Late cretaceous to miocene stratigraphy and provenance of the coastal forearc and Western Cordillera of Ecuador: Evidence for accretion of a single oceanic plateau fragment

CHAPTER

Late Cretaceous to Miocene stratigraphy and provenance of the coastal forearc and Western Cordillera of Ecuador: Evidence for accretion of a single oceanic plateau fragment

8

Cristian Vallejo⁎, Richard A. Spikings†, Brian K. Horton‡,#, Leonard Luzieux§, Christian Romero⁎, Wilfried Winkler¶, Tonny B. Thomsen‖ Departamento de Geología, Facultad de Ingeniería en Geología y Petróleos, Escuela Politécnica Nacional, Quito, Ecuador* Department of Earth Sciences, University of Geneva, Geneva, Switzerland† Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, United States‡ LH Trading Ltd, Zürich, Switzerland§ Geological Institute, ETH Zürich, Zürich, Switzerland¶ Geological Survey of Denmark and Greenland (GEUS), Department of Petrology and Economic Geology, Copenhagen, Denmark‖ Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, TX, United States♯

1 ­Introduction The Northern Andes are distinguished from the rest of the Andean orogenic belt by the presence of mafic oceanic rocks forming the basement of the coastal forearc and western Andean regions of Ecuador and Colombia (Goosens and Rose, 1973; McCourt et al., 1984). Mafic rocks of comparable geochemistry and age are exposed within Caribbean and Central American regions (Fig. 1), including the Dominican Republic, Panama, and Costa Rica (Goosens and Rose, 1973; Kerr et al., 2002). For the Western Cordillera and coastal forearc regions of western Ecuador, different models have been proposed to explain the presence of allochthonous mafic rocks that form an ocean-continent accretionary complex (e.g., Lebras et al., 1987; Eguez, 1986; Kerr et al., 2002; Jaillard et al., 2004; Spikings et al., 2005; Luzieux et al., 2006; Vallejo et al., 2009). These models invoke multiple accretion scenarios variably spanning from the Late Cretaceous through Eocene (e.g., Lebras et al., 1987; Van Thournout et al., 1992; Hughes and Pilatasig, 2002; Kerr and Tarney, 2005; Spikings et al., 2005). Contrasting interpretations result in significantly different reconstructions of western Ecuador during Late CretaceousCenozoic time, the period of orogenesis in the Northern Andes. This study reviews stratigraphic, structural, and geochronological data in order to define the history of sedimentation and tectonics along the western Ecuadorian Andes. Provenance studies of uppermost Andean Tectonics. https://doi.org/10.1016/B978-0-12-816009-1.00010-1 © 2019 Elsevier Inc. All rights reserved.

209

210

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

90°

85°

80°

75°

70°

65°

60°

Bahamas Yucatan Basin

20° h Troug

man

Cay

ise Rd ige

aR

u rag

Caribbean Plate

Colombian Basin

15° Barbados Ridge

Venezuela Basin

Aves Ridge

Be ata

a

Nic

10° Venezuela

Cocos Plate e

idg

sR

o oc

C

5°

Colombia

Galapagos. Carnegie Ridge

Ecuador

Continental crust

Subduction

Deformed continental crust

Thrust Fault

Oceanic terranes Oceanic Ridge y Rise

Nazca Plate

Strike slip Fault Direction of motion

Andean Cordilleras

FIG. 1 Map of the plate tectonic framework of the Northern Andes and Caribbean region (modified from Luzieux et al., 2006).

Cretaceous-Cenozoic sedimentary deposits that overlie basement rocks of oceanic origin help constrain the mineralogical composition, geochemistry, age, and approximate location of contributing sediment source regions, which facilitates stratigraphic correlations and tectonic reconstructions.

2 ­Regional geology Ecuador can be subdivided into five distinct morphotectonic regions (Fig. 2). (1) The coastal forearc is composed of mafic oceanic crust (Feininger and Bristow, 1980; Jaillard et al., 1995; Reynaud et al., 1999; Luzieux et al., 2006) and covered by Paleogene to Neogene forearc deposits (Fig. 3). (2) The Western Cordillera consists of mafic and intermediate extrusive and intrusive rocks tectonically juxtaposed with sedimentary deposits of Late Cretaceous to Miocene age (Jaillard et al., 2004; Vallejo et al., 2009). (3) The Interandean Valley (Interandean Depression) lies between the Western and Eastern cordilleras and hosts thick Pliocene-Pleistocene volcanic deposits. Small inliers beneath Cenozoic volcanic rocks within the Interandean basin system reveal a crystalline basement composed of metamorphic and mafic rocks

2 ­Regional geology

211

FIG. 2 Geological sketch map showing the main tectonic provinces and geologic units of Ecuador discussed in this chapter (modified from Mamberti et al., 2003).

(e.g., Cotteccia and Zezza, 1969; Bruet, 1949). On its western flank, the Interandean Valley is bound by the Calacalí-Pujilí fault system (Hughes and Pilatasig, 2002). This fault system, partially exposed along the eastern edge of the Western Cordillera, defines a reactivated suture between the South American continental margin and accreted oceanic rocks (e.g., Aspden and Litherland, 1992). (4) The Eastern Cordillera is composed of Paleozoic metamorphic rocks and Mesozoic granitoids and metasedimentary rocks (Litherland et al., 1994; Spikings et al., 2015). The range is separated from the Interandean Depression by the Peltetec Fault, which is the southward continuation of the Silvia-Pijao Fault of Colombia (Spikings et al., 2015). The eastern limit of the Eastern Cordillera is represented by the east-vergent Cosanga Fault. (5) The Oriente Basin, including the Subandean Zone, is a Late Cretaceous-Quaternary retroarc foreland basin that developed on the South American plate margin, in response to the growth of the Eastern Cordillera (Ruiz et al., 2004; Martin-Gombojav and Winkler, 2008; Horton, 2018).

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

Coastal forearc

N

S

Western Cordillera

W

Villingota Fm. Dos Bocas Fm.

Oligocene

Turupamba Fm.

El Progreso Fm. Sube y Baja Fm. El Consuelo Fm. Villingota Fm.

(southern Ecuador)

Zumbagua Gp. Quimsacocha Fm. (southern Ecuador)

Turi Fm.

Silante Fm.

Ayancay Fm.

Jubones Fm.

(southern Ecuador)

(northern Ecuador)

(southern Ecuador)

Dos Bocas Fm.

23 Ma

Chatt.

Saraguro Fm.

San Juan de Lachas Fm.

Zapotal Fm.

Pambil Fm.

(southern Ecuador)

(northern Ecuador)

Playa Rica Fm.

Rup

Rumi Cruz U.

?

34 Ma

Priab

San Mateo Fm.

Bart

Punta Blanca Fm.

Las Masas Fm.

Lut

El Laurel U.

Punta Ancón Fm.

40 Ma

Eocene

?

(southern Ecuador)

Onzole Fm.

Mioc.

E

Tarqui Fm.

2.5 Ma

Ancón Gp.

Neogene

Plioc.

Seca Fm.

Tortugo U.

Soccorro Fm.

Apagua U.

Clay Pebble Fm.

Macuchi U.

Passage beds Fm. Unacota U. Ostiones Fm.

San Eduardo Fm.

Ypr

Angamarca Group

212

Gallo Rumi U.

Saquisili U.

?

Paleocene

56 Ma

Than

Saguangual U..

Azucar Gp.

Sel

La Cubera Fm.

Guayaquil Fm.

Dan

66 Ma

Pilalo U.

Tandapi U.

Santa Elena Fm.

Maa

Camp

83.5 Ma

San Lorenzo Fm.

Las Orquideas Fm.

Sant Con Tur Cen

Cayo Fm.

Rio Cala Group

Late Cretaceous

72 Ma

Yunguilla Fm.

Rio Cala U. Natividad U.

Naranjal U. La Portada U.

Pilatón U.

Mulaute U.

Calentura Fm.

?

99 Ma

Pallatanga Fm.

Pujili Granite

San Juan U.

?

Piñon Fm.

Oceanic plateau

Pelagic sediments Calciturbidites, deep marine deposits

Submarine arc volcanics

Submarine arc volcaniclastic deposits

Limestones

Samples for U-Pb detrital zircon geochronology

Coastal to continental siliciclastic deposits Sedimentary series with volcanic source

Continental arc volcanics Marine sedimentary series with continental crust source

FIG. 3 Regional stratigraphic framework of Cretaceous to Neogene accreted oceanic materials, volcanic rocks, and sedimentary rocks in the coastal forearc and Western Cordillera of Ecuador (after Jaillard et al., 1995; Benitez, 1995; Vallejo, 2007; Luzieux, 2007).

3 ­Western Cordillera and allochthonous basement

213

3 ­The Western Cordillera and the allochthonous origin of the basement The basement of the Western Cordillera of Ecuador consists of mafic rocks commonly interpreted to have accreted to South America during the Late Cretaceous-Paleogene convergence (Goosens and Rose, 1973; Jaillard et al., 1995; Vallejo et al., 2006). Fault displacement along approximately N-S striking faults has resulted in a complex assemblage of tectonostratigraphic units (Hughes and Pilatasig, 2002; Vallejo et al., 2009). In addition, the juxtaposition of volcano-sedimentary and turbidite successions of similar lithology yet contrasting depositional ages has further complicated stratigraphic correlations and tectonic reconstructions. From 1996 to 2001, the British Geological Survey (BGS) introduced a new nomenclature to refer to the suspected allochthonous terranes of the Western Cordillera (e.g., Kerr et al., 2002). The BGS defined the Pallatanga Terrane as the ultramafic and mafic basement of the Western Cordillera, and distinguished oceanic arcs of Late Cretaceous (Naranjal Terrane) and Cenozoic (Macuchi Terrane) ages. Here we prefer to use the term blocks, due to uncertainties regarding their allochthonous origin.

