scholarly journals Lithium, Oxygen and Magnesium Isotope Systematics of Volcanic Rocks in the Okinawa Trough: Implications for Plate Subduction Studies

2021 ◽  
Vol 10 (1) ◽  
pp. 40
Author(s):  
Zhigang Zeng ◽  
Xiaohui Li ◽  
Yuxiang Zhang ◽  
Haiyan Qi
Keyword(s):  
Basaltic Andesite ◽  
Subduction Zones ◽  
Okinawa Trough ◽  
Volcanic Rocks ◽  
Philippine Sea Plate ◽  
Material Transfer ◽  
Magma Compositions ◽  
Subduction Input ◽  
Back Arc ◽  
Plate Subduction

Determining the influence of subduction input on back-arc basin magmatism is important for understanding material transfer and circulation in subduction zones. Although the mantle source of Okinawa Trough (OT) magmas is widely accepted to be modified by subducted components, the role of slab-derived fluids is poorly defined. Here, major element, trace element, and Li, O and Mg isotopic compositions of volcanic lavas from the middle OT (MOT) and southern OT (SOT) were analyzed. Compared with the MOT volcanic lavas, the T9-1 basaltic andesite from the SOT exhibited positive Pb anomalies, significantly lower Nd/Pb and Ce/Pb ratios, and higher Ba/La ratios, indicating that subducted sedimentary components affected SOT magma compositions. The δ7Li, δ18O, and δ26Mg values of the SOT basaltic andesite (−5.05‰ to 4.98‰, 4.83‰ to 5.80‰ and −0.16‰ to −0.09‰, respectively) differed from those of MOT volcanic lavas. Hence, the effect of the Philippine Sea Plate subduction component, (low δ7Li and δ18O and high δ26Mg) on magmas in the SOT was clearer than that in the MOT. This contrast likely appears because the amounts of fluids and/or melts derived from altered oceanic crust (AOC, lower δ18O) and/or subducted sediment (lower δ7Li, higher δ18O and δ26Mg) injected into magmas in the SOT are larger than those in the MOT and because the injection ratio between subducted AOC and sediment is always >1 in the OT. The distance between the subducting slab and overlying magma may play a significant role in controlling the differences in subduction components injected into magmas between the MOT and SOT.

scholarly journals Zircon Record of Supercontinent Amalgamation in Back-arc Volcanic Rocks

2020 ◽  
Author(s):  
Zhigang Zeng ◽  
Zuxing Chen ◽  
Yuxiang Zhang
Keyword(s):  
Continental Crust ◽  
Detrital Zircon ◽  
Okinawa Trough ◽  
Volcanic Rocks ◽  
Parental Magma ◽  
Crustal Thickening ◽  
The Okinawa Trough ◽  
Global Age ◽  
Back Arc

Abstract Episodic supercontinental amalgamation has profoundly influenced the evolution of the geosphere, hydrosphere, atmosphere and biosphere. However, the timing of supercontinent formation has mainly been constrained by the global age spectra of detrital zircon. Here, we show that the zircons in back-arc volcanic rocks not only reflect the evolution of local magmatism but also contain a record of global continental amalgamation events. We found that the young (<100 ka) zircons in volcanic rocks from the Okinawa Trough have old (108 Ma to 2.7 Ga) inherited zircon, which were captured as the magma ascended through the rifting continental crust. Moreover, the ages of the inherited zircons correspond to five supercontinent amalgamation events. Specifically, the Archaean inherited zircons, which have positive ɛHf(t) and low δ18O values, correspond to the formation of juvenile global continental crust. In contrast, the negative ɛHf(t) and high δ18O values of post-Archaean inherited zircons indicate that their parental magma contained recycled, old crust due to the enhanced crustal thickening and crust-mantle interactions during supercontinent assembly. Therefore, inherited zircons in back-arc volcanic rocks not only reflect the evolution of local magmatism but also contain a record of global supercontinental amalgamation events.

scholarly journals Two Processes of Anglesite Formation and a Model of Secondary Supergene Enrichment of Bi and Ag in Seafloor Hydrothermal Sulfide Deposits

2021 ◽  
Vol 10 (1) ◽  
pp. 35
Author(s):  
Zhigang Zeng ◽  
Zuxing Chen ◽  
Haiyan Qi
Keyword(s):  
Okinawa Trough ◽  
Volcanic Rocks ◽  
Hydrothermal Systems ◽  
Sulfide Deposits ◽  
The Okinawa Trough ◽  
Supergene Enrichment ◽  
Seawater Environment ◽  
Back Arc ◽  
Enrichment Process

