Acidic Rocks Research Articles

Petrological, whole–rock geochemical, geochronological, and Lu–Hf isotope constraints on the regional tectonic evolution of the Laoling Group in northeastern Jiao–Liao–Ji Belt, North China Craton

This study examines the original nature, tectonic setting, and evolution of Paleoproterozoic metasedimentary rocks in the Laoling Group of northern Jiao–Liao–Ji Belt (JLJB), in the northeastern margin of the Eastern Block of the North China Craton (NCC), using new petrological, whole–rock geochemical, geochronological, and Lu–Hf isotope data. The youngest detrital zircons constrain the maximum deposition age of the metasedimentary rocks to 1.97 Ga, and two metamorphic zircon age peaks correspond to 1.91 and 1.84 Ga for their metamorphism. The protoliths of the metasedimentary rocks in the Laoling Group were medium- to fine-grained clastic sediments, dominated by shale, graywacke, and claystone, with a smaller amount of sandstone, derived from Paleoproterozoic granites and coeval acidic meta-volcanic rocks, with minor contributions from Mesoarchean–Neoarchean basement rocks and Paleoproterozoic meta-mafic rocks. The protoliths of the metasedimentary rocks in the Dalizi Formation of the Laoling Group were deposited in a convergent margin setting, and subduction along the northern JLJB likely ended before ca. 1.91 Ga when the Longgang and Nangrim blocks collided. The εHf(t) values of ca. 2.14 Ga zircons mostly lie between the depletion mantle and the chondrite evolution line, coupled with extensive coeval magmatism, are consistent with the ca. 2.14 Ga significant continental crust growth in this region. An integrated study of petrology, geochemistry, metamorphic P–T paths, and tectonic evolution suggests that the JLJB experienced two metamorphic events at ca. 1.91 and 1.84 Ga.

CSAMT constraints on the metallogenic mechanism of the Zhaishang gold deposit, West Qinling, China

Whether the ore-forming fluids and materials of Zhaishang Carlin/Carlin-like type gold deposit were derived from concealed Mesozoic intermediate–acidic intrusive rocks through deep faults is controversial. In this study, eight CSAMT profiles were used to investigate the electrical resistivity structure of this deposit using high-resolution 2-D inversion. A ∼1 km wide high-resistivity (>3000 Ωm) body was observed at the base of the resistivity model (∼600 m). Two slightly NE-dipping high-conductivity channels were also observed along two sides of the high-resistivity body that connected to the gold-bearing quartz veins at the surface. The data suggest that the high-resistivity body is a Mesozoic granite and the two high-conductivity channels are fault zone conductors, which may be the wings of an NE-trending anticline that formed under regional compressive stress during the Caledonian orogeny. Their reactivation during the Indosinian and Yanshanian periods likely formed conduits for rising deeply-sourced ore-forming fluids (likely magmatic water). These conduits also promoted ground and meteoric water infiltration and mixing with the rising fluids. Accordingly, at least some of the ore-forming fluids and materials in the Zhaishang deposit were derived from Mesozoic granites through concealed faults, which can provide new geophysical constraints for discussions of the deposit’s metallogenic mechanism.

Geothermobarometry of acidic rocks of Dehsard area (southwest of Kerman Province): Constraint on using mineral chemistry of amphibole to determine characteristics of parental magma

Geothermobarometry of acidic rocks of Dehsard area (southwest of Kerman Province): Constraint on using mineral chemistry of amphibole to determine characteristics of parental magma

Geochemistry, U[sbnd]Pb geochronology, and Sr-Nd-Hf isotope systematics of a SW-NE transect in the southern Peninsular Ranges batholith, Mexico: Cretaceous magmatism developed on a juvenile island-arc crust

