Development of an Ancient Back‐Arc Basin Overlying Continental Crust: The Archean Peltier Formation, Northwest Territories, Canada

Ordovician metamorphic rocks of the Casco Bay Group are exposed in an approximately 170 km long NE-trending belt (Liberty-Orrington belt) in southern and south-central Maine. Geochemical analysis of rocks within the Spring Point Formation (469±3 Ma) of the Casco Bay Group indicate that it is an assemblage of metamorphosed bimodal volcanic rocks. The mafic rocks (originally basalts) have trace element and Nd isotopic characteristics consistent with derivation from a mantle source enriched by a crustal and/or subduction component. The felsic rocks (originally rhyolites and dacites) were likely generated through partial melting of continental crust in response to intrusion of the mafic magma. Relatively low initial εNd values for both the mafic (−1.3 to +0.6) and felsic (−4.1 to −3.8) rocks suggest interactions with Gander zone continental crust and support a correlation between the Casco Bay Group and the Bathurst Supergroup in the Miramichi belt of New Brunswick. This correlation suggests that elements of the Early to Middle Ordovician Tetagouche-Exploits back-arc basin can be traced well into southern Maine. A possible tectonic model for the evolution of the Casco Bay Group involves the initiation of arc volcanism in Early Ordovician time along the Gander continental margin on the eastern side of the Iapetus Ocean basin. Slab rollback and trenchward migration of arc magmatism initiated crustal thinning and rifting of the volcanic arc around 470 Ma and resulted in the eruption of the Spring Point volcanic rocks in a back-arc tectonic setting.

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Pliocene granodioritic knoll with continental crust affinities discovered in the intra-oceanic Izu–Bonin–Mariana Arc: Syntectonic granitic crust formation during back-arc rifting

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2015.05.019 ◽

2015 ◽

Vol 424 ◽

pp. 84-94 ◽

Cited By ~ 13

Author(s):

Kenichiro Tani ◽

Daniel J. Dunkley ◽

Qing Chang ◽

Alexander R.L. Nichols ◽

Hiroshi Shukuno ◽

...

Keyword(s):

Continental Crust ◽

Crust Formation ◽

Mariana Arc ◽

Back Arc

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Zircon Record of Supercontinent Amalgamation in Back-arc Volcanic Rocks

10.21203/rs.3.rs-109172/v1 ◽

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.

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Crustal assimilation in the Burnt Lake metavolcanics, Grenville Province, southeastern Ontario, and its tectonic significance

Canadian Journal of Earth Sciences ◽

10.1139/e17-101 ◽

1997 ◽

Vol 34 (9) ◽

pp. 1272-1285 ◽

Cited By ~ 5

Author(s):

T. E. Smith ◽

P. E. Holm ◽

N. M. Dennison ◽

M. J. Harris

Keyword(s):

Rare Earth ◽

Trace Element ◽

Partial Melting ◽

Continental Crust ◽

Fractional Crystallization ◽

Volcanic Rocks ◽

Lake Area ◽

Depleted Mantle ◽

Mafic Magmas ◽

Back Arc

Three intimately interbedded suites of volcanic rocks are identified geochemically in the Burnt Lake area of the Belmont Domain in the Central Metasedimentary Belt, and their petrogenesis is evaluated. The Burnt Lake back-arc tholeiitic suite comprises basalts similar in trace element signature to tholeiitic basalts emplaced in back-arc basins formed in continental crust. The Burnt Lake continental tholeiitic suite comprises basalts and andésites similar in trace element composition to continental tholeiitic sequences. The Burnt Lake felsic pyroclastic suite comprises rhyolitic pyroclastics having major and trace element compositions that suggest that they were derived from crustal melts. Rare earth element models suggest that the Burnt Lake back-arc tholeiitic rocks were formed by fractional crystallization of mafic magmas derived by approximately 5% partial melting of an amphibole-bearing depleted mantle, enriched in light rare earth elements by a subduction component. The modelling also suggests that the Burnt Lake continental tholeiitic rocks were formed by contamination – fractional crystallization of mixtures of mafic magmas, derived by ~3% partial melting of the subduction-modified source, and rhyolitic crustal melts. These models are consistent with the suggestion that the Belmont Domain of the Central Metasedimentary Belt formed as a back-arc basin by attenuation of preexisting continental crust above a westerly dipping subduction zone.

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The occurrence of Mesozoic oceanic floor and ancient continental crust on South Georgia

Geological Magazine ◽

10.1017/s0016756800044770 ◽

1977 ◽

Vol 114 (3) ◽

pp. 203-208 ◽

Cited By ~ 20

Author(s):

B. C. Storey ◽

B. F. Mair ◽

C. M. Bell

Keyword(s):

Continental Crust ◽

Early Cretaceous ◽

Regional Metamorphism ◽

Igneous Rocks ◽

Polyphase Deformation ◽

South Georgia ◽

Back Arc

SummaryThe Larsen Harbour Formation of southern South Georgia is part of an ophiolite sequence of submarine lavas and sheeted dykes emplaced into metasedimentary country rocks. The metasediments are remnants of a pre-Cretaceous continental crust which had been subject to regional metamorphism and polyphase deformation prior to intrusion by a variety of acid and basic igneous rocks (roots of the ophiolitic sequence). It is proposed that the segment of continental crust and the Larsen Harbour Formation formed the floor of a back-arc basin which was infilled during Early Cretaceous time by a thick sequence of volcaniclastic sediments (Cumberland Bay Formation).

