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GEOSPHERE Secular variations of magma source compositions in the North Patagonian batholith from the Jurassic to Tertiary: GEOSPHERE, v. 17, no. 3 Was mélange melting involved? https://doi.org/10.1130/GES02338.1 Antonio Castro1, Carmen Rodriguez2, Carlos Fernández3, Eugenio Aragón4, Manuel Francisco Pereira5, and José Francisco Molina6 12 figures; 1 table; 1 set of supplemental files 1Instituto Andaluz de Ciencias de la Tierra (IACT), Consejo Superior de Investigaciones Científicas–Universidad de Granada (CSIC-UGR), 18100 Armilla, Granada, Spain 2Geosciences Barcelona (formerly ICTJA), Consejo Superior de Investigaciones Científicas (CSIC), 08028 Barcelona, Spain 3 CORRESPONDENCE: Departamento de Ciencias de la Tierra, Universidad de Huelva, 21007 Huelva, Spain 4 [email protected] Facultad de Ciencias Naturales y Museo, Universidad Nacional de la Plata, B1900 La Plata, Buenos Aires, Argentina 5Instituto de Ciências da Terra (ICT), Departamento de Geociências, Escola de Ciências e Tecnologia (ECT), Universidade de Évora, 7000-670 Évora, Portugal 6Departamento de Mineralogía y Petrología, Universidad de Granada, Campus Univeristario de Fuentenueva, 18071 Granada, Spain CITATION: Castro, A., Rodriguez, C., Fernández, C., Aragón, E., Pereira, M.F., and Molina, J.F., 2021, Secular variations of magma source compositions ABSTRACT subduction of lithosphere is, directly or indirectly, the triggering process for in the North Patagonian batholith from the Jurassic to Tertiary: Was mélange melting involved?: Geo‑ magma generation. However, fundamental issues like the source of magmas sphere, v. 17, no. 3, p. 766–785, https://doi.org/10.1130 This study of Sr-Nd initial isotopic ratios of plutons from the North Patago- and the locus of melting, mantle or crust, still remain debated. Competing /GES02338.1. nian batholith (Argentina and Chile) revealed that a secular evolution spanning processes have been proposed, such as (1) the melting of a metasomatized 180 m.y., from the Jurassic to Neogene, can be established in terms of magma mantle wedge by action of fluids from a downgoing slab (Grove et al., 2002, Science Editor: Shanaka de Silva sources, which in turn are correlated with changes in the tectonic regime. The 2005; Kushiro, 1974) (2) assimilation and melting of continental crustal rocks Guest Associate Editor: Robert J. Stern provenance and composition of end-member components in the source of mag- triggered by invasion of basalts at the lower crust (Hildreth and Moorbath, 87 86 143 144 Received 20 August 2020 mas are represented by the Sr-Nd initial isotopic ratios ( Sr/ Sr and Nd/ Nd) 1988), and, more recently, (3) melting of subducted mélanges within the man- Revision received 18 November 2020 of the plutonic rocks. Our results support the interpretation that source compo- tle wedge (Castro et al., 2010; Codillo et al., 2018; Cruz-Uribe et al., 2018). In Accepted 3 February 2021 sition was determined by incorporation of varied crustal materials and trench principle, the three mechanisms may result in the generation of silicic melts sediments via subduction erosion and sediment subduction into a subduction and/or their intermediate parental magmas, leading finally to the formation Published online 21 April 2021 channel mélange. Subsequent melting of subducted mélanges at mantle depths of batholiths. However, requirements imposed by geochemical and isotopic and eventual reaction with the ultramafic mantle are proposed as the main causes ratios are better accounted for by mechanisms involving mixing of sources that of batholith magma generation, which was favored during periods of fast conver- occurred previous to melting within the mantle (Nielsen and Marschall, 2017) gence and high obliquity between the involved plates. We propose that a parental rather than mixing of melts from different sources or assimilation of crustal diorite (= andesite) precursor arrived at the lower arc crust, where it underwent contaminants by mantle-derived basaltic melts (Davidson et al., 1991; Hildreth fractionation to yield the silicic melts (granodiorites and granites) that formed and Moorbath, 1988). Consequently, determining whether isotopic features the batholiths. The diorite precursor could have been in turn fractionated from are inherited from the source or acquired by magmas during their ascent and a more mafic melt of basaltic andesite composition, which was formed within emplacement is an essential step to decipher the role of isotopic ratios in the mantle by complete reaction of the bulk mélanges and the peridotite. Our supporting or rejecting the aforementioned mechanisms. We show here new proposal follows model predictions on the formation of mélange diapirs that U-Pb sensitive high-resolution ion microprobe (SHRIMP) zircon ages and Sr-Nd carry fertile subducted materials into hot regions of the suprasubduction mantle isotopic data from plutons of the North Patagonian batholith (Chile and Argen- wedge, where mafic parental magmas of batholiths originate. This model not tina), which can unravel the secular geochemical evolution of magma source only accounts for the secular geochemical variations of Andean batholiths, but it compositions from the Jurassic onwards. In subduction zones, this evolution also avoids a fundamental paradox of the classical basalt model: the absence of is expected to entail changes in the relative contributions of geochemically ultramafic cumulates in the lower arc crust and in the continental crust in general. evolved continental reservoirs (e.g., sediments and ancient continental crust) and altered oceanic crust. Although there is agreement about the presence of these end members in the composition of Andean (= Cordilleran) batholiths ■■ INTRODUCTION (DePaolo, 1981b; Hervé et al., 2007; Lee et al., 2006; Pankhurst et al., 1999), the mechanisms by which they are incorporated into magmas remain poorly con- This paper is published under the terms of the Andean (= Cordilleran)–type batholiths represent large volumes of silicic strained. We discuss the determination of these mechanisms through study of CC‑BY-NC license. (SiO2 > 53 wt%) magmas that are generated at active continental margins. The geochemical secular variations in plutons of the North Patagonian batholith.