The Peninsular Ranges batholith (PRB) is a North American Cordillera segment with a protracted record of subduction-related magmatism (177–92 Ma). However, such a record is regionally fragmented, showing broad petrologic variations challenging to integrate into a coherent geologic evolution history. Here, we present a petrogenetic study of Cretaceous plutons in the southern PRB along the Sierra El Arco-San Francisquito transect (SW-NE) perpendicular to the paleotrench. The Middle Jurassic-Early Cretaceous (166–140 Ma) magmatism developed as an island arc with sedimentary rocks of intra-arc and oceanic marginal basins. At the Sierra El Arco, the Calmallí pluton intruded the Jurassic arc sequence. The basic to intermediate rocks of the Calmallí pluton show εSrt (average –3.6), εNdt (average +3.3), and εHft values (average +6.0) that suggest an origin from mantle-derived melts with minor contamination. These rocks display almost flat rare earth elements (REE) patterns and Eu anomalies suggesting plagioclase fractionation. East of the Calmallí pluton from the Piedra Blanca to the San Francisquito region, granodiorite and granite (100–92 Ma) are continuously exposed. The εSrt (average +3.1), εNdt (average +1.1), and εHft (average +2.6) isotopic signatures in the acid rocks suggest a mantle-derived melt genesis with increased contamination. Most granodioritic and granitic rocks display a characteristic depleted-HREE pattern without Eu anomalies, suggesting differentiation under the influence of garnet. The Jurassic-Cretaceous (166–92 Ma) magmatism displays an εSrt vs. εNdt correlation trend, indicating progressive contamination of mantle-derived magmas with a recycled crust. SrNd and NdHf isotopic mixing curves suggest the assimilation of the metasedimentary Triassic basement of NW Mexico instead of the considerably older and isotopically evolved Precambrian basement. The integration of this work with data from NW Mexico suggests a continuous magmatic activity from the Middle Jurassic to the Late Cretaceous. We consider the geochemical, isotopic, and temporal variation of the PRB indicative of natural heterogeneities along the trench axis of a long-lived arc system (crustal thickness and paleogeography) due to continuous subduction of the Farallon plate below the North American plate.

P-T-t-d evolution of Brattnevet Peninsula, Larsemann Hills, East Antarctica

Brattnevet Peninsula, Larsemann Hills, comprises metamorphosed acidic rocks, sedimentary rocks and basic igneous suite belonging to timespan of 920-478 Ma and have experienced three phases of deformation and metamorphism. The first and second phase of deformation gave rise to moderately plunging isoclinal and open to closed folds, respectively and the third phase resulted into broad warping. M1 prograde (amphibolite) and M2 peak (granulite) and M3 retrograde (decompression) events have been inferred. In pyroxene granulite, inclusion assemblage of quartz, biotite, plagioclase and ilmenite in hornblende correspond to the relict M1 amphibolite grade event associated with D1-D2 deformation events (occurred at ~920 Ma; 538–692 °C at ~6kb). However, the presence of enstatite, diopside, quartz, biotite, ilmenite and plagioclase in pyroxene granulite and sillimanite, biotite and almandine garnet and plagioclase in metapelite indicates granulite facies during M2 event (~530 Ma; 868–920 °C at ~6.7 kb). The retrograde M3 event (500-480 Ma; ~620 °C at ~5kb) is largely depicted in pyroxene granulite and metapelite by coronal and symplectite cooling textures. The study shows a clockwise P-T path and suggests the crustal evolution of Larsemann Hills area have commenced at the wanning stages of Grenvillian Orogeny and imprinted by the Pan-African orogenic event in the terrane.

Geochemical aspects of the formation of Neogene volcanism in the central part of the Lesser Caucasus

The article considers the formation of Neogene volcanism in the central part of the Lesser Caucasus on the basis of geochemical features. It was found that in the andesite-dasite-rhyolite association rocks, where volcanism is expressed, light lanthanides predominate over weight, and therefore the La/Sm, La/Yb ratios are high. In medium rocks (quartz latites, andesites) the Eu/Eu* ratio is close to unity (Eu/Eu* = 0.94-1.05), in more acidic rocks the weak Eu-minimum (Eu/Eu* = 0.58-0 ,63) and indicates the fractionation of plagioclase in the formation of acidic rocks. Enrichment melts and fluids with a relatively high melting point caused the increase of Ba/Y, Rb/Y, Th/Yb, Nb/Y, Nb/Yb ratios in the association rocks and their enrichment with Ba, Sr, rare earth elements. It was concluded that the source of the enriched mantle played a key role in the formation of andesite-dasite-riolite association rocks of the central part of the Lesser Caucasus. Keywords: Central part of the Lesser Caucasus, Neogene volcanism, distribution of rare earth and rare elements, source of enriched mantle.

