Article

Constraints on the ages of the crystalline basement and Palaeozoic cover exposed in the Cordillera real, Ecuador: 40Ar/39Ar analyses and detrital zircon U/Pb geochronology

SPIKINGS, Richard Alan, et al.

Abstract

Gabbros and ultramafic rocks of the Huarguallá Gabbro unit exposed in faulted slivers along the western Cordillera Real of Ecuador crystallised between 623and531 Ma (40Ar/39Ar dates), were derived from asthenospheric sources with minor crustal contamination, and form part of the Central Iapetus Magmatic Province. These rocks formed in an early rift environment during the opening of the Iapetus Ocean, and represent the only igneous record of Iapetus rifting north of the Huancabamba deflection (5°S) in South America. The age and composition of the Huarguallá Gabbro unit is consistentwith the reconstruction of Tegner et al. (2019),which juxtaposes Baltica and northwestern Gondwana within Panotia. 206Pb/238U dates of detrital zircons combinedwith fossil assemblages shows that the Chiguinda unit of the Cordillera Real, and La Victoria Unit of the Amotape Complex were deposited during the Carboniferous. These new data, combined with previous studies of magmatism and sedimentation from southern Peru, Colombia and Venezuela, imply that the rocks of the Cordillera Real were in the Ordovician and Carboniferous back-arcs, while [...]

Reference

SPIKINGS, Richard Alan, et al. Constraints on the ages of the crystalline basement and Palaeozoic cover exposed in the Cordillera real, Ecuador: 40Ar/39Ar analyses and detrital zircon U/Pb geochronology. Gondwana Research, 2021, vol. 90, p. 77-101

DOI : 10.1016/j.gr.2020.10.009

Available at: http://archive-ouverte.unige.ch/unige:146042

Disclaimer: layout of this document may differ from the published version.

1 / 1 Gondwana Research 90 (2021) 77–101

Contents lists available at ScienceDirect

Gondwana Research

journal homepage: www.elsevier.com/locate/gr

Constraints on the ages of the crystalline basement and Palaeozoic cover exposed in the Cordillera real, Ecuador: 40Ar/39Ar analyses and detrital zircon U/Pb geochronology

R. Spikings a,⁎,A.Paula,C.Vallejob,P.Reyesb a Department of Earth Sciences, University of Geneva, Switzerland b Facultad de Geología, Minas y Petróleos, Escuela Politécnica Nacional, A.P. 17-01-2759, Quito, Ecuador article info abstract

Article history: Gabbros and ultramafic rocks of the Huarguallá Gabbro unit exposed in faulted slivers along the western Cordil- Received 16 July 2020 lera Real of Ecuador crystallised between 623and531 Ma (40Ar/39Ar dates), were derived from asthenospheric Received in revised form 4 September 2020 sources with minor crustal contamination, and form part of the Central Iapetus Magmatic Province. These Accepted 31 October 2020 rocks formed in an early rift environment during the opening of the Iapetus Ocean, and represent the only igne- Available online 06 November 2020 ous record of Iapetus rifting north of the Huancabamba deflection (5°S) in South America. The age and composi-

Keywords: tion of the Huarguallá Gabbro unit is consistent with the reconstruction of Tegner et al. (2019), which juxtaposes 206 238 Pangaea Baltica and northwestern Gondwana within Panotia. Pb/ U dates of detrital zircons combined with fossil as- Iapetus rift semblages shows that the Chiguinda unit of the Cordillera Real, and La Victoria Unit of the Amotape Complex Palaeozoic were deposited during the Carboniferous. These new data, combined with previous studies of magmatism and Detrital zircon dates sedimentation from southern Peru, Colombia and Venezuela, imply that the rocks of the Cordillera Real were 40Ar/39Ar dating in the Ordovician and Carboniferous back-arcs, while the arcs occur in conjugate margins that separated during the Triassic rifting of Pangaea. Faulted remnants of Ordovician arc rocks in the Cordillera Central of Colombia are probably allochthonous, and have been displaced from an Ordovician margin that did not face the rifted crustal sections. © 2020 Published by Elsevier B.V. on behalf of International Association for Gondwana Research.

1. Introduction Crystalline rocks of the Eastern Cordillera of Peru provide substantial evidence for continental arc magmatism between 474 and 442 Ma, and The Cordillera Real of Ecuador forms part of the Northern Andes metamorphism at ~478 Ma (Famatinian Arc; Chew et al., 2007; (north of the Huancabamba Deflection; ~5°S), and hosts metamor- Mišković et al., 2009) followed by a Devonian magmatic lull. Carbonifer- phosed sedimentary and igneous rocks that span from the Early Creta- ous continental arc magmatism occurred during 333–313 Ma and ter- ceous to the Palaeozoic, and perhaps older. The Triassic – Late minated during high-grade regional metamorphism at 313–310 Ma Cretaceous history has been extensively studied (e.g. Litherland et al., (Chew et al., 2007). Migmatitic granitoids have been dated between 1994; Cochrane et al., 2014a, 2014b; Spikings et al., 2015), and docu- 285 and 223, while the Triassic igneous rocks of the Mitu Group have ments the disassembly of Pangaea and subsequent evolution of the Pa- been assigned to a continental rift setting during 245–220 Ma cific margin. However, a paucity of studies of the pre-Triassic units (e.g. (Spikings et al., 2016). Within Colombia and Venezuela, remnants of Or- see Chew et al., 2008; Suhr et al., 2019) hinders geological models of the dovician continental arc magmatism are mainly preserved in the Pacific margin along southwestern Pangaea, which are currently heavily Santande Cawood et al., 2001r Massif and the Merida Andes, respec- founded on the evolution of the Argentinian and Peruvian Andes (e.g. tively, where zircon U\\Pb concordia ages of intrusions span between Cawood, 2005; Chew et al., 2007; Mišković et al., 2009). Here we pro- 500 and 415 Ma, and metamorphism is recorded at 477–472 Ma (Van vide new geochronological constraints for the deposition of poorly stud- der Lelij et al., 2016). Ordovician orthogneisses have also been recorded ied, Palaeozoic metasedimentary units of the Cordillera Real of Ecuador, in the northern Central Cordillera of Colombia (La Miel Orthogneiss), and estimates of the crystallisation ages of metamorphosed ultramafic where they yield zircon U\\Pb concordia ages ranging between 485 and mafic slivers that are entrained in the anastomosing Peltetec Fault and 440 Ma (Villagómez et al., 2011; Martens et al., 2014), and in the Zone, which is located along the western flank of the Cordillera Real. Floresta and Quetame massifs, with ages of 520–420 Ma (Horton et al., 2010). Similar to Peru, these intrusions predate a Devonian magmatic ⁎ Corresponding author. hiatus, although in contrast to Peru there is no record of substantial Car- E-mail address: [email protected] (R. Spikings). boniferous arc magmatism. Permian intrusions (278–253 Ma; Vinasco

https://doi.org/10.1016/j.gr.2020.10.009 1342-937X/© 2020 Published by Elsevier B.V. on behalf of International Association for Gondwana Research. R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101 et al., 2006; Cardona et al., 2010; Cochrane et al., 2014b; Bustamante depositional age to the Late Devonian (Chew et al., 2008). No radiomet- et al., 2017; Paul et al., 2018; Spikings and Paul, 2019) are geographically ric dates have been obtained from the metavolcanic strata. Traversing scattered and reveal a continental arc in a collisional setting, culminat- westwards, the southern Cordillera Real is dominated by exposures of ing in regional metamorphism that is best preserved in the Sierra Ne- quartzites, phyllites and semi-pelites (Fig. 1;e.g.Litherland et al., vada de Santa Marta of northern Colombia (Piraquive, 2017). Finally, 1994) of the Chiguinda Fm., which are fault bounded against Triassic S-type anatectites of the Cajamarca Group were emplaced during the anatectites to the west, and Lower Cretaceous metasedimentary rocks evolution of the Palanda rift during 247–222 Ma, which was synchro- of the exhumed Salado Basin to the east. Depositional age constraints nous with the Mitu Rift in Peru (Spikings et al., 2016). These events for the Chiguinda Fm. are sparse and include i) pre-Triassic on the have been previously used to construct a Palaeozoic history for the Pa- basis of their correlation with metamorphic rocks in the Olmos Massif cific margin of the Central and Northern Andes of South America during in Peru (Kennerley, 1973), which yield Ordovician – Silurian fauna the evolution of western Gondwana and the amalgamation of Pangaea (Mourier et al., 1988), and where they are overlain by the Triassic (e.g. Chew et al., 2007). However, along-strike discrepancies such as a Mitu Group (Spikings et al., 2016), ii) fossilised microspores, which con- lack of Carboniferous arc magmatism north of Peru, have not been ad- strain deposition to the post-Silurian (Owens, 1992), which collectively dressed, partly due to a lack of data from the Pre-Triassic rocks in lead Litherland et al. (1994) to propose a Devonian – Permian deposi- Ecuador. tional age for the Chiguinda Formation. More recently, Chew et al. We combine new U–Pb data from detrital zircons extracted from the (2008) report U–Pb ages of detrital zircons extracted from a quartzite, pre-Triassic Chiguinda, and La Victoria (Amotape Complex) units with which yield a youngest age of 367 ± 12 Ma (Fig. 1), consistent with previous work to constrain their depositional ages and source regions. the interpretation of Litherland et al. (1994). The age of a newly defined basement to the Palaeozoic sedimentary The Peltetec Fault Zone (Fig. 2)isexposedalongthewesternflank of units is constrained by 40Ar/39Ar analyses of weakly metamorphosed the Cordillera Real, where it juxtaposes Early Cretaceous continental arc and foliated gabbros and ultramafic rocks that were exhumed along the rocks of the Alao Arc against parautochthonous Jurassic metasedimentary western flank of the Cordillera Real within the Peltetec Fault Zone. The rocks of the Chaucha Block (the Chaucha Block hosts the Guamote Se- magmatic source regions and tectonic environment are investigated quence; Figs. 1 and 2). A majority of the fault zone is buried beneath Ter- using bulk rock chemical and Nd isotopic compositions. These informa- tiary volcanic units, although it is interpreted to be geographically tion are combined to constrain the Palaeozoic history of the Pre-Triassic extensive (e.g. Litherland et al., 1994; Spikings et al., 2015), and may jux- units in Ecuador, and refine previous models for the Iapetus and Rheic tapose Early Cretaceous continental crust against allochthonous oceanic margins of northwestern Gondwana. crust of the Pallatanga-Piñon terrane where the Chaucha Block is not present. Therefore, the Peltetec Fault is considered to be equivalent to 2. Geological framework and previous work the Cauca-Almaguer Fault along the western flank of the Cordillera Cen- tral in Colombia (e.g. Villagómez et al., 2011). Anastomosed faulted blocks Phanerozoic rocks north of the Huancabamba Deflection at 5°S host numerous different lithologies, which are interpreted via lithological (Fig. 1) can be separated into an allochthonous, oceanic Late Cretaceous associations to include Palaeozoic metasedimentary units (Chiguinda sequence, which is faulted against older, differentiated crust via a Late Unit) and Triassic anatectites (Tres Lagunas Granite). Early Cretaceous Cretaceous suture (Vallejo et al., 2006; Spikings et al., 2015). Exhuma- metagabbros yield 40Ar/39Ar plateau (plagioclase; Fig. 2) plateau dates tion of the continental crust during mainly compressive events in the of ~134 Ma, and are interpreted as transitional oceanic crust that formed Late Cretaceous – Cenozoic exposed Palaeozoic sequences within the in an Early Cretaceous marginal basin (Spikings et al., 2015). We provide Cordillera Real and the Amotape Block (e.g. Spikings et al., 2010; new 40Ar/39Ar dates from fault-bounded, metamorphosed maficandul- Martin-Gombojav and Winkler, 2008; Gutierrez et al., 2019), which tramafic slivers within the Peltetec Fault Zone (Fig. 2) that reveal the pres- were mapped and differentiated by the British Geological Survey during ence of late Neoproterozoic basement (see section 4.2). 1986–1993 (Litherland et al., 1994). The Cordillera Real is an approxi- The E-W striking Amotape Complex is a large inlier of metamorphic mate N-S trending topographic ridge, which is geographically and geo- rocks located in southwestern Ecuador (Fig. 1), and is considered to be a logically continuous with the Cordillera Central of Colombia (e.g. parautochthonous section of the Andean margin which decoupled from Villagómez et al., 2011; Spikings et al., 2015), and is oblique to the East- rocks of the Cordillera Real and rotated into the Andean forearc (e.g. ern Cordillera of Peru across the Huancabamba Deflection. Mourier et al., 1988; Mitouard et al., 1990) after ~115–110 Ma Within Ecuador, evidence for Precambrian rocks is extremely cur- (Jaillard et al., 1999; Spikings et al., 2005). Weakly metamorphosed ar- sory, and includes a single Rb–Sr data point of ~1600 Ma, which is re- koses, wackes and quartz arenites of the El Tigre Formation are consid- ported as a personal communication in Litherland et al. (1994). ered to be turbiditic and are devoid of volcanic debris (Litherland et al., Equally as vague, rafts of migmatitic gneisses within the Jurassic Zamora 1994). These sedimentary rocks are unconformably overlain by late Batholith (Fig. 1; eastern flank of the Cordillera Real) are reported in Aptian sedimentary rocks of the Celica Lancones Basin along the south- Litherland et al. (1994) as Precambrian, although they remain undated. ern exposure of the Amotape Complex (Fig. 1; Jaillard et al., 1999; Stratigraphic relationships suggest that black slates of the Pumbuiza Valarezo et al., 2019), and are intruded by the Marcabeli Pluton (U–Pb Formation are pre-Upper Carboniferous and they were assigned to the zircon ages 227–238 Ma; Aspden et al., 1995; Cochrane et al., 2014b; Devonian by Litherland et al. (1994). Limestones, shales and sandstones Paul et al., 2018) and host pre-Devonian acritarchs and spores of the Macuma Formation unconformably overly the Pumbuiza Fm., and (Zamora and Pothe de Baldis, 1988). U–Pb concordia dates of the youn- have been assigned to the Lower Pennsylvanian – Permian on the basis gest detrital zircons within a sandstone of the El Tigre Unit (sample of fossil assemblages (Tschopp, 1953; Litherland et al., 1994). The EO4) constrain its maximum depositional age to 512 ± 21 Ma (Suhr Pumbuiza and Macuma formations are exposed in small inliers in the et al., 2019). These constraints suggest a Cambrian – Silurian age for Oriente retroforeland basin, and were not sampled in this study (they the El Tigre unit. The El Tigre Unit is fault bounded against higher are exposed to the east of the map shown in Fig. 1). Low grade phyllites, grade paraschists and paragneisses of the La Victoria Unit along its marbles and metamorphosed tuffs of the Isimanchi unit are exposed in northern boundary (Fig. 1), which is considered by Litherland et al. the southern Cordillera Real (Fig. 1), where they are faulted against Tri- (1994) to be the metamorphosed equivalent of the El Tigre Unit, via el- assic anatectites to the west, and Jurassic continental arc intrusions to evated temperatures during the intrusion of the Moromoro granites the east (Fig. 1). Fossilised fish remains loosely assign deposition to (228–237 Ma; Aspden et al., 1995; Cochrane et al., 2014b; Spikings the Carboniferous to Late Triassic (British Geological Survey, 1989). et al., 2015; Paul et al., 2018). Suhr et al. (2019) report overlapping U– More recently, U–Pb concordia dates of detrital zircons from a black Pb concordia ages of detrital zircon cores from the La Victoria Unit of phyllite (368 ± 14 Ma) of the Isimanchi unit constrain its maximum 365 ± 14 Ma and 357 ± 15 Ma, with typically magmatic Th/U ratios

78 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

Fig. 1. Geological map of the southern Cordillera Real and Amotape Complex of Ecuador (after Litherland et al., 1994, Aspden et al., 1995). New and previous (Chew et al., 2008; Suhr et al., 2019)U\\Pb concordia dates of the youngest detrital zircons are shown, along with new 40Ar/39Ar dates of gabbros and ultramafic rocks of the Huarguallá Gabbro Unit, within the Peltetec Fault Zone. The red box highlights the location of Fig. 2. F: Floresta Massif, M: Merida Andes, Q: Quetame Massif, PF: Peltetec Fault, S: Santander Massif. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) 79 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101 of 0.68 and 0.52, respectively. Therefore, it is likely that the La Victoria multi-collector Argus V mass spectrometer, equipped with one Faraday Unit has a younger depositional age than the El Tigre Unit. The Bocana with a 1E11 ohm feedback resistor (40Ar), and four Faradays with 1E12 Unit is defined by Aspden et al. (1995) as a series of anatectic ohm feedback resistors (39-36Ar). Data were reduced using ArArCalc metasedimentary rocks that form part of the Triassic (see above) (Koppers, 2002), and baseline and blank corrected data are presented Moromoro Granite Complex (Fig. 1). Suhr et al. (2019) constrain its in Table 2. maximum depositional age to 367 ± 20 Ma (sample EO6) on the basis of U–Pb concordia ages of detrital zircons. U–Pb monazite dates of gar- net bearing migmatites constrain the timing of metamorphism of the 3.3. Whole Rock Geochemistry sedimentary protolith to 229–223 Ma (Riel et al., 2013). These Palaeozoic sedimentary units, which underwent Triassic anatexis Representative whole rock powders were prepared using an agate (Spikings et al., 2015), are bound to the north by a highly sheared mill and major and trace elements were measured using a Philips zone that separates them from medium grade semi-pelites and schists PW2400 X-Ray Fluorescence (XRF) spectrometer at the University of of the Palenque Mélange (Aspden et al., 1995; Fig. 1). Suhr et al. Lausanne, Switzerland. The NIMN, NIMG, BHVO and SY2 standards – (2019) report U Pb concordia ages of detrital zircons extracted from a were used for quality control. Glass fused disks prepared for XRF analy- sandstone within the Palenque Mélange, which yield a maximum depo- ses were fragmented and mounted for additional analyses of trace and sitional age of 391 ± 17 Ma. rare earth elements (REE). Measurements were made using a Perkin This summary highlights the lack of currently exposed Precambrian Elmer ELAN 6100 DRC quadrupole ICP-MS, and depending on the ex- source regions within Ecuador. However, within South America, Pre- pected enrichment within samples, either NIST SRM 610 or 612 fused cambrian rocks are exposed within Colombia (E.g. Cordani et al., glasses were used as external standards. The laser settings used for anal- š ć 2005), Peru (Mi kovi et al., 2009), and within the Amazonian craton yses were 10 Hz frequency, 140 mJ energy and 80–120 μm spot size. that is exposed to the east (e.g. Chew et al., 2011). Cambrian - Ordovi- Blanks were measured for ~90s, after which the laser was switched on cian zircons may be derived from the Famatinian Arc, which is exposed and the signal was measured for 45 s. The Sr or Al O concentrations š ć 2 3 within Peru (e.g. Mi kovi et al., 2009), Colombia (e.g. Van der Lelij et al., (previously determined by XRF) were used as an internal standard. 2016) and Venezuela (e.g. Van der Lelij et al., 2016), while Carbonifer- Each sample was ablated 3 times, and average concentrations were cal- ous zircons may be derived from the Carboniferous arc of the Eastern culated offline using LAMTRACE (Jackson, 2008). The uncertainties of 3 š ć Cordillera of Peru (e.g. Mi kovi et al., 2009). The relict conjugate mar- spots per sample are ±10% for rare earth elements (REE), and ± 5% for gins to South America within the Mixteca Terrane and the Maya Block other trace elements. Whole rock compositions (Table 3) have been (Spikings and Paul, 2019) are also potential sediment source regions normalised to an anhydrous state in the graphical representations. for Gondwanan basins within Ecuador, and these are discussed in detail in section 5.3.

