High-potassium Calc-alkaline Series Research Articles

Ordovician−Early Devonian granitic magmatism as the consequence of intracontinental orogenic activity along the Qinhang belt in South China

The early Paleozoic tectono-magmatic activity within the South China block, which is well illustrated by Ordovician−Devonian granites in the western Qinhang belt, was the response to closure of the Proto-Tethys Ocean and convergence of continental blocks. The spatiotemporal distribution and source characteristics of the granites provide us the opportunity to understand the processes and driving mechanisms of intracontinental orogeny. As an example, the Miaoershan-Yuechengling granite batholith in northern Guangxi, located along the western margin of the Qinhang orogenic belt, is mainly composed of quartz monzonite and monzogranite. All the granitic rocks from Miaoershan-Yuechengling batholith are composed of K-feldspar, quartz, plagioclase, biotite, and hornblende. Geochronologic dating indicates that the Miaoershan-Yuechengling batholith was emplaced during the late Silurian and Early Devonian, respectively. The rocks have high SiO2, with an average value of 73.29 wt%, and total alkalis (Na2O + K2O = 7.21−10.03 wt%), but low Al2O3 (12.96−15.51 wt%), showing characteristics of the high-potassium calc-alkaline series of S-type peraluminous granites (Al2O3/[CaO + Na2O + K2O] = 1.03−1.22). Trace elements in the Miaoershan-Yuechengling granitic rocks are characterized by enrichment of large ion lithophile elements and depletion of high field strength elements. Their rare earth element (REE) trends are characterized by relatively flat distribution patterns with weak light REE enrichment, weak heavy REE fractionation, and negative Eu anomalies. Zircons from the rocks have negative εHf(t) values ranging from −13.24 to −5.1, with crustal model ages (THf2) of 2.2−1.7 Ga. These features indicate that they are S-type granites with parental magmas originating from partial melting of sandy argillaceous sources of Paleoproterozoic lower continental crust. The thermal budget for Ordovician to Early Devonian magmatism is attributed either to crustal thickening in relation to intracontinental orogenic compression or to crustal thinning due to postorogenic tectonic extension during assembly and breakup of Greater Gondwana. This study reveals that the change in mantle convection systems during plate interactions acted as a major driving force for the early orogenic processes, late collapse of the orogenic belt, and massive syncollisional to postorogenic magmatism.

Permian Granitic Plutons from the Northern Margin of the North China Craton: Implications for the Tectonic Evolution of the Central Asian Orogenic Belt

As the world’s largest accretionary orogen, the Central Asian Orogenic Belt (CAOB) underwent continuous juvenile crustal growth in the Phanerozoic. The northern margin of the North China Craton (NCC) and its adjacent area form the eastern segment of the CAOB, which is a key area for learning about the geological evolution of the Paleo-Asian Ocean (PAO). In the Permian, the west of the northern margin of the NCC was a post-collision extensional environment, while the east was in a subduction stage. As a connecting area, the Permian evolution of the PAO in the middle of the northern margin of the NCC has not been systematically studied. In order to fill the gap and understand the continuous temporal and spatial evolutionary process of the PAO, this paper focuses on the Permian granitic rocks in the Chifeng area. Zircon U-Pb dating and the geochemical analysis of whole-rock major and trace elements were conducted to build a granite chronological framework, and to discuss the genesis and tectonic background of the granitic rocks, along with tectono-magmatic evolutionary history in the Chifeng area. The respective LA-ICP-MS zircon U-Pb dating results from eight samples are 269 ± 1, 268 ± 3, 260 ± 4, 260 ± 1, 260 ± 1, 255 ± 2, 254 ± 2 and 256 ± 1 Ma, respectively. These results, combined with previous data, revealed that the Permian granitic rocks had undergone three events of magmatism: (1) monzogranitic-syenitic phase (294–284 Ma; Cisuralian); (2) monzogranitic phase (269–260 Ma; Guadalupian) and (3) late monzogranitic-syenitic phase (256–254 Ma; Lopingian). From the Early Permian (294–284 Ma) to the Middle Permian (269–260 Ma), granites with fine-medium-grained locally porphyritic texture and massive structure showed a high-potassium calc-alkaline series formed in a compressional setting, indicating a continuous collision between the Xing’an-Mongolian Orogenic Belt (XMOB) and the NCC. During the Late Permian-Early Triassic (256–248 Ma), granites with massive structure and medium-grained texture in the Chifeng area were magmatism dominated by A- and I-type granites of high-potassium calc-alkaline series, combined with the coeval basic rocks, which constituted a typical “bimodal” rock assemblage. This suggests that the Chifeng area was located in an extensional setting where the subducting slab broke off during the collision between the XMOB and NCC. These granitic plutons from the Permian are believed to have been generated by the subduction-collision of the Paleo-Asian oceanic crust beneath the NCC, according to emplacement time and occurrence location. Our findings provide strong evidence for Permian continuous temporal and spatial tectonic evolution and the characterization of the eventual closure of the PAO in Chifeng area at the northern margin of the NCC.

