Intense Magmatic Activity Research Articles

Tungsten speciation and its geochemical behavior in geothermal water: A review

Tungsten and most of its compounds remain one of the least regulated substances. As the potential toxicity of tungsten has been reported, the stereotypes about tungsten are gradually being broken. Areas with intense magmatic hydrothermal activity are likely threatened by geothermal tungsten (up to 1037 μg/L of tungsten was detected in the geothermal waters from a magmatic hydrothermal system in Tibet, Daggyai), and the geothermal developers should be cautious during the utilization of geothermal resource. This paper reviews the studies on transformation of aqueous tungsten species, distribution of tungsten in geothermal waters, and critical geochemical processes (or parameters) controlling geothermal tungsten concentrations. The mobility of aqueous tungsten depends on environmental pH, its complexation with sulfide, and its sorption onto Fe(III) oxides/oxyhydroxides. More attention still needs to be paid to environmental geochemistry of tungsten, in view that there are limited literatures reporting the thermodynamic properties of tungsten compounds at high temperatures and the models delineating the geochemical behavior of tungsten.

Genetic causes of oil-rich and oil-poor reservoirs: Implications from two Cenozoic basins in the eastern North China Craton

The Bohai Bay and Hehuai (southern North China) rift basins in the eastern part of the North China Craton are south-north-adjacent. They have shown synchronous evolutionary processes, and possess generally identical superficial and shallow structural characteristics as well as similar basin areas. However, there is a large difference in the richness of oil resources between the two basins. The Bohai Bay Basin has extremely abundant oil reserves, while commercial oil reserves have not been found in the Hehuai Basin. The deep tectonic structures, magmatic activities, and modern and paleo-geothermal fields of the two basins are significantly different. Compared with the Hehuai Basin, the Bohai Bay Basin has a thinner crust and more complex structure with multiple low-velocity layers. It is also characterized by intense magmatic activity, high modern and paleo-geothermal fields, frequent seismic activity, and active deep interactions, small effective elastic thickness of the isotropic lithosphere, and shorter balanced transformation wavelength of the lithosphere with a high likelihood of local compensation. The Hehuai Basin has a simple deep structure and homogeneous crustal composition, with a high likelihood of regional compensation. The characteristics of the deep structures mentioned above are generally similar to those of the southern part of the stable Ordos Basin, except for the smaller crust thickness. This indicates the presence of differences in Mesozoic destruction between the southern and northern zones in the eastern part of the North China Craton. The northern zone was subjected to significant destruction, while the southern zone was subjected to modifications, primarily in the form of local changes in the structures and/or properties of the crust or lithospheric mantle, with the overall structure and stability of the craton kept intact. The formation of high-quality source rock is primarily influenced by the abnormal flourishment of organisms in water bodies during the syndepositional period, and is also strongly associated with the high geothermal setting of basins and nutrients from hydrothermal solutions and volcanoes. In other words, it is mainly controlled by deep processes and deep-major fault activity. The differences in the deep structures and modern and paleo geothermal fields of the two basins correspond to the difference in richness of oil resources, suggesting that there is an important internal or causal relationship between the two aspects. This viewpoint coincides with the conditions and environments required for the development of high-quality source rock in hydrocarbon-rich basins (sags) in China and other countries, and is evidenced by the modern lake basin of the East African Rift. A new hydrocarbon generation model is proposed in this work: petroleum is a comprehensive product of the integration of bioenergy, thermal energy, and other related energies (such as chemical and kinetic energy) and their interactions; the degree of richness of petroleum is generally controlled by the regional tectonic structure, thermal environment, and deep processes; nonmarine basins or depressions with abundant resources are closely related to active deep processes, intense exchange of material between the deep and shallow layers, participation of external hydrocarbons, and energy integration and conversion.

