Pub Date : 2025-04-03DOI: 10.1134/S0869591124700292
E. A. Krasnova, S. A. Silantyev, V. V. Shabykova, A. S. Gryaznova
Carbonate minerals in oceanic crust are formed through CO2 interaction with silicate minerals of ultramafic and mafic rocks. Carbonation leads to the generation of numerous carbonate veins, filling interstices in the rock matrix and producing partially and/or completely carbonated rocks that compose the protolith of slow-spreading mid-ocean ridges and are present in ophiolite complexes. Silantyev et al. (2023) proposed a conceptual model of the main stages in the formation of carbonated serpentinites in different segments of the Mid-Atlantic Ridge. In this study, we examined isotope variations (δ18O, δ13С, Rb, Sr, Sm, Nd) in the previously studied carbonated ultramafic rocks from oceanic core complexes of the slow-spreading mid-oceanic ridge. The carbon and oxygen isotope compositions obtained in our study are well consistent with results of our previous studies and make it possible to quantify the duration and spatial position of sea fluid interaction with serpentinites of different segments of the Mid-Atlatnic Ridge in the oceanic crust sequence. Peridotite groups previously distinguished based on the mineral and petrographic features are well consistent with relations of obtained parameters or with water/rock ratio calculated using Sr-Nd isotope systematics, and reflect the sequence of carbonation stages in the ultramafic protolith of oceanic crust and duration of its residence on the seafloor. Our results indicate that the oceanic core complexes containing the studied rocks were exhumed to the seafloor surface during different time periods.
{"title":"Carbonation of Serpentinites of the Mid-Atlantic Ridge: 2. Evolution of Chemical and Isotopic (δ18O, δ13С, Rb, Sr, Sm, Nd) Compositions during Exhumation of Abyssal Peridotites","authors":"E. A. Krasnova, S. A. Silantyev, V. V. Shabykova, A. S. Gryaznova","doi":"10.1134/S0869591124700292","DOIUrl":"10.1134/S0869591124700292","url":null,"abstract":"<div><p>Carbonate minerals in oceanic crust are formed through CO<sub>2</sub> interaction with silicate minerals of ultramafic and mafic rocks. Carbonation leads to the generation of numerous carbonate veins, filling interstices in the rock matrix and producing partially and/or completely carbonated rocks that compose the protolith of slow-spreading mid-ocean ridges and are present in ophiolite complexes. Silantyev et al. (2023) proposed a conceptual model of the main stages in the formation of carbonated serpentinites in different segments of the Mid-Atlantic Ridge. In this study, we examined isotope variations (δ<sup>18</sup>O, δ<sup>13</sup>С, Rb, Sr, Sm, Nd) in the previously studied carbonated ultramafic rocks from oceanic core complexes of the slow-spreading mid-oceanic ridge. The carbon and oxygen isotope compositions obtained in our study are well consistent with results of our previous studies and make it possible to quantify the duration and spatial position of sea fluid interaction with serpentinites of different segments of the Mid-Atlatnic Ridge in the oceanic crust sequence. Peridotite groups previously distinguished based on the mineral and petrographic features are well consistent with relations of obtained parameters or with water/rock ratio calculated using Sr-Nd isotope systematics, and reflect the sequence of carbonation stages in the ultramafic protolith of oceanic crust and duration of its residence on the seafloor. Our results indicate that the oceanic core complexes containing the studied rocks were exhumed to the seafloor surface during different time periods.</p></div>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"33 1","pages":"23 - 39"},"PeriodicalIF":1.0,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143769876","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-04-03DOI: 10.1134/S0869591124700309
T. Yu. Timina, S. Z. Smirnov, D. V. Kuzmin, A. A. Kotov, A. V. Rybin, V. A. Danilovsky, A. E. Izokh
Klumba basaltic andesite volcano is the only postcaldera volcano in the eruptive center of one of the most powerful explosive eruptions that occurred at the end of the Late Pleistocene in the Great Kuril Arc (GKA) and formed a thick sequence of dacitic pumice tuffs on the Vetrovoy Isthmus on Iturup Island. A detailed study of the mineralogy of the basaltic andesites of Klumba volcano and olivine-hosted fluid and melt inclusions showed that the feeding magma evolved within the arc crust at depths between 15.5 and 7 km and was related to Mg-rich (up to 9.8 wt % MgO), low-K and low-Al basaltic andesite melts that initially contained about 5–6 wt % H2O. Olivine and Cr–Al spinel were the first to crystallize in the magma and later were joined by plagioclase and pyroxenes. The phenocrysts crystallized at temperatures of about ~1000–1200°C. The melt was saturated with CO2 fluid with minor amounts of SO2. Pleistocene basaltic andesitic magmatism in the central part of Iturup Island was predominantly intrusive and resulted in the formation of a large transcrustal magmatic system (TCMS), which could include the dacitic chamber that fed the explosive eruption of the Vetrovoy Isthmus. The plumbing system of Klumba volcano is considered to be a part of this TCMS, which was intermittently recharged by variously differentiated basaltic andesite magmas. It is assumed that such systems may have developed on the scale of the whole island. The duration of the processes and the amount of intruded magma may have been sufficient to cause partial melting in the upper parts of the island-arc crust and to form magma reservoirs of powerful explosive caldera-forming eruptions.