GEOSPHERE | Volume 17 | Number 3 Castro et al. | Secular variations of magma source compositions in the North Patagonian batholith Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/17/3/766/5319384/766.pdf 766 by guest on 28 September 2021 Research Paper

It has been demonstrated, on the basis of partitioning of Sr and Nd between Central Valley, Patagonian Andes, and extra-Andean Patagonia. The geology subducted rocks and fluids (Nielsen and Marschall, 2017), that metasomatism of this region is dominated by Late Jurassic, Cretaceous, and Neogene granit- by fluids and/or melts derived from the subducted slab (the classical model) oids of the North Patagonian batholith (Aragón et al., 2011; Castro et al., 2011; is unable to account for the observed geochemical and isotopic features of arc Hervé et al., 2007; Pankhurst et al., 1999; Suárez and De La Cruz, 2001), and magmas. Alternatively, the direct participation of the whole subducted mélange, Cretaceous volcanic rocks (Fig. 1B). In the forearc, the morphological units are and not only fluids or melts from it, accounts for observed geochemical features. the southward continuation of the Coastal Cordillera and the Central Valley. The The participation of the mélange as a whole in the generation of arc magmas basement in the area is represented by a late Paleozoic–Triassic accretionary may be accomplished in two ways: (1) melting of mélange materials (closed prism (Duhart et al., 2001; Forsythe, 1982; Hervé et al., 2008; Thomson and system) at the core of silicic diapirs, as predicted by thermomechanical mod- Hervé, 2002; Willner et al., 2000). The Coastal Cordillera shows the westward els (Gerya and Yuen, 2003; Gerya et al., 2004), and (2) reaction and complete outcrops of Eocene plutons of the North Patagonian batholith. digestion of the partially molten mélange, forming narrow channels within the The tectonic history of the studied region shows two periods of alternating surrounding peridotite (Kelemen, 1995; Kelemen et al., 2003). The two mech- extension-contraction: It started with extension and crustal thinning from the anisms have been experimentally tested for fertility and melt compositions. Late Jurassic to the Early Cretaceous, followed by contraction during mid- Experimental results matched the geochemical features of batholiths and arc Cretaceous time. New extension and crustal thinning took place from the magmas in general (Castro et al., 2010). Those results are central to the new Late Cretaceous to late Oligocene, followed by contraction in the Neogene. paradigm of arc magma generation, which is referred to as the mélange diapir The mid-Cretaceous deformational event was coeval with the mid-Cretaceous model (Marschall and Schumacher, 2012). In the first case, more than 50% of peak of magmatic input to the North Patagonian batholith. granodiorite melt—the most abundant rock type in Andean-type batholiths—is formed in equilibrium with plagioclase and pyroxene at 1100 °C and 1.5 GPa, and with garnet at 2.0 GPa (Castro et al., 2010, 2013). At temperatures >1100 °C, ■■ SAMPLING AND ANALYTICAL TECHNIQUES the melt composition tends to be dioritic, approaching the composition of the whole mélange system. In the second case, experiments using a homogeneous Sampling for this study was carried out in two campaigns in 2011 and mixture of the KLB-1 lherzolite and mélange composed of a mid-ocean-ridge 2015, mostly concentrated in the area of Aysén (Chile), where a Mesozoic– basalt (MORB)–amphibolite and Bt-rich gneiss at 1050–1300 °C and 1.0–1.5 GPa Tertiary paired belt of plutons extends parallel to the present-day trench and (Castro et al., 2013) yielded mafic melts matching the composition of andesites represents the Mesozoic (mostly Cretaceous) plutons dominating in volume and basaltic andesites. Those mafic magmas will have hybrid geochemical in the inner belt. Also, dated samples from the area of Bariloche to the north signatures and can be the precursors of parental diorites and batholiths by of Aysén (Castro et al., 2011) were analyzed for Sr and Nd isotopes for this fractionation within upper mantle and crust. study. In total, 40 representative samples, collected across the two traverses The selection of the North Patagonian batholith for this study was based on of the North Patagonian batholith in Aysén (Chile) and Bariloche (Argentina) several grounds: (1) the protracted magmatic activity for ~180 m.y., from the (Figs. 1A and 1B), were analyzed to determine whole-rock geochemistry (major Jurassic to Tertiary, (2) the changes marked in various tectonic regimes with and trace elements) and isotopic ratios (Sr and Nd). A selection of samples time, and (3) the accessibility and previous knowledge of regional geology. from the Aysén area was analyzed by in situ SHRIMP U-Pb age determination. Based on these particular conditions, we carried out a study of plutons across Petrographic studies and microprobe analyses of relevant mineral phases two traverses, aiming to correlate secular geochemical changes with variations (amphibole, pyroxene, and plagioclase) were also carried out on the dated in the tectonic regime of plate convergence and subduction. samples, with particular attention to amphibole chemistry in order to determine pressure and temperature conditions of crystallization. Thin sections of intrusive rocks were polished and subsequently analyzed. Microprobe analyses ■■ GEOLOGICAL SETTING were carried out by wavelength-dispersive (WD) spectrometry with a JEOL JXA-8200 Superprobe at the University of Huelva, Huelva, Spain. A combi- The North Patagonian batholith is mostly composed of calc-alkaline granitic nation of silicates and oxides was used for calibration, and a 5-μm-diameter and intermediate rocks (diorites, quartz-diorites, tonalites, granodiorites, and beam was selected to reduce the Na migration. monzogranites) that extend for ~800 km, from latitude 39°S to 46°S, along the Approximately 500 g aliquots of each sample were ground for whole- western continental margin of South America. The North Patagonian batholith rock geochemical analysis. Major elements and Zr were determined by X-ray forms the core of the Southern Andes, a subduction orogenic belt active since fluorescence (XRF) at the Centro de Instrumentación Científica, University the Middle Jurassic to present day. The study area includes the subduction of of Granada, Granada, Spain. Trace elements, including rare earth elements the Nazca plate beneath South America (Fig. 1C). The main geomorphologi- (REEs), were determined by inductively coupled plasma–mass spectrometry cal units present at this latitude are, from west to east: the Coastal Cordillera, (ICP-MS), also at the University of Granada, following standard procedures

