Acid Volcanic Rocks Research Articles

Effect of acidic volcanic perlite rock on physio-mechanical properties and microstructure of natural pozzolan based geopolymers

The paper presents the combined effect of pozzolan, as an alkaline volcanic rock, and perlite, as an acidic volcanic rock, in the synthesis of geopolymers. The perlite proportion varied between 0% and 50% by weight. A mixture of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) was used as an alkaline activator. The effect of perlite on the physio-mechanical properties of the synthesized geopolymers was evaluated by the compressive strength (Rc), P-wave velocity (Vp), bulk density (D), and porosity (P). The microstructural aspects have been explored by X-ray Diffractometry (XRD), Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), and Energy-Dispersive X-ray spectroscopy (EDS). The results highlight the possibility of obtaining an eco-efficient geopolymer, with compressive strength of up to 50 MPa at 28 days by partially replacing the pozzolan by 40% of the perlite, due to the formation of higher amorphous N-A-S-H type gel. However, the excessive content (more than 40%) of perlite favored the formation of zeolitic phases in the geopolymer matrix, resulting in a heterogeneous structure, which has a negative effect on the development of the compressive strength and microstructure of the pozzolan-based geopolymer. This study confirms the promise of using pozzolan-perlite-based geopolymers as sustainable building materials, which could significantly promote the development of geo-resources and environmental protection in the construction sector.

An inorganic thermal insulation material with good performance prepared from obsidian

Both obsidian and perlite belong to acid volcanic rock and have a similar structure and chemical composition, but the insulation material prepared from expanded obsidian cannot reach the performance level of that prepared from expanded perlite. To date, obsidian cannot be used in large quantities, although its resource is abundant. In order to comprehensively utilise this resource, in the present work the authors developed a new type of lightweight thermal insulation material by using obsidian as a main raw material which is energy-efficient and environmentally friendly. The effects of raw materials such as obsidian, sodium silicate, hydrogen peroxide and cetyltrimethylammonium bromide on physical properties including thermal conductivity, porosity, density and compressive strength were studied in detail. The optimised thermal insulation material exhibits low thermal conductivity (0.051–0.86 W m−1 K−1), low density (0.1–0.24 g/cm3) and adjustable compressive strength (0.09–1.52 MPa). Compared to other inorganic insulation materials, this new thermal insulation material is very light and has a better thermal insulation performance. Therefore, this work proposes a new energy-efficient way to prepare a promising noncombustible thermal insulation material, and also provides a way to use obsidian resources in large quantities.

Multiple Hydrothermal Iron-Formation Upgrading Events in Southeastern São Francisco Craton

Large-scale, hypogene iron mineralization systems developed recurrently in the São Francisco craton in association with two orogenies. During the ca. 2.1–2.0 Ga Trans-Amazonian orogeny, low-temperature and low-to-moderate-salinity metamorphic fluids resulted in carbonatization-related iron enrichment of the early Paleoproterozoic Cauê Iron Formation (IF) of the Minas Supergroup (MSG) as well as short-distance iron mobilization. Monazite from the iron-oxide veins yielded a SHRIMP 232Th/208Pb date corresponding to fluid circulation coeval with the migmatization of the Archean tonalite-trondhjemite-granodiorite crust. During the Ediacaran to Cambrian Brasiliano orogeny, when the São Francisco craton was consolidated in its present configuration, hydrothermal fluids repeatedly mineralized the Cauê IF and the younger IFs of the lower Espinhaço Supergroup. Far-field hydrothermal alteration associated with distinct Fe mineralization episodes widely affected Meso- to Neoproterozoic sequences as well as Archean to Paleoproterozoic terranes of the cratonic core. Circulation of hydrothermal fluids during the Brasiliano orogeny caused desilicification, iron mobilization, and widespread alteration of the rocks. The alteration events are dated with monazite and xenotime intergrown with hematite, anatase, and recrystallized rims of detrital zircons from interlayered quartzites and of igneous zircons from pegmatites, granites, acidic volcanic rocks, and orthogneisses, yielding U-Pb dates between 542 and 493 Ma. U-Pb dates point to five Cambrian hydrothermal events from the waning stages to the aftermath of the Brasiliano orogeny. These hydrothermal fluid circulation events correspond to the emplacement ages of four granite suites and pegmatites that lasted from the final stages of the collision to the collapse of the Araçuaí-West Congo orogen. Episodic circulation of fluids continued for approximately 2 billion years after IF deposition on the eastern São Francisco craton with the formation of high-grade iron ore deposits and resetting of the IF trace-element inventory.