{"title":"Late Pleistocene Mafic Magmatism and Its Relation to Large Caldera-Forming Eruptions on Iturup Island: An Example of Klumba Volcano, Kuril Islands","authors":"T. Yu. Timina, S. Z. Smirnov, D. V. Kuzmin, A. A. Kotov, A. V. Rybin, V. A. Danilovsky, A. E. Izokh","doi":"10.1134/S0869591124700309","DOIUrl":"10.1134/S0869591124700309","url":null,"abstract":"<p>Klumba basaltic andesite volcano is the only postcaldera volcano in the eruptive center of one of the most powerful explosive eruptions that occurred at the end of the Late Pleistocene in the Great Kuril Arc (GKA) and formed a thick sequence of dacitic pumice tuffs on the Vetrovoy Isthmus on Iturup Island. A detailed study of the mineralogy of the basaltic andesites of Klumba volcano and olivine-hosted fluid and melt inclusions showed that the feeding magma evolved within the arc crust at depths between 15.5 and 7 km and was related to Mg-rich (up to 9.8 wt % MgO), low-K and low-Al basaltic andesite melts that initially contained about 5–6 wt % H<sub>2</sub>O. Olivine and Cr–Al spinel were the first to crystallize in the magma and later were joined by plagioclase and pyroxenes. The phenocrysts crystallized at temperatures of about ~1000–1200°C. The melt was saturated with CO<sub>2</sub> fluid with minor amounts of SO<sub>2</sub>. Pleistocene basaltic andesitic magmatism in the central part of Iturup Island was predominantly intrusive and resulted in the formation of a large transcrustal magmatic system (TCMS), which could include the dacitic chamber that fed the explosive eruption of the Vetrovoy Isthmus. The plumbing system of Klumba volcano is considered to be a part of this TCMS, which was intermittently recharged by variously differentiated basaltic andesite magmas. It is assumed that such systems may have developed on the scale of the whole island. The duration of the processes and the amount of intruded magma may have been sufficient to cause partial melting in the upper parts of the island-arc crust and to form magma reservoirs of powerful explosive caldera-forming eruptions.</p>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"33 1","pages":"1 - 22"},"PeriodicalIF":1.0,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143769907","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-05DOI: 10.1134/S0869591124700218
K. A. Savko, A. V. Samsonov, E. Kh. Korish, A. N. Larionov, E. B. Salnikova, A. A. Ivanova, N. S. Bazikov, S. V. Tsybulyaev, M. V. Chervyakovskaya
Paleoproterozoic diorite–granodiorite magmatic rocks dated at 2.04–2.08 Ga are widespread at the eastern border of the Archean Kursk block of Sarmatia. The granitoids of the intrusive massifs are metaluminous calc-alkaline I-type rocks enriched in incompatible elements (LILE and LREE), with negative Ti, P, and Nb anomalies. The rocks show widely varying negative εNdT values, their zircons have broadly ranging εHfT values, and the melts were derived within a broad range of depths from heterogeneous Archean lower crustal mafic sources. The diorites were melted from the least radiogenic ancient crustal sources. The granodiorites were derived from Paleo- and Mesoarchean and more juvenile Neoarchean sources. The intense 2.06-Ga magmatism was triggered by the upwelling of the asthenospheric mantle during the break-up of subducted oceanic slab due to low-angle subduction. The break of the slab and the mafic underplating led to the crustal melting of the upper slab, which consisted of Archean and Paleoproterozoic crustal fragments of different age that had been welded as a result of earlier accretion. Diorite−granodiorite magmas were generated in chambers at different depth in the ancient Archean crust at the periphery of Kursk block, with the incorporation of Paleoproterozoic lithospheric fragments of the Eastern Sarmatian orogen into the melting sources.
