Lithium concentrations and isotope signatures of Palaeozoic basement rocks and Cenozoic volcanic rocks from the Central Andean arc and back-arc

Abstract Significant uncertainty remains regarding the exact timing and nature of subduction events during the closure of the Tethyan seas in what is now NW Iran. This study thus presents new geochemical compositions and U–Pb ages for a suite of volcanic rocks emplaced during Cenozoic volcanism in the west Alborz Magmatic Assemblage, which is commonly regarded as the back-arc of the Neotethyan magmatism in Central Iran. The subalkali basalts and andesites are dated to 57 ± 1.2 Ma, and are likely derived from a supra-subduction mantle wedge. Later, trachytic A-type rocks erupted from ~42 to 25 Ma during an anorogenic (extensional) stage triggered by slab retreat and associated asthenospheric mantle influx. A-type melts were at least partly concurrent with lithospheric mantle magmatism implied by eruption of subalkali basalts–andesites around 26–24 Ma. Next, Amp-Bt trachybasaltic volcanism with high-Nb basaltic affinity at ~19 Ma likely records slab deepening and slab partial melting, which reacted with the mantle wedge to produce the source material for the high-Nb basalts. Sr–Nd isotopic ratios for SE Ahar mafic as well as A-type rocks imply rather enriched mantle source(s). Some crustal contamination is implied by the presence of inherited zircons dominated by those derived from Neoproterozoic–Cambrian basement rocks and Carboniferous magmatism. Rhyolitic rocks with adakitic affinity probably mark the final volcanism in the study area. The adakitic rocks show crustal signatures such as high K and Th, probably formed as a consequence of higher temperature gradients, at crustal levels, imposed by both slab and mantle partial melts.

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Where is the Iapetus suture in northern New England? A study of the Ammonoosuc Volcanics, Bronson Hill terrane, New Hampshire1This article is one of a series of papers published in this CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology.

Canadian Journal of Earth Sciences ◽

10.1139/e10-108 ◽

2012 ◽

Vol 49 (1) ◽

pp. 189-205 ◽

Cited By ~ 6

Author(s):

Michael J. Dorais ◽

Miles Atkinson ◽

Jon Kim ◽

David P. West ◽

Gregory A. Kirby

Keyword(s):

New England ◽

Subduction Zone ◽

Volcanic Rocks ◽

Middle Ordovician ◽

Isotopic Signatures ◽

Basement Rocks ◽

Iapetus Ocean ◽

Maritime Canada ◽

Laurentian Margin ◽

Back Arc

The ∼470 Ma Ammonoosuc Volcanics of the Bronson Hill terrane of New Hampshire have back-arc basin basalt compositions. Major and trace element compositions compare favorably to coeval volcanic rocks in the Miramichi Highlands of New Brunswick and the Munsangan and Casco Bay volcanics of Maine, back-arc basin basalts of known peri-Gondwanan origins. Additionally, the Ammonoosuc Volcanics have Nd and Pb isotopic compositions indicative of peri-Gondwanan provenance. Thus, the Ammonoosuc Volcanics correlate with Middle Ordovician, peri-Gondwanan, Tetagouche–Exploits back-arc rocks of eastern New England and Maritime Canada. This correlation indicates that the Red Indian Line, the principle Iapetus suture, lies along the western margin of the Bronson Hill terrane. However, the younger (∼450 Ma) Oliverian Plutonic Suite rocks that intruded the Ammonoosuc Volcanics, forming domes along the core of the Bronson Hill anticlinorium, have Laurentian isotopic signatures. This suggests that the Ammonoosuc Volcanics were thrust westwardly over the Laurentian margin, and that Laurentian basement rocks are present under the Bronson Hill terrane. A plausible explanation for these relationships is that an easterly dipping subduction zone formed the Ammonoosuc Volcanics in the Tetagoughe–Exploits oceanic tract, just east of the coeval Popelogan arc. With the closure of the Iapetus Ocean, this terrane was thrust over the Laurentian margin. Subsequent to obduction of the Ammonoosuc Volcanics, subduction polarity flipped to the west, with the Oliverian arc resulting from a westerly dipping subduction zone that formed under the Taconic Orogeny-modified Laurentian margin.

