Search

The Table Mountains, a flat-topped series of ridges capped by a 10.4 Ma latite flow in the Stanislaus River watershed, are considered to be evidence for late Cenozoic uplift-driven landscape rejuvenation in the northern Sierra Nevada range (California, USA). The commonly accepted theory for the formation of these mesas posits that the latite flowed and cooled within a bedrock paleovalley and, since then, the surrounding landscape has eroded away, leaving behind the volcanic deposit as a ridge. Although this theory is accepted by many, it has not been thoroughly tested. In this study, I examine a series of geological cross-sections extracted along the length of the latite deposit to determine whether the evidence supports the existence of bedrock valley walls on both sides of the 10.4 Ma flow. I find that the presence of older Cenozoic deposits adjacent to the latite flow precludes the possibility that the flow would have been constrained within a bedrock valley. Moreover, the cross-section from an 1865 report that has been offered as evidence of topographic inversion (and subsequently reproduced in numerous publications) does not accurately represent the topography at that site. I conclude that there is no evidence that the bedrock topography has been inverted and that instead, the latite flowed within a channel cut into underlying Cenozoic deposits, which have since mostly eroded away. This study, therefore, refutes the hypothesis that the Stanislaus River watershed was rejuvenated in the late Cenozoic and challenges the claim for recent significant uplift of the region.

The characteristic features of the manifestations of acid magmatism and metasomatic hydrothermal alteration processes in Southeastern Transbaikalia, an important mining region in Russia, are discussed. The zoned or beltlike distribution of the ores of various metals, uranium in particular, and other mineral deposits is due to the general evolutionary trends of the geodynamic regimes of the respective blocks of the territory and the subsequent magmatic differentiation trends. The highly differentiated and fluorine-rich granitoids of Southeastern Transbaikalia are located only in the zones of the consolidated crust, which are characterized by low gravity and negative quiet magnetic field values. In other zones, i.e., volcanic belts, volcanogenic troughs, and the regions dominated by the intrusive massifs of the Shakhtama complex, rare metal manifestations are absent. It was demonstrated that there is no correlation between the localization of large uranium deposits and leucocratic rare metal granite domains and that these deposits are concentrated in large volcanic calderas or volcanic troughs, controlled by long-lived fault systems. In addition to uranium, these volcanogenic structures control base metal, molybdenum, gold, fluorite, and some other mineral deposits. The results of a comparative analysis of the geochemical features of the acid volcanics that host the uranium mineralization and are classified as the last differentiation products of the contrasting latite volcanism, on the one hand, and the subvolcanic and hypabyssal derivatives of the rare metal granites, on the other, are presented. The analysis revealed the signatures of their fundamental difference from each other and that they belong to different branches of magmatic differentiation. A comparative analysis of the metasomatic aureoles of the altered wallrocks in the Late Mesozoic volcanics and the Shakhtama granitoid domains, on the one hand, and the leucocratic rare metal granite domain, on the other, is given. The data presented attest to the existence of a mixed geodynamic regime within the study area of the Central Asian mobile belt during the Jurassic and the earliest Cretaceous time: residual collisions with strong deformations in a compressional setting, accompanied by the development of late acid differentiation products of the magmatic latite series, and the incipient rifting associated with the intrusion of the leucogranites of the Kukul’bei complex in a more quiet extensional setting.

It is shown that the ore-forming systems (OFS) of the Vendian-Riphean Greenstone belts (GSB) in the Transbaikalia region were formed in a wide age range: from the Riphean to the Cenozoic. They are grouped into 6 metallogenic types. The noble metal type is divided into 6 metallogenic subtypes differed in time duration intervals of functioning. OFS evolution wore multistage nature inherited from the composition of the GSB primary rocks, with a tendency of the ore generating processes remobilization and regeneration (dynamometamorphism) changing over time by rejuvenation (shoshonite latite and picrobasalt magmatism, mud volcanism).

Modal classifications of common volcanic rocks are expensive, difficult, or impossible to attain. As a consequence, these rocks are classified using the chemical composition. However, existing classificatory diagrams are unable to identify all 16 families of common volcanic rocks; the most used is the total alkali-silica (TAS) diagram that identifies six families. Rocks not in the TAS diagram are misclassified with other rock names; their names are evolving to extinction, e.g. latite and rhyodacite. Some diagrams use Na2O, which is a complicating element rather than discriminant. Na2O is present both in alkali feldspar and plagioclase making difficult the separation of the amount associated to either feldspar. Silicon, potassium, and calcium are the three major elements with highest variations among volcanic rocks. They are selected for use in two new diagrams confronting CaO/K2O ratio with K2O content (KCK diagrams). One diagram is designed for saturated (intermediate) rocks (quartz 5%). These diagrams are tested using compositions of volcanic rocks from Uatumã magmatism in the Amazon Craton and also by plotting compositions of rocks from type-localities and the world averages. The proposed limits between rock families agree with plotted rock compositions. The KCK diagrams are an alternative to existing diagrams to classify volcanic rocks.

In this article, the stress–dilatancy relationship for crushed latite basalt is analysed by using Frictional State Theory. The relationship is bilinear, and the parameters α and β determine these two straight lines. At the initial stage of shearing, the mean normal stress increment mainly influences breakage, but at the advanced stage, it is shear deformation that influences breakage. At the advanced stage of shearing, the parameter αpt represents energy consumption because of breakage and βpt mainly represents changes in volume caused by breakage during shear. It is also shown that breakage effect is significant at small stress levels and the η-Dp plane is important to fully understand the stress–strain behaviour of crushed latite basalt in triaxial compression tests.

U–Pb dating of zircon from amphibole latite of the central stock of the Nikolka shield volcano in Kamchatka provided the first data on its age. The end of activity falls to about 0.73 Ma (10 analyses). The local U–Pb analyses were carried out at the Isotope Research Center, Schmidt Joint Institute of Physics of the Earth (St. Petersburg) (VSEGEI) using SIMS SHRIMP II. Here, brief information about the geological structure, petrography, and chemistry of the rocks of the volcano are presented. A unique feature of the volcano is the occurrence of a gabbro–anorthosite sheet intrusion with derivates of monzonite and syenite composition in its central part. The correlation of the age obtained with the paleomagnetic data, indicating the formation of the volcano during the magnetic age of Matuyama, is also discussed. The date refers to the period of the change in epochs from the Brunhes to the Matuyama. The obtained age allows dating of the Pliocene volcanic stage in Kamchatka, when large shield volcanoes and plateaus formed.

En el valle superior del Magdalena se presentan cuerpos subvolcánicos de andesitas y latitas porfídicas que intruyen las lavas y tobas de la formación Saldaña del Jurásico Inferior. Estos cuerpos se caracterizan por presentar fenocristales de plagioclasa hasta de 2 cm, junto a piroxenos, olivino y sanidina que flotan en una matriz hialocristalina. Corresponden a plutones hipoabisales alcalinos, metaluminosos, con contenidos altos de álcalis, que clasifican químicamente como andesitas. Se interpreta que estas rocas fueron generadas por subducción en un ambiente de arco, con anomalías negativas de Nb y Ti y a la relación LREE/HREE en los diagramas multielementales. Se obtuvo una edad de meseta en plagioclasa, por el método Ar-Ar, de 159,35 ± 3,55 Ma, que sugiere, junto con las características químicas y relaciones estratigráficas, que corresponde a un evento magmático más joven que el de las lavas de la formación Saldaña (186,8 ± 2,0 Ma – 188,9 ± 1,6 Ma), las vulcanitas de Pitalito (168 ± 2,5 Ma – 172,4 ± 1,7 Ma) y los plutones jurásicos que afloran en el valle superior del Magdalena (169,4 ± 3 – 195,8 ± 1,5 Ma).

The high-grade (8.1 million ounces of gold; 15.6 Mt grading 16.1 g/t Au; Pretium, 2016) Brucejack epithermal Au-Ag deposits are located in the Canadian Cordillera of northwestern British Columbia, and formed in association with extensive early Mesozoic island arc magmatism. Porphyry-type Cu-Au-Mo mineralization occurs nearby at the Kerr-Sulphurets-Mitchell (196–190 Ma; Febbo et al., 2015), Bridge Zone (191.7 ± 0.8 Ma, 191.5 ± 0.8 Ma), and West Zone (188.9 ± 0.9 Ma) prospects. Gold-silver vein-type mineralization at Brucejack is hosted by variably altered and deformed Early Jurassic porphyritic latite lava flows, volcaniclastic rocks, and volcanic-derived sandstones, siltstones, and conglomerates. This study focuses on the Valley of the Kings Zone at Brucejack, where host rocks have been dated at 188–184 Ma (U-Pb, zircon). Post-mineralization (but not post-alteration) basaltic and trachybasaltic dikes that cut the veins are geochemically similar to the host volcanic sequence and follow the same structural trends of the mineralized vein corridors. We suggest these dikes are broadly coeval with mineralization, and that ore formation at the Valley of the Kings formed during the overall Jurassic tectonomagmatic event. Gold-silver mineralization is hosted by quartz-carbonate veins that cut sericitized and pyritized volcaniclastic rocks. Six stages of veining are defined, with Au-Ag mineralization (electrum) focused in stages III–V: stage I–III veins consist of quartz with minor carbonate, chlorite, sericite, and sulfide minerals; stage IV quartz veins contain more abundant base metal sulfides (pyrite, sphalerite, and galena with minor sulfosalts); stage V veins are dominantly calcitic; late post-mineralization stage VI veins are quartz-calcite and contain sparse pyrite and chlorite, but no electrum. The veins are interpreted to be syn- to late-tectonic, with deformation decreasing from locally penetrative in the host-rocks prior to veining (resulting in local foliation of sericite and pressure shadows around pyrite), to dismemberment and shearing of early stage I–II quartz veins, brittle disruption of stage III–IV quartz and stage V carbonate veins, and minimal deformation of post-mineralization stage VI quartz-carbonate veins. A much younger set of extensional muscovite veins locally cuts the deposit with Late Cretaceous apparent ages, and appears to be associated with a weak thermal overprint that has reset K-Ar and 40Ar/39Ar ages in sericite throughout the district. The deformation experienced by the vein system, particularly in the later stages (III–V), was not uniform, and original undeformed vein textures and fluid inclusion assemblages are locally preserved. We report fluid inclusion microthermometric data from carefully selected primary fluid inclusion assemblages from quartz, calcite, and sphalerite from vein stages III–IV, many of which show evidence for boiling (coexisting liquid- and vapor-rich primary fluid inclusions). Liquid-rich fluid inclusions from stage III and V veins have moderate homogenization temperatures (∼170 °C and ∼160 °C respectively) and salinities of 2–8 wt% NaCl equiv., whereas inclusions from base-metal-sulfide-bearing stage IV veins show evidence of mixing with a cooler, more saline brine (∼140 °C, ∼10–15 wt% NaCl equiv.). Carbon dioxide was observed as clathrate during cooling in some fluid inclusions, suggesting that minor amounts of CO2 were present in the fluids. Calculated oxygen isotopic compositions of fluids in equilibrium with quartz and calcite from vein stages III–V range from δ18Ofluid = −10.7 to +1.8‰, whereas δ13CCO2 ranges from −9.5 to −4.5‰, and δ34Spyrite ranges from −1.7 to +0.6‰. Taken together, these data suggest a magmatic source for S and some C, carried by a fluid of evolved or diluted magmatic origin, which variably mixed with meteoric-derived groundwater or seawater containing carbon of sedimentary (organic) origin. Mixing is supported by large salinity ranges of vein stage IV fluid inclusions, where individual assemblages range from ∼1 to 15 wt% NaCl equiv. These fluid temperatures, salinities, and isotopic compositions are typical of epithermal deposits where distal magmatic fluids mix with local heated groundwaters. The low fluid temperatures but evidence of boiling suggest formation at shallow crustal depths. This is despite the evidence for penetrative deformation in the sericitized volcanosedimetary host rocks, which we attribute to rapid uplift immediately prior to or during the earliest stages of mineralization. The vein system is therefore interpreted to have formed during the later stages of a deformational event related to arc accretion.