{"title":"Granitoid Intrusions at the Periphery of the Kursk Block as Part of a Paleoproterozoic Silicic Large Igneous Province in Eastern Sarmatia","authors":"K. A. Savko, A. V. Samsonov, E. Kh. Korish, A. N. Larionov, E. B. Salnikova, A. A. Ivanova, N. S. Bazikov, S. V. Tsybulyaev, M. V. Chervyakovskaya","doi":"10.1134/S0869591124700218","DOIUrl":"10.1134/S0869591124700218","url":null,"abstract":"<p>Paleoproterozoic diorite–granodiorite magmatic rocks dated at 2.04–2.08 Ga are widespread at the eastern border of the Archean Kursk block of Sarmatia. The granitoids of the intrusive massifs are metaluminous calc-alkaline I-type rocks enriched in incompatible elements (LILE and LREE), with negative Ti, P, and Nb anomalies. The rocks show widely varying negative ε<sub>Nd</sub>T values, their zircons have broadly ranging ε<sub>Hf</sub>T values, and the melts were derived within a broad range of depths from heterogeneous Archean lower crustal mafic sources. The diorites were melted from the least radiogenic ancient crustal sources. The granodiorites were derived from Paleo- and Mesoarchean and more juvenile Neoarchean sources. The intense 2.06-Ga magmatism was triggered by the upwelling of the asthenospheric mantle during the break-up of subducted oceanic slab due to low-angle subduction. The break of the slab and the mafic underplating led to the crustal melting of the upper slab, which consisted of Archean and Paleoproterozoic crustal fragments of different age that had been welded as a result of earlier accretion. Diorite−granodiorite magmas were generated in chambers at different depth in the ancient Archean crust at the periphery of Kursk block, with the incorporation of Paleoproterozoic lithospheric fragments of the Eastern Sarmatian orogen into the melting sources.</p>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"32 6","pages":"719 - 771"},"PeriodicalIF":1.0,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142778119","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-05DOI: 10.1134/S0869591124700231
Yu. A. Martynov, V. A. Rashidov, S. I. Dril
New major-, trace-element and Sr-Nd-Pb isotope data are presented on the Holocene high-potassium basic lavas of Alaid volcano, which is located in the north of the Kuril island arc, in the junction zone with the Kamchatka volcanic segment. According to the petrochemical criteria, two groups of coeval rocks are distinguished: Ne-normative shoshonites and high-potassium subalkaline basalts, which have many similar geochemical characteristics. Chondrite-normalized REE distribution patterns show LREE enrichment, with flat HREE pattern, and the absence of Eu and Ce anomalies. MORB-normalized incompatible element patterns show LILE enrichment and a well-defined negative Ta–Nb–Ti anomaly typical of suprasubduction volcanics. The high K2O/Rb and Rb/Sr ratios indicate the presence of biotite and amphibole in the magmatic source, while the low Sr/Y ratios and flat MREE and HREE distribution patterns indicate the absence of residual garnet. Significant variations in the contents of major- and trace elements at similar MgO concentrations indicate a heterogeneous magma source, while linear mixing trends in isotope and discrimination diagrams, as well as experimental data, suggest the involvement in magmogenesis of not only peridotite mantle, but also amphibole–clinopyroxene mineral paragenesis. An analysis of literature data shows that the manifestations of potassium alkaline magmatism in “cold” island arcs are frequently, if not always, confined to local extension zones. Since such zones are associated with the adiabatic rise of a hot and ductile asthenosphere, it can be assumed that melting involved subduction mélange, which is formed along the boundary of the slab and supra-subduction mantle and consists of hydrated fragments of ultrabasites and metamorphosed oceanic crust transformed into amphibole-bearing pyroxenites. This mechanism makes it possible to logically explain the geochemical and isotopic features of the anomalous alkaline magmatism of the Kuril island arc and the relation of its northern segment with anomalous tectonics. The results obtained may be important in discussing the genesis of potassium alkaline magmas occurred in subduction geodynamic settings.
{"title":"Potassium Alkaline Volcanism of Alaid Volcano, Kuril Islands: the Role of Subduction Melange in Magma Genesis","authors":"Yu. A. Martynov, V. A. Rashidov, S. I. Dril","doi":"10.1134/S0869591124700231","DOIUrl":"10.1134/S0869591124700231","url":null,"abstract":"<div><p>New major-, trace-element and Sr-Nd-Pb isotope data are presented on the Holocene high-potassium basic lavas of Alaid volcano, which is located in the north of the Kuril island arc, in the junction zone with the Kamchatka volcanic segment. According to the petrochemical criteria, two groups of coeval rocks are distinguished: Ne-normative shoshonites and high-potassium subalkaline basalts, which have many similar geochemical characteristics. Chondrite-normalized REE distribution patterns show LREE enrichment, with flat HREE pattern, and the absence of Eu and Ce anomalies. MORB-normalized incompatible element patterns show LILE enrichment and a well-defined negative Ta–Nb–Ti anomaly typical of suprasubduction volcanics. The high K<sub>2</sub>O/Rb and Rb/Sr ratios indicate the presence of biotite and amphibole in the magmatic source, while the low Sr/Y ratios and flat MREE and HREE distribution patterns indicate the absence of residual garnet. Significant variations in the contents of major- and trace elements at similar MgO concentrations indicate a heterogeneous magma source, while linear mixing trends in isotope and discrimination diagrams, as well as experimental data, suggest the involvement in magmogenesis of not only peridotite mantle, but also amphibole–clinopyroxene mineral paragenesis. An analysis of literature data shows that the manifestations of potassium alkaline magmatism in “cold” island arcs are frequently, if not always, confined to local extension zones. Since such zones are associated with the adiabatic rise of a hot and ductile asthenosphere, it can be assumed that melting involved subduction mélange, which is formed along the boundary of the slab and supra-subduction mantle and consists of hydrated fragments of ultrabasites and metamorphosed oceanic crust transformed into amphibole-bearing pyroxenites. This mechanism makes it possible to logically explain the geochemical and isotopic features of the anomalous alkaline magmatism of the Kuril island arc and the relation of its northern segment with anomalous tectonics. The results obtained may be important in discussing the genesis of potassium alkaline magmas occurred in subduction geodynamic settings.</p></div>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"32 6","pages":"828 - 858"},"PeriodicalIF":1.0,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142778258","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Lower Urgen deposit is a newly discovered porphyry Mo deposit in the northern and central Great Xing’an Range. Mineralization predominantly occurs within granite porphyry, yielding a zircon U-Pb age of 142.3 ± 1.5 Ma, thereby endorsing an Early Cretaceous Mo mineralization event. Zircon εHf(T) values (5.5–7.7) and T(DM2-st) (707–844 Ma) suggest that the granite porphyry originated from the partial melting of the Neoproterozoic lower crust. These granite porphyries exhibit coherent geochemical signatures with regional Late Mesozoic Mo-causative granites. Classified as highly fractionated A-type granites, they are enriched in Rb, Th, U, and K, and depleted in Ba, Sr, P, Ti, and Eu. Notably, they possess higher Rb/Sr and Rb/Ba ratios, and lower (La/Yb)N, Eu/Eu*, LREE/HREE, K/Rb, and Zr/Hf ratios than coeval Cu-causative granites, implying the extent of fractional crystallization plays a pivotal role in determining the mineralization styles (Mo- versus Cu-dominant). Two possible tectonic models are proposed. In one model, Late Jurassic Mo- and Cu-causative granites were formed in an intra-plate extensional setting and compressional setting induced by the flat-slab subduction of the Mongol-Okhotsk Ocean (MOO) plate, respectively, while Early Cretaceous Mo-causative granites were formed in a post-collision extensional setting following the final closure of the MOO. The post-orogenic lithospheric extension model related to the closure of the MOO provides another plausible explanation for the origin of the ore-causative granites. Early Cretaceous highly fractionated A-type granites and Late Jurassic low fractionated adakitic granites represent potential targets for future exploration of Mo- and Cu-dominant porphyry deposits, respectively.
