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Ancient and Modern Subduction Zones: Tectonic, Petrological and Geochemical Aspects of Ore and Magma Genesis

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A special issue of Geosciences (ISSN 2076-3263). This special issue belongs to the section "Geochemistry".

Deadline for manuscript submissions: closed (15 December 2021) | Viewed by 14168

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Special Issue Editors

Dr. Pavel Kepezhinskas

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Guest Editor

1. Kosygin Institute of Tectonics and Geophysics, Russian Academy of Sciences, Khabarovsk, Russia
2. PNK GeoScience, Tampa, FL, USA
Interests: Igneous rocks; mantle petrology and geochemistry; subduction zone processes; volcanic arc geochemistry; ore-forming processes and fluids; highly siderophile and chalcophile metals; diamonds; geology and geochemistry of wine

Dr. Manuel Roda

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Guest Editor

Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Mangiagalli, 34, 20133 Milano, Italy
Interests: geodynamics of convergent and divergent margins; numerical modeling of geological processes; Structural Geology; evolution of European Alps and Variscan chain geological mapping

Special Issue Information

Dear Colleagues,

Subduction zones are the loci for generation of continental crust throughout most of the Earth’s geologic history. They are associated with prolific volcanism and plutonism, accretionary tectonics and mountain building as well as large-scale recycling of chemical elements between mantle and crustal reservoirs (‘the subduction factory”). Geochemical fingerprinting of subduction magmas and fluids, role of mantle and slab melting and mantle wedge metasomatism, crustal contamination and magmatic differentiation (with insights into explosive volcanic eruptions) have been for a long time at the forefront of subduction zone research. Ancient and modern subduction zones are associated with a wide range of ore deposits, such as epithermal, porphyry, VMS, IOCG, base metal sulfide, plutonic PGE and chromite and many others. Deciphering these mineralized systems requires better understanding of possible role of hydrous and halogen-rich fluids, mobility of highly siderophile and chalcophile elements in magmas and hydrothermal brines as well as impact of various tectonic (crustal thickness) and petrologic (oxygen and sulfur fugacity) factors on ore formation in subduction settings. Subduction zones also play an integral role in recycling volatile elements (carbon and sulfur) between the surficial and internal reservoirs of the Earth. The progress and level of our knowledge achieved so far clearly demonstrates the importance of multifaceted approach in subduction zone research. This Thematic Issue focuses on interdisciplinary studies in subduction zone processes with emphasis on tectonic, petrological and geochemical controls on mantle and crustal evolution, petrogenesis of arc magmas and formation of subduction-related ore deposits. We welcome contributors from all branches of geosciences dealing with geologic, structural and tectonic aspects of subduction zones, geology and geochemistry of young and old volcanic terranes, arc petrogenesis, recycling of chemical elements in the crust-mantle system and ore-forming processes in subduction environments.

Dr. Pavel Kepezhinskas
Dr. Manuel Roda
Guest Editors

Manuscript Submission Information

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Keywords

Accretionary tectonics and mountain building
Ancient sutures and ophiolites
Volcanic arc geology and geochemistry
Origin of subduction-related magmas
Slab melting and mantle wedge metasomatism
Element transfer between mantle and crust
Role of fluids in ore-forming processes
Subduction-related ore deposits

Published Papers (4 papers)

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Research

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19 pages, 17941 KiB

Open AccessArticle

Formation of Gold Alloys during Crustal Differentiation of Convergent Zone Magmas: Constraints from an AU-Rich Websterite in the Stanovoy Suture Zone (Russian Far East)

by Nikolai Berdnikov, Pavel Kepezhinskas, Natalia Konovalova and Nikita Kepezhinskas

Geosciences 2022, 12(3), 126; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences12030126 - 08 Mar 2022