Structural evolution of the Paleoproterozoic Trans-North China Orogen: Evidence from the Xiaoqinling region, central China

High-grade metamorphic rocks of Archean to Paleoproterozoic age, collectively called the Taihua Complex, are well exposed in the Xiaoqinling region in the western part of the southern segment of the Trans-North China Orogen (TNCO), central China. However, the evolution of orogenic events in this part of the TNCO remains unclear. Here we present structural and zircon U–Pb data to constrain the structural evolution of the rocks in the Xiaoqinling region. The first phase of deformation (D1) produced penetrative, ductile fabrics and localized ductile shear belts, and it was accompanied by a regional high-grade metamorphism. The D1 structures were the result of WNW-directed thrusting movements that have been dated at 1863–1840 Ma, and the microstructures suggest temperatures of 600–650 °C, which correspond to the conditions of exhumation of these orogenic rocks. These data support the ca. 1.85 Ga collision model for the Western and Eastern blocks that involves the SE-directed subduction of the Western Block. The second phase of deformation (D2) produced localized E–W-striking normal shear belts, and the D2 structures provide reliable evidence for N–S extension during the late Paleoproterozoic. Intense magmatic activity accompanied this period of extension. Zircon U–Pb dating constrains the extension to the period between 1829 and 1703 Ma. Post-orogenic extension in the TNCO accounts for D2 and the associated magmatism, and orogen-parallel extension is indicated by the structures. Thus, the Paleoproterozoic structural evolution of the rocks in the Xiaoqinling region of the TNCO records orogenic processes from exhumation to post-orogenic extension.

Interpretation of gravity data for fault distribution near the Mongolia–Hinggan metallogenic belt in the eastern China-Mongolia frontier area

The Central Asian Orogenic Belt (CAOB) is a giant suture zone produced by the reduction of the Paleo- Asian Ocean between the Siberian, North China, and Tarim cratons. The CAOB formed in three main stages, including continental accretion, late collision, and intracontinental orogeny. Strong crust-mantle interaction also occurred during these stages. The eastern China-Mongolia frontier area is an important part of the CAOB. Since the Caledonian period, this region has frequently experienced polycyclic tectonic reformation and intense magmatic activities. All of these geological activities lay the foundation for abundant metal resources. In the past, several large metal ore deposits have been founded there. However, the deep structure of different tectonic units and the fault distribution in the eastern China-Mongolia border frontier area are still not clear owing to the complex geological environment. Existing works in that region are insufficient for an in-depth understanding of the metallogenic deposits. The work discussed in this paper was carried out in the eastern China-Mongolia frontier area with measured gravity data along a profile and gravity data extracted from the WGM2012 earth’s gravity model for detailed fault distribution. In this study, empirical mode decomposition (EMD) and tilt angle analysis (TDR) were utilized for processing the gridded gravity data. The measured gravity data were inverted with a 2D inversion algorithm for density distribution along the survey line. The inversion result was used to verify the existence of known faults and describe their deeper extensions. Meanwhile, new faults were also identified along the survey line and then marked on the gridded data to get their horizontal distribution. These results provide significant information for the in-depth understanding of the tectonic units in the study area.

In-situ sulfur isotope analysis of pyrite from the Pangjiahe gold deposit: Implications for variable sulfur sources in the north and south gold belt of the South Qinling orogen