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

Canadian Journal of Earth Sciences ◽

10.1139/e03-010 ◽

2003 ◽

Vol 40 (6) ◽

pp. 833-852 ◽

Cited By ~ 3

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.

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Volatiles in submarine volcanic rocks from the spreading axis of the East Scotia Sea back-arc basin

Earth and Planetary Science Letters ◽

10.1016/0012-821x(80)90043-6 ◽

1980 ◽

Vol 47 (2) ◽

pp. 272-278 ◽

Cited By ~ 63

Author(s):

David W. Muenow ◽

Norman W.K. Liu ◽

Michael O. Garcia ◽

Andrew D. Saunders

Keyword(s):

Volcanic Rocks ◽

Scotia Sea ◽

Spreading Axis ◽

Back Arc

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Age, chemistry, and tectonic setting of Miramichi terrane (Early Paleozoic) volcanic rocks, eastern and east-central Maine, USA

Atlantic Geology ◽

10.4138/atlgeol.2021.012 ◽

2021 ◽

Vol 57 ◽

pp. 239-273

Author(s):

Allan Ludman ◽

Christopher McFarlane ◽

Amber T.H. Whittaker

Keyword(s):

New Brunswick ◽

Subduction Zone ◽

Tectonic Setting ◽

Volcanic Rocks ◽

Calc Alkaline ◽

East Central ◽

Arc Volcanism ◽

Middle Ordovician ◽

Volcanic Suite ◽

Back Arc

Volcanic rocks in the Miramichi inlier in Maine occur in two areas separated by the Bottle Lake plutonic complex: the Danforth segment (Stetson Mountain Formation) north of the complex and Greenfield segment to the south (Olamon Stream Formation). Both suites are dominantly pyroclastic, with abundant andesite, dacite, and rhyolite tuffs and subordinate lavas, breccias, and agglomerates. Rare basaltic tuffs and a small area of basaltic tuffs, agglomerates, and lavas are restricted to the Greenfield segment. U–Pb zircon geochronology dates Greenfield segment volcanism at ca. 469 Ma, the Floian–Dapingian boundary between the Lower and Middle Ordovician. Chemical analyses reveal a calc-alkaline suite erupted in a continental volcanic arc, either the Meductic or earliest Balmoral phase of Popelogan arc activity. The Maine Miramichi volcanic rocks are most likely correlative with the Meductic Group volcanic suite in west-central New Brunswick. Orogen-parallel lithologic and chemical variations from New Brunswick to east-central Maine may result from eruptions at different volcanic centers. The bimodal Poplar Mountain volcanic suite at the Maine–New Brunswick border is 10–20 myr younger than the Miramichi volcanic rocks and more likely an early phase of back-arc basin rifting than a late-stage Meductic phase event. Coeval calc-alkaline arc volcanism in the Miramichi, Weeksboro–Lunksoos Lake, and Munsungun Cambrian–Ordovician inliers in Maine is not consistent with tectonic models involving northwestward migration of arc volcanism. This >150 km span cannot be explained by a single east-facing subduction zone, suggesting more than one subduction zone/arc complex in the region.

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

Canadian Journal of Earth Sciences ◽

10.1139/e92-116 ◽

1992 ◽

Vol 29 (7) ◽

pp. 1448-1458 ◽

Cited By ~ 60

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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Gold-hosting supracrustal rocks on Storø, southern West Greenland: lithologies and geological environment

Geological Survey of Denmark and Greenland Bulletin ◽

10.34194/geusb.v13.4972 ◽

2007 ◽

Vol 13 ◽

pp. 41-44 ◽

Cited By ~ 8

Author(s):

Christian Knudsen ◽

Jeroen A.M. Van Gool ◽

Claus Østergaard ◽

Julie A. Hollis ◽

Matilde Rink-Jørgensen ◽

...

