Article Formation of intra-arc volcanosedimentary basins in the western flank of the central Peruvian Andes during Late Cretaceous oblique subduction: field evidence and constraints from U-Pb ages and Hf isotopes POLLIAND, Marc, et al. Reference POLLIAND, Marc, et al. Formation of intra-arc volcanosedimentary basins in the western flank of the central Peruvian Andes during Late Cretaceous oblique subduction: field evidence and constraints from U-Pb ages and Hf isotopes. International Journal of Earth Sciences, 2005, vol. 94, no. 2, p. 231-242 DOI : 10.1007/s00531-005-0464-5 Available at: http://archive-ouverte.unige.ch/unige:21629 Disclaimer: layout of this document may differ from the published version. 1 / 1 Int J Earth Sci (Geol Rundsch) (2005) 94: 231–242 DOI 10.1007/s00531-005-0464-5 ORIGINAL PAPER Marc Polliand Æ Urs Schaltegger Æ Martin Frank Lluis Fontbote´ Formation of intra-arc volcanosedimentary basins in the western flank of the central Peruvian Andes during Late Cretaceous oblique subduction: field evidence and constraints from U–Pb ages and Hf isotopes Received: 16 October 2003 / Accepted: 11 December 2004 / Published online: 16 February 2005 Ó Springer-Verlag 2005 Abstract During late Early to Late Cretaceous, the of old basement below the WPT, in agreement with Peruvian coastal margin underwent fast and oblique previous U–Pb and Sr isotopic data for batholithic rocks subduction and was characterized by important arc emplaced in the WPT area. This is supported by the plutonism (the Peruvian Coastal Batholith) and forma- presence of a most likely continuous block of dense tion of volcanosedimentary basins known as the Wes- (3.0 g/cm3) material observed beneath the WPT area tern Peruvian Trough (WPT). We present high-precision on gravimetric crustal cross sections. We suggest that U–Pb ages and initial Hf isotopic compositions of zircon this gravimetric anomaly may correspond to a piece of from conformable volcanic and crosscutting intrusive lithospheric mantle and/or oceanic crust inherited from rocks within submarine volcanosedimentary strata of a possible Late Permian–Triassic rifting. Such young the WPT hosting the Perubar massive sulfide deposit. and mafic crust was the most probable source for arc Zircons extracted from both the volcanic and intrusive magmatism in the WPT area. rocks yield concordant U–Pb ages ranging from 67.89±0.18 Ma to 69.71±0.18 Ma, indicating that ba- Keywords Andean magmatism Æ Continental arc Æ sin subsidence, submarine volcanism and plutonic U–Pb dating Æ Hf isotopes Æ Strike-slip basins activity occurred in close spatial and temporal rela- tionship within the Andean magmatic arc during the Late Cretaceous. Field observations, satellite image interpretation, and plate reconstructions, suggest that Introduction dextral wrenching movements along crustal lineaments were related to oblique subduction. Wrench tectonics is During late-Early to Late Cretaceous the relative motion therefore considered to be the trigger for the formation between the oceanic Farallon (previously Phoenix) and of the WPT as a series of pull-apart basins and for the South American plates along the central Andean margin emplacement of the Coastal Batholith. The zircon initial was characterized by a period of high convergence rate Hf values of the dated magmatic rocks fall between 5.5 (e.g., Jaillard et al. 2000; Larson 1991; Soler and Bon- and 7.4, and indicate only very subordinate influence of homme 1990) with a significant oblique component a sedimentary or continental component. The absence (northerly to north–northeasterly motion) of the sub- of inherited cores in the zircons suggest a complete lack ducted lithosphere (e.g., Jaillard 1994; Gordon and Jurdy 1986; Duncan and Hargraves 1984) and a most M. Polliand Æ U. Schaltegger (&) Æ L. Fontbote´ likely absolute trenchward motion of the South Ameri- Department of Mineralogy, can plate (e.g., Jaillard and Soler 1996; Jaillard 1994;P. University of Geneva, Rue des Maraıˆ chers 13, 1205 Geneve, Switzerland Soler, unpublished PhD thesis) due to the definitive E-mail: [email protected] opening of the South Atlantic ocean at about 110 Ma E-mail: [email protected] (e.g., Scotese et al. 1988; Larson and Pitman 1972). Tel.: +41-22-3796638 Along the coastal margin of Peru, this period of fast and Fax: +41-22-3793210 oblique subduction was characterized by important arc E-mail: [email protected] magmatism and formation of volcanosedimentary ba- U. Schaltegger Æ M. Frank sins with high average subsidence rates, known as the Department of Isotope Geology and Mineral Resources, Federal Institute of Technology ETH, Mesozoic Western Peruvian Trough (WPT; e.g., Cob- Sonneggstrasse 5, 8092 Zurich, Switzerland bing 1978; Atherton et al. 1983; Fig. 1a). The develop- E-mail: [email protected] ment of the WPT was accompanied and followed by 232 Fig. 1 a Geologic map of the Peruvian Coastal Batholith and Mesozoic Western Peruvian Trough (WPT) with related volcanosedimentary basins hosting massive sulfide deposits. Volcanosedimentary basin