Depositional age and genesis of the host strata of the Shuangjianzishan Ag–Pb–Zn deposit: Implications for the Late Carboniferous magmatic–hydrothermal activities and tectonic evolution of the eastern central Asia orogenic belt

The Shuangjianzishan Ag–Pb–Zn deposit is hosted by an over 2030-m-thick succession of Late Carboniferous slate-dominated deep-water sediments. Three tuff layers interbedded with slates yield zircon U–Pb ages of 314.4 ± 2.5 Ma, 315.9 ± 3.6 Ma, and 317.9 ± 2.3 Ma. Using Monte-Carlo simulations, we constrain the maximum time span between the bottom tuff and the top tuff to no longer than 6.9 Myr at a 2σ (95.3%) confidence level. On the basis of this time span, the long-term accumulation rate of the Shuangjianzishan slates is 294 m/Myr. This accumulation rate is faster than any subduction-related accumulation rates by at least 30%; it is similar to that of fine deposits in a rift setting. The variably low δ18O of the zircons from the interbedded tuffs also suggest that a high-temperature hydrothermal alteration occurred during the generation of the low δ18O parental magma. Magmatic–hydrothermal events related to a rifting event are the most likely mechanism that caused the low δ18O signature. The chemical compositions of the slates suggest that their source rocks were very immature, probably similar to contemporary intermediate to acidic volcanic rocks. On the basis of down-well logging data, the dipping angle data are plotted with the stratigraphic depth of each stratum. The stable dipping angle of the slates also supports a sedimentation processes in an active rifting environment.

Petrogenesis of the 2.3 Ga Lengkou metavolcanic rocks in the North China Craton: Implications for tectonic settings during the magmatic quiescence

Paleoproterozoic (~2.3) Ga metavolcanic rocks occur in the Lengkou area, northern Zhongtiao Mountains of the North China Craton (NCC). The area is dominated by metabasic volcanic rocks, intercalated with metamorphosed intermediate to acid volcanic rocks. The Lengkou metavolcanic rocks have a magmatic zircon U-Pb age of 2317 ± 13 Ma, but also contain some 2508 Ma inherited zircons. The Lengkou metabasic and intermediate volcanic rocks are calc-alkaline with high SiO2 and K2O contents. They display fractionation of the HREE relative to the LREE, relative enrichments in large ion lithophile elements and depletion in high field strength elements resulting in negative Nb-Ta-Ti and Zr-Hf anomalies. Therefore, they are inferred to have formed in a volcanic arc setting. The meta-acid volcanic rocks of the Lengkou series have geochemical features similar to the surrounding Sushui Complex (Neoarchaean tonalitic gneiss), resulting from partial melting of ancient crust. The Lengkou metabasic volcanic rocks have a low 143Nd/144Nd ratio and εNd(t) value of 0.8–1.5, with TDM of 2.57–2.63 Ga, indicating the mantle-derived mafic rocks were variably contaminated by older continental material. The integrated data from the Lengkou metavolcanic rocks indicate a convergent subduction-related regime in the early Paleoproterozoic. The isotopic signatures and the xenocrystic zircons demonstrate that subduction occurred at a margin of continental crust, rather than within intra-ocean, exploring an Andean-like setting in the NCC at that time.

Petrography and geochemical characteristics of Chang 7 sandstone in Yanhe profile, Ordos Basin: Implication for paleoenvironment and tectonic background

The Chang 7 oil layer from the upper Triassic Yanchang Formation is an important layer for hydrocarbon exploration. Most studies on the Chang 7 oil layer have focused on the source rocks, while research on the sandstone is still inadequate, especially on the petrography and geochemical characteristics. Using seven sandstone samples of the Chang 7 oil layer in the Yanhe profile, the grain-size analysis, major elements, trace elements, and rare earth elements were tested. The results find that the sandstone of fine-grained sediments of the Chang 7 oil layer is dominated by arkose with a minor number of lithic arkose. The range of grain size (Mz) is from 2.72 to 3.92 Φ, and the C value and M value of the sandstone samples suggest characteristics of turbidity deposition. The Al/Si ratios of all of the samples imply high clay mineral content. The results of trace and rare earth elements demonstrate the reducing condition, freshwater, and cold and dry weather. The provenance of the sandstone samples is mainly from island arc acidic volcanic rock, and the type of provenance is mixed with sedimentary rock, granite, and alkaline basalt. The tectonic background is continental island arc. This study provides a systematic geologic foundation for the formation of sandstone of Chang 7 oil layer in Ordos Basin.

