The geochemistry and geochronology of Early Jurassic igneous rocks from the Sierra Nevada de Santa Marta, NW Colombia, and tectono-magmatic implications

Accepted Manuscript The geochemistry and geochronology of Early Jurassic igneous rocks from the Sierra Nevada de Santa Marta, NW Colombia, and tectono-magmatic implications Dennis Quandt, Robert B. Trumbull, Uwe Altenberger, Agustin Cardona, Rolf L. Romer, German Bayona, Mihai Ducea, Victor Valencia, Monica Vásquez, Elizabeth Cortes, Georgina Guzman PII:

S0895-9811(17)30458-3

DOI:

10.1016/j.jsames.2018.06.019

Reference:

SAMES 1959

To appear in:

Journal of South American Earth Sciences

Received Date: 10 November 2017 Revised Date:

27 June 2018

Accepted Date: 27 June 2018

Please cite this article as: Quandt, D., Trumbull, R.B., Altenberger, U., Cardona, A., Romer, R.L., Bayona, G., Ducea, M., Valencia, V., Vásquez, M., Cortes, E., Guzman, G., The geochemistry and geochronology of Early Jurassic igneous rocks from the Sierra Nevada de Santa Marta, NW Colombia, and tectono-magmatic implications, Journal of South American Earth Sciences (2018), doi: 10.1016/ j.jsames.2018.06.019. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT 1

The geochemistry and geochronology of Early Jurassic igneous rocks from the Sierra

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Nevada de Santa Marta, NW Colombia, and tectono-magmatic implications

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Dennis Quandta1, Robert B. Trumbullb2, Uwe Altenbergera, Agustin Cardonac, Rolf L. Romerb,

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German Bayonad, Mihai Duceae, Victor Valenciaf, Monica Vásquezg, Elizabeth Cortesh,

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Georgina Guzmani

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a

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[email protected], [email protected]

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b

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potsdam.de, [email protected]

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Institute of Earth and Environmental Science, University of Potsdam, Germany:

GFZ German Research Centre for Geosciences, Potsdam, Germany: bobby@gfz-

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c

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[email protected]

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Corporación Geológica ARES, Bogotá, Colombia: [email protected]

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Department of Geosciences, University of Arizona, USA: [email protected]

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School of the Environment, Washington State University, USA: [email protected]

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Hauptstrasse 2, 14822 Brück, Germany: [email protected]

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Servicio Geológico Colombiano, Bogotá: [email protected]

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Dept. de Procesos y Energía, Universidad Nacional de Colombia, Medellín, Colombia:

INVEMAR, Santa Marta, Colombia, [email protected]

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now at: Dept. of Earth Sciences, University of Graz, Austria, [email protected]

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corresponding author: GFZ German Research Centre for Geosciences, Telegrafenberg,

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14473 Potsdam, Germany; email: bobbygfz-potsdam.de; tel. +49 3312881495

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Abstract

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The Sierra Nevada de Santa Marta in NW Colombia is an isolated massif at the

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northernmost end of the Andes chain near the boundary with the Caribbean plate. Previous

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geologic mapping and K-Ar dating have shown that Jurassic plutonic and volcanic units

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make up a large part of the Santa Marta Massif (SMM). These rocks have been considered

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to be part of a Jurassic magmatic arc extending from NW Colombia to northern Chile, but

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without any geochemical basis for comparison. This paper reports on a geochemical and Sr-

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Nd-Pb isotope study of the Jurassic rocks in the SMM and provides 12 new U-Pb zircon ages

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from in-situ laser ICP-MS dating. The plutonic and volcanic units span a range from 44 to 77

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wt.% SiO2, with a dominance of intermediate to felsic compositions with SiO2 > 57 wt.%.

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They classify as calc-alkaline, medium to high-K, metaluminous rocks with trace-element

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features typical for arc-derived magma series. In terms of their major and trace-element

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compositions, the SMM Jurassic units overlap with contemporary plutonic and volcanic rocks

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from other regions of the Central and Eastern Cordilleras of Colombia, and confirm an arc

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affinity. The new U-Pb ages range from 176 ± 1 Ma to 191 ± 1 Ma (n=12), with most between

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180 and 188 Ma (n=7). The initial Sr isotope ratios (at 180 Ma) cluster between 0.7012 and

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0.7071 (n= 29), with 3 outliers attributed to mobilization of Rb and/or Sr. Nearly all samples

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have negative εNd(180) values between -10.3 and 0.0 (n=30), the two exceptions being only

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slightly positive (1.1 and 1.9). Measured Pb isotope ratios fall in a narrow range, with

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to 39.04 (n= 28).

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Pb/204Pb from 15.56 to 15.67 and

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Pb/204Pb from 37.76

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Pb/204Pb from 18.02 to 19.95,

In the regional context of previous studies, these results confirm early Jurassic ages

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and an arc affinity for the widespread magmatism exposed in the eastern and northeastern

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Colombian Andes. We also note patterns in the distribution and composition of magmas. The

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magmatic activity in the Central Cordillera tends to be younger than in the Eastern Cordillera

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and is spatially more restricted to the vicinity of regional fault systems. In terms of

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composition, Jurassic igneous rocks in the Eastern Cordillera have systematically lower

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εNd(180) values than those from the Central Cordillera, whereas the Pb isotope ratios overlap.

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We ascribe the Nd isotope variations to heterogeneity in the mantle source and/or degree of

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crustal contamination, whereas the Pb isotope ratios are crust-dominated and similar

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throughout the region. The spatio-temporal and compositional evolution of Jurassic

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magmatic rocks in the Northern Andes reflect the major plate kinematic readjustment

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between the Triassic and the Early Jurassic in the proto-Andean margin.

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Key words: Jurassic arc; northern Andes; Sr-Nd-Pb isotopes; geochronology

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1

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Jurassic igneous rocks are widely distributed along the northwestern edge of South America.

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They are considered to be part of a once-continuous continental arc related to eastward

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subduction of the Farallon plate under South America (e.g., Villagómez et al., 2011;

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Bustamante et al., 2016), but present outcrops are in discontinuous, fault- and basin-

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bounded massifs with uncertain correlations among them. In Colombia, Jurassic igneous

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rocks extend from the border with Ecuador to the Caribbean Sea, and are hosted by

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Precambrian to Triassic igneous and metamorphic units of the Central and Eastern

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Cordilleras, and in the Magdalena Valley between them (Fig. 1). The discontinuous nature of

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the Jurassic magmatic arc in Colombia is due to the complex tectonic setting in the Jurassic,

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which involved intra-continental extension related to the opening of the Gulf of Mexico and

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the proto-Caribbean (Pindell and Keenan, 2009; Martini and Ortega-Gutiérrez, 2016).

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Oblique subduction of the Farallon plate during the Jurassic (Seton et al., 2012) also played

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a role, with along-strike transfer of arc segments as suggested by paleomagnetic data from

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ACCEPTED MANUSCRIPT volcanic units in Colombia (Bayona et al., 2006, 2010). Several studies have provided details

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on the ages and chemical diversity of Jurassic plutonic and volcanic rocks in central and SE

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Colombia where those rocks are most abundant (e.g.,Rodríguez et al., 2016, Cochrane et

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al., 2014; Cardona et al., 2010a; Vásquez et al., 2011; Bustamante et al., 2010, 2016;

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Villagómez et al., 2011; Zapata et al. 2016), in the Santander Massif (van der Lelij et al.

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2015; Rodríguez et al., 2017), on the Guajira Peninsula (Zuluaga et al. 2015) and in the

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Serranía del Perijá (Maze, 1984). The consensus from the geochemical studies is that the

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Jurassic magmas have a subduction-related origin. Regional variations in the U-Pb ages led

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Cochrane et al. (2014) and Spikings et al. (2015) to postulate a westward-migration of the

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Jurassic arc with time, possibly due to slab roll-back. Bustamante et al. (2016) also noted

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compositional variations with age and attributed the changes to increasing arc maturity with

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time.

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The Santa Marta Massif (SMM) in northeastern Colombia contains a prominent area

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of Jurassic igneous rocks, but they have so far been scarcely studied and the SMM was not

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fully considered in regional geodynamic models. Previous K-Ar dates of 129 to 183 Ma

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suggested Jurassic to Early Cretaceous ages for the plutonic and volcanic rocks in the SMM

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(Tschanz et al., 1974; Aspden et al., 1987; Bayona et al., 2010). This range of apparent ages

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is large, and it was suggested that the K-Ar dates reflect cooling and/or resetting after

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emplacement and are not reliable for regional comparisons (Tschanz et al., 1974; Bayona et

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al., 2010; Spikings et al., 2015). Two U-Pb zircon dates (179 Ma, 183 Ma) from the

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southwestern edge of the SMM were reported in a PhD thesis by Leal-Mejía (2011). The

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limited age constraints and the lack of a modern geochemical study of the Jurassic units in

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the SMM motivated the work reported here. In this paper, we present U-Pb zircon dates of 12

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samples from plutonic and volcanic rocks of the SMM, 79 whole-rock geochemical analyses

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and 30 analyses of radiogenic Sr, Nd, Pb isotope ratios. The results are discussed in

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combination with existing studies to better assess the geodynamic implications of Middle

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Jurassic magmatism in northern South America.

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The Andean province in western Colombia is divided into Western, Central and Eastern

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Cordilleras (Fig. 1). The Western Cordillera and coastal ranges are made up of

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allochthonous oceanic terranes with mafic-ultramafic crust that are thought to have formed

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as part of the Caribbean Large Igneous Province and accreted to NW South America in the

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Late Cretaceous (Restrepo and Toussaint, 1988; Villagómez et al., 2011). The Central

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Cordillera basement consists of late Paleozoic to Triassic metamorphic rocks and bimodal,

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mylonitized plutonic rocks of granitic and gabbroic composition that represent the accretion

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and fragmentation of continental terranes to South America during the Late Paleozoic to

Regional setting

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ACCEPTED MANUSCRIPT Triassic assembly and the disruption of Pangaea (Vinasco et al., 2006; Villagómez et al.,

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2011; Cochrane et al., 2014). The Eastern Cordillera and its prolongation to the Caribbean

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region contains several basement-cored massifs with high-grade metamorphic and grantitic

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rocks of Neoproterozoic "Grenvillian" age (ca. 990-1160 Ma), overlain by Paleozoic

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sedimentary and metasedimentary rocks that are authochthonous or para-authocthonous to

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the Amazon Craton (Restrepo-Pace and Cediel, 2010; Cordani et al., 2005; Cardona-Molina

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et al., 2006; Ordóñez-Carmona et al., 2006; Ibañez-Mejía et al., 2011). From south to north,

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these massifs include the Garzón and Santander Massif in the Eastern Cordillera, the Santa

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Marta Massif and nearby Serranía del Perijá, and finally the Guajira Peninsula in the

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Caribbean region (Fig. 1).