The obliteration of the Neo-Tethyan Ocean and collision of the microplates along the northern part of Turkey led to the development of the Izmir-Ankara-Erzincan suture zone (IAESZ). After the collision of Pontides with the Central-Anatolian Crystalline Complex (CACC) in the Paleocene, a new phase of extension and volcanism concomitantly developed along the northern (Almus; Pontides) and southern (Yildizeli; CACC) sides and along the IAESZ during the Middle Eocene time interval. The first products of the Middle Eocene volcanism in these areas are represented by calc-alkaline to alkaline (basic-intermediate) volcanic and volcanoclastic units together with late-stage trachytic dikes, plugs, and stocks. The mantle source area of both volcanic units displays a metasomatized character, which was dominantly fluxed by sediment-sourced melts. The partial melting of the metasomatized source area gave rise to first-stage basic-intermediate volcanism in the crustal levels. Simultaneously with the generation of the first-stage volcanism, basaltic trachyandesitic shallow-seated magma mushes were also developed. The reactivation of these shallow-seated mushes by late-stage extensional tectonics gave rise to the development of trachytic volcanism in both regions, which have a high-K to shoshonitic character. Almus trachytic lavas are phenocryst-poor and have differentiated Mg# numbers (avg. 26). On the other hand, Yildizeli trachytic lavas have a broad compositional range (benmoreite to latite); they are phenocryst-rich and show more basic character (Mg# avg. 40). Trachytic volcanism in both areas is largely controlled by fractional crystallization of similar basaltic trachyandesitic parental magma with minor assimilation of the upper crustal lithologies. 40Ar-39Ar ages from sanidine phenocrysts from both areas also confirm that trachytic volcanism in both regions developed nearly coevally in different tectonic blocks (~41?40 Ma). Generation of similar volcanism on the different tectonic blocks during the postcollisional stage was probably governed by a regional-scale delamination and/or lithospheric removal-related tectonomagmatic processes.

The eruptive products of the last 1000 years at La Fossa volcano on the island of Vulcano (Italy) are characterized by abrupt changes of chemical composition that span from latite to rhyolite. The wide variety of textural features of these products has given rise to several petrological models dealing with the mingling/mixing processes involving mafic-intermediate and rhyolitic magmas. In this paper, we use published whole-rock data for the erupted products of La Fossa and combine them in geochemical and thermodynamic modelling in order to provide new constrains for the interpretations of the dynamics of the active magmatic system. The obtained results allow us to picture a polybaric plumbing system characterized by multiple magma reservoirs and related crystal mushes, formed from time to time during the differentiation of shoshonitic magmas, to produce latites, trachytes and rhyolites. The residing crystal mushes are periodically perturbated by new, fresh magma injections that, on one hand, induce the partial melting of the mush and, on the other hand, favor the extraction of highly differentiated interstitial melts. The subsequent mixing and mingling of mush-derived melts ultimately determine the formation of magmas erupted at La Fossa, whose textural and chemical features are otherwise not explained by simple assimilation and fractional crystallization models. In such a system, the compositional variability of the erupted products reflects the complexity of the physical and chemical interactions among recharging magmas and the crystal mushes.

Bingham Canyon is one of the world's largest porphyry Cu–Mo–Au deposits and was previously used as an example to emphasize the role of magma mixing and magmatic sulphide saturation in the enhancement of ore fertility of magmatic systems. We analyzed whole rocks, minerals, and silicate melt inclusions (SMI) from the co-genetic, ore-contemporaneous volcanic package (∼38 Ma). As opposed to previous propositions, whole-rock trace element signatures preclude shoshonite–latite genesis via mixing of melanephelinite and trachyte or rhyolite, whereas core to rim compositional profiles of large clinopyroxene phenocrysts suggests the amalgamation of the ore-related magma reservoir by episodic recharge of shoshonitic to latitic magmas with various degrees of differentiation. Major and trace element and Sr and Nd isotopic signatures indicate that the ore-related shoshonite–latite series were generated by low-degree partial melting of an ancient metasomatized mantle source yielding volatile and ore metal rich magmas. Latite and SMI compositions can be reproduced by MELTS modeling assuming 2-step lower and upper crustal fractionation of a primary shoshonite with minimal country rock assimilation. High oxygen fugacities ( ≈ NNO + 1 ) are prevalent as evidenced by olivine-spinel oxybarometry, high SO3 in apatite, and anhydrite saturation. The magma could therefore carry significantly more S than would have been possible at more reducing conditions, and the extent of ore metal sequestration by magmatic sulphide saturation was minimal. The SMI data show that the latites were Cu rich, with Cu concentrations in the silicate melt reaching up to 300–400 ppm at about 60 wt% SiO2. The Au and Ag concentrations are also high (1.5–4 and 50–200 ppb, respectively), but show less variation with SiO2. A sudden drop in Cu and S concentrations in the silicate melt at around 65 wt% SiO2 in the presence of high Cl, Mo, Ag, and Au shows that the onset of effective metal extraction by fluid exsolution occurred at a relatively late stage of magma evolution. Overall, our results show that fluid exsolution during simple magmatic differentiation of oxidized alkaline magmas is capable of producing giant porphyry Cu deposits.

Combined with in-situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U Pb geochronology, published and unpublished literature on the Caotaobei uranium deposit in southern Jiangxi province, China, is re-examined to provide an improved understanding of the origin of the main ore (103 Ma). The Caotaobei deposit lies in the Hecaokeng ore field and is currently one of China's largest, volcanic-related uranium producers. Unlike commonly known volcanogenic uranium deposits throughout the world, it is spatially associated with intermediate lavas with a shoshonitic composition. Uranium mineralization (pitchblende) occurs predominantly as veinlets, disseminations, and massive ores, hosted by the cryptoexplosive breccias rimming the Caotaobei crater. Zircons from one latite define four distinct 206 Pb/ 238 U age groups at 220–235 Ma (Triassic), 188 Ma (Early Jurassic), 131–137 Ma (Early Cretaceous), and 97–103 Ma (Early-Late Cretaceous transition, hereafter termed mid-Cretaceous). The integrated age (134 ± 2 Ma) of Early Cretaceous zircons (group III) is interpreted as representing the time of lava emplacement. The age data, together with the re-examination of literature, does not definitively support a volcanogenic origin for the generation of the deposit, which was proposed by the previous workers based mainly on the close spatial relationship and the age similarity between the main ore and volcanic lavas. Drill core and grade-control data reveal that rich concentrations of primary uranium ore are common around the granite porphyry dikes cutting the lavas, and that the cryptoexplosive breccias away from the dikes are barren or unmineralized. These observations indicate that the emplacement of the granite porphyries exerts a fundamental control on ore distribution and thus a genetic link exists between main-stage uranium mineralization and the intrusions of the dikes. Zircon overgrowths of mid-Cretaceous age (99.6 ± 5.7 Ma) in the shoshonitic volcanic rock is broadly coeval with main-stage U mineralization, which is probably attributable to a tectonothermal event related to the intrusion of the granite porphyries and further supports our genetic reinterpretation. It is thus concluded that the granite porphyry intrusions and associated magma may provide the fluids, ore components, and the thermal energy for U mineralization. However, some other types of fluids and metal sources (e.g., meteoric-derived fluids, which are yet to be identified) could have been substantially involved in the mineralization process. Our new genetic explanation may point to significant potential for mid-Cretaceous granite-related hydrothermal U deposits in Jiangxi and other parts of Southeast China.

Paleomagnetic and geochronologic data from the eastern margin of Gondwana have been obtained from the Gerringong Volcanics in the southern Sydney Basin, Australia. The corresponding paleomagnetic pole at 56.9°S, 154.8°E (N = 131; A95 = 9.1°) has a 40Ar/39Ar plagioclase plateau age of 265.05 ± 0.35 [0.46] Ma from the Bumbo Latite, and overlaps with recent radio-isotopic and paleomagnetic results published from Western Gondwana. The long-documented inconsistency between Middle Permian Eastern and Western Gondwanan paleomagnetic datasets is most likely an artefact of a lack of reliable paleomagnetic data from Eastern Gondwana for this period. A number of well-dated and recently published ca. 265 Ma paleomagnetic results from Gondwana and Laurussia are shown to be consistent with the Wegenerian Pangea A configuration, with a loose N-S fit of the continents for the Middle Permian. The lack of crustal overlap negates the need for a Pangea B configuration, which if valid must have been assembled to Pangea A by ca. 265 Ma. The reverse polarity Bumbo Latite was sampled from the Kiaman type-section located in the southern Sydney Basin. Three cases of normal polarity were detected in the overlying Saddleback, Dapto, and Berkeley Latites, previously assigned to the Kiaman Reverse Superchron (KRS). We review KRS-aged magnetostratigraphic data and propose that an age assignment of 265 Ma most likely represents the termination of the non-reversing field, with longer stable intervals of normal polarity recorded and able to be correlated globally.

Porphyry Cu deposits are commonly thought to have formed by magmas that were unusually rich in metal and/or sulfur. In this study, we test this assumption by reconstructing the metal and sulfur content of an ore-related latite magma at Bingham Canyon and comparing it with that of intermediate magmas in several other arc magma systems. The ore-related latite magma at Bingham Canyon records strong evidence for magma mixing and has a major to trace element composition that can successfully be modeled by a mixture of ~40 wt % mafic magma, which was similar to the most mafic rock found at Bingham Canyon (a melanephelinite containing 45 wt % SiO 2 ), and ~60 wt % felsic magma of rhyolitic composition. Based on the modal abundance of 0.19 ± 0.01 vol % sulfides and laser ablation-inductively coupled plasma-mass spectrometry analyses of unaltered sulfide inclusions preserved within hornblende and plagioclase phenocrysts, the latite magma contained 50 to 90 ppm Cu, 0.8 to 2.0 ppb Au, 2 to 3 ppm Mo, and ≥0.12 to 0.14 wt % S. Whole-rock and melt and sulfide inclusion data suggest that the bulk of copper and Au in the latite magma was derived from the mafic end member, whereas significant amounts of sulfur were also provided by the felsic end member. A rough, independent estimate of the amount of Cu present in the mixed magma can be obtained by taking the Cu content of mafic, sulfide-undersaturated silicate melt inclusions and multiplying it with the mass fraction of mafic magma involved in the magma mixing. Applying this latter approach to two other porphyry Cu-mineralized magma systems (Santa Rita, USA; Bajo de la Alumbrera, Argentina) and several modern arc magma systems suggests that ore-forming intermediate magmas in mineralized systems were not unusually Cu rich. Whether or not they were unusually sulfur rich could not be answered with the available data. If the sulfur contents of mineralizing magmas prove to be normal, then the most distinctive feature of fertile magma systems may be the formation of large, long-lived magma chambers at 5- to 15-km depth and the development of vent structures that enable focused fluid flow.