3.1 ­The Pallatanga block The Pallatanga block includes several volcanic and sedimentary formations, which can be grouped into: (a) basement rocks of the Pallatanga Formation (Fig. 4A) and the San Juan unit; (b) Late Cretaceous volcaniclastic rocks with associated basaltic lavas (Rio Cala arc); (c) Calc-alkaline volcanic rocks of the Tandapi unit of latest Maastrichtian-Paleocene age (Cosma et  al., 1998); (d) Paleocene-Eocene subaqueous deposits of the Angamarca Group (Hughes and Pilatasig, 2002); and (e) OligoceneMiocene subaerial volcanic and volcaniclastic rocks of calc-alkaline affinity, including the San Juan de Lachas and Silante formations in northern Ecuador (Van Thournout et al., 1992; Herrera, 2018), and the Saraguro, Jubones, Tarqui, Quimsacocha, and Turi formations in southern Ecuador (Dunkley and Gaibor, 1997; Boland et al., 2000). The Pallatanga Formation is the basement of the Western Cordillera and includes submarine basaltic lavas and dolerites. The basalts, with their flat primitive mantle- and chondrite-normalized patterns, are interpreted as formed in an oceanic plateau setting (Reynaud et al., 1999). Oceanic plateaus form in deep-ocean basins as broad, flat-topped features lying 2000 m or more above the seafloor (e.g., Mann and Taira, 2004). These mantle-plume driven eruptions have large aerial extents (>1015 km2) with anomalously high eruption rates (Saunders et al., 1996). Typically, their thickness is >10 km, and locally can exceed 30 km (Sinton et al., 1998), and are not readily subductable because of their inherent buoyancy. Rocks of the Pallatanga Formation are very similar in chemical composition to basalts from the Caribbean Plateau (Kerr et al., 2002). To the southwest of Quito, the San Juan ultramafic complex includes layered gabbros, peridotites, and dunites. Geochemical and isotopic data suggest that the San Juan unit represents the intrusive components of an oceanic plateau (Mamberti et al., 2004). Radiometric ages obtained from mafic rocks of the San Juan unit include a plagioclase, whole rock, and amphibole Sm-Nd isochron age of 123 ± 13 Ma (Lapierre et al., 2000) and a U-Pb zircon concordia age of 87.1 ± 1.7 Ma (Vallejo et al., 2006). According to Spikings et al. (2015), rocks that yield ages of 123 Ma are probably a detached fragment of the Peltetec unit of the Eastern Cordillera, which has a different origin than Western Cordillera basement. Therefore, we consider the zircon U-Pb age of 87.1 ± 1.7 Ma to be the best estimation of the crystallization age of the oceanic plateau basement (Pallatanga Formation) exposed in the Western Cordillera.

214

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

(A)

(B)

(C)

(D) Apagua unit

Macuchi unit

(E)

(F)

(G)

(H)

FIG. 4 See figure caption on opposite page.

3 ­Western Cordillera and allochthonous basement

215

3.1.1 ­The Rio Cala arc

The Rio Cala magmatic arc includes volcanic and volcaniclastic rocks that unconformably overlie the Pallatanga Formation (Vallejo et al., 2009). They were deposited as turbidite beds with intercalated debris flows of Late Cretaceous age (Fig. 3). The Rio Cala arc includes the Natividad, Rio Cala, Mulaute, and Pilaton units (Fig. 4B). Geochemical data from volcanic components suggest an intraoceanic island arc setting (Vallejo, 2007; Allibon et al., 2008; Chiaradia, 2009). Biostratigraphic ages from intercalated mudstones indicate ages ranging from Santonian to early Maastrichtian (Hughes and Pilatasig, 2002). Nd and Pb isotopic compositions suggest a magmatic evolution characterized by mixing of signatures from oceanic plateau, Pacific MORB mantle, and subducted pelagic sediments (Vallejo et al., 2006; Allibon et al., 2008; Whattam and Stern, 2015). The Pujili Granite is a foliated granite that intrudes the Pallatanga unit in the central part of the Western Cordillera (Fig.  4A). Zircon U-Pb geochronology results indicate a crystallization age of 85.5 ± 1.4 Ma (Vallejo et al., 2006). The Pujili Granite is considered part of the Rio Cala magmatic arc and may represent the intrusive roots of this intraoceanic arc. Volcanism within the Rio Cala arc terminated at ~70 Ma (Vallejo, 2007; Whattam and Stern, 2015).

3.1.2 ­The Yunguilla Formation, Angamarca Group, and Zumbagua Group

The Yunguilla Formation is a sedimentary package restricted to the eastern border of the Western Cordillera and is composed of shales and fine sandstones in turbidite beds lithologically similar to the Apagua and Saquisili units. However, biostratigraphic ages indicate a Campanian to Maastrichtian age (Hughes and Pilatasig, 2002; Jaillard et  al., 2004). The Yunguilla Formation is interpreted as part of a forearc basin that formed along the continental margin during the Late Cretaceous and was deformed during the ensuing accretion of the allochtonous blocks of western Ecuador (Hughes and Pilatasig, 2002). The Angamarca Group is a siliciclastic basin fill sequence deposited along the Western Cordillera consisting of the Saquisili, Apagua, Pilalo, Unacota, El Laurel, and Rumi Cruz units (Hughes and Pilatasig, 2002), which span from Paleocene to late Eocene (Fig. 3). The Saquisili unit includes a series of medium-to-fine-grained turbidite sandstones (Fig.  4C) with early to middle Paleocene biostratigraphic ages (Hughes and Pilatasig, 2002). To the south, the Saquisili unit is intercalated with conglomerates (Gallo Rumi conglomerates), which represent the proximal part of a submarine fan system. The Apagua unit overlies the Saquisili unit and consists of turbiditic shales, siltstones, and ­medium-grained sandstones. The sandstones are typically feldspathic and contain mafic minerals and lithic fragments. Foraminiferal fauna from this unit indicate a middle Paleocene to middle Eocene age FIG. 4 Photographs of representative outcrops of basement and sedimentary cover in the Western Cordillera and coastal region of Ecuador. (A) Foliated Pujili granite intruding basalts of the Pallatanga Formation (UTM: 755300/9898600). (B) Thick-bedded turbidites and sandy debrites of the Pilaton unit, part of the Rio Cala Group (UTM: 0810301/0079791). (C) Thin-bedded turbidites and debrites of the Saquisili unit (UTM: 738259/9821523). (D) Stratigraphic contact between volcanic rocks of the Macuchi unit and turbidites of the Apagua unit, Pallatanga-Bucay road (UTM: 721613/9766370). (E) Thin-bedded turbidite beds of the Macuchi unit (UTM: 728072/9965008). (F) Subhorizontal turbidites and debrites of the Cayo Formation in the Guayaquil area. (G) Pillow lavas of Upper Cretaceous San Lorenzo Formation (UTM: 546730/9876750). (H) Turbidites of the Ancon Group in the Ancon area, Santa Elena Peninsula (UTM: 517752/9740859).

216

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

(Hughes and Pilatasig, 2002). The Apagua unit is intercalated with the middle to upper Eocene Unacota Limestone (Eguez, 1986). Andesitic to basaltic volcanic rocks are observed near the type locality of the Apagua unit. In the central part of the Western Cordillera, near Bucay (Fig. 2), sediments of the Apagua unit conformably overlie and interfinger with volcanic and volcaniclastic rocks of the Macuchi unit (Fig. 4D). The Rumi Cruz unit is the youngest part of the Angamarca Group and includes massive nonmarine conglomerates, sandstones, and red shales likely deposited in a fan delta system (Hughes and Bermudez, 1997). Collectively, the Angamarca Group represents an upward-shallowing progradational succession that recorded a shift from a submarine fan to fan delta environment (Hughes and Pilatasig, 2002). The Angamarca Group is unconformably overlain by volcanic rocks of the Saraguro Group (Fig. 3), considered to represent late Eocene-Oligocene continental margin volcanism (McCourt et al., 1997). K-Ar (hornblende) and zircon fission track (ZFT) ages range from 38 to 20 Ma (Dunkley and Gaibor, 1997; Pratt et al., 1997). In the northern part of the Western Cordillera, the San Juan de Lachas unit yield hornblende K-Ar and 40Ar/39Ar ages ranging from 36 to 32 Ma (Van Thournout, 1991; Vallejo, 2007), suggesting the unit is the northward continuation of Saraguro volcanic deposits. The Neogene Zumbagua Group unconformably overlies deformed Cretaceous-Paleogene deposits. In the northern part of the Western Cordillera, reported fission-track ages of 15.3 ± 1.9 M and 14.5 ± 2.7 Ma for tuffaceous sandstones (Hughes and Bermudez, 1997) indicate a middle Miocene or younger age of deposition. The Zumbagua Group includes alternating beds of laterally continuous conglomerate, sandstone, and siltstone rich in volcaniclastic material, principally deposited in lacustrine settings in intermontane or intra-arc basins. The deposits were locally folded prior to overlap by Quaternary volcanic ash of the Cangahua Formation (Hall and Calle, 1982).

3.2 ­The Macuchi block The Macuchi block is a lithotectonic unit composed of volcanic and volcaniclastic rocks of oceanic origin. It is located along the western edge of the Western Cordillera (Fig. 2), where its western limit is buried below the alluvial fan deposits of the coastal plain and its eastern limit is defined by the ChimboToachi Fault. Several authors have proposed that the Macuchi block was allochthonous and collided against the continental margin during the late Eocene (e.g., Spikings et al., 2001; Hughes and Pilatasig, 2002; Kerr et al., 2002).

3.2.1 ­The Macuchi unit

The Macuchi unit is included within the Macuchi block and comprises a thick series of volcaniclastic and primary volcanic rocks of basaltic to andesitic compositions. This unit hosts gold-rich volcanogenic massive sulfide deposits (VMS), including the La Plata, Macuchi, and El Domo deposits (Vallejo et al., 2016). This unit shows variegated volcaniclastic and primary volcanic rocks, including andesites, pillow lavas, hyaloclastites, and breccias, deposited in a submarine volcanic arc succession that is at least 2000-m thick (Aguirre and Atherton, 1987). Volcaniclastic rocks are the most common lithofacies (Fig. 4E) and comprise ~80% of the Macuchi unit (Vallejo, 2007). Rhyodacites and dacites are volumetrically less significant and are poorly mapped (Vallejo et  al., 2016). Low-temperature prehnite-pumpellyite sea-floor hydrothermal alteration is ubiquitous in these rocks (Aguirre and Atherton, 1987).

4 ­ The coastal forearc and the Piñon block

217

Rocks mapped in the Macuchi unit were previously included within the basic igneous complex (BIC) of Goosens and Rose (1973). Henderson (1979) interpreted the Macuchi unit to be of Late Cretaceous-Eocene age; this was based in part upon inclusion of Upper Cretaceous turbidites, which are now considered to be part of the Pilaton unit (Hughes and Pilatasig, 2002).

4 ­The coastal forearc and the Piñon block The distribution of Bouguer gravity anomalies reveals that the northern two-thirds of the coastal forearc in Ecuador is underlain by oceanic crust (Feininger and Seguin, 1983), which is defined in this study as the Piñon block. The Piñon Formation is regarded as the basement of the Piñon block and is exposed in (i) the Chongon Colonche Cordillera to the north of Guayaquil, (ii) the southwestern part of the Santa Elena peninsula, and (iii) the Manabí Basin (Fig. 2), suggesting that it forms the regional basement of the entire coastal forearc (Jaillard et al., 1995; Luzieux, 2007). Previous authors have included rocks of the Piñon Formation within the BIC (Goosens and Rose, 1973) and have correlated these rocks with basalts of the Nicoya peninsula of Costa Rica and Cretaceous basalts in the Western Cordillera of Colombia (Goosens and Rose, 1973; Feininger and Bristow, 1980). Basalts and dolerites of the Piñon Formation are geochemically very similar to those of the Pallatanga unit (Kerr et al., 2002), with flat-to-slightly LREE-depleted REE patterns and nearly identical multielement patterns (Kerr et al., 2002; Luzieux, 2007). These geochemical data led to Reynaud et al. (1999) to propose that the volcanic rocks of the Piñon Formation had an oceanic plateau origin. Luzieux et al. (2006) obtained a hornblende 40Ar/39Ar age of 88.8 ± 1.6 Ma, and proposed that the Piñon Formation represent fragments of the Caribbean Plateau. Macias (2018) obtained U-Pb zircon ages (SHRIMP) ranging between 98.4 ± 1.7 Ma to 90 ± 1.6 Ma from intrusions crosscutting the Piñon Formation. These ages overlap those reported for intrusions in the Western Cordillera of Colombia (Villagomez et al., 2011) and the Caribbean region (Wright and Wyld, 2011) erupted above oceanic plateau rocks prior to its collision with the South American margin. This suggests that the Piñon Formation can be older than 98.4 Ma, and may represent the oldest phase of the Caribbean Plateau volcanism.

