Western Ecuador is made up of oceanic allochthonous terranes accreted between the Late Cretaceous and the Late Paleocene. Boulders of calc-alkaline microdiorites are found in a Latest Paleocene-Earliest Eocene conglomerate exposed near Paita. The geochemistry of the microdiorites indicates that they developed in an intra-oceanic arc setting. Their occurrence in the conglomerate demonstrates that oceanic terranes were being eroded ~ 55 Ma ago in northwestern Peru. Since the closest oceanic terranes are presently located in Ecuador, i.e. 250 km farther north, these terranes have migrated NNE-ward along dextral wrench faults, at a minimum rate of 4.5 mm·yr−1. L'Ouest de l'Équateur est formé de terrains allochtones d'origine océanique, accrétés entre le Crétacé supérieur et le Paléocène supérieur. La présence, dans la région de Paita, de galets de microdiorites issus d'un arc insulaire, resédimentés vers la limite Paléocène-Éocène, prouve que des terrains océaniques étaient à l'érosion vers 55 Ma dans le Nord-Ouest du Pérou. Les terrains océaniques les plus proches étant situés actuellement en Équateur, 250 km plus au nord, ils ont nécessairement dérivé le long de décrochements dextres, à une vitesse minimale de 4,5 mm·an−1.
Research Article| July 01, 1988 Geochemical study of an early Paleozoic island-arc-back-arc basin system. Part 2: Eastern Klamath, early to middle Paleozoic island-arc volcanic rocks (northern California) MARC BROUXEL; MARC BROUXEL 1Centre de Recherches Pétrographiques et Géochimiques, BP 20, 54501 Vandoeuvre-les-Nancy cedex, France2Laboratoire de Pétrologie, U.A. 735, Université de Nancy 1, BP 239, 54506 Vandceuvre-les-Nancy cedex, France Search for other works by this author on: GSW Google Scholar HENRIETTE LAPIERRE; HENRIETTE LAPIERRE 2Laboratoire de Pétrologie, U.A. 735, Université de Nancy 1, BP 239, 54506 Vandceuvre-les-Nancy cedex, France3Département des Sciences de la Terre, Université d'Orléans, 45046 Orléans cedex, France Search for other works by this author on: GSW Google Scholar ANNIE MICHARD; ANNIE MICHARD 1Centre de Recherches Pétrographiques et Géochimiques, BP 20, 54501 Vandoeuvre-les-Nancy cedex, France Search for other works by this author on: GSW Google Scholar FRANCIS ALBARÉDE FRANCIS ALBARÉDE 1Centre de Recherches Pétrographiques et Géochimiques, BP 20, 54501 Vandoeuvre-les-Nancy cedex, France4Ecole Nationale Supérieure de Géologie, 94 Avenue de-Lattre-de-Tassigny, BP 452, 54001 Nancy cedex, France Search for other works by this author on: GSW Google Scholar GSA Bulletin (1988) 100 (7): 1120–1130. https://doi.org/10.1130/0016-7606(1988)100<1120:GSOAEP>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation MARC BROUXEL, HENRIETTE LAPIERRE, ANNIE MICHARD, FRANCIS ALBARÉDE; Geochemical study of an early Paleozoic island-arc-back-arc basin system. Part 2: Eastern Klamath, early to middle Paleozoic island-arc volcanic rocks (northern California). GSA Bulletin 1988;; 100 (7): 1120–1130. doi: https://doi.org/10.1130/0016-7606(1988)100<1120:GSOAEP>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A systematic mineralogical, REE and Sr-Nd isotopic study of the eastern Klamath Mountains pre- to Early Devonian volcanism (Copley tholeiites, Lovers Leap volcanic rocks, Trinity ophiolitic basalts) show that all of the rocks belong to a low-K, island-arc, tholelitic suite, with the exception of the Late Ordovician Lovers Leap Butte calc-alkalic volcanic rocks. All of the latter have low ϵNd values (ϵNd(T)= 3.9), suggesting that they suffered crustal contamination.The Copley and Lovers Leap low-K tholeiites exhibit variable LREE enrichment or depletion and variable ϵNd values (ϵNd(T)range mostly between 5 and 8), suggesting that variable partial melting degree and/or contamination by sediments occur(s). The isotopic features of the Copley high-Mg andesites (boninitic affinities, ϵNd(T) range between 6.2 and 7.9) show that they were derived from the same source as the low-K tholeiites. The Trinity ophiolitic basalts, along with the LREE-depleted Copley and Lovers Leap tholeiites, show similar geochemical and isotopic features (ϵNd(T) = 7.3 and 7.4), suggesting that they belong to the same island-arc-back-arc basin system. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
The main petrological, mineralogical, and geochemical features of the metavolcanites belonging to the Late Proterozoic tectono-sedimentary units of southern Mauritanides (Termessé and Niokolo Koba – Koulountou) and western Hoggar, Algeria (Timesselarsine), permit a reconstruction of the geodynamic environment that controlled the evolution of the Pan-African ranges of western Africa. Flows and pyroclastic beds metamorphosed under greenschist-facies conditions are interbedded within detritic and carbonate platform sediments, suggesting an unstable environment in the vicinity of a continental margin.The association of oceanic tholeiites slightly enriched in LREE and basalts more enriched in TiO 2 , Zr, Nb, and LREE displaying alkalic affinities suggests intracontinental rifting succeeded by expansion. The lack of ultrabasic – basic complexes (oceanic paleosutures) in southern Mauritanides and their occurrence in the Hoggar suggest that the opening was bigger in the north than in the south.The later calc-alkalic sequences of the Niokolo Koba – Koulountou units are tectonically associated with the Termessé unit. In the Timesselarsine unit, calc-alkalic acid rocks coexist with the basic lavas previously mentioned. Thus, the closure of the rift related to a continental collision appears to be later in southern Mauritanides than in the Hoggar.
