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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...

The Middle Cenozoic evolution of magmatism in the Schmidt Peninsula between 37 and 25 Ma began with eruptions of subalkaline and moderately alkaline andesite, latite, trachyandesite, and trachyrhyolite lavas and ended with subvolcanic intrusions of highly alkaline strongly undersaturated essexites. According to trace-element data, magmatism evolved from melting of a mantle source in the zone of ocean-continent plate convergence to small-degree partial melting in lithospheric mantle at the final stage. This succession is generally typical of Late Cenozoic continental-margin magmatism in southeastern Russia. The similarity in the Middle and Late Cenozoic stages of magmatism is evidence for their individual significance.

A continuous-coring borehole recently drilled at Camaldoli dellaTorre on the southern slopes of Somma^Vesuvius provides constraints on the volcanic and magmatic history of the Vesuvian volcanic area since c. 126 ka BP. The cored sequence includes volcanic units, defined on stratigraphical, sedimentological, petrological and geochemical grounds, emitted from both local and distal vents. Some of these units are of known age, such as one Phlegraean pre-Campanian Ignimbrite, Campanian Ignimbrite (3 9 ka), Neapolitan Yellow Tuff (14 ?9 ka) and Vesuvian Plinian deposits, which helps to constrain the relative age of the other units. The main rock types encountered are shoshonite, phonotephrite, latite, trachyte and phonolite. The seque nce includes, from the base upwards: a thick succession of pyroclastic units emplaced between 126 and 3 9 ka, most of them attributed to eruptions that occurred in the Phlegraean area; the Campanian Ignimbrite; the products of a local tuff cone formed between 3 9 ka and the deposition of the products of the earliest activity of the Mt. Somma volcano; the products of the Somma^Vesuvius volcano, which include from the base upwards a thick sequence of lavas, pyroclastic rocks and the products of a local spatter cone dated between 3 ?7 ka and AD 79.The data obtained from the study of the borehole show that, before the Campanian Ignimbrite eruption, low-energy explosive volcanism took place in the Vesuvian area, whereas mostly high-energy explosive eruptions characterized the Campi Flegrei activity. In the Vesuvian area, Campanian Ignimbrite deposition was followed by the eruption of a local tuff cone and a long repose time, which predated the formation of the Mt. Somma edifice. Since 18 ?3 ka (Pomici di Base eruption) the activity of Somma^Vesuvius became mostly explosive with rare lava effusions. The shallowest cored deposits belong to the Camaldoli dellaTorre cone, formed between the Pomici di Avellino and Pomici di Pompei eruptions (3 ?7 ka^AD 79). New geochemical and Sr^Nd^Pb^ B-isotopic data on samples from the drilled core, together with those available from the literature, allow us to further distinguish the volcanic rocks as a function of both their provenance (i.e. Phlegraean or Vesuvian areas) and age, and to identify different magmatic processes acting through time in the Vesuvian mantle source(s) and during magma ascent towards the surface. Isotopically distinct magmas, rising from a mantle source variably contaminated by slab- derived components, stagnated at mid-crustal depths (8^10 km below sea level) where magmas differentiated and were probably contaminated. Contamination occurred either with Hercynian continental crust, mostly during the oldest stages of Vesuvian activity (from 3 9 to 16 ka), or with Mesozoic limestone, mostly during recent Vesuvian activity. Energy constrained assimilation and fractional crystallization (EC-AFC) modelling results show that contamina- tion with Hercynian crust probably occurred during differentiation from shoshonite to latite. Contamination with limestone, which is not well constrained with the available data, might have occurred only during the transition from shoshonite to tephrite. From the 'deep' reservoir, magmas rose towards a series of shallow reservoirs, in which they differentiated further, mixed, and fed volcanic activity.

