scholarly journals Metals in subduction related magmatism: Insights from melt inclusions and associated glassy groundmass from the Southern Kermadec Arc, New Zealand

2021 ◽  
Author(s):  
◽  
Jacob Leath
Keyword(s):  
Trace Elements ◽  
Base Metal ◽  
Mantle Source ◽  
Melt Inclusions ◽  
Crystal Fractionation ◽  
Base Metals ◽  
Arc Magmas ◽  
Vms Deposits ◽  
Arc Setting ◽  
Back Arc

<p>The southern Kermadec Arc – Havre Trough (SKAHT) is an intra-oceanic arc – back-arc system where the Pacific plate is subducting beneath the Australian plate. The Kermadec volcanic arc front consists of 33 volcanic centres, four of which host hydrothermal mineralization (Brothers, Haungaroa, Rumble II West, and Clark) such as volcanogenic massive sulfide (VMS) deposits, which are characterised by high concentrations of base and precious metals (e.g., Au, Cu, Zn, Pb). The sources of these metals are strongly tied to the metal contents within underlying magmatic rocks and associated magmatic systems with which the hydrothermal fluids interact. Understanding the sources, movements, and accumulation of metals associated with porphyry copper and exhalative base metal deposits within a subduction – arc setting remains limited.  This study reports major, trace, and volatile element contents in basaltic groundmass glasses and olivine-hosted melt inclusions from lavas from four locations within the arc – back-arc setting of the SKAHT. The focus is on understanding the controls on base metal (Pb, Cu, Zn, Mo, V) contents in the magmas. The sample locations, Rumble III and Rumble II West volcanoes, and back-arc Basins D and I, form an arc-perpendicular transect extending from arc front into the back-arc. The analysed melt inclusion and groundmass glasses are all basalt to basaltic andesite in composition, with back-arc basin samples more mafic than arc front volcano samples. The magmatic evolution of the melts is primarily controlled by crystal fractionation of olivine + pyroxene + plagioclase. All glasses have undergone variable degassing, indicated by an absence of detectable CO₂ and curvilinear decreases in S contents with increasing SiO₂. Of the volatile phases analysed, only Cl appears unaffected by degassing.  Distinct compositional differences are apparent between arc front and back-arc melts. The arc front magmas formed from higher degrees of melting of a less fertile mantle source and are more enriched in trace elements then the back-arc magmas due to greater additions of slab-derived aqueous fluids to their source. Magmas from a single arc front volcano (Rumble II West) incorporate melts that have tapped variably enriched sources, indicating heterogeneity of the mantle at small scales. Significant variation in mantle composition, however, is also apparent laterally along strike of the arc. Rumble III volcano and Basin I lie on an arc-perpendicular transect south of Rumble II West volcano and Basin D. Their greater enrichment in trace elements and higher concentrations of base metals than Rumble II West and Basin D lavas can be attributed to higher fluxes of subduction derived components.  Base metals (Cu, Zn, Pb, Mo, and V) are variably enriched in the SKAHT melts compared with typical mid-ocean ridge basalts with relative enrichments in the order Pb >> Cu > Mo, V > Zn. All metals appear to be affected by mantle metasomatism related to slab-derived fluids, either directly from slab components introduced to the mantle source (e.g., Pb) or through mobilisation of metals within the ambient mantle wedge. The apparently compatible behaviour of Zn, Cu, and V in the mantle means that these elements may be enriched in arc front magmas relative to back-arc magmas by higher degrees of partial melting and/or melting of more depleted sources.  All base metals behave incompatibly in the magma during crystal fractionation between 48 – 56 wt.% SiO₂. Lead and Cu concentrations, however, begin to level out from ~ 52 wt.% SiO₂ suggesting some subsequent loss to fractionating volatile phases as metal sulfide complexes. Rumble III samples show a decrease in metal concentration (Pb, Cu, V), from melt inclusions to groundmass glasses, suggestive of more significant loss associated with sulfur degassing.  Although other factors such as heat generation, hydrothermal flow, fault systems, and magma venting are key in the development of VMS deposits, this study shows that variations in subduction parameters can significantly affect metal concentrations in arc magmas that may host hydrothermal systems, and hence the amount of metals available to be scavenged into the deposits.</p>

scholarly journals Metals in subduction related magmatism: Insights from melt inclusions and associated glassy groundmass from the Southern Kermadec Arc, New Zealand