The use of biologically active agents in the methods of intensification of oil production

The article considers the formation of Neogene volcanism in the central part of the Lesser Caucasus on the basis of geochemical features. It was found that in the andesite-dasite-rhyolite association rocks, where volcanism is expressed, light lanthanides predominate over weight, and therefore the La/Sm, La/Yb ratios are high. In medium rocks (quartz latites, andesites) the Eu/Eu* ratio is close to unity (Eu/Eu* = 0.94-1.05), in more acidic rocks the weak Eu-minimum (Eu/Eu* = 0.58-0 ,63) and indicates the fractionation of plagioclase in the formation of acidic rocks. Enrichment melts and fluids with a relatively high melting point caused the increase of Ba/Y, Rb/Y, Th/Yb, Nb/Y, Nb/Yb ratios in the association rocks and their enrichment with Ba, Sr, rare earth elements. It was concluded that the source of the enriched mantle played a key role in the formation of andesite-dasite-riolite association rocks of the central part of the Lesser Caucasus. Keywords: Central part of the Lesser Caucasus, Neogene volcanism, distribution of rare earth and rare elements, source of enriched mantle.

Four Pan-African plutonic sets of the Colomines gold district (East-Cameroon): Petrogenesis, K-Ar dating and geodynamic significance

The study of Colomines area (eastern Cameroon) is designed to furnish petrological, mineralogical, geochemical and K-Ar data on granitoids in order to discuss the thermodynamic conditions of crystallization of different magmas, the magma series and differentiation processes, the characteristics of magmas’ sources and the geodynamic implications. The Colomines area is made up of four intrusive sets (heterogeneous granodiorites and their mafic enclaves, mafic plutonic suite (MPS), porphyritic biotite granites, Ms-Bt granites). Mineralogical assemblage is constant in MPS and mafic enclaves (Cpx+Hbl+Bt+Pl+Qtz+Op+Sph+Zrn+Ap), and granodiorite and granites sets (Hbl+Bt+Ms+Pl+Kfs+Op+Sph+Zrn+Ap), except the leucocratic Ms-Bt granites which are amphibole-free. Amphibole in diorite (MPS) and heterogeneous granodiorite has a composition of edenite and ferroedenite, respectively, whereas biotite composition varies with an increase of Fe content from basic to acidic rocks. Concomitantly, plagioclase show an increase of albite component. Crystallization of magmas started at great depths >22 km but the coexistence of heterogeneous granodiorites, MPS plutonic suite rocks, porphyritic biotite-granites and Ms-Bt granites at the same crustal level indicates that magmas migrated upwards and emplaced at a depth <4.5 km, in the upper crust. Chemical analyses show that all rocks are magnesian except ferroan Ms-Bt granites and a few samples of microgranites and porphyritic granites. Granodiorites, few monzonites of MPS and all granites are peraluminous whereas mafic enclaves in heterogeneous granodiorites are metaluminous. Heterogeneous granodiorites, gabbros and diorites of the MPS are calcic and calc-alkalic while other rock types are alkali-calcic and alkalic. Porphyritic granites and Ms-Bt granites trend from calc-alkaline to shoshonitic series. It is suggested that a fractional crystallization process may have contributed to the transition from blind primary magmas to these evolved granitoids. However, each group of rocks does not correspond to a magmatic sequence resulting from a single parent magma by fractional crystallization. They are rather indicative of the heterogeneity of magmatic sources and complex melting processes. The granitoids and associated rocks of Colomines correspond to complex mixtures in varying proportions of magmas resulting from the melting of the subducted crust and associated sediments, the mantle wedge and the lower crust. Biotite and rock compositions typical of volcanic-arc and syn-collision-related granites, and the compositions of Ms-Bt granites typical of post-collisional granites point to an active continental margin setting. The Colomines area has recorded most of the main magmatic events of the Pan-African orogeny from ante-collisional D1 (e.g. > 640 Ma heterogeneous granodiorites of Kaleka hill), syn-collisional D2 (620-600 Ma migmatisation and anatexis: leucosomes of Kaleka hill), late collisional D3 (590-580 Ma MPS) to Post-collisional D4 (580-560 Ma porphyritic biotite granites and Mu-Bt granites) intrusions.