From magma replenishment to epithermal mineralization: Combined evidence from zircon U-Pb, (U-Th)/He and trace element data

The Dahalajunshan Formation volcano-volcanoclastic rocks in Chinese Western Tianshan host specific Paleozoic epithermal gold deposits as well as volcanogenic Fe-Cu mineralization. Although numerous studies have been taken to constraint its geological, geochemical, geochronological features as well as petrogenesis, the link between volcanism and mineralization is not well constrained. In this contribution, accessory zircon was collected from the intermediate to felsic volcanic rocks outcropped at the Jingxi-Yelmand gold deposit. Detailed cathodoluminescence imaging illustrates ubiquitous resorption surfaces and embayments, and in situ LA-ICPMS trace element analysis further indicates periodic recharge of magma chamber by mafic magma input from depths. U-Pb geochronology constrains two main pulses of magmatism at ~370 Ma and 365–362 Ma, respectively. The duration of magmatic activity in the magma chamber is estimated to 52 ± 6 Myrs, using the U-Pb age of the oldest zircon antecryst (406.9 ± 5.4 Ma) and the youngest zircon autocryst (354.6 ± 3.0 Ma) as cutting edge and taking the analytical uncertainty into consideration. (U-Th)/He dating of zircon from the first pulse yields an age of 354 ± 15 Ma, which is identical to U-Pb age within analytical uncertainty. However, zircons from the second pulse of volcanic rocks yield much younger (U-Th)/He centered at 292.6 ± 7.6 Ma due to significant post-eruption reheating events. We propose that the intermediate to acid volcanic rocks are constructed by incremental addition of small magma batches. The periodic injection of more mafic magma and subsequent mixing may act as important trigger of not only volcanic eruption but also epithermal mineralization. Gold mineralization at the deposit should be no later than 292.6 Ma.

The formation and genesis of the rhyolite series of the Upper Chegem Highlands (the North Caucasus)

On the basis of new materials this article deals with the structure and origin of a huge (up to 2 km) thick massif of acidic volcanic rocks located in a volcanic-tectonic depression in the Upper Chegem River in the North Caucasus. Discussion on the lava’s, rather than pyroclastic, origin of the main part of the rock mass as a result of repeated outpourings of lava flows, which formed the series of acidic volcanic rocks without interruptions with perfectly pronounced columnar jointing in a limited volume of a deep volcanic-tectonic depression, which was forming simultaneously with eruptions in the Late Pliocene. Volcanic rocks formed as a result of boiling silicate meltas the exit from the vent, which could be due to the nature of the phase transition of the supercritical water fluid.

Magmatic systems beneath Ashikule volcanic cluster (Western Kunlun, China): insights from compositional and textural features of lavas

This study considered the petrology, chemical composition, texture, and magma temperature and pressure of the volcanic rocks in the Ashikule volcanic cluster (AVC), Western Kunlun, China, to investigate the magmatic systems prior to eruption. The whole rock geochemistry of AVC lavas revealed a wide compositional range that included phonotephrite, basaltic trachyandesite, trachyandesite, trachyte, and acid rhyolite but mainly trachyandesite. The K2O/Na2O ratios were greater than 1, falling into the shoshonite series in a K2O vs. SiO2 diagram. Oxide diagrams showed that intermediate and acidic volcanic rocks have similar magmatic evolutions, mainly related to the fractional crystallization of pyroxene, plagioclase, apatite, and ilmenite. Acidic magma was found as the product of magmatic crystallization in the final stage. Trace element contents indicated that the magma underwent mixing with crustal components in the process of crystallization before eruption. Xishan phonotephrite revealed a different evolutionary series compared with the intermediate and acidic volcanic rocks, highlighting the differences of their magmatic sources. The equilibrium temperature and pressure of phonotephrite were 1146–1316 °C and 0.38–1.70 GPa, respectively, which correspond to a depth of 14–62 km. The equivalent values for intermediate rocks were 1062–1215 °C and 0.22–1.18 GPa, respectively, corresponding to a depth of 8–43 km. Acidic rocks had lower magmatic temperatures (778–889 °C). Active tectonics led to multiple events of magma upwelling, and the magma in each event underwent its own evolution. There were many different components of magma beneath the study area contemporaneously, i.e., multiple magma capsules with different compositions.

Paleoproterozoic multiphase magmatism and metamorphism recorded in metamorphic basement rocks of the northern Altyn Tagh, southeastern Tarim Craton