The sedimentary- and granite porphyry-hosted Pangjiahe gold deposit is located in the north belt of the South Qinling Orogen, with a proven reserve of 38 t Au at 6.3 g/t. A total of 26 samples, from various rock types and locations from the Panjiahe deposit, were taken in order to determine the paragenesis, sulfur source and absolute age of mineralization. Magmatic activities of ca. 240 Ma occurred around the whole study area, which is common in the northwest part of the West Qinling orogen. Field observations confirm that the emplacement of granite porphyry dykes is earlier than the gold mineralization, because they were both altered and mineralized. Moreover, post ore stage diabase dykes, which cut cross the ore bodies, display an age of ca. 220 Ma. Zircons from strongly mineralized granite porphyry samples show typical hydrothermal trace element characteristics. Theses zircons return a concordia age at ca. 230 Ma. Therefore, we infer that the ore-forming age of the Pangjiahe deposit is at ca. 230 Ma.Optical microscopy, EMPA and LA-(MC)-ICPMS have been used to determine the physical and chemical features of pyrite. Five stages of pyrite have been identified in mineralized phyllite and granite porphyry rocks. Diagenetic pyrite in phyllite, Py1-P, displays a wide range of δ34S (−1.5% to +9.4%). The magmatic pyrite in the granite porphyry, Py1-G, display relatively narrow range of δ34S (+2% to +5%) consistent with magmatic sulfur. The main ore stage pyrite in both rocks, Py2 (Py2-P and Py2-G), is the most common sulfide in the deposit. Py2 grains predominantly show oscillatory zoning and either replace or overgrown the Py1-P and Py1-G, or occur as individual fine grains. Arsenopyrite is typically associated with Py2. Pyrite grains in late stage quartz (Qz) veins that cross cut phyllite and granite, Py-Qz, display weak oscillatory zoning. Native gold is commonly observed as inclusions in the Py-Qz grains or within/proximal to quartz veins. Py3 pyrite (Py3-P and Py3-G), which also belong to the later ore stage and can be distinguished by the native gold inclusions in them, all occur as the outer rims that overgrown or replace on Py2. The ore stage Py2, Apy, Py-Qz and Py3 have a similar narrow range in sulfur isotopic composition, from +8% to +10%. This range is slightly lower than the age equivalent SEDEX Pb-Zn deposits situated in graben basins to the East, but totally different from the earlier Py1-P and Py1-G. EMPA element mapping and spot analyses, and in-situ sulfur isotope analyses indicate that the ore stage pyrites in both phyllite and granite rocks have similar major element chemistry and sulfur isotopic composition, indicating that they are likely sourced from the same ore fluids. Therefore, we propose that prograde metamorphism of the underlying Devonian sedimentary sequences during the seafloor exhalation, which are thought to be enriched in Au, As, Sb, B, F and S, may have released H2S that forming these auriferous sulfides.Gold mineralization in the south belt of the South Qinling orogen shows the same mineralization style as observed in the North belt. However, mineralization is younger and the δ34S values of the hydrothermal ore stage sulfide are consistent with magmatic sulfur, which is consistent with intense magmatic activities within the South Qinling orogen. The δ34S values in the South Belt are distinctly different from those of gold deposits in the north belt. We propose that the source of the sulfur and gold in north belt came from the Devonian graben basins, and in the south belt came from a deep magmatic source. More focused studies of the gold and Devonian graben basin hosted SEDEX Pb-Zn deposits are required to further prove or develop this hypothesis.

Geochemistry and chronology of the granites in Alasituo, west Tianshan Orogen: Implications for a magma mixing origin

There are intense magmatic activities in the Alasituo integrated gold exploration area, west Tianshan Orogen. On the basis of field characteristics, geochemistry features, and chronology in Alasituo, the formation mechanism of complex granite rocks was explored. The intrusive rocks are divided into 3 parts: a silicic endmember, a mafic endmember, and intermediate rocks. Mafic microgranular enclaves, as well as spotted structure, silicic veins intruding mafic rocks and plagioclase xenocrysts, developed in rocks. Under the microscope, there are many unbalanced mineral combinations, needle‐like apatites, and poikilitic structures. Futhermore, there is an obvious linear trend between the mafic endmember samples, intermediate samples, and the silicic endmember samples in Harker diagrams. All samples were evolved from magma mixing in TFe2O3‐MgO diagram. The trace element concentrations of intermediate rocks have the transitional features of both silicic and mafic endmember rocks. The above characteristics show that rocks have experienced low degree and uneven physical and chemical magma mixing. The silicic endmember rocks have a high content of K2O + Na2O, Zr, Nb, Y, and REE; high Ga/Al ratios, and; low content of Sr, Eu, Ti, and P, which have the characteristics of A‐type granites with a crustal source. The high content of MgO, TFe2O3, and low K2O/Na2O in mafic endmember rocks indicate a mantle source. The LA‐ICP‐MS U–Pb zircon age of the granodiorites is 350.3 ± 3.0 Ma. Combined with regional geological background and geochemical characteristics, the intrusive rocks were formed when the thinning lithosphere triggered mafic magma underplating, heating upper crust granites, and causing them partial melt.