A mina Cuajone é uma jazida de tipo pórfiro de cobre (porphyry copper), localizada na Província Cuprífera do Pacífico, nos flancos ocidentais da Cadeia Andina, no estado de Moquegua, sul do Perú, em coordenadas 17° 02\'(S) e 70° 42\'(W) e altitudes entre 3100 e 3830 m. A região é caracterizada pela ocorrência, na base, de derrames vulcânicos (andesitos e riolitos) cretácicos do Grupo Toquepala, que s~ao invadidos por um complexo intrusivo (quartzo monzonitos - quartzo latitos) associado à mineralização. Fluxos vulcânicos mais recentes, compostos principalmente por traquitos, tufos e aglomerados traquíticos e conglomerados riolíticos das Formações Huaylillas e Chuncatala recobrem todo o conjunto. A análise petrográfica de 77 amostras representativas de 22 testemunhos de furos de sondagem distribuídos em três perfis da jazida de Cuajone permitiu a caracterização das seguintes rochas: andesitos, riolitos, quartzo latitos, latitos, micro-granodioritos porfiríticos, microtonalitos porfiríticos, pórfiros-I (micro quartzo monzonitos - micro monzogranitos (?)), pórfiros- II (micro tonalitos - micro leucoquartzo dioritos (?)) e micro-brechas. Estas rochas encontram-se afetadas por alterações hidrotermais em graus variáveis, identificando-se oito tipos ou combinações de tipos principais: potássica, potássica-propílica, propílica-potássica, potássica-propí?lica/fílica, propílica, propílica-fílica, fílica-propílica e fílica. O exame microscópico em detalhe sob luz refletida das fases sulfetadas demonstrou que a pirita (py), o sulfeto mais abundante, apresenta freqüentemente inclusões diminutas de calcopirita, cp, (X0,0 e 0,X ?m), quase sempre acompanhada de pirrotita (po), cubanita (cb) e mackinawita (mck), que aparecem formando intercrescimentos tí?picos. Estas inclusões apresentam formas arredondadas, ovais ou mesmo idiomórficas que, devido às suas dimensões, quase sempre não são reconhecidas em exames convencionais ao microscópio. Os intercrescimentos identificados foram classificados de acordo com a sua morfologia, utilizando-se para tanto de nomenclatura específica, e suas abundâncias relativas. Os resultados mostram que os mais abundantes são: tipo cp/po:1b (calcopirita + pirrotita, morfologia de tipo 1b) e py/po:1e na zona de alteração potássica, py/po:1e e cp/mck:4f nas zonas potássicapropílica e propílica-potássica, cp/mck:4f e py/po:1e na zona propílica e cp/po:1b e cp/mck:4f nas zonas de alteração potássica-propílica/fílica, propílica-fílica, fílica-propílica e zona de alteração fílica. A análise de distribuição das inclusões/intercrescimentos indica que a sua mineralogia pode ser correlacionada com a tipologia da alteração hidrotermal, particularmente quando se consideram as freqüências e/ou abundâncias relativas. Assim, observa-se que a pirrotita ocorre em todos os tipos de alteração, porém sua freqüência é notadamente superior nas amostras com alteraçãao potássica. A cubanita, ainda que seja pouco abundante, é freqüente nas zonas onde há contribuição da alteração fílica. Apesar de ser encontrada também nas zonas potássica-propílica e propílica-potássica, a sua freqüência é praticamente insignificante quando comparada com a das demais fases encontradas, enquanto a mackinawita apresenta freqüência significativamente superior nas rochas afetadas pela alteração propílica. A tipologia e a distribuição das inclusões/intercrescimentos, aliadas às informações experimentais disponíveis para o diagrama de fases Cu-Fe-S, são compatíveis com temperaturas entre ca. 180 e 500 °C para a origem da mineralização de Cu (calcopirita, cubanita). The Cuajone mine is a porphyritic copper deposit (porphyry copper), located in the Pacific Copper Province, eastern flanks of the Andean Cordillera, state of Moquegua, south of Peru, with geographic coordinates 17 ° 02 \'(S) and 70 ° 42 \'(W) and altitudes between 3100 and 3830 m. The region is characterized from base to top by cretaceous volcanics (andesites and rhyolites) from Toquepala Group, which are invaded by a intrusive complex (quartz monzonites-quartz latites) associated to the ore deposits. Covering these units there are more recent volcanic flows composed mainly by trachyte, trachytic tuff, rhyolitic conglomerates and trachytic agglomerate from Huaylillas and Chuncatala Formations. Petrographic analysis of 77 samples representing 22 drilling cores distributed in three profiles of Cuajone Mine allowed the identification of the following lithotypes: andesite, rhyolite, quartz latite, latite, porphyritic micro-granodiorite, porphyritic micro-tonalite, porphyry-I (micro quartz monzonites-monzogranites (?)), porphyry-II (micro tonalites-micro leucoquartz diorites (?)) and micro-breccias.These rocks are affected by variable degrees of hydrothermal alteration with predominance of eight types or combinations of the following main types: potassic, potassic-propylitic, propylitic-potassic, potassic-propylitic/phylic, propylic, propylitic-phylic, phylic and propylitic-phylic. Detailed microscopic investigation under reflected light revealed that among the sulphide phases, pyrite (py) is the most abundant, with frequent chalcopyrite (cp) tiny inclusions (X0, 0 and 0, X ?m), almost always accompanied by pirrotite (po), cubanite (cb) and mackinawite (mck), occurring as typical intergrowths. These inclusions show round to oval or idiomorphic shapes and are commonly overlooked during conventional microscopic analyses due to their small dimensions. The intergrowths identified during petrographic analysis were classified according to their morphology, using specific nomenclature and relative abundances. The results show that the most abundant types are: cp/po:1b (chalcopyrite + pirrotite, morphology type 1b) and py/po:1e in the potassic alteration zone, py/po:1e and cp/mck:4f in areas of potassic-propylitic and propylitic-potassic alteration, cp/mck:4f and py/po:1e in the propylitic zone and cp/po:1b and cp/mck:4f in potassic-propylic/phylic alteration zones; propylitic-phylic, phylic-propylitic and phylic zones. The distribution pattern of inclusions/intergrowths indicates that their mineralogy can be correlated with the type of hydrothermal alteration. This is particularly evident when considering frequency and/or relative abundance. Thus, pirrotite occurs in all types of alteration, although its frequency is especially higher in samples with potassic alteration. Cubanite is more characteristic in the potassic-propylic and propylic-potassic zones, while mackinawite is significantly more frequent in rocks affected by propylic alteration. The type and distribution of inclusions/intergrowths, allied to current experimental results for the Cu-Fe-S system, are compatible with temperatures between ca. 180 and 500 ° C for the genesis of the studied copper deposits (chalcopyrite, cubanite).