4.1 ­Late Cretaceous to Miocene stratigraphy of the central and southern part of the coastal forearc A representative Cretaceous-Cenozoic succession of the coastal forearc is exposed north of Guayaquil, along the Chongon Colonche Cordillera (Fig. 2). Here the Piñon Formation is conformably overlain by shales, laminated black limestone, and thin-bedded turbidite deposits of the Calentura Formation. The basal unit, the Calentura Formation, was originally assigned a Cenomanian to Coniacian biostratigraphic age (Thalmann, 1946; Jaillard et al., 1995), suggesting a pre-Cenomanian age for the Piñon Formation (Jaillard et al., 1995; Reynaud et al., 1999; Kerr and Tarney, 2005). However, Luzieux et al. (2006) obtained younger Coniacian to Santonian biostratigraphic ages. The Cayo Formation overlies the Calentura Formation and corresponds to a thick series of turbidite and debris flows (Fig.  4F) deposited in a submarine fan setting with considerable volcanic input (Benitez, 1995; Jaillard et al., 1995). Biostratigraphic ages suggest a middle-late Campanian age (Luzieux, 2007; Van Melle et  al., 2008). In the Guayaquil area, primary volcanic rocks of the

218

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

Las Orquideas unit are considered to be of similar age (Benitez, 1995; Luzieux, 2007). The Cayo Formation includes basalts and dolerites, with geochemical data indicating an island arc setting (Reynaud et al., 1999). In the San Lorenzo area of the Manabi Basin (Fig. 2), volcaniclastic rocks intercalated with basaltic flows (Fig. 4G), ash beds, and dikes of the San Lorenzo Formation rest on the Piñon Formation. Geochemical data indicate an intraoceanic arc setting (Lebras et  al., 1987; Jaillard et  al., 1995; Reynaud et al., 1999). Radiometric and biostratigraphic ages support a middle Campanian to middle Maastrichtian age (Lebras et al., 1987; Luzieux et al., 2006; Van Melle et al., 2008), which is partly coeval with the Cayo Formation of the Guayaquil area (Fig. 3). In the Guayaquil region, the Cayo Formation is conformably overlain by the Guayaquil Formation, a sedimentary succession composed of ~300 m of evenly bedded (cm- to dm-scale) siliceous limestones with chert nodules interbedded with turbidite sandstones, tuffaceous siltstones, shales, and ash beds (Luzieux, 2007). Biostratigraphic ages indicate a Maastrichtian to late Paleocene for the Guayaquil Formation (Benitez, 1995; Keller et  al., 1997; Luzieux, 2007). The Santa Elena Formation, located along the Santa Elena Peninsula west of Guayaquil, is considered a strongly deformed lateral equivalent of the Guayaquil Formation (Jaillard et al., 1995). In the Guayaquil area, the Guayaquil Formation is conformably overlain by turbiditic limestones of the lower to middle Eocene San Eduardo Formation; whereas, along the Santa Elena Peninsula, the Santa Elena Formation is overlain by a succession of high density turbiditic sandstones, conglomerates, and shales of the upper Paleocene Azucar Group. Benitez (1995) suggests a submarine fan environment for the Azucar Group. Dark gray and green-yellow laminated shales, marlstones, siltstones, and turbidite beds of the middle Eocene Las Masas Formation overlie the San Eduardo Formation near Guayaquil. In the Santa Elena Peninsula, the middle Eocene Ancon Group caps the Azucar Formation and is composed of a rhythmic succession of cm-to-dm-thick turbidite beds of yellow, brown, and green shales, siltstones, and sandstones (Fig. 4H), intercalated with sandy debris flows and conglomerates representing the infilling of submarine channels. The depositional environment is interpreted as a submarine fan environment. Luzieux (2007) suggests that the Las Masas and Ancon formations are part of a progradational upward-coarsening submarine fan succession. The San Mateo Formation is a 700-m-thick upward-fining sequence composed of dm-to-m-thick conglomerates and pebbly sandstones and laminated sandstones deposited by high-density turbidity flows in a submarine fan system (Luzieux, 2007). The San Mateo Formation includes tuffaceous intervals that probably represent coeval eruptive episodes (Luzieux, 2007). The San Mateo Formation unconformably overlies the San Lorenzo and Cayo formations. It is unconformably overlain by the Zapotal Formation in the south and Tosagua Formation in the center and the north of the Manabi Basin. To the north, the San Mateo Formation can be correlated with siliceous shales, radiolarian-rich marlstones, fine tuffs, and dm-thick, calcareous turbidite sandstones of the Punta Blanca Formation, which may represent distal facies of the San Mateo submarine fan. Biostratigraphic analysis suggests a middle to late Eocene age for the San Mateo and Punta Blanca formations (Luzieux, 2007). The Zapotal Formation unconformably overlies the Ancon Group, and consists of coarsegrained sandstones and conglomerates, including paleosols and freshwater gastropods, suggestive of a nonmarine to coastal environment. The lower part of the Zapotal Formation is considered to have been deposited in an alluvial environment. In the northern part of the coastal forearc, shales

5 ­ Accretion models for Ecuador

219

and siltstones of the Pambil and Playa Rica formations were coeval with the Zapotal Formation, and were deposited in a marine environment. Stratigraphic relationships suggest an Oligocene age for the base of the Zapotal Formation (Luzieux, 2007). During the Miocene, the Ecuadorian forearc was characterized by a period of regional strike-slip deformation and a localized extension that affected the coastal region (Benitez, 1995; Luzieux, 2007), resulting in the formation of a series of extensional pull-apart basins that are filled with siliciclastic sediments. These basins are, from south to north, the Progreso, Manabi, and the Borbon basins. Miocene sedimentary fill of the southern part of the coastal forearc includes coastal to marine deposits of the Dos Bocas, Villingota, El Consuelo, Sube y Baja, and Progreso formations, whereas the Dos Bocas, Villingota, and Onzole formations were deposited in the north.

5 ­Models for the accretion of the coastal region and Western Cordillera blocks Several models have been proposed for the tectonic evolution of the Western Cordillera and coastal region of Ecuador (e.g., Feininger and Bristow, 1980; Eguez, 1986; Lebras et al., 1987; Van Thournout, 1991; Kerr et  al., 2002; Spikings et  al., 2005). The prevailing models and reconstructions (Fig.  5) propose that allochthonous oceanic blocks (i.e., Pallatanga, Piñon, and/or Macuchi) approached South America with double eastward subduction of oceanic crust with an intervening island arc, and collided between the Late Cretaceous and late Eocene (Aspden and Litherland, 1992; Lebras et al., 1987; Kerr et al., 2002; Spikings et al., 2005). Lebras et al. (1987) proposed that the Macuchi arc was an intraoceanic arc that formed on top of the Piñon Formation by east-dipping subduction of normal-thickness oceanic crust (Fig. 5A). These authors considered the Macuchi arc to be Turonian-Santonian in age, coeval with the Cayo Formation of the coastal region and the Celica arc of southern Ecuador. However, as indicated earlier, radiometric and biostratigraphic dating of the Macuchi unit supports an Eocene age for this submarine arc. Van Thournout et al. (1992) proposed that during the Early Cretaceous to Paleocene, eastward subduction of oceanic crust beneath the Piñon Formation produced the San Lorenzo arc, and associated volcanic and sedimentary rocks of the Cayo Formation (Fig. 5B). This island arc was accreted to the margin at 70–50 Ma, deforming the flyschoid continental-margin deposits of the Yunguilla Formation. During the middle Eocene to early Oligocene, after a westward jump in the subduction zone, the Macuchi submarine arc formed atop accreted oceanic crust of the Piñon Formation. For these authors, the Apagua unit represents a backarc basin deposit, whereas to the west the San Mateo and Punta Blanca formations correspond to forearc deposits. Kerr et al. (2002) and Hughes and Pilatasig (2002) primarily used geochemical data to interpret that the Western Cordillera is composed of rocks from a variety of oceanic tectonic settings, including anomalously thick oceanic crust of oceanic plateau origin (Pallatanga and Piñon formations), island arc tholeiites (Naranjal and Macuchi units), and backarc basin basalts (La Portada Formation). These authors proposed that the Pallatanga block accreted during a prolonged Late Cretaceous episode, whereas the Late Cretaceous Naranjal and Eocene Macuchi island arcs may have accreted against the continental margin during the Eocene, along the Chimbo-Toachi and Mulaute faults, respectively (Fig. 5C). Kerr et al. (2002) proposed that accretion of the Macuchi block had gradually closed the

220

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

(A)

(B)

W

Lower Cretaceous - Paleocene

E

Piñón Fm Cayo Fm

Macuchi arc

SOAM

Turonian to Santonian period

CAMPANIAN PERIOD

W Cayo Fm.

Piñón Fm

South North San Lorenzo Fm. Yunguilla Fm. Celica Fm. Cayo Fm. Cayo Fm. Silante Fm.

SW

Celica arc

NE

Piñon

Piñon

Middle Eocene - early Oligocene

SW

San Mateo Fm. Punta Blanca Fm. Macuchi arc Apagua unit Zapallo Fm.

NE

E Upthrust D.G.M. T-type MORB Cenozoic Volc. Macuchi Fm. S Celica Fm. SOAM

Oligocene - Recent

W

Miocene to recent volcanics intrusives

Resent trench

E

Present-day profile

Lebras et al. (1987)

(C) Campanian

W

E

Pallatanga

? Mid Maastrichtian Piñon oceanic plateau San Lorenzo arc

Van Thournout et al. (1992) Mid Eocene

Pallatanga Piñon oceanic oceanic plateau Macuchi arc San Lorenzo arc plateau

Pallatanga oceanic plateau

Eocene Saraguro arc Angamarca Late Paleocene back arc basin Piñon Pallatanga San Lorenzo arc oceanic plateau Macuchi arc oceanic plateau

Mulaute shear zone

Kerr et al. (2002) FIG. 5 Contrasting models proposed for the evolution of the Western Cordillera and coastal region of Ecuador (A: After Lebras et al., 1987; B: Van Thournout et al., 1992; C: Kerr et al., 2002).