Uranium-lead ages and trace element compositions of zircon from a series of shallow porphyry intrusions document the temporal, chemical, and thermal magmatic evolution of magmatic-hydrothermal porphyry Cu (Mo-Au) ores in the El Salvador district, Chile. Zircons ( n = 240) from 15 Eocene age diorite, granodiorite, and granite porphyry intrusions were analyzed by SHRIMP-RG ion microprobe. The weighted means of 207 Pb-corrected 206 Pb/ 238 U zircon ages span 3 m.y. from about 44 to 41 Ma, with peak magmatic flux at 44 to 43 Ma. The granodiorite porphyries at the Turquoise Gulch copper deposit record waning stages of magmatism at 42.5 to 42.0 Ma and were followed by postmineral latite dikes at about 41.6 Ma. Porphyry copper ores formed contemporaneously with porphyry intrusion centers that progressed temporally from north to south, from the small deposits at Cerro Pelado (~44.2 Ma), Old Camp (~43.6 Ma), and at M Gulch-Copper Hill (~43.5–43.1 Ma) to the main ore deposit at Turquoise Gulch (~42 Ma). The Eocene porphyry intrusions contain a few Mesozoic ( n = 9) inherited zircons and numerous ( n ≥19) antecrystic zircons about 1 to 2 m.y. older than the host intrusion that provide evidence of extensive Eocene magmatic recycling. The Ti-in-zircon geothermometer provides estimates of 890° to 620°C for zircon crystallization and records both core to rim cooling and locally high-temperature rim overgrowths. Most zircon in ore-related K, L, and R porphyries yields near-solidus temperatures of 750° to 650°C and crystallized from compositionally diverse granodiorite porphyries that are a product of crystal fractionation of hornblende, apatite, and titanite with lesser crustal contamination and mixing with high-temperature deep-sourced mafic magma. During a 3-m.y. period, porphyry intrusions tapped an evolving granodioritic magma chamber that was periodically heated, locally remelted, and mixed with mafic magma during recharge events but cooled between recharge events to evolve ore fluids. Europium anomalies (chondrite-normalized Eu N /Eu N * ) in zircons become more pronounced with increased Hf content and cooling but display two distinct evolutionary paths: Eu N /Eu N * of early quartz porphyry evolves from 0.8 to 0.3, whereas the late synmineralization porphyries evolve from 0.8 to 0.65. The Eu N /Eu N * ratio of zircon reflects the Eu 3 +/Eu 2 + ratio of the melt, and therefore the granodiorite porphyries at Turquoise Gulch were the most strongly oxidized of the El Salvador magmas. The strongly oxidized trend porphyry magmas at Turquoise Gulch are apparently directly linked to magmatic degassing at ~700°C to produce large amounts of ore-forming copper, sulfur, and chlorine-enriched magmatic-hydrothermal aqueous fluids.

The evolution of the geological structure in the Southern Argun’ Region is studied in terms of changing geodynamic conditions of the Proterozoic, Caledonian, and Variscan Tectonomagmatic Cycles, which also under Mesozoic tectonomagmatic activation led to the formation of latite igneous rocks enriched in Au, Cu–Mo, Pb–Zn–Ag, volcanic and plutonic complexes of the caldera structures with Mo–U, Pb–Zn, and fluorite ores, and rare-metal granites with a Sn–W–Li–Ta spectrum.

In the west and south-west part of Salafchegan near Zavarian village in Iran (in central Iranian volcano plotonic belt), there are some volcanic rocks. Based on petrography and geochemistry findings, these volcanic rocks are Basalt, Andesite, Tracky-Andesite, Trackyte, Latite, Dacite. Tectono-magmatic diagram Y versus Zr shows the magmatic arc setting and Zr/TiO2 versus Ce/P2O5 diagram contrasts post colligenal magmatic arcs. The HFSE depletion in the MORB spider diagram shows significant volcanic arc magmatism. The high enrichment of Eu, Sr, Th, Rb, Cs, K (LFS elements) and Y, Zr, Hf shows negative anomaly and subduction tectonic setting. Based on MORB, Chondrite and primitive mantle spider diagrams, LREE have enriched to HREE in this area. The results of petrography, geochemistry and tectonic setting studies in this area, indicate that neogene magmatism occurred in post colligenal tectonic setting—subduction of Neo-thetise ocean under central Iranian plate in neogen era.

The Masjed Daghi mineralization is located 30 km southeast of Jolfa city at the bank of Araxes River, northwest Iran. This area is situated in the Alborz-Azarbaijan structural zone of Iran. The most widespread rocks in the mineralization area are andesite and trachyandesite, while there are rock units of latite tuff, andesitic agglomerate, and hornblende porphyry basalt in eastern hills and Eocene flysch in the southern part of the area. Several intrusive bodies are present in the study area, from which the dominant intrusive rock hosting the mineralization is diorite porphyry. The mineralized rock units of the area are cut by different diorite ad mafic dikes. The most prevalent texture of mineralization is dissemination, while open space filling textures including veins and veinlets, are common as well. Diverse types of alteration including potassic, phyllic, argillic, silicification, and a little of carbonatization were recognized in the field and microscopic observations as well as by XRD. In addition to thick silica veins and stockwork zones, some silica, barite, sulfide, and calcite veins and veinlets have occurred in the Masjed Daghi mineralization area. In this research, 26 doubly polished thin sections (wafers) were prepared and investigated. Four samples were taken from surface veins, while 22 samples were chosen from core samples (of 6 boreholes) of white and grey-white silica, and silica-barite veins. The fluid inclusion studies on 105 primary fluid inclusions indicated five phases for inclusions including: 1) liquid or gas, 2) liquid and gas, 3) liquid, gas, and solid, 4) liquid, gas, halite, and solid, and 5) liquid, gas, halite, and two types of solids. The data gained from fluid inclusions approved two mineralization fluids which caused porphyry and epithermal mineralizations. The porphyry fluid inclusions were homogenized in temperatures of 122°C to 550°C with a maximum of 700°C and average salinity of 55 wt% NaCl equivalent, while the epithermal inclusions indicated an average homogenization temperature of 186°C with an average salinity of 6.23 wt% NaCl equivalent.

In the Vila Tancredo Neves locality, Amazonian craton, northern Brazil, occur Paleoproterozoic well-preserved volcano–plutonic centers. The lower 1.88 Ga Sobreiro Formation has overlapped lavas comprising andesite at the base; andesi-basalt and latite at middle; and quartz-latite and rhyolite at the top; besides associated pyroclastic and autoclastic lithofacies. Reveals high-K calc-alkaline and metaluminous signature. This unit shows K, Ba, Sr, and Rb enrichments; and Nb and Ta negative anomalies. Occurs an LREE-enriched pattern relative to HREE. Eu anomaly is absent in the most primitive rocks, whereas the evolved rocks reveal a minor negative Eu anomaly. These chemical characteristics are compatible with arc-related andesites. The upper, fissure-controlled, 1.87 Ga Santa Rosa Formation has peraluminous rhyolites and intrusions of rhyolitic porphyries and granites. These alkali rhyolites erupted in several vents within greater brittle faults, with outflows of ignimbrites and volcaniclastic deposits with variable textures. They reveal HFSE enrichment (Nb and Ta) and strong negative anomalies of LILE (Ba and Sr). Some evolved rhyolitic samples usually attributed to the Santa Rosa Formation are calc-alkaline and have geochemical constraints closer to those of the Sobreiro Formation andesitic rocks. Observations of the volcano–plutonic complex point to a Paleoproterozoic volcanic caldera related to several pulses of felsic and andesitic–rhyodacitic–rhyolitic lavas that comprise a stratovolcano evolution in the pre-caldera stage. Pyroclastic sin-caldera deposits with ignimbrite, ash tuff, crystal-rich tuff, and minor polymictic breccia are less preserved. Later evolved domes, dikes, and volcaniclastic rocks represent the recurrent magmatism in the post-caldera stage. This work supplies new support for more systematic stratigraphic and geochemical studies of these poorly studied, but promising, Proterozoic units.

The Vathi porphyry Cu-Au &plusmn, Mo mineralization is located in the Serbo-Macedonian metallogenic province of the Western Tethyan Metallogenic Belt. It is mainly hosted by a latite and is genetically associated with a quartz monzonite intrusion, which intruded the basement rocks of the Vertiskos Unit and the latite, 18 to 17 Ma ago. A phreatic breccia crosscuts the latite. The quartz monzonite was affected by potassic alteration, whereas the latite was subjected to local propylitic alteration. Both styles of alteration were subsequently overprinted by intense sericitic alteration. M-type and A-type veins are spatially associated with potassic alteration, whereas D-type veins are related to the sericitic alteration. Three ore assemblages are associated with the porphyry stage: (1) pyrite + chalcopyrite + bornite + molybdenite + magnetite associated with potassic alteration, (2) pyrite + chalcopyrite related to propylitic alteration, and (3) pyrite + chalcopyrite + native gold &plusmn, tetradymite associated with sericitic alteration. A fourth assemblage consisting of sphalerite + galena + arsenopyrite + pyrrhotite + pyrite &plusmn, stibnite &plusmn, tennantite is related to an epithermal overprint. Fluid inclusion data indicate that the A-type veins and related porphyry-style mineralization formed at 390&ndash, 540 &deg, C and pressures of up to 646 bars (&lt, 2.6 km depth) from boiling hydrothermal fluids. A later condensation of vapor-rich inclusions resulted in a moderately saline fluid (8.4&ndash, 11.2 wt % NaCl equiv) at temperatures between 311 and 392 &deg, C, which were related to sericitic alteration, D-type veins, and associated metallic mineralization. Subsequent dilution of the moderately saline fluid at lower temperatures (205&ndash, 259 &deg, C) produced a less saline (1.4&ndash, 2.9 wt % NaCl equiv.) fluid, which is likely associated with the late epithermal overprint.