Geochemical and Mineralogical Characteristics of Ion-Adsorption Type REE Mineralization in the Mosuoying Granite, Panxi Area, Southwest China

The ion-adsorption rare earth deposit developed on the Mosuoying granite in the Panxi area of southwestern China represents a significant advancement in the exploration of ion-adsorption rare earth deposits in Sichuan. Being the first and currently the sole ion-adsorption rare earth deposit in Sichuan, studying its rare earth mineralization characteristics holds great importance. This paper aims to investigate the geochemical properties of the Mosuoying granite and its overlying weathered crust using rock geochemical methods based on field geological investigations. The findings reveal that the deposit belongs to the light rare earth type, with the ore-forming parent rock attributed to the high-potassium calc-alkaline series. It exhibits a high rock REE content ranging from 419 to 578 ppm, indicating favorable mineralization potential. Hydrothermal alteration reduces the REE content of the parent rock, leading to a notable increase in the LREE/HREE ratio, thus impacting the partitioning of rare earth elements and subsequent ore formation. The distribution characteristics of rare earth elements in each layer of the weathered crust are controlled by the parent rock and exhibit a light rare earth distribution pattern. The completely weathered layer is the main enrichment zone for rare earth elements, and the migration and enrichment patterns of rare earth elements in the weathered crust are evident. From the semi-weathered layer to the completely weathered layer, all REEs were gained, with a higher degree of migration for LREE. From the completely weathered layer to the clay layer, all REEs were lost, and the vertical distribution of rare earth content shows a “low-high-low” pattern.

Zircon U-Pb chronology and geochemistry of porphyritic granites: A case study of the Dalancun granites in Zhaoyuan, Shandong Province

The granite in Dalancun, Zhaoyuan, Shandong Province is mainly porphyry granite. In this paper, detailed field geology, petrology, isotopic chronology and whole-rock principal and microgeochemistry have been studied. LA-ICP-MS zircon U-Pb chronology shows that it was formed in the Early Cretaceous (129.7 ± 0.8 Ma), later than Linglong granite (160-150 Ma) and earlier than Laoshan granite (120-114 Ma). It is consistent with the main ore-forming age of Jiaodong large gold deposit and the diagenetic age of Guojialing granite (130-126 Ma). K2O+Na2O=7.41%~9.37%, K2O/Na2O=0.78~1.24; A/CNK=0.89~1.06, MgO=0.63%~1.01%, with high K, Al characteristics, belongs to the quasi-aluminum-peralumin high potassium calc-alkaline series. The strong differentiation of rare earth elements (La/Yb) N=68.24~93.96, weak positive Eu anomaly (δEu=1.26~1.769), enrichment of large ion lithophile elements Ba, Sr, high field strength elements Nb, Ta, Ti deficit, indicating the geochemical characteristics of continental lithosphere. In addition, high Sr (1817×10-6~2017×10-6), low Y (7.55×10-6~9.36×10-6), Sr/Y ratio between 199.89~262.29, Nb/Ta ratio between 14.67~16.73, consistent with continental crust ratio, It shows the characteristics of type I granite and Adakite. Combined with other geochemical indexes and regional geological studies, this paper suggests that the Dellancun porphyritic granite belongs to crust-mantle granite, which may have been formed in the arc environment of continental margin during the transition from compressive to extensional tectonic system in Jiaodong area, and is closely related to the subduction of the paleo-Pacific plate. This study not only helps to understand the Mesozoic tectonic evolution in eastern China, but also provides a basis for revealing the formation mechanism of Jiaodong gold deposit.