5 ­ Accretion models for Ecuador

221

Angamarca Basin, and was complete by the late Eocene. In this model, the Macuchi submarine arc formed between the Piñon and Pallatanga blocks, and was separated from the Piñon block by a trench. For these authors, late Eocene accretion of the Piñon block was supported by elevated cooling rates up to ~30–20°C/Myr during the Eocene-early Oligocene (Fig. 6) along the entire Ecuadorian Andes (Spikings et al., 2001). WESTERN CORDILLERA Accretion of the Pallatanga and Piñon blocks

APAZ

140 180 220 260

00RS18 Macuchi unit

? 00RS37 Silante unit

incorporation into the melange

00RS42 Yungilla unit (northern Ecuador)

00RS43 Pilatón unit (northern 00RS28 Ecuador) Silante unit

ZPAZ

100

300

380

?

40Ar/39Ar

Bt

40Ar/39Ar

WM

?

180

Far Northern Ecuador

220 260

ZPAZ

?

?

300

? 40Ar/39Ar

340

40Ar/39Ar

380 100

90

80

70

60

50 40 Time (Ma)

30

20 10 0 Spikings et al. (2005)

IAD

CPFZ

coastal forearc

CTSZ

Western Cordilera

W

APAZ

140

70

60

50

40 30 Time (Ma)

Biotite

White Mica

20 10 0 Spikings et al. (2005)

Eastern Cordillera

PF

340

Increase in convergence rates between the Farallon and the South American Plate

Unconstrained region

60

Temperature (˚C)

100

00RS32 Saquisilli unit

cooling of the

Temperature (˚C)

60

Accretion of the Pallatanga and Piñon blocks

20

Unconstrained region

source rocks

20

EASTERN CORDILLERA

Increase in convergence rates between the Farallon and South

E

SAZ Oriente

Subducted oceanic crust

Mesozoic sediments (Oriente Basin and Subandean zone) Island arc suites (Late Cretaceous)

Neogene sediments

Oceanic plateau

Paleogene sediments

Metamorphic basament

Yunguilla Fm. (Late Cretaceous)

Continental crust

Quaternary arc complexes

Fault

FIG. 6 Schematic cross-section of the Andean margin with representative thermal history envelopes for samples from the Western Cordillera and Eastern Cordillera (Cordillera Real) and their relationship to significant tectonic events in Ecuador (Spikings et al., 2001, 2005).

222

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

6 ­Provenance analysis of the Western Cordillera and coastal forearc region Provenance analyses of clastic deposits overlying the Pallatanga and Piñon blocks were performed to decipher shifts in sediment source and source area location, associated with the evolution of the sedimentary basins and hence the tectonic setting. A critical aim is to determine a temporal framework for the accretion of tectonostratigraphic blocks, and to seek evidence for the identification and first appearance of continental crustal sources that overlie suspected allochthonous blocks. In this study, we combine stratigraphic data, heavy mineral analyses, and U-Pb detrital zircon dates. For many samples, consideration of the youngest available U-Pb ages provides estimates of maximum depositional age (MDA) that, in cases of close proximity to the magmatic arc, may approach the actual stratigraphic age (e.g., Perez and Horton, 2014; Horton et al., 2015a,b). The detrital assemblages reflect the mineralogical composition of the source regions that fed various basin catchments (Morton and Hallsworth, 1994; Luzieux, 2007).

6.1 ­Heavy mineral data Forty-nine sedimentary rocks that overlie the Pallatanga, Macuchi, and Piñon blocks were selected for heavy mineral analyses (Fig.  7). The analyzed sedimentary succession ranges in age from Late Cretaceous to Miocene, the time frame proposed for accretion of various blocks (e.g., Jaillard et al., 2004; Kerr et al., 2002; Kerr and Tarney, 2005; Luzieux et al., 2006). For the Piñon block, rock samples analyzed for heavy mineral compositions include the Upper Cretaceous Cayo and Calentura formations, the Paleocene Azucar Group and Guayaquil Formation, the Eocene Ancon Group, San Mateo and Las Masas formations, the Oligocene Zapotal Formation, and the Miocene Villingota, El Consuelo, and Progreso formations. Samples selected for heavy mineral analysis from the Western Cordillera include sedimentary rocks of the Rio Cala arc, Yunguilla Formation, and Angamarca Group.

6.1.1 ­Heavy mineral data from the Western Cordillera

In the Western Cordillera, heavy mineral assemblages within Coniacian to Campanian sedimentary rocks of the Rio Cala Group (Pilaton, Mulaute and Natividad formations) show a likely derivation from a volcanic arc (Fig. 7). The lack of continental material (e.g., detrital zircon, rutile, tourmaline) suggests that these units were deposited far from continental influence. For the sedimentary rocks of the Yunguilla Formation, heavy mineral assemblages indicate a strong metamorphic and continental crust input, with a minor mineral assemblage from volcanic sources. The heavy mineral assemblage for the Paleocene Pilalo unit includes several crystals of euhedral and acicular zircons, with minor amounts of alteration minerals (e.g., pumpellyite, chlorite). The presence of euhedral zircons of possibly volcanic origin may indicate that the sandstone contains reworked tuffaceous material. Additional heavy minerals include brookite, pyroxene, diagenetic apatite and chlorite. Overall, the heavy mineral association for the Pilalo unit is considered indicative of a volcanic source. For the Angamarca Group (Saquisili, Apagua, El Laurel, and Rumi Cruz units), heavy mineral assemblages show a strong input of zircon, tourmaline, and rutile mineral (ZTR). Minerals derived from metamorphic rocks are also important, whereas volcanic-derived minerals are of minor importance, except for the Apagua unit, which is clearly enriched in pyroxenes and thus derived from a volcanic source.

6 ­Provenance analysis

Coastal forearc

223

Western Cordillera

Olig.

Neogene

Plioc. Mioc.

Chatt. Rup

El Progreso Fm

05LL433

El Consuelo Fm Villangota Fm

05LL437

Zapotal Fm

05LL435

02CV136

Silante Fm.

02CV56 00RS28

05LL436

Rumi Cruz U.

00RS12 03CV250 03CV240

Priab

El Laurel U.

03CV197

Bart

02LL20 02CV18

03LL269

San Mateo Fm

04LL340

Seca Fm

05LL442

Socorro Fm Clay Pebble Fm

05LL439

Apagua U.

00RS7 00RS3

03LL186

Ypr

Las Masas Fm Azúcar Fm

Macuchi U.

03CV197

05LL431

Saquisili U.

Lut

Ancon Group

Eocene

02CV223

Pta. Ancón Fm

LM 05LL438 02LL18

03CV215 02CV125 03CV204 00RS32

Paleocene

Than 03CV137

Sanguangal U.

Sel

00RS38 00RS39

Dan

03LL254

Guayaquil Fm

02CV223 00RS34 00RS14 02CV33

Pilalo U.

03LL252 03LL251

02CV51

Maa

Late Cretaceous

Yunguilla Fm

02CV42 00RS4 00RS2

03LL143

Camp

Cayo Fm

0% 10% 20% 30% 40% 50% 60% 70% 80% 90%100%

02CV72

05LL430

Pilaton U.

02LL15

02CV131 00RS25

Mulaute U. Sant

Calentura Fm

02CV62

03LL241

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Con

00RS24

Continental - cratonic minerals

0% 10% 20% 30% 40% 50% 60% 70% 80% 90%100%

Metamorphic minerals

Volcanic minerals

(ZTR) zircon + Turmalina + Rutilo

Garnet

Staurolite

Espinel

Monazite

Epidote + Zoiite + Clinozoisite

Kyanite + Sillimanite

Horblende

Brokite + Titanite + Anatasa

Chloritoid

Tremolite

Pyroxene Others

FIG. 7 Stratigraphic charts showing heavy mineral assemblages for Upper Cretaceous to Neogene sedimentary rocks of the Western Cordillera and coastal forearc of Ecuador.

224

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

Heavy mineral data from the Miocene Silante Formation show a strong input of pyroxene, hornblende and euhedral zircon, with minor epidote and espinel. The mineral assemblage suggests derivation from a coeval volcanic source.

6.1.2 ­Heavy mineral data from the coastal forearc

Heavy mineral assemblages from the Calentura and Cayo formations are characterized by typical volcanic arc minerals, including diopsidic augite and brown hornblende. Heavy minerals from the Guayaquil Formation consist of green and brown hornblende, diopsidic augite, and a significant proportion of volcanic and authigenic apatite. One sample from the upper Guayaquil Formation contains 4%–9% rounded zircons and limited tourmaline, brookite, barite, and biotite. These assemblages suggest that the Guayaquil Formation received material from volcanic and continental crustal sources. Sedimentary rocks of the Azucar Group are characterized by a dominance of metamorphic minerals (Fig. 7), along with a significant amount of ZTR minerals. Mafic volcanic-derived assemblages were not detected in these rocks. The heavy mineral assemblages of five sedimentary rock samples of the Ancon Group (the Clay Pebble, Socorro, Seca, and Punta Ancon formations) have been determined (Fig. 7). Except for the Punta Ancon Formation, where volcanic-derived green and brown hornblendes dominate the assemblage, all Ancon Group samples contain equal proportions of ZTR and metamorphic mineral groups. These heavy mineral associations suggest a volcanic and continental crustal input. Siliciclastic rocks of the Eocene San Mateo Formation show similar compositions as the Cayo Formation, and their heavy mineral assemblages are dominated by diopsidic augite, hypersthene, and brown and green hornblendes (Fig. 7). The remaining portion (<5%) is composed of apatite and anatase. The Oligocene Zapotal Formation hosts abundant material derived from a volcanic source, and minor amounts of minerals derived from metamorphic and ZTR dominated sources. Heavy mineral assemblages from the Miocene Villingota, El Consuelo, and El Progreso formations contain variable amounts of volcanic, metamorphic, and continental crust minerals. This suggests that the Miocene coastal forearc received detrital material from both a volcanic arc and metamorphic rocks.

6.2 ­Detrital zircon U-Pb ages of Late Cretaceous to Cenozoic strata capping the Pallatanga and Piñon blocks For the detrital zircon U-Pb geochronological component of our study, we selected samples of Campanian-Eocene sedimentary rocks overlying the Piñon and Pallatanga blocks (Fig. 3). From the coastal forearc region, we analyzed samples of the Paleocene Guayaquil Formation (EC1628), Eocene Ancon Group (EC1629), Oligocene Zapotal Formation (EC1630), and Progreso Formation (EC1631, EC1633). In addition, we compiled data published by Witt et al. (2016) from the Paleocene Azucar Group (CP007, CP103) and Eocene Ancon Group (CP017 and CP212). Concordant U-Pb ages generated for individual zircon grains (typically 100–120 grains per sample) define U-Pb age distributions for individual samples (Fig. 8) and provide the basis for the identification and interpretation of diagnostic age populations representative of various sediment source regions. For the Western Cordillera sample, CV33 is a sandstone of the Yunguilla Formation; sample CV26 corresponds to thin-bedded turbidites mapped as the Paleocene Saquisili unit of the Angamarca Group; sample ECGG24 was collected along the western border of the Western Cordillera in a zone mapped as undifferentiated rocks of the Angamarca Group; Samples EC1647 and EC1504 correspond to turbidite sediments of the Apagua unit; sample EC1647 was collected at the stratigraphic contact with the

Coastal forearc

Western Cordillera Detrital ages younger than 40 Ma (Saraguro Gp. and younger volcanics)

32 24 16 8 0 37

EC1633 Progreso Fm. (Miocene) (n=111)

MDA: 11.5 ± 1.3 Ma n=4

Detrital ages between 40 and 65 Ma (Tandapi and Macuchi arcs) Detrital zircon ages between 65 and 100 Ma (Late Cretaceous continental arc?)