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Ridge Jumps and Mantle Exhumation in Back-Arc Basins

Geosciences ◽

10.3390/geosciences11110475 ◽

2021 ◽

Vol 11 (11) ◽

pp. 475

Author(s):

Valentina Magni ◽

John Naliboff ◽

Manel Prada ◽

Carmen Gaina

Keyword(s):

Continental Crust ◽

Oceanic Crust ◽

Numerical Models ◽

Spreading Ridge ◽

Transient Nature ◽

Mid Ocean Ridge ◽

Thinned Continental Crust ◽

Mantle Exhumation ◽

Back Arc ◽

Ocean Ridge

Back-arc basins in continental settings can develop into oceanic basins, when extension lasts long enough to break up the continental lithosphere and allow mantle melting that generates new oceanic crust. Often, the basement of these basins is not only composed of oceanic crust, but also of exhumed mantle, fragments of continental crust, intrusive magmatic bodies, and a complex mid-ocean ridge system characterised by distinct relocations of the spreading centre. To better understand the dynamics that lead to these characteristic structures in back-arc basins, we performed 2D numerical models of continental extension with asymmetric and time-dependent boundary conditions that simulate episodic trench retreat. We find that, in all models, episodic extension leads to rift and/or ridge jumps. In our parameter space, the length of the jump ranges between 1 and 65 km and the timing necessary to produce a new spreading ridge varies between 0.4 and 7 Myr. With the shortest duration of the first extensional phase, we observe a strong asymmetry in the margins of the basin, with the margin further from trench being characterised by outcropping lithospheric mantle and a long section of thinned continental crust. In other cases, ridge jump creates two consecutive oceanic basins, leaving a continental fragment and exhumed mantle in between the two basins. Finally, when the first extensional phase is long enough to form a well-developed oceanic basin (>35 km long), we observe a very short intra-oceanic ridge jump. Our models are able to reproduce many of the structures observed in back-arc basins today, showing that the transient nature of trench retreat that leads to episodes of fast and slow extension is the cause of ridge jumps, mantle exhumation, and continental fragments formation.

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Convergent margin on southeastern Laurentia during the Mesoproterozoic: tectonic implications

Canadian Journal of Earth Sciences ◽

10.1139/e99-067 ◽

2000 ◽

Vol 37 (2-3) ◽

pp. 359-383 ◽

Cited By ~ 114

Author(s):

Toby Rivers ◽

David Corrigan

Keyword(s):

Continental Crust ◽

Continental Margin ◽

Isotopic Signature ◽

Convergent Margin ◽

Grenville Province ◽

Magmatic Arc ◽

Marginal Basin ◽

Arc Setting ◽

Back Arc ◽

Dyke Swarms

A continental-margin magmatic arc is inferred to have existed on the southeastern (present coordinates) margin of Laurentia from Labrador to Texas from ~1500-1230 Ma, with part of the arc subsequently being incorporated into the 1190-990 Ma collisional Grenville Orogen. Outside the Grenville Province, where the arc is known as the Granite-Rhyolite Belt, it is undeformed, whereas within the Grenville Province it is deformed and metamorphosed. The arc comprises two igneous suites, an inboard, principally quartz monzonitic to granodioritic suite, and an outboard tonalitic to granodioritic suite. The quartz monzonite-granodiorite suite was largely derived from continental crust, whereas the tonalitic-granodiorite suite is calc-alkaline and has a juvenile isotopic signature. Available evidence from the Grenville Province suggests that the arc oscillated between extensional and compressional settings several times during the Mesoproterozoic. Back-arc deposits of several ages, that formed during relatively brief periods of extension, include (1) mafic dyke swarms subparallel to the arc; (2) continental sediments, bimodal volcanics and plateau basalts; (3) marine sediments and volcanics formed on stretched continental crust; and (4) ocean crust in a marginal basin. Closure of the back-arc basins occurred during the accretionary Pinwarian (~1495-1445 Ma) and Elzevirian (~1250-1190 Ma) orogenies, as well as during three pulses of crustal shortening associated with the 1190-990 Ma collisional Grenvillian Orogeny. During the Elzevirian Orogeny, closure of the Central Metasedimentary Belt marginal basin in the southeastern Grenville Province was marked by subduction-related magmatism as well as by imbrication of back-arc deposits. The presence of a continental-margin magmatic arc on southeastern Laurentia during the Mesoproterozoic implies that other coeval magmatism inboard from the arc took place in a back-arc setting. Such magmatism was widespread and chemically diverse and included large volume "anorogenic" anorthosite-mangerite-charnockite-granite (AMCG) complexes as well as small volume alkaline, quartz-saturated and -undersaturated "within-plate" granitoids. Recognition of the ~300 million year duration of the Mesoproterozoic convergent margin of southeastern Laurentia suggests that there may be useful parallels with the evolution of the Andes, which has been a convergent margin since the early Paleozoic.