Abstract Paleogene magmatism is widespread in the western Alps and its origin is still a matter of debate. It consists of calc-alkaline and shoshonitic suites with mainly granodioritic intrusions in the Internal Zone (northern Italy), andesitic volcanism in the Delphino-Helvetic Zone (French-Swiss domain) and the Esterellite intrusions in Provence. In the External Alpine Zone, the Taveyannaz Sandstones and the Champsaur Sandstones preserve andesitic pebbles and mineral fragments dated at 32 Ma. On the basis of trace-element and isotopic geochemistry (Sr, Nd, Pb and O) of mineral separates (amphibole, pyroxene and plagioclase) and andesitic clasts, we characterise the nature of magmatic source(s) and compare the isotopic compositions of the andesites with those of well known Paleogene igneous suites.
Introduction Ecuador is part of the northern Andes, which comprise accreted oceanic terranes on their western part. In Ecuador, these terranes are underplated, and form the crustal root of the Western Cordillera (Guillier et al. 2001). On the other hand, Recent arc magmatism is marked by abundant volcanic rocks of adakitic affinity (Bourdon et al. 2002, 2003). This led to the hypothesis that the adakitic products derive from the partial melting of the deeply buried accreted oceanic material (Arculus et al. 1999, Beaudon et al. 2005). The aim of this paper is to present new geochemical results on Miocene intrusions sampled in the Western Cordillera (Fig. 1), in order to check wether adakites occur, and if so, to constrain their origin.
Abstract In the southwestern part of the French Massif central (Decazeville basin, at the Sillon Houiller fault termination; Figeac and Lacapelle-Marival basins along the Argentat fault), Stephanian volcanism exhibits shoshonitic affinities. Their chondrite-normalized rare earth element (REE) patterns are enriched in light REE, but almost flat for heavy REE, with marked negative Eu anomalies. Primitive mantle-normalized element spectra show negative Nb, Ta, P, Sm, Ti, and positive Th, U, Pb anomalies, respectively. εNd values are negative and homogeneous (−6 to −4). This volcanism shares the same geochemical patterns as the late-orogenic Stephanian-Permian magmatism from the southern part of the Variscan belt (Pyrénées, Alps, Sardinia). We explain these geochemical characteristics as resulting from the partial melting of a metasomatised mantle. We propose a new mechanism to explain this melting process: horizontal displacement along the main late-orogenic strike-slip faults might bring into contact a hydrated lower crust with the lithospheric mantle. Mantle metasomatism within the strike-slip fault zone may then induce partial melting.
The margins of the Caribbean plate are marked by Cretaceous island‐arc basalts associated with accreted fragments of the Cretaceous Colombian Caribbean oceanic plateau. In Cuba, the Cretaceous volcanic island‐arc rocks are in fault contact with the Mabujina complex, interpreted as an oceanic Jurassic to Early Cretaceous arc basement with local island‐arc rocks. The Cuban Cretaceous island arc consists of Early to Late Cretaceous volcanic series associated with limestones. While the pre‐Albian arc rocks consist of tholeiitic basalts and rhyolites, the post‐Albian volcanic series is characterized by calc‐alkaline andesites. The Cretaceous lavas have Sr and Nd isotopic compositions similar to the intraoceanic arcs, and the Pb isotopic initial ratios are close to the East Pacific Rise mid‐ocean ridge basalt field. According to our data, the Mabujina arc rocks are tholeiites and calc‐alkaline basalts, developed in a Jurassic and/or Early Cretaceous intraoceanic island arc. Their Nd, Sr, and Pb isotopic compositions indicate that they derive from a depleted mantle source contaminated by sediments. This subduction magmatism is not related to the classic Early Cretaceous Caribbean tholeiitic series but is similar to the Late Jurassic to Early Cretaceous Guerrero arc terrane from Mexico and may represent its southernmost extension. Thus, the different tectonic units of central Cuba cannot be easily correlated with those of Hispaniola. Our data also indicate that two different island arcs were tectonically juxtaposed in central Cuba: the classical Lower and Upper Cretaceous suites of the Greater Antilles arc and a Jurassic to Early Cretaceous island‐arc suite with a Pacific provenance.
The Celica-Lancones Basin is located in the present-day forearc zone of Southern Ecuador and Northern Peru (Fig. 1). It is characterized by unusual turbiditic series of Cretaceous age. According to the authors, this basin has been interpretad as an extensional basin (Kennerley 1973), an aborted marginal basin (Aguirre 1992), or a transcurrent forearc Basin (Jaillard et al. 1999). New observations presented here support the latter interpretation and suggest that the evolution of this forearc zone was controlled by the convergence regime.