The Paleoproterozoic is a pivotal time for understanding the geochronological framework of the Tarim Craton. Located at the southeastern margin of the Tarim Craton, the northern Altyn Tagh is the main region of exposed Paleoproterozoic magmatic and metamorphic rocks. These rocks are diverse, diachronous, and modified by multiphase tectonothermal events. In this study, we performed systematic analyses on the amphibolite, felsic gneisses, and metasedimentary rocks in the Aketashitage area, southeastern Tarim Craton, including petrography, mineral chemistry, and whole-rock geochemistry, as well as in-situ zircon U-Pb ages and Hf isotopes, to examine the Paleoproterozoic magmatic-metamorphic events in the northern Altyn Tagh. Results from our study indicate that geochemically, the amphibolite and felsic gneisses in the Aketashitage area resemble the typical bimodal associations of mafic and acidic volcanic rocks. In addition, felsic gneisses are characterized by high Sr and low Y contents, high Sr/Y and (La/Yb) N ratios, and indistinctive Eu anomalies, closely resembling high-SiO2 adakites derived from subducted basaltic slab-melt. The palimpsest textures and geochemical features of the Aketashitage metasedimentary rocks suggest that their protoliths are argillaceous rocks. The amphibolite from the study area has a metamorphic age of 1.96 Ga, and the felsic gneisses yield crystallization ages of 2.54–2.52 Ga. The major age peaks of metasedimentary rocks in the Aketashitage area, namely 2.72 Ga, 2.05 Ga, and 1.97 Ga, are remarkably consistent with the magmatic and/or metamorphic events in the same area. Furthermore, the minimum age peak of the studied metasedimentary rocks suggests a depositional age no earlier than 1.97 Ga. Geochemical and geochronological evidence from the exposed rock associations in the Aketashitage area suggest a subduction-related tectonic setting during the Paleoproterozoic. Our new data combined with the findings of previous studies indicate that Paleoproterozoic magmatism and metamorphism in the northern Altyn Tagh area are nearly synchronous, and that both are likely related to oceanic subduction.

3-D lithospheric conductivity structures in the Cathaysia Block and the Jiangnan suture zone: implications for origins of metallogenic belts

Influenced by the subduction of the Izanagi plate, the South China Block underwent explosive mineralization in the Mesozoic, and a series of important ore concentration areas and metallogenic belts, such as the Nanling metallogenic belt (NMB) and northeastern Jiangxi metallogenic Province (NJMP), were formed in the Early Jurassic. The NMB is composed of a series of non-ferrous metal deposits and rare earth element deposits. The ore-forming rock source of the NMB is granite that mainly originated crustal partial melting and mantle material rising in the Mesozoic. The NJMP consists of a series of copper, lead, zinc, gold and silver deposits associated with acid volcanic and intrusive rocks. The boundary fault zone between the Yangtze Block and the Jiangnan orogenic belt penetrates into the mantle. As certain mantle materials have participated in the ore-forming diagenesis, both the NMB and NJMP benefited from the crust-mantle mixed sources. To study the deep electrical structures and metallogenic types of the NMB and NJMP, 333 magnetotelluric (MT) stations in the eastern part of South China were employed to obtain a lithospheric 3-D electrical structure model. The results show a low-resistivity anomaly extending from the mantle to the crust beneath the NJMP, which is explained as a magma channel of ore-formed materials. The upper crust of the NJMP has high resistivity, and it has been affected by large regional faults, such as the northeastern Jiangxi fault. The low-resistivity bodies in the mantle and crust of the NMB are connected by small low-resistivity channels, which could be pathways of upwelling asthenosphereic materials. According to the 3-D electrical structure model, the deep upwelling asthenospheric materials beneath the NMB were blocked by the high-resistivity lower crust. The heat and metallogenic elements from the mantle upwelling may have triggered partial melting of the overlying crust and crust-mantle mixing, resulting in the formation of non-ferrous metal deposits such as tungsten, tin and rare earth elements. The low-resistivity anomaly zones of the NMB and the NJMP connected with upwelling low-resistivity deep anomalies may reflect shallow deposits.

The link between hydrothermal nickel mineralization and an iron oxide-copper–gold (IOCG) system: Constraints based on mineral chemistry in the Jatobá deposit, Carajás Province