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The Central and Eastern Cordilleras record subduction-related orogeny that started in

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the late Triassic and continued through the Cretaceous following the initial disruption of

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Pangaea and re-organization of the convergent margin after a major phase of slow and

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oblique subduction of the Pacific plates during the Triassic (Mpodozis and Ramos, 2008;

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Spikings et al., 2015, 2016). Since the late Cretaceous, oblique convergence of South

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America with the Caribbean plate produced the present distribution of uplifts and basins in

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northwestern Colombia, with considerable tectonic offset, rotation and uplift of basement

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massifs in the Caribbean region including the SMM and the Guajira Peninsula (Muessig,

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1984; Kellogg, 1984; Macellari, 1995; Montes et al., 2010; Mora-Bohórquez et al., 2017).

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The triangular Santa Marta Massif is part of the northern termination of the Andean chain

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against the Caribbean plate, a region in which the linear continuity of the Andean belt

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changes to a series of isolated massifs separated by major faults and Cenozoic basins. The

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Santa Marta Massif is bounded by three regional fault systems (Figs. 1 and 2): the Oca Fault

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in the north, a dextral strike-slip fault with a vertical component; the sinistral Santa Marta -

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Bucaramanga fault system in the west, and the Cesar Lineament in the southeast which is

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linked to thrusting of the adjacent Serranía del Perijá over the SMM during the Cenozoic

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(Tschanz et al., 1974; Kellogg, 1984; Idárraga-García and Romero, 2010; Montes et al.,

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2010). Internally, the SMM is divided into three NE-SW trending provinces (Tschanz et al.,

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1974). The Santa Marta Province in the northwest is a Late Cretaceous metamorphic belt of

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greenschist to amphibolite facies mafic schists (Cardona et al., 2010b). The adjacent Sevilla

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Province is made up of amphibolites, migmatites, mica schists and mylonitized Permian

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granitoids (Tschanz et al., 1974; Cardona et al., 2010a). The Santa Marta and the Sevilla

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Province are intruded by Late Paleocene to Eocene plutons (Cardona et al., 2011). The

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Sierra Nevada Province in the southeastern SMM is the largest of the three. It comprises a

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basement of Neoproterozoic (Grenvillian) granulite to upper amphibolite facies rocks

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(Tschanz et al., 1974; Cordani et al., 2005), which are intruded and covered by Jurassic

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granitoids and volcanic rocks (Tschanz et al., 1974). Poorly-dated outcrops of Mesozoic

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volcanoclastic rocks intercalated with clastic, calcareous and pyroclastic rocks are also found

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(Tschanz et al., 1974; Gómez and Kammer, 2017). These units are unconformably overlain

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by Aptian to Paleogene sedimentary rocks (Tschanz et al., 1974; Bayona et al., 2011). This

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study of Jurassic magmatism focuses on the Sierra Nevada Province.

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This study is based on a set of 115 rock samples representing plutonic, sub-volcanic and

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volcanic units collected during regional mapping along 13 transects distributed across the

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Sierra Nevada Province of the SMM (Invemar and Geosearch, 2007). After petrographic

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examination, 79 samples were used for geochemical analyses and subsets of these were

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selected for radiogenic isotope (Sr and Nd: n=32, Pb: n=28) and for U-Pb zircon dating

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(n=12). Based on variations in K-feldspar contents and apparent depth of emplacement,

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Tschanz et al. (1974) divided the Jurassic plutonic rocks of the SMM into a Central and a

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Southeastern Belt. Both of these areas are included in our sample coverage. We emphasize

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that this is a regional-scale study and that sampling is not adequate for investigating the

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compositional variations and petrogenesis of individual units. Descriptions of analytical

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methods used for whole-rock major and trace element analyses, Sr, Nd and Pb isotope

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measurements, and zircon U-Pb age determination are given in the Appendix. The sample

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numbers, location coordinates and petrographic descriptions are given in supplementary

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table A1, the zircon U-Pb data are in supplementary table A2, and all geochemical analyses

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are reported in supplementary table A3.

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The Jurassic igneous rocks in the SMM, both plutonic and volcanic, are dominated by

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intermediate to felsic compositions with SiO2 > 57 wt.%. Mafic rocks with basalt and basaltic

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andesite compositions are much less common, but they have special significance for

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understanding the mantle component involved in the Jurassic magmatism (see section 6.1).

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For some descriptions that follow it is helpful to treat the mafic and felsic rocks separately,

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using a cutoff value of 57 wt.% SiO2 (normalized volatile-free) to divide them. These two

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groups are referred to as the mafic and felsic suites, and are represented by 10 and 69

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samples, respectively. The grouping is for descriptive purpose only and it does not imply a

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separation between the groups in terms of magma origin (see section 5.3.1).

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5.1

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5.1.1 Rocks of the felsic suite

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The felsic plutonic rocks contain various proportions of quartz, plagioclase and K-feldspar

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(typically orthoclase with local patchy microcline). The mafic silicates are mainly hornblende

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and biotite with modal proportions of 2-20 % and 1-15% respectively (see supplement table

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A1). Rock textures are typically medium-to coarse-grained, equigranular to seriate. Patches

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of myrmekite are common, graphic intergrowths of quartz and orthoclase occur in some

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granite samples. Typical accessory minerals are magnetite (up to 1.6 vol.%), zircon, titanite,

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allanite and apatite. Secondary minerals include chlorite, epidote, sericite and calcite.

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Petrography

The felsic volcanic rocks (mostly lavas, exceptionally ignimbrite tuff) and dikes

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classify as rhyolites and dacites on the total alkali-silica diagram (Fig. 4a). The samples are

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typically porphyritic, rarely aphyric and some display flow texture. The phenocrysts comprise

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plagioclase, alkali feldspar and subordinate quartz, with biotite and amphibole as the main

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mafic minerals. The biotite and amphibole are commonly altered to chlorite, epidote and

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opaque minerals, locally hematite. Feldspar phenocrysts are affected by sericitization and

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epidotization. The matrix is predominantly microcrystalline and composed of intergrowths of

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quartz and feldspar with high proportions of chlorite and epidote. The tuff samples contain

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the same phenocryst assemblage as the lavas, but these are set in a partially to totally

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devitrified matrix containing lithic fragments and glass shards.

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5.1.2 Rocks of the mafic suite

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Mafic rocks are not abundant in the sample suite, and they are about equally distributed

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between plutonic rocks (diorite, quartz-diorite, monzodiorite) and volcanic rocks (basaltic

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andesites, basaltic trachy-andesites, tephrite and trahchy-basalt). The plutonic samples are

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medium-grained, equigranular rocks some showing protoclastic textures and oriented fabric.

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Quartz and K-feldspar are typically present (2-13 and 3-6 vol. %, resp.), but the rocks are

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dominated by plagioclase (45-63 vol.%) and 30 to 40 vol.% of mafic silicates, which are

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typically hornblende and biotite but locally also clinopyroxene. Primary minor minerals are

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titanite, apatite and opaque phases, whereas epidote and chlorite are common secondary

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minerals.

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The mafic volcanic rocks have porphyritic textures with microcrystalline, typically

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strongly altered, matrix. Some samples display flow textures. The phenocryst assemblage is

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mainly plagioclase, hornblende and/or pyroxene, but in many cases the mafic phenocrysts

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are replaced by epidote and chlorite. The matrix phases include hornblende, opaque

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minerals, chlorite, epidote, apatite and locally quartz and K-feldspar.

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5.2

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Zircon grains separated from twelve samples were dated by the U/Pb LA-ICP-MS technique,

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with typically about 30 grains or sub-grains being analyzed in each sample. A total of 396

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spots were measured, and the data were processed using the ISOPLOT 4.15 program of

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Ludwig (2009). The results are summarized on Table 1 and Figure 3, and the full data set is

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given in supplement Table A2. More than 90% of the zircon analyses yielded concordant

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ages within the weighted mean value of the respective sample (supplement Table A2), but

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there are several cases of Paleozoic and Neoproterozoic ages in granitic samples (e.g.,

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EAM-20-121L) that match the basement ages in the region (Cordani et al., 2005; Cardona et

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al., 2010a), and are interpreted at inherited zircon. Due to the low contents of

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higher measurement uncertainty relative to

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weighted mean values of

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total) that yielded significantly older or discordant ages (see supplement table A2). The

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preferred ages (Table 1) range from 176.0 ± 0.9 Ma to 191.1 ± 1.4 Ma (errors are at 2 sigma

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level). The three volcanic samples yielded ages from 176.0 ± 0.9 Ma to 187.2 ± 1.0 Ma.,

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which is in the same range as the plutonic and dike samples (178.9 ± 1.1 to 191.1 ± 1.4 Ma).

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The U-Pb ages are much less variable than the K-Ar ages (129-183 Ma) reported by

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Tschanz et al. (1974) and Bayona et al (2010), and they overlap with the upper end of the K-

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Ar range, confirming the suggestion that some K-Ar ages reflect cooling, resetting or

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hydrothermal events. The U-Pb ages are in agreement with two U-Pb dates of Leal-Mejía

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(2011) from the SW part of the SMM (179 and 183 Ma).