Major and trace element compositions with Sr–Nd isotopic ratios, as well as Ar–Ar radiometric ages of the Miocene volcanic rocks from the Neogene units around Simav region (western Anatolia), are used to discuss the genetic relationship between (1) high-voluminous Lower–Middle Miocene high-potassic, calc-alkaline (HKCA) and (2) Middle Miocene small-voluminous high-MgO shoshonitic–ultrapotassic (SHO–UK) magmatic units in the region. All the HKCA rocks, including basaltic to rhyolitic (and granitic) samples, share similar trace element characteristics (enrichments of LILE and LREE and depletions in HFSE as a common feature of orogenic magmatic rocks), with subtle differences in their 87Sr/86Sr(i) ratios (basalts and rhyolites ~0.708, dacites ~0.710). Most of the samples of the high-MgO SHO–UK group are classified as shoshonite and latite, with some lamproites, sharing similar geochemical features with the other ultrapotassic rocks of the Mediterranean. All the rock groups have similar and high abundances of incompatible trace elements, and radiogenic Sr. Geochemical modeling of the trace element and isotopic ratios of the samples reveals that both the SHO–UK and HKCA groups were derived from a common mantle source which had been highly metasomatized and enriched by continental materials during partial subduction of the crustal metamorphic slices in a continental collision setting. The geochemical variations of these rocks were mainly controlled by source characteristics (such as heterogeneity) and variable degrees of partial melting and subsequent effects of fractional crystallization, with low degrees of crustal contamination. The HKCA series were derived by higher degrees of partial melting of the lithospheric mantle source than the SHO–UK rocks. The HKCA rocks then underwent two-stage fractional crystallization (clinopyroxene-dominated followed by feldspar-dominated fractionating mineral assemblages) to form the high-K calc-alkaline basalt to rhyolite series, whereas the SHO–UK rocks experienced comparatively little fractional crystallization. A tectonic scenario involving the rapidly extending and thinning of orogenic crust is compatible with the time-dependent compositional variation of the magmatic rocks. © 2015, Springer-Verlag Berlin Heidelberg.