The Jatobá deposit represents a specific portion of an Archean-Paleoproterozoic iron oxide–copper–gold system, notable due to its hydrothermal nickel-rich zones. Neoarchean mafic and acid volcanic rocks of the Itacaiúnas Supergroup host the mineralized zones. Pre-, syn- and late shearing hydrothermal alteration, associated with the Canaã shear zone development, was pervasive and intense. Early distal hydrothermal alteration encompasses potassic-iron-silica (quartz–biotite–magnetite–apatite), sodic (albite, scapolite), and sodic-calcic (ferro-pargasite) alteration. The main syn-tectonic hydrothermal alteration stage resulted in scapolite–hastingsite–biotite controlled by the mylonitic foliation. Syn-deformation massive magnetite bodies represent proximal envelopes of the mineralized zones. They were intercepted by actinolite-apatite-magnetite and potassic-iron (biotite–magnetite) alteration fronts. Late tectonic hydrothermal alteration comprises chlorite–(epidote–quartz–calcite), fibrous scapolite veins, and green biotite–scapolite–F-Cl-apatite veinlets. The copper–(nickel) mineralized zones in the Jatobá deposit were formed in four stages, coeval to ductile and ductile-brittle deformational events. The mineralization stage (I), spatially related to massive magnetite–(apatite–actinolite) bodies, has the highest nickel content. It is characterized by Ni-pyrrhotite, Ni-pyrite, and subordinately, Co-chalcopyrite, Ce-allanite, Co-pentlandite, and Ce-monazite. The mineralization style evolved from replacement fronts controlled by the mylonitic foliation to hydraulic breccia zones. The mineralization stage (II) was synchronous to the development of syn-tectonic potassic-iron alteration and Co-chalcopyrite (±Ni-pyrite ± Ni-pyrrhotite). The mineralization stage (III), controlled by ductile-brittle and brittle structures, enabled the formation of veins with typical open-space filling textures infilled by paler brown or green biotite, Co-chalcopyrite, and siegenite (±Co-pyrite, ±Co-magnetite, ± cassiterite). The late mineralization stage (IV), coeval to widespread chlorite alteration, formed the most important copper mineralization at Jatobá. It is represented by branching veinlets and breccias with chalcopyrite, Co-chalcopyrite, Co-pyrite, sphalerite, molybdenite, uraninite, monazite, W-bearing hematite, and rare earth carbonates (bastnäsite, coskrenite, and sahamalite). The high chlorine contents of halogen-rich minerals (e.g., scapolite, biotite, apatite, and amphibole) imply the participation of highly saline, supersaturated fluids in the system evolution. Metalliferous fluids were highly focused, and mineralized zones represent the hotter hydrothermal centers. The high V and Ti contents in magnetite and its coexistence with hercynite and ilmenite indicate temperatures above 600 °C. These conditions would be similar to that of magnetite formed in the transition from magmatic to deep magmatic-hydrothermal systems, including the IOA deposits, especially on the onset of the early nickel-enriched mineralization stage. Such conditions enabled nickel leaching from mafic and mafic-ultramafic rocks, its transport in Cl-rich hydrothermal fluids, and precipitation related to episodic decompression. Temperature decrease (<380 °C), indicated by chlorite geothermometers, favored the bulk of chalcopyrite precipitation in late mineralization stages. The Jatobá deposit has attributes comparable to those of relatively deep portions of IOCG mineral systems formed from the channeling of overpressured superheated deep-seated fluids of probable magmatic origin.

Mineralogical and geochemical changes due to hydrothermal alteration of the volcanic rocks at Acoculco geothermal system, Mexico

Most of the volcanic rocks in the Acoculco geothermal system (AGS), near to the surface manifestations, are intensively altered. Thirty‐four surface volcanic rocks and five rocks from outcrop sections are considered in this work. Silica polymorphs (quartz, cristobalite and tridymite) are the dominant hydrothermal minerals in almost all the rock samples. The following other minerals are present in minor concentrations: alkali‐feldspars (sanidine potassic, anorthoclase and microcline), plagioclase feldspars (albite and anorthite), clay minerals (illite, kaolinite and montmorillonite), anhydrite, buddingtonite, titanoaugite, magnetite and anatase. This type of mineral assemblage of the rocks indicates an intensive silicic and argillic alteration. Comparison of the elemental concentrations of the surface acid rocks of the AGS with that of the precursor rock has indicated alteration‐induced changes in (a) chemical mobility in the concentrations of major element oxides, with an increase in the concentrations of SiO2, and TiO2, loss in those of Al2O3, Fe2O3, MnO, MgO, CaO, Na2O and K2O, and no statistically significant changes in those of P2O5, (b) no significant changes in the concentrations of LREE and MREE (except Dy and Ho), however, less but significant loss in the concentrations of Dy and Ho, and HREE, and (c) there is an enrichment in the concentrations of Nd, Sr, Sc, V, Nb, Ag, Sn, Pb, Tl, Ta, U and Th; and depletion in Be, Co, Zn, Ga, Ge, Rb, Y, Zr, Mo, Cs, Ba and Hf compared to those of the precursor rock. This type of distribution of the elements may indicate (a) an intense silicic alteration; and (b) REEs might have been leached from the original rocks because of hydrothermal alteration processes, but only LREEs, and MREEs (except Dy and Ho) can be redistributed and accommodated in the hydrothermal minerals, providing them with somewhat inert (immobile) behaviour. The mass change calculations have indicated that MnO and Sr have experienced the greatest and smallest mass changes, respectively. The identification of outliers in chemical data has revealed the presence of two distinctive groups of rocks. Ten out of the total 27 acid volcanic rocks with several elements as outlier data are negligibly to moderately altered (Group‐1), and the remaining 17 acid rocks without outlier data are intensively altered rocks (Group‐2).

