Geochemistry and tectonic setting of pre-collision Cretaceous and Paleogene volcanic rocks of Ecuador

Abstract

GEOLOGIC SETTING Pre-collision Cretaceous-lower Tertiary volcanic rocks of western Ecuador from the coastal area (Piii6n and San Lorenzo Formations) and Western Cordillera (Macuchi and Celica Formations) consist of three rock suites. The first suite includes tholeiites of oceanfloor affinities that have distinct light REE-depleted patterns and low La/Nb, La/Hf, and Th/Wf ratios. The island-arc tholeiites of the second suite have lower contents of Ti, Zr, Hf, and Nb. The third suite comprises calc-alkalic rocks, mainly continental-margin andesites and dacites. The continental volcanic-arc rocks crop out in an area east of the tholeiitic rocks. The boundary between the two areas is the major suture separating continental South America from accreted terranes to the west. A model is suggested for the geodynamic evolution of what is now western Ecuador during the Late Cretaceous. It includes two east-dipping subduction zones of Turonian to Santonian ages and the b accretion of the oceanic island arc to the continent. 1977, Effects ofalteration on element distributions in Archean tholeiites from thc Barberton greenslone belt, South Africa: ConlributioN Io Miiieralogy and Petrology. v. 64, p. 75-89. DaMel, I.

Stratigraphy of the late Cretaceous–Paleogene deposits of the cordillera occidental of central ecuador: geodynamic implications

“…However, the widespread hiatuses of Late SantonianLate Campanian deposits in the eastern Andean basins (Mathalone and Montoya, 1995;Jaillard, 1997) suggests that the accretion took place during the Late Santonian -Late Campanian time-span, i.e. between 85 and 77 Ma (Lebrat et al, 1987;Aspden et al, 1992;Reynaud et al, 1999;Kerr et al, 2002;Fig. 9).…”

“…However, the nature, age and accretion date of these oceanic terranes are poorly known and still debated. According to various authors, accretions took place in the Campanian (Lebrat et al, 1987;Aspden et al, 1992;Hughes and Pilatasig, 2002), the Late Paleocene (Daly, 1989;Jaillard et al, 1995;Reynaud et al, 1999), and/or the Eocene (Feininger and Bristow, 1980;Egüez, 1986;Bourgois et al, 1990;Spikings et al, 2001;Kerr et al, 2002). Most authors agree that the Cordillera Occidental of central Ecuador comprises a western island arc terrane (Macuchi terrane, Kehrer and Van der Kaaden, 1979;Baldock, 1982;Egüez, 1986;Hughes and Pilatasig, 2002), and an eastern oceanic terrane of oceanic floor to oceanic plateau nature (Lebrat et al, 1987; Pallatanga terrane of McCourt et al, 1998;Hughes and Pilatasig, 2002;Kerr et al, 2002).…”

Geologic Setting, Mineralogy, and Geochemistry of the Early Tertiary Au-Rich Volcanic-Hosted Massive Sulfide Deposit of La Plata, Western Cordillera, Ecuador

“…Poorly exposed limestones as well as mudstones occur in the lower part of the Macuchi unit. The volcanic and volcaniclastic facies of the Macuchi unit are a product of submarine eruptions, ranging in composition from basalt to basaltic andesite with lesser dacite and rhyolite of tholeiitic to calc-alkaline affinity (Lebrat et al, 1985(Lebrat et al, , 1987Aguirre and Atherton, 1987;BGS and CODI-GEM, 1999). Chiaradia and Fontboté (2001) divided the Macuchi unit into a Paleocene (?)…”

Investigation of the Lead Isotope Signatures of Marine Sediments in Relation to the Lead Isotope Signatures of Northern Andean Ores

“…The Macuchi Formation includes lavas that range from fine-grained basalt to porphyritic dacite, volcaniclastic rocks, tuffs, and some fine-grained sedimentary rocks (Lebras et al, 1987). The basalts and dacites are composed of plagioclase and augite, with a variety of accessory minerals (Lebras et al, 1987).…”

“…The rocks within the foundation of coastal Ecuador are composed of a belt of rocks that are interpreted to be pieces of oceanic crust (Wollard and Klum, 1981 Composed mostly of Mesozoic to Tertiary age igneous rocks, some portions of the Ecuadorian Andes rest on older rock (Lebras et al, 1987). In coastal areas and the Western Cordillera there are widespread outcrops of Cretaceous to Eocene volcanic and plutonic rocks with a basic to intermediate composition (Lebras et al, 1987). The coastal rocks of Ecuador consist of three collections of rock types (Feininger and Bristow, 1980).…”