3. Analytical methods 3.4. Nd bulk rock isotopes

3.1. U–Pb analyses of zircons 100 mg of whole rock powder was dissolved in 4 ml of concentrated HF and 1 ml of 15 M HNO3 in closed Teflon vials at 140 °C for seven days. The U–Pb isotopic composition of zircons was obtained using Laser The samples were dried down and re-dissolved in 3 ml of 15 M HNO3 – Ablation Inductively Coupled Mass Spectrometry (LA-ICP-MS) at the before being dried down again. Sr Nd chemical separation followed University of Lausanne. Polished zircons (in epoxy) were ablated with the methods described in Pin and Zalduegui (1997) and Chiaradia an UP-193FX ArF 193 nm excimer ablation system (ESI) using the fol- et al. (2011). Radiogenic isotopes of Sr and Nd were analysed at the Uni- lowing parameters: 35 μm beam size, 5 Hz repetition rate, 30 s signal versity of Geneva using a Thermo Neptune PLUS Multi-Collector ICP-MS and a beam energy density of 2.2–2.5 J/ cm2. Isotopic intensities were following the methods described by Chiaradia et al. (2011). measured using an Element XR single-collector sector-field ICP-MS Isotopic ratios were corrected for internal fractionation using 146 144 143 144 143 144 (Thermo Scientific). GEMOC GJ-1 zircon (CA-ID-TIMS 206Pb–238U age Nd/ Nd = 0.7219 for the Nd/ Nd ratio. JNdi-1 ( Nd/ Nd = of 600.5 ± 0.4 Ma; Boekhout et al., 2012; Ulianov et al., 2012)was 0.512115; Tanaka et al., 2000; long-term external reproducibility: used as a primary standard. Secondary standards used to monitor con- 10 ppm) was used as an external standard. Due to a systematic difference sistency in the measured U–Pb dates were either Harvard 91,500 between measured and accepted standard ratios, Nd isotope ratios were (1065.4 ± 0.3 Ma; Wiedenbeck et al., 1995) zircon, or Plešovice further corrected for external fractionation by a value of +0.047 144 144 (337.13 ± 0.37 Ma; Sláma et al., 2008) zircon. Dates (Table 1)werecal- and + 0.5 amu, respectively. The interference of Sm on Nd 147 culated using LAMTRACE (Jackson, 2008). More details regarding was monitored on Sm and corrected with a value of 0.206700 144 147 the spectrometer setup and data reduction can be found in Ulianov ( Sm/ Sm). The data are presented in Table 4. et al. (2012).

3.2. 40Ar/39Ar analyses 4. Results

Two gabbros and an ultramafic rock were crushed and sieved to In-situ (LA-ICPMS) U–Pb dates have been obtained from detrital zir- ≤300 μm, and plagioclase was extracted using conventional magnetic cons extracted from nine, weakly metamorphosed sedimentary rocks and gravimetric methods. Translucent-transparent, inclusion free pla- that were mapped as the Chiguinda (Cordillera Real) and La Victoria gioclase grains were hand-picked using a binocular microscope, and (Amotape Complex) units by the British Geological Survey (Litherland washed using ultra-sound in di-ionized water for ten minutes. Plagio- et al., 1994). These data have been combined with previous U–Pb anal- clase separates were irradiated at the shielded CLICIT position at the Or- yses of detrital zircons from the same, and other Palaeozoic sedimentary egon State University TRIGA reactor for 15 h, along with evenly spaced sequences within Ecuador (Table 1; Chew et al., 2007; Suhr et al., 2019; aliquots of Fish Canyon Tuff sanidine (28.201 ± 0.046 Ma; Kuiper raw U and Pb isotopic data are presented in Supplementary Table 5). et al., 2008) to track neutron fluences. The irradiated plagioclase sepa- Representative cathodoluminescence images of detrital zircons are pre- 40 39 rates were degassed using a 50 W, CO2-IR laser (Photon Machines sented as a supplementary figure. We also present new Ar/ Ar, step- Inc.), and the gas was cleaned via a cold finger held at −130 °C, and heating analyses of plagioclase extracted from exhumed mafic and ul- hot GP50 (S101) and AP10 getters. Ar isotopes were measured on a tramafic rocks within the Peltetec Fault Zone (Table 2).

80 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

0770 78°34’ 78°33’ 0774 Jurassic - Lower Cretaceous Yunguilla Unit Bayo Pungu Unit Alao Arc

R. Alao Metagabbro 1°51’ Metasedimentary rocks 04PR98, 566±35 Metabasalts Peltetec Unit Peltetec

Peltetec Guamote Sequence 9794 Triassic

1°52’ Tres Lagunas Unit Carboniferous 09PR48, 135±1 Pr 04PR116, 586±14 09PR47, 134±13 Chiguinda Unit Late Neoproterozoic Huarguallá 04PR68, 582±41 1°53’ Metagabbro

Unit Peridotite Huarguallá

Previous analyses Pr (Spikings et al., 2015) 9790 2 km

Road and track

Fig. 2. Geological map of the Peltetec Fault Zone after Reyes (2006), showing the location of new 40Ar/39Ar dates (plagioclase) of the Huarguallá Gabbro Unit, and previous 40Ar/40Ar analyses (Spikings et al., 2015). Outcrops are accessible along the River Huarguallá. Universal Transverse Mercator coordinates are provided (zone 17 M).

4.1. U–Pb analyses of detrital zircons The YSG, Y3 and YDZ dates overlap within uncertainty in all 9 newly studied samples (Fig. 3; Table 1), and define the youngest possible detri- Prior palaeontological constraints on the depositional ages of the tal zircon dates that mainly span the Devonian - Carboniferous. The sampled units are poor, and thus we rely heavily on the youngest zircon Mean Squared Weighted Deviate (MSWD; equivalence) vales for the ages to provide maximum depositional age constraints. However, the Y3 dates range from 8 to >300, suggesting they do not define a single low precision of LA-ICPMS dates can result in inaccuracies related to un- date population. The YC2 + (1σ) and YC3 + (2σ) dates are more con- identified discordance. We have attempted to mitigate low-precision servative and statistically robust, and yield older dates that are consis- spot analyses by applying a similar approach to Dickinson and Gehrels tently older than the YSG. Dickinson and Gehrels (2009) showed that (2009), and derive temporal depositional constraints with several dif- the youngest single grain age was equivalent to the depositional age ferent statistical tolerances that trade-off precision and accuracy, in 90% of their sedimentary rocks from the Colorado Plateau, which while only considering grains that are concordant within 2σ(Fig. 3). probably reflects the proximity of their sampling sites to contempora- These different dates are i) the youngest single grain (YSG), which is neous volcanic activity. Similarly, Carboniferous arc magmatism was particularly prone to inaccuracy as a result of unidentifiable lead loss abundant in Peru, and crust that was outboard of Ecuador (see sec- within the precision of LA-ICPMS analyses, and a potential lack of repre- tion 5), and thus it is reasonable to suggest that there was a abundant sentation, ii) weighted mean of the youngest three (Y3) grains, which supply of Carboniferous zircons into the Chiguinda and La Victoria mitigates the effect of lead loss, but can group dates that clearly do not units. Therefore, we consider the YSG dates to be the best estimates of define a single date population, iii) weighted mean of the youngest clus- the minimum detrital zircon age of the sedimentary rocks, while we ter of 2 or more grains with overlapping dates at 1σ (YC2 + (1σ); e.g. also consider the YC2 + (1σ) dates to be the best conservative estimates Jones et al., 2009), iv) weighted mean of the youngest cluster of 3 or of the detrital zircon ages, given that the YC3 + (2σ) dates were typi- more grains with overlapping dates at 2σ(YC3 + (2σ)), and v) the cally >10 Ma older than the timing of deposition in the study of youngest detrital zircon (YDZ) calculation of Ludwig (2012), which is Dickinson and Gehrels (2009). determined by a Monte Carlo analysis of the youngest subset of detrital Metasedimentary rocks 99RS38, 99RS39, 11RC20, 13AP53 and zircon dates in a detrital zircon population. All dates are reported with 13AP54 were all sampled from low grade, gently folded strata that are 2σ uncertainties (Table 1). mapped as the Chiguinda Unit (Litherland et al., 1994). The rocks

81 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

Table 1 Summary of new zircon (detrital) U-Pb dates obtained from the Chiguinda and La Victoria Fms., including previously published data from the Cordillera Real and the Amotape Complex.

Sample Lithology Unit Latitude Longitude No. of YSG Y3 YDZ YC1σ YC2σ Prominant age peaks Chord (2+) (3+) Intercepts

analysed 206Pb/238U 206Pb/238U 206Pb/238U 206Pb/238U 206Pb/238U 206Pb/238U (Ma)* (Ma)ǂ

spots$ ±2σ (Ma) ±2σ (Ma)# ±2σ (Ma) ±2σ ±2σ (Ma)# (Ma)#

This study Cordillera Real 99RS38 Quartzite Chiguinda 03° 59′ 79° 08′ 119 (90) 441.9 446 ± 32 423 506 ± 3 508 ± 6 480–620, 720–780, 195–700, 38.0” 21.9” ± 9.1 (8.3) + 10/−8 (1.2) (2.2) 1000–1080 1080. 555–1080 435–1080, 2130, 2800 99RS39 Quartzite Chiguinda 03° 59′ 79° 05′ 119 (91) 348.6 419 ± 87 349 484 ± 10 517 ± 6 520–680, 1040–1100 500–1210, 15.2” 37.9” ± 5.5 (279) +6/−7 (1.8) (1.4) 2740 11RC20 Paraschist Chiguinda 03° 59′ 79° 06′ 109 (82) 358.1 401 ± 55 358.3 451 ± 7 449 ± 6 480–640, 700–720, 400–1010 15.2” 24.0” ± 4.9 (228) +5/−6 (1.3) (3.8) 880–1020 13AP53 Metasandstone Chiguinda 03° 59′ 79° 06′ 100 (88) 313.7 336 ± 38 314 511 ± 3 510 ± 4 310–370, 480–580, 525–1010 26.2” 27.4” ± 2.6 (178) +3/−3 (0.6) (1.3) 960–1040 13AP54 Metasandstone Chiguinda 03° 59′ 79° 06′ 88 (68) 317.8 373 ± 100 318 467 ± 5 501 ± 13 320–380, 460–560, 325–945, 32.4” 25.2” ± 7.8 (323) +9/−9 (0.38) (3.3) 700. 720, 940–1080 1050 99RS53 Black quartzite Chiguinda 03° 00′ 78° 35′ 120 (92) 346.5 366 ± 28 347 394 ± 15 496 ± 20 560–640, 840–960, 515–1110, 45.4” 56.2” ± 10.6 (9.2) + 11/−12 (0.38) (3.2) 1040–1100, 2020–2100 2090 99RS55 Bt paraschist Chiguinda 03° 00′ 78° 39′ 108 (83) 324.7 339 ± 17 325 459 ± 3.3 489 ± 3 440–680, 960–1080, 270–600 09.4” 14.9” ± 4.7 (56) +5/−5 (0.20) (0.79) 2660–2720 515–1100, 1890 11RC27 Hbl quartzite Chiguinda 02° 12′ 78° 21′ 118 (81) 334.9 391 336 498 ± 11 488 ± 26 480–620, 940–1060, 515–1090, 15.4” 57.4” ± 7.3 ± 100,263) +8/−8 (0.01) (2.4) 1740–1860, 2500–2580 2130, 2750

Amotape Complex 13AP33 Bt paraschist La 03° 42′ 79° 51′ 120 (84) 327.5 372 ± 76 327 448 ± 13 456 ± 17 480–640, 760–780, 110–655 Victoria 52.6” 10.1” ± 10.5 (38) + 12/−12 (0.64) (1.3) 980–1040, 1700–1760 485–1140 Previous Work Cordillera Real Chew et al. (2008) 99RS28 Quartzite Chiguinda 04° 24′ 79° 09′ 49 (42) 367 ± 12 400 ± 80 377 365 ± 9 529 ± 26 500–800, 900–1100, N.D. 38.3” 32.4” (39) + 43/−45 (0.25) (3.6) 2500–2700 99RS65 Phyllite Isimanchi 04° 49′ 79° 06′ 50 (41) 368 ± 14 387 ± 40 409 448 ± 39 460 ± 9 480–620, 920–1180, N.D. 42.3” 59.9” (0.78) + 19/−20 (0.04) (2.0) 1800–2000 Amotape Complex N.D. Suhr et al. (2019) N.D. EO2 Sandstone Palenque 03° 37′ 80° 03′ 38 (31) 391 ± 17 474 ± 100 396 561 ± 10 568 ± 13 540–640, 880–1060, N.D. 7.50” 19.5” (69) + 18/−18 (0.53) (1.6) 2020–2040 EO4 Sandstone El Tigre 03° 51′ 80° 05′ 40 (37) 512 ± 21 516 ± 12 512 521 ± 9 528 ± 11 512–640, 680–720, N.D. 49.8” 56.7” (0.19) + 12/−16 (0.59) (1.5) 960–1100 EO5 Paragneiss La 03° 44′ 79° 50′ 38(36) 357 ± 15 390 ± 65 366 361 ± 10 539 ± 18 500–640, 778–971, N.D. Victoria 01.7” 07.7” (33) + 15/−13 (0.61) (3.6) 1039–1149 EO6 Sandstone La Bocana 03° 45′ 79° 38′ 70 (63) 367 ± 20 390 ± 21 394 399 ± 7 399 ± 7 500–620, 900–1060 N.D. 25.0” 36.2” (4.3) +9/−17 (0.07) (0.07)

$ Values in parentheses are the number of grains remaining after filtering with a discordance of ±5% # Values in parentheses are the MSWD of equivalence * Discordia ±5% N.D.: Not Determined ǂ Each row should be read as lower intercept - upper intercept1, upper intercept2 etc. (i.e. a common lower intercept). Multiple rows per sample indicate more than one lower intercept.

Table 2 Summary of 40Ar/39Ar (plagioclase) dates, and whole rock Nd and Sr compositions of the Huargualla Gabbro unit

40 39 40 39 40 36 87 86 Sample Lithology Unit Latitude Longitude Ar/ Ar Ar/ Ar ( Ar/ Ar)i ENdi Sr/ Sr plateau date inverse isochron

±2σ (Ma) date ± 2σ (Ma)*

04PR68 Metagabbro Huarguallá Gabbro 01° 52′ 35.85” 78° 33′ 45.37” 581.8 ± 41.1 582.1 ± 497.1 (0.12) 298.4 ± 169.5 2.40 0.706097 04PR98 Metagabbro Huarguallá Gabbro 01° 51′ 19.39” 78° 33′ 30.27” 565.5 ± 34.4 230.2 ± 234.5 (1.22) 172.6 ± 238.4 04PR116 Peridotite Huarguallá Gabbro 01° 51′ 19.37” 78° 33′ 30.26” 585.5 ± 14.1 519.4 ± 135.8 (0.74) 321.3 ± 51.3 −0.57 0.704296

Plateau dates defined as three contiguous heating steps that account for 50% or more of the total 39Ar released *Numbers in parentheses are the MSWD

