calc-alkaline) series, displaying compositions from basaltic andesites to rhyolites. Chondrite normalized REE and incompatible elements spidergrams show typical features of subduction-related magmatism and depict three groups of rocks (basic, intermediate, and acid) with contrasting geochemical behaviors. Hence, each group could have formed during single magmatic events associated with different magmatic suites. Nevertheless, the three groups have features that suggest a genesis related to an Andean-type supra-subduction zone, which agrees with the regional tectonic assemblage during Triassic-Jurassic times.

Lithostratigraphy, Lithogeochemistry, and Tectono-Magmatic Framework of the ABM Replacement-Style Volcanogenic Massive Sulfide (VMS) Deposit, Finlayson Lake District, Yukon, Canada

Abstract The Upper Devonian ABM deposit is a bimodal-felsic, replacement-style volcanogenic massive sulfide (VMS) deposit within the Finlayson Lake district in Yukon, Canada. The deposit is hosted by predominantly felsic volcanic rocks of the upper Kudz Ze Kayah formation that were deposited in an active back-arc basin in three sequences consisting of interbedded felsic volcaniclastic rocks and argillites, and felsic lava flows and domes, and felsic and mafic sills. The felsic rocks fall into two groups, Felsic A and Felsic B (FA and FB), based on immobile elements and their ratios. Relative to the FB group, the FA group has high Zr concentrations (&amp;gt;550 ppm) and generally higher contents of high field strength elements. The FA/FB chemostratigraphy roughly coincides with the lithostratigraphic sequences. Sequence 2 hosting the mineralization consists of FB felsic rocks; the hanging-wall Sequence 3 and footwall Sequence 1 felsic rocks have FA signatures. An argillite lens, recording a period of volcanic quiescence, occurs at the upper contact of Sequence 2. From reconstruction of the basin architecture, two sets of synvolcanic faults are inferred. The synvolcanic faults were interpreted based on thickness changes of volcanosedimentary units and the distribution of coherent rocks. During breaks in volcanism, synvolcanic faults acted as conduits for upwelling hydrothermal fluids, which were diverted laterally into unconsolidated volcaniclastic rocks and formed the replacement-style VMS mineralization. Although the mineralized lenses are hosted by FB felsic rocks, their replacement-style nature implies that the mineralizing processes occurred during the break in volcanism and were genetically associated with the overlying FA felsic volcanic rocks.

Geochemistry of Volcano-sedimentary and Plutonic Formations of the Agbaou Gold Deposit, Ivory Coast

Located in the south-west part of the Fettekro greenstone belt, Agbaou gold deposit is marked by three major lithological units: (i) a volcano-plutonic unit composed of basaltic to andesitic lavas, amphibolites, chlorite-schists and sills of microdiorite and microgabbro; (ii) a volcano-sedimentary unit containing pyroclastic lavas (basaltic and dacitic) and sediments (shale and grauwacke); (iii) the late felsic dikes (rhyolite and rhyodacite) probably contemporary with the formation of granitoids form the third unit. These host rocks are mostly intensely deformed and altered. Alteration phenomena were revealed by the high values in fire loss, the decreasing of silica contents, the sometimes high values of alkaline for rocks also basic, the constant depletion in LREE and LILE. The Eu and Nb negative anomalies reveal a crustal contamination of magmatic series. Basaltic lavas are volcanic arc tholeiites nearing N-MORB type; they are associated to a magmatogenesis of ocean floor. Their magmatic source would probably be spinel lherzolitic type. Andesites have a calc-alkaline composition and seem far link to active subduction margin. Geodynamics context would be that of an area where transcurrent faults of lithospheric extension generate heat corridors able of generating by fusion the andesitic calc-alkaline magma. This context would probably be the one that prevailed during the establishment of the gold mineralization. Pyroclastic rocks of dacitic composition as acid lavas (rhyolite and rhyodacite) have also evolved in this same geotectonic context. Plutonic rocks are located in arc-volcanic granites field, while metasediment are linked to active continental margin field.