The Pliocene Etrusk stratovolcano, located in the northeast of Lake Van (Eastern Anatolia; Turkey), is one of the important volcanic centres in the Eastern Anatolian collision zone. Mt. Etrusk overlies a widespread volcanic plateau, consisting of basaltic and hawaiitic lavas formed by fissure eruptions between 4.9–4.5 Ma. These basic lavas contain a phenocryst phase consisting of olivine, plagioclase and clinopyroxene. Trace element ratio diagrams imply that these basic magmas were generated from a mantle that contained a clear subduction component that is related to the subducted sediments rather than fluids or altered oceanic crust. Results of the melting models on the basaltic plateau lavas indicate that there was a marked variation both in the mantle source mineralogy (i.e. the ratio of garnet peridotite to spinel peridotite in the source varies between 60/40% and 40/60%) and the degree of melting (i.e. F between 0.8–4%). This can be explained by a model in which magmas were generated by partial melting of both metasomatised lithospheric and deeper asthenospheric mantle sources in an extensional setting in response to the partial delamination of the lithospheric mantle of Eastern Anatolia and then mixed with each other during Pliocene times. Central eruptions that formed the Etrusk volcano lasted ~ 600 kyr between 4.3–3.7 Ma during Zanclean times. The estimated depth of the Etrusk magma chamber is ~ 9–12 km. The volcano erupted lavas with a rather narrow compositional range from latite to rhyolite, which are either transitional or mildly alkaline in character. The Etrusk lavas contain plagioclase, clino- and orthopyroxene, biotite, K-feldspar and rarely, minor amounts of olivine and amphibole in the phenocryst phase. A composite chemo-stratigraphic section of the volcano and petrological models indicate that the evolved lavas of the Etrusk volcano differentiated from a parental magma composition, which is similar to that of the most primitive plateau basalt lavas underlying the volcano, via the AFC process, and experienced at least two major magma replenishment episodes at 4.1 Ma and 3.8 Ma during the magma chamber evolution.

The paper presents new data on age, geochemistry, and Sr and Nd isotope composition of rocks from the Akatui massif and comagmatic rocks from the lower unit of the Kailas Formation (Akatui volcano-plutonic association), localized within the Aleksandrovskii Zavod depression. The amphibole 40Ar/39Ar age date the monzogabbro of the early phase of the Akatui massif at 154.8 ± 4.4 Ma; the monzonite of the main phase yields a 40Ar/39Ar age of 160.7 ± 3.9 Ma, and the shoshonite basalt of the lower unit of the Kailas Formation yields a 40Ar/39Ar age of 161.5 ± 1.7 Ma. The leading petrogenetic mechanism for the Akatui volcano-plutonic association is crystal fractional differentiation of melts with minor crustal contamination, which can be suggested from the mineralogical and petrographic features and geochemical and isotope characteristics of rocks. The geochemical data for the Akatui volcano-plutonic association show LILE, LREE, U, Th, and Pb enrichment with a characteristic depletion in high-field strength elements (HFSE), such as Nb and Ti. They are also depleted in P. Sr–Nd isotope data (87Sr/86Sr(160 Ma) = 0.70642–0.70688 and εNd(160 Ma) = – 0.6 to – 2.2) suggest an EMII-type mantle source and could also indicate a negligible degree of crustal contamination in the evolved melts.

A spectacular feature of the Arabian-Nubian Shield (ANS) is the abundance of well-exposed and extensive Neoproterozoic dike swarms of variable compositions. Most of these dikes are late to post-orogenic with respect to the East African Orogen (EAO) and are unmetamorphosed. We dated a composite dike with latite margins and a rhyolite core (607 ± 6 Ma, U-Pb), a biotite rhyolite dike (600 ± 4 Ma, 40Ar/39Ar age of biotite), an andesite dike (594 ± 3, 40Ar/39Ar age of amphibole) and a dolerite dike (~579 Ma, 40Ar/39Ar whole rock total gas age). We propose that the first three dikes represent one generation that was emplaced at different episodes extending between 607 and 590 Ma. Time and composition equivalent dikes are common in the northern ANS. The dikes crosscut late collisional granitoids and geochemically display a subduction-related character as evidenced by a negative Nb-Ta anomaly. These dikes are absent in the alkali feldspar A-type Humrat Syenogranite dated at 586 ± 5 Ma in Jordan and equivalent rocks in the northern ANS, which are crosscut only by the (~579 Ma) dolerite dikes. The within-plate character of the dolerite dikes is supported by the absence of the Nb-Ta anomaly and high field strength element geochemistry. We propose that the dolerite dikes are a generation, distinct from the ~607–590 Ma dikes, that reflects a change in tectonic regime and represents the last magmatic activity of the Neoproterozoic in the northern ANS. The ages of the dikes dated in this study agree with the published age range of the transitional stage from late orogenic calc-alkaline to extensional alkaline tectono-magmatic setting for the ANS. We propose that the magmatic activity was terminated ~50 m.y. before the age of the Cambrian unconformity at ~530 Ma. Correlation with ages of dikes and magmatic rocks in the northern ANS favors this supposition. The dike geochemistry and geochronology are compatible with a tectonic model that involves mantle lithosphere delamination from below the northern ANS after a significant crust-mantle thickening caused by the EAO, followed by thermal relaxation, subsidence and gradual denudation until the age of the unconformity at ~530 Ma.

Resumen En la cordillera de Talamanca los productos del magmatismo se encuentran ampliamente distribuidos, y corresponden con episodios intrusivos y extrusivos del Neógeno y del Cuaternario. En general es posible reconocer tres fases magmáticas: 1) vulcanismo anterior al Mioceno Superior, de unos 17 a 11 millones de años atrás; 2) plutonismo durante el Mioceno Medio-Superior, entre 12,5 y 7,5 millones de años, conocido como Grupo Intrusivo de Talamanca o Granito-Gabro de Talamanca; 3) pulsos magmáticos post-intrusivos del Neógeno al Cuaternario, cuyo rango temporal se extiende entre 5 y 2 millones de años. Por primera vez se propone una diferenciación del magmatismo post-intrusivo en tres unidades, separables por aspectos petrográficos: a) Unidad Kámuk, constituida por andesitas con plagioclasa de tipo labradorita y ocasionalmente con ortopiroxeno; b) Unidad Dúrika, definida por plagioclasa de tipo andesina y biotita como fenocristal ferromagnesiano predominante; c) Unidad Río Lori, cuyos productos no fueron recolectados, pero con base en trabajos previos se caracteriza por la presencia de cuarzo, anfíbol y biotita. Se realiza además una contribución a la cartografía geológica de la cordillera de Talamanca, con una descripción geológica de las cimas de Cuericí, Ena, Dúrika, Utyum, Kámuk, fila Pittier y Echandi. También se presentan nuevos datos sobre la geología del cerro Chirripó. Abstract In the Talamanca Cordillera, the widespread magmatic products record Neogene and Quaternary intrusive and extrusive phases. Generally, it is possible to recognize three magmatic stages: 1) Volcanic series older than Upper Miocene, ranging from ~17 to 11 mya; 2) Plutonic events during the Middle-Upper Miocene, between 12,5 and 7,5 mya, known as Talamanca Intrusive Group or Granite-Gabbro Series of Talamanca; c) Post-intrusive magmatic pulses from Neogene-Quaternary, whose temporal range extends from ~5 to 2 mya. For the first time it is proposed here a differentiation of post-intrusive magmas into three units by petrographic criteria: a) Kamuk Unit, andesites with labradorite-type plagioclase and occasional orthopyroxene. b) Durika Unit, defined by andesine-type plagioclase and the presence of biotite phenocrysts as the predominant ferromagnesian phase. c) Rio Lori Unit, whose products were not sampled in this study, but based in previous work they are characterized by the presence of quartz, amphibole and biotite phenocrysts. Additionally, we provide a new contribution to the geologic cartography of the Talamanca Cordillera, with a geological description of the summits of Cuerici, Ena, Durika, Utyum, Kamuk, fila Pittier and Echandi. We also present new data referring to the geology of the summit of Chirripo.

In the Talamanca Cordillera, the widespread magmatic products record Neogene and Quaternary intrusive and extrusive phases. Generally, it is possible to recognize three magmatic stages: 1) Volcanic series older than Upper Miocene, ranging from ~17 to 11 mya; 2) Plutonic events during the Middle-Upper Miocene, between 12,5 and 7,5 mya, known as Talamanca Intrusive Group or Granite-Gabbro Series of Talamanca; c) Post-intrusive magmatic pulses from Neogene-Quaternary, whose temporal range extends from ~5 to 2 mya. For the first time it is proposed here a differentiation of post-intrusive magmas into three units by petrographic criteria: a) Kamuk Unit, andesites with labradorite-type plagioclase and occasional orthopyroxene. b) Durika Unit, defined by andesine-type plagioclase and the presence of biotite phenocrysts as the predominant ferromagnesian phase. c) Rio Lori Unit, whose products were not sampled in this study, but based in previous work they are characterized by the presence of quartz, amphibole and biotite phenocrysts. Additionally, we provide a new contribution to the geologic cartography of the Talamanca Cordillera, with a geological description of the summits of Cuericí, Ena, Dúrika, Utyum, Kámuk, fila Pittier and Echandi. We also present new data referring to the geology of the summit of Chirripo. En la cordillera de Talamanca los productos del magmatismo se encuentran ampliamente distribuidos, y corresponden con episodios intrusivos y extrusivos del Neógeno y del Cuaternario. En general es posible reconocer tres fases magmáticas: 1) Vulcanismo anterior al Mioceno Superior, de unos 17 a 11 millones de años atrás; 2) Plutonismo durante el Mioceno Medio-Superior, entre 12,5 y 7,5 millones de años, conocido como Grupo Intrusivo de Talamanca o Granito-Gabro de Talamanca; 3) Pulsos magmáticos post-intrusivos del Neógeno al Cuaternario, cuyo rango temporal se extiende entre 5 y 2 millones de años. Por primera vez se propone una diferenciación del magmatismo post-intrusivo en tres unidades, separables por aspectos petrográficos: a) Unidad Kámuk, constituida por andesitas con plagioclasa de tipo labradorita y ocasionalmente con ortopiroxeno; b) Unidad Dúrika, definida por plagioclasa de tipo andesina y biotita como fenocristal ferromagnesiano predominante; c) Unidad Río Lori, cuyos productos no fueron recolectados, pero con base en trabajos previos se caracteriza por la presencia de cuarzo, anfíbol y biotita. Se realiza además una contribución a la cartografía geológica de la cordillera de Talamanca, con una descripción geológica de las cimas de Cuericí, Ena, Dúrika, Utyum, Kámuk, fila Pittier y Echandi. También se presentan nuevos datos sobre la geología del cerro Chirripó.