82 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

Table 3 analysis yields numerous best-fitchords(Fig. 5a; Reimink et al., 2016). Whole rock geochemistry of the Huargualla Gabbro unit A lower intercept of ~195 Ma is younger than all of the concordant 04PR68 04PR116 dates, and is common to upper intercepts at ~700 and ~ 1080 Ma. A Gabbro Peridotite lower intercept at 435 Ma is common to upper intercepts at 1080, wt% wt% 2130 and 2800 Ma, and a statistically likely chord has an older lower in- SiO2 48.94 47.83 tercept at 555 Ma and an upper intercept at ~1080 (Table 1). Quartz P2O5 0.19 0.17 TiO2 0.77 0.49 arenite 99RS39 yielded 91 concordia dates from zircon cores and rims Al2O3 11.32 8.93 with dates ranging between 349 ± 6–2627 ± 77 Ma (Fig. 4b). The CaO 8.49 14.91 youngest spot age, YDZ and Y3 are indistinguishable, and thus the youn- Na2O 3.03 0.83 gest detrital zircon age is considered to be 349 ± 6 Ma, with a K2O 0.26 0.00 σ MnO 0.16 0.17 YC2 + (1 ) age of 484 ± 10 Ma. Kernel Density Estimates of the 206 238 Fe2O3 11.19 9.11 Pb/ U dates with ±5% discordance yield prominent peaks at Cr2O3 0.13 0.14 520–680 and 1040–1100 (Fig. 4b). Best fit analyses of the discordant MgO 12.08 14.96 data yielded two chords with a common lower intercept at ~500 Ma, ppm ppm and upper intercepts of ~1210 and ~ 2740 Ma (Fig. 5b). 109 spot analy- Rb 3.53 0.31 ses of zircon cores and rims from paraschist 11RC20 yielded 82 concor- Ba 85.72 11.02 dant analyses with 206Pb/238U concordia dates ranging between 358 ± 5 Th 1.07 0.47 and 2599 ± 16 Ma (Fig. 4c). The youngest spot age, YDZ and Y3 are in- U 0.11 0.04 Nb 3.40 2.00 distinguishable, and thus the youngest detrital zircon age is considered Ta 0.32 0.60 to be 358 ± 5 Ma, while the YC2 + (1σ) and YC3 + (2σ) dates overlap, Pb 0.54 0.40 with a YC2 + (1σ) age of 451 ± 7 Ma. Kernel Density Estimates of the Sr 75.00 30.00 206Pb/238U dates with ±5% discordance yield prominent peaks at Zr 41.78 16.33 – – fi Hf 1.27 0.57 480 640 Ma and 880 1020 Ma, and a weakly de ned peak at 206 238 207 238 Ti 4634.07 2915.46 1980–2140 (Fig. 4c). Best fits to the discordant Pb/ Uand / U Tb 0.43 0.30 dates yield a single chord with intercepts at ~400 and ~ 1010 Ma Y 15.30 10.30 (Fig. 5c). 100 spot analyses of zircon rims and cores from quartzite Tm 0.26 0.16 13AP53 yielded 88 206Pb/238U concordia dates ranging between Yb 1.64 1.00 – Co 57.86 60.44 314 ± 3 3128 ± 23 Ma (Fig. 4d). The youngest spot age, YDZ and Y3 La 5.60 2.16 are indistinguishable, and thus youngest detrital zircon age is consid- Ce 12.13 5.20 ered to be 314 ± 3 Ma, while the YC2 + (1σ) and YC3 + (2σ) dates Pr 1.80 0.84 overlap, with a YC2 + (1σ) age of 511 ± 3 Ma. Kernel density estimates Nd 7.98 4.09 206 238 Sm 2.36 1.47 of the Pb/ U dates with ±5% discordance yield prominent peaks at Eu 0.80 0.44 310–370 Ma, 480–450 Ma and 960–1040 Ma (Fig. 4d). Statistical analy- Gd 2.67 1.70 sis of the discordant dates yielded a single chord with lower and upper Tb 0.43 0.30 intercepts of 525 Ma and 1010 Ma, respectively (Fig. 5d). Finally, quartz- Dy 2.78 1.85 ite 13AP54 yielded 68 206Pb/238U concordia dates from 88 spot analyses Ho 0.60 0.38 Er 1.77 1.21 of rims and cores, which span between 318 ± 8 Ma and 3045 ± 20 Ma Yb 1.64 1.00 (Fig. 4e). The youngest spot age, YDZ and Y3 are indistinguishable, and Lu 0.24 0.16 thus the youngest detrital zircon age is considered to be 318 ± 8 Ma, V 349.00 303.00 with a YC2 + (1σ) age of 467 ± 5 Ma. Kernel Density Estimates of the 206Pb/238U dates with ±5% discordance yield prominent peaks at 320–380 Ma, 460–560 Ma and 940–1080 Ma (Fig. 4e). Best fits to the discordant 206Pb/238Uand207/238U dates yield a chord with a lower in- were sampled along the road between Loja and Zamora that transects tercept at ~325 Ma, with upper intercepts at ~945 Ma and ~ 1050 Ma the southern Cordillera Real (Fig. 1) and are deformed by regional (Fig. 5e). scale N-S fold axes. 119 spot analyses of zircon cores and rims from Farther north within the Cordillera Real (roads between Riobamba quartz arenite 99RS38 yielded 90 concordant analyses with 206Pb/238U and Macas, and Cuenca and Indanza), metasedimentary rocks 99RS53, concordia dates ranging between 442 ± 9 Ma and 1939 ± 25 Ma 99RS55 and 11RC27 were also sampled from low grade strata that pre- (Fig. 4a). The youngest spot age, YDZ and Y3 are indistinguishable, serve original bedding and are deformed by low amplitude E-W fold and thus the youngest detrital zircon age is considered to be 442 ± axes (Fig. 1). These strata were mapped as the Chiguinda Fm. by 9 Ma, while the YC2 + (1σ) and YC3 + (2σ) dates overlap, with a Litherland et al. (1994). Black quartzite 99RS53 yielded 92 206Pb/238U YC2 + (1σ) age of 506 ± 3 Ma. Kernel Density Estimates of the concordia dates from 120 spot analyses of rims and cores, which span 206Pb/238U dates with ±5% discordance yield prominent peaks at between 347 ± 11 Ma and 2656.8 ± 129.7 Ma (Fig. 6a). The youngest 480–620 Ma, 720–780 Ma and 1000–1080 Ma (Fig. 4a). Discordant spot age, YDZ and Y3 are indistinguishable, and thus the youngest detri- 206Pb/238Uand207Pb/235U dates yield a complex array and statistical tal zircon age is considered to be 347 ± 11 Ma, with a YC2 + (1σ)ageof

Table 4 Sm and Nd isotopic compositions of the Huargualla Gabbro Unit

Sample Age ± 2σ Sm Nd 147Sm/144Nd 143Nd/144Nd (143Nd/144Nd)i εNd εNdi 2σ

(Ma)# (ppm) (ppm) (±2σ)* (±2σ)

585 ± 14 2.36 7.98 0.182140 0.512692 (21) 0.511994 1.05 2.16 (0.4) 585 ± 14 1.47 4.09 0.217060 0.512686 (36) 0.511854 0.94 −0.57 (0.69)

# 40Ar/39Ar age of 04PR116, which is assumed to be valid for 04PR68. *Numbers in parentheses are the 5th and 6th decimal place.

83 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

600 Youngest Single Grain (YSG) 580 Youngest Detrital Zircon (YDZ) Youngest 3 zircons (Y3) 560 Youngest ≥2 zircons (1 overlap; YC2+1) Youngest ≥3 zircons (2 overlap; YC3+2) 540

520

500

480

460 date (Ma)  440

Pb ±2 420 206

U/ 400 238

380

360

340

320 Carboniferous Devonian Silurian Ordovician Cambrian 300

280

CORDILLERA REAL AMOTAPE COMPLEX 260 99RS38 99RS39 11RS20 13AP53 13AP54 99RS53 99RS55 11RC27 99RS28 99RS6513AP33 EO5 EO2 EO4 EO6

Chiguinda Fm. Isimanchi La Victoria Palenque El Tigre La Bocana Fm. Fm. Fm. Fm. Fm.

Fig. 3. Summary of youngest detrital zircon U\\Pb dates for Palaeozoic metasedimentary rocks of the Cordillera Real and Amotape Complex of Ecuador, including new and previous (Chew et al., 2008; Suhr et al., 2019)work.Definitions of each date are provided in the text.

394 ± 15 Ma. Kernel Density Estimates of the 206Pb/238U dates with ± ~515 Ma, and upper intercepts of ~1090 Ma, ~2130 Ma and ~ 2750 Ma 5% discordance yield prominent peaks at 560–640 Ma, 840–960 Ma, (Fig. 7c). 1040–1100 Ma and 2020–2100 Ma (Fig. 6a). Best fits to the discordant Biotite bearing paraschist 13AP33 was sampled from the La Victoria 206Pb/238U and 207/238U dates yield two chords with a common lower unit within the Amotape Complex, along the road between La Bocana intercept of ~515 Ma, and upper intercepts of ~1110 Ma and ~ 2090 Ma and Balsas (Fig. 1). 120 spot analyses of zircon rims and cores yielded (Fig. 7a). 108 spot analyses of zircons within biotite bearing paraschists 84 206Pb/238U concordia dates that span between 328 ± 11 and 99RS55 yielded 83 206Pb/238U concordia dates spanning between 2671 ± 63 Ma (Fig. 6d). The youngest spot age, YDZ and Y3 are indistin- 325 ± 5 Ma and 2647 ± 21 Ma (Fig. 6b). The youngest spot age, YDZ guishable, and thus youngest detrital zircon age is considered to be and Y3 are indistinguishable, and thus youngest detrital zircon age is 328 ± 11 Ma, while the YC2 + (1σ)andYC3+(2σ) dates overlap, considered to be 325 ± 5 Ma, while the YC2 + (1σ)yieldsanof with a YC2 + (1σ) age of 448 ± 13 Ma. Kernel Density Estimates of 459 ± 3 Ma. Kernel density estimates of the 206Pb/238U dates with ± the 206Pb/238U dates with ±5% discordance yield numerous prominent 5% discordance yield prominent peaks at 440–680 Ma, 960–1080 Ma peaks at 480–640 Ma, 980–1040 Ma and 1700–1760 Ma (Fig. 6d). and 2660–2720 Ma (Fig. 6b). Discordant 206Pb/238Uand207/238Udates Best-fit analysis of the discordant dates yields two chords, with lower yield a complex array (Figs. 7b) and statistical analysis yields numerous – upper intercept pairs at ~110 Ma and ~ 655 Ma, and ~ 485 Ma best-fit chords. The first chord has lower and upper intercepts at and ~ 1140 Ma (Fig. 7d). ~270 Ma and ~ 600 Ma. Two chords have a common lower intercept Chew et al. (2007) and Suhr et al. (2019) published U–Pb dates of at ~515 Ma, with upper intercepts at ~1100 Ma and ~ 1890 Ma. The detrital zircon grains extracted from six rocks with the Eastern Cordil- youngest chord intercepts are younger than all of the 206Pb/238U lera and the Amotape Complex, and they assumed the youngest single concordia dates. Finally, hornblende bearing quartzite 11RC27 yielded grains were consistently the best estimates of the maximum time of de- 81 206Pb/238U concordia spot dates from zircon rims and cores, which position. In all cases, the youngest spot age, YDZ and Y3 are indistin- span between 335 ± 7 Ma and 2677 ± 58 Ma (Fig. 6c). The youngest guishable, and thus the youngest grain ages (Table 1; Fig. 3) are also spot age, YDZ and Y3 are indistinguishable, and thus youngest detrital considered here to represent the statistically youngest zircon detrital zircon age is considered to be 335 ± 7 Ma, while the YC2 + (1σ) and ages. However, more conservative estimates provided by the YC3 + (2σ) dates overlap, with a YC2 + (1σ) age of 498 ± 11 Ma. Ker- YC2 + (1σ;Table 1) statistic are 365 ± 9 Ma (99RS28, Chiguinda Fm.) nel Density Estimates of the 206Pb/238U dates with ±5% discordance and 448 ± 39 Ma (99RS65, Isimanchi Fm.), for the Eastern Cordillera. yield prominent peaks at 480–640 Ma, 940–1060 Ma, 1740–1860 Ma YC2 + (1σ;Table 1) dates for the Amotape Complex are 561 ± 10 Ma and 2500–2580 Ma (Fig. 6c). Best fits to the discordant 206Pb/238Uand (EO2, Palenque Fm.), 521 ± 9 Ma (EO4, El Tigre Fm.), 361 ± 10 Ma 207Pb/235U dates yield three chords with a common lower intercept at (EO5, La Victoria Fm.) and 399 ± 7 Ma (EO6, La Bocana Fm.).

84 i.4. Fig. .Siig,A al .Vleoe al. et Vallejo C. Paul, A. Spikings, R. AIPS The LA-ICPMS. ehrl ocri n rqec itgas(nysoswt 5 icrac)soigteKre est itiuin fso U spot of Distributions Density Kernel the showing discordance) ±5% with spots (only histograms frequency and concordia Wetherill E D C B A 206Pb/238U 206Pb/238U 206Pb/238U 206Pb/238U 206Pb/238U 206 0.045 0.055 0.065 0.075 0.085 0.045 0.055 0.065 0.075 0.085 0.054 0.058 0.062 0.066 0.070 0.074 0.078 0.082 0.045 0.055 0.065 0.075 0.085 11RC20 99RS39 13AP54 13AP53 99RS38 0.055 0.065 0.075 0.085 Pb/ .804 .605 .405 0.62 0.58 0.54 0.50 0.46 0.42 0.38 . . . . 0.7 0.6 0.5 0.4 0.3 . . . . 0.7 0.6 0.5 0.4 0.3 . . . . 0.7 0.6 0.5 0.4 0.3 . . . 0.7 0.6 0.5 0.4 235 300 340 300 300 gso h onettrezrosaesoni h ne ftehsorm.Lbl ntecnodaposhglgtbest- highlight plots concordia the in Labels histograms. the of inset the in shown are zircons three youngest the of ages U 380 , paraschist,ChiguindaUnit , micaceousquartzarrenite,ChiguindaUnit , metasandstone,ChiguindaUnit , metasandstone,ChiguindaUnit , micaceousquartzarrenite,ChiguindaUnit 340 340 340 380 420 380 380 207 380 Pb/ 420 420 420 420 460 235 460 U 460 460 500 500 500 460 500 540 540 540 540 0.6 0.0 0.2 0.4 0.0 0.1 0.2 0.3 0.4 0.5 0.0 0.2 0.4 0.6 0.0 0.2 0.4 0.6 0.0 0.2 0.4 0.6 04812162024 12162024 8 4 0 02468101214 04812162024 0481216 1000 1400 1400 1400 1400 1400 1000 1000 1800 1800 1000 1000 1800 1800 C2 1800 2200 2200 2200

2200 C3 207 A2 2600 2600 2200 2600 Pb/ 2600 85 235 U 3000 3000 3000 2600 3000

20 N 15 10 10 12 10 0 1 2 4 5 3 6 N N N 7 0 1 2 3 4 0 5 5 6 0 2 4 6 8 0 2 4 6 8 N 0 0010 0020 3000 2500 2000 1500 1000 500 0 0 0010 0020 3000 2500 2000 1500 1000 500 0 0 0010 0020 003500 3000 2500 2000 1500 1000 500 0 0 0010 0020 3000 2500 2000 1500 1000 500 0 0 0010 0020 3000 2500 2000 1500 1000 500 0 Youngest zircon441.9±9.1Ma n=90 (±5%discordance) Youngest zircon348.6±5.5Ma n=91 (±5%discordance) Youngest zircon313.7±2.6Ma n=88 Youngest zircon358.1±4.9Ma n=82 (±5%discordance) 206 Youngest zircon317.8±7.8Ma n=68 300 320 340 360 380 Pb/ \ \ baaye fdtia icn,aqie using acquired zircons, detrital of analyses Pb 238 360 400 440 U age(Ma) fi 206Pb/238U age (Ma) hrsta r lodpce in depicted also are that chords t 320 360 400 440 480 420 460 500 odaaRsac 0(01 77 (2021) 90 Research Gondwana 3500 i.5 Fig. – 101 . R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

AB99RS38, Chiguinda Unit, n=119 99RS39, Chiguinda Unit, n=119

A2, B1, C1 A B A A1 350 C A1 50

300 C2 45 A2 40 250 C3 35 200 30 25 1000 Likelihood 150 Likelihood 1000 20 100 15 0 0 1000 2000 3000 0 10 50 0 1000 2000 5 0 0 05001000 1500 2000 2500 3000 3500 0 500 1000 1500 2000 2500 3000 3500 Age (Ma) Age (Ma)

C 11RC20, Chiguinda Unit, n=109 D 99RS53, Chiguinda Unit, n=120 A1 A A1 90 A 1000 300 80 500 70 250 0 0 1000 2000 A2

Lower Intercept (Ma) Upper Intercept (Ma) 60 200 50

150 Likelihood Likelihood 40 1000

30 100 Upper intercept 20 0 Lower intercept 0 1000 2000 50 10

0 0 0 500 1000 1500 2000 2500 3000 3500 0 500 1000 1500 2000 2500 3000 3500 Age (Ma) Age (Ma) E 13AP54, Chiguinda Unit, n=88

250 A A2 B1 1000 A1

B 200 0 0 1000 2000

150 Likelihood 100

50

0 05001000 1500 2000 2500 3000 3500 Age (Ma)

Fig. 5. Highest likelihood upper and lower intercepts of chords defined by discordant U\\Pb data obtained from detrital zircons of the Chiguinda unit of Ecuador. Likelihoods were deter- mined using the algorithm described in Reimink et al. (2016). Insets show the same data, with darker blue colours depicting the highest likelihood. Labels, A, B, C are intercept values of distinct chords, where, for example, A depicts a lower intercept, while A1, A2 etc. depict different upper intercepts with the same lower intercept. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

4.2. Mafic and ultramafic rocks entrained within the Peltetec Fault Zone Cretaceous continental Alao Arc (Fig. 2). The 1–2 km wide fault zone hosts a series of N-S oriented litho-tectonic slices ranging in thickness The Peltetec Fault Zone separates parautochthonous continental from one to hundreds of meters (e.g. Litherland et al., 1994). We present crust of the Chaucha Block (Guamote Sequence) from the Early 40Ar/39Ar, geochemical and isotopic data from metagabbros and an

86 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

99RS53, metasandstone, Chiguinda Unit A N 540 2600 346.5±10.6 Ma (1 grain) 0.5 0.085 10 n=92 (±5% discordance) Youngest zircon 346.5±10.6 Ma 500 2200 0.4 8 440 0.075 460

U 1800 0.3

238 6 400 420 1400

Pb/ 0.065 A2 380 0.2 1000 4 360 206

0.055 340 0.1 2 320 300 0.045 0.0 0 0.3 0.4 0.5 0.6 0.7 02468101214 0 500 1000 1500 2000 2500 3000

B 99RS55, biotite paraschist, Chiguinda Unit N 540 n=83 (±5% discordance) 324.7±4.7 Ma (1 grain) 2600 0.085 0.5 8 Youngest zircon 324.7±4.7 Ma 500 2200 0.4 355

U 0.075 460 6 1800

238 345 420 0.3 Pb/ 0.065 1400 4 335

206 380 0.2 1000 325 B2 0.055 340 2 0.1 315

0.045 0.0 0 0.3 0.4 0.5 0.6 0.7 02468101214 0 500 1000 1500 2000 2500 3000

C 11RC27, hornblende quartz arrenite, Chiguinda Unit 0.085 10 n=81 (±5% discordance) 334.9±7.3 Ma (1 grain) 500 2600 0.5 N Youngest zircon 334.9±7.3 Ma 8 2200 0.075 460 0.4

U 460 420 1800 6

238 0.3 0.065 A3 1400 Pb/ 380 380 4 0.2 A2 206 1000 0.055 340 300 0.1 2

0.045 0.0 0 0.34 0.38 0.42 0.46 0.50 0.54 0.58 0.62 0 2 4 6 8 10 12 14 0 500 1000 1500 2000 2500 3000 D 13AP33, biotite paraschist, La Victoria Unit 10 540 n=84 2600 0.085 0.5 N Youngest zircon 327.5±10.5 Ma 500 2200 8 0.4 460 U 0.075 460 1800

238 6 420 0.3 Pb/ 1400 U age (Ma) 0.065 380 206 380 4 238 0.2 1000 Pb/ 0.055 340 0.1 2 206 300 300 0.045 0.0 0 0.3 0.4 0.5 0.6 0.7 02468101214 0 500 1000 1500 2000 2500 3000 207Pb/235U 207Pb/235U 206Pb/238U age (Ma)

Fig. 6. Wetherill concordia and frequency histograms (only spots with ±5% discordance) showing the Kernel Density Distributions of spot U\\Pb analyses of detrital zircons, acquired using LA-ICPMS. The 206Pb/235U ages of the youngest three zircons are shown in the inset of the histograms. Labels in the concordia plots highlight best-fit chords that are also depicted in Fig. 7.