Mature petroleum hydrocarbons contamination in surface and subsurface waters of Kızılırmak Graben (Central Anatolia, Turkey): Geochemical evidence for a working petroleum system associated with a possible salt diapir

Salt formations exist in Kızılırmak Graben (Central Anatolia, Turkey), which consists of volcano-sedimentary units, and it was stated in previous studies that these formations have a diapiric structure. The adjacent basin, Ayhan Basin, contains bituminous shale and operated coal deposits. For this reason, in this study, it is aimed to investigate the oil and gas potential of the Kızılırmak Graben by conducting TPH (Total Petroleum Hydrocarbons) analysis on the samples taken from natural cold-water resources by making use of the thought that hydrocarbon generation may come into existence from those units in the Ayhan basin. As a consequence of the analyses performed, hydrocarbons have been brought into the open in all the water samples. The organic geochemical methods have been used to find out the source of hydrocarbons determined in the water resources. The disclosed n-alkane hydrocarbons are the mature petroleum hydrocarbons derived from peat/coal type organic matter (Type III kerogen, gas-prone). These mature hydrocarbon-rich waters can be regarded as evidence for the availability of a working hydrocarbon system associated with possible salt diapir identified by using gravity and magnetic data obtained from the investigation area.

Mapping and Petro-Structural Study of Northern Komborodougou Formations, in Korhogo Gold District: A Substantial Contribution to the Discovery of a Potential Gold Mineralization in Birimian Greenstone Belts

The Gold District of Korhogo, in the northern region of C?te d’Ivoire, holds enormous potential for gold mineralizations, some of which are under exploration phase and others in exploitation phase (example of Tongon Gold Mine). Dormant since 1998, Mapping Services of most of the West African countries hardly provide geological maps at the scales of: 1/200,000, 1/50,000 and 1/25,000. This situation of unavailability of detailed geological maps does not help mining operators in the selection of prolific areas and also in the interpretation of in soil geochem anomies or gold mineralizations. Consequently, during the years 2020 and 2021, we have undertaken a campaign of geological mapping and petro-structural study of the northern sector of Komborodougou, located in the southern extension of Banfora Birimian Belt. This work, which allowed the realization of a geological map at 1/20,000 scale, reveals that: the mapped area includes three (3) major lithological units: 1) a volcano-sedimentary unit made up of metasediments (metaarenites, metasiltites and metaflyschs) and metavolcanites (metabasalts), which are metamorphosed and outcrop in the form of schists; 2) a metaplutonic and intrusive unit composed on the one hand of quartz-diorites and metagabbros, and on the other hand of granites and granodiorites; 3) and finally, a unit of dikes formed by microgranites, microgabbros, aplites and quartzites. The volcano-sedimentary complex is affected by a regional fold with an axis subparallel to the regional tectonic grain and an S1 schistosity oriented NE-SW to NNE-SSW with steep dips (>60o), except for those of the metaflyschs which are weak (o); a regional NW-SE compression would be at the origin of the setting of this schistosity. The volcano-sediment and metaplutonite complex is crossed in a NNE-SSW direction by a senetral shear-zone or main shear-zone and secondary shear-zones oriented sometimes NE-SW or N-S. These shear-zones are intersected by more or less dextral or senestral strike-slip faults of NW-SE and E-W trends. N-S to NNE-SSW (N0o - N20o) and NW-SE (N130o - N160o) vein systems associated with the various shear-zones are the hosts of the gold mineralization in the region. These veins have been mined by orpaillors for more than two decades. The northern sector of Komborodougou is in the NNE continuity of the gold mineralization highlighted by the mining company Mako Gold Sarl on its Gogbala and Tchaga prospects, Napie project.