limits after Vidal (1987), Atherton et al. (1983), and Cobbing (1978). The yellow doted lines encompass the 3.0 g/cm3 wedge at 10-km depth. Distribution of the Cretaceous Peruvian Costal Batholith, Casma Group, and Early Cretaceous strata after the digital version of the geological map of Peru (INGEMMET 2000). b Main lineaments and structures based on Landsat-5 TM image (Red Band 7; Green Band 4; Blue Band 2) interpretation, downloaded from http:// www.zulu.ssc.nasa.gov/mrsid/. c Geologic interpretation of the deep sturctures along the 9°S and 12°S gravimetric, crustal and subcrustal cross sections (Couch et al. 1981; Jones 1981) of the continental margin of Peru intrusion of numerous plutons that form the present-day two major basin units known as the Huarmey and the Peruvian Coastal Batholith (Fig. 1), mostly emplaced Can˜ ete basins (e.g., Atherton et al. 1983; Cobbing 1978; between about 100 Ma and 30 Ma (e.g., Soler and Ro- Fig. 1). According to several authors (e.g., Atherton and tach-Toulhoat 1990a; Mukasa 1986a). Within the vol- Aguirre 1992; Atherton and Webb 1989; Cobbing et al. canosedimentary basins, several massive sulfide deposits 1981), both the Huarmey and Can˜ ete basins had their were formed (i.e., Aurora Augusta, Cerro Lindo, Maria main period of subsidence in the Albian, during which Teresa, Palma, Perubar; Fig. 1a, b), amongst which the up to 9,000 m of volcanic (mainly basalt flows), volca- Perubar deposit has been exploited from 1978 to 2000 niclastic, and subordinate sedimentary rocks were and is the best studied (Polliand 2005; Polliand and deposited. These dominantly submarine volcanic and Fontbote´2000; Vidal 1987). volcaniclastic successions have been attributed in the The WPT in the central coastal margin of Peru, be- literature to the Casma Group and been described as tween about Trujillo and Pisco, has been subdivided into Albian to Cenomanian in age (e.g., Atherton and Webb 233 1989; Cobbing et al. 1981). The extensional tectonic zircon U–Pb age of 67.89±0.18 Ma (Table 1). The Ri- setting during which the Casma Group and related cardo Palma tonalite, delimiting the western part of the volcanosedimentary basins were formed was essentially basin (Fig. 2), is overlain by the volcanosedimentary attributed either to an extensional marginal basin with strata and most probably constituted the western bed- incipient formation of oceanic crust (e.g., Atherton and rock shoulder of the basin (Fig. 2). According to Vidal Aguirre 1992; Atherton 1990; Atherton and Webb 1989; (1987) and Mukasa (1986a), the Ricardo Palma tonalite Atherton et al. 1985), or to the extensional tectonic yields a 82.0±2.3 Ma hornblende K–Ar age and con- (pull-apart?) subsidence within the volcanic arc (e.g., cordant zircon U–Pb ages of 86.4 and 84.4 Ma, respec- Jaillard 1994; P. Soler, unpublished PhD thesis; Soler tively. It was emplaced into older magmatic rocks of the 1991). The overall geologic, lithologic and geometric Coastal Batholith and Early Cretaceous sedimentary framework of the WPT and related volcanosedimentary strata such as those exposed further west of the study basins remains, however, poorly known, except in some area along the coast line (Fig. 1a, b). Both the older and areas near Huarmey and Culebras (Webb 1976; Myers younger intrusions occurring in the Perubar area belong 1980), and more detailed work is necessary to reach to the Cretaceous Peruvian Coastal Batholith. more sound geodynamic conclusions. The stratigraphy of the studied volcanosedimentary We present new U–Pb age determinations and initial succession at Perubar has been divided into four main Hf isotopic compositions of zircon from conformable lithological units defined, from bottom to top, as the volcanic and crosscutting intrusive rocks within sub- Footwall, Prospective, Hangingwall and Upper Units, marine volcanosedimentary strata attributed so far to respectively. Their lithological description is given in the Casma Group and hosting the Perubar massive Fig. 3a. These volcanic and sedimentary strata were sulfide deposit in the northeastern part of the Can˜ ete erupted and deposited in a pull-apart marine basin basin (50 km east of Lima, 11°55¢S76°34¢W; Fig. 1). environment (Fig. 3b; Polliand 2005) without impor- These new data (1) demonstrate that the volcanosedi- tant periods of interrupted sedimentation, since less mentary rocks of the Perubar area are much younger than 2 Ma separate the end of the Footwall Unit sedi- (Maastrichtian) than the Albian to Cenomanian age so mentation and the deposition of the Upper Unit far assumed for the Casma Group; (2) allow a better (Fig. 3a). understanding of the temporal relationships between The Hangingwall and Upper Unit deposits (Fig. 3) are basin subsidence, subaqueous volcanism, hydrothermal interpreted as the result of a tectonically controlled massive sulfide mineralization, and plutonism during the caldera collapse, where collapse and magmatic plumbing uppermost Cretaceous in this region of the Peruvian were influenced by pre-existing faults (Polliand 2005).