87 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

A 13AP53, Chiguinda Unit, n=120 B 99RS55, Chiguinda Unit, n=108 350 A A1 A A1 1000 1000 B B1 300 500

0 450 0 0 1000 2000 250 0 1000 2000 400 B2 350 200 300

Likelihood 150 250 Likelihood 200 100 150 100 50 50 0 0 0 500 1000 1500 2000 2500 3000 3500 0 500 1000 1500 2000 2500 3000 3500 Age (Ma) Age (Ma)

C 11RC27, Chiguinda Unit, n=118 D 13AP33, La Victoria Unit, n=120

A A1 1000 B B1 150 A A1 A3 A2 150 0 125 0 1000 2000 Upper Intercept (Ma) Lower Intercept (Ma) 125 100 B2 100 B3 1000 75

Likelihood 75 Upper intercept 50 0 Likelihood Lower intercept 0 1000 2000 3000 50 25 25 0 0 500 1000 1500 2000 2500 3000 3500 0 Age (Ma) 0 500 1000 1500 2000 2500 3000 3500 Age (Ma)

Fig. 7. Highest likelihood upper and lower intercepts of chords defined by discordant U\\Pb data obtained from detrital zircons of the Chiguinda and La Victoria units of Ecuador. Likeli- hoods were determined using the algorithm described in Reimink et al. (2016). Insets show the same data, with darker blue colours depicting the highest likelihood. Labels, A, B, C are intercept values of distinct chords, where, for example, A depicts a lower intercept, while A1, A2 etc. depict different upper intercepts with the same lower intercept. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) ultramafic rock, which were sampled from two mapped fault slices 1.22), and an extremely imprecise initial 40Ar/36Ar value of 172.6 ± (Fig. 2; Tables 2–4; raw Ar isotopic data are presented in Supplementary 238.4, which does not unequivocally reveal the presence of excess Table 6). 40Ar. Finally, plagioclase from peridotite 04PR116 yields a plateau date of 585.5 ± 14.1 Ma (Fig. 8c), while the topology of the age spectrum suggests the lowest temperature steps include excess 40Ar. The steps 4.2.1. 40Ar/39Ar data that define the plateau yield an imprecise, albeit overlapping inverse Step heating of plagioclase extracted from metagabbro 04PR68 isochron date of 519.4 ± 135.8 Ma (MSWD = 0.74), with an yielded an imprecise plateau 40Ar/39Ar date of 581.8 ± 41.1 Ma atmospheric initial 40Ar/36Ar value of 321.3 ± 51.3, which overlaps (Fig. 8a) obtained from three contiguous heating steps that span 78.4% with the atmospheric 40Ar/36Ar composition. Previous studies of of 39Ar released. The elevated dates of the initial heating steps are diag- metagabbros from a juxtaposed faulted slice that hosts metagabbros nostic of the presence of excess 40Ar in these steps. The clustering of 04PR68 and 98 yielded Early Cretaceous plateau ages (Fig. 2; Spikings data within inverse isochron space yields an extremely imprecise date et al., 2015), and thus the three samples in this study were irradiated of 582.1 ± 497.1 Ma (MSWD 0.12), which nevertheless overlaps with for a duration anticipating Early Cretaceous plagioclase dates, ultimately the plateau date. The initial 40Ar/36Ar intercept of 298.4 ± 169.5 is yielding poor precision for late Neoproterozoic, low K/Ca minerals. Re- also extremely imprecise due to clustering of the data in isotope corre- gardless of the poor precision, all three plagioclase plateau dates, lation space, although it overlaps with an atmospheric composition of which span from 531 to 623 Ma (including the 2σ uncertainties; 298.6 ± 0.3 (Lee et al., 2006), and thus does not prove the presence 566–586 Ma ignoring the uncertainties), are considered to be accurate of excess 40Ar. The age spectrum for plagioclase obtained from estimates of the time of crystallisation. These late Neoproterozoic metagabbro 04PR98 (Fig. 8b) shows evidence for 40Ar loss, which is gabbros are assigned the name Huarguallá Gabbro unit, after the river probably due to observable alteration to chlorite, although temperature valley where they crop out. driven diffusive loss during low temperature Mesozoic events may also contribute to the date gradient in the age spectrum. The three steps degassed at the highest temperatures yield indistinguishable dates 4.2.2. Whole rock major oxide, trace, rare earth element and Nd isotopic with a weighted average of 565.5 ± 34.4 Ma, and we interpret these compositions to be the best estimate of the 40Ar/39Ar age of the plagioclase, although Whole rock cationic compositions of medium grained, greenschist they only span 29.7% of the total 39Ar released. These three steps also grade mafic rocks 04PR68 and 04PR116 (Huarguallá Gabbro unit) yield an imprecise inverse isochron date of 230.2 ± 234.5 Ma (MSWD = places them within the olivine gabbro and ultramafic fields of

88 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

A. 04PR68 plagioclase B. 04PR98 plagioclase 800 3100 700 2500 600

1900 500 Ar date (Ma) Ar date (Ma) 400

39 1300 581.8±41.1 Ma 39 300 Ar/ 565.5±34.4 Ma 700 Ar/ 40 40 200 100 100 0 102030405060708090100 0 102030405060708090100 39 Ar released (%) 39Ar released (%) 8 0.10

6 0.08

K/Ca 4 0.06 0.001±0.001 Ma K/Ca

2 0.04

0 0.02 0.043±0.006 Ma 0 102030405060708090100 0 102030405060708090100 39Ar released (%) 39Ar released (%)

4 4 ) ) -3

3 -3 3 Ar (10 Ar (10

40 2 2 40 Ar/ Ar/ 36 1 1 36

0 0 0246810 024681012 39Ar/40Ar (10-3) 39Ar/40Ar (10-3)

C. 04PR116 plagioclase 2200 2000 4 1800 )

1600 -3 3 1400

1200 Ar (10 2 Ar date (Ma) 585.5±14.1 Ma 40

39 1000 Ar/

Ar/ 800 1 36 40 600 400 0 0 102030405060708090100 0246810 39Ar released (%) 39Ar/40Ar (10-3) 0.30

0.20 0.041±0.020 Ma K/Ca 0.10

0.00 0 102030405060708090100 39Ar released (%)

Fig. 8. 40Ar/39Ar age spectra, K/Ca plots and inverse isochrons for the Huarguallá Gabbro unit.

Batchelor and Bowden (1985); Fig. 9a), respectively, which is consistent AcomparisonofSiO2 and Zr/TiO2 places rocks 04PR68 and 04PR116 with their mineralogical assemblages that are dominated by plagioclase, of the Huarguallá Gabbro unit in the sub-alkali basaltic field (Fig. 9b), pyroxene and olivine. Gabbro 04PR98 was not analysed, although its and thus they are similar to late Neoproterozoic rift-basalts of the Scan- mineralogical composition is extremely similar to coarse grained gabbro dinavian Dyke Complex in Baltica, and younger Triassic rift-basalts in 04PR68, and is dominated by plagioclase (35% modal; bytownite - lab- Ecuador and Colombia. However, they are less alkaline than rift- radorite) and pyroxene (15% augite and 45% enstatite, modal). The cat- related basalts of the Egersund Dyke Complex (Bingen and Demaiffe, ionic composition of gabbro 04PR68 overlaps with fields defined by 1999). N-MORB normalised trace element abundances of the gabbros, dolerites and basalts of the Egersund (~616 Ma; Bingen et al., Huarguallá Gabbro unit (Fig. 9c) reveal slight enrichments in Light Ion 1998) and Scandinavian Dyke (615–590 Ma; Tegner et al., 2019)com- Lithophile Elements, and a lack of significant Nb, Ta and Ti anomalies as- plexes of Baltica. Gabbro 04PR68 also has a similar cationic composition sociated with dehydration of a subducted slab, or significant contamina- to younger, Triassic rift-basalts of the Cordilleras Real and Central of tion with a metasomatised continental lithospheric mantle, supporting Ecuador and Colombia, respectively (Spikings et al., 2015, 2016). an origin within the asthenosphere. Similarly, N-MORB normalised

89 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

A B SiO wt% 2600 2 60 2400 Ecuador Ultramafic rock Early Cretaceous 2200 Andesite continental arc (Alao) 2000 Triassic continental 55 rift (gabbros) 1800 Gabbronorite Phonolite Huarguallá Alkali Sub-alkali 04PR68 1600 Gabbro Ol. Gabbro basalt lt Gabbro 04PR116 Unit 1400 Gabbro 50 Baltica

1200 Syeno- Alkali basa Scandinavian Dyke

6Ca+2Mg+Al (millications) Diorite diorite Bas/Trach/ Complex (615-590 Ma) 1000 Neph Late Neoproterozoic 1000 1500 2000 2500 3000 45 Egersund Dyke Complex 4Si - 11(Na+K)-2(Fe+Ti) (millications) 0.001 0.01 0.1 (~616 Ma) Zr/TiO2 C D

100 04PR68 04PR116 10 04PR68 10 04PR116

1 1

N-MORB N-MORB 0.1 0.1 Rb Ba Th U Nb Ta La Ce Pb Pr Sr Nd Zr Hf Sm Eu Ti Tb Y Tm Yb La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Yb Lu

E Nb/La F Th/Yb 1.6 10 1.4 E-MORB seamounts Connental 1.2 crust 1.0 25% OIB 1 crust 0.8 MORB 0.6 connental arc 0.4 E-MORB 0.2 oceanic arc 0.1 0 0 0.5 1.0 1.5 2.0 2.5 3.0 N-MORB (La/Sm)n

0.01 0.1 1 10 100 Nb/Yb GHTiO2/Yb 10 12

10 Nd 8 OIB array (deep melng) OIB 1 6

MORB array 4 (shallow melng) N-MORB E-MORB 2 0 5 10152025 0.1 -2 0.1 1 10 100 (La/Yb)n Nb/Yb

Fig. 9. Chemical composition of gabbro 04PR68 and peridotite 04PR116 of the Huarguallá Gabbro unit. Multi-element plots are normalised to N-MORB (Sun and McDonough, 1989). Data are also shown from Triassic rift gabbros (Spikings et al., 2015), Early Cretaceous continental (Alao) Arc (Spikings et al., 2015), Egersund Dyke Complex (Bingen and Demaiffe, 1999)and the Scandinavian Dyke Complex (Tegner et al., 2019). Lithological discriminatory field in (A) are from Batchelor and Bowden (1985). The ocean-mantle array in (F) and (G) is from Pearce (2008), and the compositions of N-MORB, E-MORB and OIB are from Sun and McDonough (1989). Average continental crust is from Taylor and McLennan (1995). Mixing line between continental crust and N-MORB is taken from Tegner et al. (2019).

REE abundances (Fig. 9d) reveal a slight enrichment in LREE relative to rifting (Spikings et al., 2015, 2016), and basalts of the Scandinavian HREE. REE abundances of peridotite 04PR116 are depleted relative to N- Dyke Complex (Tegner et al., 2019), while the REE content of peridotite MORB. Gabbro 04PR68 yields similar trace and rare earth element com- 04PR116 is generally more depleted. A comparison of Nb/La and (La/ positions to meta-gabbros that formed during Triassic continental Sm)n places the Huarguallá Gabbro Unit within the E-MORB and

90 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101 transitionary fields (Fig. 9e), which is consistent with an asthenospheric tentatively assign the sampled rocks to the Carboniferous, and perhaps source, and a lack of evidence for subduction of oceanic lithosphere. younger. This conclusion is consistent with Chew et al. (2008) who ob- These overlap with the field for the rift-related, Neoproterozoic Scandi- tained a youngest detrital zircon age of 367 ± 12 Ma from a quartzite of navian Dyke Complex, and Triassic meta-gabbros in Ecuador. The sub- the Chiguinda Unit, which was sampled ~50 km south of our analysed alkali compositions of the Huarguallá Gabbro unit are depleted in (La/ rocks, close to the Peruvian border (Fig. 1). Our new dates, combined Sm)n relative to basaltic andesites of the Early Cretaceous Alao Arc with those of Suhr et al. (2019), also assign the La Victoria Unit to the within Ecuador (Spikings et al., 2015), further supporting an intra- Carboniferous. Therefore, we suggest that the La Victoria and Chiguinda plate/rift origin. The Egersund Dyke Complex yields higher (La/Sm)n units formed in the same Carboniferous basin, given that i) the Amotape values at similar Nb/La values than the Huarguallá Gabbro, and plots Complex is considered to be a detached and rotated fault block that was within the seamount field, suggesting the magmas were derived from originally strike-parallel to the rocks exposed in the Cordillera Real (e.g. a more fertile source. Nb/Yb ratios of ~2 reveal a more enriched source Spikings et al., 2005), and ii) the Chiguinda and La Victoria units are lith- region for the Huarguallá Gabbro Unit relative to N-MORB (Fig. 9f), ologically equivalent. and are more typical of E-MORB compositions. Furthermore, these Quartz arenite 99RS38 is generally lithologically indistinguishable in rocks are slightly enriched in Th relative to Yb, compared to typical hand specimen from other rocks of the Chiguinda Fm. within the Cordil- values that define the MORB-OIB array, suggesting these asthenospheric lera Real, although it yields a Silurian youngest detrital zircon age of derived magmas have been contamination with ~25% continental crust 442 ± 9 Ma, and a Cambrian YC2 + (1σ) age of 506 ± 3 Ma. Given (Fig. 9f). Similarly, the enrichment in Th/Yb in some Triassic rift basalts that this is a single sedimentary rock, is lithologically similar to other in Ecuador and Colombia was interpreted to be a result of crustal con- rocks of the Chiguinda Unit, and has extremely similar detrital zircon tamination (Spikings et al., 2015, 2016). Basalts of the Egersund Dyke age population to rocks of the Chiguinda Unit (Fig. 4), we suggest that Complex yield higher Nb/La and Th/Yb values compared to the this rock also forms part of the Chiguinda Unit, although its minimum Huarguallá Gabbro and Scandinavian Dyke Complex, suggesting they detrital zircon age is not an accurate representation of the time of are derived from a deeper, less depleted mantle source, which has deposition. stronger affinities towards a mantle plume setting (Tegner et al., 2019) that slightly predates the onset of rifting (Fig. 9g). 5.2. Correlations with Colombia and Peru Peridotite 04PR116 and gabbro 04PR68 yield whole rock εNd values of −0.57 ± 0.6 and 2.4 ± 0.4 (Fig. 9h), respectively, when corrected for Devonian - Carboniferous sedimentary rocks in Colombia are mainly their 40Ar/39Ar age estimates (Table 2), which are less radiogenic than preserved within structurally distinct inliers within the Eastern Cordil- Triassic metagabbros that formed during Triassic continental rifting lera that also expose crystalline basement (inset of Fig. 1). These include (εNd 3.4–10.2; Spikings et al., 2015). The paucity of data renders any in- the shallow marine Cuche Fm. of the Floresta Massif (Fig. 10), which terpretation tentative, although we suggest these reflect larger amounts yields maximum stratigraphic ages of ~409–384 Ma (U–Pb dates of de- of assimilation of continental crust by mantle derived melts, which also trital zircons; Horton et al., 2010; Cardona et al., 2016) that are consis- gave rise to slightly higher Th/Yb ratios in the Huarguallá Gabbro. This tent with Late Devonian fossil assemblages (e.g. Janvier and Villarroel, would be consistent with mafic magmatism during a pre- or early con- 2000; Burrow et al., 2003). Detrital zircons from siliclastic rocks of the tinental rift phase, where asthenosphere derived melts percolate Floresta Fm. of the Floresta Massif yield a maximum stratigraphic date through thicker crustal sections (Spikings et al., 2016). of ~362 Ma (Cardona et al., 2016). Horton et al. (2010) present U–Pb dates of detrital zircons from sandstones of the overlying Capas Rojas 5. Interpretation del Valle del Guataquia Fm. of the Floresta Massif, which yields a youn- gest detrital zircon spot date of 347.1 ± 27.4 Ma, suggesting it extends 5.1. Depositional Ages of the Sedimentary Rocks into the Carboniferous. Brachiopod assemblages were used to assign the El Imam Fm. of the Cordillera Central to the Pennsylvanian Given the consistent overlap between the youngest single concor- (Angiolini et al., 2003; Fig. 10). The Floresta Fm. of the Santander Massif dant spot age, weighted mean age of the youngest three spots (Y3; was initially considered to be Middle Devonian (Ward et al., 1974; with very large uncertainties) and the youngest detrital zircon (YDZ) Boinet et al., 1986), although Moreno-Sanchez et al. (2007) suggest it age of Ludwig (2012), we assign the youngest single date as the maxi- may be Carboniferous based on lithofacies correlations. Ward et al. mum stratigraphic age of the sedimentary units (e.g. Dickinson and (1974) and Patarroyo and Senff (2001) assign a Late Carboniferous – Gehrels, 2009; Fig. 3). Our approach does not discount the possibility Permian depositional age to fossils found within sandstones and that the youngest single spot dates have been affected by lead loss, carbonates of the Diamante Fm. of the Santander Massif. Further east, and thus we also consider the YC2 + (1σ) dates given that they are shallow marine sedimentary rocks of the Llanos Orientales Basin yield more conservative estimates. Early Carboniferous fossil assemblages (Duenas and Cesari, 2006). With the exception of a single quartz arenite (99RS38) that was Slates and shales of the Muchuchachi Fm. of the Merida Andes host sampled close to the town of Loja, all of the sampled sedimentary upper Carboniferous fossil assemblages (Odreman and Useche, 1997), rocks of the Chiguinda Fm. yield youngest dates spanning between and is unconformably overlain by the Sabanetta Fm. (Fig. 10), which is 318 and 358 Ma, and thus are considered to be Carboniferous (using temporally constrained by conformably overlying Permian limestones the timescale of Walker et al., 2013; Fig. 10). These dates are consistent of the Palmarito Fm. (Laya and Tucker, 2012). The Devonian – Carbonif- with fossilised microspores, which constrain deposition to the post- erous tectonic setting of the Floresta Massif is generally undetermined, Silurian (Owens, 1992). Similarly, paraschist of the La Victoria Unit of while Laya and Tucker (2012) suggest the Palmarito Fm. (Merida the Amotape Complex yielded a Carboniferous youngest detrital zircon Andes) was deposited in a foreland basin setting. age of 328 ± 11 Ma, which is significantly younger than the previous Carboniferous sedimentary rocks within Peru include lower sections zircon U/Pb estimate of deposition of 357 ± 15 Ma (Suhr et al., 2019). of the siliciclastic Yamayo Group, which is exposed along coastal Are- More conservative (YC2 + (1σ) dates) estimates of the maximum age quipa and was deposited within alluvial fans (detrital zircon U–Pb of deposition of the Chiguinda Fm. range between 511 and 394 Ma concordia ages 337–320 Ma; Boekhout et al., 2013). These rocks host (Fig. 3). However, 6 out of 7 of these dates are older than 451 ± 7 Ma, the same brachiopod genus as those of the El Imam Fm. of the Cordillera which is inconsistent with the presence of fossilised Silurian micro- Central of Colombia (Angiolini et al., 2003), although these have not spores, assuming that they were accurately identified (Owens, 1992). been documented in the Chiguinda and La Victoria Fms. in Ecuador. Therefore, we consider the Carboniferous dates to be the best estimates U–Pb concordia dates of detrital zircons extracted from siliclastic rocks of the maximum timing of deposition of the Chiguinda Fm., and of the Ambo, Tarma-Copacabana and Oqoruro groups of the Eastern