The Ludicovian of the Raahe–Ladoga Zone of the Fennoscandian Shield (Isotope-Geochemical Composition and Geodynamic Nature)

Abstract —In the northern Ladoga area, the age of the Sortavala Group rocks in the southeast of the Raahe–Ladoga zone of junction of the epi-Archean Fenno-Karelian Craton and the Paleoproterozoic Svecofennian province, their relationship with dome granitoids, the age of the provenances, and the time of metamorphic processes were estimated. The study was focused on the Nd isotope composition of rocks, the geochemical and isotope-geochronological parameters of zircon from the granite-gneisses of the Kirjavalakhti dome, the basal graywackes of the lower unit and the trachytes of the middle unit of the Sortavala Group, and the plagio- and diorite-porphyry dikes cutting the volcanosedimentary units of this group. The new isotope-geochemical data show a Neoarchean age of the granitoids of the Kirjavalakhti dome (2695 ± 13 Ma) and their juvenile nature (εNd(T) = +1.5). The granitoids underwent tectonometamorphic transformations (rheomorphism) in the Paleoproterozoic (Sumian) (2.50–2.45 Ga), which are recorded in the U–Th–Pb isotope system of the rims of the ancient cores of zircon crystals. The volcanosedimentary complex of the Sortavala Group formed on the heterogeneous polychronous (3.10–2.46 Ga) continental crust of the epi-Archean Fenno-Karelian Craton. With regard to the errors in determination of the age of clastic zircon, the minimum concordant U–Th–Pb ages of 1940–1990 Ma of detrital zircon from volcanomictic graywackes of the Pitkyaranta Formation can be taken as the upper age bound of terrigenous rocks, which agrees with the maximum age of the Sortavala Group rocks estimated from the U–Th–Pb (SIMS) age of 1922 ± 11 Ma of the Tervaoya diorites (Matrenichev et al., 2006). According to the proposed new tectonic model, the accumulation of the volcanosedimentary complex of the Sortavala Group, its metamorphism, erosion, and overlapping by the Ladoga Group turbidites had already occurred in the pericratonic part of the epi-Archean Fenno-Karelian Craton by the time of the Svecofennian continent–island arc collision, subduction, and formation of bimodal volcanoplutonic complexes of the young Pyhäsalmi island arcs and felsic volcanics of the Savo schist belt (1920–1890 Ma).

Dispersed Gold and Associated Disseminated Mineralization of Leucogranites of the Dukat Ore Field as Indicators of the Generation Conditions of Magmatogene Gold-Bearing Fluids

Abstract —We present data on dispersed gold and associated disseminated mineralization of leucogranites controlling the location of the Dukat epithermal Au–Ag deposit. The data suggest the formation and burial of small portions of oversaturated gold-bearing fluids in hypabyssal magmatic bodies. The lower (relative to silver) contents of gold in the deposit ores and the high Ag/Au ratios (350–550) are due to the limited occurrence of oxidized gold-bearing fractions of magmatogene fluids. This limitation is explained by the active interaction of late magmatic portions of fluids and the material of the host carbonaceous volcanosedimentary unit and by the formation of an environment favorable for the concentration, migration, and deposition of manganese, silver, and nonferrous-metal compounds.

Distribution of geothermal arsenic in relation to geothermal play types: A global review and case study from the Anatolian plate (Turkey)

Arsenic has a natural cycle as it travels underground. It can mix with geothermal fluid in different ways under the control of magmatic and tectonic processes. Geogenic arsenic is present in many geothermal fields in the world at concentrations above the limits set for human health. The arsenic content of geothermal fluids is also related to the concept of geothermal play type, which forms geothermal systems, because the natural processes that form the geothermal system also control the arsenic cycle. In this study, an attempt is made to explain the relationship between the geothermal play type concept and geothermal arsenic circulation. For this purpose, geothermal field examples are given from around the world and Turkey. The result shows that arsenic concentrations can reach significant levels along with plate tectonic boundaries in the world. When arsenic concentrations were evaluated, the effect of major faults on the Anatolian Plate was clearly seen. Also, in the Anatolian plate where volcano-sedimentary units are common, geothermal fluids caused more effective alteration along with structural control and increased arsenic concentrations in geothermal systems. This interaction between structural elements, geothermal fluid, and the arsenic cycle shows that the concept of play type in geothermal systems should also be taken into consideration. It was determined that the places with high arsenic values are located within the convective-non-magmatic extensional geothermal play types such as Western Anatolian Extensional System and the North Anatolian Fault. The concept of play type in geothermal systems includes all systematic and external factors that make up these processes. For this reason, it is very important to evaluate the play type classification together with the arsenic cycle.