The active volcano of Ischia, the well-known island off-shore the city of Naples, has had a discontinuous volcanic activity characterised by caldera-forming paroxysmal eruptions, lava flows, and lava domes for >150 kyr. The overall geochemical composition of erupted magmas includes shoshonite, latite, and trachyte/ trachyphonolite. In a complementary study, we demonstrated that the evolution of Ischia trachytes with Sr

The active volcano of Ischia, an island off-shore the city of Naples, Southern Italy, has a discontinuous volcanic activity characterized by caldera-forming paroxysmal eruptions, lava flows, and lava domes, and thus offers the opportunity to study the complexity of magma storage, differentiation, and extraction mechanisms in a long-lived magma reservoir. The overall geochemical composition of erupted magmas varies from shoshonite to latite and trachyte/trachyphonolite. Their Sr and Nd, isotope composition variation is typical of subduction-related magmas, akin to other potassic magmas of the Neapolitan District, and there is a complete overlap of radiogenic isotope composition among shoshonite, latite, and trachyte/trachyphonolite. The lack of systematic radiogenic isotope covariation during differentiation suggests that the radiogenic isotope variability could be a signature of each magma pulse that subsequently evolved in a closed-system environment. Erupted magmas record a recurrent evolutionary process consisting of two-step fractional crystallization along similar liquid lines of descent for each magma pulse, suggesting near steady-state magma chamber conditions with balanced alternating periods of replenishment, differentiation, and eruption. The dominant role of fractionating feldspars determines a significant depletion of Sr ( 200) in the residual trachyte magma. Several more-evolved trachytes have anomalous radiogenic 87 Sr/ 86 Sr i (>0.707) coupled with high 87 Rb/ 86 Sr (>50), all other geochemical and isotopic characteristics being similar to normal 87 Sr/ 86 Sr i trachytes at the same degree of evolution. This radiogenic Sr isotope signature is not consistent with assimilation of crustal material and demands for a time-related in-growth of 87 Sr during storage within the magma chamber. Rb-Sr isochrons on separated mineral-groundmass pairs provide robust constraints on a prolonged pre-eruptive history ranging from a few tens to hundreds of thousands of years at relatively low temperature (~750 °C). Remarkably, also normal trachytes with high 87 Rb/ 86 Sr (>200) yield a magma residence time from some 4 to 27 kyr, implying that the long-lived history of Ischia magmas is not limited to the anomalous 87 Sr/ 86 Sr i trachytes. This long-lived history could be a characteristic feature of the magma chamber reservoir of this active volcano, which other volcanic products (i.e., shoshonite and latite) cannot disclose due to their lower Rb/Sr (i.e., low 87 Sr in-growth rate) and higher magma storage temperature (>900 °C) (i.e., rapid Sr isotope homogenization via diffusion). The magma chamber dynamics of the active volcano of Ischia, probed on the basis of geochemical and radiogenic isotope tools, is consistent with recent models of complex magma chamber reservoirs made up of multiple discrete melt pockets, isolated by largely crystalline mush portions, maintained in a steady-state thermal flux regime with no mass exchange, and with reactivation shortly before eruption.

Dissected caldera structures expose thick intracaldera tuff and, uncommonly, cogenetic shallow plutons, while remnants of correlative outflow tuffs deposited on the pre-eruption ground surface record elements of ancient landscapes. The Middle Fork caldera encompasses a 10 km × 20 km area of rhyolite welded tuff and granite porphyry in east-central Alaska, ∼100 km west of the Yukon border. Intracaldera tuff is at least 850 m thick. The K-feldspar megacrystic granite porphyry is exposed over much of a 7 km × 12 km area having 650 m of relief within the western part of the caldera fill. Sensitive high-resolution ion microprobe with reverse geometry (SHRIMP-RG) analyses of zircon from intracaldera tuff, granite porphyry, and outflow tuff yield U-Pb ages of 70.0 ± 1.2, 69.7 ± 1.2, and 71.1 ± 0.5 Ma (95% confidence), respectively. An aeromagnetic survey indicates that the tuff is reversely magnetized, and, therefore, that the caldera-forming eruption occurred in the C31r geomagnetic polarity chron. The tuff and porphyry have arc geochemical signatures and a limited range in SiO 2 of 69 to 72 wt%. Although their phenocrysts differ in size and abundance, similar quartz + K-feldspar + plagioclase + biotite mineralogy, whole-rock geochemistry, and analytically indistinguishable ages indicate that the tuff and porphyry were comagmatic. Resorption of phenocrysts in tuff and porphyry suggests that these magmas formed by thermal rejuvenation of near-solidus or solidified crystal mush. A rare magmatic enclave (54% SiO 2 , arc geochemical signature) in the porphyry may be similar to parental magma and provides evidence of mafic magma and thermal input. The Middle Fork is a relatively well preserved caldera within a broad region of Paleozoic metamorphic rocks and Mesozoic plutons bounded by northeast-trending faults. In the relatively downdropped and less deeply exhumed crustal blocks, Cretaceous–Early Tertiary silicic volcanic rocks attest to long-term stability of the landscape. Within the Middle Fork caldera, the granite porphyry is interpreted to have been exposed by erosion of thick intracaldera tuff from an asymmetric resurgent dome. The Middle Fork of the North Fork of the Fortymile River incised an arcuate valley into and around the caldera fill on the west and north and may have cut down from within an original caldera moat. The 70 Ma land surface is preserved beneath proximal outflow tuff at the west margin of the caldera structure and beneath welded outflow tuff 16–23 km east-southeast of the caldera in a paleovalley. Within ∼50 km of the Middle Fork caldera are 14 examples of Late Cretaceous (?)–Tertiary felsic volcanic and hypabyssal intrusive rocks that range in area from 2 to ∼100 km 2 . Rhyolite dome clusters north and northwest of the caldera occupy tectonic basins associated with northeast-trending faults and are relatively little eroded. Lava of a latite complex, 12–19 km northeast of the caldera, apparently flowed into the paleovalley of the Middle Fork of the North Fork of the Fortymile River. To the northwest of the Middle Fork caldera, in the Mount Harper crustal block, mid-Cretaceous plutonic rocks are widely exposed, indicating greater total exhumation. To the southeast of the Middle Fork block, the Mount Veta block has been uplifted sufficiently to expose a ca. 68–66 Ma equigranular granitic pluton. Farther to the southeast, in the Kechumstuk block, the flat-lying outflow tuff remnant in Gold Creek and a regionally extensive high terrace indicate that the landscape there has been little modified since 70 Ma other than entrenchment of tributaries in response to post–2.7 Ma lowering of base level of the Yukon River associated with advance of the Cordilleran ice sheet.

Twenty vapour-phase garnets were studied in two samples of the Topopah Spring Tuff of the Paintbrush Group from Yucca Mountain, in southern Nevada. The Miocene-age Topopah Spring Tuff is a 350 m thick, devitrified, moderately to densely welded ash-flow tuff that is zoned compositionally from high-silica rhyolite to latite. During cooling of the tuff, escaping vapour produced lithophysae (former gas cavities) lined with an assemblage of tridymite (commonly inverted to cristobalite or quartz), sanidine and locally, hematite and/or garnet. Vapour-phase topaz and economic deposits associated commonly with topaz-bearing rhyolites (characteristically enriched in F) were not found in the Topopah Spring Tuff at Yucca Mountain. Based on their occurrence only in lithophysae, the garnets are not primary igneous phenocrysts, but rather crystals that grew from a F-poor magmaderived vapour trapped during and after emplacement of the tuff. The garnets are euhedral, vitreous, reddish brown, trapezohedral, as large as 2 mm in diameter and fractured. The garnets also contain inclusions of tridymite. Electron microprobe analyses of the garnets reveal that they are almandinespessartine (48.0 and 47.9 mol.%, respectively), have an average composition of (Fe1.46Mn1.45Mg0.03Ca0.10)(Al1.93Ti0.02)Si3.01O12and are comparatively homogeneous in Fe and Mn concentrations from core to rim. Composited garnets from each sample site have δ18O values of 7.2 and 7.4%. The associated quartz (after tridymite) has δ18O values of 17.4 and 17.6%, values indicative of reaction with later, low-temperature water. Unaltered tridymite from higher in the stratigraphic section has a δ18O of 11.1% which, when coupled with the garnet δ18O values in a quartz-garnet fractionation equation, indicates isotopic equilibration (vapour-phase crystallization) at temperatures of ∼600°C. This high-temperature mineralization, formed during cooling of the tuffs, is distinct from the later and commonly recognized low-temperature stage (generally 50−70°C) of calcite, quartz and opal secondary mineralization, formed from downward-percolating meteoric water, that locally coats fracture footwalls and lithophysal floors.

Sulfide minerals from the El Salvador porphyry Cu–Mo deposit, Chile, were dated by Re–Os geochronology to clarify the timing and duration of mineralization. As these data are collected over the past 10 years, they chronicle the evolution of Re–Os analytical procedures and improvements in spike-sample equilibration, mass spectrometry and data reduction. Included in the data is the first tennantite–pyrite Re–Os isochron along with tennantite–enargite–pyrite Os tracing of ore metals based on initial osmium systematics (187Os/188Osi). Porphyry-associated mineralization follows the traditional early (A), transitional (B), and late (D) stage classification of relative timing of vein formation. Most Cu- and Mo-bearing sulfides were deposited during stages A and B. Field relationships clearly show the B-stage veins are older than the D-stage veins. Samples analyzed with Carius tube digestion and mixed-double spike indicate B-stage molybdenite mineralization between 41.8 and 41.2 Ma. These ages best represent the timing of main-stage mineralization at El Salvador. A five-point 187Re–187Os isochron for pyrite–tennantite from the latest D-stage veins yields an age of 42.37 ± 0.45 Ma. The isochron age, while older, is within error of early analyses of molybdenite by alkaline fusion digestion using single Re and Os spikes (42.4–42.0 Ma). A separate pyrite and tennantite–enargite pair containing significant common Os yields an initial 187Os/188Os ratio of 0.134 ± 0.042, compatible with a predominantly mantle origin. We appreciate the early analyses for their historical significance while emphasize the geological implications of the 41.8–41.2 Ma molybdenite ages. Temperature estimates by sulfur thermometry and fluid inclusions are 390–510 °C for the B-stage molybdenites and 230–240 °C for the latest D-stage pyrite and tennantite. Analyses based on Carius tube digestion and updated spike calibrations suggest a ∼0.6 m.y. duration (∼41.8 to 41.2 Ma) in-line with published deposit geochronology. The timing and duration of mineralization from Re–Os dating of ore minerals is more precise than estimates from previously reported 40Ar/39Ar and K–Ar ages on alteration minerals. The Re–Os results suggest that the mineralization is temporally distinct from pre-mineral rhyolite porphyry (42.63 ± 0.28 Ma) and is immediately prior to or overlapping with post-mineral latite dike emplacement (41.16 ± 0.48 Ma). Based on the Re–Os and other geochronologic data, the Middle Eocene intrusive activity in the El Salvador district is divided into three pulses: (1) 44–42.5 Ma for weakly mineralized porphyry intrusions, (2) 41.8–41.2 Ma for intensely mineralized porphyry intrusions, and (3) ∼41 Ma for small latite dike intrusions without major porphyry stocks. The orientation of igneous dikes and porphyry stocks changed from NNE-SSW during the first pulse to WNW-ESE for the second and third pulses. This implies that the WNW-ESE striking stress changed from σ3 (minimum principal compressive stress) during the first pulse to σHmax (maximum principal compressional stress in a horizontal plane) during the second and third pulses. Therefore, the focus of intense porphyry Cu–Mo mineralization occurred during a transient geodynamic reconfiguration just before extinction of major intrusive activity in the region.