91 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

Peru Ecuador Colombia Venezuela Time Eastern Cordillera Cordillera Central, Eastern Cordillera, Santander Massif, Merida Andes Amotape Cordillera Foreland Centre- North Sierra Nevada de Quetame, Floresta, Guajira Peninsula (Ma) Complex Real South Santa Marta Garzon 225 Mitu * Moromoro* Tres Lagunas* Cajamarca Complex * Mucubaji Unit* Las Palmas Paragneiss Unit Unit Sabanilla La Secreta Mylonites 250 Huancayo,* m m m m Bocas Fm. * Parihuanca Rovira Complex * m m El Encanto Orthogneiss Malacatos 275 granites Oqoruro- * Gaira Amphibolite Tiburon Fm. Palmarito Fm. Ene Complex m ? m ? Permian Tarma- * * Macuma Huachón Copacabana 300 * Unit Diamante Fm. Sabanea Fm. granite * * m m Tingo Machu P’ * Progresso * El Imam Fm. 325 Pataz Guaquia Fm. Mucuchachi Fm. Ambo/Yamayo granites * La Victoria & Chiguinda Unit La Bocana Isimanchi Unit 350 units Las Palmas Protolith * 375 * Tibet, Cuche and Palenque Floresta Fms. Pumbuiza Unit Floresta Fm. 400 Cabanillas Unit DevonianGp. Carboniferous * 425 Sitabamba E.g. La Soledad, Sil. Othogneiss Timotes * * Bucaramanga Gneiss* East Cusco * granites 450 Granite Berlin Orthogneiss La Miel Orthogneiss m m m m m m m m 475 m m Rio Humea Granite E.g. Cerro Azul, * * Ordovician Otenga Granite La Raya Marañon granites 500 Complex * Leucosomes El Tigre Unit Silgara Fm. ** 525 Sierra Nevada Cambrian Suite 550 40Ar/39Ar

Pungal 575 Gabbro Unit

600 Proterozoic

Sierra Nevada Protolith 1000 * Pariah’ * * Las Margaritas * M-J Granite* Los Mangos Paragneiss 1100 Paragneiss * Querobamba- * 1200 Sucre Guapotón * Granite Fossil assemblage Orthogneiss Zircon U/Pb (primary Jojoncito Paragneiss 1300 * or detrital) Dibulla Gneiss protolith protolith m m Regional * 1400 Metamorphism M-J: Mariposa-Junin

Fig. 10. Stratigraphy of igneous and sedimentary units of the Cordillera Real and Amotape Complex of Ecuador, along with various structural elements within Peru, Colombia and Venezuela. Regional metamorphic events are also shown. Data sources are, Ecuador: British Geological Survey (1989), Chew et al. (2008), Kennerley (1973), Litherland et al. (1994), Owens (1992), Spikings et al. (2015), Suhr et al. (2019), Tschopp (1953),Peru:Boekhout et al. (2013, 2018), Chew et al. (2007, 2008), Miskovic et al. (2009), Colombia: Angiolini et al. (2003), Boinet et al. (1986), Cardona et al. (2016), Cordani et al. (2005), Horton et al. (2010), Janvier and Villarroel (2000), Mantilla-Figueroa et al. (2012), Patarroyo and Senff (2001), Piraquive (2017), Spikings et al. (2015, 2016), Villagomez et al. (2011), Vinasco et al. (2006), Ward et al. (1974),Venezuela:Aleman and Ramos (2000), Laya and Tucker (2012),Odremán and Useche (1997), Van der Lelij et al. (2016).

Cordillera of Peru and coastal Arequipa suggest they were deposited proportion of detrital zircons with dates spanning 420–700 Ma, during 335–270 Ma (Boekhout et al., 2018) within a back-basin setting. showing that Carboniferous basins in far northwestern South A comparison of the Kernel Density Estimates of 206Pb/238Uagesof America were clearly starved of Late Neoproterozoic – Early detrital zircons in Carboniferous sedimentary rocks in Colombia Palaeozoic zircons relative to regions further south, perhaps (Guatiquia Fm.), Ecuador (Chiguinda and La Victoria Fms.) and Peru supporting an interpretation that zircons with dates spanning (Ambo Fm.) yields distinct differences (Fig. 11b, c), highlighting differ- 530–680 Ma may be far travelled and derived from arcs associated ences in their bulk source regions. The proportion of Ordovician and with the closure of Pampia (E.g. Ramos, 1988; see section 5.3). Car- Carboniferous zircons is significantly higher in the Ambo Fm. (Eastern boniferous basins in Colombia received a far greater proportion of Cordillera of Peru), which is consistent with current abundant exposure Sunsas-aged zircons than regions within Ecuador and Peru, suggest- of Ordovician and Carboniferous arc plutons along the Eastern Cordil- ing that Precambrian highlands were probably a prominent feature lera, combined with their paucity in Ecuador and Colombia. The of the Palaeogeography of Carboniferous Colombia. Guatiquia Fm. of Colombia (Eastern Cordillera) hosts the lowest

92 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

A Pampean Orogeny Famatinian Arc Continental Pan-African Orogeny Sunsas Amazonian Craton Arc (Guayana Shield)

13AP53 13AP54

99RS55 13AP33 La Victoria 11RC27 99RS53 99RS39 Chiguinda and La Victoria 11RC20

99RS38 ?

0 500 1000 1500 2000 2500 3000 3500

All samples 60 Chiguinda, La Victoria N units 40 n=764

20

0 0 500 1000 1500 2000 2500 3000 3500 206Pb/238U age (Ma) B C

60 60 Carboniferous sedimentary units Guatiquia Fm., Colombia, N=78 Ambo Group, Peru, N=131 Chiguinda and La Victoria Fms., Ecuador, N=633 40 40 N

20 20

0 0 0 500 1000 1500 2000 2500 500 1000 206Pb/238U age (Ma) 206Pb/238U age (Ma)

Fig. 11. A, B) A summary of the detrital zircon age populations (defined by Kernel Density distributions) for the Chiguinda and La Victoria units (not including previous work). Grey rect- angles highlight the main age populations of the samples, collectively, while red bars indicate the main populations of individual rocks. The rocks are arranged in order according to the maximum stratigraphic age of the rock as determined by the zircon U\\Pb ages (shown by the dashed line). Blue, green and purple squares indicate concordia intercepts of best-fit chords, where each colour indicates a different lower intercept, while squares of the same colour share the same lower intercept, with various upper intercepts. C) Kernel Density Estimates (KDE) of detrital zircon ages determined with an adaptive KDE (Vermeesch, 2012) for Carboniferous sedimentary rocks in Colombia, Ecuador and Peru, showing the true frequencies (Guatiquia Fm., 1 rock, Horten et al., 2010; Chiguinda and La Victoria Fms., 9 rocks, this study; Ambo Group, 2 rocks, Boekhout et al., 2018). D) The same plot as C, where the KDE's of the Ambo Group and the Guatiquia Fm. are normalised to the same quantity of spot analyses of the Chiguinda and La Victoria Fms. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

93 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

5.3. Origin of prominent peaks in detrital zircon spot ages 5.3.3. 700–800 Ma A relatively minor quantity of detrital zircons yield concordia dates Kernel density distributions of zircon dates obtained from the that span between 700 and 800 Ma (Fig. 11), although an origin within Chiguinda and La Victoria units reveal prominent peaks at northwest Gondwana is enigmatic because no contemporaneous mag- 310–380 Ma, 440–680 Ma and 840–1100 Ma, with minor peaks at matic events are recorded within Venezuela, Colombia or Ecuador. 1700–1860 Ma, 2010–2100 Ma, 2500–2580 Ma and 2660–2720 Ma A-type plutons with U–Pb zircon concordia ages of 752–691 Ma are re- (Fig. 11). These sedimentary rocks also contain a small percentage of corded in the Eastern Cordillera of Peru (Miskovic et al., 2009), and zircons with dates that span between 700 and 800 Ma, although they these may have shed detritus into Palaeozoic basins of western Gond- are more abundant in quartz arenites 99RS38 and 99RS53 of the Car- wana. Baldo et al. (2006) report A-type orthogneisses in the Laurentian boniferous Chiguinda unit (Figs. 4, 6). Precordillera Terrane in northwestern Argentina, which yield a zircon U–Pb concordia age of 774 ± 6 Ma. A-type granites and bimodal volca- 5.3.1. >1700 Ma nic rocks in the Appalachian mountains yield crystallisation ages of A minor proportion of detrital zircons within the Carboniferous ba- 765–680 Ma (Tollo et al., 2004). Baldo et al. (2006) and Miskovic et al. sins within Ecuador were derived from old primary sources with ages (2009) suggest these rocks formed during an early and perhaps failed of 1700–1860 Ma, 2010–2100 Ma, 2500–2580 Ma and 2660–2720 Ma rifting phase along eastern Laurentia within Rodinia. Finally, the Brasília (Fig. 11). These age groups overlap with the timing of formation of mo- belt hosts syn-collisional granitoids with dates spanning between 0.8 bile belts that now form the Amazonian craton, including the Rio Negro- and 0.7 Ma (Pimentel et al., 1999), although these are distal to western Jurena Belt and Ventuari-Tapajós belts (1.55–1.98 Ga), the Maroni- Gondwana, and a paucity of detritus from the intervening Amazonian Itacaiunas belt (2.25–2.05 Ga) and the Central Amazon belt (>2.6 Ga; craton renders this as an unlikely dominant source region (e.g. Chew See Chew et al., 2011 for a review of these dates). Detrital zircons with et al., 2007). similar ages also occur within craton-derived sedimentary rocks in the Oriente Basin (e.g. Hollin and Napo Fms.; Martin-Gombojav and 5.3.4. Ordovician – Ediacaran 440–680 Ma Winkler, 2008; Gutierrez et al., 2019) of Ecuador. The Amazonian Craton The most prominent Kernel density peak in all of the analysed sedi- is the most likely candidate for the original source of Mesoproterozoic mentary rocks of the Chiguinda and La Victoria units spans 440–680 Ma detritus within the Carboniferous basins in Ecuador. Similarly, Horton (Fig. 11), with the highest frequencies at ~540–600 Ma. Zircons with et al. (2010) proposed the same source regions for Palaeozoic 206Pb–238U dates of 440–680 Ma are frequently found in Ecuador, in- depocenters that are now exposed in the Eastern Cordillera of Colombia. cluding within Triassic S-type anatectites (Spikings et al., 2015)and the Isimanchi Unit (Chew et al., 2008) of the Cordillera Real, the Palen- 5.3.2. 840–1100 Ma que Mélange Division, El Tigre, Limón Playa and La Bocana units of the U–Pb zircon concordia dates clearly define a Kernel density peak Amotape Complex (Suhr et al., 2019), and the dominantly craton de- spanning between 840 and 1100 Ma in the Carboniferous Chiguinda rived Early Cretaceous Hollin Fm. of the Oriente Basin (Martin- and La Victoria units (Fig. 11). Within Ecuador, this age population is Gombojav and Winkler, 2008; Gutierrez et al., 2019). also prominent within Cambrian and Devonian – Carboniferous sedi- The Pampean Orogeny and the Famatinian arc (~530–415 Ma; e.g. mentary units of the Amotape Complex (Suhr et al., 2019), craton- see zircon U–Pb ages in Pankhurst et al., 2000; Chew et al., 2007; derived sedimentary rocks at the base of the Cretaceous Oriente Basin Bahlburg et al., 2009; Mišković et al., 2009; Villagómez et al., 2011; (Martin-Gombojav and Winkler, 2008; Gutierrez et al., 2019), and Trias- Van der Lelij et al., 2016) formed during subduction of Pacificlitho- sic rift granitoids and Jurassic intra-arc basins of the Cordillera Real sphere beneath South America subsequent to the opening of the Iapetus (Spikings et al., 2015). The same-aged zircons are ubiquitous within Ocean, and arc magmatic rocks are recorded in Venezuela, Colombia, Cretaceous-Devonian sedimentary rocks (Horton et al., 2010; Cardona Peru and Argentina, although they are not exposed in Ecuador et al., 2016) and Ordovician orthogneisses (Villagomez et al., 2011) of (Fig. 10). Ordovician magmatism has also been recognised in the the Eastern and Central cordilleras of Colombia, respectively, and Chiapas Massif and Maya Mountains (Maya Block; 482–405 Ma; occur as xenocrysts in Cenozoic intrusions in the Sierra Nevada de Steiner and Walker, 1996; Weber et al., 2008; Estrada-Carmona et al., Santa Marta (Piraquive, 2017). Elsewhere within western Gondwana, 2012), the Rabinal Complex and Altos Cuchumatanes (Guatemala; this age peak is also common within Ordovician igneous and sedimen- ~462–453 Ma; Ortega-Obregón et al., 2008; Solari et al., 2010) and the tary units of the Eastern Cordillera of Peru (Chew et al., 2007, 2008; Acatlán Complex (478–442 Ma; Keppie et al., 2008). A paucity of high Cardona et al., 2009; George et al., 2019). This Proterozoic peak is quality geochemical data from these regions within North America has most likely derived from a dissected belt of Sunsas-aged rocks that are led to contrasting tectonic interpretations. For example, Estrada- exposed in basement inliers along the Amazonian margin (Chew et al., Carmona et al. (2012) and Keppie et al. (2012) suggest that Early Ordo- 2008). Basement inliers within northern Colombia (Fig. 10)are vician magmatism formed during rifting in a transtensional regime, interpreted to be late Mesoproterozoic arcs that were metamorphosed followed by arc magmatism in the Late Ordovician. Alternatively, during collision events at ~1 Ga (e.g. Restrepo-Pace et al., 1997; Solari et al. (2013) and Van der Lelij et al. (2016))suggesttheOrdovi- Cordani et al., 2005). These include the Guapotón Gneiss (Garzón Mas- cian rocks formed within a continental arc setting. Regardless, Ordovi- sif, 1158 ± 22 Ma with overgrowths at 1000 ± 25 Ma; Cordani et al., cian magmatic units have not been recorded in Ecuador, and within 2005), Las Margaritas paragneiss (Garzón Massif, 1015 ± 8 Ma; Colombia they are only found within the northern Cordillera Central Cordani et al., 2005), and the Dibulla Gneiss (~1140 and ~ 1000 Ma (440–470 Ma, La Miel orthogneiss; Villagómez et al., 2011; Martens metamorphic ages; Cordani et al., 2005), Muchachitos Gneiss et al., 2014), and the Quetame, Floresta and Santander Massifs (~1000 Ma metamorphic age; Piraquive, 2017 Ma) and Buritaca Gneiss (Horton et al., 2010; Mantilla-Figueroa et al., 2012; Van der Lelij et al., (~900 Ma; Piraquive, 2017 Ma) of the Sierra Nevada de Santa Marta. 2016). Similarly, Ordovician arc plutons are extensively exposed Miskovic et al. (2009) report U–Pb crystallisation ages ranging between throughout the Merida Andes of Venezuela (Van der Lelij et al., 2016; 1123 and 985 Ma from granitoids within the Eastern Cordillera of Peru Fig. 10). Thus, it is likely that zircons with crystallisation ages younger (Fig. 10), which are considered to be an extension of the collisional than ~515 Ma within Carboniferous sedimentary rocks in Ecuador Sunsás province in eastern Bolivia. Gneisses within the Arequipa- were derived from Famatinian-aged units that surrounded Ecuadorian Antofalla basement yield metamorphic zircon U–Pb ages of 1.2–1.0 Ma crust to the south, north, and west. (Martignole and Martelat, 2003), and granulites within the western Si- Detrital zircons with dates of 530–680 Ma are also frequently found erras Pampeanas give U–Pb zircon ages of ~1.2 Ma (e.g. Casquet et al., in autochthonous sedimentary rocks from the northern and central 2006). western Amazonian margin in Peru (Chew et al., 2008; George et al.,