Mineral chemistry and geothermobarometry of gabbroic rocks from the Gysel area, Alborz mountains, north Iran

The gabbroic rocks in the Gysel area of the Central Alborz Mountains in north Iran are intruded into the Eocene Volcano-sedimentary units. The main gabbroic rocks varieties include gabbro porphyry, olivine gabbro, olivine dolerite and olivine monzo-gabbro. The main minerals phases in the rocks are plagioclase and pyroxene and the chief textures are sub-hedral granular, trachytoidic, porphyritic, intergranular and poikilitic. Electron microprobe analyses on minerals in the rock samples shows that plagioclase composition ranges from labradorite to bytonite, with oscillatory and normal chemical zonings. Clinopyroxene is augite and orthopyroxene is hypersthene to ferro-hypersthene. Thermometry calculations indicate temperatures of 650˚C to 750˚C for plagioclase crystallization and 950˚C to 1130˚C for pyroxene crystallization. Clinopyroxene chemistry reveals sub-alkaline and calc-alkaline nature for the parental magma emplaced in a volcanic arc setting.

Lithostratigraphy, sedimentary petrography and geochemistry of the Upper Karoo Supergroup in the Central Kalahari Karoo Sub-Basin, Botswana

The Kalahari Karoo Basin of Botswana is an intracratonic basin developed in south-central Gondwana and is filled with Upper Carboniferous–Lower Jurassic Karoo Supergroup volcano-sedimentary units. The Karoo Supergroup units are unconformably covered by the Cretaceous to recent Kalahari Group. The Upper Karoo Supergroup in the Central Kalahari Karoo Sub-Basin of Botswana consists of the lacustrine sediments of the Beaufort Group (Tlhabala Formation), overlaid unconformably by the continental sediments of the Lebung Group, and by the continental basalts of the Stormberg Group. The Late Triassic to Early Jurassic Lebung Group is subdivided into the Mosolotsane Formation and the Ntane Formation. This sedimentary sequence is poorly exposed, and formation boundaries are tentatively identified by lithological changes in boreholes. Here, new sedimentological and geochemical data are used for the refinement of the stratigraphy of the Upper Karoo Supergroup in the Central Kalahari Karoo Sub-Basin of Botswana, new criteria for the identification of unit boundaries are set and provenance of the Lebung Group sediments has been defined. The geochemical investigation of the Upper Karoo Supergroup in the Central Kalahari Karoo Sub-Basin of Botswana revealed clear geochemical markers that have allowed the pinpointing of unit boundaries between the Tlhabala Formation (Beaufort Group), Mosolotsane Formation (lowermost Lebung Group). The sediments from the Tlhabala Formation have a geochemical signature typical of wackes, while the sandstones from the overlying Mosolotsane Formation and the Ntane Formation are dominated by arkose to subarkose. The transition from wacke to subarkose pinpoints the boundary between the Beaufort Group and the base of the Lebung Group. The Tlhabala Formation is characterized by increasing SiO2/Al2O3 ratio, with a maximum at the base of the Lebung Group, and by an upward decrease in the abundance of Na, K and transition metals such as Cr, Mn and Fe. The SiO2/Al2O3 ratio decreases upward in the Lebung Group. Similarly, the abundances of Na, K, Cr, Mn and Fe slightly increase upward only to show a negative peak at the Lebung Group and the Kalahari Group boundary. This contact is marked by a clear increase in the total REE content.The chemical composition of the Lebung Group sandstones also indicates a quartzose sedimentary provenance. The CIA (chemical index of alteration) values for these sandstones ranged from 63 to 73, indicating a high degree of chemical weathering. This type of intense weathering should produce high volumes of clay minerals, which are rather scarce in the studied samples. This indicates that the large amount of quartz in the Lebung Group has been recycled from the Paleoproterozoic sedimentary sequences of the Palapye Group, located southeast from the study area.