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.

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.

Test and application of the geochemical lithogene on weathering profiles developed over granitic and basaltic rocks in China

Geochemical gene is a new technique presented recently and its property needs to be tested. Two weathering profiles developed over granitic and basaltic rocks were sampled and analyzed in Dunhua area in Northeast China with a cool temperate monsoon climate. Based on their major and trace elemental compositions, the geochemical lithogene numbered as LG01 was coded and samples' gene similarities were calculated relative to their parent rocks and top soils respectively. According to the similar gene criterion of ≥80% on gene similarity, the geochemical lithogene LG01 shows not only good heredity (on similar gene from parent rock to top soil) but also good inheritance (on similar gene from top soil to parent rock) in each weathering profile. That is to say, the geochemical lithogene LG01 illustrates good stability during weathering. According to the composition classification method based on the acidic similarity (a gene similarity relative to the acidic rock with the LG01 gene of 10202020202), the weathered products of the profile developed over granite are acidic-like composition (with acidic similarity of ≥80%) and those formed on basalt are basic-like composition (with acidic similarity of ≤20%). These indicate the validity of the composition classification method based on the geochemical lithogene LG01. In order to test the property and application of LG01 in a wider range, four newly reported weathering profiles (a granitic profile and a basaltic profile located in a warm temperate monsoon climate zone, another granitic profile in a subtropical monsoon climate zone, and another basaltic profile in a tropical monsoon climate zone) were also discussed. Their results verify the conclusion that the geochemical lithogene LG01 not only illustrates good stability among samples due to rock weathering but also is a potential tool on classification of rocks and their weathered products.

Mineralogical fingerprinting to characterize spatial distribution of coastal and riverine sediments in southern Japan

Knowledge of the provenance and transport processes of coastal sediments is central to safeguarding against coastal erosion. However, to date coastal sediments have been poorly investigated without considering complex artificial and natural attributes such as coastal structures and watershed geology of potential source rivers. In this study, mineralogical fingerprinting technique was used to track the sources of sediments along a coastline in southwest Japan with reference to sediments of outflowing rivers. The sediment samples were collected from 65 beach sites along the Miyazaki Coast and its surrounding coastal area, and five river sites nearby. To determine the size distribution and geochemical and mineralogical compositions of the sediments, grain size, X-ray fluorescence, and X-ray diffraction (XRD) analyses were performed. Subsequently, cluster analysis was used to classify mineralogically similar groups in terms of XRD peak intensity ratio. The coastal sediment clusters corresponded well to nearby riverine clusters, suggesting that the coastal sediments were primarily transported from these river watersheds, although uncertainty as contributions of oceanic flows might be involved. The concordance ascribes to the major geological classifications in the watersheds of major rivers, as well as smaller rivers flowing in the northern area (e.g., the Shimanto Supergroup and Osuzuyama Acid Rocks). In addition to the major tendency, we also observed potential effects of manmade structures on the coastal sediment prevalence; the mineralogical similarities decreased across jetties in the Hitotsuse River mouth. The vertical mineralogical distribution of the core sediment samples observed on the left and right banks of the Hitotsuse River mouth supported the general trend of uniform cluster patterns in each core sample with horizontally different clusters across the river mouth. Mineralogical analysis targeting both coastal and riverine sediments is effective for understanding the characteristics of sediment distribution, which in turn is useful for efforts devoted to protection against coastal erosion.

