Pub Date : 2024-11-01DOI: 10.1016/j.geogeo.2023.100247
Yazgul Nugumanova , Anna Doroshkevich , Anastasia Starikova , Jonathan Garcia
The potential sources and conditions that control the formation and evolution of alkaline melts are far from being fully understood. To address some of these fundamental questions, we have focused on the composition of olivines and spinel group minerals in aillikites from the Bushkanay dyke in the Siberian Craton. These ultramafic carbonate-rich lamprophyres contain 40–50 vol% fresh olivine macrocrysts (200–600 µm) within a groundmass consisting of phlogopite (60%), magnetite (15%), perovskite (10%), apatite (5%), calcite (3%), chromite (1%), clinopyroxene (up to 1%), barite (up to 1%), serpentine and chlorite (up to 4%). Two types of compositional zoning in olivine have been recognized: (1) Mg-rich cores consisting of a relatively high #Mg (86-89) and NiO (0.25–0.4 wt%); (2) Fe-rich cores with a relatively low #Mg (82-86) and NiO (0.10–0.25 wt%). Both types of olivine cores are igneous and crystallize from an ultramafic carbonate-rich melt. The Mg#-poor (Fe-rich) cores were derived from an early and more evolved aillikitic melt and were later entrained by a more primitive melt, responsible for the formation of the Mg#-rich (Mg-rich) cores. The spinels exhibit a more complex zoning with four major growth zones: (1) an aluminum chromite core; (2) an Fe-chromite and Cr-magnetite transitional zone; and (3) a Ti-magnetite rim. The most primitive spinels of Al-chromite compositions crystallized directly from undifferentiated pulse of the melt, while further growth involved a gradual decrease in Cr due to the crystallization of Cr-rich spinels, while Al remained the same due to the absence of early phlogopite. Our results on olivines and spinels suggest that the aillikites of the Bushkanay dyke were derived from a phlogopite-bearing carbonatized peridotite source. This idea is also supported by the presence of phlogopite, calcite, and amphibole as major phases in the chromite melt inclusions.
{"title":"Composition of olivines and spinel group minerals in aillikites from the Bushkanay dyke, South Siberian Craton: Insights into alkaline melt sources and evolution","authors":"Yazgul Nugumanova , Anna Doroshkevich , Anastasia Starikova , Jonathan Garcia","doi":"10.1016/j.geogeo.2023.100247","DOIUrl":"10.1016/j.geogeo.2023.100247","url":null,"abstract":"<div><div>The potential sources and conditions that control the formation and evolution of alkaline melts are far from being fully understood. To address some of these fundamental questions, we have focused on the composition of olivines and spinel group minerals in aillikites from the Bushkanay dyke in the Siberian Craton. These ultramafic carbonate-rich lamprophyres contain 40–50 vol% fresh olivine macrocrysts (200–600 µm) within a groundmass consisting of phlogopite (60%), magnetite (15%), perovskite (10%), apatite (5%), calcite (3%), chromite (1%), clinopyroxene (up to 1%), barite (up to 1%), serpentine and chlorite (up to 4%). Two types of compositional zoning in olivine have been recognized: (1) Mg-rich cores consisting of a relatively high #Mg (86-89) and NiO (0.25–0.4 wt%); (2) Fe-rich cores with a relatively low #Mg (82-86) and NiO (0.10–0.25 wt%). Both types of olivine cores are igneous and crystallize from an ultramafic carbonate-rich melt. The Mg#-poor (Fe-rich) cores were derived from an early and more evolved aillikitic melt and were later entrained by a more primitive melt, responsible for the formation of the Mg#-rich (Mg-rich) cores. The spinels exhibit a more complex zoning with four major growth zones: (1) an aluminum chromite core; (2) an Fe-chromite and Cr-magnetite transitional zone; and (3) a Ti-magnetite rim. The most primitive spinels of Al-chromite compositions crystallized directly from undifferentiated pulse of the melt, while further growth involved a gradual decrease in Cr due to the crystallization of Cr-rich spinels, while Al remained the same due to the absence of early phlogopite. Our results on olivines and spinels suggest that the aillikites of the Bushkanay dyke were derived from a phlogopite-bearing carbonatized peridotite source. This idea is also supported by the presence of phlogopite, calcite, and amphibole as major phases in the chromite melt inclusions.</div></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"3 4","pages":"Article 100247"},"PeriodicalIF":0.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138991160","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-01DOI: 10.1016/j.geogeo.2024.100271
Mikhail Nikolaevich Kruk , Anna Gennadievna Doroshkevich , Ilya Romanovich Prokopyev , Ivan Aleksandrovich Izbrodin
The alkaline-ultrabasic carbonatite complex Arbarastakh is located in the southwestern part of the Siberian Craton. In addition to ultrabasic rocks such as pyroxenites and ijolites, various types of carbonatite dikes, phoscorites, and aillikites are present in the massif. Based on their modal and compositional characteristics, as well as the chemical composition of minerals, the rocks of the Arbarastakh complex have been divided into three groups: "aillikite", "phoscorite", and "alkaline-silicate and carbonatite" groups. The chemical compositions of olivines, phlogopites and spinellides indicate that aillikites are the least differentiated rocks in the complex. The compositional differences of micas from the "phoscorite" and "alkaline-silicate and carbonatite" groups support the liquation of the aillikite melt into two immiscible silicates and CPIO (carbonate-phosphate/iron-oxide-rich) melts. After liquation, for the "phoscorite" and "alkaline-silicate and carbonatite" groups, evolution follows fractional crystallization. Pyroxene-phlogopite-calcite and calcite carbonatites probably resulted from metasomatic alteration of silicate phases by apatite-dolomite carbonatites, which is confirmed by structural-textural features and the overlapping compositions of phlogopites, apatites and pyroxenes from calcite carbonatites and those from pyroxenites and ijolites.