The duration of the Mt. Amiata volcanic activity is still a matter of debate, in spite of the presence of several geochronological data in the literature. We performed new 40Ar-39Ar dating on the sanidinegroundmass pairs of the upper stratigraphic units: Dome and massive Lava flows Complex (DLC) and Olivine Latitic final Lavas (OLF). The aim was twofold: to check the reliability of sanidine ages as geochronometer in these products, questioned in the literature, and to better define the chronology of the late activity of this volcano. Ages obtained on coexisting sanidine and groundmass of the Dome and massive Lava flows Complex (DLC) samples overlap within errors, demonstrating that sanidine crystals recorded reliable emplacement ages in these rocks. The Olivine Latite final lavas (OLF) display a different scenario, where the groundmass has an age younger than that of the sanidine, which is xenocrystic and, evidently, retains inherited Ar. Preferred ages for analysed DLC samples are comprised between 301 and 294 ka, an interval of time too short to resolve the ages of the four dome samples taken into account. The Ermeta lava is about 60 ka younger. We propose that the majority of Mt. Amiata volcanic rocks were emplaced in a narrow interval of time, whilst a temporal gap, which needs more detailed constraints, exists with at least one of the Olivine Latite final lavas (OLF).

Textures of hydrothermal quartz revealed by cathodoluminescence using a scanning electron microscope (SEM-CL) refl ect the physical and chemical environment of quartz formation. Variations in intensity of SEM-CL can be used to distinguish among quartz from superimposed mineralization events in a single vein. In this study, we present a technique to quantify the cathodoluminescent intensity of quartz within individual and among multiple samples to relate luminescence intensity to specific mineralizing events. This technique has been applied to plutonic quartz and three generations of hydrothermal veins at the porphyry copper deposit in Butte, Montana. Analyzed veins include early quartz-molybdenite veins with potassic alteration, pyrite-quartz veins with sericitic alteration, and Main Stage veins with intense sericitic alteration. CL intensity of quartz is diagnostic of each mineralizing event and can be used to fingerprint quartz and its fluid inclusions, isotopes, trace elements, etc., from specific mineralizing episodes. Furthermore, CL intensity increases proportional to temperature of quartz formation, such that plutonic quartz from the Butte quartz monzonite (BQM) that crystallized at temperatures near 750 °C luminesces with the highest intensity, whereas quartz that precipitated at ~250 °C in Main Stage veins luminesces with the least intensity Trace-element analyses via electron microprobe and laser ablation-ICP-MS indicate that plutonic quartz and each generation of hydrothermal quartz from Butte is dominated by characteristic trace amounts of Al, P, Ti, and Fe. Thus, in addition to CL intensity, each generation of quartz can be distinguished based on its unique trace-element content. Aluminum is generally the most abundant element in all generations of quartz, typically between 50 and 200 ppm, but low-temperature, Main Stage quartz containing 400 to 3600 ppm Al is enriched by an order of magnitude relative to all other quartz generations. Phosphorous is present in abundances between 25 and 75 ppm, and P concentrations in quartz show little variation among quartz generations. Iron is the least abundant of these elements in most quartz types and is slightly enriched in CL-dark quartz in pyrite-quartz veins with sericitic alteration. Titanium is directly correlated with both temperature of quartz precipitation, and intensity of quartz luminescence, such that BQM quartz contains hundreds of ppm Ti, whereas Main Stage quartz contains less than 10 ppm Ti. Our results suggest that Ti concentration in quartz is controlled by temperature of quartz precipitation and that increased Ti concentrations in quartz may be responsible for increased CL intensities.