27 18 9 0 68 51 34 17 0 68 51 34 17 0 36 27 18 9 0 36 27 18 9 0 10

Detrital zircon ages older than 200 Ma (Eastern Cordillera and recycled craton sources)

EC1631 Progreso Fm. (Miocene) (n=102)

MDA: 19.3 ± 0.9 Ma n=8

MDA: 30.7 ± 0.7 Ma n=16

EC1630 Zapotal Fm. (Oligocene) (n=113)

MDA: 42.6 ± 0.7 Ma n=9

EC1629 Ancón Gp. (Eocene) (n=113)

MDA: Maximum depositional age 112 84 56 28 0 42 31

EC1502 Zumbagua Gp. (Miocene) (n=112)

MDA: 39.9 ± 0.9 Ma n=4

EC1504 Apagua unit (Eocene) (n=111)

MDA: 43 ± 2.2 Ma

EC1647 Apagua unit (Eocene)

21 10

MDA: 47.9 ± 0.8 Ma n=3

CP017 Ancón Gp. (Eocene) (n=81)

MDA: 51.7 ± 2.4 Ma n=3

Witt et al. (2016)

0 30

n=1

22 15

Witt et al. (2016)

CP212 Ancón Gp. (Eocene) (n=82)

MDA: 56.1 ± 0.7 Ma n=4

7 5

7 0 15 11 7

Witt et al. (2016)

CP103 Azúcar Fm. (Paleocene) (n=43)

3 0 13 9

(n=69)

MDA: 44.3 ± 1.8 Ma n=3

CV26 Apagua unit (Eocene)

MDA: 56.2 ± 2.8 Ma n=3

CV137 Saguangal unit (Paleocene)

MDA: 58.2 ± 0.6 Ma n=1

ECGG24 Saquisili unit (Paleocene-Eocene)

MDA: 72.4 ± 6.4 Ma

CV33 Yunguilla Fm. (Campanian-Maastrichtian)

(n=29)

(n=43)

6 3 0

Age (Ma)

FIG. 8 Age histograms (black line) and probability density functions (red curves) showing detrital zircon U-Pb age distributions for Upper Cretaceous to Neogene sedimentary units of the coastal region (left) and Western Cordillera (right) of Ecuador. Shaded color bars denote major age populations.

1800

1600

1400

1200

(n=27)

n=3

800

1800

1600

1400

1200

1000

800

600

400

200

40 80 120

Age (Ma)

0

(n=103)

600

0

EC1628 Guayaquil Fm. (Maastrichtian to Paleocene) (n=5)

400

0

MDA: 67.2 ± 1.5 Ma n=1

2

200

1

9 0 9 7 5 3

1000

39 29 19

40 80 120

Witt et al. (2016)

CP007 Azúcar Fm. (Paleocene) (n=79)

MDA: 60.4 ± 0.7 Ma n=5

6 ­Provenance analysis

2 0 32 24 16 8 0 3

0

MDA: 6.5 ± 0.4 Ma n=8

225

226

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

Macuchi unit (Fig. 4D). Sample CV137 was collected from the Paleocene Saguangal unit, exposed northwest of Quito and considered a lateral equivalent of the Angamarca Group (Vallejo, 2007). In addition, one sample from the Miocene Zumbagua Group (EC1502) was analyzed in this study.

6.2.1 ­Detrital zircon ages from the Western Cordillera

For the Campanian-Maastrichtian Yunguilla Formation (sample CV33), detrital zircon ages range from 2642 to 72 Ma. An important population at 72–115 Ma partially overlaps the age of Cretaceous magmatism in southeastern Ecuador (Valarezo et al., 2017), and the Pimampiro and Magtayan plutons in the Eastern Cordillera (Aspden et al., 1992). Detrital zircons with ages older than 400 Ma overlap with ages reported for source rocks in the Eastern Cordillera and South American craton (Chew et al., 2007; Horton et al., 2010, 2015a; Horton, 2018; George et  al., 2019). This shows that the Yunguilla Formation was sourced from the Eastern Cordillera. The maximum depositional age (MDA) obtained from the youngest zircon population indicates 72.4 ± 6.4 Ma, coeval with biostratigraphic ages proposed for the Yunguilla Formation, suggesting syndepositional volcanism. The Paleocene Saguangal unit (CV137) shows distinctive age populations ranging from 1914 to 58.8 Ma. Proterozoic ages overlap the ages reported for the South American craton and Eastern Cordillera (Chew et  al., 2007; Martin-Gombojav and Winkler, 2008). A weighted mean age of 56.2 ± 2.8 Ma was calculated for the euhedral youngest zircons, which may indicate derivation from a coeval volcanic source, probably the Tandapi continental magmatic arc of Maastrichtian to Paleocene age (Vallejo, 2007). Samples from sedimentary rocks mapped as the Saquisili unit (ECGG24) show distinctive age populations ranging from 2720 to 44 Ma. The MDA for sample ECGG24 is 58.2 ± 0.6 Ma, and is consistent with biostratigraphic ages for the Saquisili unit. MDA for sample CV26 is 44.3 ± 1.8, suggesting that sample CV26 can be part of the Eocene Apagua unit that overlie the Saquisili unit. For both samples, the most abundant ages are concentrated at 100–65 Ma, which overlaps ages reported for magmatic rocks of southeastern Ecuador (Valarezo et al., 2017). Subordinate grains older than 200 Ma are derived from the erosion of source rocks located in the Eastern Cordillera, including the Triassic Tres Lagunas Granite (Litherland et al., 1994), and Proterozoic-Paleozoic metamorphic rocks in the Eastern Cordillera (Litherland et al., 1994; Spikings et al., 2015). Detrital zircon U-Pb results for the lower Apagua sandstone (EC1647), at the contact with the Macuchi unit, show a relatively wide distribution of ages from 1600 to 43 Ma. The MDA for this sample is 43 ± 2.2 Ma, which overlaps biostratigraphic ages determined for the Apagua unit (Hughes and Pilatasig, 2002). Precambrian-Ordovician zircon grains represent recycled material from pre-Andean rocks at deep structural levels of the fold-thrust belt (Martin-Gombojav and Winkler, 2008; Horton et al., 2010; Gutierrez et al., 2019). A 51–44 Ma population in this sample is consistent with erosion of the underlying and partially coeval Macuchi submarine arc. Ages of 97–61 Ma overlap with ages reported for continental arc magmatism farther east (Aspden et al., 1992; Valarezo et al., 2017). A similar U-Pb age distribution characterizes an additional sample from the Apagua unit (EC1504), where a strong 81–69 Ma population indicates principal derivation from a Late Cretaceous magmatic arc. This sample, however, contains a series of ages clustered at 42–39 Ma, suggesting a younger stratigraphic age. An MDA of 39.9 ± 0.9 Ma is consistent with accumulation of the Apagua unit during the middle Eocene.

6 ­Provenance analysis

227

A sample from the Miocene Zumbagua Group (EC1502) shows a remarkably unimodal population of late Miocene ages, with nearly all ages focused in the 6–12 Ma range. The complete absence of pre-Miocene grains indicates dominance of magmatic arc sources, with no contributions from older magmatic-arc components and no recycling of older sedimentary rocks. An MDA of 6.5 ± 0.4 Ma demonstrates a latest Miocene age of basin accumulation, likely within an intermontane or intra-arc setting. This age for the Zumbagua Group also helps bracket a latest Miocene-Pliocene phase of folding, prior to overlap by Quaternary volcanic ash of the Cangahua Formation (Hall and Calle, 1982).

6.2.2 ­Detrital zircon ages from the coastal forearc

In the coastal forearc region, a sample from the Guayaquil Formation (EC1628) contains several zircon grains with Maastrichtian, Devonian, and Precambrian ages. The MDA for this sample is 67.2 ± 0.4 Ma and overlaps the depositional age of the unit, suggesting an active volcanic source at the time of deposition. Maastrichtian volcanic rocks have been dated in the Tandapi volcanics underlying volcano-sedimentary rocks of the Silante Formation (Vallejo, 2007). The Tandapi volcanics are part of a continental volcanic arc in the Western Cordillera overlying rocks of the Pallatanga block (Vallejo et al., 2009). The Devonian and Precambrian ages are related to the Eastern Cordillera and recycled cratonic sources. For the Azucar Group (samples CP007 and CP103 compiled from Witt et al., 2016), the youngest zircon age populations are 59 and 55 Ma, overlapping biostratigraphic ages. These ages are also related to magmatic activity of the Tandapi continental arc within the Western Cordillera. For these samples, detrital ages of 87–64 Ma are also important and can be related to a Cretaceous continental arc volcanism (Valarezo et al., 2017). An important group of zircons showing ages from 250 to 200 Ma must be derived from Triassic intrusions of the Eastern Cordillera (Aspden and Litherland, 1992). Additional Proterozoic ages are also derived from the Eastern Cordillera. Results for turbidite beds mapped as the Eocene Ancon Group (EC1629) are combined with additional samples (CP017 and CP212 compiled from Witt et al., 2016). These samples share young zircon age populations, including a 65–40 Ma group suggesting input from the Tandapi and Macuchi arcs, and a 100–65 Ma group probably derived from a Cretaceous continental arc volcanism within the Eastern Cordillera (Valarezo et al., 2017). The youngest ages overlap with the stratigraphic age proposed for the Ancon Group, suggesting contemporaneous volcanism, likely the Macuchi submarine arc of the Western Cordillera. The Oligocene Zapotal Formation (EC1630) contain zircons ranging in age from 1978 to 30 Ma, with an MDA of 30.7 ± 0.7 Ma. Among the youngest ages, a major group at 38–30 Ma overlaps with radiometric ages for the voluminous Saraguro volcanic rocks of the Western Cordillera. Detrital ages of 65–40 Ma are interpreted to be sourced from the Tandapi and Macuchi arcs, whereas a 113–65 Ma population overlaps with ages reported for Cretaceous continental arc magmatic rocks (Barragan et al., 2005; Valarezo et al., 2017). For the Miocene Progreso Formation (samples EC1633 and EC1631), the youngest ages reveal stratigraphic ages of 19 and 9.7 Ma. The main populations are comparable to the previously described samples, including Triassic and Proterozoic ages, and 65–40 Ma and 100–65 Ma populations. Detrital zircon ages younger than 38 Ma can be correlated to upper Eocene-Oligocene Saraguro volcanic rocks and their younger successor units. In general, a well-defined upsection decrease in ages of the youngest age populations for the sedimentary cover of the Piñon and Pallatanga blocks (Fig. 8A and B) is compatible with syndepositional

228

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

volcanic input. Such a pattern is consistent with sustained arc magmatism and a continuous close proximity to the Andean magmatic arc (e.g., Horton et al., 2015a,b).