The quartz monzonite porphyry stock at Kighal in northwestern Iran intruded the Upper Eocene andesite to latite and basalt units, and the resulted hydrothermal activities led to the development of hydrothermal alteration zones, including potassic, phyllic, argillic and propylitic, coupled with Cu mineralization. Hypogene sulfide mineralization principally occurred within the potassic, transitional potassic–phyllic and phyllic alteration zones as disseminations, stockwork veinlets and open-space fillings. These hypogene minerals include pyrite, chalcopyrite and molybdenite, along with lesser amounts of sphalerite and galena at the marginal parts of the porphyry stock. By taking into account the development of hydrothermal alteration zones and their spatial distribution, stockwork-type mineralization of Cu–Mo minerals, and even the occurrence of mineralization zoning with Cu–Mo-rich ore within the stock and Cu–Pb–Zn ore in the marginal parts, mineralization at Kighal in association with the quartz monzonite sub-volcanic stock can be regarded as of porphyry copper type. However, its low Cu and Mo grade detracts its economic potential. Zircon U–Pb geochronology of the porphyry stock yielded Early Miocene ages of 20.0 ± 0.2 to 18.8 ± 0.2 Ma with a weighted mean of 19.24 ± 0.17 Ma, which correspond to the third porphyry Cu metallogenic epoch in NW Iran. The age data show that it is a little younger than the quartz monzonite porphyry stock in the Sungun porphyry copper deposit (PCD) and the porphyritic granodiorite stock in the Niaz prospect, while it is almost coeval with the porphyritic granodiorite stock in the Haft Cheshmeh PCD, as well as with the mineralization at the Masjed Daghi PCD in NW Iran. The Th/U ratios of the zircons range between 0.37 and 0.59, corresponding to the values for magmatic zircons. The analyzed zircons mainly possess initial eHf(t) values of 6.7 to 10.0, which suggest a juvenile and homogeneous magmatic source and the predominance of mantle-derived magmas with limited crustal assimilation.

This work reports a geochemical overview and modelling of the lavas erupted ~ 4.4 Ma ago at San Vincenzo (Tuscan Magmatic Province, TMP). Although these lavas cover a relatively small area (~ 10 km2), they show very large geochemical variations caused by the interaction of mantle-derived and crustal-anatectic magmas. The lavas consist of peraluminous rhyolites (87Sr/86Sr(i) up to 0.726) hosting primarily variably sized magmatic enclaves with shoshonite/latite compositions (87Sr/86Sr(i) down to 0.708). New whole-rock data for a large shoshonite enclave show high concentrations of LREE, LILE, and tetravalent HFSE, coupled with pentavalent HFSE depletions and enrichments in compatible elements such as Cr and Co. The chondrite-normalised REE pattern is strongly fractionated and characterised by a negative Eu anomaly (Eu/Eu* = 0.79). Hybridisation and AFC models suggest that the shoshonite enclave is the result of 12% rhyolite contamination of a mantle-derived magma akin to the potassic trachybasalt/shoshonite lavas of Capraia Island (~ 4.6 Ma; TMP), following an 18.5% assimilation of Late Triassic metasediments (13% evaporite and 5.5% carbonate) and 56% fractionation of clinopyroxene (39%), plagioclase (10%), and biotite (7%). Each rhyolite sample is characterised by mineral-scale isotopic disequilibria (e.g., 87Sr/86Sr(i) = 0.711–0.726), glass inclusions with large K2O/Na2O variations (1.1–3.4) and a poli-thermobarometric history of crustal melt production at eutectic conditions. A multi-parametric approach accounting for K2O/Na2O (1.3–2.2), 87Sr/86Sr(i) (0.713–0.725), Sr (104–311 ppm) and Rb (294–403 ppm) whole-rock variations, allowed us to divide the anatectic (A) rhyolites into five groups (A1, A2.1, A2.2, A2.3, A3). Group A1 shows the highest 87Sr/86Sr(i) ratios and the lowest values of Sr, K2O/Na2O and Rb. It is related to A2.1 and A3 rhyolites by positive K2O/Na2O–Rb and K2O/Na2O–FeO correlations. These three rhyolite groups crop out in the south of San Vincenzo and are interpreted to derive from mixing and ascent of peraluminous magma batches locally extracted at progressively higher temperatures from the heterogeneous Paleozoic metamorphic basement. The A2.3 rhyolites show the highest Rb concentrations (up to 403 ppm) and inverse Sr–Rb and K2O–FeO correlations, suggesting reactions involving the incongruent melting of a biotite-bearing crustal source, which was previously depleted in low-temperature melting components such as muscovite and albite. Most of the A2.3 rhyolites crop out in the northern SVVC area and appear spatially and geochemically related to the A2.2 rhyolites by similarly low 87Sr/86Sr(i) ratios. However, A2.2 rhyolites show lower Rb contents (296–316 ppm) and geochemical correlations (e.g., 87Sr/86Sr(i)–Rb, Sr–Rb, MgO–FeO) clearly indicating hybridisation (mixing) with the shoshonite mantle-derived magma (Rb = 109–122 ppm). Finally, we propose a four-stage model for the magma plumbing system of San Vincenzo, produced by the uprising of a mantle-derived magma in a normally faulted (and doubled) crustal basement characterised by two sections of Paleozoic siliciclastic rocks separated by Late Triassic evaporite-carbonate sequences.

Tertiary volcanism (34.3 ± 1.2 Ma and 0.4 ± 0.7 Ma) in NW Turkey produced lead + zinc bearing trachyte, latite, dacite and rhyodacite tuffs, and agglomerates, as well as basaltic andesite, andesite, dacite, and rhyolite lavas. The primary objective of this study is to develop quantitative models for the evolution of magmas that produced these rocks and for the dissolution, transport, and deposition of disseminated ore as sphalerite and galena vein deposits. Our petrogenetic modelling using the MELTS algorithm (Ghiorso, M.S., and Sack, R.O., 1995, Chemical mass transfer in magmatic processes IV: a revised and internally consistent thermodynamic model for the interpolation and extrapolation of liquid-solid equilibria in magmatic systems at elevated temperatures and pressures: Contributions to Mineralogy and Petrology, v. 119, p. 197–212) indicates that the ore-bearing volcanic rocks reflect mixing of a basaltic andesite parental magma with a rhyolite magma. In addition, our aqueous geochemistry modelling us...

The 60 km 3 Hamblin–Cleopatra stratovolcano produced shoshonite, latite, and trachyte lavas throughout its Miocene eruptive history. Low-silica rhyolite and silica-undersaturated hawaiite erupted before and after lavas of the Hamblin–Cleopatra volcano. Shoshonite, latite, and trachyte resulted from contamination of felsic (trachyte to low-silica rhyolite) anatectic liquids with crystals from hawaiite. Most of the entrained crystals were not in equilibrium with liquid represented by groundmass, but were mingled with liquid shortly before eruption. Crystal aggregates are common inclusions in the lavas, and are sources of the contaminating minerals. The resulting bulk compositions of these porphyritic lavas form a continuum that resembles a liquid line of descent, as dictated by mass balance.

This study focuses on age and evolution of the Oligocene quartz latite of the Rogozna Mts. (Central Balkan Peninsula), in order to better understand the link between magmatism and formation of Pb–Zn±Ag mineralization. New 40Ar/39Ar biotite and amphibole plateau ages suggest that the Rogozna Mts. quartz latite originated through a continuous volcanic episode from 27.3±0.1 to 29.5±0.1 Ma which was immediately followed by a hydrothermal phase. The quartz latites are hypocrystalline porphyritic with phenocrysts and microphenocrysts (~60 vol.%) of plagioclase (An37–49), biotite Mg# [100×Mg / (Mg+Fetot)] b50, calcic amphibole, quartz, sanidine clinopyroxene and phlogopite (Mg#=79 to 84). The rocks display numerous disequilibrium textures, such as: sieved plagioclase phenocrysts, dissolution effects on quartz, phlogopitized biotite and amphibole crystals, and phlogopite microphenocrysts showing effects of incomplete growth (or dissolution?) and biotitization. The Rogozna Mts. quartz latites are shoshonitic in character with Na2O/K2Ob1, high LILE/HFSE ratios, strong depletions at Nb and Ti and K, Pb and U peaks on primitive mantle-normalized diagrams. They are similar to other potassic/ultrapotassic rocks in this region, in particular to those of Veliki Majdan and Rudnik (West Serbia), which are also related to Pb–Zn deposits. The evolution of the Rogozna Mts. quartz latite is modeled using a trace element binary mixing model adopting a lamproite magma and a dacite-like calc-alkaline melt as end-members. The model implies that a fractionating magma chamber (~4.5–9.5 km) undergoes cooling in the range of >850 °C–~720 °C and injection of lamproite-like melts. The injection causes an increase of temperature and a decrease of viscosity of the resulting hybrid magma, facilitating its upwelling and triggering pyroclastic eruptions. The addition of new volatiles by lamproitic melts most probably established the conditions for a hydrothermal phase above the magma chamber that was previously degassed explosively. This implies that magma mixing processes can be of great importance for the formation of Pb–Zn deposits. Similar processes are likely to have occurred in other areas with economically significant Pb–Zn–Ag± other metal mineralization in the region of the Central Balkan Peninsula (Veliki Majdan, Rudnik, Golija, Kopaonik, Avala, etc.).

This contribution examines two types of Mn deposits, which were exploited in the past in Sardinia. Both types are Tertiary in age, but not strictly coeval and they are both linked to a continental arc setting characterized by the presence of calcalkaline volcanics and shallow marine sediments. Mn-deposits formed in terrestrial or shallow marine environments are unusual compared to the most common deep oceanic ones, and therefore poorly studied. The Mn-ores of Sardinia occur either as stratabound deposits with stratiform geometry associated to rudites with littoral facies or as vein-type deposits hosted within volcanic rocks. In the stratiform deposits the Mn ores form the matrix or cement of a transgressive conglomeratic bed overlain by shallow water limestones and underlain by calc-alkaline volcanics. The vein-type deposits consist of Mn oxides hosted by latite lava domes, comenditic lava flows and rhyolitic ignimbrites. Although these geological settings are markedly different, the main Mn-bearing phases are the same, namely pyrolusite and hollandite. The deposits differ in the presence of accessory minerals, such as todorokite, manganite, coronadite, cryptomelane and gangue minerals. Rare earth element geochemistry is the most effective tool in discriminating the two types of Mn deposits. These analyses indicate that the vein-type deposits were formed from geofluid mixtures linked to the Oligocene–Miocene calcalkaline volcanic cycle. Mineralogical and geochemical data indicate that the crystallization of the Mn oxides in the stratabound deposits was diagenetic, related to sudden changes in Eh and pH in coastal, meteoric waters that came in touch with the marine coastal water after having flushed the calcalkaline volcanics.