{"title":"Chemical evolution of major and minor minerals in rocks of the Arbarastakh complex (Aldan shield, Republic of Sakha, Yakutia)","authors":"Mikhail Nikolaevich Kruk , Anna Gennadievna Doroshkevich , Ilya Romanovich Prokopyev , Ivan Aleksandrovich Izbrodin","doi":"10.1016/j.geogeo.2024.100271","DOIUrl":"10.1016/j.geogeo.2024.100271","url":null,"abstract":"<div><div>The alkaline-ultrabasic carbonatite complex Arbarastakh is located in the southwestern part of the Siberian Craton. In addition to ultrabasic rocks such as pyroxenites and ijolites, various types of carbonatite dikes, phoscorites, and aillikites are present in the massif. Based on their modal and compositional characteristics, as well as the chemical composition of minerals, the rocks of the Arbarastakh complex have been divided into three groups: \"aillikite\", \"phoscorite\", and \"alkaline-silicate and carbonatite\" groups. The chemical compositions of olivines, phlogopites and spinellides indicate that aillikites are the least differentiated rocks in the complex. The compositional differences of micas from the \"phoscorite\" and \"alkaline-silicate and carbonatite\" groups support the liquation of the aillikite melt into two immiscible silicates and CPIO (carbonate-phosphate/iron-oxide-rich) melts. After liquation, for the \"phoscorite\" and \"alkaline-silicate and carbonatite\" groups, evolution follows fractional crystallization. Pyroxene-phlogopite-calcite and calcite carbonatites probably resulted from metasomatic alteration of silicate phases by apatite-dolomite carbonatites, which is confirmed by structural-textural features and the overlapping compositions of phlogopites, apatites and pyroxenes from calcite carbonatites and those from pyroxenites and ijolites.</div></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"3 4","pages":"Article 100271"},"PeriodicalIF":0.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140282740","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-01DOI: 10.1016/j.geogeo.2024.100282
Igor V. Aschepkov , Sergei I. Kostrovitsky , Svetlana A. Babushkina , Nikolai S. Medvedev
<div><div>Comparisons of mantle xenocrysts from Lower Triassic kimberlites in the Anabar Shield (Ary-Mastakh, Dyuken, Kuranakh and Orto-Yargyn fields) have shown essential differences from the xenocrysts in the Olenek River Basin (Chomurdakh field). Xenoliths in the Anabar Shield and its northern fields are very rare; they include mainly garnet dunites and harzburgites, and less commonly, pyroxenites and eclogites.</div><div>PTXFO<sub>2</sub> diagram reconstructions for the Boomerang pipe in the Ary-Mastakh field located in the suture zone of the Daldyn and Magan terranes have used monomineral thermobarometry to show that the Opx in rare lherzolitic pyropes formed between 6 and 7.5 GPa. Eclogites represent the mantle heated to the middle pyroxenite layer, and in these terranes the formation of Cr-less pyroxenites are linked to plume melt interactions with the eclogites. In the Dyuken, Kuranakh and Orto-Yargyn fields, the garnet advective trend starts from 7.5 GPa, while the asthenosphere – lithosphere boundary is found at 6 GPa, suggesting that the middle pyroxenite layer was heated and metasomatized. The lower and particularly mid-mantle parts of these fields also contain abundant eclogites. In the Chomur field, lherzolitic and pyroxenitic pyropes form from 7 GPa, while the captured materials mainly represent the upper mantle (4 GPa). All pipes show a similar mantle layering, consisting of seven parts and determined by the clustering of PT estimates for garnets, Cr-spinels, and pyroxenes. In the Boomerang pipe, the Cr-clinopyroxenes and pyropes show REE spectra with varying fan-shaped slopes, (La/Yb)n of 10–100 for pyropes, and HREE for garnets. Spider diagrams reveal peaks for Th, and troughs for U, Nb, Ta, and Pb. Eclogitic garnets and omphacites show minimum values of Eu and Nb, Ta, Zr, and Hf. REEs in ilmenites show a joint increase in LREE and HFSE for Mg to Fe-rich varieties with the degree of differentiation. Most depleted pyropes from Kuranakh have V-U shaped REE patterns, Ba and U peaks. The HFSE minima represents dunites from the arc and back-arc mantle, and the fertilization produces an increase in incompatible elements and sometimes large ion lithophile element (LILE) levels for lherzolitic pyropes. The pyroxenitic garnets display happed REE and the Cpx shows varying LILE and HFSE correlating with the (La/Yb)<sub>n</sub>.</div><div>The Chomur pipe contains predominantly harzburgite-lherzolite garnets with minima Ba and Sr, in addition to various incompatible elements. Cpx shows similar variations with mainly depleted HFSE patterns. The marginal parts of the subcratonic lithospheric mantle (SCLM) of the Anabar Shield are extremely enriched in eclogitic deep-seated material. This is especially seen in the lower SCLM parts, demonstrating thermobarometric trends and features similar to the diamond inclusions from the Ebelyakh (Mayat) placers. The mantle column beneath several pipes (Los’, Universitetskaya, Kuranakh) contain Cr amphiboles