Geochemical features of the devonian plutonic rocks of the Reftinsky massif (Middle Urals)

This article examines the Devonian plutonic rocks of two massifs – Khomutinsky and Yuzhno-Khomutinsky, which are located in the western part of the Reftinsky massif. The rocks of the Khomutinsky and Yuzhno-Khomutinsky massifs are divided into gabbroid and granitoid associations. Their chemical composition, the content of pertrogenic, rare and trace elements were studied. Based on the data obtained, the rocks were assigned to the calc-alkaline series, according to the ratio of sodium and potassium, they are rocks with a sodium type of alkalinity. The peculiarity of the studied formations lies in the differences in the nature of alkalinity, thus the rocks of the gabbroid association in terms of the K2 O content are transitional from low to moderate potassium varieties, and the rocks of the granitoid association are characterized by a sufficiently high potassium content and correspond to the high potassium calc-alkaline series. Comparative analysis with basalts and granites of island arcs allows us to conclude that the Khomutinsky and YuzhnoKhomutinsky massifs were formed in an island arc geodynamic setting. Relevance. The geochemical features of the rocks of the Devonian intrusions in the Eastern zone of the Middle Urals have been studied very poorly to date, which makes it difficult to restore the geodynamic conditions of their formation and compare the processes of magmatism in the East of the Middle Urals with other regions of the mobile belt. The data presented in the work will make it possible to fill the existing gap to some extent and thereby help to clarify the patterns of magmatism evolution and the history of the formation of the Urals. The purpose of the work. Study of the contents of petrogenic, rare and trace elements of the Khomutinsky and Yuzhno-Khomutinsky massifs. Comparison of the geochemical features of the rocks of these intrusions with similar formations formed in island-arc geodynamic conditions. Research methodology. The chemical composition of rocks was studied by the X-ray fluorescence method, which was performed on a multichannel spectrometer SRM-35 with the determination of losses on ignition by the gravimetric method and the determination of the content of ferrous iron by the titrimetric method. Analysis of the content of rare and trace elements in rocks was carried out on inductively coupled plasma mass spectrometers ELAN 9000 and NexION 300S. Analytical data are presented in the form of discrimination diagrams. Results. The rocks of the Khomutinsky and Yuzhno-Khomutinsky massifs are divided into gabbroid and granitoid associations. Based on the obtained geochemical data, the rocks were assigned to the calc-alkaline series. According to the ratio of sodium and potassium, they are rocks with a sodium type of alkalinity. It is shown that the rocks of the gabbroid and granitoid associations differ in the character of alkalinity. The former in terms of K2O content are transitional from low to moderate potassium varieties, the latter are characterized by a fairly high content of potassium and correspond to the high potassium calc-alkaline series. Conclusion. Comparison of the studied rocks in terms of geochemical features with basalts and granites of island arcs allows us to conclude that the Khomutinsky and Yuzhno-Khomutinsky massifs were formed in an island-arc geodynamic setting.

Chemical Composition of the Mesozoic Alkaline Rocks of the Medvedev Massif (South Yakutia, Aldan-Stanovoy Shield, Leglier Ore Cluster)

The study shows chemical composition of the Mesozoic igneous rocks of the Medvedev massif. The massif is a part of the Central Aldan ore region. It is spatially located in the central part of the Nimnyr Block and is a part of the Leglier ore cluster. The massif is a multiphase structure of the most productive stage of the territory development – the Mesozoic tectonic-magmatic activation of the Aldan-Stanovoy shield. According to the materials of previous researchers, the rocks of the massif are represented by the augite hornblende and hornblende syenite porphyry. As a result of field work, we found that the massif has a zonal structure and is represented by three phases of intrusion. The rocks of the selected phases differ in their structural and compositional characteristics. The main objective of the work was to establish compositional characteristics by studying the chemical compositions of potential gold mineralization rocks of the Medvedev massif. In the course of studies and interpretation of chemical analysis of the massif Mesozoic magmatic rocks, we have identified the following characteristics. According to various classification data the following groups of rocks in Medvedev massif are identified – quartz syenites (Phase I), quartz monzodiorites of shoshonite series (Phase II) and monzonites of high-potassium calc-alkaline series (Phase III). The total alkali content (Na2O+K2O)>5% in them corresponds to alkaline rocks. All rocks are characterized by high Al2O3%>14 and low TiO2<1%. The potassium type of alkalinity Na2O/K2O<1 is typical for quartz syenites of the massif, while for quartz monzodiorites this indicator is intermediate, and in monzonites of the massif this parameter Na2O/K2O>1 corresponds to rocks of the alkaline potassium-sodium series. The massif rocks characteristic feature is the decrease of rocks alumina (al’) values from quartz syenites to quartz monzodiorites followed by the increase to monzonites, while the value of the rocks AG coefficient is significantly reduced in the series. Based on these facts, it was suggested that there are two sources of the mantle and mantle-crustal nature. Also, based on the study of the material composition of the Medvedev massif magmatic rocks and the similarity of the geological development with the Mesozoic magmatism of the Samolazovsky and Ryabinovy deposits, it was concluded that gold manifestations can be associated with such multiphase massifs within the Leglier ore cluster.