2021 ◽  
Author(s):  
◽  
Jacob Leath
Keyword(s):  
Trace Elements ◽  
Base Metal ◽  
Mantle Source ◽  
Melt Inclusions ◽  
Crystal Fractionation ◽  
Base Metals ◽  
Arc Magmas ◽  
Vms Deposits ◽  
Arc Setting ◽  
Back Arc

<p>The southern Kermadec Arc – Havre Trough (SKAHT) is an intra-oceanic arc – back-arc system where the Pacific plate is subducting beneath the Australian plate. The Kermadec volcanic arc front consists of 33 volcanic centres, four of which host hydrothermal mineralization (Brothers, Haungaroa, Rumble II West, and Clark) such as volcanogenic massive sulfide (VMS) deposits, which are characterised by high concentrations of base and precious metals (e.g., Au, Cu, Zn, Pb). The sources of these metals are strongly tied to the metal contents within underlying magmatic rocks and associated magmatic systems with which the hydrothermal fluids interact. Understanding the sources, movements, and accumulation of metals associated with porphyry copper and exhalative base metal deposits within a subduction – arc setting remains limited.  This study reports major, trace, and volatile element contents in basaltic groundmass glasses and olivine-hosted melt inclusions from lavas from four locations within the arc – back-arc setting of the SKAHT. The focus is on understanding the controls on base metal (Pb, Cu, Zn, Mo, V) contents in the magmas. The sample locations, Rumble III and Rumble II West volcanoes, and back-arc Basins D and I, form an arc-perpendicular transect extending from arc front into the back-arc. The analysed melt inclusion and groundmass glasses are all basalt to basaltic andesite in composition, with back-arc basin samples more mafic than arc front volcano samples. The magmatic evolution of the melts is primarily controlled by crystal fractionation of olivine + pyroxene + plagioclase. All glasses have undergone variable degassing, indicated by an absence of detectable CO₂ and curvilinear decreases in S contents with increasing SiO₂. Of the volatile phases analysed, only Cl appears unaffected by degassing.  Distinct compositional differences are apparent between arc front and back-arc melts. The arc front magmas formed from higher degrees of melting of a less fertile mantle source and are more enriched in trace elements then the back-arc magmas due to greater additions of slab-derived aqueous fluids to their source. Magmas from a single arc front volcano (Rumble II West) incorporate melts that have tapped variably enriched sources, indicating heterogeneity of the mantle at small scales. Significant variation in mantle composition, however, is also apparent laterally along strike of the arc. Rumble III volcano and Basin I lie on an arc-perpendicular transect south of Rumble II West volcano and Basin D. Their greater enrichment in trace elements and higher concentrations of base metals than Rumble II West and Basin D lavas can be attributed to higher fluxes of subduction derived components.  Base metals (Cu, Zn, Pb, Mo, and V) are variably enriched in the SKAHT melts compared with typical mid-ocean ridge basalts with relative enrichments in the order Pb >> Cu > Mo, V > Zn. All metals appear to be affected by mantle metasomatism related to slab-derived fluids, either directly from slab components introduced to the mantle source (e.g., Pb) or through mobilisation of metals within the ambient mantle wedge. The apparently compatible behaviour of Zn, Cu, and V in the mantle means that these elements may be enriched in arc front magmas relative to back-arc magmas by higher degrees of partial melting and/or melting of more depleted sources.  All base metals behave incompatibly in the magma during crystal fractionation between 48 – 56 wt.% SiO₂. Lead and Cu concentrations, however, begin to level out from ~ 52 wt.% SiO₂ suggesting some subsequent loss to fractionating volatile phases as metal sulfide complexes. Rumble III samples show a decrease in metal concentration (Pb, Cu, V), from melt inclusions to groundmass glasses, suggestive of more significant loss associated with sulfur degassing.  Although other factors such as heat generation, hydrothermal flow, fault systems, and magma venting are key in the development of VMS deposits, this study shows that variations in subduction parameters can significantly affect metal concentrations in arc magmas that may host hydrothermal systems, and hence the amount of metals available to be scavenged into the deposits.</p>

scholarly journals Evidence for voluminous bimodal pyroclastic volcanism during rifting of a Paleoproterozoic arc at Snow Lake, Manitoba

2017 ◽  
Vol 54 (6) ◽  
pp. 654-676 ◽  
Author(s):  
Kate E. Rubingh ◽  
Harold L. Gibson ◽  
Bruno Lafrance
Keyword(s):  
Massive Sulfide ◽  
Hydrothermal Activity ◽  
Stratigraphic Correlation ◽  
Pyroclastic Deposits ◽  
Volcanic Event ◽  
Vms Deposits ◽  
Flin Flon ◽  
Arc Setting ◽  
Gold Producer ◽  
Back Arc