Terrestrial heat flow and geothermal field characteristics in the Bide-Santang basin, western Guizhou, South China

Geothermal fields in coal-bearing strata significantly influence coal mining and coalbed methane accumulation and development. Based on temperature data from 135 coalfield exploration boreholes and thermophysical tests of 43 rock and coal samples from the Upper Permian coal-bearing strata of the Bide-Santang basin in western Guizhou, South China, the distribution of terrestrial heat flow and the geothermal gradient in the study area are revealed, and the geological controls are analysed. The results show that the thermal conductivity of the coal-bearing strata ranges from 0.357 to 3.878 W (m K)−1 and averages 1.962 W (m K)−1. Thermal conductivity is controlled by lithology and burial depth. Thermal conductivity progressively increases for the following lithologies: coal, mudstone, siltstone, fine sandstone, and limestone. For the same lithology, the thermal conductivity increases with the burial depth. The present geothermal gradient ranges from 15.5 to 30.3°C km−1 and averages 23.5°C km−1; the terrestrial heat flow ranges from 46.94 to 69.44 mW m−2 and averages 57.55 mW m−2. These values are lower than the averages for South China, indicating the relative tectonic stability of the study area. The spatial distribution of the terrestrial heat flow and geothermal gradient is consistent with the main structural orientation, indicating that the geothermal field distribution is tectonically controlled at the macro-scale. This distribution is also controlled by active groundwater, which reduces the terrestrial heat flow and geotemperature. The high geothermal gradient in the shallow strata (<200 m) is mainly caused by the low thermal conductivity of the unconsolidated sedimentary cover. The gas content of the coal seam is positively correlated with terrestrial heat flow, indicating that inherited palaeogeothermal heat flow from when coalbed methane was generated in large quantities during the Yanshanian period due to intense magmatic activity.

The birth of the Xigaze forearc basin in southern Tibet

The stratigraphic succession of a forearc basin provides crucial information on the history of a convergent plate margin. In particular, it helps to establish the origin of the underlying ophiolites and to unravel the earliest evolutionary stage of arc-trench systems, which remain poorly understood. The Xigaze forearc basin in southern Tibet is one of the best examples of a fossil forearc basin. This study illustrates detailed stratigraphic and high-precision SIMS U–Pb zircon geochronological and Hf isotopic data from the Chongdui Formation, representing the very base of the Xigaze forearc-basin succession, and reconstructs when and how the basin was formed. The Chongdui Formation includes tuffaceous chert and siliceous mudrocks deposited directly on top of pillow basalts of the Xigaze ophiolite and conformably overlain by volcaniclastic turbidites. Tuff layers are interbedded throughout the unit, and their U–Pb zircon ages range from 119 to 113 Ma in the lower member and from 113 to 110 Ma in the upper member, broadly consistent with the established radiolarian biostratigraphy. U–Pb ages and Hf isotope signatures of zircons contained in both tuff layers and turbiditic sandstones indicate clear affinity with magmatic rocks of the Lhasa terrane. Direct depositional and chronostratigraphic relationship with the underlying oceanic crust, dated between 131 and 124 Ma, proves that the Xigaze ophiolite is the basement of the Xigaze forearc basin. After an initial prolonged stage of starved siliceous sedimentation, influx of terrigenous detritus began at 113–110 Ma, reflecting the onset of topographic growth and erosion of the Lhasa terrane in response to intense magmatic activity. Formation of the ophiolitic basement during the early stage of subduction and the subsequent topographic growth of the arc source induced by subduction-related magmatism are thus two critical factors for the birth of the Xigaze forearc basin. Similar stratigraphies were identified in the Great Valley and Luzon Central Valley forearc basins, suggesting that the initial geodynamic evolution of the Xigaze forearc basin may be common to many other forearc basins worldwide.