{"title":"Reconstructions of mantle structure beneath the Anabar Shield kimberlites – Similarities and differences","authors":"Igor V. Aschepkov , Sergei I. Kostrovitsky , Svetlana A. Babushkina , Nikolai S. Medvedev","doi":"10.1016/j.geogeo.2024.100282","DOIUrl":"10.1016/j.geogeo.2024.100282","url":null,"abstract":"<div><div>Comparisons of mantle xenocrysts from Lower Triassic kimberlites in the Anabar Shield (Ary-Mastakh, Dyuken, Kuranakh and Orto-Yargyn fields) have shown essential differences from the xenocrysts in the Olenek River Basin (Chomurdakh field). Xenoliths in the Anabar Shield and its northern fields are very rare; they include mainly garnet dunites and harzburgites, and less commonly, pyroxenites and eclogites.</div><div>PTXFO<sub>2</sub> diagram reconstructions for the Boomerang pipe in the Ary-Mastakh field located in the suture zone of the Daldyn and Magan terranes have used monomineral thermobarometry to show that the Opx in rare lherzolitic pyropes formed between 6 and 7.5 GPa. Eclogites represent the mantle heated to the middle pyroxenite layer, and in these terranes the formation of Cr-less pyroxenites are linked to plume melt interactions with the eclogites. In the Dyuken, Kuranakh and Orto-Yargyn fields, the garnet advective trend starts from 7.5 GPa, while the asthenosphere – lithosphere boundary is found at 6 GPa, suggesting that the middle pyroxenite layer was heated and metasomatized. The lower and particularly mid-mantle parts of these fields also contain abundant eclogites. In the Chomur field, lherzolitic and pyroxenitic pyropes form from 7 GPa, while the captured materials mainly represent the upper mantle (4 GPa). All pipes show a similar mantle layering, consisting of seven parts and determined by the clustering of PT estimates for garnets, Cr-spinels, and pyroxenes. In the Boomerang pipe, the Cr-clinopyroxenes and pyropes show REE spectra with varying fan-shaped slopes, (La/Yb)n of 10–100 for pyropes, and HREE for garnets. Spider diagrams reveal peaks for Th, and troughs for U, Nb, Ta, and Pb. Eclogitic garnets and omphacites show minimum values of Eu and Nb, Ta, Zr, and Hf. REEs in ilmenites show a joint increase in LREE and HFSE for Mg to Fe-rich varieties with the degree of differentiation. Most depleted pyropes from Kuranakh have V-U shaped REE patterns, Ba and U peaks. The HFSE minima represents dunites from the arc and back-arc mantle, and the fertilization produces an increase in incompatible elements and sometimes large ion lithophile element (LILE) levels for lherzolitic pyropes. The pyroxenitic garnets display happed REE and the Cpx shows varying LILE and HFSE correlating with the (La/Yb)<sub>n</sub>.</div><div>The Chomur pipe contains predominantly harzburgite-lherzolite garnets with minima Ba and Sr, in addition to various incompatible elements. Cpx shows similar variations with mainly depleted HFSE patterns. The marginal parts of the subcratonic lithospheric mantle (SCLM) of the Anabar Shield are extremely enriched in eclogitic deep-seated material. This is especially seen in the lower SCLM parts, demonstrating thermobarometric trends and features similar to the diamond inclusions from the Ebelyakh (Mayat) placers. The mantle column beneath several pipes (Los’, Universitetskaya, Kuranakh) contain Cr amphiboles","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"3 4","pages":"Article 100282"},"PeriodicalIF":0.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142704345","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-01DOI: 10.1016/j.geogeo.2023.100235
Tushar Meshram , Kirtikumar Randive
Olivine in carbonatites worldwide is mainly of Mg-rich composition (forsterite: Fo85 and Fo99). However, the occurrence of fayalite (Fo<50) is extremely rare except few localities. The Sevvattur carbonatite alkaline complex (SCAC) is part of large Tirrupattur carbonatite-alkaline complex (TCAC), Southern India, which consists of early to late differentiated/fractionated products from dunite-wehrlite-shonkinite-carbonatite to ferrosyenite. In TCAC olivine composition shows decreasing Fo93 to Fo06 contents from early dunite to more evolved ferrosyenite. We report here an occurrence of low-Ni, olivine with intermediate Fo60-65 content and low 100*Mn/Fe, Ni/Co, V/Sc ratios from the SCAC. Textural and compositional evidence reveals the xenocrystic (exotic) nature of olivine and possibly linked with multiple stages of crystal melt interaction in the protracted magmatic evolution and associated metasomatic processes during the interaction of peridotite lithosphere with carbonatite magma in the TCAC at low temperature and shallow depth. It is concluded that the olivine in the Sevvattur Carbonatite Olivine provide the missing link or compositional gap during the evolution of the TCAC of early to late differentiated products from dunite (Fo90-91)-wehrlite (Fo70-72)-shonkinite (Fo72-77)-carbonatite (Fo∼90and 63–65 present study) to ferrosyenite (Fo03-06).