The Miocene Tatatila–Las Minas IOCG skarn deposits (Veracruz) as a result of adakitic magmatism in the Trans-Mexican Volcanic Belt

The Cu- and Au-rich Tatatila–Las Minas IOCG skarn deposits in Veracruz (central-east Mexico) are circumscribed to the earliest stages of the Trans-Mexican Volcanic Belt (TMVB) and stand for a metallogenic province directly linked to its tectonomagmatic dynamics. This is the first well-documented case for such metallogenic province. These deposits were formed as skarns between rocks of the Mesozoic carbonate series and Miocene intermediate to acid hypabyssal rocks. New U-Pb zircon and 40Ar/39Ar ages provide evidence for four epochs of magmatic activity in the area: (1) early Permian (Artinskian), in association with the Paleozoic basement, (2) late Oligocene to early Miocene suite of pre-TMVB intrusive rocks, (3) middle to late Miocene suite of early TMVB-related intrusive rocks, and (4) Pliocene intrusive and extrusive rocks of the TMVB, possibly associated with the Los Humeros post-caldera stage. The obtained ages range between 24.60 ± 1.10 and 19.04 ± 0.69 Ma for stage 2, and between 16.34 ± 0.20 and 13.92 ± 0.22 Ma for stage 3. Stage 2 corresponds to a magmatic stage unheard of in the area, until this study. Only stage 3 rocks are associated with the IOCG skarn mineralization, with retrograde stages dated at 12.44 ± 0.09 (chromian muscovite, phyllic association) and 12.18 ± 0.21 Ma (zircon, potassic association). Therefore, the ages of stage-3 intrusive rocks are interpreted to date the formation of the prograde skarn associations (mostly ~15.4 to &lt;14 Ma). The petrogenetic affinity of stage-2 and stage-3 rocks is about the same—the main difference has to do with higher Y and Yb contents in stage-3 rocks (although no affinity with within-plate granites was found), which is suggestive of an interaction of their parental magmas with alkaline magmas that most likely belong to the conterminous and contemporaneous Eastern Mexico Alkaline Province. Petrological indicators (elemental and isotopic) in Cenozoic rocks consistently point to intermediate to acid, metaluminous, I- and S-type rocks that were emplaced in a subduction-related continental arc, within the medium- to high-potassium calc-alkaline series, with high-silica adakitic signatures due associated to deep-sourced magmas that underwent crustal contamination to some degree. The various possible sources for the magmas with adakitic signature in this context can be narrowed down to two of them that are not mutually exclusive: adakitic derived from subducted slab melting and melting-assimilation-storage-homogenization (MASH)-derived adakites. Both sources are, in principle, capable of generating magmas that would eventually produce magmatic-hydrothermal mineralizing systems with an associated variety of ore deposit types, including IOCG. Also, both possible sources for adakites are compatible with the renewed steepening of the subducted slab after a period of flat subduction, for the earliest stage in the evolution of the TMVB.

Zircon U–Pb ages and geochemistry of newly discovered Neoproterozoic orthogneisses in the Mishan region, NE China: Constraints on the high-grade metamorphism and tectonic affinity of the Jiamusi–Khanka Block

The Jiamusi–Khanka Block, located in the easternmost segment of the Central Asian Orogenic Belt (CAOB), is one of the least understood blocks in northeastern China. The age of its basement, the timing of the high-grade metamorphism, and the tectonic affinity of this block have all been subjects of controversy. Here we describe newly discovered Neoproterozoic orthogneisses from the Mishan region in the central Jiamusi–Khanka Block. SIMS and LA–ICP–MS U–Pb dating of the magmatic cores of zircons from three of these high-grade orthogneisses yielded weighted mean ages that range from 898±4 to 891±13Ma, indicating that early Neoproterozoic magmatism did occur in the Jiamusi–Khanka Block. Twenty-two analyses of metamorphic zircons (rims as well as some grains) gave two groups of concordant ages, one at ca. 563Ma, interpreted as the timing of the high-grade metamorphism, and the other around 518–496Ma, interpreted as representing a subsequent retrograde metamorphism. The orthogneisses represent metamorphosed peraluminous syn-collisional syenogranites with SiO2=71.29–78.08wt%, A/CNK=1.06–1.99, and Na2O/K2O=0.03–1.49, and they belong chemically to the high-potassium calc-alkaline series. They have low Sr (32–134ppm) contents and Sr/Y ratios (1.6–16.9), and display strongly fractionated to nearly flat REE patterns with negative Eu anomalies (δEu=0.22–0.95) and depletions in Nb–Ta. These geochemical characteristics suggest that the syenogranitic rocks were derived under low pressures from a crustal source with a high proportion of sedimentary rocks, perhaps in a subduction-related setting that was undergoing transition from compression to extension. In the context of the reconstruction of Gondwana, the ca. 898–891Ma magmatic activity and the ca. 563Ma high-grade metamorphism in the Mishan region provide constraints on the possible linkages between the Jiamusi–Khanka Block and East Gondwana during the Neoproterozoic to early Paleozoic.