Petrology of Teofilândia granitoids: An example of 2.1 Ga crustal accretion in the São Francisco Craton (Bahia, Brazil)

Teofilândia granitoids are representative of the Paleoproterozoic plutonic rocks, which intruded the Serrinha block, an Archean crustal fragment of the Sao Francisco Craton (Bahia, Brazil). Three plutons were emplaced, the Teofilândia granodiorite, the Barrocas trondhjemite and the Santa Rosa granite, respectively dated at 2130, 2127 and 2073 Ma. The two first plutons are calc-alkaline rocks following a trondhjemitic trend. They resemble Archean TTGs (tonalites-trondhjemites-granodiorites) by their major and trace element compositions and especially by their fractionated REE patterns, with very low HREE contents. These juvenile magmas resulted from partial melting of a young mafic protolith, likely represented by the nearby Rio Itapicuru greenstone belt. Barrocas trondhjemite and Teofilândia granodiorite derive from similar sources, possibly at different depths and with a different degree of melting. The rocks were deformed at high temperature during the Trans-Amazonian collision and are therefore pre-collisional and ascribed to a subduction stage. The younger Santa Rosa pluton is a small, syn-to post-collisional granite that derived from anatexis of the Archean crust. It is representative of a second, volumetrically minor, plutonic episode of potassic, shoshonitic or alkaline affinities. The large amount of 2.1 Ga granitoids emplaced in Brazil as well as in the West African craton, suggests that, at that time, a global event of possible mantle origin was responsible for the intense magmatic activity that involved both crustal accretion and crustal reworking in many places of the world.

The CMB Line: the southern margin of the Ivrea–Verbano Zone (basement of Southern Alps, Italy): a re-appraisal

A new interpretation of the Cossato–Mergozzo–Brissago Line (CMB) is presented here. This tectonic discontinuity divides the lower crustal Ivrea–Verbano Zone from the middle crustal Serie dei Laghi. The association of the two units was considered by some researchers as a cross section of the continental crust. The CMB is here seen as a transpressional dextral shear zone about 6 km thick, probably connected to an Early Permian intra-Pangea dextral shear zone. Ivrea–Verbano and Serie dei Laghi were brought together only after the Variscan metamorphism. The CMB is the seat of an intense magmatic activity ranging from mafic dykes to large granitic plutons, probably triggered by an inversion of the sense of shear from dextral to sinistral. The sinistral Pogallo Line may have played a major role in this context.

Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U–Pb geochronology on zircon and monazite

U–Th–Pb (zircon and monazite) ion probe data have provided constraints on the timing of emplacement and metamorphism of magmatic rocks close to the Palaeoproterozoic, Falun base metal sulphide deposit in the Bergslagen lithotectonic unit, Fennoscandian Shield, Sweden, and, thereby the timing of mineralisation. Hydrothermal alteration and mineralisation at Falun are constrained to a short interval of several million years between a 207Pb/206Pb weighted average age of 1894±3Ma for a rhyolitic sub-volcanic rock in the felsic volcanic to sub-volcanic host rock suite, and a 207Pb/206Pb weighted average age of 1891±3Ma for a post-sulphide, porphyritic dacite dyke. Magmatism also included the emplacement of granite plutons with igneous crystallization ages of 1894±3, 1894±2Ma and 1893±3Ma. The felsic sub-volcanic to volcanic activity and the emplacement of dacite dykes and granite plutons overlap in age within their respective analytical uncertainties, indicating hydrothermal alteration and sulphide mineralisation inside a narrow time span of intense magmatic activity, and burial of the supracrustal rocks. Two distinct patchy and homogeneous metamorphic monazite types in a felsic volcanic rock around and hydrothermally altered rocks at the Falun deposit yield 207Pb/206Pb weighted average ages of 1831±8Ma and 1822±5Ma, respectively. These ages fall well within the temporal range of a younger 1.84–1.81Ga (M2) metamorphic episode during the 2.0–1.8Ga Svecokarelian orogeny, with the older episode (M1) inside the Bergslagen lithotectonic unit at around 1.86Ga. This shows the major influence of the M2 event in the north-western part of this unit, leading to a complete resetting of the U–Th–Pb isotope system in monazite.

