A BACK-ARC SETTING IS PROBLEMATIC FOR GRENVILLIAN ANORTHOSITE-FERROAN GRANITE SUITES

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.

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

Geosciences ◽

10.3390/geosciences11030117 ◽

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.

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

Minerals ◽

10.3390/min11010085 ◽

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

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.

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.

Alkali basalt from the Seifu Seamount in the Sea of Japan: post-spreading magmatism in a back-arc setting

Solid Earth ◽

10.5194/se-11-23-2020 ◽

2020 ◽

Vol 11 (1) ◽

pp. 23-36

Author(s):

Tomoaki Morishita ◽

Naoto Hirano ◽

Hirochika Sumino ◽

Hiroshi Sato ◽

Tomoyuki Shibata ◽

...

Keyword(s):

Partial Melting ◽

Sea Of Japan ◽

Alkali Basalt ◽

Spinel Peridotite ◽

The Sea Of Japan ◽

Low Degree ◽

Tsushima Basin ◽

Arc Setting ◽

Element Enrichment ◽

Back Arc

Abstract. We present geochemical and 40Ar∕39Ar age data for a peridotite xenolith-bearing basalt dredged from the Seifu Seamount (SSM basalt) in the northeast Tsushima Basin, southwest Sea of Japan. An 40Ar∕39Ar plateau age of 8.33±0.15 Ma (2σ) was obtained for the SSM basalt, indicating that it erupted shortly after the termination of back-arc spreading in the Sea of Japan. The SSM basalt is a high-K to shoshonitic alkali basalt that is characterized by light rare earth element enrichment. The trace element features of the basalt are similar to those of ocean island basalt, although the Yb content is much higher, indicating formation by the low-degree partial melting of spinel peridotite. The Nd, Sr, and Pb isotopic compositions of the SSM basalt differ from those of back-arc basin basalts in the Sea of Japan. The Sr–Nd isotopic composition of the SSM basalt suggests its source was depleted mid-ocean ridge mantle containing an enriched mantle (EM1) component. The SSM basalt was formed in a post-back-arc extension setting by the low-degree partial melting of an upwelling asthenosphere that had previously been associated with the main phase of back-arc magmatism.

New insights into the geologic evolution of the Grenvillian Trenton Prong inlier, Central Appalachian Piedmont, USA

Canadian Journal of Earth Sciences ◽

10.1139/cjes-2019-0140 ◽

2020 ◽

Vol 57 (7) ◽

pp. 840-854

Author(s):

Richard A. Volkert

Keyword(s):

Tectonic Setting ◽

Hanging Wall ◽

Sediment Source ◽

Slow Cooling ◽

Grenville Province ◽

Magmatic Arc ◽

Metamorphic History ◽

Arc Setting ◽

Appalachian Piedmont ◽

Back Arc

New geochemical and 40Ar/39Ar hornblende and biotite data from the Grenvillian Trenton Prong inlier provide the first constraints for the identification of lithotectonic units, their tectonic setting, and their metamorphic to post-metamorphic history. Gneissic tonalite, diorite, and gabbro compose the Colonial Lake Suite magmatic arc that developed along eastern Laurentia prior to 1.2 Ga. Spatially associated low- and high-TiO2 amphibolites were formed from island-arc basalt proximal to the arc front and mid-ocean ridge basalt-like basalt in a back-arc setting, respectively. Supracrustal paragneisses include meta-arkose derived from a continental sediment source of Laurentian affinity and metagraywacke and metapelite from an arc-like sediment source deposited in a back-arc basin, inboard of the Colonial Lake arc. The Assunpink Creek Granite was emplaced post-tectonically as small bodies of peraluminous syenogranite produced through partial melting of a subduction-modified felsic crustal source. Prograde mineral assemblages reached granulite- to amphibolite-facies metamorphic conditions during the Ottawan phase of the Grenvillian Orogeny. Hornblende 40Ar/39Ar ages of 935–923 Ma and a biotite age of 868 Ma record slow cooling in the northern part of the inlier following the metamorphic peak. Elsewhere in the inlier, biotite 40Ar/39Ar ages of 440 Ma and 377–341 Ma record partial to complete thermal resetting or new growth during the Taconian and Acadian orogens. The results of this study are consistent with the Trenton Prong being the down-dropped continuation of the Grenvillian New Jersey Highlands on the hanging wall of a major detachment fault. The Trenton Prong therefore correlates to other central and northern Appalachian Grenvillian inliers and to parts of the Grenville Province proper.