Rio Maria granodiorite and associated rocks of Ourilândia do Norte – Carajás province: Petrography, geochemistry and implications for sanukitoid petrogenesis

Ourilândia do Norte rocks are located near Rio Maria-Carajás domains boundary and are associated to Rio Maria Mesoarchean sanukitoid. Two groups were defined on the basis of geochemistry: (i) quartz-monzodiorites and granitoids (tonalite and granodiorite) which match to the sanukitoid (stricto sensu); and (ii) enclaves and (quartz) diorites that do not. Despite this, these rocks are spatially and temporally associated and they develop microstructures under three dynamic recrystallization regimes: (i) bulging recrystallization (300–700 °C); (ii) subgrain rotation recrystallization (<700 °C); (iii) grain boundary migration recrystallization (>600 °C). Furthermore, they belong to medium to high potassium calc-alkaline series, being magnesian and mainly metaluminous. The Mg#, Cr and Ni abundances point out an ultramafic mantle source. Variation of LILE, Nb/Y, (La/Yb)N and Sr/Y contents indicate a metasomatized mantle by two independent agents, namely TTG-like melt and aqueous fluids, at different depths. In this way, quartz-monzodiorites and granitoids were derived from fractionation of a mafic magma, whose source is a TTG-metasomatized mantle, at greater depths, while enclaves and (quartz) diorites were generated from a fluid-metasomatized mantle, at shallower depths. The close spatial and temporal association of rocks with sanukitoid (quartz-monzodiorites and granitoids) and BADR (enclaves and (quartz) diorites) signature suggest that Ourilândia do Norte granitoids were generated in close spatial and temporal association with active subduction.

Genesis and implications of the Late Jurassic Hailesitai granites in the northern Greater Khingan Range: evidence from zircon U–Pb dating and Hf isotope

AbstractThe tectonic setting and geodynamic model of the Greater Khingan Range (GKR) is highly controversial due to the lack of reliable geological, isotopic and geochronological evidence. In the current study, the Hailesitai pluton, located at the west of the suture between the northern and southern GKR in the east of the Central Asian Orogenic Belt, is selected to address this issue. These granites of the high potassium calc-alkaline series belong to the A1-type granites with typical geochemical characteristics including high contents of Al2O3, extremely low contents of Ti, P, enriched LREE, LILE, depleted HFSE, and a medium Eu negative anomaly. Laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) zircon U−Pb dating indicates that the granites can be divided into two stages: c. 152 and c. 161 Ma. The intrusion of A1-type granites at ~161 Ma implies that intra-plate orogenesis of the northern GKR started at c. 161 Ma at latest. The Hailesitai pluton has relatively homogeneous Hf isotope compositions with a εHf (t) value (+6.0 − +9.0), and two-stage depleted mantle model ages of 579−738 Ma show that the original magma is a mixture of juvenile and crustal source rocks. Extensional collapse of the Mongol−Okhotsk belt between the Siberia block and the northern GKR resulted in the formation of late Jurassic A1-type granites in the northern GKR. The Hailesitai pluton formed in response to post-orogenic extensional collapse of the Mongol–Okhotsk belt, coupled with back-arc extension related to Palaeo-Pacific plate subduction.

Rare earth elements upon assessment of reasons of the geophagy in Sikhote-Alin region (Russian Federation), Africa and other world regions.