{"title":"Olivine composition of calcite-carbonatite from Sevvattur carbonatite alkaline complex, Dharmapuri Rift Zone, Southern Granulite Terrain, India","authors":"Tushar Meshram , Kirtikumar Randive","doi":"10.1016/j.geogeo.2023.100235","DOIUrl":"10.1016/j.geogeo.2023.100235","url":null,"abstract":"<div><div>Olivine in carbonatites worldwide is mainly of Mg-rich composition (forsterite: Fo<sub>85</sub> and Fo<sub>99</sub>). However, the occurrence of fayalite (Fo<sub><50</sub>) is extremely rare except few localities. The Sevvattur carbonatite alkaline complex (SCAC) is part of large Tirrupattur carbonatite-alkaline complex (TCAC), Southern India, which consists of early to late differentiated/fractionated products from dunite-wehrlite-shonkinite-carbonatite to ferrosyenite. In TCAC olivine composition shows decreasing Fo<sub>93</sub> to Fo<sub>06</sub> contents from early dunite to more evolved ferrosyenite. We report here an occurrence of low-Ni, olivine with intermediate Fo<sub>60-65</sub> content and low 100*Mn/Fe, Ni/Co, V/Sc ratios from the SCAC. Textural and compositional evidence reveals the xenocrystic (exotic) nature of olivine and possibly linked with multiple stages of crystal melt interaction in the protracted magmatic evolution and associated metasomatic processes during the interaction of peridotite lithosphere with carbonatite magma in the TCAC at low temperature and shallow depth. It is concluded that the olivine in the Sevvattur Carbonatite Olivine provide the missing link or compositional gap during the evolution of the TCAC of early to late differentiated products from dunite (Fo<sub>90-91</sub>)-wehrlite (Fo<sub>70-72</sub>)-shonkinite (Fo<sub>72-77</sub>)-carbonatite (Fo<sub>∼90</sub> <sub>and 63–65</sub> present study) to ferrosyenite (Fo<sub>03-06</sub>).</div></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"3 4","pages":"Article 100235"},"PeriodicalIF":0.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134918273","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-01DOI: 10.1016/j.geogeo.2024.100309
Igor V. Ashchepkov , Sergei M. Zhmodik , Dmitry M. Belyanin , Olga N. Kiseleva , Nikolai S. Karmanov , Nikolai S. Medvedev
<div><div>The Beloziminsky Massif (BZM) is an alkaline ultramafic carbonatite complex that includes carbonatites, ijolites, meltegites, and syenites (abbreviated as the CIMS suite) as well as aillikite intrusions that range in age from 645–621 Ma. Aillikite intrusions also occur in the Yuzhnaya Pipe (YuP), located about 16 km eastward of the BZM. Over 5400 analyses in total were conducted to compare mineralogy and geochemistry of different rock types in this study; of these, 24 CIMS samples (>1100 analyses) and about 16 aillikites (>2300 analyses) were collected from within the BZM; the rest are aillikite mineral samples from pipes and dykes outside the massif (>2000 analyses). The results suggest significant differences in sources for rock-forming minerals, less so for the accessories. The pyroxenes in aillikite correspond either to mantle Cr-diopside xenocrysts or megacrystic augites. Low-Na Ti-augites and diopsides as well as aegirines are prevalent in the CIMS intrusive suite. Amphiboles show a considerably long compositional trend, from hornblendes to richterites. Dolomitic carbonatites include admixtures of Na, K, and Ba while calcium carbonatites often contain Sr. The carbonate-rich aillikitics are enriched either in Mg or Ca. The CIMS rocks, particularly the Ca-Mg carbonatites, often include siderites. Thermobarometry for the YuP samples, collected from outside the BZM and containing Cr-diopsides, Cr-phlogopites and Cr-spinels, suggest a formation pressure of 2–4 GPa and a temperature of 800–1250°C; augite xenocrysts with elevated HFSE, U, Th, and Al-augites trace a 90 mW/m<sup>2</sup> geotherm.</div><div>The huge thermal impact of the plume that triggered the break-up of Rodinia also created a series of ultramafic–alkaline–carbonatite massifs. Initially, the aillikites in the mantle were likely produced by the plume-induced melting of carbonated metasomatites containing ilmenite, perovskites, apatites, amphiboles and phlogopites which, in turn, were created by subduction-related melts. Any additional enrichment in the ore components might have occurred subsequentlty in the lower crust, due to liquation. The aillikites inside the BZM contain low-temperature clinopyroxenes tracing a steep advective geotherm (0.4–1.5 GPa); they also contain clots, related to intermediate depth magma chambers, together with CIMS pyroxenes and amphiboles. This suggests that the liquation of aillikites was accompanied by density separation and assimilation and fractional crystallization (AFC) fractionation with the participation of crustal material. Trace elements (especially REEs) in silicate minerals, carbonates, apatites, and accessories (perovskites, pyrochlores, monazites, columbites, zircons, ancylites, etc.) show a general rise in REE levels and La/Yb<sub>n</sub> ratios from aillikites to ijolites, and later to Fe- carbonatites. The presence of zircons, monazites, columbite-tantalites, and other Zr-Hf and Ta-Nb minerals like perovskites and tan
{"title":"Comparative mineralogy, geochemistry and petrology of the Beloziminsky Massif and its aillikite intrusions","authors":"Igor V. Ashchepkov , Sergei M. Zhmodik , Dmitry M. Belyanin , Olga N. Kiseleva , Nikolai S. Karmanov , Nikolai S. Medvedev","doi":"10.1016/j.geogeo.2024.100309","DOIUrl":"10.1016/j.geogeo.2024.100309","url":null,"abstract":"<div><div>The Beloziminsky Massif (BZM) is an alkaline ultramafic carbonatite complex that includes carbonatites, ijolites, meltegites, and syenites (abbreviated as the CIMS suite) as well as aillikite intrusions that range in age from 645–621 Ma. Aillikite intrusions also occur in the Yuzhnaya Pipe (YuP), located about 16 km eastward of the BZM. Over 5400 analyses in total were conducted to compare mineralogy and geochemistry of different rock types in this study; of these, 24 CIMS samples (>1100 analyses) and about 16 aillikites (>2300 analyses) were collected from within the BZM; the rest are aillikite mineral samples from pipes and dykes outside the massif (>2000 analyses). The results suggest significant differences in sources for rock-forming minerals, less so for the accessories. The pyroxenes in aillikite correspond either to mantle Cr-diopside xenocrysts or megacrystic augites. Low-Na Ti-augites and diopsides as well as aegirines are prevalent in the CIMS intrusive suite. Amphiboles show a considerably long compositional trend, from hornblendes to richterites. Dolomitic carbonatites include admixtures of Na, K, and Ba while calcium carbonatites often contain Sr. The carbonate-rich aillikitics are enriched either in Mg or Ca. The CIMS rocks, particularly the Ca-Mg carbonatites, often include siderites. Thermobarometry for the YuP samples, collected from outside the BZM and containing Cr-diopsides, Cr-phlogopites and Cr-spinels, suggest a formation pressure of 2–4 GPa and a temperature of 800–1250°C; augite xenocrysts with elevated HFSE, U, Th, and Al-augites trace a 90 mW/m<sup>2</sup> geotherm.