94 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

2019), although their magmatic source regions are cryptic given that America during the Carboniferous – Permian, accounting for the lack few magmatic source regions with late Neoproterozoic crystallisation of Carboniferous, and the paucity of Permian arc rocks with present- ages are found along western Gondwana. Alternatively, mobile belts day Colombia and Ecuador (e.g. see Spikings et al., 2016). Therefore, that formed during the protracted Brasiliano/Pan African orogeny, we suggest that the Chiguinda and La Victoria units formed in the Car- which are mainly exposed in eastern South America may represent via- boniferous back-arc. Prior to ~330 Ma, Carboniferous zircons may have ble sources. We interpret new 40Ar/39Ar dates from the rift-related drained northwards from arc magmatism that is currently preserved Huarguallá Gabbro unit exposed along the Peltetec Fault Zone in in Peru, whereas after ~330 Ma Carboniferous zircons may have also Ecuador to yield crystallisation ages of ~585 Ma, although these are been sourced from regions that now form southwestern North dominantly mafic rocks, and it is unlikely they represent a source of America, and were located to the west. The contemporaneity of proxi- abundant zircons. Similarly, Omarini et al. (1999) report undated mal arc magmatism and the age of the youngest single detrital zircons mafic rocks intercalated within the Puncoviscana fold belt in northwest- support the conclusion that these youngest dates are reasonable esti- ern Argentina that is stratigraphically constrained to ~600–540 Ma, al- mates of the time of deposition of the Chiguinda and La Victoria though these mafic units are also unlikely to be an abundant source of units. The Tarma-Copacabana and Ambo groups of the southern Eastern zircons. Ramos (1988) propose that a late Neoproterozoic magmatic Cordillera and Arequipa regions of Peru are also considered to have arc may exist within the eastern Sierras Pampeanas, while Escayola formed in a Carboniferous back-arc (Fig. 10; Boekhout et al., 2013), al- et al. (2007) record ophiolitic remnants of a Neoproterozoic back-arc though it is likely that this southern region of the Peruvian arc was re- basin in the same region. Chew et al. (2008) postulated the existence moved by subduction erosion (Boekhout et al., 2018), as opposed to of a buried late Neoproterozoic magmatic arc, which may be contiguous rifting. with the Brasiliano-aged Tucavaca Belt in Bolivia (Litherland et al., 1994), to account for a significant detrital age peak at 550–650 Ma in 5.4. Concordia Intercepts Palaeozoic and Mesozoic sedimentary rocks of the Eastern Cordillera of Peru. However, the same authors base this interpretation on the exis- Approximately 15–30% of the spot U–Pb dates obtained from all of tence and continuation of late Neoproterozoic granitoids in Venezuela, the analysed samples are more than 5% discordant with respect to which have since been shown to be Ordovician (Van der Lelij et al., 206Pb/238Uand207Pb/235U dates. The discordant dates yield complex ar- 2016). Assuming that the Huarguallá Gabbro unit represents rift- rays in Wetherill Concordia space (Figs. 4 and 6), and statistical analysis related magmatism at ~585 Ma, then arc magmatism at >600 Ma (Reimink et al., 2016) has been used to seek best-fitchordstoinvesti- along the boundaries of the Iapetus Ocean is unlikely to exist in the pres- gate the possibility that lower and upper intercept dates (Figs. 5 ent subsurface of the foreland in Ecuador. This is consistent with evi- and 7) can facilitate an interpretation of the pre-Triassic geological his- dence for rifting along the Laurentian margin during 620–550 Ma (e.g. tory of Ecuador. Fig. 11 presents a comparison of the best-fit upper and Cawood et al., 2001), which is generally regarded to have separated lower intercept dates with maximum stratigraphic ages and detrital zir- Laurentia and west Gondwana (e.g. Li et al., 2007). Rather, we propose con age (Kernel density) groups. The algorithm of Reimink et al. (2016) that a significant quantity of zircons older than ~530 Ma within autoch- generates a discrete set of chords with pre-defined upper and lower thonous sedimentary rocks of Ecuador may be either far travelled from Wetherill concordia intercepts, which are evenly spaced in time. The arcs associated with the closure of Pampia, or are derived from contem- likelihood of each chord is assessed by generating a summed probability poraneous orogenic belts that are now exposed within eastern South density contributed by zircon U–Pb analyses. America. A majority of samples yield upper and lower intercept dates for best- fit chords that are older than the youngest detrital zircon age constraints 5.3.5. Carboniferous – Devonian (310–380 Ma) on the maximum depositional ages of the rocks (Fig. 11). These results No igneous units have been recorded in Ecuador or Colombia with reflect distinct periods when the U–Pb isotopic system of primary mag- crystallisation ages that span 310–380 Ma (Fig. 10), and thus they matic zircons was disturbed to varying degrees. The discordant data in were either never present or formed and are either buried or not pre- some sedimentary units can be fit with a single common lower intercept served. Alternatively, the Carboniferous – Permian Arc of the Eastern (11RC27), whereas others require two (13AP33, 99RS55) or more Cordillera of Peru (360–285 Ma, Mišković et al., 2009; Fig. 10)may (99RS38) lower intercepts. A set of chords span between a lower inter- have shed Carboniferous zircons into the Chiguinda and La Victoria cept ranging between 435 and 555 Ma and an upper intercept that Fms. For example, the Balsas-Callangate and Pataz plutons (~7–8°S) of spans between 1010 and 1210 Ma, in all rock samples. These chords re- the Eastern Cordillera (Peru) are currently located ~350 km to the flect an isotopic disturbance of zircons that were derived from Sunsas- southeast of the Chiguinda Unit in Ecuador. Carboniferous zircons may aged belts (see above) during Ordovician – Cambrian orogenesis and have also been derived from continental crust that rifted from north- Famatinian arc magmatism. Other chords with lower intercepts at western South America during the Triassic (Spikings et al., 2016; 435–515 Ma have upper intercepts at ~1900, ~2090, ~2130, ~2740 Spikings and Paul, 2019). Carboniferous magmatism is currently discon- and ~ 2800 Ma, reflecting a Palaeoproterozoic and Archaean origin, tinuously exposed between California and Guatemala (e.g. Dickinson and subsequent partially to fully isotopic resetting during Ordovician – and Lawton, 2001), within the present North American Plate. Carbonif- Cambrian orogenesis and Famatinian arc magmatism. With the excep- erous units include a tholeiitic to calc-alkaline arc in the Acatlán Com- tion of quartz arenite 99RS38 the lack of potential chord intercepts be- plex (Mixteca Terrane; Kirsch et al., 2012; zircon U–Pb 306–289 Ma), tween 600 and 800 Ma suggests a general absence of disturbance of continental arc plutons that intrude the microcontinent of Oaxaquia Proterozoic and Archaean zircon populations during 600–800 Ma. This (e.g. see references in Ortega-Obregón et al., 2014,U–Pb zircon observation supports the premise that arc magmatism may have been 310–287 Ma), granitic intrusions of the Altos Cuchumatanes (Maya absent north of the present day Huancabamba Deflection during Block) in Guatemala (Solari et al., 2009;zirconU–Pb 313–318 Ma), ~600–800 Ma, and thus zircons with concordia dates spanning between the Aserradero Rhyolite of the Sierra Madre terrane (Stewart et al., ~800–600 Ma are far travelled. Metasandstone 13AP54 (Chiguinda 1999;zirconU–Pb 334 ± 39 Ma), and the La Pezuña Rhyolite of the Coa- Unit) yields two chords with a common lower intercept at ~325 Ma, huila Terrane (López, 1997;zirconU–Pb 331 ± 4 Ma). Kirsch et al. and upper intercepts of ~945 Ma and 1050 Ma. The lower intercept (2012) and Ortega-Obregón et al. (2014) utilised a limited geochemical overlaps with the youngest single concordia age of 318 ± 8 Ma, suggest- dataset to suggest these rocks formed within a continental arc setting ing the Carboniferous arc reset the isotopic composition of Sunsas-aged that commenced as early as ~330 Ma. Several reconstructions (e.g. zircons to various degrees, during their incorporation into Carbonifer- Elías-Herrera and Ortega-Gutiérrez, 2002) place the Acatlán and Oaxa- ous magmas, highlighting the Sunsas-age of the basement rocks that can complexes, and the Maya Block outboard of northwestern South host the arc (Eastern Cordillera of Peru, Mišković et al., 2009;Oaxaquia;

95 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

Keppie et al., 2003). Finally, rocks 99RS55 (Chiguinda Unit), 99RS38 Iapetus Ocean. A-type plutons in the Eastern Cordillera of Peru (Chiguinda Unit) and 13AP33 (La Victoria Unit) yield lower intercept (Miskovic et al., 2009), Precordillera Terrane (Baldo et al., 2006) and ages of ~270 Ma, ~195 Ma and ~ 110 Ma, respectively, reflecting the Appalachian mountains (Tollo et al., 2004) that formed during post-depositional disturbance to the U–Pb system (Fig. 11). These 774–691 Ma may reveal an early albeit failed rifting phase along eastern time periods coincide with spatially sporadic Permian, Jurassic and Laurentia within Rodinia. Coeval rocks are not exposed north of Peru, Early Cretaceous continental arc magmatism in the Northern Andes, in- although they were minor source regions for sediments that were cluding compressional events at 120–110 Ma (Spikings et al., 2016, ultimately deposited within Carboniferous basins in northwestern Spikings and Paul, 2019). Gondwana. Intrusion of the Huarguallá Gabbro unit temporally overlaps with mafic intrusions, carbonatites and kimberlites that collectively form – 5.5. Tectonic Synthesis (Late Neoproterozoic Carboniferous) the Central Iapetus Magmatic Province (CIMP; Ernst and Bell, 2010; Tegner et al., 2019; Fig. 12). According to Tegner et al. (2019),the Several studies have correlated magmatic and metamorphic events CIMP includes the Grenville and Adirondack dyke swarms in Laurentia along western Gondwana from prior to the Iapetus Wilson Cycle to with ages of ~590 Ma (Kamo et al., 1995), which yield compositions fi the evolution of western South America within the Paci crealm.How- consistent with a flood-basalt origin, and a younger group at ~565 Ma ever, a lack of data from Palaeozoic sequences in Ecuador forced geo- (Hodych and Cox, 2007; Chew and Van Staal, 2014)thatyieldsan graphic interpolations, which we can now improve. ocean island basalt affinity. Within Europe, the CIMP is represented by Gabbros of the newly named Huarguallá Gabbro unit, which is ex- older dyke swarms in Egersund, Norway (616 ± 3 Ma; Bingen et al., posed along slivers within the anastomosing Peltetec Fault Zone 1998), Dalradian, Scotland (601 ± 4 Ma; Fettes et al., 2011) and the – crystallised during 565.5 ± 34.3 581.8 ± 41.1 Ma, yield E-MORB type Scandinavian Dyke Complex (610–590 Ma; Tegner et al., 2019). Youn- signatures with evidence for crustal contamination and formed in a ger ultramaficandmafic plutons are exposed in the Seiland Igneous rift environment. These rocks are coeval with syn-rift alkaline lava Complex, Norway (580–560 Ma; Roberts et al., 2006), which are consid- fl ows that are intercalated within the intra-continental, Puncoviscana ered to have Ocean Island Basalt affinities. Our new dates are consistent Fold Belt in northwestern Argentina, which formed during rift-drift tec- with the continental reconstruction of Tegner et al. (2019) at 615 Ma, ≥ – tonics during 600 535 Ma (Omarini et al., 1999). Consequently, the which juxtaposes the basement of the northern Andes with mafic simplest explanation for the Huarguallá Gabbro unit is it also formed dyke complexes in Baltica (as part of Panotia; Fig. 12). The 40Ar/39Ar during attenuation of Gondwanan crust, that ultimately lead to the for- dates of gabbro 04PR98 (565.5 ± 34.4 Ma) and peridotite 04PR116 mation of Iapetus oceanic lithosphere by ~550 Ma. In this sense, the (585.5 ± 14.1 Ma) of the Huarguallá Gabbro unit post-date the Huarguallá Gabbro unit is the only documented direct record of Iapetan crystallisation age (616 ± 3 Ma; U–Pb Baddeleyite; Bingen et al., rift-related igneous rocks north of Argentina, and thus provides a crucial 1998) of basaltic, tholeiitic dykes at Egersund by 30–50 Ma, although temporal record of the rifting phase that heralded the opening of the

615 Ma Kimberlites Central Iapetus 613-535 Ma Magmatic Province Dykes, lavas Laurentia 616-550 Ma

Future Iapetus GD 531-586 Ma

Puncoviscana LR 615 Ma 30°S 600 - 540 Ma SD 615-590 Ma Amazonia

623 - 531 Ma ED 616 Ma Huarguallá Gabbro

Baltica

Fig. 12. Tectonic setting of Laurentia, Baltica and Amazonia at the end of the Neoproterozoic, according to Tegner et al. (2019), showing the Central Iapetus Magmatic Province, and associated mafic and kimberlite assemblages (white dashed line; modified from Tegner et al., 2019). ED: Egersund Dyke Complex (Bingen et al., 1998), GD: Grenville Dyke Complex, LR: Long Range Dyke Complex, SD; Scandinavian Dyke Complex (Tegner et al., 2019).

96 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

AB535 Ma Early Cambrian 500 Ma Late Cambrian El Tigre Fm. deposited along Iapetus passive margin El Tigre Fm. deposited along Iapetus passive margin

IAPETUS

ET ET

IAPETUS

IAPETUS 30°S 30°S

CDE450 Ma Middle Ordovician 415 Ma Late Silurian 370 Ma Late Devonian Arco Iris Unit, deposited in Famatinian back-arc? Establishment of a passive margin

RHEIC

30°S 30°S RHEIC

Merida Santander Cuche Quetame Palenque La Miel Pumbuiza Cuche Palenque 30°S Pumbuiza Cabanillas

FG340 Ma Early Carboniferous 280 Ma Early Permian Sedimentation within a Carboniferous back-arc? Active margin record (now segmented) in N. Andes

30°S

PALAEOTETHYS

Rovira Malacatos 30°S Guaquia Chiguinda La Victoria Isimanchi Ambo

Fig. 13. Plate reconstructions for the Palaeozoic margin of northwestern Gondwana, modified and simplified from Cocks and Torsvik (2006) and Van der Lelij et al. (2016).ET: El Tigre unit.

97 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101 this is consistent with i) Phanerozoic rift-to-drift transitions, which typ- deposited within Carboniferous basins in northwestern Gondwana, ically span ~40 Ma, and ii) the conclusions of Tegner et al. (2019),who which have been subsequently tectonically dissected, forming the compiled geochemical and geochronological data from the CIMP to sug- siliclastic Chiguinda and Isimanchi (Cordillera Real), and La Victoria gest that it records a rift-to-drift transition during ~616–590 Ma. Fur- (Amotape Massif) Fms. within Ecuador, and the El Imam and Guatiquia thermore, despite the paucity in geochemical data, a comparison of Fms. in Colombia (Fig. 10). the elemental and Nd isotopic compositions of the Scandinavian Carboniferous to Permian sedimentary successions in the Merida and Egersund Dyke complexes with the Huarguallá Gabbro unit sug- Andes (Fig. 10) have been interpreted to form part of a foreland basin gests these ultramaficandmafic rocks formed with a mantle plume (Laya and Tucker, 2012) that formed during the closure of the Rheic setting at ~616 Ma, which progressed towards early continental rifting Ocean and the development of the Alleghenian Orogen (Fig. 13g). How- within ~50 Ma. ever, the tectonic setting of Carboniferous units in Ecuador and Famatinian arc magmatism (Figs. 13a – d) commenced along Colombia has not been well constrained, while Permian sedimentary western Gondwana at ~530 Ma. We consider the lack of Cambrian and rocks have not been identified within the cordilleras. Vinasco et al. Ordovician magmatism in Ecuador to be a consequence of its inboard, (2006) and Piraquive (2017) suggested that a regional metamorphic back-arc position (Fig. 13c) due to the presence of basement rocks event affected Permian intrusions in the Cordillera Central and Sierra that now form part of southwestern North America (e.g. Spikings Nevada de Santa Marta, respectively, at ~278 Ma. However, there is no et al., 2016). A detailed reconstruction is beyond the scope of this clear evidence that zircon growth at ~278 Ma had a metamorphic origin work, although Ordovician magmatism is recorded in the Maya Block (e.g. Th/U ratios are close to 1; Piraquive et al., 2017). On the contrary, (e.g. Solari et al., 2010) and the Acatlán Complex (Keppie et al., 2008), garnets within the La Secreta Mylonites of the Inner Santa Marta Meta- which rifted from Gondwana during 245–216 Ma (Spikings et al., morphic Belt (northern Colombia) reveal clear evidence for regional 2016). Abundant Ordovician magmatism within the Merida Andes scale metamorphism at ~250 Ma, while contemporary zircons with and Santander Massif, along with minor exposures in the Central Cordil- Th/U ratios of ~0.1 supports a metamorphic origin (Piraquive, 2017), lera, Quetame and Floresta Massifs of Colombia suggests that these which coincides with high-temperature metamorphism in the Maya rocks originated within an arc zone located north of the outboard ter- (Weber et al., 2007)andChortis(Ratschbacher et al., 2009) blocks. Col- ranes (Fig. 13c), which was distal to the Triassic rift. This interpretation lisional events at ~250 Ma (Spikings et al., 2016) may be responsible for is consistent with the lack of Triassic rift-related rocks in these units. The Permian sedimentary gaps in the Cordilleras Real (Ecuador) and Central oldest Ordovician magmatism recorded in the outboard blocks occurred (Colombia), as a distal response to continent-continent collision. Perm- at ~480 Ma, suggesting these blocks may have faced a Cambrian passive ian arc magmatism occurred during 298–253 Ma within northwestern margin (e.g. Fig. 13b), and subduction was delayed relative to regions to Gondwana (including the contemporary conjugate margin that cur- the west (e.g. Eastern Cordillera of Peru), and south (e.g. Merida Andes rently forms part of the North America Plate), although the abundance of Venezuela). Thus, the weakly metamorphosed quartzites, wackes and of Permian intrusions decreases from northern Colombia to Ecuador. lutites of the Cambrian El Tigre Fm. (maximum depositional age 512 ± Only one Permian magmatic rock has been identified within Ecuador 21 Ma; Suhr et al., 2019) may have been deposited in a passive margin, (Rovira Complex; Spikings et al., 2016; Fig. 10), and thus it is likely which received detritus from distal arcs. that present-day Ecuadorian continental crust mainly existed in the Sandstones of the Devonian(?) Pumbuiza Unit that forms part of the Permian back-arc. basement of the Oriente Basin, and the Palenque Unit (maximum depo- sitional age of 391 ± 17 Ma; Suhr et al., 2019), which is exposed in the 6. Conclusions northern Amotape Massif may be coeval with deposition of the Cabanillas Gp. in Peru, and the Floresta, Cuche and Tibet Fms. in 1. The Huarguallá Gabbro unit is defined as a series of olivine bearing Colombia, while no Devonian units have been identified in the Merida gabbros and ultramafic rocks exposed in fault bounded slivers of Andes (Fig. 10). This period coincides with a Devonian magmatic gap the anastomosing Peltetec Fault Zone along the western flank of and a passive margin environment along western Gondwana the Cordillera Real. Argon isotope data from plagioclase yields (Fig. 13e), which is reflected in a paucity of Devonian-aged detrital zir- 40Ar/39Ar dates that span between 565.5 ± 34.4 Ma and 581.8 ± cons in Carboniferous basins in Ecuador (this study), Peru (Chew et al., 41.1 Ma, which are interpreted as crystallisation ages and reveal 2007; George et al., 2019) and farther south (e.g. Bahlburg et al., 2009). the presence of late Neoproterozoic mafic rocks, regardless of the However, Horton et al. (2010) found a peak in Devonian-aged detrital poor precision. Geochemical compositions are consistent with an as- zircons in Devonian sedimentary rocks in Colombia, with high Th/U ra- thenospheric magma source that was contaminated with ~25% of tios that allude to an igneous provenance, leading them to conclude that continental crust in a rift setting. The Huarguallá Gabbro forms part a Devonian arc may have shed detritus into northwestern Gondwana. of the geographically dispersed Central Iapetus Magmatic Province, With the exception of a rhyolite within the volcanic Bladen Fm. and its location in Ecuador is consistent with the continental recon- (406 + 7/−6 Ma; Martens, 2010), and granites of the Mountain Pine struction of Tegner et al. (2019), which juxtaposes northwestern Ridge (420–405 Ma; Steiner and Walker, 1996) of the Maya Mountains, Gondwana with late Neoproterozoic dyke complexes within Baltica. Maya Block, Devonian-aged magmatism within southwestern North Stratigraphic constraints on the formation of rift-basalts of the America is sparse. However, Martens et al. (2010) suggest that Devo- Puncoviscana Belt (Argentina), suggests they formed within the nian magmatism may be extensive in the subsurface of the Maya same setting, during the rift stage of the Iapetus Wilson Cycle. Block, although a lack of geochemical data precludes a tectonic 2. The Cambrian, siliclastic El Tigre Unit of the Amotape Complex in interpretation. Ecuador may have been deposited prior to the onset of arc Carboniferous magmatism occurred within the Acatlán and Oaxacan magmatism in either the conjugate margins of the Maya Block and complexes, and the Maya Block during 334–289 Ma (Kirsch et al., 2012; Mixteca Terrane, and to the west (Peru) and south (Venezuela), Ortega-Obregón et al., 2014; Solari et al., 2010), and the Eastern Cordil- and thus is considered to be a passive margin sequence. lera of Peru during 360–285 Ma (Miskovic et al., 2009), although it is 3. Ecuadorian lithosphere was in the back-arc during the Ordovician, lacking in the present-day cordilleras of Ecuador and Colombia while the arc rocks are currently preserved in dispersed locations (Fig. 10), presumably due to an inboard, back-arc position (Fig. 13f). within the conjugate margins of the Maya Block and the Acatlán The lack of Carboniferous magmatism in the Merida Andes (Van der Complex (Mixteca Terrane). Consequently, we do not predict that Lelij et al., 2016)reflects the consumption of Rheic oceanic lithosphere Ordovician arc rocks form part of the contemporary basement to beneath the North American Plate (e.g. Nance et al., 2010), and passive Ecuador. Ordovician intrusions form a substantial component of the margin conditions along northern South America. Siliclastic rocks were basement of the Merida Andes, Santander Massif, and dispersed