Rocks eaten by wild animals on the Bolshoy Shanduyskiy kudur in the Sikhote-Alin region (Russian Federation) are zeolite-clay mineral complexes-products of weathering of zeolitized vitric tuffs of rhyolite composition, deposited in aqueous medium within the volcanic caldera of about 55 million years ago. By composition of rock-forming oxides, the tuffs refer to high-potassium calc-alkaline series. In trace elements of most favorite kudurites of the Bolshoy Shanduyskiy kudur, there are significantly increased contents of most of rare earth elements (2-5 times in comparison with surrounding rocks). The results of our analysis of geological and geochemical data on kudurs and kudurites in another part of the Sikhote-Alin, as well as on other regions of the world (particularly, in Africa and Indonesia), taking into account new data on the prevalence of rare earth elements in living matter and their medical and biological properties, enable us to consider the version of causal connection of the geophagy with rare earth elements.

Petrogenesis of Dongguashan skarn-porphyry Cu-Au deposit related intrusion in the Tongling district, eastern China: Geochronological, mineralogical, geochemical and Hf isotopic evidence

The Dongguashan skarn-porphyry Cu-Au deposit, located in the Tongling district of the Middle-Lower Yangtze River Valley metallogenic belt (MLYB), consists of skarn ore bodies in the upper part and porphyry ore bodies in the lower part, both of which are hosted in quartz diorite and quartz monzodiorite. Zircon U-Pb age and geochemical studies show that the quartz diorite of the Dongguashan intrusion formed at 140.3±2.0Ma (MSWD=0.19) and belongs to the high potassium calc-alkaline series. It is enriched in large ion lithophile elements (LILE) and light rare earth elements (LREE), depleted in high field-strength elements (HFSE) and heavy rare earth elements (HREE), and has a slightly negative Eu anomaly. 176Hf/177Hf values of the rims of zircons show a variable range (0.282087–0.282391), corresponding with calculated εHf(t) values of −10.72 to −21.46. Plagioclases in the quartz diorite have unbalanced structure characterized by bright andesine and labradorite (An=37.0–65.5) cores with higher contents of Fe and Sr and are corroded by dark oligoclase (An=13.8–27.6) rim. Major elements, trace elements, Hf isotope, and the composition of plagioclases indicate that the parental magma of the Dongguashan intrusion was produced by the mixing of underplating mafic magma and felsic magma formed by remelting of Paleoproterozoic and Neoarchean crustal rocks, Neoproterozoic crust may also provide some material to the felsic magma. Mafic magma played a key role and made the parental magma rich in water, sulfur, metals (Cu, Au) and gave it a high oxygen fugacity. During its magmatic evolution, the parental magma underwent fractional crystallization of hornblende, apatite, sphene and other mafic minerals. Some quartz diorite and quartz monzodiorite samples that show adakitic signatures, may result from injection of mafic magma. Some inherited zircons of the quartz diorite in the Dongguashan intrusion gave ages of 2.40–2.50Ga, 1.95–2.05Ga and 0.74–0.81Ga, coming from ultramafic, mafic and andesitic igneous rocks, and this indicates that there may have been three periods (2.4, 2.0, and 0.8Ga) of magmatic activity in the Tongling district.

The Middle Riphean volcanogenic complex of Kokchetav massif (Northern Kazakhstan): Structural position and age substantiation

The volcanogenic Kuuspek Formation is a well-defined part of the succession of the Pre-Vendian complexes of the Kokchetav massif (Northern Kazakhstan). The formation is built up of mildly metamorphosed acid lavas, tuffs, and tuffaceous sandstones. At the reference site to the west of the Kokchetav Mountains, the rocks of the Kuuspek Formation compose hinges of small anticlinal folds with sericite-quartz schists of the Late Riphean Sharyk Formation forming the limbs. The Kuuspek Formation lavas are high-alumina rhyolites of high-potassium calc-alkaline series. The U-Pb zircon age of the rhyolites is 1136 ± 4 Ma, thus referring to the Middle Riphean. The Kuuspek rhyolites form the basal part of the Precambrian sedimentary cover of the Kokchetav massif. The cover also comprises schists, limestones, and dolomites of the Sharyk Formation, and quartzites and quartzitic schists of the Late Riphean Kokchetav Formation.