</div><div>The huge thermal impact of the plume that triggered the break-up of Rodinia also created a series of ultramafic–alkaline–carbonatite massifs. Initially, the aillikites in the mantle were likely produced by the plume-induced melting of carbonated metasomatites containing ilmenite, perovskites, apatites, amphiboles and phlogopites which, in turn, were created by subduction-related melts. Any additional enrichment in the ore components might have occurred subsequentlty in the lower crust, due to liquation. The aillikites inside the BZM contain low-temperature clinopyroxenes tracing a steep advective geotherm (0.4–1.5 GPa); they also contain clots, related to intermediate depth magma chambers, together with CIMS pyroxenes and amphiboles. This suggests that the liquation of aillikites was accompanied by density separation and assimilation and fractional crystallization (AFC) fractionation with the participation of crustal material. Trace elements (especially REEs) in silicate minerals, carbonates, apatites, and accessories (perovskites, pyrochlores, monazites, columbites, zircons, ancylites, etc.) show a general rise in REE levels and La/Yb<sub>n</sub> ratios from aillikites to ijolites, and later to Fe- carbonatites. The presence of zircons, monazites, columbite-tantalites, and other Zr-Hf and Ta-Nb minerals like perovskites and tan","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"3 4","pages":"Article 100309"},"PeriodicalIF":0.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142704316","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-01DOI: 10.1016/j.geogeo.2024.100308
Swetasree Nag , Malabika Biswas Roy , Pankaj Kumar Roy
This study employs the SWAT hydrologic model to integrate climatological and hydrological processes for an in-depth analysis of the Mayurakshi River Basin. Utilizing the Markov chain model, the study evaluates water availability, flow patterns, and the basin's response to various climatic and land-use scenarios. Over 30 years of daily observed river discharge data were rigorously calibrated, validated, and analyzed for uncertainty, with critical data from the Massanjore Dam and Tilpara Barrage gauge stations characterizing the river's hydrological behavior. The result suggests the watershed received an average annual precipitation of 1432.4 mm, with evapotranspiration accounting for 40% of total water loss (578.4 mm). Surface runoff constituted over 90% of the total discharge, highlighting its importance for agricultural practices, particularly during the dry season. However future projections (2021–2031) indicate a significant decrease in mean annual precipitation (1404.7 mm) and a drop in evapotranspiration (542.1 mm or 38% of mean precipitation), attributed to reduced vegetation cover and increased settlement, leading to enhanced surface runoff. By quantifying internal renewable blue water, evapotranspiration, and soil water, this research provides crucial data for long-term water resource planning and assessment. The findings are valuable for national, regional, and transboundary water management agencies, offering insights into sustainable water resource management under changing climatic and different land-use conditions.
{"title":"Integrated hydrological modeling and water resource assessment in the Mayurakshi River Basin: A comprehensive study from historical data to future predictions","authors":"Swetasree Nag , Malabika Biswas Roy , Pankaj Kumar Roy","doi":"10.1016/j.geogeo.2024.100308","DOIUrl":"10.1016/j.geogeo.2024.100308","url":null,"abstract":"<div><div>This study employs the SWAT hydrologic model to integrate climatological and hydrological processes for an in-depth analysis of the Mayurakshi River Basin. Utilizing the Markov chain model, the study evaluates water availability, flow patterns, and the basin's response to various climatic and land-use scenarios. Over 30 years of daily observed river discharge data were rigorously calibrated, validated, and analyzed for uncertainty, with critical data from the Massanjore Dam and Tilpara Barrage gauge stations characterizing the river's hydrological behavior. The result suggests the watershed received an average annual precipitation of 1432.4 mm, with evapotranspiration accounting for 40% of total water loss (578.4 mm). Surface runoff constituted over 90% of the total discharge, highlighting its importance for agricultural practices, particularly during the dry season. However future projections (2021–2031) indicate a significant decrease in mean annual precipitation (1404.7 mm) and a drop in evapotranspiration (542.1 mm or 38% of mean precipitation), attributed to reduced vegetation cover and increased settlement, leading to enhanced surface runoff. By quantifying internal renewable blue water, evapotranspiration, and soil water, this research provides crucial data for long-term water resource planning and assessment. The findings are valuable for national, regional, and transboundary water management agencies, offering insights into sustainable water resource management under changing climatic and different land-use conditions.</div></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"3 4","pages":"Article 100308"},"PeriodicalIF":0.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141843241","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The Late Cretaceous (89–65 Ma) Sarnu-Dandali alkaline complex is intrusive into the Neoproterozoic (∼750 Ma) Malani Igneous Suite of rocks in North-Western India. This complex represents a polychronous setup owing to the available age groups of varied rock types involving nephelinites, alkali pyroxenites, syenites, phonolites, ijolites, carbonatites and lamprophyres. In this study, we report xenoliths of ijolite up to 2 mm in size, comprising minerals such as aegirine, nepheline, sodalite, apatite, sphene, fluorite, Ti-rich andradite, and perovskite entrained in the host nephelinite from this complex. Pyroxene thermobarometry for both host and xenoliths reveals that the xenoliths crystallized around 876–1114°C; 4.6–18 kbar (Kdcpx−melt ∼0.164), whereas the host magma crystallized around 800–1165°C and 4.5–17.9 kbar (Kdcpx−melt ∼0.44). The redox conditions of the magma are also estimated from Fe-Nb oxy barometry of perovskite and the log oxygen fugacity varies from -2.5 to -3.7 (ΔNNO), showing a resemblance with that of the world-wide kimberlites derived from the cratonic mantle. Furthermore, the composition as well as the barometric study of clinopyroxenes from both the host and the xenoliths, suggest multiple shallower magma chambers composed of ijolite and nephelinite magmas which were activated by different magmatic pulses, thereby forming a complex magmatic plumbing system.