Pb and

Pb, the sample ages were calculated as the

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U ages, neglecting the few points (about 10% of the

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5.3

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The whole-rock SiO2 contents of the Jurassic igneous rocks from the SMM vary between 45

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and 78 wt.%. Most samples show weak to moderate evidence of alteration, which is typically

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stronger in the volcanic rocks than in the plutonic ones. However, the values of loss-on-

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ignition (LOI) are rarely above 2 wt. % and there are no systematic correlations of fluid-

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mobile elements with LOI (e.g. Na, K, Rb) to suggest that alteration has strongly affected the

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rock compositions. Nevertheless, for the major-element plots and description that follow we

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use recalculated values normalized to 100% on a volatile-free basis. On many of the plots we

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also show a compositional field from published data for other Jurassic and Late Cretaceous

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units in the Central Cordillera of Colombia and northern Bolivia (Segovia Batholith, Ibagué

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Batholith, Rosa Florida Batholith, Abitagua Batholith, Zamora Batholith: Cochrane et al.,

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2014; Ibagué Batholith, Mariquita Stock, Payandé Stock: Bustamante et al., 2016; Mocoa

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Batholith: Zapata et al., 2016) and from the Eastern Cordillera (Santander Massif: van der

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Lelij et al., 2015; Guajira Peninsula: Zuluaga et al., 2015). For these comparisons, we

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ignored analyses with LOI > 5 wt.% to avoid possible bias due to alteration.

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ACCEPTED MANUSCRIPT 5.3.1 Major-element variations

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The major-element variations of the SMM samples are shown with SiO2 on the X-axis as a

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differentiation index. Different symbols designate volcanic and dike rocks vs. plutonic rocks,

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whereas the separation of felsic and mafic suites is implied by the cutoff value of 57 wt.%

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SiO2. The classification fields shown on the total alkali - silica diagram (Fig. 4a) apply only to

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volcanic rocks, which span the range from basalt to rhyolite, but the compositional range of

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plutonic samples is only slightly narrower and there is no gap between the two groups. Most

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samples plot in the medium-K and high-K fields of Gill's (1981) diagram for arc-related

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magmas (Fig. 4b). The plots of SiO2 with MgO and Al2O3 (Figs. 4c, 4d) show systematic

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trends among these components that are consistent with magmatic differentiation, whereby

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the kinked trends, highlighted by dashed lines, presumably reflect different crystallizing

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assemblages. The felsic suite is plotted separately on granitic magma classification plots on

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Figure 5. The SMM samples plot at the transition between the metaluminous and

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peraluminous fields in terms of molar A/CNK and A/NK components (defined in caption Fig.

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5a) and there is a complete overlap with the compositional field for other Jurassic massifs in

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Colombia (data sources in caption). Figure 5b shows the composition of felsic samples on

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the trace-element tectonic discrimination plot of Pearce et al. (1984), where all samples from

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the SMM and those from other massifs in Colombia plot within the Volcanic Arc (VAG) field.

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5.3.2 Trace-element features

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An overview of trace element variations in the SMM igneous rocks is shown on primitive

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mantle - normalized multi-element plots in Figure 6 and chondrite-normalized REE plots in

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Figure 7 (normalizing values for both from McDonough and Sun, 1995). A comparison with

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trace-element compositions of other Colombian Jurassic massifs is also shown (all > 57 wt.%

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SiO2; data sources in the caption to Fig. 4). Important features of the trace-element

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distributions are:

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1) the pronounced negative anomalies of Nb and Ta in all samples from the SMM as well as

280

the other Colombian Jurassic massifs, which are typical for subduction-related magmas,

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support the arc assignment based on Figure 5b;

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2) the strong compositional similarity between the plutonic rocks and the volcanic rocks/dikes

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3) the greater diversity in the felsic suite, which may be due to the larger number of samples

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(69 vs. 10) but also to the presence of highly-differentiated rocks (SiO2 greater than 75

285

wt.%);

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4) the low MREE/HREE ratios in the mafic suite (chondrite-normalized Gd/Yb(cn) = 1.1 to 2),

287

which rule out a significant role of residual garnet in the mantle source (see also section 6.2).

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In general, there is a positive correlation of incompatible trace elements like Rb and

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La with SiO2 in the data set that is consistent with magmatic differentiation. Examples of

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Rb/Sr and La/Sm ratio variations in Figure 8a and 8b respectively, where the similarity with

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ratio (Fig. 8c), which displays a negative correlation with silica in rocks with SiO2 greater than

293

about 70 wt.%). Figure 9 shows the position of the SMM mafic and felsic suites from the

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SMM on a plot of incompatible trace element ratios Nb/Yb vs. Th/Yb compared with the

295

mantle array, average N-MORB, E-MORB and OIB from Pearce (2008), and the field of

296

volcanic arc-related rocks from Pearce and Peate (1995). The SMM mafic suite plots close to

297

the mantle array and overlaps it one case, whereas the felsic suite (and other Jurassic

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massifs) plot above the mantle array in a position typical for continental arcs according to the

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compilation of Pearce and Peate (1995).

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5.4

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The

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with initial Sr and Nd isotope ratios calculated for an age of 180 Ma (designated

304

and εNd180 in the following). Although U-Pb ages range from 176 to 191 Ma (Table 1) we

305

prefer to use a single age for all samples since less than half of them were dated. This

306

introduces no significant bias because the initial εNd values are not sensitive to small age

307

variations for rocks with these compositions. For example, age-corrected εNd values vary by

308

only 0.3 units for a 30 Ma age range. The total range of εNd180 for all samples is -10.3 to 1.9

309

(n=32), but only 2 have positive values and 21 yielded values below -2. The 87Sr/86Sr180 ratios

310

of 29 of 32 samples are between 0.7012 and 0.7071, with one sample below this range at a

311

geologically unreasonable 0.6915 and two above it (0.7160, 0.7469). We attribute the outlier

312

values to post-magmatic change in the Rb/Sr ratio of the samples, leading to over- or

313

underestimation of the age correction. The 3 outliers are listed in parenthesis on Table 2.

Sr/86Sr and

143

Nd/144Nd ratios from the Santa Marta Massif are reported on Table 2 87

Sr/86Sr180

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Sr-Nd-Pb isotopic composition

Figure 10a displays the SMM data on a Sr-Nd isotope plot with comparison to the

315

field of basement rocks, which covers late Paleozoic granites and granitic gneisses in the

316

Central Cordillera (Vinasco et al., 2006) as well as Neoproterozoic gneisses and granulites

317

from the Eastern Cordillera (Ordóñez-Carmona et al., 2006). Also shown for comparison are

318

data from Early Cretaceous mafic intrusions in the Eastern Cordillera of Colombia (Vásquez

319

et al., 2010), and from the Jurassic arc in the Chilean coastal ranges (Lucassen et al., 2001).

320

With 2 exceptions, the SMM data plots in the enriched quadrant of the Sr-Nd isotope plot

321

(high

322

correlation between Sr and Nd initial ratios, which may be due to greater sensitivity of Sr and

323

Rb to alteration than Sm and Nd. Most published studies of other Jurassic massifs in

324

Colombia report only Nd isotope ratios (Cochrane et al., 2014; Bustamante et al., 2016;

325

Zapata et al. 2016) and cannot be compared on Fig. 10a. Two exceptions are Jurassic

326

volcanic rocks from the Guajira Peninsula studied by Zuluaga et al. (2015), which yielded

327

87

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Sr/86Sr180 and low εNd180 compared to bulk earth). In general, there is a poor

87

Sr/86Sr(180) values very similar to those of the SMM (0.7073 to 0.7077). The comparison of

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εNd180 values of the SMM samples and other Jurassic massifs from the literature is shown in

329

Figure 10b, plotted against the chondrite-normalized La/Sm ratio. The latter increases with

330

differentiation because of the more incompatible behavior of La than Sm (see Fig. 8b), so the

331

lack of correlation between εNd values and La/Sm confirms that the isotope ratios are

332

insensitive to differentiation.

333

The Pb isotope composition of the SMM samples (n=28) is characterized by 206

Pb/204Pb ratios between 18.02 and 19.95,

335

range of

336

the Pb, Sr and Nd isotope ratios are poor for the SMM samples and are not shown. The

337

close correspondence of SMM Pb isotope ratios with those of other Jurassic massifs in the

338

Central and Eastern Cordillera is shown on Figure 11. The Pb evolution curves A, B and C

339

on this plot are from Zartman and Doe (1981) and represent respectively the mantle,

340

“orogenic” crust (i.e., juvenile crust at active margins) and the upper continental crust. The

341

Jurassic rocks correspond best to the “orogenic” curve B, in keeping with other geochemical

342

evidence for an arc affinity of the magmas (see section 6.1).

343

6.

Discussion

Pb/204Pb values from 15.56 to 15.67 and a

345

6.1

Magma diversity and source constraints

346

The mafic and felsic suites from the SMM, including both volcanic and plutonic rocks define

347

similar differentiation trends on major-element variation diagrams (Fig. 4) and there are no

348

compositional gaps between them. Some of these chemical variations may be explained by

349

fractional crystallization but there are significant differences in the radiogenic isotope ratios

350

among the samples (Fig. 10a) which, along with their age differences, show that the SMM

351

igneous units are not part of a single comagmatic series. Very likely there are more than one

352

magma types involved in the igneous units of the SMM., but the sampling coverage does not

353

permit a discussion of specific units and their relation to one another. Instead, we treat the

354

SMM data as a group and the discussion focuses on their significance in the regional context

355

of Jurassic magmatism in northern Colombia.

Pb/204Pb from 37.76 to 39.04 (Table 3; not age-corrected). Correlations among

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The geochemical compositions of the Jurassic rocks in the SMM, other units from the

357

Central Cordillera and those in Eastern Colombia have in common an arc affinity and a

358

predominance of intermediate to felsic compositions. Constraining the magma source in

359

continental arc magmas is complicated by processes related to magma evolution

360

(differentiation and crustal assimilation) as well as magma mixing. The most direct

361

constraints on magma source are thus expected from the least-evolved samples, i.e. from

362

the SMM mafic suite On the discrimination plot of oceanic and arc magma sources based on

363

Nb/Yb vs. Th/Yb ratios (Fig. 9), the mafic suite (black symbols) plots close to the mantle

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array whereas the felsic suite and the other Jurassic massifs in Colombia fall outside that

365

range. On the Sr-Nd isotope diagram (Fig. 10a) 3 samples are from the mafic suite (black

366

squares) and they have εNd180 values of 0, -3.1 and -3.3, with

367

0.7066. The mafic samples and most of the felsic suite as well, plot in the enriched quadrant

368

of the Sr-Nd isotope plot (high

369

isotopic signatures can result from crustal contamination, but the fact that the mafic samples

370

also have enriched signatures suggests that this is a feature of the mantle source. This

371

implies that the depleted mantle was not the predominant source for the SMM Jurassic

372

magmas.