Middle Eocene magmatism in the Khur region (Lut Block, Eastern Iran): implications for petrogenesis and tectonic setting

ABSTRACT The Khur region is located in the Late Mesozoic-Cenozoic volcanic-plutonic rocks of the Lut Block, eastern Iran. There are several outcrops of subvolcanic rocks in the region which occur mainly as dike (granitoid and mafic dikes) and stock (monzonite porphyry). Volcanic rocks (basaltic andesites, andesites, trachyandesites, dacites and rhyodacites) are also abundant and cover pyroclastic rocks. U–Pb zircon ages indicate that granitic-dioritic dikes and monzonite porphyries were emplaced at 44.97 to 40.86 Ma and 41.11 Ma, respectively. Granitoid dikes are high-K calc-alkaline and metaluminous and geochemically belong to the I-type granitoids. Monzonite porphyries show I-type (and rarely A-type) signatures, with typical enrichments in alkalis, Zr and Ce, high FeOt/(FeOt+MgO) ratio and depletion in Sr and Nb. Primitive magmas of dikes, stocks and acidic volcanic rocks have formed in the lower crust and have undergone different degrees of AFC, while primitive magmas of mafic volcanic rocks have formed in the mantle and have presumably been modified by melts/fluids. Moreover, a syn to post-collision-related zone is responsible for the high magmatic rate during the Middle Eocene in the Lut Block.

Geochronology and geochemistry of the Early Carboniferous meta-volcanic rocks, northern Liaoning Province: Implications for the tectonic evolution of the eastern segment of the northern margin of the North China Block

华北板块北缘东段分布的构造混杂岩带为研究古亚洲洋的演化提供了重要的依据，下二台岩群作为该构造混杂岩带的重要组成部分，其形成时代和构造属性仍存在争议。详细的研究表明下二台地区变质火山岩原岩包括流纹岩、英安岩、安山岩，为一套钙碱性火山岩，属于准铝质-弱过铝质岩石，根据岩相学和地球化学特征将其分为变质酸性火山岩和变质中性火山岩；二者均相对富集轻稀土元素，亏损重稀土元素，轻重稀土元素分馏明显，Eu负异常不明显，但变质中性火山岩稀土总量低于变质酸性火山岩，变质酸性火山岩明显亏损Sr、P元素，结合野外产出面积和高场强元素相关性特征，认为二者不是同一基性岩浆分异的产物。变质火山岩锆石LA-ICP-MS U-Pb年龄为341~348Ma，代表其原岩结晶年龄。变质酸性火山岩原始岩浆来自于地壳物质的部分熔融，变质中性火山岩原始岩浆来自于俯冲带附近岩石圈地幔，并遭受了地壳物质的混染，二者均形成于活动大陆边缘火山弧环境。最新研究成果表明下二台岩群由不同时代、不同构造环境下形成的地质单元叠置混杂而成，称其为下二台构造杂岩更为准确。下二台地区变质火山岩表明在早石炭世初，古亚洲洋板块已经南向俯冲，在华北板块北缘形成活动大陆边缘弧环境，早石炭世变质火山岩原岩为这一俯冲阶段的产物。;The tectonic mélange belt distributed in the eastern segment of the northern margin of the North China Block provides an important evidence for studying the evolution of the Paleo-Asian Ocean. The Xia’ertai Group is located in this belt, its formative age and tectonic properties have also been controversial. The detailed research indicates that the protolith of meta-volcanic rocks in the Xia’ertai area includes rhyolite, dacite and andesite, they are calc-alkaline series and metaluminous-weak peraluminous rocks. The meta-volcanic rocks in the Xia’ertai area can be divided into metamorphic acid volcanic rocks and metamorphic intermediate volcanic rocks according to the petrography and trace element characteristics. The trace elements of them all show that LREEs are relatively enriched, while HREEs are relatively deficient and obvious REEs fractionation, meanwhile, negative Eu anomalies is not obvious, but the total amount of REEs in metamorphic intermediate volcanic rocks is lower than that in metamorphic acidic volcanic rocks, and the metamorphic acid volcanic rocks are depleted in Sr and P, combined with the distribution area and the correlation of HSFEs, we believe that they are not the product of the same basic magma differentiation. The zircon LA-ICP-MS U-Pb ages of the meta-volcanic rocks are 341~348Ma, represents the crystallization age of their protolith. The primordial magma of the metamorphic acidic volcanic rocks came from partial melting of material in the crust, but the primordial magma of the metamorphic intermediate volcanic rocks was originated from the lithospheric mantle near the subduction zone with the mixing of crustal materials, meanwhile, they were all formed in the volcanic arc environment of an active continental margin. The material composition of the Xia’ertai Group is characterized by different times and different tectonic backgrounds, we suggest to the Xia’ertai Group as a tectonic complex. The meta-volcanic rocks in the Xia’ertai area indicate that the Paleo-Asian Ocean was subducted southward no later than the early Early Carboniferous, the active continental marginal arc environment was formed at the northern margin of the North China Block, and the protolith of meta-volcanic rocks in the Xia’ertai area were the products of this subduction stage.