Keyword(s):

Volcanic Rocks ◽

West Greenland ◽

Metasedimentary Rocks ◽

Quartz Veins ◽

Rock Types ◽

Minimum Age ◽

Arc Setting ◽

Basic Volcanic ◽

Back Arc ◽

Different Sources

A gold prospect on central Storø in the Nuuk region of southern West Greenland is hosted by a sequence of intensely deformed, amphibolite facies supracrustal rocks of late Mesoto Neoarchaean age. The prospect is at present being explored by the Greenlandic mining company NunaMinerals A/S. Amphibolites likely to be derived from basaltic volcanic rocks dominate, and ultrabasic to intermediate rocks are also interpreted to be derived from volcanic rocks. The sequence also contains metasedimentary rocks including quartzites and cordierite-, sillimanite-, garnet- and biotite-bearing aluminous gneisses. The metasediments contain detrital zircon from different sources indicating a maximum age of the mineralisation of c. 2.8 Ga. The original deposition of the various rock types is believed to have taken place in a back-arc setting. Gold is mainly hosted in garnet- and biotite-rich zones in amphibolites often associated with quartz veins. Gold has been found within garnets indicating that the mineralisation is pre-metamorphic, which points to a minimum age of the mineralisation of c. 2.6 Ga. The geochemistry of the goldbearing zones indicates that the initial gold mineralisation is tied to fluid-induced sericitisation of a basic volcanic protolith. The hosting rocks and the mineralisation are affected by several generations of folding.

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Lower Palaeozoic and Precambrian igneous rocks from eastern England, and their bearing on late Ordovician closure of the Tornquist Sea: constraints from U-Pb and Nd isotopes

Geological Magazine ◽

10.1017/s0016756800023190 ◽

1993 ◽

Vol 130 (6) ◽

pp. 835-846 ◽

Cited By ~ 80

Author(s):

S. R. Noble ◽

R. D. Tucker ◽

T. C. Pharaoh

Keyword(s):

Volcanic Rocks ◽

Igneous Rocks ◽

Calc Alkaline ◽

Nd Isotopes ◽

Nd Isotope ◽

Magmatic Arc ◽

The North ◽

Basement Rocks ◽

Continental Arc ◽

Lower Palaeozoic

AbstractThe U-Pb isotope ages and Nd isotope characteristics of asuite of igneous rocks from the basement of eastern England show that Ordovician calc-alkaline igneous rocks are tectonically interleaved with late Precambrian volcanic rocks distinct from Precambrian rocks exposed in southern Britain. New U-Pb ages for the North Creake tuff (zircon, 449±13 Ma), Moorby Microgranite (zircon, 457 ± 20 Ma), and the Nuneaton lamprophyre (zircon and baddeleyite, 442 ± 3 Ma) confirm the presence ofan Ordovician magmatic arc. Tectonically interleaved Precambrian volcanic rocks within this arc are verified by new U-Pb zircon ages for tuffs at Glinton (612 ± 21 Ma) and Orton (616 ± 6 Ma). Initial εNd values for these basement rocks range from +4 to - 6, consistent with generation of both c. 615 Ma and c. 450 Ma groups of rocksin continental arc settings. The U-Pb and Sm-Nd isotope data support arguments for an Ordovician fold/thrust belt extending from England to Belgium, and that the Ordovician calc-alkaline rocks formed in response to subductionof Tornquist Sea oceanic crust beneath Avalonia.

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Subduction-related magmatic imprint of most Philippine ophiolites: implications on the early geodynamic evolution of the Philippine archipelago

BSGF - Earth Sciences Bulletin ◽

10.2113/175.5.443 ◽

2004 ◽

Vol 175 (5) ◽

pp. 443-460 ◽

Cited By ~ 53

Author(s):

Rodolfo A. Tamayo* ◽

René C. Maury* ◽

Graciano P. Yumul ◽

Mireille Polvé ◽

Joseph Cotten ◽

...

Keyword(s):