下急钼矿床是大兴安岭中北部新近发现的斑岩型钼矿床。成矿作用主要发生在花岗斑岩中，锆石U-Pb年龄为142.3±1.5 Ma，因此支持早白垩世Mo成矿事件。锆石εHf(T)值（5.5 ~ 7.7）和T（DM2-st）值（707 ~ 844 Ma）表明花岗岩斑岩起源于新元古代下地壳的部分熔融。这些花岗斑岩的地球化学特征与区域性晚中生代钼成因花岗岩一致。属高分选a型花岗岩，富Rb、Th、U、K，贫Ba、Sr、P、Ti、Eu。值得注意的是，它们具有较高的Rb/Sr和Rb/Ba比值，而较低的（La/Yb）N、Eu/Eu*、LREE/HREE、K/Rb和Zr/Hf比值，这表明分离结晶程度在决定成矿类型（Mo- vs Cu-dominant）中起关键作用。提出了两种可能的构造模式。其中，晚侏罗世Mo-花岗岩和cu -花岗岩分别形成于蒙古-鄂霍次克洋（MOO）板块的平板俯冲引起的板块内伸展和挤压环境，而早白垩世Mo-花岗岩形成于MOO板块最终闭合后的碰撞后伸展环境。与MOO闭合有关的造山后岩石圈伸展模式为成矿花岗岩的成因提供了另一种合理的解释。早白垩世高分馏a型花岗岩和晚侏罗世低分馏埃达质花岗岩分别是未来以钼为主和以铜为主斑岩矿床的潜在勘探目标。
{"title":"Zircon U-Pb-Hf Isotopes and Geochemistry of Mo-bearing Granite Porphyry in the Lower Urgen Mo Deposit: Implications for the Late Mesozoic Porphyry Mo and Cu Mineralization in the Northern and Central Great Xing’an Range, NE China","authors":"Wei Xie, Guangliang Zhang, Chao Jin, Qingdong Zeng, Shouqin Wen, Lingli Zhou, Tieqiao Tang, Pengcheng Ma, Hui Wang, Kailun Zhang","doi":"10.1134/S0869591124700243","DOIUrl":"10.1134/S0869591124700243","url":null,"abstract":"<p>The Lower Urgen deposit is a newly discovered porphyry Mo deposit in the northern and central Great Xing’an Range. Mineralization predominantly occurs within granite porphyry, yielding a zircon U-Pb age of 142.3 ± 1.5 Ma, thereby endorsing an Early Cretaceous Mo mineralization event. Zircon ε<sub>Hf</sub>(T) values (5.5–7.7) and T(DM2-st) (707–844 Ma) suggest that the granite porphyry originated from the partial melting of the Neoproterozoic lower crust. These granite porphyries exhibit coherent geochemical signatures with regional Late Mesozoic Mo-causative granites. Classified as highly fractionated A-type granites, they are enriched in Rb, Th, U, and K, and depleted in Ba, Sr, P, Ti, and Eu. Notably, they possess higher Rb/Sr and Rb/Ba ratios, and lower (La/Yb)<sub>N</sub>, Eu/Eu*, LREE/HREE, K/Rb, and Zr/Hf ratios than coeval Cu-causative granites, implying the extent of fractional crystallization plays a pivotal role in determining the mineralization styles (Mo- versus Cu-dominant). Two possible tectonic models are proposed. In one model, Late Jurassic Mo- and Cu-causative granites were formed in an intra-plate extensional setting and compressional setting induced by the flat-slab subduction of the Mongol-Okhotsk Ocean (MOO) plate, respectively, while Early Cretaceous Mo-causative granites were formed in a post-collision extensional setting following the final closure of the MOO. The post-orogenic lithospheric extension model related to the closure of the MOO provides another plausible explanation for the origin of the ore-causative granites. Early Cretaceous highly fractionated A-type granites and Late Jurassic low fractionated adakitic granites represent potential targets for future exploration of Mo- and Cu-dominant porphyry deposits, respectively.</p>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"32 6","pages":"859 - 890"},"PeriodicalIF":1.0,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142778259","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-05DOI: 10.1134/S0869591124700255
Bishaw Mihret, Ajebush Wuletaw, Tarekegn Tadesse
The deformation and metamorphic history of the Precambrian high-grade rocks in the Key Afer area, southwestern Ethiopia within the Mozambique belt is described. It comprises poly-deformed, metamorphosed, and migmatized rocks with intrusion of granitoids and overlain by Quaternary sediments. A combination of field litho-structural mapping, metamorphic mineral assemblages, and microstructural analysis there are three metamorphic events and four phases of ductile deformation, and one Cenozoic brittle fracture (D5) are recognized. The development of the relatively steep NNW-SSE trending S1 relict gneissic banding and the rise of pyroxene and anhydrous minerals indicate that the peak metamorphism (M1) is synchronous with D1. Subsequently, the hydration of M1 assemblages leads to the formation of amphibolite facies (M2). This is followed by the development of amphibolite facies (M2) caused by the hydration of M1 assemblages synchronous with the D2 deformation. It is defined by the major regional fabric (S2) of the area trending NW-SE, tight to isoclinal upright F2 folds, and local L2 lineation. These D2 upright folds are orthogonally superimposed by another upright F3 folds during D3 resulting in a type-I fold interference pattern. The replacement and breakdown of hornblende to epidote, biotite to chlorite, and plagioclase to sericite give a retrogressive event to greenschist facies (M3) syn-D4. It gave rise to NNE-SSW-oriented S4 mylonitic foliations associated with F4 drag folds. Both sinistral and dextral shear sense is recorded but dextral shear sense appears dominant. The fifth phase of deformation (D5) is characterized by brittle fracture and joint structures of the area with varying orientations. The three metamorphic events with deformational episodes of the study show a clockwise P-T path loop from burial to uplift similar to the collision-parallel shearing orogenic setting.