Integrated major and trace element study of clinopyroxene in basic, intermediate and acidic volcanic rocks from the middle Okinawa Trough: Insights into petrogenesis and the influence of subduction component

Magmatism is very common in the Okinawa Trough. However, the influence of magmatic processes, including fractional crystallization and magma mixing, on the petrogenesis of volcanic rocks is poorly understood. The in situ major and trace element compositions of clinopyroxene in co-genetic basalts, andesites, trachyandesites and rhyolites from the Iheya Ridge in the middle Okinawa Trough are examined to determine their petrogenesis and the influence of slab subduction. Regarding the types of mineral zoning, in basalt and andesite, clinopyroxene phenocrysts are unzoned. In trachyandesite, the clinopyroxene phenocrysts can be classified into three groups: normal zoned, oscillatory zoned and unzoned. Similarly, unzoned and reverse zoned clinopyroxene phenocrysts are the two main structures in rhyolites. According to the major element contents and distinct distribution patterns of rare earth elements (REEs), we identify various clinopyroxene domains in their host volcanic rocks. Type 1 clinopyroxene domains in basalts and trachyandesites are dark, have high Mg# values and are strongly depleted in light REEs (LREEs) with no significant Eu anomalies. The Type 2 clinopyroxene domains in basalts and trachyandesites and all clinopyroxene phenocrysts in andesites are bright, have low Mg# values and are strongly depleted in LREEs and have significant negative Eu anomalies. Clinopyroxene domains in rhyolites have significant negative Eu anomalies and can be divided into two types: Type 1 clinopyroxene domains are characterized by strong depletion in LREEs, Sr, P and high field strength elements (HFSEs), while Type 2 clinopyroxene domains are slightly depleted in LREEs and have small negative P anomalies. The continuously changing major element composition and parallel distribution of trace element spider diagrams suggest that all these clinopyroxene phenocrysts in the studied volcanic rocks were derived from co-genetic magmas and the compositional transition of clinopyroxene from basalts to rhyolites attributed to different extents of fractional crystallization of various minerals (e.g., clinopyroxene, orthopyroxene, plagioclase and apatite). The oscillatory zoned and reversed zoned clinopyroxene phenocrysts show that magma mixing and recharge events with co-genetic magmas are common in the middle Okinawa Trough magma system. The origin of clinopyroxene phenocrysts involves contributions from subducted sedimentary components of 2.5% sediment melts and 1.5% sediment fluids and is deduced based on the equilibrium melts of clinopyroxene phenocrysts in basalts. The geochemical study of clinopyroxene provides evidence for the contributions of magmatic processes and slab subduction to the petrogenesis of Okinawa Trough volcanic rocks.

Chemical, mineralogical and structural features of native and expanded perlite from Macedonia

The physico-mechanical, chemical and mineralogical characteristics of volcanic glass (perlite) from the Mariovo region (Macedonia) as well as the mineralogical changes that occur during its thermal treatment were investigated to demonstrate its utilization for industrial use. The native perlite was characterized by chemical analysis, X-ray powder diffraction (XRPD), infrared (IR) spectroscopy, thermal analysis (TGA/DTA), scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM), and solid- state NMR. The chemical examination suggests that the perlite represents an acidic volcanic rock with a high percentage of SiO2 (72.45%), high in alkali metal oxides (4.21 wt.% K2O, 3.56 wt.% Na2O), with a loss of ignition 3.54 wt.%. Results from the XRPD indicated major amorphous behaviour, with low amounts of feldspars, quartz, and cristobalite. SEM examinations revealed glassy structure with presence of certain pores (dimensions ranging from 50–100 μm). The determined expansion coefficient was 20 times its original volume. XRPD of expanded perlite compared to the native perlite depicted new intensive peaks of cristobalite. SEM and TEM revealed irregular morphology with broken or ragged edges. On the basis of the chemical and mineralogical composition, the studied perlite is classified as an appropriate material suitable as ceramic flux to lower the sintering temperature.