7 ­Late Cretaceous to Miocene Tectonic history of western Ecuador 7.1  ­Evolution of the Piñon and Pallatanga blocks and their volcanic and sedimentary cover 7.1.1 ­Origin and timing of accretion of the mafic basement of western Ecuador

Radiometric and geochemical data indicate that basement rocks of the coastal region and Western Cordillera of Ecuador belong to fragments of the Caribbean Plateau that crystallized during ~100 to 87 Ma. Paleomagnetic data (Luzieux et al., 2006) suggest that this plateau formed in the Pacific Ocean at nearly equatorial latitudes (Fig. 9A). Heavy mineral data of sedimentary rocks of the Upper Cretaceous Rio Cala Group (Pilatón, Mulaute, and Natividad formations) show that they were sourced from a volcanic arc without receiving continental material (e.g., detrital zircon, rutile, tourmaline), suggesting deposition in an intraoceanic setting separated from continental influence (Fig. 9B). The Upper Cretaceous Cayo, San Lorenzo, and Las Orquideas formations of the Piñon block are correlatable with the Rio Cala Group of the Western Cordillera (Fig. 3). These island arc sequences were formed in an intraoceanic arc setting, distant from continental crust, as suggested by the heavy mineral analysis. Therefore, we suggest that island arc successions in the coastal region and Western Cordillera were part of a single island arc sequence of Late Cretaceous age (Fig. 9B); this feature can be related to the Great arc or the Caribbean, produced by possible westward subduction beneath the Caribbean Plateau (Burke, 1988). The Caribbean Plateau and its overlying island arc drifted eastward and collided with the South American continental margin during the Campanian (~73 Ma). Westward subduction beneath the plateau may have had accommodated considerable eastward advance of the Caribbean Plateau and the overlying island arc sequence (Fig. 9B). As indicated by Whattam and Stern (2015), eastward obduction of the Caribbean Plateau upon South America requires a west-dipping subduction zone below the plateau. Alternatively, if subduction had been east-dipping, then the plateau would have been more likely to have been subducted, at least partially, beneath South America. The termination of island arc magmatism within the oceanic plateau in the early Maastrichtian (~70 Ma) likely corresponds to the choking of the subduction zone by collision between the buoyant Caribbean Plateau and the South American plate (Fig. 9C). This accretion event was accompanied by significant cooling and exhumation along the continental margin recorded by 40Ar/39Ar and fission track thermochronological ages (Fig. 6), indicative of cooling at 75–65 Ma in the Eastern Cordillera and sediment source regions in the Western Cordillera (Spikings et al., 2001, 2005). Paleomagnetic data from basement and sedimentary cover rocks in the coastal region (Luzieux et al., 2006) indicate a 20–50° clockwise rotation during the late Campanian (73–70 Ma), synchronous with collision of the oceanic plateau and arc assemblage with South America, suggesting that collision may have been oblique. Vallejo (2007) suggested that the absence of large-scale subduction-related igneous activity along the Ecuadorian continental margin from roughly 85 to 65 Ma may indicate a cessation of subduction beneath the continental margin. However, detrital zircon U-Pb ages from this study suggest sustained volcanic activity during this period. Late Cretaceous-Cenozoic strata in the backarc and forearc basins

Cenomanian to Coniacian

Paleocene

W

E

W

Pilalo U.

Saquisili U.

SL Guayaquil Fm.

Eastern Cordillera

Caribbean plateau

E

Tandapi Arc Azucar Gp.

SL

Eastern Cordillera

Pallatanga

Piñon

?

(A) W

Santonian to Campanian Cayo Fm.

San Lorenzo arc

E

(D) Eocene

W

Macuchi Arc El Tortugo U. El Laurel U. San Mateo Fm.. Ancón Gp.

Rio Cala Gp. SL

Yunguilla Fm.

SL

Eastern Cordillera

?

Piñon

(B)

(E)

Latest Campanian

Oligocene

W

E SL

Guayaquil Fm.

Piñon

Cayo Fm.

P

Eastern Cordillera

a

ang

t alla

Rio Cala Gp.

W

Yunguilla Fm. SL

Saraguro U. N Pambil Zapotal Fm. Playa Rica fms.

Rumicruz U.

ga

an

Eastern Cordillera

Piñon

Pallatanga

(C)

E

San Juan de Lachas

t lla

Eastern Cordillera

Pa

(F)

FIG. 9

229

Proposed paleogeographic reconstruction showing Late Cretaceous to Oligocene evolution of the Coastal, Western Cordillera, and Eastern Cordillera regions. (A) Extrusion of the Caribbean Plateau in the Pacific region at nearly equatorial latitudes. (B) Westward subduction below the Caribbean Plateau and formation of the Island arc sequences of the Rio Cala Group, San Lorenzo arc and Cayo Formation. (C) Accretion of the Caribbean Plateau and overlying island arc sequence. (D) Establishment of the Maastrichtian-Paleocene Tandapi volcanic arc of the Western Cordillera. (E) The Macuchi submarine arc formed on top of the accreted oceanic plateau basement and sourced detrital material to the coeval coastal forearc deposits and the Angamarca Group. (F) Oligocene upward-shallowing depositional trend in the Western Cordillera and coastal forearc regions, coeval with the establishment of the Saraguro and San Juan de Lachas volcanic arcs.

7 ­ Late Cretaceous to Miocene tectonic history

Pujillí Gr.

E Apagua U.

230

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

also contain zircon ages ranging in age from 90 to 70 Ma (Vallejo et al., 2017; Valarezo et al., 2017; Gutierrez et al., 2019), likely derived from arc magmatism in the westernmost Eastern Cordillera of Ecuador. The Pimampiro and Magtayan I type intrusions within the Eastern Cordillera have yielded K-Ar ages of 94–68 Ma (Aspden et al., 1992) and can be related to the Late Cretaceous continental margin magmatism. The Antioquia Batholith in the Central Cordillera of Colombia with U-Pb ages of 95–85 Ma (Villagomez et al., 2011) is considered part of this Late Cretaceous arc (Spikings et al., 2015). Thus, eastward subduction beneath the continental margin during the Late Cretaceous interval can be considered, although further studies are required to pinpoint the position of the magmatic arc.

7.1.2 ­Paleocene to Miocene tectonostratigraphic evolution of western Ecuador

Sedimentological information and stratigraphic correlations between the coastal forearc and Western Cordillera show that turbidite deposition prevailed during the Paleocene in most forearc regions. Provenance analysis of the Guayaquil and Azucar formations suggest that detrital material derived from the continental margin arrived in coastal regions during the Paleocene. In the Western Cordillera, the coeval Saquisili unit is also enriched in material derived from continental crust. In addition, detrital zircon U-Pb results for the Guayaquil, Azucar, and Saquisili units include age populations of 50–64 Ma, which generally agree with ages determined for the Maastrichtian-Paleocene Tandapi volcanic arc of the Western Cordillera (Vallejo, 2007). Proterozoic zircon ages further support delivery of detritus from the Eastern Cordillera to the Piñon and Pallatanga blocks during the Paleocene, suggesting that both blocks were previously accreted to the continental margin (Fig. 9D). During the Eocene, deposition of submarine fans prevailed across the forearc region, including the Apagua unit of the Western Cordillera and the Ancon Group along the coast. Heavy mineral assemblages reveal both continental crustal and volcanic contributions. The continental assemblages are interpreted to derive from the erosion of the Eastern Cordillera, consistent with the aforementioned detrital zircon U-Pb age populations. Furthermore, in the coastal region, paleocurrent data indicate a WSW transport direction (Benitez, 1995; Luzieux, 2007), consistent with an eastern source. Although Luzieux (2007) proposed that Eocene volcanic input to coastal regions represented erosion of the Late Cretaceous San Lorenzo arc, our detrital ages and those of Witt et  al. (2016) indicate a 42–50 Ma source. We interpret this eastern volcanic source as the Macuchi submarine arc (Fig. 9E). This is in accord with provenance results for the Eocene Angamarca Group in the Western Cordillera, which also contains abundant ~44 Ma volcanic material attributable to the Macuchi arc. Therefore, Eocene submarine fan deposits of the Coastal region and Western Cordillera were partially sourced from an emerging Eastern Cordillera and Macuchi submarine arc (Fig. 9E), consistent with the plate tectonic model proposed by Van Thournout et al. (1992). From the Oligocene onward, nonmarine conditions started to dominate the Western Cordillera, with the Rumi Cruz unit deposited in a lacustrine fan-delta environment (Fig. 9F). This coincided with establishment of widespread Saraguro magmatism in the south and the San Juan de Lachas arc in the northern sector of the Western Cordillera. In coastal regions, Oligocene-Miocene strata recorded an upward-shallowing trend with coastal to marine sediments derived from the Eastern Cordillera and Saraguro subaerial volcanic province in the Western Cordillera.

7.2 ­Autochthonous origin for the Macuchi block The Macuchi arc was active during the late Eocene, as shown by extrusive and intrusive igneous rocks in the Western Cordillera, which yield ages from 42 to 38 Ma (Vallejo et  al., 2016). According to

8 ­Conclusions

231

Chiaradia (2009) and Vallejo et al. (2016), felsic magmatism of the Macuchi unit involved contributions from hot deep crustal levels and a juvenile oceanic plateau source resulting in partial melting and generation of granitoid melts that ascended to the subseafloor level. This history is consistent with formation of the Macuchi arc on top of thickened crust of the Pallatanga and Piñon oceanic plateaus. The presence of detrital zircons of Cambrian age within the Macuchi unit (Vallejo et al., 2009) suggests that the submarine arc was close to older basement rocks in the Eastern Cordillera of Ecuador. Furthermore, the Apagua unit of the Pallatanga block and the Ancon Group and San Mateo Formation of the Piñon block received large quantities of volcanic derived material from the coeval Macuchi arc and Eastern Cordillera (Fig. 9E). This suggests that the Pallatanga and Piñon blocks spanned parts of the coeval backarc and forearc regions of a single continental margin. Therefore, it is unlikely that the Macuchi submarine arc was inserted between the previously amalgamated Pallatanga block (in the east) and Piñon block (in the west). We propose that any level of increased deformation during the Eocene need not be associated with collisional events. In addition, Vallejo et al. (2016) indicated that during the Eocene, considerable extension occurred in the Macuchi block of the Western Cordillera, whereas shortening characterized the forearc region, possibly suggesting a transpressional tectonic regime. Elevated exhumation rates within the Andes of Ecuador at 45–30 Ma (Fig. 6) are in agreement with thermochronological records for the Central Andes (Gillis et al., 2006; Spikings et al., 2010; Anderson et  al., 2018), suggesting they may have been driven by plate-scale kinematic changes. This change coincided with tectonic activity in the Northern Andes, further emphasizing that Eocene reactivation in Ecuador was not driven simply by accretion of the Macuchi block but by broader geodynamic processes.