Cited by 9 | Viewed by 2585

Abstract

Gold is typically transported by mafic and evolved magmas into the upper crust to be deposited in shallow oxidized porphyry and epithermal environments. However, the magmatic behavior of gold is still poorly understood and warrants further attention. Additional insights into the magmatic evolution of gold and other noble metals can be provided by investigations of primitive convergent zone magmas and products of their differentiation that contain primary-textured Au-alloys. One of the best examples of such Au-rich ultramafic cumulates is the Triassic (232–233 Ma) Ildeus intrusion, which was emplaced within the Mesozoic Stanovoy subduction zone in the Russian Far East. Some websterites from the Ildeus intrusion, representing cumulates crystallized from a primitive convergent zone magma, are enriched in Au (up to 596 ppm) and contain abundant Cu-Ag-Au micro-particles. Most of these Au-alloy micro-particles display compositions similar to those previously found in explosive pyroclastic rocks in the Lesser Khingan iron district, mantle wedge peridotites in Kamchatka and Cretaceous adakites in the Stanovoy suture zone. Textural and compositional characteristics suggest that Cu-Ag-Au alloys precipitated from a primitive calc-alkaline melt during its crustal differentiation in a Mesozoic paleo-subduction zone. Some large Cu-Ag-Au grains display an internal honeycomb-like structure with alternating Cu-rich and Cu-poor zones. Heating experiments under atmospheric conditions recorded a substantial loss of Cu from primary magmatic Cu-Ag-Au alloys, which appears to be a process characteristic of oxidized hydrothermal ore systems. We suggest that the later-stage hydrothermal alteration of differentiated igneous conduits containing magmatic gold alloys results in the formation of Cu-free gold mineralization comparable to the upper crustal porphyry and epithermal environments. Full article

(This article belongs to the Special Issue Ancient and Modern Subduction Zones: Tectonic, Petrological and Geochemical Aspects of Ore and Magma Genesis)

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23 pages, 7483 KiB

Open AccessEditor’s ChoiceArticle

Sediment-Peridotite Reaction Controls Fore-Arc Metasomatism and Arc Magma Geochemical Signatures

by Michael W. Förster, Yannick Bussweiler, Dejan Prelević, Nathan R. Daczko, Stephan Buhre, Regina Mertz-Kraus and Stephen F. Foley

Geosciences 2021, 11(9), 372; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences11090372 - 03 Sep 2021

Cited by 13 | Viewed by 3501

Abstract

Subduction of oceanic crust buries an average thickness of 300–500 m of sediment that eventually dehydrates or partially melts. Progressive release of fluid/melt metasomatizes the fore-arc mantle, forming serpentinite at low temperatures and phlogopite-bearing pyroxenite where slab surface reaches 700–900 °C. This is sufficiently high to partially melt subducted sediments before they approach the depths where arc magmas are formed. Here, we present experiments on reactions between melts of subducted sediments and peridotite at 2–6 GPa/750–1100 °C, which correspond to the surface of a subducting slab. The reaction of volatile-bearing partial melts derived from sediments with depleted peridotite leads to separation of elements and a layered arrangement of metasomatic phases, with layers consisting of orthopyroxene, mica-pyroxenite, and clinopyroxenite. The selective incorporation of elements in these metasomatic layers closely resembles chemical patterns found in K-rich magmas. Trace elements were imaged using LA-ICP-TOFMS, which is applied here to investigate the distribution of trace elements within the metasomatic layers. Experiments of different duration enabled estimates of the growth of the metasomatic front, which ranges from 1–5 m/ky. These experiments explain the low contents of high-field strength elements in arc magmas as being due to their loss during melting of sedimentary materials in the fore-arc. Full article

(This article belongs to the Special Issue Ancient and Modern Subduction Zones: Tectonic, Petrological and Geochemical Aspects of Ore and Magma Genesis)

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30 pages, 13571 KiB

Open AccessArticle

Gold in Mineralized Volcanic Systems from the Lesser Khingan Range (Russian Far East): Textural Types, Composition and Possible Origins

by Nikolai Berdnikov, Victor Nevstruev, Pavel Kepezhinskas, Ivan Astapov and Natalia Konovalova

Geosciences 2021, 11(2), 103; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences11020103 - 20 Feb 2021