The in situ element concentrations and the sulfur (S), and lead (Pb) isotopic compositions in anglesite were investigated for samples from seafloor hydrothermal fields in the Okinawa Trough (OT), Western Pacific. The anglesite grains are of two kinds: (1) low Pb/high S primary hydrothermal anglesite (PHA), which is formed by mixing of fluid and seawater, and (2) high Pb/low S secondary supergene anglesite (SSA), which is the product of low-temperature (<100 °C) alteration of galena in the seawater environment. The Ag and Bi in the SSA go through a second enrichment process during the formation of high Pb/low S anglesite by galena alteration, indicating that the SSA and galena, which may be the major minerals host for considerable quantities of Ag and Bi, are potentially Ag-Bi-enriched in the back-arc hydrothermal field. Moreover, REEs, S and Pb in the OT anglesite are likely to have been leached by fluids from local sub-seafloor volcanic rocks and/or sediments. A knowledge of the anglesite is useful for understanding the influence of volcanic rocks, sediments and altered subducted oceanic plate in hydrothermal systems, showing how trace metals behave during the formation of secondary minerals.

scholarly journals A Systematic Assessment of Stable Sr Isotopic Compositions of Vent Fluids in Arc/Back-Arc Hydrothermal Systems: Effects of Host Rock Type, Phase Separation, and Overlying Sediment

2020 ◽  
Vol 8 ◽  
Author(s):  
Toshihiro Yoshimura ◽  
Shigeyuki Wakaki ◽  
Tsuyoshi Ishikawa ◽  
Toshitaka Gamo ◽  
Daisuke Araoka ◽  
...  
Keyword(s):  
Host Rock ◽  
Okinawa Trough ◽  
Volcanic Rocks ◽  
Hydrothermal Systems ◽  
Systematic Assessment ◽  
Average Value ◽  
Carbonate Sedimentation ◽  
The North ◽  
Back Arc ◽  
Hydrothermal Fields

Variations in the stable isotopic composition of seawater Sr (δ88Sr) is a new tool for estimating the rates of global carbonate sedimentation over geologic time, yet the isotope compositions of the major sources and sinks of Sr to the world oceans are still in need of further constraint. We report δ88Sr values of vent fluids from arc/back-arc seafloor hydrothermal systems in the western Pacific. In the sediment-starved hydrothermal fields of the Manus Basin, Izu-Bonin Arc, and Mariana Trough, the δ88Sr values of end-member fluids for each site showed little variation (0.29–0.30‰) and were close to the average value of oceanic volcanic rocks, reflecting dissolved Sr sourced from host rocks. Chlorine-depleted fluids from phase-separated hydrothermal systems in the North Fiji Basin had the end-member δ88Sr values of 0.26, 0.28, and 0.29‰. Thus, both sediment-starved and phase-separated vent fluids had the end-member δ88Sr values indistinguishable from or very close to the range of oceanic volcanic rocks. Therefore, the δ88Sr compositions in these hydrothermal sites are controlled predominantly by Sr sourced from host rock with a small influence from secondary mineral precipitation/re-dissolution. Fluids from the sediment-hosted hydrothermal fields of the Okinawa Trough, however, were characterized by low δ88Sr values of approximately 0.22‰ and high 87Sr/86Sr ratios, indicating interactions with sedimentary carbonates. As for the modern oceanic δ88Sr budget, the sediment-hosted sites lower the global hydrothermal δ88Sr. Since both sediment-starved and -hosted hydrothermal systems provide a long-term control on the global Sr cycle, the end-member δ88Sr value is an important constraint on the evolution of Sr cycling in past oceans.

scholarly journals Zircon record of an Archaean crustal fragment and supercontinent amalgamation in quaternary back-arc volcanic rocks

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Zhi-gang Zeng ◽  
Zu-xing Chen ◽  
Yu-xiang Zhang
Keyword(s):  
Continental Crust ◽  
Okinawa Trough ◽  
Volcanic Rocks ◽  
Parental Magma ◽  
The Okinawa Trough ◽  
O Isotopes ◽  
Back Arc ◽  
First Time ◽  
Integrated Study