Tonalite-trondjemite-granodiorite formation of the Archaean. Special features of composition and conditions of formation, Ukrainian Shield as an example

Tonalite-trondjemite-granodiorite formation (TTG) produces the main volume of acidic rocks of the continental crust. Similar rocks are never met later. Therefore the problems of their production are directly connected with the problem of the crust and mantle formation.&#x0D; The structure of the Archean TTG formation of granite-gneiss area of the Bug megablock and granite-grrenstone area of the Middle Dnieper megablock (MDMB) has been considered. Similar and different features have been found. The analysis of these data resulted in a conclusion that within the MDMB, West Periazovian and Khashchevate-Zavalie block of the Middle Bug area the events of formation of the Archean granite-greenstone area were similar, however these three blocks of the Ukrainian Shield demonstrate different levels of erosion damage reflected in PT-conditions of metamorphic transformations.&#x0D; The rocks of TTG formation are a part of complex structured stratum appeared as a result of impregnation (migmatization) by quartz-albite melt of the primary crust and/or of more ancient strata of predominantly basic composition. In the middle-lower crust a partial replacement of the primary crust occurred and in the upper one — the deposition of new portions of the melt on the earlier ones, piercement of granite masses and migmatization of volcanogenic stratum. During the Archean these events happened repeatedly, that resulted in partial replacement of the primary crust with plagiogranites.&#x0D; Modern notions have been considered on the processes of producing of TTG granite formation. It has been shown that according to thermal model distribution of temperatures in the crust does not cross the line of basalt water solidus. That is why the appearance of granite melts could not be the result of submergence to big depths (ultrametamorphism). Chronological and genetic relation with mantle melting, of which komatiites and spilites of green-stone structures were crystallized, assumed convective flows in the mantle. To explain the formation of tonalite and trondjemite melt a model of two-leveled crystallization differentiation of ultrabasic melt has been used. However appearance of primary basalt replacement in such a scale and assimilation of green-stone roots by granite melt are possible only in case of interaction of mantle fluids with the rocks of primary crust. An assumption has been made that the composition of some part of these fluids could be close to composition of granite (trondjemite). According to the author’s opinion such assumption confirms a hypothesis of V. Griffin and N. Pirson about formation of crystalline mantle on the border between the Archean and Proterozoic.

A New Magma Type in the Continental Collision Zone. The Case of Capraia Island (Tuscany, Italy)

The Tuscany Magmatic Province consists of a Miocene to Pleistocene association of a wide variety of rock types, including peraluminous crustal anatectic granites and rhyolites, calcalkaline and shoshonitic suites and ultrapotassic lamproites. In addition to the magma types already recognised, the occurrence of a new, distinct magma type at Capraia and Elba islands and in mafic enclaves in the San Vincenzo rhyolites has been suggested by recent studies. This particular type of magma, represented by intermediate to acidic calcalkaline rocks showing high Sr, Ba, and LREE, is restricted to the northwestern sector of the province and to a time interval of about 8 to 4.5 Ma. New data obtained on rocks from Capraia Island have allowed for the verification of the occurrence of this new magma type, the exploration of its origin and a discussion of its possible geodynamic significance. The high-Sr-Ba andesite-dacite rocks occurring in the Laghetto area at Capraia display a composition that is intermediate between adakitic and calcalkaline rocks. It is suggested that they represent a distinct type of magma that originated at mantle pressure by melting of the lower continental crust, followed by mixing with other Capraia magmas. The geodynamic model that best explains the composition of the studied rocks is the thickening of the continental crust during continental collision, followed by extension that favoured melting of the lower crust.

Geochemistry and zircon U-Pb ages of the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin

In this study, element geochemistry and zircon chronology are used to analyze the Oligocene sediments in the Baiyun Sag, Zhujiang River Mouth Basin. The experimental results are discussed with respect to weathering conditions, parent rock lithologies, and provenances. The chemical index of alteration and the chemical index of weathering values of mudstone samples from the lower Oligocene Enping Formation indicate that clastic particles in the study area underwent moderate weathering. Mudstone samples exhibit relatively enriched light rare earth elements and depleted heavy rare earth elements, “V”-shaped negative Eu anomalies, and negligible Ce anomalies. The rare earth element distribution curves are obviously right-inclined, with shapes and contents similar to those of post-Archean Australian shale and upper continental crust, indicating that the samples originated from acid rocks in the upper crust. The Hf-La/Th and La/Sc-Co/Th diagrams show this same origin for the sediments in the study area. For the samples from the upper Enping deltas, the overall age spectrum shows four major age peaks ca. 59–68 Ma, 98–136 Ma, 153–168 Ma and 239–260 Ma. For the Zhuhai Formation samples, the overall age spectrum shows three major age peaks ca. 149 Ma, 252 Ma and 380 Ma. The detrital zircon shapes and U-Pb ages reveal that during Oligocene sedimentation, the sediments on the northwestern margin of the Baiyun Sag were supplied jointly from two provenances: Precambrian-Paleozoic metamorphic rocks in the extrabasinal South China fold zone and Mesozoic volcanic rocks in the intrabasinal Panyu Low Uplift, and the former supply became stronger through time. Thus, the provenance of the Oligocene deltas experienced a transition from an early proximal intrabasinal source to a late distal extrabasinal source.