Segment-scale volcanic episodicity: Evidence from the North Kolbeinsey Ridge, Atlantic

The upper oceanic crust is produced by magmatism at mid-ocean ridges, a process thought to be characterized by cyclic bouts of intense magmatic activity, separated by periods when faulting accommodates most or even all of the plate motion. It is not known whether there is a distinct periodicity to such magmatic–tectonic cycles. Here we present high-resolution sidescan sonar data from the neovolcanic zone of the North Kolbeinsey Ridge, a shallow slow-spreading ridge where high glacial and steady post-glacial sedimentation rates allow relative flow ages to be determined with a resolution of around 2 kyr using backscatter amplitude as a proxy for sediment thickness and hence age. We identify 18 lava flow fields covering 40% of the area surveyed. A group of 7 flow fields showing the highest (and similar) backscatter intensity are scattered along 75 km of axial valley surveyed, suggesting that at least this length of the segment was magmatically active within a 1.2 kyr time window. Based on conservative age estimates for all datable flows and estimated eruption volumes, the post-glacial volcanic activity imaged is insufficient to maintain crustal thickness, implying that episode(s) of enhanced activity must have preceded the volcanism we image.

Two main Sedimentary cycles and two different rift system during the Pangea break-up in the Alps

Two main sedimentary cycles are recognized in the Alps during the Pangea Break-up. 1) The first one began in the Early Permian with an intense magmatic activity (oldest radiometric age around 280 Ma) and ended in the Carnian not for an orogenesis, but solely because extension and subsidence stopped. This sedimentary cycle reflects the evolution of the northern branch of the Tethys. 2) The second cycle was connected to the oceanic rifting that split Adria from Europe, generating the Alpine or Ligurian – Piedmont Ocean. This rifting began in the Norian together with the opening of the Central Atlantic Ocean that, around the Triassic/Jurassic boundary, was affected by an intense magmatic activity (CAMP 200 Ma).

Early Mesozoic southward subduction history of the Mongol–Okhotsk oceanic plate: Evidence from geochronology and geochemistry of Early Mesozoic intrusive rocks in the Erguna Massif, NE China

In this paper we present new zircon U–Pb ages, Hf isotope data, and whole-rock major and trace element data for Early Mesozoic intrusive rocks in the Erguna Massif of NE China, and we use these data to constrain the history of southward subduction of the Mongol–Okhotsk oceanic plate, and its influence on NE China as a whole. The zircon U–Pb dating indicates that Early Mesozoic magmatic activity in the Erguna Massif can be subdivided into four stages at ~246Ma, ~225Ma, ~205Ma, and ~185Ma. The ~246Ma intrusive rocks comprise a suite of high-K calc-alkaline diorites, quartz diorites, granodiorites, monzogranites, and syenogranites, with I-type affinities. The ~225Ma intrusive rocks consist of gabbro–diorites and granitoids, and they constitute a bimodal igneous association. The ~205Ma intrusive rocks are dominated by calc-alkaline I-type granitoids that are accompanied by subordinate intermediate–mafic rocks. The ~185Ma intrusive rocks are dominated by I-type granitoids, accompanied by minor amounts of A-types. These Early Mesozoic granitoids mainly originated by partial melting of a depleted and heterogeneous lower crust, whereas the coeval mafic rocks were probably derived from partial melting of a depleted mantle modified by subduction-related fluids. The rock associations and their geochemical features indicate that the ~246Ma, ~205Ma, and ~185Ma intrusive rocks formed in an active continental margin setting related to the southward subduction of the Mongol–Okhotsk oceanic plate. The ~225Ma bimodal igneous rock association formed within an extensional environment in a pause during the subduction process of the Mongol–Okhotsk oceanic plate. Every magmatic stage has its own corresponding set of porphyry deposits in the southeast of the Mongol–Okhotsk suture belt. Taking all this into account, we conclude the following: (1) during the Early Mesozoic, the Mongol–Okhotsk oceanic plate was subducted towards the south beneath the Erguna Massif, but with a pause in subduction at ~225Ma; and (2) the southward subduction of the Mongol–Okhotsk oceanic plate not only caused the intense magmatic activity, but was also favorable to the formation of porphyry deposits.