87

Sr/86Sr180 from 0.7055 to

Sr/86Sr180 and low εNd180 compared to bulk earth). Enriched

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The comparison with published data from other Jurassic massifs on the Sr-Nd isotope

374

plot is limited to the Nd-isotope ratios (Fig. 10b), and they show an important difference. All

375

but two SMM samples yielded εNd180 values below zero (0.0 to -10.3, n=30), and the same is

376

true for other Jurassic massifs in the Eastern Cordillera (Santander, Guajira massifs, see Fig.

377

1). In contrast, all available data from Jurassic massifs in the Central Cordillera and

378

Magdalena Valley (stars on Fig. 10b) show positive εNd180 values (0.5 to 5.6, n=14). This

379

contrast is not an artifact of the age correction in calculating initial Nd isotope ratios since an

380

age difference of 30 Ma shifts the εNd value in these samples by only 0.3 units. Whether the

381

contrast in Nd-isotope ratio between the two regions is a feature of the mantle source or to

382

differences in crustal contamination is not easy to distinguish, especially in light of the

383

complex terrane amalgamation that affected NW Colombia before and during establishment

384

of the Jurassic arc. There is no direct information about the mantle composition on a regional

385

scale from xenolith studies or other means, so differences in the primary source cannot be

386

evaluated at present. As far as crustal influence is concerned, one factor that may be

387

important is the difference in the age and composition of the basement. Autochthonous

388

Precambrian basement is present in the Eastern Cordillera but lacking in the Central

389

Cordillera (see section 2). On the other hand, there is no difference in the Pb-isotope

390

composition of SMM Jurassic rocks compared with the range of other Jurassic massifs (Fig.

391

11), implying that all are dominated by Pb derived from the same kind of source regardless of

392

location and age. With reference to the model curves of Zartman and Doe (1981), the source

393

is mostly of the “orogenic” or arc-type juvenile crust (curve B), with a contribution from more

394

radiogenic lead of the upper continental crust (curve C). Crustal contamination is confirmed

395

by the pre-Jurassic zircons found in some SMM samples (see section 5.2 and supplement

396

Table A2). The high Pb concentration in crust vs. mantle rocks means that Pb isotope

397

compositions of arc magmas is dominated by the crustal component, and the narrow Pb-

398

isotope range of the Jurassic massifs in Colombia implies a uniform crustal composition with

399

respect to Pb. If this is also true for Nd isotopes, the contrast shown in Figure 10b may be

400

explained by a change in the mantle vs. crustal input to the magmatism with time. Older

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ACCEPTED MANUSCRIPT magmas, related to onset of subduction, will have variable input from asthenospheric,

402

lithospheric and crustal sources, whereas later magmas in a more mature arc may have a

403

different, possibly more constant mixture of sources as the system is closer to a steady state.

404

Bustamante et al. (2016) suggested there may be less crustal input with time as the crust

405

becomes more refractory and less fertile for melting. Added to that may be the overall shift to

406

a more mafic crustal composition with time due to the continued intrusion by mantle-derived

407

magma (Annen and Sparks, 2002).

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6.2

410

The new U-Pb dating of the SMM igneous units confirms an early Jurassic age for

411

magmatism in northern Colombia and the geochemical features of these rocks indicate an

412

arc setting, supporting the concept that an Early Jurassic continental arc extended

413

throughout Colombia (Aspden et al., 1987). In addition to the arc affinity of the SMM

414

magmatism, the trace-element data also give some insights on the crustal thickness. This is

415

based on the high-pressure stability range of garnet, and its affinity for Y and Yb. Empirical

416

studies in arcs with known Moho depth demonstrated a good correlation of the Sr/Y and

417

La/Yb ratios of arc rocks with crustal thickness (Charadia, 2015; Profeta et al., 2015;

418

Chapman et al., 2015). The SMM data set suggests that the Sr/Y ratio is better suited than

419

La/Yb as an index for crustal thickness because the correlation between Sr and Y is higher

420

than for La and Yb, implying that the La/Yb is more affected by differentiation or post-

421

emplacement processes (see also Profeta et al. 2015). The Sr/Y is also affected by

422

differentiation, but only at high levels of SiO2 (Fig. 8c). To minimize the influence of magma

423

evolution and alteration on the Sr/Y ratio, we limited samples to a range of SiO2 from 55 to

424

70 wt.%, Rb/Sr from 0.05 to 0.2 and LOI values below 2 wt.%. The 23 samples that pass this

425

filter have Sr/Y values of 19 to 37, which correspond to paleodepth values of 30 to 50 km

426

according to the empirical relationship in Profeta et al. (2015). This range is characteristic of

427

a normal to moderately thickened continental crust, suggesting that the Jurassic arc was built

428

on a crust that had not been significantly thinned by previous extension.

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Jurassic magmatism in a regional context

The range of U-Pb ages for the Jurassic magmatism from the Colombian Andes is

430

shown in a frequency histogram in Figure 12. If we include the youngest ages from igneous

431

units in the Central Cordillera (Mariquita Stock: Bustamante et al., 2016) the total span of

432

ages in the Colombian Andes and the Caribbean region together is about 80 million years,

433

from 210 to 130 Ma. Importantly, there is a spatial pattern in the distribution of ages with the

434

region. There is a peak of activity from about 200 to 180 Ma that affected the eastern part of

435

the Central Cordillera as well as the Eastern Cordillera. This can be related to a change in

436

plate motions at the western margin of South America at that time. Global plate

437

reconstructions indicate north-northeast displacements of the South American, Phoenix and

12

ACCEPTED MANUSCRIPT Farallon plates prior to about 200 Ma and a shift to westward-displacement of the South

439

American plate between 200 Ma and 180 Ma (Seton et al., 2012). This caused a re-

440

organization of the subduction zone, promoting more vigorous mantle flow and enhanced

441

melting of asthenospheric and lithospheric mantle beneath the margin, with additional heat

442

input to the crust. The younger ages of Jurassic arc activity, i.e., less than about 170 Ma, are

443

preferentially found near major NNE trending fault zones in the eastern margin of the Central

444

Cordillera and the Magdalena Valley (e.g., the Palestina, Ibaqué, Otu faults, Fig. 1). These

445

fault systems mark boundaries between the Quebrada Grande Complex (e.g. Gómez et al.,

446

2007) or Tahamí Terrane (Feininger et al., 1972; Restrepo and Toussaint, 1988) with Permo-

447

Triassic metamorphic ages and the Grenvillian metamorphic basement of the Chibcha

448

Terrane (e.g Restrepo and Toussaint, 1988). The faults are probably related to the Jurassic

449

tectonic reorganizations and changes in convergence obliquity described above. A reason for

450

the association of younger ages with major faults can be that the faults facilitated continued

451

emplacement of magmas in this part of the Central Cordillera. For example, Bustamante et

452

al. (2016) and Rodriguez et al. (2017) attributed contrasting ages within the Ibagué Batholith

453

(ca. 140 Ma vs.180 Ma) to their locations relative to the Ibagué fault. A westward shift of

454

Jurassic magmatism with time was attributed to slab rollback and/or trench retreat by

455

Spikings et al. (2015) based on data from the Eastern and Central Cordilleras. Whatever its

456

underlying cause may be, the evidence for a westward-younging trend is now stronger with

457

addition of the SMM age results from this study, which more than doubles the coverage from

458

the Eastern Cordillera. Further support comes from U-Pb dating of rocks in central and

459

southern Colombia by Ródriguez et al. (2016, 2017) and by Chinchilla and Vlach (2017).

460

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461

7

462

This study of Jurassic igneous units in the SMM, combining whole-rock geochemical

463

analyses, Sr-Nd-Pb isotope determinations and in-situ U-Pb dating of zircon, confirms and

464

refines the suggestion that the igneous rocks in the SMM are part of a regional Jurassic

465

magmatic arc exposed in discontinuous outcrops from the Central and Eastern Cordilleras of

466

Colombia. The new U-Pb ages for the SMM units range from 176 ± 1 Ma to 191 ± 1 Ma. The

467

data establish the presence of subduction-related magmatism in the northern Andes by at

468

least in the Early Jurassic. Published data from Central Cordillera overlap with the ages from

469

the SMM, and also extend to younger ages, as young as about 130 Ma. The comparison of

470

all age data suggests that magmatism become more spatially localized in the Central

471

Cordillera toward the Late Jurassic, possibly related to slab roll-back as the arc matured.

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Conclusions

472

The Jurassic plutonic rocks, subvolcanic dikes as well as lavas and pyroclastic

473

volcanic units in the SMM span a compositional range from 44 to 77 wt.% SiO2, with a

474

dominance of intermediate compositions. The rocks have a calc-alkaline, medium to high-K

13

ACCEPTED MANUSCRIPT metaluminous affinity typical for continental arc magmas. The arc affinity is further

476

demonstrated by negative Nb-Ta anomalies on mantle-normalized trace element diagram

477

and by Pearce et al. (1984) granite discrimination plots. There is no systematic difference in

478

composition between the plutonic and volcanic units in the SMM although the volcanic rocks

479

tend to have higher degree of alteration. The major and trace element compositions of the

480

SMM rocks overlap with the range of other Jurassic arc units from Colombia. The initial Sr

481

isotope ratios calculated at 180 Ma are between 0.7012 and 0.7071 (n=29), with 3 outliers

482

attributed to post-magmatic mobilization of Rb and/or Sr. Nearly all SMM samples have

483

negative εNd(180) values between -10.3 and 0.0 (n=30), the two exceptions being only slightly

484

positive (1.1 and 1.9). Negative εNd(180) values are typical for the Jurassic magmas in other

485

parts of the Eastern Cordillera (Santander massif, Guajira Peninsula), but in contrast, the

486

Jurassic rocks from the Central Cordillera have neutral to positive εNd(180) values (0 to 5).