The thrust-bounded McLeod Road – Birch Lake (MB) sequence occurs within the Paleoproterozoic Snow Lake arc (SLA) assemblage of the Flin Flon belt. Stratigraphic correlation of volcanic strata of the MB sequence with strata of the thrust-bounded Chisel sequence indicates that distinctive, submarine, eruption-fed, pyroclastic flow deposits are more extensive and voluminous than previously recognized (>10 km3). These voluminous felsic pyroclastic deposits define a distinct magmatic and explosive volcanic event during bimodal volcanism that accompanied rifting of the SLA. The felsic pyroclastic deposits define the remnants of a basin, or of nested basins, that formed during arc rifting and subsidence, and their eruption immediately preceded formation of the Chisel sequence volcanogenic massive sulfide (VMS) deposits. Although the Chisel sequence ore interval is recognized in the MB sequence, the lack of VMS-related alteration indicates that VMS hydrothermal activity was restricted to the Chisel portion of the basin. However, the MB sequence is host to the younger Snow Lake gold mine, a 1.4M oz (43 699 kg) gold producer. The overlying MORB-like Birch Lake basalts, if conformable with the MB sequence, may represent a progression from a rifted-arc to a back-arc setting. However, if they are thrust fault bounded, then they may represent the initial phases of arc-rifting, prior to the voluminous felsic pyroclastic eruptions. Correlation and integrity of stratigraphy between the thrust-bounded MB and SLA sequences indicates that the bounding thrust faults, which developed during accretionary processes, have less regional significance than previously interpreted.

The heterogeneous nature of the Southern Tyrrhenian mantle: Evidence from olivine-hosted melt inclusions from back-arc magmas of the Marsili seamount

Lithos ◽  
2010 ◽  
Vol 118 (1-2) ◽  
pp. 1-16 ◽  
Author(s):  
Teresa Trua ◽  
Roberto Clocchiatti ◽  
Pierre Schiano ◽  
Luisa Ottolini ◽  
Michael Marani
Keyword(s):  
Melt Inclusions ◽  
Arc Magmas ◽  
Heterogeneous Nature ◽  
Back Arc

Trace element composition of clinopyroxene in gabbros and dolerites of the Tortuga Ophiolitic Complex, southernmost Patagonia.

2021 ◽  
Author(s):  
Fernanda Torres Garcia ◽  
Mauricio Calderón ◽  
Leonardo Fadel Cury ◽  
Thomas Theye ◽  
Joachim Opitz ◽  
...  
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Partial Melting ◽  
Mantle Source ◽  
Trace Element Composition ◽  
Element Composition ◽  
Mid Ocean Ridge ◽  
Back Arc ◽  
Ocean Ridge ◽  
Ophiolitic Complex

&lt;p&gt;During the Upper Jurassic-Lower Cretaceous times the western margin of Gondwana in southern Patagonia experienced extreme lithospheric extension and generation of rift and marginal back-arc basins. The ophiolitic complexes of the Rocas Verdes basin comprises incomplete ophiolite pseudostratigraphy lacking ultramafic rocks. The Tortuga Ophiolitic Complex, the southernmost seafloor remnant of the Rocas Verdes basin, record the most advanced evolutionary stage of the back-arc basin evolution in a mid-ocean ridge-type setting. The base of the Tortuga Complex consists of massive and layered gabbros, most of which are two pyroxene and olivine gabbros, leucogabbros, and clinopyroxene troctolites intruded by dikes of basalt and diabase with chilled margins. We present new major and trace element composition of clinopyroxene from the gabbros and sheeted dikes complexes to assess the geochemical affinity of parental basaltic magmas. Clinopyroxene in gabbros is mostly augite and have Al contents of 0.06-0.14 a.p.f.u. and Mg# of 80-92. Clinopyroxene in dolerites in the sheeted dike unit (augite and diopside) have Al content of 0.11-0.12 a.p.f.u. and Mg# of 85-92. Some immobile trace elements (e.g. Zr, Ti, Y) are sensitive to the degree of partial melting and mantle source composition, and can be used as a proxy for distinguishing tectonic environments. The Ti+Cr vs. Ca diagram, coupled with moderate-high TiO&lt;sub&gt;2&lt;/sub&gt; content of clinopyroxene (0.4-1.4 wt.%) suggests their generation in mid-oceanic ridge-type environment (cf. Beccaluva et al., 1989).&amp;#160; The high Ti/Zr ratios (of ~4-11) coupled with low Zr contents (~0.2-1.1) are expected for higher degrees of partial melting or for melting of more depleted mantle sources. Conversely, low Zr/Y ratios (0.05-0.13) plot between the range of arc basalts. Chondrite-normalized REE patterns in clinopyroxene display a strong depletion of LREE compared to HREE and have an almost flat pattern in the MREE to HREE with a positive Eu (Eu*= 0.9-1.1) anomaly, indicating that clinopyroxene crystallized from a strongly depleted mid-ocean-ridge-type basalt, formed by extensive fractional melting of the mantle source and/or fractional crystallization and accumulation of anhydrous phases. The general trend of the incompatible trace elements patterns exhibit depletion in LILEs, minor HFSEs depletion, positive anomaly of Rb and negative anomalies in Ba, Zr, Ti and Nb, consistent with their generation from a refractory mantle source barely influenced by subduction components derived from the oceanic slab. This agrees with basalt generation in a back-arc basin located far away from the convergent margin. This study was supported by the Fondecyt grant 1161818 and the Anillo Project ACT-105.&lt;/p&gt;