The style of volcanism of post-Eocene volcanism in the Alborz zone of northern Iran is different to that of Eocene volcanism (Karaj Formation). Indeed, the volcanic succession of the Abazar district, located in a narrow volcanic strip within the Alborz magmatic assemblage, is characterized by distinct mineralogical and chemical compositions linked to a complex magmatic evolution. The succession was produced by explosive eruptions followed by effusive eruptions. Two main volcanic events are recognized: (1) a thin rhyolitic ignimbritic sheet underlain by a thicker lithic breccia, and (2) lava flows including shoshonite, latite, and andesite that overlie the first event across a reddish soil horizon. Plagioclase in shoshonite (An48–92) shows normal zoning, whereas plagioclase in latite and andesite (An48–75) has a similar composition but shows reverse and oscillatory zoning. QUILF temperature calculations for shoshonites and andesites yield temperatures of 1035 °C and 1029 °C, respectively. The geothermometers proposed by Ridolfi et al. (2010) and Holland and Blundy (1994) yield temperatures of 960 °C and 944 °C for latitic lava, respectively. The samples of volcanic rock show a typical geochemical signature of the continental arc regime, but the andesites clearly differ from the shoshonites, the latites and the rhyolites. The mineralogical and chemical characteristics of these rocks are explained by the following petrogenesis: (1) intrusion of a hot, mantle-depth mafic (shoshonitic) magma, which differentiated in the magma chamber to produce a latitic and then a rhyolitic liquid; (2) rhyolitic ignimbritic eruptions from the top of the magma chamber, following by shoshonitic and then latitic extrusions; (3) magma mingling between the latitic and andesitic magmas, as indicated by the occurrence of andesite clasts within the latite; and (4) andesitic effusions. The youngest volcanic events in the Alborz zone show a close chemical relationship with continental arc rocks, indicating that they formed in a continental collision setting.

Rock samples recovered during the Australian–French AUSFAIR MD153 Survey in 2006 from the northern Lord Howe Rise and the Fairway Ridge provide new constraints on the tectonostratigraphic evolution of the region and represent significant new information from a region in which few rocks have been dated. SHRIMP U–Pb dating of zircon from rocks from the Lord Howe Rise indicates alkali volcanism in the area at 97 Ma (trachyte) and 74 Ma (latite). The older volcanic activity is probably related to the widespread Late Cretaceous magmatism along the eastern Gondwana margin, whereas the younger activity may be related to the opening of the Tasman Sea or rifting in the New Caledonia Basin. The pebbly clasts and shell fossils in some of the associated volcaniclastic rocks provide evidence for the existence of landmasses as a sediment source area in the northern Lord Howe Rise region, and the initial marine incursion into the area around Campanian time.

To develop a model of both the structure and evolution of the Campi Flegrei caldera (CFc) magmatic feeding system, geochronological, geochemical and Sr, Nd, Pb and B isotopic data of representative volcanic products of the past 15 ka have been combined with geophysical and melt inclusion literature data, structural setting and dynamics of the resurgent caldera. According to previous petrological data, the CFc magmatic feeding system consists of a deep reservoir, in which mantle-derived K-basaltic parental magmas differentiate to shoshonite, latite and trachyte, through combined crustal contamination and fractional crystallization processes, and shallow reservoirs where the evolved magmas further differentiate and mingle/mix before eruptions. The Sr, Nd, Pb, and B isotope data allow recognition of three distinct magmatic components. One component is believed to be residual magma from the Neapolitan Yellow Tuff (NYT) caldera forming eruption. The NYT component (87Sr/86Sr of 0.70750–53, 143Nd/144Nd ratio of ca. 0.51246, 206Pb/204Pb of ca. 19.04 and δ11B of ca. –7.9‰), has been the most prevalent component over the past 15 ka being mixed, in most cases, with the other two components. One of these other components is best recognized in the Minopoli 2 magma, first erupted 10 ka ago. Minopoli 2 magma is shoshonitic in composition and is the most enriched in radiogenic Sr (87Sr/86Sr of ca. 0.70860) and unradiogenic Nd and Pb (143Nd/144Nd ratio of ca. 0.51236, 206Pb/204Pb of ca. 18.90), and is characterised by δ11B value of ca. –7.32‰. The third component is trachytic in composition and has higher 206Pb/204Pb (ca. 19.08), lower 87Sr/86Sr (ca. 0.70726) and δ11B (−9.8‰) and higher 143Nd/144Nd (ca. 0.51250), with respect to the NYT component. This third component is best recognized in the Astroni 6 magma and did not appear until ca. 4 ka. The identified isotopically distinct magmatic components were erupted in different sectors of the CFc. During both I (

Study of the oxygen isotopic composition in highpotassic rocks of preore magmatic bodies from thezones of pay datolite mineralization in skarns of theDal’negorskoe borosilicate deposit allowing us torefine the nature of oreforming fluids was undertakenfor the first time. The concepts on the relationshipsbetween datolite mineralization with magmas of alkaline basaltic chambers and parental juvenile fluids prevailed in special publications [1–4]. As this took place,high and ultrapotassic magmatic bodies usuallycalled trachyte or latite were considered as late orebearing phases of the alkaline basaltic chamber. However, mineralogical and geochemical investigations ofthese rocks [5] demonstrated that these were preoredykes of Paleogene basalt intruded in the zone of afluid canal, so oreforming solutions modified basaltsto a state of highpotassic rocks. Alteration was carriedout by aqueous fluids enriched in Ba, K, B, and Rband depleted in lowsoluble elements, namely Zr, Nb,Ta, La, and Ce. The estimations of oxygen isotopeshifts and their correlations in pre and postore igneous rocks of the deposit obtained in this study confirmthese assumptions.The Dal’negorskoe deposit (44°34

The Upper Cretaceous Timok Magmatic Complex (TMC) developed on a continental crust composed of different types of Proterozoic to Lower Cretaceous rocks. The TMC consists of the magmatic suites: Timok andesite (AT) - Turonian-Santonian, Metovnica epiclastite (EM) - Coniacian-Campanian, Osnic basaltic andesite (AO) and Jezevica andesite (AJ) - Santonian-Campanian, Valja Strz plutonite (PVS) - Campanian and Boljevac latite (LB). The sedimentary processes and volcanic activity of the TMC lasted nearly continuously throughout nearly the whole Late Cretaceous. The sedimentation lasted from the Albian to the Maastrichtian and the magmatism lasted for 10 million years, from the Upper Turonian to the Upper Campanian. The volcanic front migrated from East to West. The volcanic processes were characterized by the domination of extrusive volcanic facies, a great amount of volcanic material, a change in the depositional environment during the volcanic cycle, sharp facial transitions and a huge deposition of syn- and post-eruptive resedimented volcaniclastics.

The Bingham Canyon porphyry copper-gold-molybdenum deposit is one of the largest and highest-grade porphyry orebodies in the world. This study focused on the northwest side of the deposit where quartz mon-zonite porphyry (QMP), the first and largest porphyry intrusion, hosts the bulk of the high-grade copper-gold ore (>1.0% Cu, >1.0 ppm Au). The north-northeast–trending, high-grade zone had pre-mining dimensions of 1,500 m strike, >300 m vertical, and 500 m width and contained more than 500 million tonnes (Mt) of ore associated with potassic alteration and abundant quartz veins. The lack of superimposed sericitic alteration yielded ideal exposures in which to study the early, high-temperature stages of ore formation, a style of mineralization that in many porphyry deposits represents the major period of copper introduction. We mapped multiple porphyry dikes in the sequence: (1) QMP, (2) latite porphyry (LP), (3) biotite porphyry (BP), (4) quartz latite porphyry breccia (QLPbx), and (5) quartz latite porphyry (QLP). Porphyry dikes, faults, and quartz veins are steeply dipping and have two dominant orientations; north-northeast– and northwest-striking. Dikes have a north-northeast strike but they thicken and develop northwest-trending apophyses and host high-grade copper-gold zones at intersections with northwest-faults, indicating that magmatic-hydrothermal fluids were focused by these structural intersections. Each porphyry intrusion was accompanied by a similar sequence of veins, potassic alteration, and sulfides. Biotite veinlets were followed by fractures with early dark micaceous (EDM) halos of sericite, K-feldspar, biotite, andalusite, and local corundum containing disseminated bornite-chalcopyrite-gold. EDM halos are cut by multiple generations of A-quartz veins representing the main Cu-Au ore-forming event. Postdating all intrusions are quartz-molybdenite veins followed by quartz-sericite-pyrite veins. Cathodoluminescence (CL) petrography identified distinct A-quartz veinlets consisting of dark-luminescing quartz filling fractures and dissolution vugs in earlier A-quartz veins and adjacent porphyry wall rock. These veinlets contain abundant bornite and chalcopyrite and minor K-feldspar and are closely linked in time to the introduction of the bulk of the copper and gold. Although a similar sequence of veins was repeated on emplacement of all porphyry intrusions, the vein density and intensity of potassic alteration declined with time. The youngest porphyry, QLP, is mostly weakly mineralized and locally unaltered. These observations indicate that magmatic-hydrothermal fluids underwent a similar physiochemical evolution during and immediately following emplacement of each of several porphyry dikes. The relationship between EDM veins and A-quartz veins requires that the flux of magmatic fluid from the magma chamber occurred in an episodic manner as opposed to a continuous discharge. Vein truncation relationships coupled with abrupt changes in copper-gold grades, sulfide ratios, and potassic alteration intensity at porphyry intrusive contacts indicate that the mass of introduced copper and gold decreased significantly during successive porphyry intrusive-hydrothermal cycles, presumably due to depletion of metals and volatiles in the underlying magma chamber.

High-K volcanic rocks of the Stanislaus Group record magmatic events that occurred when the Sierra Nevada microplate began to calve off from the western edge of the Nevadaplano at 10–9 Ma. Despite the fact that these rocks have been studied in the Sierra Nevada for 120 years, their stratigraphy is not well known, because they were largely deposited in a complicated palaeocanyon network that drained the Nevadaplano and are preserved on high peaks in roadless areas. We present new 1:6000 scale mapping and a detailed measured section in the Bald Peak–Red Peak area of the Sonora Pass, in the upper reach of the ‘Cataract’ palaeocanyon, or palaeo-Stanislaus river. The Bald Peak–Red Peak area was proposed as the type section for the Stanislaus Group in 1953 but had not been mapped or measured in sufficient detail to demonstrate stratigraphic relations. Our work demonstrates the following stratigraphy (from base to top): (1) Table Mountain Latite (TML) trachyandesite (latite) and basaltic trachyandesite (shoshoni...

The Miocene Stanislaus Group (Stanislaus, Calaveras, Tuolomne, Alpine and Mono counties, CA), composed of intercalated latite and quartz-latite (trachyandesite and trachyte/trachydacite) lavas and ignimbrites, provides an important marker for reconstructing the elevation history and tectonic development of the Sierra Nevada and Walker Lane. We present new 40Ar/39Ar geochronology and magnetostratigraphy indicating that the Stanislaus Group was emplaced in two pulses: (1) major outpouring of latite lavas at ca. 10.4 Ma and (2) ignimbrite eruptions alternating with lesser lava flow eruptions during ca. 9.4–9.8 Ma. These two events filled the ancestral Stanislaus River drainage in the region of the present Sierra Nevada crest, whereas the ignimbrite eruptions formed the Little Walker Caldera. Our new and previous results date these topographic changes and yield improvements to the Stanislaus Group stratigraphy.