Partial Melting ◽

Subduction Zone ◽

Volcanic Rocks ◽

The Philippines ◽

Island Arc ◽

Island Arcs ◽

Geodynamic Evolution ◽

Wide Range ◽

Opening And Closing ◽

Back Arc

Abstract The basement complexes of the Philippine archipelago include at least 20 ophiolites and ophiolitic complexes. These complexes are characterised by volcanic sequences displaying geochemical compositions similar to those observed in MORB, transitional MORB-island arc tholeiites and arc volcanic rocks originating from modern Pacific-type oceans, back-arc basins and island arcs. Ocean island basalt-like rocks are rarely encountered in the volcanic sequences. The gabbros from the ophiolites contain clinopyroxenes and plagioclases showing a wide range of XMg and An values, respectively. Some of these gabbros exhibit mineral chemistries suggesting their derivation from basaltic liquids formed from mantle sources that underwent either high degrees of partial melting or several partial melting episodes. Moreover, some of the gabbros display a crystallization sequence where orthopyroxene and clinopyroxene appeared before plagioclase. The major element compositions of coexisting orthopyroxenes and olivines from the mantle peridotites are consistent with low to high degrees of partial melting. Accessory spinels in these peridotites display a wide range of XCr values as well with some of them above the empirical upper limit of 0.6 often observed in most modern mid-oceanic ridge (MOR) mantle rocks. Co-existing olivines and spinels from the peridotites also exhibit compositions suggesting that they lastly equilibrated under oxidizing mantle conditions. The juxtaposition of volcanic rocks showing affinities with modern MOR and island arc environments suggests that most of the volcanic sequences in Philippine ophiolites formed in subduction-related geodynamic settings. Similarly, their associated gabbros and peridotites display mineralogical characteristics and mineral chemistries consistent with their derivation from modern supra-subduction zone-like environments. Alternatively, these rocks could have, in part, evolved in a supra-subduction zone even though they originated from a MOR-like setting. A simplified scenario regarding the early geodynamic evolution of the Philippines is proposed on the basis of the geochemical signatures of the ophiolites, their ages of formation and the ages and origins of the oceanic basins actually bounding the archipelago, including basins presumed to be now totally consumed. This scenario envisages the early development of the archipelago to be largely dominated by the opening and closing of oceanic basins. Fragments of these basins provided the substratum on top of which the Cretaceous to Recent volcanic arcs of the Philippines were emplaced.

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Refining the Paleoproterozoic tectonothermal history of the Penokean Orogen: New U-Pb age constraints from the Pembine-Wausau terrane, Wisconsin, USA

Geological Society of America Bulletin ◽

10.1130/b36114.1 ◽

2021 ◽

Author(s):

Jian-Wei Zi ◽

Stephen Sheppard ◽

Janet R. Muhling ◽

Birger Rasmussen

Keyword(s):

Volcanic Rocks ◽

Massive Sulfide ◽

Time Frame ◽

Metamorphic Event ◽

Published Data ◽

Banded Iron Formations ◽

Time Space ◽

Lithospheric Extension ◽

History Of ◽

Back Arc

An enduring problem in the assembly of Laurentia is uncertainty about the nature and timing of magmatism, deformation, and metamorphism in the Paleoproterozoic Wisconsin magmatic terranes, which have been variously interpreted as an intra-oceanic arc, foredeep or continental back-arc. Resolving these competing models is difficult due in part to a lack of a robust time-frame for magmatism in the terranes. The northeast part of the terranes in northern Wisconsin (USA) comprise mafic and felsic volcanic rocks and syn-volcanic granites thought to have been emplaced and metamorphosed during the 1890−1830 Ma Penokean orogeny. New in situ U-Pb geochronology of igneous zircon from the volcanic rocks (Beecher Formation), and from two tonalitic plutons (the Dunbar Gneiss and Newingham Tonalite) intruding the volcanic rocks, yielded crystallization ages ranging from 1847 ± 10 Ma to 1842 ± 7 Ma (95% confidence). Thus, these rocks record a magmatic episode that is synchronous with bimodal volcanism in the Wausau domain and Marshfield terrane farther south. Our results, integrated with published data into a time-space diagram, highlight two bimodal magmatic cycles, the first at 1890−1860 Ma and the second at 1845−1830 Ma, developed on extended crust of the Superior Craton. The magmatic episodes are broadly synchronous with volcanogenic massive sulfide mineralization and deposition of Lake Superior banded iron formations. Our data and interpretation are consistent with the Penokean orogeny marking west Pacific-style accretionary orogenesis involving lithospheric extension of the continental margin, punctuated by transient crustal shortening that was accommodated by folding and thrusting of the arc-back-arc system. The model explains the shared magmatic history of the Pembine-Wausau and Marshfield terranes. Our study also reveals an overprinting metamorphic event recorded by reset zircon and new monazite growth dated at 1775 ± 10 Ma suggesting that the main metamorphic event in the terranes is related to the Yavapai-interval accretion rather than the Penokean orogeny.

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