晚白垩世（89-65 Ma）萨尔努-丹达利碱性复合岩是印度西北部新近纪（750 Ma）马拉尼火成岩组的侵入岩。这个复合体是一个多时相设置，因为它有不同岩石类型的年龄组，包括霞石、碱性辉长岩、正长岩、辉绿岩、黝帘石、碳酸盐岩和灯泡岩。在这项研究中，我们报告了来自这一复合体的尺寸达 2 毫米的黝帘石异长岩，其中包括夹杂在宿主霞石中的埃吉林石、霞石、钠长石、磷灰石、榍石、萤石、富钛安山岩和透辉石等矿物。主岩浆和氙石的辉石热压计显示，氙石的结晶温度约为 876-1114°C; 4.6-18 kbar (Kdcpx-melt ∼ 0.164)，而主岩浆的结晶温度约为 800-1165°C 和 4.5-17.9 kbar (Kdcpx-melt ∼ 0.44)。岩浆的氧化还原条件也是通过包晶的Fe-Nb氧压测定法估算出来的，对数氧富集度在-2.5到-3.7（ΔNNO）之间，这与世界上源自板块地幔的金伯利岩相似。此外，对主岩和鳞片辉石的成分以及气压研究表明，由黝帘石和霞石岩浆组成的多个较浅的岩浆室被不同的岩浆脉冲激活，从而形成了一个复杂的岩浆管道系统。
{"title":"Petrology of ijolite xenoliths entrained in a nephelinite dyke from the Kamthai area, Late Cretaceous polychronous Sarnu-Dandali alkaline complex, North-West India: Evidence for recurrent magmatic pulses and magma mixing","authors":"Sudipa Bhunia , N.V. Chalapathi Rao , Debojit Talukdar , Rohit Pandey , Bernd Lehmann","doi":"10.1016/j.geogeo.2023.100248","DOIUrl":"10.1016/j.geogeo.2023.100248","url":null,"abstract":"<div><div>The Late Cretaceous (89–65 Ma) Sarnu-Dandali alkaline complex is intrusive into the Neoproterozoic (∼750 Ma) Malani Igneous Suite of rocks in North-Western India. This complex represents a polychronous setup owing to the available age groups of varied rock types involving nephelinites, alkali pyroxenites, syenites, phonolites, ijolites, carbonatites and lamprophyres. In this study, we report xenoliths of ijolite up to 2 mm in size, comprising minerals such as aegirine, nepheline, sodalite, apatite, sphene, fluorite, Ti-rich andradite, and perovskite entrained in the host nephelinite from this complex. Pyroxene thermobarometry for both host and xenoliths reveals that the xenoliths crystallized around 876–1114°C; 4.6–18 kbar (<em>Kd<sub>cpx</sub></em><sub>−melt</sub> ∼0.164), whereas the host magma crystallized around 800–1165°C and 4.5–17.9 kbar (<em>Kd<sub>cpx</sub></em><sub>−melt</sub> ∼0.44). The redox conditions of the magma are also estimated from Fe-Nb oxy barometry of perovskite and the log oxygen fugacity varies from -2.5 to -3.7 (ΔNNO), showing a resemblance with that of the world-wide kimberlites derived from the cratonic mantle. Furthermore, the composition as well as the barometric study of clinopyroxenes from both the host and the xenoliths, suggest multiple shallower magma chambers composed of ijolite and nephelinite magmas which were activated by different magmatic pulses, thereby forming a complex magmatic plumbing system.</div></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"3 4","pages":"Article 100248"},"PeriodicalIF":0.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139023265","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Preliminary studied lower crust and Moho of Baikal Rift (BR) was investigated using pyroxenite xenoliths and xenocrysts from Cenozoic volcanoes to determine the structure, thermal conditions and composition of the transitional zone from the crust to mantle and influence of plumes on it. Samples from Vitim Plateau (Miocene picrite basalts) SW part of BR, Dzhida River Basin (Bartoy volcanoes) located at SE of BR and Tunka axial Valley (Karierny volcanoes) to the West from Baikal were studied for major components using electron microprobe and electron microscope and for trace elements with the inductively connected mass-spectrometry with laser ablation. For the comparison, the lower crust xenocrysts from the Angara Vitim batholite were also included in this study. The PT estimates for minerals are mostly refer to the Moho boundary or are locating just beneath it giving the vast range of temperatures. Beneath the Moho, they trace 90 mw/m2 geotherm. Within the crust, temperature regime varies from the conductive to advective. Pyroxene xenocrysts and pyroxenite xenoliths mainly trace 90 mw/m2 SEA plume geotherm. The levels of the melt intrusions are overheated to 1350°C. The granulites are typically represent the colder conditions than SEA geotherm. Xenocrysts from Angara Vitim batholith magmas reveal more depleted material of lower crust than those found in Cenozoic lavas and possibly are skialites. The xenocrysts and granulite xenoliths in Cenozoic lavas are mainly basic cumulates. The rocks of the lower crust became more acid to the upper part.
The lateral variations in the lower crust sampled material show enrichment in K2O at the boundary with the Siberian Craton in Tunka, more metasomatic and hydrous nature in Dzhida zone and more basic and CaO rich characteristic in Vitim area. These data give the evidence for the conditions of origin of the magmas of Angara-Vitim Batholith (AVP) (275–310 Ma), which was created due to interaction of hot spot with the crust in Baikal and Transbaikalia. Initially this hot generated kimberlites and basalts in northern (420–390 Ma) and central part of Yakutia (370–440 Ma) in time, migrated to – and eeastern Sayan Mountain formed Ingashi lamproites -kimberlites (310 Ma), than plume was spreading to south beneath the crust in Transbaikalia and created AVP. After it returned to central and northern Siberia, it generated Permo-Triassic Siberian trap province.