Evolution of calc-alkaline magmas of the Okhotsk-Chukotka volcanic belt

Petrological, geochemical, and isotope geochronological aspects of the evolution of calc-alkaline magmatism were investigated in the Western Okhotsk flank zone, the Okhotsk segment, and the Eastern Chukchi flank zone of the Okhotsk-Chukotka volcanic belt (OCVB). The OCVB is a tectonotype of continental margin volcanic belts comprising much greater volumes of felsic ignimbritic volcanics compared with mature island arcs (MIA, Kuril-Kamchatka and Aleutian) and the Andean continental margin. The volcanic rocks of continental margin volcanic belts (OCVB and Andean belt) are enriched in K, Ti, and P compared with the rocks of MIA and show a trend toward the field of high-potassium calc-alkaline series. Primitive andesite varieties (Mg# > 0.6) were not yet found in the OCVB, but there are relatively calcic varieties unknown in Andean-type structures and a significant fraction of moderately alkaline rocks, which are not typical of MIA. Variations in trace and major element characteristics in the basalts and andesites of the OCVB were interpreted as reflecting the competing processes of assimilation/mixing and fractional crystallization during the evolution of the parental basaltic magma. Significant lateral variations were established in the composition of the mantle sources of calc-alkaline magmas along the OCVB over more than 2500 km. The initial isotopic ratios of Sr, Nd, and Pb in the volcanics of the Okhotsk segment are relatively depleted and fall near the mixing line between PREMA and BSE. The magma source of the Western Okhotsk flank zone is most enriched and approaches EMI, whereas that of the central and eastern Chukchi zones contains an admixture of the EMII component. The geochronological characteristics of all the main stages of OCVB magmatism were comprehensively studied by U-Pb SHRIMP and ID-TIMS zircon dating (86 samples) and 40Ar/39Ar analysis (73 samples). In general, a discontinuous character was established for the OCVB magmatism from the middle Albian to the early Campanian (106–77 Ma). The volcanism is laterally asynchronous. There are several peaks of volcanism with modes at approximately 105, 100, 96, 92.5, 87, 82, and 77 Ma. The Coniacian-Santonian peaks correspond to the most extensive stages of the middle and late cycles of felsic volcanism. A decreases and a hiatus in magmatic activity were reconstructed for the end of the Cenomanian and the beginning of the Turonian. The volcanism was terminated by plateau basalts with ages of 76–78 Ma, which mark a change in the geodynamic setting from frontal subduction to the regime of a transform margin with local extension in zones normal to the slip direction. A catastrophic character of eruptions with rather narrow ranges of volcanism (<2 Myr) were established taking into account new reliable age estimates for some individual large calderas. The accumulation rate of volcanic materials in such structures was up to 0.15–0.36 km3/yr and even higher.

Indosinian Tectonic Setting of the Southern Yidun Arc: Constraints from SHRIMP Zircon Chronology and Geochemistry of Dioritic Porphyries and Granites

Abstract A mass of granitoid and dioritic intrusions are distributed in the southern Yidun Arc, among which the representative Indosinian intrusions include the Dongco and Maxionggou granitoid intrusions in Daocheng County and hypabyssal intrusions intruding into arc volcanic rocks near the Xiangcheng town. The Dongco and Maxionggou granitoid intrusions consist mainly of porphyraceous monzogranites, megacryst monzogranites and aplite granites. The Xiangcheng hypabyssal intrusions are composed dominantly of dioritic porphyries. SHRIMP zircon ages of 224±3 Ma and 222±3 Ma have been obtained for the Dongco granitoid intrusion and the Xiangcheng dioritic porphyries, respectively. The Xiongcheng dioritic porphyries show a calc-alkaline geochemical feature, and are characterized by higher Sr/Y ratios, depletive Nb, Ta, P and Ti, enriched LILEs, and lower ɛNd (t) (= −3.27), suggesting that they might be derived from mantle source magmas that were obviously contaminated by continent crustal materials. However, the Dongco and Maxionggou granitoids belong to high-potassium calcalkaline series with a per-metaluminous feature, and are characterized by higher CaO/(σFeO+MgO) and Al2O3/(σFeO+ MgO) ratios, lower (La/Yb)n and Sr/Y ratios, depletive Nb, Ta, Sr, P and Ti, enriched LILEs, and very low ɛNd (t) (= −8.10), indicating that the granitoids might be derived from partial melting of continental crust materials mainly of graywacke. Petrogenesis of Dongco and Maxionggou granitoids implies that there was an oceanic crust between the Zongza continental block (ZCB) and western margin of the Yangtze Craton (WMYZC). And the oceanic crust slab subducted westward during the Indosinian Epoch, producing an Andes-type continent marginal arc and a back-arc basin at the WMSCC. Then the oceanic basin closed and a sinistrally lateral collision occurred at ca. 224 Ma-222 Ma between the ZCB and the WMYZC, causing partial melting of sediments in the back-arc basin to generate granitoid magmas of the Dongco and Maxionggou intrusions