Zircon U–Pb–Hf isotopes and whole rock geochemistry of magmatic rocks from the Posht-e-Badam Block: A key to tectonomagmatic evolution of Central Iran

The Posht-e-Badam Block in Central Iran likely formed part of the Neoproterozoic Arabian-Nubian Shield (ANS). However, its Phanerozoic history is not well constrained. Zircon UPb ages, Hf isotopic compositions and whole-rock geochemistry of igneous rocks from the Bafq district were determined to constrain their source and tectonomagmatic evolution. Two magmatic cycles are identified; early Paleozoic events associated with the Cadomian Orogeny resulting from Proto-Tethys subduction beneath the northern margin of Gondwana, and Cenozoic volcanism related to the Alpine-Himalayan Orogeny and closure of Neo-Tethys. The main plutonic and volcanic rocks record early Cambrian ages. The Zarigan, Narigan and Chahcholeh granitoids, volcanic rocks of the lower Cambrian volcano-sedimentary unit (CVSU) and the Zarigan gabbro have remarkably similar ages of 536 to 528 Ma. The Zarigan and Chahcholeh granitoids and volcanic rocks of the CVSU have positive εHf(t) values of 1.4 to 9.3, with Hf model ages (Hf-TDMc) of 715–1034 Ma. They are mostly A2-types, although some samples show affinity to A1- and I-types, suggesting an asthenospheric mantle source, modified by various amounts of crustal assimilation. The Narigan granite records εHf(t) values of −3.8 - 3.1, with Hf-TDMc of 970 to 1255 Ma and displays I-type characteristics, formed through mixing of mantle-derived melts with predominantly Neoproterozoic crust. All rocks were generated in a post-collisional setting. The Esfordy syenite and mafic dikes are younger and essentially coeval, with weighted mean ages of 457 ± 5 Ma and 451–448 Ma, respectively. The Esfordy syenite has A1-type characteristics, indicating possible derivation in an intraplate rift environment and was likely plume-related. The mafic dikes have OIB-like characteristics. Mafic rocks related to closure of Neo-Tethys include the ca. 23 Ma Bahabad diorite that records εHf(t) values of −16.8 to 10.1 (Hf-TDMc = 241–283 Ma) and an OIB-like signature, indicating assimilation of crustal material by asthenospheric mantle-derived melt.

Akkise-Yalıhüyük (Konya) Arasının Stratigrafisi

In the vicinity of Akkise-Yalıhüyük (south of Konya) region, the Mesozoic sequence of the autochthonous Geyikdağı and the allochthonous Bozkır units is overlain by Neogene-Quaternary Neo- autochthonous cover units with an angular unconformity. Geyikdağı Unit is represented by Late Cretaceous Saytepe formation cosisting of abundant rudist neritic carbonates at the bottom and Campanian-Maastrihtian Alan formation made up of cherty, clayey pelagic limestone and marls at the top. These autochthonous units are overlain by Maastrihtian Hatip ophiolitic melange forming the lower tectonic zone of the allochthonous Bozkır unit. The second allochthonous tectonic unit in the region is represented by Boyalıtepe formation including Late Cretaceous pelagic deposits such as cherty limestone, clayey limestone-marl and radiolarite. The upper allochthonous package of the study area is also represented by the Middle Triassic-Jurassic Gencek formation consisting of medium-thick bedded, abundantly jointed neritic carbonate. The boundaries of autochthonous and allochthonous and Neo-autochthonous rocks in the region are generally faulted. Therefore, the semi-peneplene-peneplene areas of the region are in the form of a depression area. As a result of lacustrine transgression in the Miocene-Early Pliocene period, lacustrine deposition environments were formed in these depression areas. Therefore, today, some lacustrine sediments such as gravelly-sandy-muddy detritics (Sille formation), muddy-clayey carbonates (Ulumuhsine formation) and volcano-sedimentary units (Küçükmuhsine formation) and also dacitic-andesitic volcanics (Erenlerdağı volcanics) are seen in these depression areas. The newest deposits of the study area are the foothill-alluvial fan deposits (Topraklı formation) which were deposited in Late Pliocene-Pleistocene and alluvials in Holocene age.