98 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

inliers in the cordilleras of Colombia. These crustal blocks may have Boekhout, F., Sempere, T., Spikings, R., Schaltegger, U., 2013. Late Paleozoic to Jurassic chronostratigraphy of coastal southern Peru: Temporal evolution of sedimentation been located north of the outboard conjugate Maya, Mixteca and along an active margin. J. S. Am. Earth Sci. 47, 179–200. Oaxaquia blocks, and thus resided within the Ordovician arc, which Boekhout, F., Reitsma, M.J., Spikings, R., Rodriguez, R., Ulianov, A., Gerdes, A., Schaltegger, was dismembered by younger tectonic events. U., 2018. New age constraints on the palaeoenvironmental evolution of the late Pa- 4. Maximum depositional age constraints combined with fossil assem- leozoic back-arc basin along the western Gondwana margin of southern Peru. J. S. Am. Earth Sci. 82, 165–180. blages suggest the Chiguinda and La Victoria siliciclastic units were Boinet, T., Babin, C., Bourgois, J., Broutin, J., Lardeux, H., Pons, D., Racheboeuf, P., 1986. Les deposited during the Carboniferous. The complete lack of Carbonifer- grandes étapes de l'évolution paléozoïque du massif de Santander (Andes de fi ous plutons in Ecuador and Colombia is attributed to a back-arc posi- Colombie): signi cation de la discordance du Dévonien moyen. Comptes Rendus de l'Académie des Sciences. Série 2. Mécanique, Physique, Chimie, Sciences de l'univers, tion to the relict conjugate margins of the Maya Block, Oaxaquia and Sciences de la Terre 303, 707–712. the Mixteca Terrane, while some Carboniferous detritus may have British Geological Survey, 1989. Conodont Investigation by Nottingham University been sourced from the Carboniferous arc in Peru. The lack of Carbon- of ten BGS Samples from Ecuador. British Geological Survey Technical Report WH/ fl 89/13/R 6 pp. iferous arc magmatism in the Merida Andes re ects the subduction Burrow, C.J., Janvier, P., Villarroel, C., 2003. Late Devonian acanthodians from Colombia. of remnants of the Rheic Ocean beneath Laurentia during the amal- J. S. Am. Earth Sci. 16, 155–161. gamation of Pangaea. Bustamante, C., Archanjo, C.J., Cardona, A., Bustamante, A., Valencia, V.A., 2017. U-Pb Ages and Hf Isotopes in Zircons from Parautochthonous Mesozoic Terranes in the western Supplementary data to this article can be found online at https://doi. margin of Pangaea: Implications for the Terrane Configurations in the Northern – org/10.1016/j.gr.2020.10.009. Andes. J. Geol. 125, 487 500. Cardona, A., Cordani, U.G., Ruiz, J., Valencia, V.A., Armstrong, R., Chew, D., Nutman, A., Sanchez, A.W., 2009. U-Pb Zircon Geochronology and Nd Isotopic Signatures of the Credit author statement Pre-Mesozoic Metamorphic Basement of the Eastern Peruvian Andes: growth and Provenance of a late Neoproterozoic to Carboniferous Accretionary Orogen on the Northwest margin of Gondwana. J. Geol. 117, 285–305. Richard Spikings: Raised funds, devised the concept, student super- Cardona, A., Valencia, V., Garzón, A., Montes, C., Ruiz, J., Weber, M., 2010. Permian to Tri- vision, sampled rocks, data acquisition and reduction, wrote the assic I to S-type magmatic switch in the Northeast Sierra Nevada de Santa Marta and manuscript. adjacent regions, Colombian Caribbean: Tectonic setting and implications within Pangea paleogeography. J. S. Am. Earth Sci. 29, 772–783. Andre Paul: Sampled rocks, data acquisition and reduction. Cardona, A., Valencia, V.A., Lotero, A., Villafañez, Y., Bayona, G., 2016. Provenance of mid- Cristian Vallejo: Field work collaborator. dle to late Palaeozoic sediments in the northeastern Colombian Andes: implications – Pedro Reyes: Sampled rocks, Field work collaborator. for Pangea reconstruction. Int. Geol. Rev. 58, 1914 1939. Casquet, C., Pankhurst, R.J., Fanning, M., Baldo, E., Galindo, C., Rapela, C.W., Gonzales- Casado, J.M., Dahlquist, J.A., 2006. U–Pb SHRIMP zircon dating of Grenvillian meta- morphism in Western Sierras Pampeanas (Argentina): Correlation with the Arequipa-Antofalla craton and constraints on the extent of the Precordillera Terrane. Declaration of Competing Interest Gondwana Res. 9, 524–529. Cawood, P., 2005. Terra Australis Orogen: Rodinia breakup and development of the Pacific The authors declare that they have no known competing financial and Iapetus margins of Gondwana during the Neoproterozoic and Paleozoic. Earth- – interests or personal relationships that could have appeared to influ- Sci. Rev. 69, 249 279. Chew, D.M., Van Staal, C.R., 2014. The ocean–continenttransitionzonesalongthe ence the work reported in this paper. Appalachian–Caledonian margin of Laurentia: examples of large-scale hyperexten- sion during the opening of the Iapetus Ocean. Geosci. Can. 41, 165–185. š Acknowledgements Chew, D.M., Schaltegger, U., Ko ler, J., Whitehouse, M.J., Gutjahr, M., Spikings, R.A., Mišković, A., 2007. U-Pb geochronological evidence for the evolution of the Gondwanan margin of north-central Andes. Geol. Soc. Am. Bull. 119. https://doi. The authors are grateful for the assistance of Bernado Beate during org/10.1130/B26080.1. field work and logistical planning in Ecuador. The manuscript was im- Chew, D.M., Magna, T., Kirkland, C.L., Mišković, A., Cardona, A., Spikings, R., Schaltegger, U., 2008. Detrital zircon fingerprint of the Proto-Andes: evidence for a Neoproterozoic proved by the useful and thorough reviews of Dr. Sarah George and an active margin? Precambrian Res. 167, 186–200. anonymous reviewer. Funds for the project were awarded to RS by Cawood, P, McCausland, P, Dunning, G, 2001. Opening Iapetus: Constraints from the Lau- the Swiss National Science Foundation (grants 200020_134443 and rentian margin in Newfoundland. GSA Bulletin 113(4), 443–453. https://doi.org/ 200020_146332). 10.1130/0016-7606(2001)113<0443:OICFTL>2.0.CO;2. Chew, D.M., Cardona, A., Miskovic, A., 2011. Tectonic evolution of western Amazonia from the assembly of Rodinia to its break-up. Int. Geol. Rev. 53, 1280–1296. References Chiaradia, M., Muntener, O., Beate, O., 2011. Enriched basaltic andesites from mid-crustal fractional crystallisation, recharge and assimilation (Pilavo Volcano, Western Cordil- – Aleman, A., Ramos, V.A., 2000. The Northern Andes. In: Cordani, U.G., Milani, E.J., Thomaz, lera of Ecuador). J. Petrol. 52, 1107 1141. A., Campos, D.A. (Eds.), Tectonic evolution of South America. Brazil, Rio de Janeiro, Cochrane, R., Spikings, R., Gerdes, A., Winkler, W., Ulianov, A., Mora, A., Chiaradia, M., pp. 453–480. 2014a. Distinguishing between in-situ and accretionary growth of continents along – Angiolini, L., Racheboeuf, R., Villarroel, C.A., Concha, A.E., 2003. Stratigraphy and brachio- active margins. Lithos 202, 382 394. pod fauna of the Carboniferous El Imán Formation, Colombia. Revista Espagñola de Cochrane, R., Spikings, R., Gerdes, A., Ulianov, A., Mora, A., Villagómez, D., Putlitz, B., Paleontología 18, 151–158. Chiaradia, M., 2014b. Permo-Triassic anatexis, continental rifting and the disassembly of western Pangaea. Lithos 190-191, 383–402. Aspden, J.A., Bonilla, W., Duque, P., 1995. The El Oro metamorphic complex, Ecuador: ge- Cocks, L.R.M., Torsvik, T.H., 2006. European geography in a global context from the ology and economic mineral deposits. British Geological Survey. Overseas Geol. Min- Vendian to the end of the Palaeozoic. Geol. Soc. Lond. Mem. 32, 83–95. eral Resour. 67 63 p. Cordani, U.G., Cardona, A., Jiménez, D.M., Liu, D., Nutman, A.P., 2005. Geochronology of Bahlburg, H., Vervoort, J.D., Du Frane, S.A., Bock, B., Augustsson, C., Reimann, C., 2009. Proterozoic basement inliers in the Colombian Andes: Tectonic history of remnants Timing of crust formation and recycling in accretionary orogens: Insights learned of a fragmented Grenville belt. Geol. Soc. Lond., Spec. Publ. 246, 329–346. from the western margin of South America. Earth Sci. Rev. 97, 215–241. Dickinson, W.R., Gehrels, G.E., 2009. Use of U–Pb ages of detrital zircons to infer maxi- Baldo, E., Casquet, C., Pankhurst, R.J., Galindo, C., Rapela, C.W., Fanning, C.M., Dahlquist, J., mum depositional ages of strata: a test against a Colorado Plateau Mesozoic database. Murra, J., 2006. Neoproterozoic A-type magmatism in the Western Sierras Earth Planet. Sci. Lett. 288, 115–125. Pampeanas (Argentina): evidence for Rodinia break-up along a proto-Iapetus rift? Dickinson, W.R., Lawton, T.F., 2001. Carboniferous to cretaceous assembly and fragmenta- Terra Nova 18, 388–394. tion of Mexico. Geol. Soc. Am. Bull. 113, 1142–1160. Batchelor, R.A., Bowden, P., 1985. Petrogenetic interpretation of granitoid rock series Duenas, H., Cesari, S.N., 2006. Palynological evidence of early Carboniferous sedimenta- – using multicationic parameters. Chem. Geol. 48, 43 55. tion in the Llanos Orientales Basin, Colombia. Rev. Palaeobot. Palynol. 138, 31–42. Bingen, B., Demaiffe, D., 1999. Geochemical signature of the Egersund basaltic dyke Elías-Herrera, M., Ortega-Gutiérrez, F., 2002. Caltepec fault zone: an early Permian dextral swarm, SW Norway, in the context of late-Neoproterozoic opening of the Iapetus transpressional boundary between the Proterozoic Oaxacan and Paleozoic Acatlán Ocean. Nor. Geol. Tidsskr. 79, 69–86. complexes, southern Mexico, and regional implications. Tectonics 21. https://doi. Bingen, B., Demaiffe, D., Breemen, O.V., 1998. The 616 Ma Old Egersund Basaltic Dike org/10.1029/200TC001278. Swarm, Sw Norway, and late Neoproterozoic opening of the Iapetus Ocean. J. Geol. Ernst, R.E., Bell, K., 2010. Large igneous provinces (LIPs) and carbonatites. Mineral. Petrol. 106, 565–574. 98, 55–76. Boekhout, F., Spikings, R., Sempere, T., Chiaradia, M., Ulianov, A., Schaltegger, U., 2012. Me- Escayola, M.P., Pimentel, M.M., Armstrong, R., 2007. Neoproterozoic backarc basin: Sensi- sozoic arc magmatism along the southern Peruvian margin during Gondwana tive high-resolution ion microprobe U-Pb and Sm-Nd isotopic evidence from the breakup and dispersal. Lithos 146, 48–64. Eastern Pampean Ranges, Argentina. Geology 35, 495–498.