487

This indicates a regional difference in the composition of the magma source, which we

488

believe is most readily explained by a greater contribution of lithospheric mantle and crustal

489

assimilation in the arc magmas towards the east. The east-west variation in Nd isotope ratio

490

can be explained by a greater maturity of stronger focus of the arc magmatism in the west,

491

where depleted, asthenospheric mantle plays a stronger role. The Pb isotope ratios of all

492

SMM samples are very similar and they overlap completely with those of Jurassic

493

counterparts in the Central Cordillera. We attribute this uniformity of Pb-isotope composition

494

to a dominance by the crustal component, which does not vary regionally from west to east.

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8

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Sampling for this project was funded by Ingeominas (Servicio Geológico Colombiano),

498

Instituto Colombiano del Petroleo and Invemar. A field geologist group of Geosearch Ltda

499

and STRI contributed to sampling during the 2006-2007 field seasons. We thank

500

COLCIENCIAS for financial support and travel support for international exchange in 2014. C.

501

Bustamante is acknowledged for help with data handling and major discussions on the

502

Jurassic magmatism. We also thank Patricia Larrea Márquez and Mauricio Ibañez-Mejia for

503

detailed, constructive reviews that led to many improvements of the paper.

504

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Acknowledgements

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Annen, C., Sparks, R.S.J., 2002. Effects of repetitive emplacement of basaltic intrusions on thermal evolution and melt generation in the crust. Earth and Planetary Science Letters, v. 203, no. 3–4, p. 937–955. Aspden, J.A., McCourt, W.J., Brook, M., 1987. Geometrical control of subduction-related magmatism: the Mesozoic and Cenozoic plutonic history of Western Colombia. Journal of the Geological Society, London, 144, 893-905. Bayona, G., Rapalini, A., Costanzo-Alvarez, V., 2006. Paleomagnetism in Mesozoic rocks of the Northern Andes and its Implications in Mesozoic Tectonics of Northwestern South America. Earth Planets Space, 58, 1255-1272.

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Feininger, T., Barrero, D., Castro, N., 1972. Geología de Antioquia et Caldas–Sub-zona II-B. Boletin Geología Bogota 20, 173. Galer, S.J.G., and Abouchami, W., 2004. Mass bias correction laws suitable for MC-ICP-MS measurement: Geochimica et Cosmochimica Acta, 68, A542. Gehrels, G.E., Valencia, V.A., Ruiz, J., 2008. Enhanced precision, accuracy, efficiency, and spatial resolution of U-Pb ages by laser ablation–multicollector–inductively coupled plasma–mass spectrometry. Geochemistry, Geophysics Geosystems, 9, Q03017. Gill, J.B., 1981. Orogenic andesites and plate tectonics. Springer-Verlag, Berlin, 390pp. Gómez, J., Nivia, A., Montes, N.E., Jimenez, D.M., Tejada, M.L., Sepulveda, J., Osorio, J.A., Gaona, T., Diederix, H., Uribe, H., Mora, M., 2007. Geological map of Colombia. Escala 1:1000.000. Ingeominas, 2nd Edition, Bogota. Gómez, C., and Kammer, A., 2017. Evolución tectónica y estratigráfica de margen pasivo a activo en el margen caribeño colombiano durante la separación de Pangea. Memoria XVI Congreso Colombiano de Geología, Santa Marta, 1831-1832. Ibañez-Mejía, M., Ruiz, J., Valencia, V. A., Cardona, A., Mora, A. R., 2011. The Putumayo Orogen of Amazonia and its implications for Rodinia reconstructions: New U–Pb geochronological insights into the Proterozoic tectonic evolution of northwestern South America. Precambrian Research, 191, 58-77. Idárraga-García, J., Romero, J., 2010. Neotectonic study of the Santa Marta Fault System, western foothills of the Sierra Nevada de Santa Marta, Colombia. Journal of South American Earth Sciences 29, 849-860. Invemar, Ingeominas, Ecopetrol, ICP and Geosearch Ltda, 2007. Mapa Geologico de la Sierra Nevada de Santa Marta: Santa Marta. Esc: 1:200.000. Kellogg, J.N., 1984. Cenozoic tectonic history of the Sierra de Perijá, Venezuela-Colombia, and adjacent basins. Geological Society of America Memoir, 162, 239-261. Le Maitre, R.W., Streckeisen, A., Zanettin, B., Le Bas, M.J., Bonin, B., Bateman, P., Bellieni, G., Dudek, A., Efremova, S., Keller, J., Lameyre, J., Sabine, P.A., Schmid, R., Sørensen, H., Wooley A.R., 2002. Igneous rocks: A classification and glossary of terms. Cambridge University Press, Cambridge, UK, 236pp. Leal-Mejía, H., 2011. Phanerozoic gold metallogeny in the Colombian Andes: A tectonomagmatic approach. PhD Thesis. University of Barcelona. Lucassen, F, Becchio, R., Harmon, R., Kasemann, S., Franz, G., Trumbull, R., Wilke, H.-G., Romer, R.L, Dulski, P., 2001. Composition and density model of the continental crust at an active continental margin - the Central Andes between 21° and 27°S. Tectonophysics, 341, 195-223. Ludwig, K.R., 2009. Isoplot: A Geochronological Tool Kit for Microsoft Excel. Berkeley Geochronology Center, Berkeley, CA, Special Publications 4, 76 pp. Macellari, C.E., 1995. Cenozoic Sedimentation and Tectonics of the Southwestern Caribbean Pull-Apart Basin, Venezuela and Colombia. In: Tankard, A.J., Soruco, R.S., Welsink, H.J. (Eds.), Petroleum Basins of South America: American Association of Petroleum Geologists Bulletin, 62, 757-780. Maniar, P.D. and Piccoli, P.M. 1989. Tectonic discrimination of granitoids. Geological Society of America Bulletin, 101, 635-643. Maze, W.B., 1984. Jurassic La Quinta Formation in the Sierra de Perijá, northwestern Venezuela: Geology and tectonic environment of red beds and volcanic rocks. In: Bonini, W.E., Hargraves R.B., Shagam, R. (Eds.), The Caribbean-South American Plate Boundary and Regional Tectonics. Geological Society America Memoir, 162, 263-282. McDonough, W.F., Sun, S.-S., 1995. Composition of the Earth. Chemical Geology, 120, 223253. Montes, C., Guzman, G., Bayona, G., Cardona, A., Valencia, V., Jaramillo, C., 2010. Clockwise rotation of the Santa Marta Massif and simultaneous Paleogene to Neogene deformation of the Plato-San Jorge and Cesar-Ranchería basins. Journal of South American Earth Sciences, 29, 832-848. Mora-Bohórquez, J.A., Ibañez -Mejía, M., Oncken, O., de Frietas, M., Vélez, V., Mesa, A., Serna, L., 2017. Structure and age of the Lower Magdalena Valley basin basement, northern Colombia: New reflection-seismic and U-Pb-Hf insights into the termination of the

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Central Andes against the Caribbean Basin. Journal of South American Earth Sciences, 74, 1-26. Mpodozis, C., Ramos, V., 2008. Tectónica jurásica en Argentina y Chile: extensión, subducción oblicua, rifting, deriva y colisiones? Revista Asociación Geológica Argentina, 63, 481-497. Muessig, K.W., 1984. Structure and Cenozoic tectonics of the Falcón Basin, Venezuela, and adjacent areas. Geological Society America Memoir, 162, 217-230. Ordóñez-Carmona, O., Álverez, J.J.R., Pimentel, M.M., 2006. Geochronological and isotopical review of pre-Devonian crustal basement of the Colombian Andes. J. S. Am. Earth Sci., 21, 372-382. Otamendi, J.E., Ducea, M.N., Tibaldi, A.M., Bergantz, G.W., de la Rosa, J.D., Vujovich, G.I. 2009. Generation of Tonalitic and Dioritic Magmas by Coupled Partial Melting of Gabbroic and Metasedimentary Rocks within the Deep Crust of the Famatinian Magmatic Arc, Argentina. Journal of Petrology, 50, 841-873. Pearce, J.A., 2008. Geochemical fingerprinting of oceanic basalts with applications to ophiolite classification and the search for Archean oceanic crust. Lithos, 100, 14-48. Pearce, J.A., Harris, B.W., Tindle, A.G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology, 25, 956-983. Pearce, J.A., Peate, D.W., 1995. Tectonic Implications of the Composition of Volcanic Arc Magmas. Annual Review of Earth and Planetary Sciences, 23, 251-285. Pindell, J., Kennan, L., 2009. Tectonic evolution of the Gulf of Mexico, Caribbean and northern South America in the mantle reference frame: an update. In: James, K., Lorente, M.A., Pindell, J. (Eds.). The geology and evolution of the region between North and South America. Geological Society of London Special Publication 328, 1-55. Profeta, L., Ducea, M.N., Chapman, J.B., Paterson, S.R., Henriquez-Gonzales, S.M., Kirsch, M., Petrescu, L., DeCelles, P.G., 2015. Quantifying crustal thickness over time in magmatic arcs. Scientific Reports, 5, 17786. Restrepo, J.J., Toussaint, J.F., 1988. Terranes and continental accretion in the Colombian Andes. Episodes 7, 189–193. Restrepo-Pace, P.A., Cediel, F., 2010. Northern South America basement tectonics and implications for paleocontinental reconstructions of the America. Journal of South American Earth Sciences, 29, 764-771. Rodriguez, G., Arango, M. I., Zapata, G., Bermúdez, J. G., 2016. Catalogo de unidades litoestratigráficas de Colombia: Formación Saldaña. 92p. Rodríguez, G., Obando, G., Correa Martínez, A. M., Zapata, G, Correa, T., 2017. Obando, M., Rincón, A. y Zapata, J.P. Redefinición del bloque norte del Batolito de Ibagué con base en nuevos datos de petrografía, litogeoquímica y geocronología U-Pb. Memoria XVI Congreso Colombiano de Geología, Santa Marta, 1437-1442. Romer, R.L., Hahne, K., 2010. Life of the Rheic Ocean: Scrolling through the shale record. Gondwana Research, 17, 236-253. Romer, R.L., Schröder-Smeibidl, B., Heinrich, W., Meixner, A., Fischer, C.O., Schulz, C., 2005. Elemental dispersion and stable isotope fractionation during reactive fluid-flow and fluid immiscibility in the Bufa del Diente aureole, NE-Mexico: Evidence from radiographies and Li, B, Sr, Nd, and Pb isotope systematics. Contribution to Mineralogy and Petrology, 149, 400-429. Seton, M, Müller, R.D., Zahirovic, S., Gaina C., Torsvik, T., Shephard, G., Talsma, A., Gurnis, M., Turner, M., Maus, S., Chandler, M., 2012. Global continental and ocean basin reconstructions since 200 Ma. Earth-Science Reviews 113, 212-270. Spikings, R., Cochrane, R., Villagomez, D., van der Lelij, R., Vallejo, C., Winkler, W., Beate, B., 2015. The geological history of northwestern South America: from Pangaea to the early collision of the Caribbean Large Igneous Province (290–75 Ma). Gondwana Research, 27, 95-139. Spikings, R., Reitsma, J., Boekhout, F., Miskovic, A., Ulianov, Chiaradia, M., Gerdes, A., Schaltegger, U, 2016. Characterization of Triassic rifting in Peru and implications for the early disassembly of western Pangaea. Gondwana Research, 35, 124-143. Stacey, J.S., Kramers, J.D., 1975. Approximation of Terrestrial Lead Isotope Evolution by a