{"title":"Thermal state and nature of the lower crust in the Baikal Rift Zone: Insight from xenoliths of Cenozoic and Paleozoic magmatic rocks","authors":"I.V. Ashchepkov , A.A. Tsygankov , G.N. Burmakina , N.S. Karmanov , S.V. Rasskazov , I.S. Chuvashova , Y. Ailow","doi":"10.1016/j.geogeo.2024.100305","DOIUrl":"10.1016/j.geogeo.2024.100305","url":null,"abstract":"<div><div>Preliminary studied lower crust and Moho of Baikal Rift (BR) was investigated using pyroxenite xenoliths and xenocrysts from Cenozoic volcanoes to determine the structure, thermal conditions and composition of the transitional zone from the crust to mantle and influence of plumes on it. Samples from Vitim Plateau (Miocene picrite basalts) SW part of BR, Dzhida River Basin (Bartoy volcanoes) located at SE of BR and Tunka axial Valley (Karierny volcanoes) to the West from Baikal were studied for major components using electron microprobe and electron microscope and for trace elements with the inductively connected mass-spectrometry with laser ablation. For the comparison, the lower crust xenocrysts from the Angara Vitim batholite were also included in this study. The PT estimates for minerals are mostly refer to the Moho boundary or are locating just beneath it giving the vast range of temperatures. Beneath the Moho, they trace 90 mw/m<sup>2</sup> geotherm. Within the crust, temperature regime varies from the conductive to advective. Pyroxene xenocrysts and pyroxenite xenoliths mainly trace 90 mw/m<sup>2</sup> SEA plume geotherm. The levels of the melt intrusions are overheated to 1350°C. The granulites are typically represent the colder conditions than SEA geotherm. Xenocrysts from Angara Vitim batholith magmas reveal more depleted material of lower crust than those found in Cenozoic lavas and possibly are skialites. The xenocrysts and granulite xenoliths in Cenozoic lavas are mainly basic cumulates. The rocks of the lower crust became more acid to the upper part.</div><div>The lateral variations in the lower crust sampled material show enrichment in K<sub>2</sub>O at the boundary with the Siberian Craton in Tunka, more metasomatic and hydrous nature in Dzhida zone and more basic and CaO rich characteristic in Vitim area. These data give the evidence for the conditions of origin of the magmas of Angara-Vitim Batholith (AVP) (275–310 Ma), which was created due to interaction of hot spot with the crust in Baikal and Transbaikalia. Initially this hot generated kimberlites and basalts in northern (420–390 Ma) and central part of Yakutia (370–440 Ma) in time, migrated to – and eeastern Sayan Mountain formed Ingashi lamproites -kimberlites (310 Ma), than plume was spreading to south beneath the crust in Transbaikalia and created AVP. After it returned to central and northern Siberia, it generated Permo-Triassic Siberian trap province.</div></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"3 4","pages":"Article 100305"},"PeriodicalIF":0.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141713730","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-01DOI: 10.1016/j.geogeo.2024.100315
M. Lavanya, M. Muthukumar
Recent advances in space technology are being widely utilized in resource mapping and management as they provide a high level of accuracy over a short duration and at a lower cost, when compared to traditional methods. Remote sensing and the geographical information system (GIS) play a vital role in collecting and analyzing information used to map resources and earth surface features. For example, anthropogenic activities and climate change affect the natural interaction between the surface and ground water making the monitoring and management of groundwater resources mandatory for future sustainable development. In this study, we attempt to identify the groundwater potential zones in the Dindigul district of Tamil Nadu, India using these emerging technologies. To map regions with groundwater potential, the analytical hierarchical process (AHP) was used to assign weights to all classes in each thematic layer based on groundwater-influencing factors. The sub-features of every parameter were also ranked, using a pairwise comparison method, based on the groundwater-influencing factors and expert knowledge. The parameters selected for the analysis were geology, geomorphology, soil, land use/land cover, drainage density, lineament density, slope, rainfall, thickness of top-soil, thickness of fractured zone, thickness of weathered zone, topographic wetness index, roughness and curvature. The weighted overlay analysis method was adopted for all the thematic layers, with technical support from the AHP for assigning weightages. The results were classified into five categories viz., very high, high, moderate, low, and very low potential zones, and used to prepare a groundwater potential map. This map revealed a nuanced distribution of groundwater potential across the district, with varying degrees of potentiality in different regions. Very high potential zones occupy a minimal area (0.07%) but are strategically located in areas characterized by high weathered zone thickness and conducive soil characteristics. High potential zones cover a significant area (22.33%) and are dispersed throughout the district, with specific concentrations in regions featuring highly fractured zones and favorable geological attributes. Moderate potential zones (35.12%) are primarily located in the northeastern part of the study area, while low and very low potential regions cover 19.56% and 22.92% of the study area. The low and very low potential zones appear particularly in hilly terrains, with unfavorable top soil and geological conditions. The validation of the groundwater potential zone (GWPZ) map using the annual average water level data demonstrates a substantial match (60.53%) between the identified groundwater conditions and actual well depths, affirming the reliability and significance of the findings from this study.