Major and trace element and Sr and Nd isotope data is presented from the Andagua valley scoria cone and lava field (15°32′ S 72°19′ W), Southern Peru in the northernmost part of the Central Volcanic Zone (CVZ). The rocks are all quite evolved in composition (SiO2 = 55–64 wt.%) and classify as benmoreites, latites and few mugearites and trachytes. Samples are characterized by high Na2O (4.2–5.2 wt.%), Sr (600–1300 ppm), Ba (800–1600 ppm). The main difference between the benmoreites and latites is in the Na2O content that reach the highest so far reported from CVZ for these SiO2 concentrations. The rocks are generally nearly aphyric but latites and trachytes are more porphyritic. Amphibole microphenocrysts generally are only present in latites and trachytes. The difference between benmoreite and latite samples is reflected in lower P2O5 and Zr content of the latite samples documenting the existence of two compositional different parental magma types. The investigated volcanic activity spans the Pleistocene to Recent with the historic activity concentrated in the area just south of Andagua. Combined relative stratigraphy, petrography and geochemistry define volcanic units and demonstrate that rocks from Chilcayoc Grande, Chilcayoc Chico 2, Jenchana, Sucna 1 and Chilcayoc Chico 1 represent the most recent volcanic activity. The main trend samples, each form a co-magmatic group resulting in sub-parallel trends in many variations diagrams. It is furthermore shown that these trends point towards calculated mixing lines relating the individual units through a binary mixing process, thus indicating a two stage evolution. In the case of Jenchana, Sucna 1 and Chilcayoc Chico 1, the samples define positive correlation trends in the Sr vs. Rb diagram that can be extrapolated back towards origo indicating nearly perfect incompatibility of Sr and Rb. This together with generally high Sr/Y (50–105) and low Y content (

Genetic relationships between ore mineralization and associations of potassic basaltoids and comagmatic intrusions have been established in recent decades. The works of L.V. Tauson, O.A. Bogatikov, V.I. Kovalenko, and other researchers have shown that both alkaline basaltic and granitoid magmatism of the latite petrochemical type and related multiprofile mineralization were widespread in intracontinental consolidated areas during tectonomagmatic activation. Hence, problems of petrogenesis of latite magmatism and geodynamic regimes of its manifestation acquire great scientific and practical importance. In this context, we carried out petrological studies of the Ketkap trachydacite‐monzonite‐syenite complex of the Ketkap‐Yuna magmatogenic province (KYMP) on the Aldan Shield. A significant part of this rock complex can be derived from latite melts [8]. The formation of the Ketkap Complex is related to final stages of Mesozoic magmatism on the Aldan Shield [3‐8]. The complex exhibits four phases of evolution and is confined to the second cycle of tectonomagmatic reactivation (Table 1). Near the tectonomagmatic structures, the complex postdated intense phonotephrite‐phonolite‐ trachyte volcanism in the western KYMP (the Bokur Complex in the Bokur and Ulakhan calderas of the Ulakhan Massif). Its final stages are temporally and spatially close to alkaline syenite subintrusive magmatism (the Dariin Complex in the Usmun‐Dariin, Yuna‐Dan, and Ulakhan massifs [4, 5, 8]. The main phase of monzonite‐syenite magma intrusion is related to the fourth stage of Mesozoic magmatism on the Aldan Shield and is widely represented at the western flank of the Ketkap magmatogenic uplift of the KYMP. Moreover, small exposures of Ketkap monzonitoids are known in the KYMP in a series of other magmatogenic massifs in association with alkaline magmatites of the Dariin Complex. The fifth (final) stage of the Mesozoic magmatism was marked by the intrusion of a series of dikes of subalkaline potassic rocks, which also show spatiotemporal association with dikes of alkaline magmatites of the Dariin Complex. The geological position and petrographical features of the Ketkap Complex were described previously [3, 6, 8, and others]. Representative compositions of rocks and some of the results of their petrogeochemical and geodynamic typification are given in this work (Table 2). The rock complex includes feldspathoid-free rocks (shonkinites, syenites, monzonites, and quartz monzonites), monzodiorites, subvolcanic trachydacites

Near Buckingham, Quebec, Sr-, K-rich rocks exposed in small, Mesoproterozoic, volcano-plutonic bodies of the Robitaille suite overlie or intrude the Grenville metasedimentary sequence and are cut by Neoproterozoic diabase dykes. They may represent near-surface equivalents of the Mont Laurier – Marmora alkaline plutons. The rocks includes latite and alkali-feldspar trachyte, lamprophyres (kersantite and minette), monzodiorite and alkali-feldspar syenite. Ultrapotassic compositions are common. The complexes, up to 2.7 km long and 1.0 km wide, are partly fringed with aureoles of Sr-rich, dolomitized calcitic marble. In 20 samples from three igneous complexes, Sr (up to 3960 ppm) is present in celestine (very rare), barite (rare), fluorapatite and calcite, but feldspars are the main hosts. K-feldspar without plagioclase occurs in samples with K 2 O/Na 2 O > 15 (weight ratio), and K-feldspar + plagioclase in samples with a lower ratio. Individual grains of plagioclase in the groundmass of lamprophyre are unzoned, but distinct ranges of An content are found in grains from restricted areas within a single polished thin section. The amount of Sr increases linearly with An content, from near zero at end-member albite to 1.0–2.6 wt% SrO at An 40 . In one sample of latite, Sr peaked at An 30 . Variation of Sr within a single sample is due to both differentiation (mainly by crystallization of sanidine) and equilibrium factors (such as temperature and An content). Clustering of point compositions on An – wt% diagrams for individual samples may reflect periods of volcanicity, separated by quiescent intervals, as differentiation evolved continuously in the parent magma-chamber. Barium is low, but can be correlated with Sr in one kersantite sample. The distribution of Sr between contiguous K-feldspar and plagioclase grains is governed by disequilibrium factors at low An content. For feldspar pairs, Sr preferentially enters more calcic plagioclase (An > ca. 10), but K-feldspar where plagioclase is more sodic (An ca. 10).

Detailed field and geochemical investigations in the vicinity of the type section of the Tafelberg Formation of the early Cretaceous Etendeka Group, NW Namibia, have revealed the existence of a large eruptive vent in the lower part of the regional volcanic sequence produced by Strombolian and Vulcanian eruptions. The vent is filled with the thick, differentiated, ponded Kudu-Run olivine-rich basaltic flow, which has a distinctive low Zr/Y geochemical signature as well as a Tafelberg-type tabular basalt and the Nil Desperandum latite. Field evidence indicates that the Kudu-Run basalt and the latite were erupted from fissures located within the vent. Associated with the vent is an extensive pyroclastic apron extending from the vent edge and which is interbedded with the regional stratigraphy. Blocks of Precambrain basement lithologies occur within this deposit and indicate that the vent was excavated to a depth of at least 350 m below the palaeosurface at that time. The original Tafelberg Formation type section described by Erlank et al. [Erlank, A.J., Marsh, J.S., Duncan, A.R., Miller, R.McG., Hawkesworth, C.H., Betton, P.J., Rex, D.C. 1984. Geochemistry and petrogenesis of the Etendeka volcanic rocks from SWA/Namibia, 195–247. In: Erlank, A.J. (Ed.), Petrogenesis of Volcanic Rocks of the Karoo province. Special Publication of the Geological Society of South Africa, vol. 13, 395 p.] the Tafelberg Gully section, crosses from the lower part of the regional sequence into the intra-vent sequence and returns to the regional sequence higher up. In doing so it includes some of the localized intra-vent flows and excludes a number of flows which are part of the regional sequence in its lower part, thus rendering it inappropriate as a type section. A revised type section for the Tafelberg Formation is described by combining the upper part of the Tafelberg Gully section with a new section of 14 flows at the base of the regional sequence in the Tafelberg North (TBN) section some 2 km N of the Tafeleberg Gully. Distinctive flows in the TBN section can be mapped southwards where their precise stratigraphic relationship to the northward-thinning Springbok and Goboboseb Quarts Latite members of the Awahab Formation can be demonstrated. These stratigraphic relationships are entirely consistent with palaeomagnetic reversal stratigraphy and demonstrate that the same N–R–N polarity sequence occurs in the type sections of the Awahab and Tafelberg formations. Thus, the Awahab and Tafelberg magma systems were contemporaneous but the Tafelberg system outlived that of the Awahab. The Awahab system was built from eruptive centres located S of the Huab River whereas the Tafelberg vents were located further north.

Campi Flegrei is a large volcanic complex (∼ 150 km 2 ) located west of the city of Naples, Italy. The area has been the site of volcanic activity for more than 60,000 years and represents a potential volcanic hazard owing to the large local population. In this study, the geochemistry of the magma associated with two different eruptions at Campi Flegrei has been characterized, with the aim to identify geochemical trends that may help to predict the style and nature of future eruptions. Two eruptions of different age and eruptive style have been selected for study, Fondo Riccio (9.5 ka) and Minopoli 1 (11.1 ka). A scoria (CF-FR-C1) and a bomb (CF-FR-C2) were collected from the Fondo Riccio eruption, and two scoria samples were collected from the Minopoli 1 (CF-Mi1-C1 and C2) eruptive products. The pre-eruptive volatile content of magma plays an important role in the style of eruption. The original volatile content of magma can be assessed from studies of melt inclusion (MI) contained in phenocrysts. MI data show two trends for Fondo Riccio – one from latite to trachyte for MI in Fe-rich diopside (C1) and another from trachybasalt to shoshonite for MI in Mg-rich diopside (C2) and for MI in olivine (C1). Minopoli 1 MI data show two different compositions – basaltic for MI in clinopyroxene (Mi1-C1) and trachybasalt for MI in olivine (Mi1-C1) and clinopyroxene (Mi1-C2). Major and trace element data for Fondo Riccio MI show a compositional gap between Mg# 78 and 83, whereas Minopoli 1 MI have Mg# between 85 and 89 and show no compositional gap. Clinopyroxene compositions fall in the diopside–salite field for Fondo Riccio and in the diopside field for Minopoli 1. Fondo Riccio olivine compositions show a wider range (Fo 84.60 to Fo 86.77 ), compared to Minopoli 1 olivine (Fo 77 to Fo 78.5 ). Analyses of reheated MI suggest trends in MI volatile contents that correlate with SiO 2 concentration. In particular, more evolved MI show higher Cl and lower S compared to less evolved MI. The H 2 O content of MI from the two eruptions overlap but suggest that the Fondo Riccio magma may have been more water-rich. The higher H 2 O content of the Fondo Riccio magma (2.5 to 6.9 wt.%) compared to Minopoli 1 (1–3.5 wt.%) is consistent with the more explosive nature of Fondo Riccio eruption compared to Minopoli 1.

The Ordovician volcanic and intrusive rocks of the Cadia – Neville region, in the southern Molong Volcanic Belt section of the Macquarie Arc in central-western New South Wales, display a temporal progression from shoshonitic basaltic volcanism (e.g. Mt Pleasant Basalt Member) in the late Darriwilian to Gisbornian (ca 460 – 453 Ma) to small-volume dacitic medium-K calc-alkaline magmatism (e.g. Copper Hill-type dacite) in the late Eastonian to early Bolindian (ca 450 – 445 Ma) to large-volume, high-K calc-alkaline to shoshonitic, mafic to highly evolved magmatism (e.g. Nullawonga Latite Member and Cadia Intrusive Complex) at about 445 – 440 Ma. The two episodes of shoshonitic magmatism are separated by at least 15 (but up to ∼20) million years, during which time limestones, associated with regional uplift, were deposited broadly coincident with emplacement of the medium-K calc-alkaline dacitic intrusions. Despite this, the lavas and intrusions associated with both episodes of shoshonitic magmatism have stri...