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ACCEPTED MANUSCRIPT 2-Stage Model. Earth and Planetary Science Letters, 26, 207-221. Tschanz, C.M., Marvin, R.F., Cruz, J., Mehnert, H.H., Cebula, G.T., 1974. Geologic evolution of the Sierra Nevada de Santa Marta, northeastern Colombia. Geological Society of America Bulletin, 85, 273-284. van der Lelij, R.J., Spikings, R., Ulianov, A., Chiaradia, M., Mora, A., 2015. Paleozoic to Early Jurassic history of the northwestern corner of Gondwana, and implications for the evolution of the Iapetus, Rheic and Pacific Oceans. Gondwana Research, 31, 271-294. Vásquez, M., Altenberger, U., Romer, R.L., Sudo, M., Moreno-Murillo, J.M., 2010. Magmatic evolution of the Andean Eastern Cordillera of Colombia during the Cretaceous: Influence of previous tectonic processes. Journal of South American Earth Sciences, 29, 171-186. Vásquez, P., Glodny, J., Franz, G., Frei, D., Romer, R. L. 2011. Early Mesozoic Plutonism of the Cordillera de la Costa (34°–37°S), Chile: Constraints on the Onset of the Andean Orogeny. Journal of Geology ,119, 159-184. Villagómez, D., Spikings, R., Magna, T., Kammer, A., Winkler, W., Beltrán, A., 2011. Geochronology, geochemistry and tectonic evolution of Western and Central cordilleras of Colombia. Lithos, 125, 875 – 896. Vinasco, C.J., Cordani, U.G., González, H., Weber, M., Pelaez, C., 2006. Geochronological, isotopic, and geochemical data from Permo-Triassic granitic gneisses and granitoids of the Colombian Central Andes. Journal of South American Earth Sciences, 21, 355–371. Wasserburg G.J., Jacobsen S.B., DePaolo D.J., McCulloch M.T., Wen T., 1981. Precise determination of Sm/Nd ratios, Sm and Nd isotopic abundances in standard solutions. Geochimica et Cosmochimica Acta, 45, 2311-2323. Zapata, L., Cardona, A. Jaramillo, C., Valencia, V., Vervoort, J., 2016. U-Pb LA-ICP-MS geochronology and geochemistry of Jurassic volcanic and plutonic rocks from the Putumayo region (southern Colombia): tectonic setting and regional correlations. Boletin de Geologia, 38, 21-38. Zartman, R.E., Doe, B.R., 1981. Plumbotectonics -The Model. Tectonophysics, 75, 135-162. Zuleger, E., Erzinger, J., 1988. Determination of REE and Y in silicate materials with ICPAES, Fresenius Zeitschrift für Analytische Chemie, 332, 140-143. Zuluaga, C., Pinilla, A., Mann, P., 2015. Jurassic silicic volcanism and associated Continental-arc Basin in northwestern Colombia (southern boundary of the Caribbean plate). In: C. Bartolini and P. Mann (Eds.), Petroleum geology and potential of the Colombian Caribbean Margin. American Association of Petroleum Geologists, Memoir 108, p. 137–160.

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Figure captions

719 720 721 722 723 724 725 726 727 728 729 730 731 732

Figure 1. Sketch map of Jurassic igneous units and major fault systems in the Colombian Andes with previously-published U-Pb ages, modified from Bustamante et al. (2016). The box in the upper right shows the location of Fig. 2 and the U-Pb ages from this study.

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683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717

Figure 2 Geological sketch map of the Santa Marta Massif with the most important units, after Invemar and Geosearch (2007). The sample locations and U-Pb ages from this study are shown. Figure 3. Results of zircon U-Pb geochronology from 12 samples of the SMM using ISOPLOT 4.15 (Ludwig, 2009). In each plot, the vertical bars show 206Pb* / 238U ages with 2sigma uncertainty, ordered by increasing age from left to right. Gray bars mark the rejected values. The horizontal dotted line shows the weighted mean age. MSWD = mean square of weighted deviations. See supplementary table A2 for data.

18

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Figure 4. Major-element chemical variations of the SMM samples. (a) total alkali-SiO2 plot with nomenclature from Le Maitre et al. (2002); (b) K2O-SiO2 orogenic andesite classification of Gill (1981); (c) MgO-SiO2 plot showing kinked differentiation trend highlighted by the dashed line; (d) Al2O3-SiO2 plot showing kinked differentiation trend highlighted by the dashed line. Shaded field outlines compositions of other Jurassic igneous massifs from Colombia (Segovia, Ibagué, Rosa Florida, Abitagua, Zamora batholiths: Cochrane et al., 2014; Ibagué Batholith, Mariquita Stock, Payandé Stock: Bustamante et al., 2016; Mocoa Batholith: Zapata et al., 2016; Santander Massif: van der Lelij et al., 2015; Guajira Peninsula: Zuluaga et al., 2015). See Fig. 1 for locations.

M AN U

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Figure 5. SMM samples of the felsic suite plotted on granite discrimination diagrams: (a) peraluminous, metaluminous and peralkaline discrimination after Maniar and Piccoli (1989) based on ratios of A/NK and A/CNK defined as molar Al2O3/(Na2O+K2O) and Al2O3/(CaO+Na2O+K2O), respectively; (b) trace-element plot of Pearce et al. (1984) discriminating volcanic arc granites (VAG), syn-collisional granites (Syn-COL), within-plate granites (WAG) and ocean-ridge granites (ORG). Shaded field outlines compositions of other Jurassic igneous massifs from Colombia, sources cited in Figure 4. Figure 6. Multi-element contents of the SMM samples normalized to primitive mantle composition of McDonough and Sun (1995). For clarity, data are plotted separately for the mafic suite and for volcanic and plutonic felsic rocks (a, b, d). Plot (c) shows the compositions of other Jurassic igneous massifs from Colombia, with data sources cited in Figure 4.

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Figure 7. Rare-earth-element (REE) contents of SMM samples normalized to C1 chondrite values of McDonough and Sun, (1995). Data are plotted separately for the mafic suite and for volcanic and plutonic felsic rocks (a, b, d). Plot (c) shows the compositions of other Jurassic igneous massifs from Colombia, with data sources cited in Figure 4.

EP

Figure 8. Variation of selected trace-element ratios versus SiO2 as a differentiation index for the SMM Jurassic rocks. The shaded field outlines compositions of other Jurassic igneous massifs from Colombia, with sources cited in Figure 4. The Rb/Sr ratio (a), and the chondritenormalized La/Sm (cn) ratio show a weak positive correlation with SiO2. The Sr/Y ratio (c) decreases with SiO2 in samples above about 70 wt.%, but is otherwise not correlated with differentiation.

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733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781

Figure 9. The SMM Jurassic rocks on the plot of Nb/Yb and Th/Yb after Pearce and Peate (1995) and Pearce (2008) to distinguish oceanic mantle-derived (mantle array) and arcderived magmas. The field for other Jurassic igneous massifs is based on sources cited in Figure 4. See text for discussion. Figure 10. (a) The 87Sr/86Sr180 vs. εNd180 values of SMM Jurassic rocks from this study are shown in comparison with bulk silicate Earth composition (BSE), basement granites and gneisses of the Central and Eastern Cordilleras (Vinasco et al., 2006; Ordóñez-Carmona et al., 2006), Cretaceous mafic intrusions from the Eastern Cordillera (Vásquez et al., 2010) and Jurassic arc rocks from the Coastal Cordillera of Chile (Lucassen et al., 2001). (b) The εNd180 values vs chondrite-normalized La/Sm ratio of SMM rocks plotted with the field of other Jurassic igneous massifs from Colombia cited in Figure 4. The analytical uncertainty of isotope ratios is smaller than the symbol sizes.

19

ACCEPTED MANUSCRIPT Figure 11. Pb isotope data from the SMM and other Jurassic massifs in Colombia (sources cited in Fig. 4) on a plot of 206Pb/204Pb vs. 207Pb/204Pb. The lines A, B and C are Pb evolution curves for mantle, orogenic crust (active continental margin) and upper crust, respectively, from Zartman and Doe (1981). Analytical uncertainty of isotope ratios is smaller than the symbol sizes.

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Figure 12. (a) Frequency histogram of U-Pb zircon dates of magmatic rocks from the Central and Eastern Cordilleras of Colombia (white and gray bars, resp.) compared with SMM ages from this study; (b) plot of ages vs. longitude for igneous rocks in the Central Cordillera (white triangles) and Eastern Cordillera (gray squares). Data sources: Bustamante et al. (2010, 2016), Cochrane et al. (2014), van der Lilij et al. (2015), Villagómez et al. (2011), Zuluaga et al. (2015).