The REE-composition and petrography of apatite in 2 Ga Zaonega Formation, Russia: The environmental setting for phosphogenesis

The first significant P-rich deposits appear in the global rock record during the Paleoproterozoic around 2Ga, however the specific triggers that led to apatite precipitation are still under debate. The ca. 2Ga Zaonega Formation, Karelia, Russia contains P-rich intervals in its upper part with abundantly occurring apatite. These apatites have been studied for their Rare Earth Element (REE) composition using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) with an emphasis on the environmental condition during phosphogenesis. Petrographic observations by scanning electron microscopy (SEM) integrated with LA-ICP-MS results allow recognition of variously recrystallized apatite, and distinction of best-preserved diagenetic apatite which presumably records syn-depositional REE characteristics. Diagenetic apatite exhibits moderately negative Ce anomalies that indicate an at least partially oxygenated water column. A variable but typically positive Eu anomaly is consistent with geologic evidence suggesting intensive magmatic activity and hydrothermal influence during apatite precipitation. We conclude that phosphatic sediments in the Paleoproterozoic Zaonega Formation record phosphogenesis in a vent/seep influenced setting that experienced fluctuating redox conditions at the sediment–water interface.

Analysis of relationship between belts of concentrated remote sensing linear structures and gold deposits as well as prospecting prognosis in Xiaoqinling region

Xiaoginling region has densely- distributed magama hydrothermal gold deposits. The structural framework in this region is the Neoarchean gneiss dome,where intense magmatic activities occurred in Yanshanian period. The gold deposits are closely related to the distribution of quartz veins and altered mylonite. In the ETM+remote sensing image,the deposits often find expression in linear,parallel linear intensive belts and flexible- brittle shear zones. Consequently,the distribution of remote sensing linear structures and the intensive belts of linear structures are very significant for the gold ore prediction in this region. On such a basis and with the ETM+remote sensing image as the basic map,the authors made interpretation of the linear structure intensive belts and circular structure of Yanshanian granite bodies in Xiaoginling region. The gold deposit distribution and metallogenic regularity were analyzed based on remote sensing interpretation,the maps showing the favorableness of the metallogenic remote sensing characteristic conditions for gold deposits in this region were compiled,and the remote sensing prospecting prediction of gold resources in this region was made. These results will provide some reference for the prospecting of gold deposits in Xiaoqinling region and the assessment of mineral resource potential in Henan Province.

Geochronology and petrogenesis of granitoid rocks from the Goryczkowa Unit, Tatra Mountains (Central Western Carpathians)

Abstract The geochemical characteristics as well as the LA-MC-ICP-MS U-Pb zircon age relationship between two granitoid suites found in the Goryczkowa crystalline core in the Western Tatra Mountains were studied. The petrological investigations indicate that both granitoid suites were emplaced at medium crustal level, in a VAG (volcanic arc granites) tectonic setting. However, these suites differ in source material melted and represent two different magmatic stages: suite 1 represents a high temperature, oxidized, pre-plate collision intrusion, emplaced at ca. 371 Ma while suite 2 is late orogenic/anatectic magma, which intruded at ca. 350 Ma. These data are consistent with a period of intensive magmatic activity in the Tatra Mountain crystalline basement. The emplacement of granitoids postdates the LP-HT regional metamorphism/ partial melting at ca. 387 Ma and at 433-410 Ma, imprinted in the inherited zircon cores.

Geology, geochemistry and geochronology of the Jiaojiguanliangzi Fe-polymetallic deposit, Tengchong County, Western Yunnan (China): Regional tectonic implications

The Jiaojiguanliangzi Fe-polymetallic deposit, located near the Sino-Burmese border of the Tengchong County, western Yunnan in China, is a medium to large scale skarn Fe-polymetallic deposit that was recently discovered in this area. Zircons from monzonite granite-porphyry in the mining area yield an U–Pb age of 120±0.6Ma, and show εHf(t) values ranging from −1.9 to −4.9, suggesting that the magma was derived from dominantly pelitic sedimentary protoliths. The porphyry is part of muscovite-bearing peraluminous S-type granitoid formed at the late stage of Early Cretaceous. The molybdenite Re–Os age of 122±0.7Ma from this deposit is consistent with the age of the monzonite granite-porphyry. The monzonite granite-porphyry that hosts the skarn deposit belongs to syn- to post-collisional granitoid, representing the culmination of the collision of Tengchong block with Baoshan block, and the initiation of post-collisional extension event. The Mesozoic granite and Fe-rich polymetallic deposits in the Tengchong area are similar to their counterparts in Bangong–Nujiang magmatic/metallogenic belt in terms of formation age and geological characteristics. This indicates that these two areas underwent a similar intense magmatic activities and mineralization events during the Cretaceous. The Tengchong area has considerable prospecting potential. We believe that the Tengchong area is an important part of the southeast extension of the Bangong–Nujiang metallic belt.