{"title":"Deformation and Metamorphic History of Precambrian High-Grade Rocks of Key Afer Area, Southwestern Ethiopia","authors":"Bishaw Mihret, Ajebush Wuletaw, Tarekegn Tadesse","doi":"10.1134/S0869591124700255","DOIUrl":"10.1134/S0869591124700255","url":null,"abstract":"<p>The deformation and metamorphic history of the Precambrian high-grade rocks in the Key Afer area, southwestern Ethiopia within the Mozambique belt is described. It comprises poly-deformed, metamorphosed, and migmatized rocks with intrusion of granitoids and overlain by Quaternary sediments. A combination of field litho-structural mapping, metamorphic mineral assemblages, and microstructural analysis there are three metamorphic events and four phases of ductile deformation, and one Cenozoic brittle fracture (D5) are recognized. The development of the relatively steep NNW-SSE trending S1 relict gneissic banding and the rise of pyroxene and anhydrous minerals indicate that the peak metamorphism (M1) is synchronous with D1. Subsequently, the hydration of M1 assemblages leads to the formation of amphibolite facies (M2). This is followed by the development of amphibolite facies (M2) caused by the hydration of M1 assemblages synchronous with the D2 deformation. It is defined by the major regional fabric (S2) of the area trending NW-SE, tight to isoclinal upright F2 folds, and local L2 lineation. These D2 upright folds are orthogonally superimposed by another upright F3 folds during D3 resulting in a type-I fold interference pattern. The replacement and breakdown of hornblende to epidote, biotite to chlorite, and plagioclase to sericite give a retrogressive event to greenschist facies (M3) syn-D4. It gave rise to NNE-SSW-oriented S4 mylonitic foliations associated with F4 drag folds. Both sinistral and dextral shear sense is recorded but dextral shear sense appears dominant. The fifth phase of deformation (D5) is characterized by brittle fracture and joint structures of the area with varying orientations. The three metamorphic events with deformational episodes of the study show a clockwise <i>P-T</i> path loop from burial to uplift similar to the collision-parallel shearing orogenic setting.</p>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"32 6","pages":"891 - 909"},"PeriodicalIF":1.0,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142778260","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-05DOI: 10.1134/S086959112470022X
A. A. Tsygankov, G. N. Burmakina, P. D. Kotler
Large granitoid provinces of Central and North-East Asia (Angara–Vitim, Khangai, Kalba-Narym, and Kolyma) can be divided into areal and linear types, which differ significantly in the area and volume of granitoids in their composition. It is assumed that these differences are caused by the structure of pregranitic basement and the degree of thermal impact on the lower and middle continental crust. An important factor in the formation of granitoid provinces is a mantle mafic magmatism, the estimated scale of which correlates with the volumetric and areal characteristics of the granitoid provinces. The role of mafic magmatism is an additional input of heat from the fluids into the melting region of crustal protoliths, as well as a material contribution through various mechanisms of magma mixing. Mixing at a deep level is the most efficient, resulting in the formation of significant volumes of increased basicity silicic magmas. The petrogenetic role of contrasting magmas mixing at the mesoabyssal crustal level, as well as at hypabyssal conditions is not great, but mingling dikes formed in this process serve as a key argument in justifying the simultaneous formation of mafic and granitoid magmatism. Granitoids of Silicic Large Igneous Provinces (SLIPs) are characterized by a heterogeneous isotopic composition generally corresponding to the parameters of the continental crust. The extremely high heterogeneity of spatially conjugate granitoids is caused by mixing of silicic magmas formed through the melting of a few isotopically contrasting sources, including mixing with magmas of mantle origin. The mafic rocks ascribed to the granitoid provinces correspond to the isotopic composition of the enriched mantle (Angara–Vitim batholith) or indicate a significant crustal contribution (Khangai area). The metallogeny of SLIPs is determined by the degree of erosional section and the crustal protolith type, the metamorphic grade of which largely determines the initial fluid content of silicic magmas. The melting of high-grade ancient crustal protoliths produces relatively “dry” silicic melts, the melting of low-grade crustal sources leads to the formation of “aqueous” melts, the differentiation of which ends with pegmatite formation with rare metal mineralization. The formation of non-subduction SLIPs is associated with the mantle plume impact (in the form of simultaneous basaltic magmatism) on the heated crust of young orogenic regions, where tectonic processes were completed no more than a few tens of Ma.