SC

782 783 784 785 786 787 788 789 790 791 792 793 794

Appendix 1 - Methods

796

A-1: U-Pb geochronology

797

Zircon U/Pb isotopic analyses were obtained at the Arizona LASERCHRON laboratory

798

following procedures described by Gehrels et al. (2008). Unknowns and standard zircons

799

were mounted together in polished epoxy grain mounts and analyzed with a Micromass

800

Isoprobe multicollector ICP-MS equipped with an ArF Excimer laser ablation system, which

801

has an emission wavelength of 193 nm. The laser was operated with an output energy of 32

802

mJ (at 23 kV) and a pulse rate of 9 Hz, with a beam diameter of 30-50 micrometers. The

803

collector configuration allows measurement of

804

207

805

analyses were conducted in static mode. Each analysis consisted of a 20-s integration on

806

peaks with no laser firing and twenty 1-s integrations on peaks with the laser. Hg contribution

807

to the

808

element fractionation was monitored by analyzing an in-house zircon standard, which has a

809

concordant TIMS age of 564 ± 4 Ma (2 sigma; Gehrels et al., 2008). This standard was

810

analyzed once after every four unknowns. Uranium and Th concentrations were monitored

811

by analyzing NIST 610 Glass, with 500 ppm Th and U. The lead isotopic ratios were

812

corrected for common Pb, using the measured

813

composition according to Stacey and Kramers (1975) and uncertainties of 1.0, 0.3 and 2.0

814

for

815

the age results was done with ISOPLOT 4.15 (Ludwig, 2009).

Th and

TE D

Pb,

206

Pb in the ion-counting channel while

206

Pb,

238

U are simultaneously measured with Faraday detectors. All

204

Pb mass position was corrected by subtracting on-peak background values. Inter-

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Pb,

232

204

EP

208

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795

Pb/204Pb,

207

Pb/204Pb, and

204

Pb values and assuming an initial Pb

208

Pb/204Pb, respectively. Statistical analysis and plotting of

816 817

A-2. Whole rock geochemistry

20

ACCEPTED MANUSCRIPT 818

The chemical composition of the samples was determined in three different laboratories, i.e.,

819

GFZ German Research Center for Geosciences (GFZ) in Potsdam, University Potsdam

820

(UP), and Acme Analytical Laboratories Ltd. (ACME) in Vancouver. GFZ: Samples were analyzed with methods described by Vásquez et al. (2011),

822

using a Phillips PW-2400 x-ray fluorescence (XRF) spectrometer at GeoForschungsZentrum

823

Potsdam, Germany (GFZ). Major and some trace elements (Ba, Ga, Rb, Zn, and Sr) were

824

determined on fused lithium-tetraborate disks, whereas Cr, Nb, Sc, V, Y and Zr were

825

analyzed on pressed powder pellets. For the XRF analysis, the estimated precision is better

826

than 1-3% for major elements and better than 10% for trace elements. H2O, and CO2 were

827

determined with a Vario EL III CHN elemental analyzer at the GFZ. Analytical accuracy and

828

precision was monitored using internationally accepted rock standards. The concentrations

829

of the REE and Rb, Sr, Y, Zr, Cs, Ba, Hf, Pb, Th, and U were determined by inductively

830

coupled ICP-MS (Perkin-Elmer/Sciex Elan Model 500) at the GFZ using the method of Dulski

831

(1994).

M AN U

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821

UP: Rare earth element (REE) analyses were performed by ICP-OES (Vista MPX) at

833

the Institute of Earth and Environmental Sciences of the University of Potsdam. Rock

834

powders were brought into solution using standard Na2O2 fusion and dilution techniques

835

(Zuleger and Erzinger, 1988). Analytical accuracy of the method is <1%, and the precision

836

for the REE ranges between 5 and 10% based on comparison with international reference

837

standards.

TE D

832

ACME: Major and some trace elements (Ba, Nb, Ni, Sr, Sc, Y and Zr) were analyzed

839

using an ICP emission spectrograph (Jarrel Ash Atom Comb 975), whereas other trace

840

elements, including the REE, were analyzed using an ICP-MS Perkins–Elmer Elan 6000. For

841

both methods a 0.2 g aliquot of powdered rock was mixed in a graphite crucible with 1.5 g of

842

LiBO2 flux and fused at 1050° C for 15 min, then dissolved in 5% HNO3. Analytical quality

843

was monitored by calibration standards and reagent blanks added to the sample sequence.

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844

EP

838

845

A-3. Sr-Nd isotope analyses

846

The Sr and Nd isotope composition was determined in GFZ German Research Center for

847

Geosciences (GFZ) in Potsdam and at the University of Arizona (UA), and these are

848

described separately. Methods at the GFZ laboratory were described by Romer et al. (2005)

849

and Romer and Hahne (2010). Following sample dissolution, Sr was separated using

850

standard cation exchange techniques (Bio Rad AG50 W-X8, 100-200 mesh, 3.8 ml resin) in

851

2.5 N HCl medium. Before elution of the REE with 6 N HCl, Ba was washed out with 2.5 N

852

HNO3 (Romer et al. 2005). Nd was separated from the other REE using standard cation

853

exchange techniques (HDEHP-coated Teflon, 2 ml resin) in 0.18 N HCl and 0.4 N HCl

854

medium, respectively. Sr was loaded on single Ta-filaments and its isotopic composition was

21

ACCEPTED MANUSCRIPT 855

determined on a Thermo-Fisher Triton multicollector mass-spectrometer using a double-jump

856

dynamic multicollection experiment. 87Sr/86Sr values were normalized with

86

857

Repeated measurement of Sr reference material NBS987 gave a

87

858

0.710252±6 (2σ, n=24). Nd was loaded on double Re-filaments and isotopic composition

859

was measured on a Thermo-Fisher Triton multicollector mass-spectrometer using a double-

860

jump

861

146

862

143

dynamic

multicollection

procedure.

143

Nd/144Nd

data

were

Sr/88Sr = 0.1194.

Sr/86Sr value of

normalized

with

Nd=0.7219. Repeated measurement of La Jolla Nd reference material gave a

Nd/

144

Nd value of 0.511858±6 (2σ, n=6).

RI PT

Nd/

144

Analyses at the University of Arizona were performed on rock powders dissolved in

864

Savillex vials using a mixture of hot concentrated HF-HNO3 or alternatively, a mixture of cold

865

concentrated HF-HClO4. The dissolved samples were spiked with the Caltech Rb, Sr, and

866

mixed Sm–Nd spikes (Wasserburg et al., 1981; Ducea and Saleeby, 1998) after dissolution.

867

Rb, Sr, and the bulk of the REEs were separated in cation columns containing AG50 W-X4

868

resin, using 1 N to 4 N HCl. Separation of Sm and Nd was achieved in anion column

869

containing LN Spec resin, using 0.1 N to 2.5 N HCl. Rb was loaded onto single Re filaments

870

using silica gel and H3PO4. Sr was loaded onto single Ta filaments with Ta2O5 powder. Sm

871

and Nd were loaded onto single Re filaments using platinized carbon, and resin beads,

872

respectively. Mass spectrometric analyses were carried out on an automated VG Sector

873

multicollector and a VG Sector 54 instrument fitted with adjustable 1011 W Faraday collectors

874

and a Daly photomultiplier (Otamendi et al., 2009). Concentrations of Rb, Sr, Sm, Nd were

875

determined by isotope dilution, with isotopic compositions determined on the same spiked

876

runs. Typical runs consisted of acquisition of 100 isotopic ratios. The mean result of ten

877

analyses of the standard NRbAAA performed during the course of this study is:

878

2.6123 ± 20. Fifteen analyses of standard Sr987 yielded mean ratios of: 87Sr/86Sr = 0.710265

879

± 7 and

880

performed during the course of this study are:

881

= 0.42130 ± 6. The estimated analytical uncertainties are:

882

0.0011% (2σ),

883

blanks averaged from five determinations were: Rb - 11 pg, Sr - 120 pg, Sm - 2.8 pg, and Nd

884

- 5.7 pg. The Sr isotopic ratios were normalized to 86Sr/88Sr = 0.1194, Nd isotopic ratios were

885

normalized to 146Nd/144Nd = 0.7219.

85

Rb/87Rb =

Sr/86Sr = 0.056223 ± 12. The mean results of five analyses of the standard nSmb

AC C

84

EP

TE D

M AN U

SC

863

147

148

Sm/144Nd = 0.38% (2σ), and

Sm/147Sm = 0.74882 ± 21, and

148

Sm/152Sm

87

Rb/86Sr = 0.36% (2σ), 87Sr/86Sr =

143

Nd/144Nd = 0.0011% (2σ). Procedural

886 887

A-4. Pb isotope analyses

888

Analyses of Pb isotope ratios were done at the University of Arizona. Washes from the cation

889

column in Sr Spec resin (Eichrom, Darien, Illinois) were used for separating Pb. Samples

890

were loaded in 8M HNO3 in the Sr spec columns. Pb elution was achieved via 8M HCl. Lead

891

isotope were analyzed on a GV Instruments multicollector–inductively coupled plasma–mass

22

ACCEPTED MANUSCRIPT spectrometer (MC-ICP-MS) following Drew et al. (2009). Samples were introduced into the

893

instrument by free aspiration with a low-flow concentric nebulizer into a water-cooled

894

chamber. A blank, consisting of 2% HNO3, was run before each sample. Before analysis, all

895

samples were spiked with a Tl solution to achieve a Pb/Tl ratio of ≈10. NBS-981 standard

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was run to monitor the stability of the instrument. All results were Hg corrected and

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empirically normalized to Tl by using an exponential law correction. Results were normalized

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to values reported by Galer and Abouchami (2004) for the NBS-981 standard (206Pb/204Pb =

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16.9405,

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and interlaboratory bias. Internal error reflects the reproducibility of measurements on

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individual samples, whereas external errors are derived from long-term reproducibility of the

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NBS-981 Pb standard and result in part from the mass bias effects within the instrument. In

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all cases, external error exceeded the internal errors; external errors were

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0.027%, 207Pb/204Pb = 0.026%, and 208Pb/204Pb = 0.030%.