Chemical study of the application of nonionic surfactants nonylphenol in delaying the acidizing reaction of carbonate matrices

In the acid stimulation of oil wells, slowing down the rate of the reaction between hydrochloric acid and carbonate rocks is a huge challenge, in order to increase the stimulation efficiency. In this work, acid solutions containing Nonylphenol nonionic surfactants of different degrees of ethoxylation were formulated to decrease the reaction rate of H+ ions with carbonate rocks. An experimental design plan was executed with a central compound design, showing that the reaction rate decreased up to 350 times (2.356 × 10−4 ± 0.133 grams of rock per second). It was possible to verify that the presence of the surfactant, in addition to reducing the surface tension and changing the wettability of the medium, also allowed an increase in the viscosity of the solution, which was the main factor for the delay of the reaction.

Phytosociological Analysis of Natural and Artificial Pine Forests of the Class Vaccinio-Piceetea Br.-Bl. in Br.-Bl. et al. 1939 in the Sudetes and Their Foreland (Bohemian Massif, Central Europe)

Research Highlights: Differentiation of Scots pine forests of the class Vaccinio-Piceetea in Poland has been the subject of numerous studies, including revisions. Despite that, the area of southwestern Poland was hitherto practically unexplored in this respect. Background and Objectives: The aim of this work was therefore (i) to present the diversity of the pine forests in the Sudetes and their foreland; (ii) to compare the ecology of studied communities. Materials and Methods: We analyzed 175 phytosociological relevés collected between 1991 and 2020 in natural and anthropogenic pine stands. To identify vegetation types, we used the modified TWINSPAN algorithm; principal coordinate analysis, distance-based redundancy analysis and permutational tests were applied to identify the variation explained and the main environmental gradients shaping the studied plant communities. Results: Five associations were distinguished: thermophilous Asplenio cuneifolii-Pinetum sylvestris Pišta ex Husová in Husová et al. 2002, which develops on shallow soils over ultrabasic substrates, Hieracio pallidi-Pinetum sylvestris Stöcker 1965, which prefers outcrops of acidic rocks; Betulo carpaticae-Pinetum sylvestris Mikyška 1970, which is relict in origin and occurs on the upper Cretaceous sandstones, the peatland pine–birch forests of the Vaccinio uliginosi-Betuletum pubescentis Libbert 1933 and the Vaccinio myrtilli-Pinetum sylvestris Juraszek 1928. Moreover, community Brachypodium sylvaticum-Pinus sylvestris with the occurrence of many thermophilous and basiphilous species was also found on limestone substratum. The analysis of the species composition of pine plantations established on deciduous and mixed forests habitats revealed that these anthropogenic communities were marked by a random combination of species in which a certain group of common forest generalists participated. The distinguished communities differed clearly among each other also in habitat characteristics. Particularly important for their differentiation were soil reaction and nutrients, supported by differences in moisture, temperature and light availability. Apart from the edaphic factors, altitude and the bedrock type proved to be equally important. Conclusions: Our study provides new remarks to the typology and synecology of pine forest communities in SW Poland.