Metabentonites in the Moffat Shale Group, Southern Uplands of Scotland: Geochemical evidence of ensialic marginal basin volcanism

1990 ◽  
Vol 127 (3) ◽  
pp. 259-271 ◽  
Author(s):  
R. J. Merriman ◽  
B. Roberts
Keyword(s):  
Trace Elements ◽  
Trace Element ◽  
Late Ordovician ◽  
Trace Element Data ◽  
Geochemical Evidence ◽  
Sialic Crust ◽  
Element Data ◽  
High Concentrations ◽  
Arc Setting ◽  
Back Arc

AbstractMetabentonites occur extensively in the Moffat Shale Group of the Southern Uplands of Scotland. At Dob's Linn 135 metabentonite beds, 1–50 cm thick, occur in Ashgill to Llandovery strata, representing an aggregate thickness of 6 m of compacted ash accumulated over approximately 25 Ma. The metabentonites are characterized by relatively high concentrations of trace elements, including Ba, Cs, Hf, Nb, Rb, Ta, Th, U, Y, Zr and REEs, which were inherited from evolved vitric ash. Immobile trace element data indicate that a spectrum of silicic ash compositions accumulated, ranging from subalkaline to mildly peralkaline. In the late Ordovician N. gracilis to G. persculptus biozones, subalkaline ash falls predominated, whereas peralkaline ash falls predominated in the Llandovery (Silurian) P. acuminatus to M. convolutes biozones, giving way to predominantly subalkaline ash falls during accumulation of the M. sedgwickii to R. maximus biozones. Changeovers in the dominant ash types are marked by increased proportions of ash. The magmas from which the ash types evolved were generated in an ensialic arc transitional to a back-arc setting, and involved attenuated sialic crust and mantle characterized by variable depletion in HFS elements. Lithological, petrological and REE characteristics suggest that the Moffat Shale Group is not exclusively pelagic in origin and probably accumulated in a back-arc basin bordering an ensialic arc terrane.

Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland

1999 ◽  
pp. 65-78
Author(s):  
Henrik Rasmussen ◽  
Lars Frimodt Pedersen
Keyword(s):  
Tectonic Setting ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
West Greenland ◽  
North West ◽  
North East ◽  
Metavolcanic Rocks ◽  
Arc Setting ◽  
Area North ◽  
Back Arc

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Rasmussen, H., & Frimodt Pedersen, L. (1999). Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 65-78. https://doi.org/10.34194/ggub.v181.5114 _______________ Two Archaean supracrustal sequences in the area north-east of Disko Bugt, c. 1950 and c. 800 m in thickness, are dominated by pelitic and semipelitic mica schists, interlayered with basic metavolcanic rocks. A polymict conglomerate occurs locally at the base of one of the sequences. One of the supracrustal sequences has undergone four phases of deformation; the other three phases. In both sequences an early phase, now represented by isoclinal folds, was followed by north-west-directed thrusting. A penetrative deformation represented by upright to steeply inclined folds is only recognised in one of the sequences. Steep, brittle N–S and NW–SE striking faults transect all rock units including late stage dolerites and lamprophyres. Investigation of major- and trace-element geochemistry based on discrimination diagrams for tectonic setting suggests that both metasediments and metavolcanic rocks were deposited in an environment similar to a modern back-arc setting.

scholarly journals Inverted Basins by Africa–Eurasia Convergence at the Southern Back-Arc Tyrrhenian Basin