Cited by 16 | Viewed by 2872

Abstract

While gold partitioning into hydrothermal fluids responsible for the formation of porphyry and epithermal deposits is currently well understood, its behavior during the differentiation of metal-rich silicate melts is still subject of an intense scientific debate. Typically, gold is scavenged into sulfides during crustal fractionation of sulfur-rich mafic to intermediate magmas and development of native forms and alloys of this important precious metal in igneous rocks and associated ores are still poorly documented. We present new data on gold (Cu-Ag-Au, Ni-Cu-Zn-Ag-Au, Ti-Cu-Ag-Au, Ag-Au) alloys from iron oxide deposits in the Lesser Khingan Range (LKR) of the Russian Far East. Gold alloy particles are from 10 to 100 µm in size and irregular to spherical in shape. Gold spherules were formed through silicate-metal liquid immiscibility and then injected into fissures surrounding the ascending melt column, or emplaced through a volcanic eruption. Presence of globular (occasionally with meniscus-like textures) Cu-O micro-inclusions in Cu-Ag-Au spherules confirms their crystallization from a metal melt via extremely fast cooling. Irregularly shaped Cu-Ag-Au particles were formed through hydrothermal alteration of gold-bearing volcanic rocks and ores. Association of primarily liquid Cu-Ag-Au spherules with iron-oxide mineralization in the LKR indicates possible involvement of silicate-metallic immiscibility and explosive volcanism in the formation of the Andean-type iron oxide gold-copper (IOCG) and related copper-gold porphyry deposits in the deeper parts of sub-volcanic epithermal systems. Thus, formation of gold alloys in deep roots of arc volcanoes may serve as a precursor and an exploration guide for high-grade epithermal gold mineralization at shallow structural levels of hydrothermal-volcanic environments in subduction zones. Full article

(This article belongs to the Special Issue Ancient and Modern Subduction Zones: Tectonic, Petrological and Geochemical Aspects of Ore and Magma Genesis)

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Review

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60 pages, 10119 KiB

Open AccessReview

Adakites, High-Nb Basalts and Copper–Gold Deposits in Magmatic Arcs and Collisional Orogens: An Overview

by Pavel Kepezhinskas, Nikolai Berdnikov, Nikita Kepezhinskas and Natalia Konovalova

Geosciences 2022, 12(1), 29; https://0-doi-org.brum.beds.ac.uk/10.3390/geosciences12010029 - 07 Jan 2022

Cited by 17 | Viewed by 3911

Abstract

Adakites are Y- and Yb-depleted, SiO₂- and Sr-enriched rocks with elevated Sr/Y and La/Yb ratios originally thought to represent partial melts of subducted metabasalt, based on their association with the subduction of young (<25 Ma) and hot oceanic crust. Later, adakites were found in arc segments associated with oblique, slow and flat subduction, arc–transform intersections, collision zones and post-collisional extensional environments. New models of adakite petrogenesis include the melting of thickened and delaminated mafic lower crust, basalt underplating of the continental crust and high-pressure fractionation (amphibole ± garnet) of mantle-derived, hydrous mafic melts. In some cases, adakites are associated with Nb-enriched (10 ppm < Nb < 20 ppm) and high-Nb (Nb > 20 ppm) arc basalts in ancient and modern subduction zones (HNBs). Two types of HNBs are recognized on the basis of their geochemistry. Type I HNBs (Kamchatka, Honduras) share N-MORB-like isotopic and OIB-like trace element characteristics and most probably originate from adakite-contaminated mantle sources. Type II HNBs (Sulu arc, Jamaica) display high-field strength element enrichments in respect to island-arc basalts coupled with enriched, OIB-like isotopic signatures, suggesting derivation from asthenospheric mantle sources in arcs. Adakites and, to a lesser extent, HNBs are associated with Cu–Au porphyry and epithermal deposits in Cenozoic magmatic arcs (Kamchatka, Phlippines, Indonesia, Andean margin) and Paleozoic-Mesozoic (Central Asian and Tethyan) collisional orogens. This association is believed to be not just temporal and structural but also genetic due to the hydrous (common presence of amphibole and biotite), highly oxidized (>ΔFMQ > +2) and S-rich (anhydrite in modern Pinatubo and El Chichon adakite eruptions) nature of adakite magmas. Cretaceous adakites from the Stanovoy Suture Zone in Far East Russia contain Cu–Ag–Au and Cu–Zn–Mo–Ag alloys, native Au and Pt, cupriferous Ag in association witn barite and Ag-chloride. Stanovoy adakites also have systematically higher Au contents in comparison with volcanic arc magmas, suggesting that ore-forming hydrothermal fluids responsible for Cu–Au(Mo–Ag) porphyry and epithermal mineralization in upper crustal environments could have been exsolved from metal-saturated, H₂O–S–Cl-rich adakite magmas. The interaction between depleted mantle peridotites and metal-rich adakites appears to be capable of producing (under a certain set of conditions) fertile sources for HNB melts connected with some epithermal Au (Porgera) and porphyry Cu–Au–Mo (Tibet, Iran) mineralized systems in modern and ancient subduction zones. Full article

(This article belongs to the Special Issue Ancient and Modern Subduction Zones: Tectonic, Petrological and Geochemical Aspects of Ore and Magma Genesis)

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