The Neoproterozoic basement of the Sauce Chico Inlier (Ventania System): Geochemistry and U–Pb geochronology of igneous rocks with African lineage in central-eastern Argentina

This study describes the geology, geochemistry, and LA-ICP-MS U–Pb geochronology of igneous rocks that crop out in the Sauce Chico Inlier (SCI) and constitute the Neoproterozoic basement of the Ventania System, Argentina. Magmatism registered in the SCI has developed in two phases. The first phase, of Tonian age, is represented by rift-related calc-alkaline and alkaline granites with ages of 783.8 ± 3.7 Ma (εNd(t) = −7.20) and 776.5 ± 4.7 Ma (εNd(t) = +1.65), respectively. This phase would be related to the break-up of the Rodinia supercontinent and subsequent opening of the Adamastor Ocean. In the Dom Feliciano Belt of southern Brazil and eastern Uruguay, the Tonian magmatism is represented in the Cerro Olivo Complex of the Punta del Este Terrane and in basement inliers of the Pelotas Batholith. The second phase, of Ediacaran age, started with the intrusion of syn-orogenic calc-alkaline granites (620.8 ± 5.8 Ma and 620.3 ± 2.5 Ma; εNd(t) = −9.94/−9.18) and continued with the extrusion of post-orogenic alkaline (577.3 ± 3.9 Ma; εNd(t) = −6.29) and calc-alkaline (543.6 ± 4.0 Ma; εNd(t) = −3.38) acid volcanic rocks. This phase would be related to the closure of the Adamastor Ocean, generation of a magmatic arc along the western margin of the Kalahari Craton, and collision between this and the Río de la Plata Craton. A post-collisional magmatism would have developed due to orogenic collapse (< 580 Ma). With the exception of the Tonian alkaline granite, in the remaining SCI igneous rocks, the juvenile component becomes more important as the crystallization age decreases. The available Nd model ages are between 1.80 and 1.14 Ga and suggest a mixing of older crust with juvenile material. The tectonic evolution of the Ventania System basement is consistent with that observed in the Dom Feliciano Belt and its African counterparts. We present here the first evidence of Tonian magmatism in the Ventania System basement. The results presented here also confirm those obtained previously by other authors. Zircon cores from the SCI igneous rocks have U–Pb inherited ages between ca. 1200 and 900 Ma that could be indicative of a lineage with the Gariep Belt and its Namaqua basement in southwestern Africa.

Sodium-rich volcanic rocks and their relationships with iron deposits in the Aqishan–Yamansu belt of Eastern Tianshan, NW China

The volcanic rocks hosting the iron deposits in the Aqishan–Yamansu metallogenic belt are sodium-rich. The geochronology, petrography, and geochemistry of minerals and sodium-rich rocks as well as the relationship between these rocks and the iron deposits are studied. Geochemically, the ore-hosting volcanic rocks are sodium-rich (the averages of Na2O and Na2O/K2O are 4.31 ​wt.% and 8.56, respectively) and belong to the calc-alkaline series. They are enriched in LREEs and LILEs (Ba, U, K, and Sr), but depleted in HFSEs (Nb, Ta, and Ti). SHRIMP zircon U–Pb dating of the crystal tuff in the Aqishan Formation and the dacite in the Tugutu Bulak Formation yields ages of 337.5 ​± ​2.3 ​Ma (n ​= ​15, MSWD ​= ​0.85) and 313.0 ​± ​3.3 ​Ma (n ​= ​13, MSWD ​= ​0.74), respectively, indicating that the sodium-rich volcanic rocks formed from the early–late Carboniferous. Electron microprobe data from plagioclases demonstrate that albites and/or oligoclases were formed in the basic–intermediate–acid volcanic rocks. Two stages of albitization are identified, and the latter is likely attributed to the dissolution of iron in the Aqishan–Yamansu belt. The sodium-rich volcanic rocks probably formed by the interaction between volcanic lava and seawater after volcanoes erupted on the seafloor; meanwhile, the albites formed by element substitution in a low-metamorphic environment. The spatiotemporal coupling relationship between sodium-rich volcanic rocks and iron deposits in the Aqishan–Yamansu belt is favorable. Iron dissolved from the dark minerals of basic–intermediate volcanic rocks through sodium metasomatism is one of the material sources for the iron deposits.

Volcanism and Geochemistry of the Soil and Plant Cover in Kamchatka. Part 2. The Formation of the Elemental Composition of Volcanic Soils under Cold Humid Conditions

The Kamchatka volcanic soils have low concentrations of most chemical elements relative to their general abundances in continental soils and in European volcanic soils. The soils in different areas over the peninsula most typically involve higher bulk compositions of the elements that are typical of intermediate and basic volcanic rocks: Na, Ca, Mg, Cd, Mn, Co, and Cu, and persistently lower concentrations of the elements that are characteristic for acidic volcanic rocks: La, Ce, Pr, Nd, Nb, Hf, Tl, Rb, and Th. The diversity in the chemical composition of soils in the soil areas of Kamchatka as identified previously is controlled by the different conditions of volcanism that have existed in these areas in the past that also are observed at present.