SHRIMP Zircon U‐Pb Chronology and Geochemistry of the Henglingguan and Beiyu Granitoids in the Zhongtiao Mountains, Shanxi Province

Abstract: Henglingguan and Beiyu metamorphic granitoids, distributed in the northwest of the Zhongtiaoshan Precambrian complex, comprise trondhjemites and calc‐alkaline monzogranites, displaying intrusive contacts with the Archean Zhaizi TTG gneisses. And the Beiyu metamorphic granitoids consist mainly of trondhjemites, distributed at the core of the Hujiayu anticline fold. New SHRIMP zircon U‐Pb dating data show that the weighted mean 207Pb/206Pb ages are 2435.9 Ma and 2477 Ma for the Henglingguan metamorphic calc‐alkaline monzogranites and Beiyu metamorphic trondhjemites, respectively, and reveal ∼2600 Ma inherited core in magmatic zircons. Whole‐rock geochemical data indicate that all the Henglingguan and Beiyu metamorphic trondhjemites and calcalkaline monzogranites belong to the metaluminous medium‐ and high‐potassium calc‐alkaline series. These rocks are characterized by relatively high total alkali contents (Na2O+K2O, up to 9.08%), depleted Nb, Ta, P and Ti, and right‐declined REE patterns with moderate to high LREEs/HREEs fractionation (the mean ratio of (La/Yb)n = 25). The Henglingguan and Beiyu metamorphic trondhjemites display negative Rb, Th and K anomalies in the multi‐element spider diagrams normalized by primitive mantle. Sm‐Nd isotopic data reveal that these granitoids have initial ∍Nd(t)=‐1.2 to +2.4 and Nd depleted mantle model ages of TMD= 2622 Ma‐2939 Ma. All these geochemical features indicate that these granitoids were formed in an continent‐marginal arc, and the trondhjemites mainly originated from partial melting of juvenile basaltic materials and, howbeit, the Henglingguan metamorphic calc‐alkaline monzogranites derived from recycling of materials in the ancient crust under a continent‐marginal arc. The granitic magma underwent contamination and fractional crystallization during their formation.

Geochemistry of the paleoproterozonic Nanying granitic gneisses in the Fuping complex: implications for the tectonic evolution of the Central Zone, North China Craton

The Nanying granitic gneisses represent a major ∼2.0 Ga magmatic event in the Fuping Complex of the Central Zone of the North China Craton. They occur in the Chengnanzhuang shear zone, which is chiefly developed along the contact between the Neoarchean Fuping tonalite-trondhjemite-granodiorite (TTG) gneisses and the Wanzi paragneisses. The Nanying granitic gneisses were derived from monzogranite and syenogranite, with minor amounts of quartz diorite and granodiorite, and belong to the metaluminous to peraluminous, high-potassium calc-alkaline series, correlations between major and trace elements, and similarities in chondrite-normalized rare-earth-element (REE) patterns, support field relationships (e.g. gradational contacts) indicating that the Nanying granitic gneisses originated from similar magmas. The granodioritic, monzogranitic and syenogranitic gneisses have similar ranges of initial 87Sr/ 86Sr values (0.7030–0.7093, 0.7021–0.7193 and 0.7049–0.7111, respectively), although these variations are partly attributable to local resetting of the isotopic system during late deformation/hydrothermal alteration. The whole-rock 208Pb/ 204Pb, 206Pb/ 204Pb and 207Pb/ 204Pb values of the Nanying granitic gneisses are 37.32–76.8, 15.24–23.82 and 14.92–17.92, respectively. These Sr–Pb isotope systematics, together with previously published Nd isotope compositions, suggest that the Nanying granitic gneisses were derived from partal melting of the ∼2.50 Ga Fuping TTG gneisses, with local assimilation involving the Wanzi paragneisses. The Nanying granitic gneisses are geochemically similar to the C CA and C CL groups of granitoids, except for a few samples, which plot in the H LO group. The Nanying granitic gneisses exhibit depletion in Rb, Sr, Ba, Ti and U, and enrichment in Th, Nb, Zr, Hf and REE, similar to those of syn-shear, high-potassium calc-alkaline granitoids and late-shear alkaline granitoids; they therefore represent the product of a syn-collisional to post- collisional magmatic event. This collisional event, which is significantly older than the ∼1.84–1.80 Ga event that has been proposed for the juxtaposition of the Eastern and Western Archean continental blocks in the final stabilization of the North China Craton, supports a tectonic model involving multiple collisional events for the amalgamation of the internal lithotectonic domains within the Central Zone and the assembly of the North China Craton as a whole.