99 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

Estrada-Carmona, J., Weber, B., Martens, U., López-Martinez, M., 2012. Petrogenesis of Or- Martignole, J., Martelat, J.-E., 2003. Regional-scale Grenvillian-age UHT metamorphism in dovician magmatic rocks in the southern Chiapas Massif complex: relations with the the Mollendo–Camana block (basement of the Peruvian Andes). J. Metamorph. Geol. early Palaeozoic magmatic belts of northwestern Gondwana. Int. Geol. Rev. 54, 21, 99–120. 1918–1943. Martin-Gombojav, N., Winkler, W., 2008. Recycling of Proterozoic crust in the Andean Fettes, D.J., Macdonald, R., Fitton, J.G., Stephenson, D., Cooper, M.R., 2011. Geochemical Amazon foreland of Ecuador: implications for orogenic development of the Northern evolution of Dalradian metavolcanic rocks: implications for the break-up of the Andes. Terra Nova 20, 22–31. Rodinia supercontinent. J. Geol. Soc. 168, 1133–1146. Mišković, A., Spikings, R.A., Chew, D.M., Košler, J., Ulianov, A., Schaltegger, U., 2009. George, S.W.M., Horton, B.K., Jackson, L.J., Moreno, F., Carlotto, V., Garzione, C., 2019. Sed- Tectonomagmatic evolution of Western Amazonia: Geochemical characterization iment provenance variations during contrasting Mesozoic-early Cenozoic tectonic re- and zircon U-Pb geochronologic constraints from the Peruvian Eastern Cordilleran gimes of the northern Peruvian Andes and Santiago-Marañón foreland basin. In: granitoids. Geol. Soc. Am. Bull. 121, 1298–1324. Horton, B.K., Folguera, A. (Eds.), Andean Tectonics. Elsevier, Chapter vol. 10, Mitouard, P., Kissel, C., Laj, C., 1990. Post-Oligocene rotations in southern Ecuador and – pp. 269 296. northern Peru and the formation of the Huancabamba Deflection in the Andean Cor- Gutierrez, E.G., Horton, B.K., Vallejo, C., Jackson, L.J., George, S.W.M., 2019. Chapter 9 - dillera. Earth Planet. Sci. Lett. 98, 329–339. Provenance and geochronological insights into late Cretaceous-Cenozoic foreland Moreno-Sanchez, M., Gomez, A., Castillo, H., 2007. La “Formación Floresta basin development in the Subandean Zone and Oriente Basin of Ecuador. In: metamorfoseada” (sensu Ward., 1973) no es la formación floresta sin metamorfosear. Horton, B.K., Folguera, A. (Eds.), Andean Tectonics. Elsevier, Chapter vol. 9, X Congreso Colombiano de Geología, Paipa. Resúmenes 7 p. pp. 237–268. Mourier, T., Laj, C., Megard, F., Roperch, P., Mitouard, P., Farfan Medrano, A., 1988. An ac- Hodych, J.P., Cox, R.A., 2007. Ediacaran U–Pb zircon dates for the Lac Matapédia and Mt. creted continental terrane in northwestern Peru. Earth Planet. Sci. Lett. 88, 182–192. St.-Anselme basalts of the Quebec Appalachians: Support for a long-lived mantle Nance, R.D., Gutiérrez-Alonso, G., Keppie, D., Linnemann, J.D., Murphy, J.B., Quesada, C., plume during the rifting phase of Iapetus opening. Can. J. Earth Sci. 44, 565–581. Strachan, R.A., Woodcock, N.H., 2010. Evolution of the Rheic Ocean. Gondwana Res. Horton, B.K., Saylor, J.E., Nie, J., Mora, A., Parra, M., Reyes-Harker, A., Stockli, D.F., 2010. 17, 194–222. Linking sedimentation in the northern Andes to basement configuration, Mesozoic Odreman, O., Useche, A., 1997. Formación Palmarito. Léxico Estratigráfico de Venezuela. extension, and Cenozoic shortening: evidence from detrital zircon U-Pb ages in the Ministerio de Energía y Minas. Comisión de Estratigrafía y Terminología, Caracas. Eastern Cordillera of Colombia. Geol. Soc. Am. Bull. 122, 1423–1442. fl Jackson, S., 2008. LAMTRACE data reduction software for LA-ICP-MS. In: Sylvester, P. (Ed.), Omarini, R.H., Sureda, R.J., Gotze, H.J., Seilacher, A., P uger, F., 1999. Puncoviscana folded Laser Ablation ICP-MS in the Earth Sciences: Current Practices and outstanding issues. belt in northwestern Argentina: testimony of late Proterozoic Rodinia fragmentation – Short Course Series. 40. Mineral Association of Canada, pp. 305–307. and pre-Gondwana collisional episodes. Int. J. Earth Sci. 88, 76 97. Jaillard, E., Laubacher, G., Bengston, P., Dhondt, A.V., Bulot, L.G., 1999. Stratigraphy and Ortega-Obregón, C., Solari, L.A., Keppie, J.D., Ortega-Gutiérrez, F., Solé, J., Morán-Ical, S., evolution of the cretaceous forearc Celica-Lancones basin of southwestern Ecuador. 2008. Middle-late Ordovician magmatism and late cretaceous collision in the south- J. S. Am. Earth Sci. 12, 51–68. ern Maya block, Rabinal-Salamá area, Central Guatemala: Implications for North – Janvier, P., Villarroel, C., 2000. Devonian vertebrates from Colombia. Palaeontology 43, America-Caribbean plate tectonics. Geol. Soc. Am. Bull. 120, 556 570. 729–763. Ortega-Obregón, C., Solari, L., Gómez-Tuena, A., Elías-Herrera, M., Ortega-Gutiérrez, F., Jones III, J.V., Connelly, J.N., Karlstrom, K.E., Williams, M.L., Doe, M.F., 2009. Age, prove- Marcías-Romo, C., 2014. Int. J. Earth Sci. 103, 1287–1300. nance, and tectonic setting of Paleoproterozoic quartzite successions in the south- Owens, B., 1992. Palynological Investigation of Samples Collected by M. Woods, 1991. western United States. Geol. Soc. Am. Bull. 121, 247–264. British Geological Survey Technical Report WH/92/157/R (34 pp). Kamo, S.L., Krogh, T.E., Kumarapeli, P.S., 1995. Age of the Grenville dyke swarm, Ontario– Patarroyo, P., Senff, M., 2001. Perrinites SP. En las sedimentitas del Pérmico de la Quebec: implications for the timing of lapetan rifting. Can. J. Earth Sci. 323, 273–280. Formación Diamante en cercanias de Bucaramanga (Santander – Colombia) VII Kennerley, J.B., 1973. Geology of the Loja Province. Report of the Institute of Geological Congreso Colombiano de Geología. Sciences (Overseas Division). 23. Paul, A., Spikings, R., Ulianov, A., Ovtcharova, M., 2018. High temperature (>350°C) ther- Keppie, J.D., Dostal, J., Cameron, K.L., Solari, L.A., Ortega-Gutierrez, F., Lopez, R., 2003. Geo- mal histories of the long lived (>500Ma) active margin of Ecuador and Colombia: Ap- chronology and geochemistry of Grenvillian igneous suites in the northern Oaxacan atite, titanite and rutile U-Pb thermochronology. Geochim. Cosmochim. Acta 228, complex, southern Mexico: tectonic implications. Precambrian Res. 120, 365–389. 275–300. Keppie, J.D., Dostal, J., Miller, B.V., Ramos-Arias, M.A., Morales-Gámez, M., Nance, R.D., Pearce, J.A., 2008. Geochemical fingerprinting of oceanic basalts with applications to Murphy, J.B., Ortega-Rivera, A., Lee, J.K.W., Housh, T., Cooper, P., 2008. Ordovician– ophiolite classification and the search for Archean oceanic crust. Lithos 100, 14–68. earliest Silurian rift tholeiites in the Acatlán complex, southern Mexico: evidence of Pimentel, M.M., Fuck, R.A., Botelho, N.F., 1999. Granites and the geodynamic history of the rifting on the southern margin of the Rheic Ocean. Tectonophysics 461, 130–156. neoproterozoic Brasıliá belt, Central Brazil: a review. Lithos 46, 463–483. Keppie, J.D., Dostal, J., Murphy, J.B., Galaz-Escanilla, G., Ramos-Arias, M.A., Nance, R.D., Pin, C., Zalduegui, J.S., 1997. Sequential separation of light rare-earth elements, thorium 2012. High pressure rocks of the Acatlán complex, southern Mexico: Large-scale and uranium by miniaturized extraction chromatography: application to isotopic subducted Ordovician rifted passive margin extruded into the upper plate during analyses of silicate rocks. Anal. Chim. Acta 339, 79–89. – – the Devonian Carboniferous. Tectonophysics 560, 1 21. Piraquive, A., 2017. Structural Framework, Deformation and Exhumation of the Santa – Kirsch, M., Keppie, J.D., Murphy, J.B., Solari, L.A., 2012. Permian Carboniferous arc Marta Schists: Accretion and Deformational History of the Caribbean Terrane at the magmatism and basin evolution along the western margin of Pangea: Geochemical north of the Sierra Nevada de Santa Marta. PhD thesis. Université Grenoble Alpes and geochronological evidence from the eastern Acatlán complex, southern Mexico. pp. 228. Geol. Soc. Am. Bull. 124, 1607–1628. Ramos, V.A., 1988. Late Proterozoic-early Palaeozoic of South America – a Collisional his- Koppers, A.A.P., 2002. ArArCALC – software for 40Ar/39Ar age calculations. Comput. Geosci. tory. Episodes J. Int. Geosci. 11, 168–174. 28, 605–619. Ratschbacher, L., Franz, L., Min, M., Bachmann, R., Martens, U., Stanek, K., Stübner, K., Kuiper, K.F., Deino, A., Hilgen, F.J., Krijgsman, W., Renne, P.R., Wijbrans, J.R., 2008. Nelson, B.K., Herrmann, U., Weber, B., López-Martínez, M., Jonckheere, R., Sperner, Synchronising Rock Clocks of Earth history. Science 320, 500–504. B., Tichomirowa, M., Mcwilliams, M.O., Gordon, M., Meschede, M., Bock, P., 2009. Laya, J.C., Tucker, M.E., 2012. Facies analysis and depositional environments of Permian The North American–Caribbean Plate boundary in Mexico–Guatemala–Honduras. carbonates of the Venezuelan Andes: Palaeogeographic implications for Northern In: James, K.H., Lorente, M.A., Pindell, J.L. (Eds.), The Origin and Evolution of the Carib- Gondwana. Palaeogeogr. Palaeoclimatol. Palaeoecol. 331-332, 1–26. bean Plate. Geological Society of London, Special Publication vol. 328, pp. 219–293. Lee, J.-Y., Marti, K., Severinghaus, J.P., Kawamura, K., Yoo, H.-S., Lee, J.B., Kim, J.S., 2006. A Reimink, J.R., Davies, J.H.F.L., Waldron, J.W.F., Rojas, X., 2016. Dealing with discordance: a redetermination of the isotopic abundances of atmospheric Ar. Geochim. Cosmochim. novel approach for analysing U-Pb detrital zircon datasets. J. Geol. Soc. 173, 577–585. Acta 70, 4507–4512. Li, Z.X., Bogdanova, V., Collins, A.S., Davidson, A., De Waele, B., Ernst, R.E., Fitzsimons, Restrepo-Pace, P.A., Ruiz, J., Gehrels, G., Cosca, M., 1997. Geochronology and Nd isotopic I.C.W., Fuck, R.A., Gladkochub, D.P., Jacobs, J., Karlstrom, K., Lu, S., Natapov, L.M., data of Grenville-age rocks in the Colombian Andes: new constraints for late Pease, V., Pisarevsky, S.A., Thrane, K., Vernikovsky, V., 2007. Assembly, configuration, Proterozoic-early Paleozoic paleocontinental reconstructions of the Americas. Earth – and break-up history of Rodinia: a synthesis. Precambrian Res. 160, 179–210. Planet. Sci. Lett. 150, 427 441. fi Litherland, M., Aspden, J., Jemielita, R.A., 1994. The metamorphic belts of Ecuador. Br. Reyes, P., 2006. El Complejo o olítico Peltetec y su relación con las unidades fi Geol. Surv. Overseas Memoir 11 147 p. metamór cas Jurásicas de la Cordillera Real. Ingeniero Thesis, Escuela Politecnica Na- López, R., 1997. High-Mg Andesites from the Gila Bend Mountains: Evidence for Hydrous tional, Quito, Ecuador, p. 189. Melting of the Lithosphere during Miocene Extension, and the Pre-Jurassic Geotec- Riel, N., Guillot, S., Jaillard, E., Martelat, J.-E., Paquette, J.-L., Schwartz, S., Gonclaves, P., tonic Evolution of the Coahuila Terrane, Northeastern Mexico: Grenville Basement, Duclaux, G., Thebaud, N., Lanari, P., Janots, E., Yuquilema, J., 2013. Metamorphic and a late Paleozoic arc, Triassic Plutonism, and the Events south of the Ouachita Suture. geochronological study of the Triassic El Oro metamorphic complex, Ecuador: Impli- Ph.D. thesis. Santa Cruz, University of California 147 p. cations for high-temperature metamorphism in a forearc zone. Lithos 156-159, – Ludwig, K.R., 2012. User's Manual for Isoplot 3.75: A Geochronological Toolkit for 41 68. Microsoft Excel (Berkeley CA). Roberts, R.J., Corfu, F., Torsvik, T.H., Ashwal, L.D., Ramsay, D.M., 2006. Short-lived mafic Mantilla-Figueroa, Bissig, T., Cottle, J.M., Hart, C.J.R., 2012. Remains of early Ordovician magmatism at 560–570 Ma in the northern Norwegian Caledonides: U–Pb zircon mantle-derived magmatism in the Santander Massif (Colombian Eastern Cordillera). ages from the Seiland Igneous Province. Geol. Mag. 143 887–817. J. S. Am. Earth Sci. 38, 1–12. Sláma, J., Košler, J., Condon, D.J., Crowley, J.L., Gerdes, A., Hanchar, J.M., Horstwood, M.S.A., Martens, U., Weber, B., Valencia, V.A., 2010. U/Pb geochronology of Devonian and older Morris, G.A., Nasdala, L., Norberg, N., Schaltegger, U., Schoene, B., Tubrett, M.N., Paleozoic beds in the southeastern Maya block, Central America: its affinity with Whitehouse, M.J., 2008. Plešovice zircon — a new natural reference material for U– peri-Gondwanan terranes. Geol. Soc. Am. Bull. 122, 815–829. Pb and Hf isotopic microanalysis. Chem. Geol. 1–2, 1–35. Martens, U., Restrepo, J.J., Ordonez-Carmona, O., Correa-Martinez, A.M., 2014. The Tahami Solari, L.A., Ortega-Gutiérrez, F., Elías-Herrera, M., Gómez-Tuena, A., Schaaf, P., 2009. Re- and Anacona Terranes of the Colombian Andes: Missing Links between South fining the age of magmatism in the Altos Cuchumatanes, western Guatemala, by American and Mexican Gondwana margins. J. Geol. 122, 507–530. LA–ICPMS, and tectonic implications. Int. Geol. Rev. 52, 977–998.

100 R. Spikings, A. Paul, C. Vallejo et al. Gondwana Research 90 (2021) 77–101

Solari, L.A., Ortega-Gutiérrez, F., Elías-Herrera, M., Gómez-Tuena, A., Schaaf, P., 2010. Re- Tollo, R.P., Aleinikoff, J.N., Bartholemew, M.J., Rankin, D.W., 2004. Neoproterozoic A-type fining the age of magmatism in the Altos Cuchumatanes, western Guatemala, by granitoids of the central and southern Appalachians: intraplate magmatism associ- LA-ICPMS, and tectonic implications. Int. Geol. Rev. 52, 977–998. ated with episodic rifting of the Rodinian supercontinent. Precambrian Res. 128, Solari, L.A., García-Casco, A., Martens, U., Lee, J.K.W., Ortega-Rivera, A., 2013. Late creta- 3–38. ceous subduction of the continental basement of the Maya block (Rabinal Granite, Tschopp, H.J., 1953. Oil Explorations in the Oriente of Ecuador, 1938–1950. 37. American Central Guatemala): Tectonic implications for the geodynamic evolution of Central Association of Petroleum Geology Bulletin, pp. 2303–2347. America. Geol. Soc. Am. Bull. 125, 625–639. Ulianov, A., Muntener, O., Schaltegger, U., Bussy, F., 2012. The data treatment dependent Spikings, R., Paul, A., 2019. Permian – Triassic History of Magmatic Rocks of the Northern variability of U–Pb zircon ages obtained using mono-collector, sector field, laser abla- Andes (Colombia and Ecuador): Supercontinent Assembly and Disassembly. In: tion ICPMS. J. Anal. At. Spectrom. 27, 663–676. Gómez, J., Pinilla-Pachon, A.O. (Eds.), The Geology of Colombia. vol. 2 Mesozoic. Valarezo, M.E., Vallejo, C., Horton, B.K., Gaibor, J., Esteban, J., Jackson, L.J., Carrasco, H., Servicio Geológico Colombiano, Publicaciones. Winkler, W., Bernal, C., Beate, B., 2019. Sedimentological and provenance analysis Spikings, R.A., Winkler, W., Hughes, R.A., Handler, R., 2005. Thermochronology of alloch- of the Río Playas stratigraphic section: Implications for the evolution of the Alamor- thonous terranes in Ecuador: Unravelling the accretionary and post-accretionary his- Lancones Basin of southern Ecuador and northern Peru. J. S. Am. Earth Sci. 94, 102239. tory of the Northern Andes. Tectonophysics 399, 195–220. Vallejo, C., Spikings, R.A., Luzieux, L., Winkler, W., Chew, D., Page, L., 2006. The early inter- Spikings, R., Crowhurst, P.V., Winkler, W., Villagomez, D., 2010. Syn- and post- action between the Caribbean Plateau and the NW South American Plate. Terra Nova accretionary cooling history of the Ecuadorian Andes constrained by their in-situ 18, 264–269. and detrital thermochronometric record. J. S. Am. Earth Sci. 30, 121–133. Van der Lelij, R., Spikings, R., Ulianov, A., Chiaradia, M., Mora, A., 2016. Palaeozoic to Early Spikings, R., Cochrane, R., Villagómez, D., Van der Lelij, R., Vallejo, C., Winkler, W., Beate, B., Jurassic history of the northwestern corner of Gondwana, and implications for the 2015. The geological history of northwestern South America: from Pangaea to the evolution of the Iapetus, Rheic and Pacific Oceans. Gondwana Res. 31, 271–294. early collision of the Caribbean large Igneous Province (290 – 75 Ma). Gondwana Vermeesch, P., 2012. On the visualisation of detrital age populations. Chem. Geol. 312, Res. 27, 95–139. 190–194. Spikings, R., Reitsma, M.J., Boekhout, F., Mišković, A., Ulianov, A., Chiaradia, M., Gerdes, A., Villagómez, D., Spikings, R., Magna, T., Kammer, A., Winkler, W., Beltrán, A., 2011. Geo- Schaltegger, U., 2016. Characterisation of Triassic rifting in Peru and implications for chronology, geochemistry and tectonic evolution of the Western and Central cordil- the early disassembly of western Pangaea. Gondwana Res. 35, 124–143. leras of Colombia. Lithos 125, 875–896. Steiner, M.B., Walker, J.D., 1996. Late Silurian Plutons in Yucatan. J. Geophys. Res. 101, Vinasco, C.J., Cordani, U.G., Gonzales, H., Weber, M., Pelaez, C., 2006. Geochronological, 17727–17735. isotopic, and geochemical data from Permo-Triassic granitic gneisses and granitoids Stewart, J.H., Blodgett, R.B., Boucot, A.J., Carter, J.L., López, R., 1999. Exotic Paleozoic strata of the Colombian Central Andes. J. S. Am. Earth Sci. 21, 355–371. of Gondwanan provenance near Ciudad Victoria, Tamaulipas, Mexico. In: Ramos, V.A., Walker, J.D., Geissman, J.W., Dowring, S.A., Babcock, L.E., 2013. The Geological Society of Keppie, J.D. (Eds.), Laurentia-Gondwana connections before Pangea: Geological Soci- America Geologic Time Scale. Geol. Soc. Am. Bull. 125, 259–272. ety of America Special Paper. 336, pp. 227–252. Ward, D.E., Goldsmith, R., Jaime, B., Restrepo, H.A., 1974. Geology of quadrangles H-12, H- Suhr, N., Rojas-Agramonte, Y., Chew, D.M., Pinto, A.J., Villagomez-Diaz, D., Toulkeridis, T., 13, and parts of I-12 and I-13, (zone III) in northeastern Santander Department. Mertz-Fraus, R., 2019. Detrital-zircon geochronology and provenance of the El Oro Colombia. U.S, Geological Survey. Metamorphic complex, Ecuador: Geodynamic implications for the evolution of the Weber, B., Iriondo, A., Premo, W.R., Hecht, L., Schaaf, P., 2007. New insights into the his- western Gondwana margin. J. S. Am. Earth Sci. 90, 520–539. tory and origin of the southern Maya block, SE México: U–Pb–SHRIMP zircon geo- Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: chronology from metamorphic rocks of the Chiapas massif. Int. J. Earth Sci. 96, implications for mantle composition and processes. Geol. Soc. Lond., Spec. Publ. 42, 253–269. 313–345. Weber, B., Valencia, V.A., Schaaf, P., Pompa-Mera, V., Ruiz, J., 2008. Significance of prove- Tanaka, T., Togashi, S., Kamioka, H., Amakawa, H., Kagami, H., Hamamoto, T., Yuhara, M., nance ages from the Chiapas Massif Complex (Southeastern Mexico): redefining the Orihashi, Z., Yoneda, S., Shimizu, H., Kunimaru, T., Takahashi, K., Yanagi, T., Nakano, Palaeozoic basement of the Maya Block and its evolution in a peri-Gondwanan realm. T., Fujimaki, H., Shinjo, R., Asahara, Y., Tanimizu, M., Dragusanu, C., 2000. JNdi-1: a J. Geol. 116, 619–639. neodymium isotopic reference in consistency with LaJolla neodymium. Chem. Geol. Wiedenbeck, M., Allé, P., Corfu, F., Griffin, W.L., Meier, M., Oberli, F., Quadt, A.V., Roddick, 168, 279–281. J.C., Spiegel, W., 1995. Three natural zircon standards for U–Th–Pb, Lu–Hf, trace ele- Taylor, S.R., McLennan, S.M., 1995. The geochemical evolution of the continental crust. ment and REE analyses. Geostand. Newslett. 19, 1–23. Rev. Geophys. 33, 241–265. Zamora, A., Pothe de Baldis, E., 1988. Nuevos aportes al conocimiento del Paleozoico de Tegner, C., Andersen, T.B., Kjoll, H.J., Brown, E.L., Hagen-Peter, G., Corfu, F., Planke, S., Ecuador. Minera Ecuatoriana (INEMIN, Quito) 1, 54. Torsvik, T.H., 2019. Geochemistry. Geophys. Geosyst. https://doi.org/10.1029/ 2018GC007941.

101