Discussion on Several Problems of Metallogenic Geological Condition and Genesis of Shoushan Stone

Shoushan stone is one of the four traditional stamp stones in China. The study for Shoushan stone has a long history, but mostly focuses on the classification and mineralogical and gemmological research for major varieties. And the study for metallogenic geological condition and genesis of Shoushan stone is relatively weak. The main problems of geological conditions and genesis of Shoushan stone are discussed in this paper. It considers that the acidic pyroclastic rocks of the second member of Xiaoxi formation in Shoushan Early Cretaceous volcanic eruption basin are the material basis of ore-forming. And it is proposed that the ore-forming and ore-controlling model is the NE-trending structure controling basin (Shoushan basin), NW-trending fault controling rock (volcanic rocks and volcanism), volcanic mechanism controling ore (deposit) and volcanic fault controling body. Secondary quartzite type altered mineral facies and mineral assemblage zoning in Shoushan orefield are discussed and established, which can be divided into five altered mineral facies and six mineral assemblage zoning. The discussions will promote the exploration, potential evaluation and prospecting prediction of Shoushan stone deposit, and even the interpretation of difficult problems in mineralogy.

Geochemical and Nd-Sr Isotopic Compositions of Hypabyssal Adakites in the Torud-Ahmad Abad Magmatic Belt, Northern Central Iran Zone: Analysis of Petrogenesis and Geodynamic Implications

Eocene intermediate to felsic subvolcanic rocks of the Torud-Ahmad Abad magmatic belt (TAMB), in the northern part of the Central Iran zone, are exposed between the Torud and Ahmad Abad regions in South-Southeast Shahrood. These igneous rocks include hypabyssal dacite, trachyte, andesite, trachy-andesite, and basaltic andesite; they are mainly composed of phenocrysts and microcrystalline groundmass of pyroxene, amphibole, and plagioclase, with minor biotite and titanomagnetite; they form domal structures (plugs and stocks), dikes, and sills that intruded into Neoproterozoic to cogenetic Eocene volcano-sedimentary sequences. Based on isotopic analysis of these intermediate to acidic rocks, initial ratios of 143Nd/144Nd range from 0.512 775 to 0.512 893 and initial ratios of 87Sr/86Sr range from 0.703 746 to 0.705 314, with quite positive εNd(i) values of +3.69 to +6.00. They are enriched in light rare earth elements and large ion lithophile elements and depleted in heavy rare earth elements and high-field strength elements, the SiO2 content is (52–62) wt.%, and Na2O content >3 wt.%, Al2O3 content >16 wt.%, Yb <1.8 ppm, and Y <18 ppm. These geological, geochemical, and Sr and Nd isotopic data are consistent with adakitic signatures originating by partial melting of the subducted Neo-Tethys oceanic slab (Sabzevar branch) and lithospheric suprasubduction zone mantle. The mantle signatures typifying the rapidly emplaced adakitic rocks (slab (high-silica adakite) and suprasubduction zone (low-silica adakite) melts) together with their locally voluminous extent are evidences that support a locally extensional geodynamic setting; and the evidence is consistent with an evolution to local transpression in the Late Eocene in this convergent margin arc environment to rifting (basalts to adakites) towards submarine conditions in the Neogene.

Geochemical and reflectance spectroscopy data integration to characterize emerald deposits: the case of the Paraná deposit, Brazil.

The Paraná emerald deposit is one of the few occurrences of emerald, a rare beryl variety, in Borborema Province, northeastern Brazil. We characterized the Paraná deposit by combining field geology, petrography, whole-rock geochemistry, mineral chemistry, and reflectance spectroscopy. The mineralization is associated with phlogopite-, actinolite-phlogopite-, and phlogopite-phengite schists, mylonitic gneisses, and several acidic rocks (e.g. granitic pegmatites/aplites, quartz ± feldspar veins) along the Portalegre Shear Zone. Emerald can be found in quartz-feldspar and aplite veins and veinlets interleaved with phlogopite- or actinolite-phlogopite schists, or within the foliation of the schists. The presence of albitites and the compositional variation of the schists suggest a metasomatic origin for emerald with variations of the metasomatic process. All these different lithotypes can be readily identified through reflectance spectroscopy especially in the range of 2,150-2,450 nm, where the main mafic minerals show absorption features related to Al-OH (phengite), and Fe-OH and Mg-OH bonds (phlogopite/actinolite). Our study shows that possible mineralized phlogopite schists can be distinguished from other sterile rocks, although point spectral analysis does not separate emerald-bearing phlogopite schists from schists without emerald due to the dominance of major phlogopite absorption features rather than emerald features.