8 ­Conclusions Stratigraphic correlations for the Western Cordillera and coastal forearc segments of Ecuador suggest that these regions share a similar sedimentary evolution from Late Cretaceous through Oligocene time. Rocks of the Pallatanga and Piñon formations are geochemically equivalent, and probably derived from fragments of the Caribbean Plateau that formed from ~100 to 87 Ma. Both formations are overlain by island arc sequences, including primary volcanic rocks and volcaniclastic deposits of Coniacian to Campanian age. The intrusive roots of the island arc crosscut the oceanic plateau rocks and range in age from ~98 to 85 Ma. Provenance analyses of strata capping the Piñon and Pallatanga blocks indicate a Paleocene arrival of detrital material from the Eastern Cordillera and South American craton. In both regions, Paleocene turbidite sequences also record a coeval volcanic input, likely derived from the Tandapi volcanic arc of latest Maastrichtian to Paleocene age. During the Eocene, sedimentary basins on the Piñon and Pallatanga blocks received clastic material derived from the Macuchi submarine arc and an emerging Eastern Cordillera. Oligocene basin accumulation was recorded by an upward-shallowing depositional trend in the Western Cordillera and coastal forearc regions. Oligocene-Miocene forearc deposits also received detrital material from coeval Saraguro volcanism. There is no evidence for accretion of the Macuchi and Piñon blocks during the late Eocene. It is very difficult to reconcile proposals of late Eocene accretion of the Macuchi unit given its current

232

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

l­ocation between the Piñon and Pallatanga blocks, which were accreted to the continental margin during the Late Cretaceous. Upsection decreases in the youngest detrital zircon U-Pb age populations for Paleocene to Miocene sedimentary rocks overlying the Pallatanga and Piñon blocks are compatible with sustained input of syndepositional volcanic detritus along a previously amalgamated continental margin.

­Acknowledgments We thank Bernardo Beate, E. Gabriela Gutierrez, Sarah George, and Lily Jackson for fruitful discussions about the geology of Ecuador. Fieldwork benefited from the knowledge of Efrain Montenegro, Pedro Reyes, and Luis Matamoros. We thank Janeth Gaibor and Stalin Pilatasig for their assistance in preparing the figures. Juan DíazAlvarado and an anonymous reviewer are acknowledged for their constructive comments, which helped us to improve the manuscript. This work was supported by Swiss National Science Foundation, projects 2-77193-02 and 2-77504-04, Escuela Politécnica Nacional project PIS-16-10 and the National Geographic Society (grant 9909-16).

­ ppendix: Supplementary material A Supplementary material related to this chapter can be found on the accompanying CD or online at https://doi.org/10.1016/B978-0-12-816009-1.00010-1.

­References Aguirre, L., Atherton, M.P., 1987. Low-grade metamorphism and geotectonic setting of the Macuchi Formation, Western Cordillera of Ecuador. J. Metamorph. Geol. 5, 473–494. Allibon, J., Monjoie, P., Lapierre, H., Jaillard, E., Bussy, F., Bosch, D., Senebier, F., 2008. The contribution of the young Cretaceous Caribbean Oceanic Plateau to the genesis of late Cretaceous arc magmatism in the Cordillera Occidental of Ecuador. J. S. Am. Earth Sci. 26, 355–368. Anderson, R.B., Long, S.P., Horton, B.K., Thomson, S.N., Calle, A.Z., Stockli, D.F., 2018. Orogenic wedge evolution of the Central Andes, Bolivia (21°S): implications for Cordilleran cyclicity. Tectonics 37, https://doi. org/10.1002/2018TC005132. Aspden, J.A., Litherland, M., 1992. The geology and mesozoic collisional history of the Cordillera Real, Ecuador. Andean Geodynamics. Oliver, R.A. et al. (Editors). Tectonophysics 205, 187–204. Aspden, J.A., Harrison, S.H., Rundle, C.C., 1992. New geochronological control for the tectono-magmatic evolution of the metamorphic basement, Cordillera Real and El Oro Province of Ecuador. J. S. Am. Earth Sci. 6, 77–96. Barragan, R., Baby, P., Duncan, R., 2005. Cretaceous alkaline intra-plate magmatism in the Ecuadorian Oriente Basin: geochemical, geochronological and tectonic evidence. Earth Planet. Sci. Lett. 236, 670–690. Benitez, S.B., 1995. Evolution géodynamique de la province côtière sud-équatorienne au Crétacé supérieurTertiaire. Géol. Alp. 7, 13–163. Boland, M.P., Pilatasig, L.F., Ibandango, C.E., McCourt, W.J., Aspden, J.A., Hughes, R.A., Beate, B., 2000. Geology of the Western Cordillera between 0°–1°N: Quito, Ecuador, Proyecto de Desarrollo Minero y Control Ambiental, Programa de Informacion Cartografica y Geologica, Informe 10. CODIGEM–BGS, Quito, Ecuador. 107 pp. Bruet, F., 1949. Les enclaves des laves des volcans de Quito, République de l’Équateur. B. Soc. Geol. Fr. 19, 477–491. Burke, K., 1988. Tectonic evolution of the Caribbean. Annu. Rev. Earth Planet. Sci. 16, 201–230.

­References

233

Chew, D.M., Schaltegger, U., Kosler, J., Whitehouse, M.J., Gutjahr, M., Spikings, R.A., Miskovic, A., 2007. U–Pb geochronologic evidence for the evolution of the Gondwanan margin of the north-Central Andes. Geol. Soc. Am. Bull. 119, 697–711. Chiaradia, M., 2009. Adakite-like magmas from fractional crystallization and melting-assimilation of mafic lower crust (Eocene Macuchi arc, Western Cordillera, Ecuador). Chem. Geol. 265, 468–487. Cosma, L., Lapierre, H., Jaillard, E., Laubacher, G., Bosch, D., Desmet, A., Mamberti, M., Gabriele, P., 1998. Petrographie et geochimie des unites magmatiques de la Cordillère Occidentale d’Equateur (0°30′S): Implications tectoniques. Bull. Soc. Geól. Fr. 169, 739–751. Cotteccia, V., Zezza, F., 1969. The Eocene basement of the inter-Andean corridor in the Latacunga Ambato trough (Ecuador). Geol. Appl. Idrogeol. 4, 43–46. Dunkley, P., Gaibor, A., 1997. Geology of the Cordillera Occidental of Ecuador between 2° -3°S. Proyecto de Desarollo Minero y Control Ambiental, Programa de Informacion Cartografica y Geologica, Informe 2. CODIGEM–BGS, Quito, Ecuador, p. 139. Eguez, A., 1986. Evolution Cenozoique de la Cordillere Occidentale septentrionale d’Equateur (0°15’ S -01°10’ S), les mineralisations associetees. Doc. Thesis UPMC, Paris. 116 pp. (unpublished). Feininger, T., Bristow, C.R., 1980. Cretaceous and Paleogene geologic history of coastal Ecuador. Geol. Rundsch. 69, 40–44. Feininger, T., Seguin, M.K., 1983. Simple Bouguer gravity anomaly field and the inferred crustal structure of continental Ecuador. Geology 11, 40–44. George, S.W.M., Horton, B.K., Jackson, L.J., Moreno, F., Garzione, C., Carlotto, V., 2019. Sediment provenance variations during contrasting Mesozoic-early Cenozoic tectonic regimes of the northern Peruvian Andes and Santiago-Marañón foreland basin. This volume (Chapter 10), https://doi.org/10.1016/B978-0-12-816009-1.00012-5. Gillis, R.J., Horton, B.K., Grove, M., 2006. Thermochronology, geochronology, and upper crustal structure of the Cordillera Real: implications for Cenozoic exhumation of the central Andean plateau. Tectonics 25, TC6007. https://doi.org/10.1029/2005TC001887. Goosens, P.J., Rose, W.I., 1973. Chemical composition and age determination of tholeiitic rocks in the basic igneous complex, Ecuador. Geol. Soc. Am. Bull. 84, 1043–1052. Gutierrez, E.G., Horton, B.K., Vallejo, C., Jackson, L., George, S., 2019. Provenance and geochronological insights into Late Cretaceous-Cenozoic foreland basin development in the Subandean Zone and Oriente Basin of Ecuador. This volume (Chapter 9), https://doi.org/10.1016/B978-0-12-816009-1.00011-3. Hall, M.L., Calle, J., 1982. Geochronological control for the main tectono-magmatic events of Ecuador. Earth Sci. Rev. 18, 215–239. Henderson, W.G., 1979. Cretaceous to Eocene volcanic arc activity in the Andes of northern Ecuador. J. Geol. Soc. Lond. 136, 73–78. Herrera, J.L., 2018. LA-ICPMS zircon U-Pb geochronology on the Ecuadorian Andes and forearc, constraints in their cretaceous-paleogene evolution: Silante Formation, Catacocha unit, Cañaveral Formation. Msc thesis University College, London, p. 67. Horton, B.K., 2018. Sedimentary record of Andean mountain building. Earth-Sci. Rev. 178, 279–309. https://doi. org/10.1016/j.earscirev.2017.11.025. Horton, B.K., Saylor, J.E., Nie, J., Mora, A., Parra, M., Reyes-Harker, A., Stockli, D.F., 2010. Linking sedimentation in the northern Andes to basement configuration, Mesozoic extension, and Cenozoic shortening: evidence from detrital zircon U-Pb ages, eastern cordillera, Colombia. Geol. Soc. Am. Bull. 122, 1423–1442. Horton, B.K., Anderson, V.J., Caballero, V., Saylor, J.E., Nie, J., Parra, M., Mora, A., 2015a. Application of detrital zircon U-Pb geochronology to surface and subsurface correlations of provenance, paleodrainage, and tectonics of the middle Magdalena Valley basin of Colombia. Geosphere 11, 1790–1811. https://doi.org/10.1130/GES01251.1. Horton, B.K., Perez, N.D., Fitch, J.D., Saylor, J.E., 2015b. Punctuated shortening and subsidence in the Altiplano plateau of southern Peru: implications for early Andean mountain building. Lithosphere 7, 117–137. https:// doi.org/10.1130/L397.1.