Pb/204Pb = 15.4963, and

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Pb/204Pb = 36.7219) in order to correct for machine

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Pb/204Pb =

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Sample Rock Age (Ma) Error (Ma) MSWD N CAS-33-63L Trachyte/trachydacite 176.0 0.9 4.4 33 EAM-20-121L Granodiorite 180.6 1.2 5.8 32 EAM-20-122BL Ignimbrite 187.2 1.0 5.0 38 EAM-20-129BL Felsic dike 190.3 1.2 2.3 31 EAM-27-132L Granodiorite 185.7 1.0 4.8 35 EAM-33-86L Rhyodacite 184.5 1.4 3.9 23 FCB-21-38L Granodiorite 186.0 0.7 2.7 35 JRG-20-81BL Monzogranite 186.4 1.6 10 28 JRG-20-84AL Leucosyenogranite 189.4 2.0 8.9 21 JRG-27-88AL Monzogranite 191.1 1.4 3.5 16 JRQ-19-15L Quartz diorite 178.9 1.1 4.2 30 JRQ-33-75L Monzogranite 182.2 1.0 1.0 7 LA-ICP-MS analyses from the Arizona LASERCHRON Center (University of Arizona, Tucson). Ages were calculated from 206*Pb / 238U ratios, with errors at the 2 sigma level, MSWD = mean square of weighted deviations (see text). For description of analytical procedures and measurement conditions see appendix. Full data are available in supplementary table A2.

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Table 2. Results of Sr and Nd isotope analyses

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147 87 Sample Sm Nd Sm/144Nd 143Nd/144Nd(m) std err (%) ƐNd(180) Rb Sr Rb/86Sr 87Sr/86Sr(m) std err (%) CAS-19-38L 4.4 18 0.151653 0.512519 0.0012 -1.3 7.0 616 0.033 0.705507 0.0013 CAS-26-68L* 3.8 20 n.d. 0.512324 0.0010 -4.3 35 718 0.707474 0.0010 CAS-27-87BL 0.90 5.0 0.109536 0.512403 0.0012 -2.6 124 32 11.22 0.730814 0.0019 CAS-33-63L 4.7 26 0.110943 0.512635 0.0013 1.9 78 344 0.650 0.707103 0.0014 EAM-20-118L 1.7 11 0.093257 0.512344 0.0011 -3.4 90 82 3.160 0.712961 0.0009 EAM-20-119L 2.1 13 0.097204 0.512337 0.0014 -3.6 77 120 1.843 0.709821 0.0014 EAM-20-121L 3.3 17 0.113626 0.512364 0.0011 -3.4 51 484 0.301 0.705989 0.0011 EAM-20-122AL 3.6 18 0.122038 0.512210 0.0013 -6.6 5.9 323 0.488 0.707891 0.0014 EAM-20-122CL 7.9 41.2 0.116613 0.512543 0.0012 0.0 47 471 0.289 0.706466 0.0016 EAM-20-124L 4.2 26 0.099973 0.512370 0.0014 -3.0 94 154 1.764 0.710478 0.0014 EAM-20-129BL 1.0 8.7 0.071989 0.512291 0.0020 -3.9 108 78 3.999 0.713838 0.0012 EAM-26-99L* 1.6 13 n.d. 0.512293 0.0006 -3.9 58 830 0.707045 0.0008 EAM-26-102L 4.7 8.3 0.342145 0.512282 0.0014 -10.3 30.9 405 0.220 0.70825 0.0015 EAM-27-131AL 4.6 27 0.102378 0.512500 0.0015 -0.5 49 363 0.390 0.706390 0.0010 FCB-21-37BL 4.2 26 0.097143 0.512432 0.0009 -1.7 92 425 0.621 0.706782 0.0010 FCB-21-38L 3.4 19 0.105070 0.512431 0.0012 -1.9 76 397 0.547 0.706433 0.0011 FCB-21-39L* 3.6 24 n.d. 0.512433 0.0006 -1.6 111 543 0.706501 0.0010 JRG-13-07L 3.8 15 0.148894 0.512394 0.0011 -3.7 51 585 0.252 0.707219 0.0011 JRG-13-08G* 5.0 17 n.d. 0.512358 0.0006 -5.0 101 584 0.708017 0.0008 JRG-13-42L 4.1 19 0.127539 0.512376 0.0012 -3.5 91 210 1.244 0.708351 0.0010 JRG-20-81BL 3.0 19 0.096981 0.512407 0.0015 -2.2 89 98 2.613 0.710609 0.0018 JRG-20-81CL 2.6 17 0.094360 0.512352 0.0013 -3.2 139 161 2.472 0.712034 0.0010 JRG-33-65BL* 6.6 40 n.d. 0.512579 0.0006 1.1 163 86 0.716490 0.0017 JRQ-19-16L 2.7 16 0.102106 0.512459 0.0020 -1.3 36 651 0.158 0.706046 0.0012 JRQ-26-101L 2.5 23 0.065243 0.512314 0.0009 -3.3 94 310 0.876 0.708671 0.0012 JRQ-26-102L 5.1 27 0.113092 0.512357 0.0011 -3.6 121 279 1.252 0.719161 0.0018 JRQ-26-104L* 6.1 35 n.d. 0.512356 0.0004 -3.4 162 225 0.710585 0.0007 JRQ-26-108BL 0.30 2.7 0.066914 0.512297 0.0011 -3.7 187 32 16.88 0.744383 0.0020 JRQ-26-83BL 4.3 18 0.144498 0.512405 0.0013 -3.3 40 562 0.206 0.706977 0.0011 JRQ-26-90AL 3.2 15 0.125767 0.512103 0.0014 -8.8 72 98 2.128 0.752293 0.0011 JRQ-26-93L 2.2 9.9 0.135872 0.512481 0.0019 -1.7 47 535 0.251 0.705801 0.0010 JRQ-27-125DL 2.8 15 0.108497 0.512464 0.0016 -1.4 77 425 0.524 0.706382 0.0013 *6 samples were analyzed at GFZ Potsdam, others at the University of Arizona; see appendix for methods used. Nd, Sr initial ratios are calculated for 180 Ma. Initial Sr ratios in parentheses are attributed to post-magmatic change in Rb/Sr ratios (see text).

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Sr/86Sr (180) 0.70542 0.7071 0.7022 0.70544 0.70489 0.70511 0.70521 0.70664 0.70573 0.70597 0.70362 0.7066 0.70450 0.70539 0.70520 0.70503 0.7051 0.70657 0.7068 0.70517 0.70393 0.70572 0.7031 0.70564 0.70643 (0.71596) (0.6915) 0.7012 0.70645 (0.74685) 0.70516 0.70504

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206 207 208 Pb/204Pb Pb/204Pb Pb/204Pb Sample CAS-19-38L 18.87 15.63 38.35 CAS-27-87BL 18.90 15.62 38.96 CAS-33-63L 18.73 15.61 38.53 EAM-20-118L 18.68 15.60 38.95 EAM-20-119L 18.36 15.58 38.37 EAM-20-121L 18.46 15.58 38.43 EAM-20-122AL 18.39 15.57 38.33 EAM-20-122CL 18.64 15.60 38.65 EAM-20-124L 18.50 15.58 38.56 EAM-20-129BL 18.63 15.59 38.55 EAM-26-102L 18.38 15.61 37.86 EAM-27-131AL 19.03 15.65 38.94 FCB-21-37BL 18.37 15.57 38.55 FCB-21-38L 18.35 15.57 38.43 JRG-13-07L 18.43 15.60 37.93 JRG-13-42L 18.66 15.62 38.32 JRG-20-81BL 18.36 15.57 38.42 JRG-20-81CL 18.02 15.56 38.18 JRQ-19-14L 18.84 15.62 38.48 JRQ-19-16L 18.46 15.60 38.03 JRQ-26-101L 18.39 15.59 38.09 JRQ-26-102L 18.60 15.60 38.35 JRQ-26-108BL 19.95 15.67 39.04 JRQ-26-83BL 18.37 15.59 37.92 JRQ-26-90AL 18.14 15.60 37.76 JRQ-26-93L 18.47 15.59 38.05 JRQ-27-111BL 18.42 15.59 38.40 JRQ-27-125DL 18.62 15.60 38.53 Analyses made at the University of Arizona, see Appendix. Repeatability of NBS-981 standard are 206Pb/204Pb = 0.028%, 207 Pb/204Pb =0.028%, 208Pb/204Pb = 0.031%.

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Table 3. Results of Pb isotope analyses.

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JRG-20-81BL Weighted mean age = 186.4 Ma ± 1.6 n = 29 (1 rej.), MSWD = 10.0

Pb*/238U age (Ma) 206

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186

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CAS-33-63L Weighted mean age = 176.0 Ma ± 0.9 186 n = 33, MSWD = 4.4 182

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JRQ-19-15L 200 Weighted mean age = 179.7 Ma ± 1.3 n = 35 (2 rej.), MSWD = 6.8 190

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EAM-20-122BL 205 Weighted mean age = 187.2 Ma ± 1.0 n = 38, MSWD = 5.0 195

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FCB-21-38L Weighted mean age = 186.0 Ma ± 0.7 n = 35, MSWD = 2.7

EAM-20-121L Weighted mean age = 180.6 Ma ± 1.2 n = 33 (1 rej.), MSWD = 5.8

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Pb*/238U age (Ma)

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JRG-27-88AL Weighted mean age = 192.1 Ma ± 1.7 n = 18, MSWD = 6.5

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Pb*/238U age (Ma)

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220 JRG-20-84AL Weighted mean age = 189.4 Ma ± 2.0 n = 21, MSWD = 8.9 210

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EAM-27-132L Weighted mean age = 185.7 Ma ± 1.0 n = 35, MSWD = 4.8

EAM-20-129BL Weighted mean age = 190.3 Ma ± 1.2 n = 31, MSWD = 2.3

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165 210 EAM-33-86L Weighted mean age = 184.5 Ma ± 1.4 n = 23, MSWD = 3.9

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ACCEPTED MANUSCRIPT Highlights New U-Pb zircon ages confirm early Jurassic magmatism (176–191 Ma, n=12)

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Geochemistry and Sr-Nd-Pb isotope ratios indicate an arc setting

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E-W younging of the Jurassic arc correlates with a shift in Nd-isotope ratio

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