{"title":"Petrogenesis of Granitoids from Silicic Large Igneous Provinces (Central and Northeast Asia)","authors":"A. A. Tsygankov, G. N. Burmakina, P. D. Kotler","doi":"10.1134/S086959112470022X","DOIUrl":"10.1134/S086959112470022X","url":null,"abstract":"<div><p>Large granitoid provinces of Central and North-East Asia (Angara–Vitim, Khangai, Kalba-Narym, and Kolyma) can be divided into areal and linear types, which differ significantly in the area and volume of granitoids in their composition. It is assumed that these differences are caused by the structure of pregranitic basement and the degree of thermal impact on the lower and middle continental crust. An important factor in the formation of granitoid provinces is a mantle mafic magmatism, the estimated scale of which correlates with the volumetric and areal characteristics of the granitoid provinces. The role of mafic magmatism is an additional input of heat from the fluids into the melting region of crustal protoliths, as well as a material contribution through various mechanisms of magma mixing. Mixing at a deep level is the most efficient, resulting in the formation of significant volumes of increased basicity silicic magmas. The petrogenetic role of contrasting magmas mixing at the mesoabyssal crustal level, as well as at hypabyssal conditions is not great, but mingling dikes formed in this process serve as a key argument in justifying the simultaneous formation of mafic and granitoid magmatism. Granitoids of Silicic Large Igneous Provinces (SLIPs) are characterized by a heterogeneous isotopic composition generally corresponding to the parameters of the continental crust. The extremely high heterogeneity of spatially conjugate granitoids is caused by mixing of silicic magmas formed through the melting of a few isotopically contrasting sources, including mixing with magmas of mantle origin. The mafic rocks ascribed to the granitoid provinces correspond to the isotopic composition of the enriched mantle (Angara–Vitim batholith) or indicate a significant crustal contribution (Khangai area). The metallogeny of SLIPs is determined by the degree of erosional section and the crustal protolith type, the metamorphic grade of which largely determines the initial fluid content of silicic magmas. The melting of high-grade ancient crustal protoliths produces relatively “dry” silicic melts, the melting of low-grade crustal sources leads to the formation of “aqueous” melts, the differentiation of which ends with pegmatite formation with rare metal mineralization. The formation of non-subduction SLIPs is associated with the mantle plume impact (in the form of simultaneous basaltic magmatism) on the heated crust of young orogenic regions, where tectonic processes were completed no more than a few tens of Ma.</p></div>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"32 6","pages":"772 - 803"},"PeriodicalIF":1.0,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142778120","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-05DOI: 10.1134/S0869591124700206
V. V. Yarmolyuk, A. M. Kozlovsky, V. M. Savatenkov, A. S. Novikova, Ts. Oyunchimeg
Volcanic sequences of bimodal basalt–trachyte–alkaline rhyolite character with alkaline granites are widespread in central Mongolia. They crop out in small sublatitudinal grabens scattered along the southern and western surroundings of the Khentey part of the Mongol–Okhotsk Belt. According to geochronological data, the bimodal magmatic activity continued from the latest Triassic to earliest Jurassic (at ∼220–195 Ma). Many rocks of the bimodal sequences contain high concentrations of alkalis and rare metals. Fractional crystallization was the leading process for enrichment of rare metals up to their ore-level concentrations in the most differentiated melts. Mafic magmas enriched relative to the OIB in most incompatible trace elements were parental for all rocks of these associations. At the same time, they show elevated Ba and depleted Ta and Nb contents, which indicate that a lithospheric mantle component was involved in their source. The Nd and Sr isotopic ratios of the rocks indicate that the magmas were derived from at least two sources, which are identified as enriched asthenospheric mantle and metasomatized subduction-modified lithospheric mantle. Bimodal magmatism in the Khentey segment of the Mongol–Okhotsk belt appeared ~30 Ma after collision caused by the closure of the Ada-Tsag branch of the Mongol–Okhotsk Ocean at about 250 Ma. Rifting affected the entire surroundings of the Khentey segment of the belt and controlled this magmatism. It was initiated by the collapse of the orogen with delamination of its keel caused the involvement of asthenospheric mantle in the Late Triassic–Early Jurassic magmatism of the region