Petrogenesis of Neoarchaean volcanic rocks of the MacQuoid supracrustal belt: A back-arc setting for the northwestern Hearne subdomain, western Churchill Province, Canada

Precambrian Research ◽

10.1016/j.precamres.2005.11.001 ◽

2006 ◽

Vol 144 (1-2) ◽

pp. 140-165 ◽

Cited By ~ 54

Author(s):

H SANDEMAN ◽

S HANMER ◽

S TELLA ◽

A ARMITAGE ◽

W DAVIS ◽

...

Keyword(s):

Volcanic Rocks ◽

Supracrustal Belt ◽

Arc Setting ◽

Back Arc

Geochemistry of Sainte-Marguerite volcanic rocks: implications for the evolution of Silurian–Devonian volcanism in the Gaspé Peninsula

Canadian Journal of Earth Sciences ◽

10.1139/e07-012 ◽

2008 ◽

Vol 45 (1) ◽

pp. 15-29 ◽

Cited By ~ 1

Author(s):

Alan D’hulst ◽

Georges Beaudoin ◽

Michel Malo ◽

Marc Constantin ◽

Pierre Pilote

Keyword(s):

Lower Devonian ◽

Volcanic Rocks ◽

Magma Source ◽

Volcanic Arc ◽

Lower Silurian ◽

Trace Element Signature ◽

Arc Setting ◽

Back Arc ◽

Gaspe Peninsula ◽

Gaspé Peninsula

The Lower Devonian Sainte-Marguerite volcanic rocks are part of a Silurian–Devonian volcanic sequence deposited between the Taconian and Acadian orogenies in the Gaspé Peninsula, Quebec, Canada. The Sainte-Marguerite unit includes basaltic and dacitic lava flows with calc-alkaline and volcanic-arc affinities. Such affinities are also recorded by the trace-element signature in Lower Silurian and most Lower Devonian volcanic units of the Gaspé Peninsula. However, most of the other Silurian–Devonian volcanic rocks occurring in the Gaspé Peninsula have been previously interpreted to have erupted in an intracontinental setting. A back-arc setting for the Gaspé Peninsula between the Taconian and Acadian orogenies could account for these subduction volcanic-arc signatures, though a metasomatized lithospheric mantle magma source, unrelated to subduction, cannot be excluded. Lower Silurian and Lower Devonian volcanic rocks in the central part of the Gaspé Peninsula show an arc affinity, whereas Upper Silurian and Lower to Middle Devonian volcanic rocks, located in the south and north of the Gaspé Peninsula, respectively, show a within-plate affinity. The Lower Devonian Archibald Settlement and Boutet volcanic rocks of the southern and northern Gaspé Peninsula, respectively, show a trend toward a within-plate affinity. This suggests that within-plate volcanism migrated from south to north through time in an evolving back-arc environment and that the subduction signature of Lower Silurian and Lower Devonian rocks results from a source that melted only under the central part of the Gaspé Peninsula.

Extensional vs contractional Cenozoic deformation in Ibiza (Balearic Promontory, Spain): Integration in the West Mediterranean back-arc setting

Tectonophysics ◽

10.1016/j.tecto.2016.05.037 ◽

2016 ◽

Vol 682 ◽

pp. 35-55 ◽

Cited By ~ 18

Author(s):

Nathalie Etheve ◽

Dominique Frizon de Lamotte ◽

Geoffroy Mohn ◽

Raquel Martos ◽

Eduard Roca ◽

...

Keyword(s):

The West ◽

Arc Setting ◽

Back Arc