Stratigraphy, depositional environments and zircon U-Pb (LA-ICP-MS) ages of the Statherian volcano-sedimentary Beneficente Group: Implications for tectonics and gold mineralization in SW of the Amazon Craton

The Amazon Craton exhibits preserved volcano-sedimentary paleo-basins with age intervals of 2.0–1.96 Ga, 1.90–1.87 Ga and 1.80–1.60 Ga. Recent works in this craton have shown the efficacy of the description and organization of volcanic and sedimentary lithofacies as a tool to postulate stratigraphic frameworks. In the present work we propose the first formal stratigraphy for the Beneficente Group (BG), a Statherian (~1.74 Ga) volcano-sedimentary unit outcropping in the southwestern portion of the Amazon Craton. The BG is divided into three formations: (1) Pedro Sara Formation (PSF), composed of felsic volcanic rocks represented by thick lava-like and densely welded tuffs, normal-graded tuffs, both from pyroclastic density currents, and laminated ash-fall tuffs; (2) Camaiú Formation (CF), comprising sheetfloods, low-energy alluvial channels, non-cohesive sediment-gravity flows, rubbly pahoehoe basaltic flows, stream-channel deposits, and deposits reworked in foreshore/superior shoreface settings, and; (3) Vila do Carmo Formation (VCF), formed by delta front and pro-delta lithofacies associations. The sequence of sedimentary rocks contains clasts exclusively from the related volcanic rocks (PSF), with no clasts from other volcanic sequences nearby. Geochronological analyses evidence a Statherian age for the sequence. A pheno-latite from PSF yielded a crystallization age of 1743.6 ± 7.5 Ma, the youngest zircons of a sandstone from CF have ages between 1746 and 1732 Ma and the youngest zircons of a sandstone from VCF have 1760 Ma to 1601 Ma. The Beneficente paleo-basin is preserved as a NW-SE rift in the margin of the Tapajós-Parima Province. This structure remained as an active depositional locus during the Paleozoic and is the location of the main courses of modern rivers. The development of BG is akin to Statherian taphrogenic systems which were widespread in the Amazon, São Francisco-Congo and North China cratons, and are a key tectonic feature before the Columbia (Nuna) supercontinent break-up.

Reply to discussion by A. Aftabi and S. Mohseni on “Combined igneous and hydrothermal source for the Kiruna-type Bafq magnetite-apatite deposits in Central Iran; trace element and oxygen isotope studies of magnetite” by Mehdipour Ghazi et al. [Ore Geology Reviews 105 (2019) 590–604

In this reply, we emphasize on some geological and geochemical evidence that indicate most of the studied deposits (Choghart, Chadormalu and Sechahun) have magmatic origin and they are not related to BIF deposits, as declared by Aftabi and Mohseni (2019). Field studies reveal the existence of at least three types of iron mineralization in the Posht-e-Badam Block; (1) stratiform Fe-oxide (ologist) sublayers within the Neoproterozoic meta-sedimentary units, (2) Iron lenses within the early Cambrian volcano-sedimentary unit, and (3) massive magnetite deposits. We assume that studies by Aftabi and Mohseni (2019) were focused on iron deposits mainly belonging to type 2 iron mineralization above. We proposed contamination of primary silicate magma with older units (similar to Ediacaran bands of magnetite reported by Aftabi and Mohseni, 2019) that include iron, phosphor and sodium which were responsible for triggering immiscibility of Fe-rich melt from silicate magma and formation of the studied massive Iron deposits.