Geosciences ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 117
Author(s):  
Maria Filomena Loreto ◽  
Camilla Palmiotto ◽  
Filippo Muccini ◽  
Valentina Ferrante ◽  
Nevio Zitellini
Keyword(s):  
Seismic Reflection ◽  
Magnetic Data ◽  
Normal Faults ◽  
Sedimentary Sequence ◽  
Initiation Zone ◽  
Arc Setting ◽  
Seismic Reflection Profiles ◽  
Back Arc ◽  
Flower Structures ◽  
Tyrrhenian Basin

The southern part of Tyrrhenian back-arc basin (NW Sicily), formed due to the rifting and spreading processes in back-arc setting, is currently undergoing contractional tectonics. The analysis of seismic reflection profiles integrated with bathymetry, magnetic data and seismicity allowed us to map a widespread contractional tectonics structures, such as positive flower structures, anticlines and inverted normal faults, which deform the sedimentary sequence of the intra-slope basins. Two main tectonic phases have been recognised: (i) a Pliocene extensional phase, active during the opening of the Vavilov Basin, which was responsible for the formation of elongated basins bounded by faulted continental blocks and controlled by the tear of subducting lithosphere; (ii) a contractional phase related to the Africa-Eurasia convergence coeval with the opening of the Marsili Basin during the Quaternary time. The lithospheric tear occurred along the Drepano paleo-STEP (Subduction-Transform-Edge-Propagator) fault, where the upwelling of mantle, intruding the continental crust, formed a ridge. Since Pliocene, most of the contractional deformation has been focused along this ridge, becoming a good candidate for a future subduction initiation zone.

scholarly journals 3D Geological Model of the Touro Cu Deposit, A World-Class Mafic-Siliciclastic VMS Deposit in the NW of the Iberian Peninsula

Minerals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 85
Author(s):  
Mónica Arias ◽  
Pablo Nuñez ◽  
Daniel Arias ◽  
Pablo Gumiel ◽  
Cesar Castañón ◽  
...  
Keyword(s):  
3D Model ◽  
Massive Sulfide ◽  
Geological Model ◽  
Drill Core ◽  
World Class ◽  
Hinge Zone ◽  
Arc Setting ◽  
Using Data ◽  
Back Arc ◽  
Host Rocks

The Touro volcanogenic massive sulfide (VMS) deposit is located in the NW of the Iberian Variscan massif in the Galicia-Trás-os-Montes Zone, an amalgamation of several allochthonous terrains. The Órdenes complex is the most extensive of the allochthone complexes, and amphibolites and paragneisses host the deposit, characterized as being massive or semimassive (stringers) sulfides, mostly made up of pyrrhotite and chalcopyrite. The total resources are 103 Mt, containing 0.41% copper. A 3D model of the different orebodies and host rocks was generated using data from 1090 drill core logs. The model revealed that the structure of the area is a N–S-trending antiform. The orebodies crop out in the limbs and in the hinge zone. The mineralized structures are mostly tabular, up to 100 m in thickness and subhorizontal. Based on the petrography, geochemistry and the 3D model, the Touro deposit is classified as a VMS of the mafic-siliciclastic type formed in an Ordovician back-arc setting, which was buried and metamorphosed in Middle Devonian.

Tholeiitic volcanic rocks of the late Archean Blake River Group, southern Abitibi greenstone belt: origin and geodynamic implications

1992 ◽  
Vol 29 (7) ◽  
pp. 1448-1458 ◽  
Author(s):  
M. R. Laflèche ◽  
C. Dupuy ◽  
J. Dostal
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Incompatible Trace Element ◽  
Progressive Change ◽  
Abitibi Greenstone Belt ◽  
Mid Ocean Ridge ◽  
Compositional Variations ◽  
Arc Setting ◽  
Back Arc ◽  
Ocean Ridge

The late Archean Blake River Group volcanic sequence forms the uppermost part of the southern Abitibi greenstone belt in Quebec. The group is mainly composed of mid-ocean-ridge basalt (MORB)-like tholeiites that show a progressive change of several incompatible trace element ratios (e.g., Nb/Th, Nb/Ta, La/Yb, and Zr/Y) during differentiation. The compositional variations are inferred to be the result of fractional crystallization coupled with mixing–contamination of tholeiites by calc-alkaline magma which produced the mafic–intermediate lavas intercalated with the tholeiites in the uppermost part of the sequence. The MORB-like tholeiites were probably emplaced in a back-arc setting.

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