{"title":"Early Mesozoic Bimodal Volcanic Sequences of Central Mongolia: Implications for the Evolution of the Khentey Segment of the Mongol–Okhotsk Belt","authors":"V. V. Yarmolyuk, A. M. Kozlovsky, V. M. Savatenkov, A. S. Novikova, Ts. Oyunchimeg","doi":"10.1134/S0869591124700206","DOIUrl":"10.1134/S0869591124700206","url":null,"abstract":"<p>Volcanic sequences of bimodal basalt–trachyte–alkaline rhyolite character with alkaline granites are widespread in central Mongolia. They crop out in small sublatitudinal grabens scattered along the southern and western surroundings of the Khentey part of the Mongol–Okhotsk Belt. According to geochronological data, the bimodal magmatic activity continued from the latest Triassic to earliest Jurassic (at ∼220–195 Ma). Many rocks of the bimodal sequences contain high concentrations of alkalis and rare metals. Fractional crystallization was the leading process for enrichment of rare metals up to their ore-level concentrations in the most differentiated melts. Mafic magmas enriched relative to the OIB in most incompatible trace elements were parental for all rocks of these associations. At the same time, they show elevated Ba and depleted Ta and Nb contents, which indicate that a lithospheric mantle component was involved in their source. The Nd and Sr isotopic ratios of the rocks indicate that the magmas were derived from at least two sources, which are identified as enriched asthenospheric mantle and metasomatized subduction-modified lithospheric mantle. Bimodal magmatism in the Khentey segment of the Mongol–Okhotsk belt appeared ~30 Ma after collision caused by the closure of the Ada-Tsag branch of the Mongol–Okhotsk Ocean at about 250 Ma. Rifting affected the entire surroundings of the Khentey segment of the belt and controlled this magmatism. It was initiated by the collapse of the orogen with delamination of its keel caused the involvement of asthenospheric mantle in the Late Triassic–Early Jurassic magmatism of the region</p>","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"32 6","pages":"804 - 827"},"PeriodicalIF":1.0,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142778257","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-09-17DOI: 10.1134/S0869591124700164
E. N. Kaigorodova, V. A. Lebedev, P. M. Kartashov, E. V. Kovalchuk, A. V. Chugaev
<div><p>The paper reports comprehensive petrological, geochemical and mineralogical studies of <i>osumilite-bearing andesite-dacitic lavas of Kordieritoviy Volcano (Keli Highland</i>, Greater Caucasus) erupted at the end of the Pleistocene (about 200 ka). The petrographic and microprobe analysis showed that the rocks contain three paragenetic mineral associations: (1) “xenogenic” (metamorphic) association consisting of garnet (<i>X</i><sub><i>Prp</i></sub> = 0.42, <i>X</i><sub><i>Alm</i></sub> = 0.51–0.53, <i>X</i><sub><i>Grs</i></sub> = 0.04–0.05) + hercynite + sapphire + bronzite + pargasite + ilmenite; (2) early magmatic association represented by hypersthene + hercynite + garnet (<i>X</i><sub><i>Prp</i></sub> = 0.21–0.31, <i>X</i><sub><i>Alm</i></sub> = 0.52–0.71, <i>X</i><sub><i>Grs</i></sub> = 0.04–0.13) + ferro-kaersutite + ilmenite; (3) late magmatic association including hypersthene-ferrohypersthene + labradorite + garnet (<i>X</i><sub><i>Prp</i></sub> = 0.04–0.14, <i>X</i><sub><i>Alm</i></sub> = 0.65–0.81, <i>X</i><sub><i>Grs</i></sub> = 0.06–0.18) + osumilite-(Mg) + phlogopite + tridymite + ilmenite + apatite. The osumilite-(Mg) (phenocrysts, xenomorphic aggregates in the rock matrix, and crystals in miarolic cavities), the average formula for dacites of Kordieritoviy Volcano can be written as (K<sub>0.73</sub>Na<sub>0.06</sub>Ca<sub>0.02</sub><span>({{square }_{{0.20}}})</span>)<sub>1.00</sub>(Mg<sub>1.06</sub><span>({text{Fe}}_{{{text{0}}{text{.90}}}}^{{{text{2 + }}}})</span>Mn<sub>0.04</sub>)<sub>2.00</sub>(Al<sub>2.75</sub><span>({text{Fe}}_{{{text{0}}{text{.18}}}}^{{{text{2 + }}}}{text{Fe}}_{{{text{0}}{text{.06}}}}^{{{text{3 + }}}})</span>Ti<sub>0.01</sub>)<sub>3.00</sub>(Si<sub>10.34</sub>Al<sub>1.66</sub>)<sub>12</sub>O<sub>30</sub>, formed mainly at late magmatic stages – in intermediate chambers immediately prior to the rise of the melt to the surface or after its eruption. Accordingly, this mineral in the studied lavas has a purely magmatic origin. Thermobarometric calculations and petrological modeling showed