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Silicic magmas of Protector Shoal, South Sandwich arc: indicators of generation of primitive continental crust in an island arc

Geological Magazine ◽

10.1017/s0016756806002925 ◽

2006 ◽

Vol 144 (1) ◽

pp. 179-190 ◽

Cited By ~ 31

Author(s):

P. T. LEAT ◽

R. D. LARTER ◽

I. L. MILLAR

Keyword(s):

Partial Melting ◽

Continental Crust ◽

Early Stage ◽

Geochemical Data ◽

The South ◽

Volcanic Arc ◽

Silicic Volcanic ◽

South Sandwich Islands ◽

Silicic Magmas ◽

Back Arc

Protector Shoal, the northernmost and most silicic volcano of the South Sandwich arc, erupted dacite–rhyolite pumice in 1962. We report geochemical data for a new suite of samples dredged from the volcano. Geochemically, the dredge and 1962 samples form four distinct magma groups that cannot have been related to each other, and are unlikely to have been related to a single basaltic parent, by fractional crystallization. Instead, the silicic rocks are more likely to have been generated by partial melting of basaltic lower crust within the arc. Trace element and Sr–Nd isotope data indicate that the silicic volcanics have compositions that are more similar to the volcanic arc than the oceanic basement formed at a back-arc spreading centre, and volcanic arc basalts are considered to be the likely source for the silicic magmas. The South Sandwich Islands are one of several intra-oceanic arcs (Tonga–Kermadec, Izu–Bonin) that have: (1) significant amounts of compositionally bimodal mafic–silicic volcanic products and (2) 6.0–6.5 km s−1P-wave velocity layers in their mid-crusts that have been imaged by wide-angle seismic surveys and interpreted as intermediate-silicic plutons. Geochemical and volume considerations indicate that both the silicic volcanics and plutonic layers were generated by partial melting of basaltic arc crust, representing an early stage in the fractionation of oceanic basalt to form continental crust.

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Seismic wide-angle constrains on the structure of the northern Sicily margin and Vavilov Basin: implications for the opening of the Tyrrhenian back-arc basin

10.5194/egusphere-egu2020-5130 ◽

2020 ◽

Author(s):

Ingo Grevemeyer ◽

Cesar Ranero ◽

Nevio Zitellini ◽

Valenit Sallares ◽

Manel Prada

Keyword(s):

Continental Crust ◽

Seismic Refraction ◽

Seismic Profile ◽

Passive Margin ◽

P Wave ◽

Tyrrhenian Sea ◽

Wide Angle ◽

Central Mediterranean ◽

The North ◽

Back Arc

<p>The Tyrrhenian Sea in the central Mediterranean Sea was form by Neogene slab roll-back of the retreating Ionian slab about 6 to 2 Myr ago. Yet, little is known about the structure of its southern margin off Sicily as well as back-arc extension and spreading in the southern Tyrrhenian Sea to the north of Sicily. The Sicilian margin is generally classified as a passive margin bounding a young back-arc basin. However, focal mechanisms from regional earthquakes suggest that the margins suffers presently from compressional tectonics. New seismic refraction and wide-angle data were collected along seismic profile WAS4 during the CHIANTI survey of the Spanish research vessel Sarmiento de Gamboa in 2015. The profile runs from the centre of the Tyrrhenian Sea &#8211; the Vavilov Basin &#8211; across the margin of Sicily, approaching the Gulf of Castellammare to the northwest of Sicily. Reanalyzed multi-channel seismic data supports compressional tectonics across a small basin paralleling the coastline of Sicily, revealing recent inversion of the Tyrrhenian Basin. Offshore of Sicily WAS4 indicates a roughly 120-140 km wide domain showing seismic P-wave velocities characteristic for continental crust (Vp ~4-6.7 km/s) and a base of crust defined by a wide-angle Moho reflection. Continental crust reaches a maximum thickness of 22 km to the north of the Gulf of Castellammare and is thinning to ~9 km to the north of the Ustica Ridge. The compressional belt occurs in continental crust to the south of Ustica Ridge. In the Vavilov Basin, a lithosphere was sample where seismic P-wave velocity increases from approx. 3-4 km/s to 7.5 km/s. This velocity depth-distribution clearly shows profound similarities to serpentinized mantle and hence un-roofed mantle. Thus, seismic constrains support results from Ocean Drilling Program (ODP) hole 651A, which sample serpentinized peridotites in the Vavilov Basin. The transition between serpentinized mantle and continental crust is rather abrupt. Thus, within a ~10 km wide transitional domain, continental crust with a thickness of~ 9 km is juxtaposed against un-roofed mantle. All available data from the Tyrrhenian Sea support wide-spread mantle exhumation in the Vavilov Basin. Therefore, the Tyrrhenian Sea provides a rather different structure when compared to marginal basins in the Western Pacific and hence may not have supported a mid-ocean ridge-type spreading system opening the basin.</p>

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

Scientific Reports ◽

10.1038/s41598-021-90578-9 ◽

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.

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