{"title":"AHP and geospatial technologies for identifying groundwater exploration target regions in Dindigul, southern India","authors":"M. Lavanya, M. Muthukumar","doi":"10.1016/j.geogeo.2024.100315","DOIUrl":"10.1016/j.geogeo.2024.100315","url":null,"abstract":"<div><div>Recent advances in space technology are being widely utilized in resource mapping and management as they provide a high level of accuracy over a short duration and at a lower cost, when compared to traditional methods. Remote sensing and the geographical information system (GIS) play a vital role in collecting and analyzing information used to map resources and earth surface features. For example, anthropogenic activities and climate change affect the natural interaction between the surface and ground water making the monitoring and management of groundwater resources mandatory for future sustainable development. In this study, we attempt to identify the groundwater potential zones in the Dindigul district of Tamil Nadu, India using these emerging technologies. To map regions with groundwater potential, the analytical hierarchical process (AHP) was used to assign weights to all classes in each thematic layer based on groundwater-influencing factors. The sub-features of every parameter were also ranked, using a pairwise comparison method, based on the groundwater-influencing factors and expert knowledge. The parameters selected for the analysis were geology, geomorphology, soil, land use/land cover, drainage density, lineament density, slope, rainfall, thickness of top-soil, thickness of fractured zone, thickness of weathered zone, topographic wetness index, roughness and curvature. The weighted overlay analysis method was adopted for all the thematic layers, with technical support from the AHP for assigning weightages. The results were classified into five categories viz., very high, high, moderate, low, and very low potential zones, and used to prepare a groundwater potential map. This map revealed a nuanced distribution of groundwater potential across the district, with varying degrees of potentiality in different regions. Very high potential zones occupy a minimal area (0.07%) but are strategically located in areas characterized by high weathered zone thickness and conducive soil characteristics. High potential zones cover a significant area (22.33%) and are dispersed throughout the district, with specific concentrations in regions featuring highly fractured zones and favorable geological attributes. Moderate potential zones (35.12%) are primarily located in the northeastern part of the study area, while low and very low potential regions cover 19.56% and 22.92% of the study area. The low and very low potential zones appear particularly in hilly terrains, with unfavorable top soil and geological conditions. The validation of the groundwater potential zone (GWPZ) map using the annual average water level data demonstrates a substantial match (60.53%) between the identified groundwater conditions and actual well depths, affirming the reliability and significance of the findings from this study.</div></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"3 4","pages":"Article 100315"},"PeriodicalIF":0.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142552174","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-11-01DOI: 10.1016/j.geogeo.2024.100266
A.A. Tsygankov, G.N. Burmakina, V.B. Khubanov, A.V. Ukraintsev, N.D. Guslyakov
Late Paleozoic granites of the Angara-Vitim batholith (AVB) occupy an area of 200,000 km2 in Western Transbaikalia (the eastern part of the Central Asian fold belt). Batholith granitoids form a sheet-like body with an average thickness of 7–10 km and a volume of about 1 million km3. The granitoid massifs that make up the batholith are composed of high-potassium calc-alkaline and subalkaline quartz monzonites, quartz syenites, amphibole-biotite granodiorites, and biotite granites of autochthonous and allochthonous facies. An extremely high heterogeneity of the batholith isotopic structure was established, which basically corresponds to the parameters of uneven-aged crustal metaterrigenous protoliths. There are significant variations in εNd(Т) and accordingly T(DM-2) in granitoids of different complexes. It is assumed that the isotopic heterogeneity of AVB was formed due to the melting of a limited protoliths number that are maximally contrasting in isotopic and lithological composition: the Paleoproterozoic continental crust with εNd(Т) ≈ -20 ÷ -22 and T(DM-2) = 2.9–2.5 Ga and Neoproterozoic mafic granulites of increased potassium alkalinity, enriched in the juvenile component (εNd(Т) ≈ -3.0; T(DM-2) = 1.2–1.3 Ga). The latter were the main magmas source of postbatholitic alkali granites. Melts from these contrasting protoliths were only in some cases complementary to the salic melts sources. The main mechanism that determined the isotopic composition of AVB granitoids was the mixing of isotopically contrasting magmas in different proportions. Mingling dikes, mafic inclusions in granitoids, and synplutonic mafic intrusions in the AVB indicate an additional mixing component. It was mafic magma from an enriched mantle reactivated in the Late Paleozoic under the mantle plume influence on the heated plastic crust of a young (Hercynian) orogen.
{"title":"Nd isotope systematics of Late Paleozoic granitoids from the Western Transbaikalia (Russia): Petrological consequences and plume model testing","authors":"A.A. Tsygankov, G.N. Burmakina, V.B. Khubanov, A.V. Ukraintsev, N.D. Guslyakov","doi":"10.1016/j.geogeo.2024.100266","DOIUrl":"10.1016/j.geogeo.2024.100266","url":null,"abstract":"<div><div>Late Paleozoic granites of the Angara-Vitim batholith (AVB) occupy an area of 200,000 km<sup>2</sup> in Western Transbaikalia (the eastern part of the Central Asian fold belt). Batholith granitoids form a sheet-like body with an average thickness of 7–10 km and a volume of about 1 million km<sup>3</sup>. The granitoid massifs that make up the batholith are composed of high-potassium calc-alkaline and subalkaline quartz monzonites, quartz syenites, amphibole-biotite granodiorites, and biotite granites of autochthonous and allochthonous facies. An extremely high heterogeneity of the batholith isotopic structure was established, which basically corresponds to the parameters of uneven-aged crustal metaterrigenous protoliths. There are significant variations in εNd(Т) and accordingly T(DM-2) in granitoids of different complexes. It is assumed that the isotopic heterogeneity of AVB was formed due to the melting of a limited protoliths number that are maximally contrasting in isotopic and lithological composition: the Paleoproterozoic continental crust with εNd(Т) ≈ -20 ÷ -22 and T(DM-2) = 2.9–2.5 Ga and Neoproterozoic mafic granulites of increased potassium alkalinity, enriched in the juvenile component (εNd(Т) ≈ -3.0; T(DM-2) = 1.2–1.3 Ga). The latter were the main magmas source of postbatholitic alkali granites. Melts from these contrasting protoliths were only in some cases complementary to the salic melts sources. The main mechanism that determined the isotopic composition of AVB granitoids was the mixing of isotopically contrasting magmas in different proportions. Mingling dikes, mafic inclusions in granitoids, and synplutonic mafic intrusions in the AVB indicate an additional mixing component. It was mafic magma from an enriched mantle reactivated in the Late Paleozoic under the mantle plume influence on the heated plastic crust of a young (Hercynian) orogen.</div></div>","PeriodicalId":100582,"journal":{"name":"Geosystems and Geoenvironment","volume":"3 4","pages":"Article 100266"},"PeriodicalIF":0.0,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140088105","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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