234

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

Hughes, R., Bermudez, R., 1997. Geology of the Cordillera Occidental of Ecuador between 0°00’and 1° 00’S. Proyecto de desarollo minero y control ambiental, programa de información cartográfica y geológica. Informe 4. CODIGEM–British Geological Survey, Quito, Ecuador. 75 pp. Hughes, R.A., Pilatasig, L.F., 2002. Cretaceous and tertiary block accretion in the Cordillera occidental of the Andes of Ecuador. Tectonophysics 345, 29–48. Jaillard, E., Ordoñez, M., Benitez, S., Berrones, G., Jimenez, N., Montenegro, G., Zambrano, I., 1995. Basin development in an Accretionary, oceanic-floored fore-arc setting: southern coastal Ecuador during Late Cretaceous-late Eocene time. AAPG Mem. 62, 615–631. Jaillard, E., Ordoñez, M., Suarez, J., Toro, J., Iza, D., Lugo, W., 2004. Stratigraphy of the Late Cretaceous Paleogene deposits of the cordillera occidental of Central Ecuador: geodynamic implications. J. S. Am. Earth Sci. 17, 49–58. Keller, G., Adatte, T., Hollis, C.J., Ordonez, M., Zambrano, I., Jimenez, N., Stinnesbaeck, W., Aleman, A., Hale, E., 1997. The cretaceous/tertiary boundary event in Ecuador; reduced biotic effects due to eastern boundary current setting. Mar. Micropaleontol. 31, 97–133. Kerr, A.C., Tarney, J., 2005. Tectonic evolution of the Caribbean and northwestern South America: the case for accretion of two Late Cretaceous oceanic plateaus. Geology 33, 269–272. Kerr, A.C., Aspden, J.A., Tarney, J., Pilatasig, L.F., 2002. The nature and provenance of accreted oceanic blocks in western Ecuador: geochemical and tectonic constraints. J. Geol. Soc. Lond. 159, 577–594. Lapierre, H., Bosch, D., Dupuis, V., Polve, M., Maury, R., Hernandez, J., Monie, P., Yeghicheyan, D., Jaillard, E., Tardy, M., Mercier de Lepinay, B., Mamberti, M., Desmet, A., Keller, F., Senebier, F., 2000. Multiple plume events in the genesis of the peri-Caribbean Cretaceous oceanic plateau province. J. Geophys. Res. 105, 8403–8421. Lebras, M., Megard, F., Dupuy, C., Dostal, J., 1987. Geochemistry and tectonic setting of pre-collision Cretaceous and Paleogene volcanic rocks of Ecuador. Geol. Soc. Am. Bull. 99, 569–578. Litherland, M., Aspden, J., Jemielita, R.A., 1994. The metamorphic belts of Ecuador. vol. 11. British Geological Survey, Overseas Memoir. 147 pp. Luzieux, L.D.A., 2007. Origin and Late Cretaceous-Tertiary evolution of the Ecuadorian forearc. PhD Thesis, Institute of Geology, ETH Zürich, Switzerland. 197 pp. Luzieux, L.D.A., Heller, F., Spikings, F., Vallejo, C.F., Winkler, W., 2006. Origin and Cretaceous tectonic history of the coastal Ecuadorian forearc between 1°N and 3°S: paleomagnetic, radiometric and fossil evidence. Earth Planet. Sci. Lett. 249, 400–414. Macias, K., 2018. Geoquímica de los Plutones de Pascuales y de Bajo Grande (Cantón Jipijapa): dataciones U-Pb en zircones e implicaciones geodinámicas. Eng Thesis, Universidad de Guayaquil, Ecuador. 117 pp. Mamberti, M., Lapierre, H., Bosch, D., Ethien, R., Jaillard, E., Hernandez, J., Polve, M., 2003. Accreted fragments of the Late Cretaceous Caribbean-Colombian plateau in Ecuador. Lithos 66, 173–199. Mamberti, M., Lapierre, H., Bosch, D., Jaillard, E., Hernandez, J., Polve, M., 2004. The Early Cretaceous San Juan plutonic suite, Ecuador: a magma chamber in an oceanic plateau? Can. J. Earth Sci. 41, 1237–1258. Mann, P., Taira, A., 2004. Global tectonic significance of the Solomon Islands and Ontong Java plateau convergent zone. Tectonophysics 389, 137–190. Martin-Gombojav, N., Winkler, W., 2008. Recycling of proterozoic crust in the Andean Amazon foreland of Ecuador: implications for orogenic development of the northern Andes. Terra Nova 20, 22–31. McCourt, W.J., Aspden, J.A., Brooks, M., 1984. New geological and geochronological data from the Colombian Andes: continental growth by multiple accretion. J. Geol. Soc. Lond. 141, 831–845. McCourt, W.J., Duque, P., Pilatasig, L.F., 1997. Geology of the Western Cordillera of Ecuador between 1–2°S, Proyecto de Desarrollo Minero y Contro Ambiental, Programa de Informacion Cartografica y Geologica, Informe 3. CODIGEM–British Geological Survey, Quito, Ecuador, p. 150. Morton, A.C., Hallsworth, C.R., 1994. Identifying provenance-specific features of detrital heavy mineral assemblages in sandstones. Sediment. Geol. 90, 241–256.

­References

235

Perez, N.D., Horton, B.K., 2014. Oligocene-Miocene deformational and depositional history of the Andean hinterland basin in the northern Altiplano plateau, southern Peru. Tectonics 33, 1819–1847. https://doi. org/10.1002/2014TC003647. Pratt, W., Figueroa, J., Flores, B., 1997. Geology of the Western Cordillera of Ecuador between 3–4° S, Proyecto de Desarrollo Minero y Contro Ambiental, Programa de Informacion Cartografica y Geologica, Informe 1. CODIGEM–British Geological Survey, Quito, Ecuador, p. 96. Reynaud, C., Jaillard, E., Lapierre, H., Mamberti, M., Mascle, G., 1999. Oceanic Plateau Island arcs of southwestern Ecuador: their place in the geodynamic evolution of northwestern South America. Tectonophysics 307, 235–254. Ruiz, G.M.H., Seward, D., Winkler, W., 2004. Detrital thermochronology; a new perspective on hinterland tectonics, an example from the Andean Amazon Basin, Ecuador. Basin Res. 16, 413–430. Saunders, A.D., Tarney, J., Kerr, A.C., Kent, R.W., 1996. The formation and fate of large igneous provinces. Lithos 37, 81–95. Sinton, C.W., Duncan, R.A., Storey, M., Lewis, J., Estrada, J.J., 1998. An oceanic flood basalts province within the Caribbean plate. Earth Planet. Sci. Lett. 155, 221–235. Spikings, R.A., Winkler, W., Seward, D., Handler, R., 2001. Along-strike variations in the thermal and tectonic response of the continental Ecuadorian Andes to the collision with heterogeneous oceanic crust. Earth Planet. Sci. Lett. 186, 57–73. Spikings, R.A., Winkler, W., Hughes, R.A., Handler, R., 2005. Thermochronology of Allochthonous blocks in Ecuador: unraveling the accretionary and post-accretionary history of the Northern Andes. Tectonophysics 399, 195–220. Spikings, R.A., Crowhurst, P.V., Winkler, W., Villagomez, D., 2010. Syn- and postaccretionary cooling history of the Ecuadorian Andes constrained by their in-situ and detrital thermochronometric record. J. S. Am. Earth Sci. 30, 121–133. Spikings, R.A., Cochrane, R.S., Villagomez, D., Van der Lelij, D., Vallejo, C., Winkler, W., Beate, B., 2015. The geological history of northwestern South America: from pangaea to the early collision of the caribbean large igneous province (290-75 Ma). Gondwana Res. 27, 95–139. Thalmann, H.E., 1946. Micropaleontology of upper Cretaceous and Paleocene in western Ecuador. Am. Assoc. Pet. Geol. Bull. 30, 337–347. Valarezo, M., Vallejo, M., Horton, B., Winkler, W., Spikings, R., Esteban, J., Jackson, L., 2017. Sedimentology and provenance analysis of the Alamor Lancones basin, southern Ecuador: a Late Cretaceous preaccretional forearc basin. In: Geological Society of America Annual Meeting. abstract 295-9. Vallejo, C., 2007. Evolution of the Western Cordillera in the Andes of Ecuador (Late Cretaceous–Paleogene) (Ph.D. thesis). Institute of Geology, ETH Zürich, Switzerland. 208 p, https://www.research-collection.ethz.ch/ handle/20.500.11850/150007. Vallejo, C., Spikings, R.A., Winkler, W., Luzieux, L., Chew, D., Page, L., 2006. The early interaction between the Caribbean plateau and the NW South American plate. Terra Nova 18, 264–269. Vallejo, C., Winkler, W., Spikings, R.A., Luzieux, L., Heller, F., Bussy, F., 2009. Mode and timing of terrane accretion in the forearc of the Andes in Ecuador. In: Kay, S.M., Ramos, V.A., Dickinson, W.R. (Eds.), Backbone of the Americas: Shallow Subduction, Plateau Uplift, and Ridge and Terrane Collision. vol. 204. Geological Society of America Memoirs, pp. 197–216. Vallejo, C., Soria, F., Tornos, F., Naranjo, G., Rosero, B., Salazar, F., Cochrane, R., 2016. Geology of El domo deposit in Central Ecuador: a VMS formed on top of an accreted margin. Mineral. Deposita 51, 389–409. Vallejo, C., Tapia, D., Gaibor, J., Steel, R., Cardenas, M., Winkler, W., Valdez, A., Esteban, J., Figuera, M., Leal, J., Cuenca, D., 2017. Geology of the Campanian M1 sandstone oil reservoir of eastern Ecuador: a delta system sourced from the Amazon Craton. Mar. Pet. Geol. 86, 1207–1223. Van Melle, J., Vilema, W., Faure-Brac, B., Ordoñez, M., Lapierre, H., Jimenez, N., Jaillard, E., Garcia, M., 2008. Pre-collision evolution of the Piñón oceanic terrane of SW Ecuador: stratigraphy and geochemistry of the "Calentura Formation". Bull. Soc. Geól. Fr. 179, 433–443.

236

Chapter 8  Coastal forearc and Western Cordillera, Ecuador

Van Thournout, F., 1991. Stratigraphy, Magmatism and Tectonism in the Ecuadorian Northwestern Cordillera: Metallogenic and Geodynamic Implications. (Ph.D. thesis). Katholieke Universiteit Leuven, Leuven. 150 pp. Van Thournout, F., Hertogen, J., Quevedo, L., 1992. Allochtonous blocks in northern Ecuador. Tectonophysics 205, 205–222. Villagomez, D., Spikings, R., Magna, T., Kammer, A., Winkler, W., Beltrán, A., 2011. Geochronology, geochemistry and tectonic evolution of the Western and Central cordilleras of Colombia. Lithos 125, 875–896. Whattam, S.A., Stern, R.J., 2015. Late Cretaceous plume-induced subduction initiation along the southern margin of the Caribbean and NW South America: the first documented example with implications for the onset of plate tectonics. Gondwana Res. 27, 38–63. Witt, C., Rivadeneira, M., Poujol, D., Beida, D., Beseme, G., Montenegro, G., 2016. Tracking ancient magmatism and Cenozoic topographic growth within the Northern Andes forearc: constraints from detrital U-Pb zircon ages. Geol. Soc. Am. Bull. 129, 415–428. Wright, J., Wyld, S., 2011. Late Cretaceous subduction initiation on the eastern margin of the Caribbean-Colombian Oceanic Plateau: one great arc of the Caribbean (?). Geosphere 7, 468–493.