that the deep magma chamber of Kordieritoviy Volcano was located at a depth of 45–53 km near the Moho discontinuity. The temperature of the melt at the early magmatic stage was no less than 1100°C at 17–23 kbar. Crystallization of osumilite-(Mg) in intermediate magmatic chambers (at depths of 30–40 km) and during the lava ejection occurred at 1030–870°C and pressure progressively decreasing from 14–9 to 1 kbar. A petrogenetic model has been proposed to explain the genesis of exotic osumilite-bearing lavas of Kordieritoviy Volcano. It includes several stages: (1) formation of an enriched upper-mantle source (lithospheric mantle metasomatized by permanent interaction at the Moho discontinuity with the overlying lower crust composed of metamorphosed terrigenous-volcanogenic complexes); (2) generation of “dry” basaltic magmas in the source; (3) crystallization differentiation in the source (fractionation of olivine and chro
{"title":"Osumilite-Bearing Lavas of the Keli Highland (Greater Caucasus): Petrological and Geochemical Characteristics, Mineral Composition, and Conditions of Melt Generation","authors":"E. N. Kaigorodova, V. A. Lebedev, P. M. Kartashov, E. V. Kovalchuk, A. V. Chugaev","doi":"10.1134/S0869591124700164","DOIUrl":"10.1134/S0869591124700164","url":null,"abstract":"<div><p>The paper reports comprehensive petrological, geochemical and mineralogical studies of <i>osumilite-bearing andesite-dacitic lavas of Kordieritoviy Volcano (Keli Highland</i>, Greater Caucasus) erupted at the end of the Pleistocene (about 200 ka). The petrographic and microprobe analysis showed that the rocks contain three paragenetic mineral associations: (1) “xenogenic” (metamorphic) association consisting of garnet (<i>X</i><sub><i>Prp</i></sub> = 0.42, <i>X</i><sub><i>Alm</i></sub> = 0.51–0.53, <i>X</i><sub><i>Grs</i></sub> = 0.04–0.05) + hercynite + sapphire + bronzite + pargasite + ilmenite; (2) early magmatic association represented by hypersthene + hercynite + garnet (<i>X</i><sub><i>Prp</i></sub> = 0.21–0.31, <i>X</i><sub><i>Alm</i></sub> = 0.52–0.71, <i>X</i><sub><i>Grs</i></sub> = 0.04–0.13) + ferro-kaersutite + ilmenite; (3) late magmatic association including hypersthene-ferrohypersthene + labradorite + garnet (<i>X</i><sub><i>Prp</i></sub> = 0.04–0.14, <i>X</i><sub><i>Alm</i></sub> = 0.65–0.81, <i>X</i><sub><i>Grs</i></sub> = 0.06–0.18) + osumilite-(Mg) + phlogopite + tridymite + ilmenite + apatite. The osumilite-(Mg) (phenocrysts, xenomorphic aggregates in the rock matrix, and crystals in miarolic cavities), the average formula for dacites of Kordieritoviy Volcano can be written as (K<sub>0.73</sub>Na<sub>0.06</sub>Ca<sub>0.02</sub><span>({{square }_{{0.20}}})</span>)<sub>1.00</sub>(Mg<sub>1.06</sub><span>({text{Fe}}_{{{text{0}}{text{.90}}}}^{{{text{2 + }}}})</span>Mn<sub>0.04</sub>)<sub>2.00</sub>(Al<sub>2.75</sub><span>({text{Fe}}_{{{text{0}}{text{.18}}}}^{{{text{2 + }}}}{text{Fe}}_{{{text{0}}{text{.06}}}}^{{{text{3 + }}}})</span>Ti<sub>0.01</sub>)<sub>3.00</sub>(Si<sub>10.34</sub>Al<sub>1.66</sub>)<sub>12</sub>O<sub>30</sub>, formed mainly at late magmatic stages – in intermediate chambers immediately prior to the rise of the melt to the surface or after its eruption. Accordingly, this mineral in the studied lavas has a purely magmatic origin. Thermobarometric calculations and petrological modeling showed that the deep magma chamber of Kordieritoviy Volcano was located at a depth of 45–53 km near the Moho discontinuity. The temperature of the melt at the early magmatic stage was no less than 1100°C at 17–23 kbar. Crystallization of osumilite-(Mg) in intermediate magmatic chambers (at depths of 30–40 km) and during the lava ejection occurred at 1030–870°C and pressure progressively decreasing from 14–9 to 1 kbar. A petrogenetic model has been proposed to explain the genesis of exotic osumilite-bearing lavas of Kordieritoviy Volcano. It includes several stages: (1) formation of an enriched upper-mantle source (lithospheric mantle metasomatized by permanent interaction at the Moho discontinuity with the overlying lower crust composed of metamorphosed terrigenous-volcanogenic complexes); (2) generation of “dry” basaltic magmas in the source; (3) crystallization differentiation in the source (fractionation of olivine and chro","PeriodicalId":20026,"journal":{"name":"Petrology","volume":"32 5","pages":"614 - 641"},"PeriodicalIF":1.0,"publicationDate":"2024-09-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142261366","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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