We present new viscosity measurements for melts spanning a wide range of anhydrous compositions including: rhyolite, trachyte, moldavite, andesite, latite, pantellerite, basalt and basanite. Micropenetration and concentric cylinder viscometry measurements cover a viscosity range of 10−1 to 1012 Pas and a temperature range from 700 to 1650 °C. These new measurements, combined with other published data, provide a high-quality database comprising ∼800 experimental data on 44 well-characterized melt compositions. This database is used to recalibrate the model proposed by Giordano and Dingwell [Giordano, D., Dingwell, D. B., 2003a. Non-Arrhenian multicomponent melt viscosity: a model. Earth Planet. Sci. Lett. 208, 337–349] for predicting the viscosity of natural silicate melts. The present contribution clearly shows that: (1) the viscosity (η)–temperature relationship of natural silicate liquids is very well represented by the VFT equation [log η=A+B/ (T−C)] over the full range of viscosity considered here, (2) the use of a constant high-T limiting value of melt viscosity (e.g., A) is fully consistent with the experimental data, (3) there are 3 different compositional suites (peralkaline, metaluminous and peraluminous) that exhibit different patterns in viscosity, (4) the viscosity of metaluminous liquids is well described by a simple mathematical expression involving the compositional parameter (SM) but the compositional dependence of viscosity for peralkaline and peraluminous melts is not fully controlled by SM. For these extreme compositions we refitted the model using a temperature-dependent parameter based on the excess of alkalies relative to alumina (e.g., AE/SM). The recalibrated model reproduces the entire database to within 5% relative error (e.g., RMSE of 0.45 logunits).

Boron concentration and isotopic compositions were determined in representative products from the Phlegrean Volcanic District (PVD), which includes Campi Flegrei (CF), and the islands of Procida and Ischia. The most primitive products (from Procida and Ischia islands) are moderately enriched in B (4.6-12 ppm), whereas more evolved products of CF and Ischia Island are more enriched (21-118 ppm). The content of B is positively correlated with Nb, Zr, Th, La and, generally, with all incompatible elements. delta11B values are generally lower and more uniform in samples from CF (-6.8 to - 10.6‰) compared with those from Procida (-3.6 to -8.5‰) and Ischia (-2.8 to -8.4‰) islands. Overall, B-enrichments relative to fluid-immobile elements of PVD are only slightly higher than those observed in mid-ocean ridge basalts and there is no significant correlation between delta11B and B/immobile element ratios. For CF samples including the Campanian Ignimbrite (CI) and most post-CI products, delta11B is negatively correlated with 87Sr/86Sr, with extreme compositions represented by evolved products of the CI (higher delta11B, lower 87Sr/86Sr) and less evolved shoshonite (lower delta11B, higher 87Sr/86Sr). In contrast, samples from Procida, Ischia, and pre-CI products and one young shoshonite from CF define a distinct correlation with primitive trachybasalt as the high delta11B, low 87Sr/86Sr end-member, and young shoshonites as the low delta11B, high 87Sr/86Sr end-member. The overall interpretation of the geochemical and isotopic data suggests three conclusions: (1) Geochemical and isotopic variations of post-CI products from CF can be explained by mixing/mingling between at least two distinct magmas, i.e. the CI and the young shoshonite (Minopoli 1). (2) The isotopic trend described by Procida trachybasalts, Ischia samples, pre-CI samples from CF and Pigna St. Nicola shoshonite is a mantle trend suggesting the involvement in their genesis of a distinct component depleted in B, with low delta11B and high 87Sr/86Sr. A similar component has been invoked to explain the differences between Stromboli potassic lavas and more typical calc-alkaline rocks of the Aeolian Islands. This component is consistent with ‘sediments or melts thereof' introduced into the mantle by subduction, but depleted in B due to metamorphic reactions accompanying subduction. (3) The displacement from the mantle trend of CI and Minopoli 1 shoshonite magmas is probably due to crustal contamination processes.

The evolution of a Pan-African (c. 900–550 Ma) suite of composite dikes, with latite margins and rhyolite interiors, from southwest Jordan is discussed. The dikes cut the Neoproterozoic calc-alkaline granitoids and high-grade metamorphic rocks (c. 800– 600 Ma) of the northern Arabian-Nubian Shield in Jordan and have been dated by the Rb-Sr isochron method at 566 � 7 Ma. The symmetrically distributed latite margins constitute less than one-quarter of the whole dike thickness. The rhyolite intruded a median fracture within the latite, while the latter was still hot but completely solidified. The dikes are alkaline and bimodal in composition with a gap in SiO2 between 61 and 74 wt%. Both end members display similar chondrite-normalized rare earth element patterns. The rhyolites display the compositional signature of A-type granites. The (La/Lu)N values are 6.02 and 4.91 for latites and rhyolites, respectively, and the rhyolites show a pronounced negative Eu anomaly, in contrast to the slight negative Eu anomaly of the latites. The chemical variability (e.g. Zr/Y, Zr/Nb, K/Rb) within and between latites and rhyolites does not support a fractional crystallization relationship between the felsic and mafic members of the dikes. We interpret the magma genesis of the composite dikes as the result of intrusion of mantle-derived mafic magma into the lower crust in an extensional tectonic regime. The mafic magma underwent extensive fractional crystallization, which supplied the necessary heat for melting of the lower crust. The products of the initial stages of partial melting (5–10%) mixed with the fractionating mafic magma and gave rise to the latite melts. Further partial melting of the lower crust (up to 30%) produced a felsic melt, which upon 50% fractional crystallization (hornblende 15%, biotite 5%, feldspars 60%, and quartz 20%) gave rise to the rhyolitic magma. Copyright # 2004 John Wiley & Sons, Ltd. Received 20 March 2002; revised version received 2 March 2003; accepted 20 March 2003