AbstractMagmatism has profoundly influenced the evolution of the geosphere, hydrosphere, atmosphere, and biosphere in back-arc basins. However, the timing of the magmatism in the Okinawa Trough (OT) is not well constrained by the age spectra of zircons. Here, for the first time, we carry out an integrated study combining in situ analysis of zircon U–Th–Pb and Hf–O isotopes, and trace element compositions of zircons from the volcanic rocks from the southernmost part of the OT. We found that the young (< 100 ka) zircons in these volcanic rocks have old (108 Ma to 2.7 Ga) inherited cores, which were captured as the magma ascended through the rifting continental crust. In particular, the inherited Archean zircons strongly suggest that remnants of the old East Asian continental blocks underlie the embryonic crustal rifting zone. Moreover, the ages of most of the inherited zircons correspond to five supercontinent amalgamation events. Specifically, the Archaean inherited zircons, which have positive εHf(t) and low δ18O values, correspond to the formation of juvenile continental crust. In contrast, the negative εHf(t) and high δ18O values of the post-Archaean inherited zircons indicate that their parental magma contained recycled older crust due to the enhanced crust-mantle interactions during the evolution of the early continental crust. Therefore, the inherited zircons in the back-arc volcanic rocks not only reflect the evolution of the local magmatism, but they also contain a record of the Archaean crustal fragment and of several global continental amalgamation events.

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

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 103
Author(s):  
Nikolai Berdnikov ◽  
Victor Nevstruev ◽  
Pavel Kepezhinskas ◽  
Ivan Astapov ◽  
Natalia Konovalova
Keyword(s):  
Iron Oxide ◽  
Subduction Zones ◽  
Gold Mineralization ◽  
Russian Far East ◽  
Far East ◽  
Volcanic Rocks ◽  
Liquid Immiscibility ◽  
Explosive Volcanism ◽  
Deep Roots ◽  
Scientific Debate

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.

Le terrane de Slide Mountain (Cordillères canadiennes) : une lithosphère océanique marquée par des points chauds

2003 ◽  
Vol 40 (6) ◽  
pp. 833-852 ◽  
Author(s):  
M Tardy ◽  
H Lapierre ◽  
D Bosch ◽  
A Cadoux ◽  
A Narros ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Oceanic Island ◽  
Light Rare Earth ◽  
Isotopic Compositions ◽  
Incompatible Elements ◽  
Depleted Mantle ◽  
Mantle Sources ◽  
British Colombia ◽  
Ultramafic Cumulates ◽  
Back Arc

The Slide Mountain Terrane consists of Devonian to Permian siliceous and detrital sediments in which are interbedded basalts and dolerites. Locally, ultramafic cumulates intrude these sediments. The Slide Mountain Terrane is considered to represent a back-arc basin related to the Quesnellia Paleozoic arc-terrane. However, the Slide Mountain mafic volcanic rocks exposed in central British Colombia do not exhibit features of back-arc basin basalts (BABB) but those of mid-oceanic ridge (MORB) and oceanic island (OIB) basalts. The N-MORB-type volcanic rocks are characterized by light rare-earth element (LREE)-depleted patterns, La/Nb ratios ranging between 1 and 2. Moreover, their Nd and Pb isotopic compositions suggest that they derived from a depleted mantle source. The within-plate basalts differ from those of MORB affinity by LREE-enriched patterns; higher TiO2, Nb, Ta, and Th abundances; lower εNd values; and correlatively higher isotopic Pb ratios. The Nd and Pb isotopic compositions of the ultramafic cumulates are similar to those of MORB-type volcanic rocks. The correlations between εNd and incompatible elements suggest that part of the Slide Mountain volcanic rocks derive from the mixing of two mantle sources: a depleted N-MORB type and an enriched OIB type. This indicates that some volcanic rocks of the Slide Mountain basin likely developed from a ridge-centered or near-ridge hotspot. The activity of this hotspot is probably related to the worldwide important mantle plume activity that occurred at the end of Permian times, notably in Siberia.

Active tectonics and volcanism in the southernmost Okinawa Trough back-arc basin derived from deep-towed sonar surveys

2021 ◽  
pp. 229047
Author(s):  
Ching-Hui Tsai ◽  
Shu-Kun Hsu ◽  
Song-Chuen Chen ◽  
Shiou-Ya Wang ◽  
Lien-Kai Lin ◽  
...  
Keyword(s):  
Okinawa Trough ◽  
Active Tectonics ◽  
Back Arc
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