Magmatism in the Asunción-Sapucai-Villarrica Graben (Eastern Paraguay) Revisited: Petrological, Geophysical, Geochemical, and Geodynamic Inferences

The Asunción-Sapucai-Villarrica graben (ASV) in Eastern Paraguay at the westernmost part of the Paraná Basin was the site of intense magmatic activity in Mesozoic and Tertiary times. Geological, petrological, mineralogical, and geochemical results indicate that the following magmatic events are dominant in the area: (1) tholeiitic basalt and basaltic andesites, flows and sills of low- and high-titanium types; (2) K-alkaline magmatism, where two suites are distinguished, that is, basanite to phonolite and alkali basalt to trachyte and their intrusive analogues; (3) ankaratrite to phonolite with strong Na-alkaline affinity, where mantle xenoliths in ultramafic rocks are high- and low-potassium suites, respectively. The structural and geophysical data show extensional characteristics for ASV. On the whole, the geochemical features imply different mantle sources, consistently with Sr-Nd isotopes that are Rb-Nd enriched and depleted for the potassic and sodic rocks, respectively. Nd model ages suggest that some notional distinct “metasomatic events” may have occurred during Paleoproterozoic to Neoproterozoic times as precursor to the alkaline and tholeiitic magmas. It seems, therefore, that the genesis of the ASV magmatism is dominated by a lithospheric mantle, characterized by small-scale heterogeneity.

Jurassic–Cretaceous tectonic evolution of Southeast China: geochronological and geochemical constraints of Yanshanian granitoids

We report results of laser ablation inductively coupled plasma-mass spectrometry-based dating, as well as the analysis of bulk-rock major and trace elements, and Sr–Nd isotopes to address the genesis and tectonic settings of the Yanshanian granitoids in neighbouring sections of Zhejiang, Jiangxi, and Anhui provinces (the WZG region) within the Yangtze block. Geochronological results indicate that intense magmatic activity took place during Jurassic to Cretaceous time in the WZG region. Three episodes can be clearly distinguished by their bulk-rock geochemistry. (1) Early–Middle Jurassic granitoids (180–170 Ma) have high Sr and low Yb content, high ϵNd(t) and low initial 87Sr/86Sr ratios, and weakly negative Eu anomalies. These granitoids are strongly enriched with LREE, Rb, K, and Th but are depleted of HREE, Nb, and Ta. (2) Late Jurassic to Early Cretaceous granitoids (165–140 Ma) have relatively low Sr and low Yb contents, as well as low ϵNd(t) and high initial 87Sr/86Sr ratios, with characteristics similar to those of the Early–Middle Jurassic granitoids in terms of the rare earth element and trace element patterns. (3) Early Cretaceous granitoids (140–120 Ma) have extremely low Sr and high Yb concentrations, as well as high SiO2 but low MgO, CaO, and Al2O3 content, with strong negative anomalies in Eu, Ba, Sr, P, and Ti. These characteristics indicate that the WZG Jurassic granitoids were related to northwestward subduction of the Izanagi plate, whereas the Early Cretaceous granitoids formed in a within-plate extensional setting. The time of transition between the two tectonic environments can be constrained to ∼140 Ma. This tectonic transition may be attributed to progressive slab roll-back of the Izanagi plate. The presence of two A-type granite belts in the WZG region probably reflects lithospheric thinning. The NE trend of the A-type granite belts indicates that this extension in Southeast China was controlled by underflow of the Izanagi plate.