As a result of their relative concentration towards the respective Atlantic margins, the silicic eruptives of the Parana (Brazil)-Etendeka large igneous province are disproportionately abundant in the Etendeka of Namibia. The NW Etendeka silicic units, dated at similar to132 Ma, occupy the upper stratigraphic levels of the volcanic sequences, restricted to the coastal zone, and comprise three latites and five quartz latites (QL). The large-volume Fria QL is the only low-Ti type. Its trace element and isotopic signatures indicate massive crustal input. The remaining NW Etendeka silicic units are enigmatic high-Ti types, geochemically different from low-Ti types. They exhibit chemical affinities with the temporally overlapping Khumib high-Ti basalt (see Ewart et al. Part 1) and high crystallization temperatures (greater than or equal to980 to 1120degreesC) inferred from augite and pigeonite phenocrysts, both consistent with their evolution from a mafic source. Geochemically, the high-Ti units define three groups, thought genetically related. We test whether these represent independent liquid lines of descent from a common high-Ti mafic parent. Although the recognition of latites reduces the apparent silica gap, difficulty is encountered in fractional crystallization models by the large volumes of two QL units. Numerical modelling does, however, support large-scale open-system fractional crystallization, assimilation of silicic to basaltic materials, and magma mixing, but cannot entirely exclude partial melting processes within the temporally active extensional environment. The fractional crystallization and mixing signatures add to the complexity of these enigmatic and controversial silicic magmas. The existence, however, of temporally and spatially overlapping high-Ti basalts is, in our view, not coincidental and the high-Ti character of the silicic magmas ultimately reflects a mantle signature.

¶Fine- to coarse-grained plutonic nodules within the Petrazza pyroclastics (Paleo-Stromboli I period) consist of gabbroic rocks with variable amounts of interstitial material. They are characterised by cumulate textures and low pressure modal mineralogy formed by plagioclase (An96–87)+clinopyroxene (Mg-v 82–94)+olivine (Fo83–74)±amphibole±opaque minerals; the interstitial material consists of newly crystallised microlites (quenching) of plagioclase (An73–55)+amphibole+clinopyroxene±olivine±biotite±opaques and highly variable amounts of residual glasses that range in composition from shoshonite and high-K basaltic andesite to high-K andesite and latite. The interstitial material has a relatively high but variable degree of vesicularity. The whole rock incompatible element abundances are lower than – but the patterns are typical of – in subduction related magmas and the incompatible trace-elements are well correlated with the amount of the interstitial material. The Sr, Pb and Nd isotopic ratios resemble those of the extrusive rocks of Stromboli older series and the mineral chemistry of the gabbros is similar to that of the HKCA Paleo-Stromboli lavas. Modal mineralogy, mineral chemistry and chemical-isotopic whole rock compositions suggest that the cumulus portions of the gabbroic nodules crystallised from basaltic magmas compositionally compatible with those erupted by Stromboli volcano. The interstitial material does not represent the residual liquid after in situ crystallisation of the gabbros; it is also distinct from the juvenile host andesite magma. Textural evidence, Fe–Mg mineral/liquid partioning and mass balance calculations indicate that the interstitial material (quench crystals and vesicular glass) derived from infiltrated hydrous basaltic liquid undercooling and vesiculation of which occurred during the eruption of the Petrazza pyroclastics.