72°00’ W 71°45’ W 79°W 75°W 70°W 65°W 37°S 37°S B CHILE ARGENTINA BARILOCHE AREA CHILE ARGENTINA

Nazca 40°30’ S South 40°S plate 40°S American A208-48 b plate 173.2±2.7

TRAFUL

VILLA DE LA c ANGOSTURA N

North 45°S Patagonian 45°S Batholith 41°00’ S South A208-1 163.5±2.7 0 5 10 15 20 25 km Patagonian A208-31 SAN CARLOS Batholith 171.0±3.0 DE BARILOCHE A208-29 172.5±3.1 A208-20 171.6±2.6 50°S 50°S A208-33 A208-22 Figure 1. (A) Tectonic environment 156.8±2.5 167.7±2.2 of the North Patagonian batholith in South America. (B–C) Geology and Post-Mesozoic materials A208-6 sample locations in the studied tra- 149.9±1.9 Middle to Late Jurassic granites 41°30’ S verses of Bariloche (B) and Aysén A208-8 Early Jurassic granites 154.5±1.8 (C). U-Pb zircon ages are labeled. A208-11 Early Jurassic volcanic rocks Geological schematic maps of B Antarctic 161.7±2.6 Paleozoic basement and C are after published maps from 55°S plate 55°S A208-13 the Geological Surveys of Argentina Andean reverse faults 168.9±2.3 and Chile (downloaded from the 56°S 56°S Inverted Mesozoic normal faults 79°W 75°W 70°W 65°W A208-14 Servicio Geológico Minero Argen- 171.0±5.0 Anticlinal Synclinal tino, SEGEMAR, Digital Cartography, https://sigam .segemar .gov.ar/ , and EL BOLSÓN the Servicio Nacional de Geología 42°00’ S y Minería, Chile, SERNAGEOMIN, AYSÉN AREA 72°00’ W 71°45’ W Geological Map of Chile, digital ver- sion, http://www.ipgp.fr/~dechabal ANDES PATAGONIDES /Geol-millon.pdf). Michinmahuida volcano

74ºW ANDES A1015-26 V Volcanoes 123.5±0.8 Corcovado A1015-27 + Miocene granites (s.l.) volcano Neogene 121.5±0.8 A1015-25 A1015-21 Unconformity PAL14-15 115.0±1.0 89.9±1.5 142.3±1.0 V Traiguen PATAGONIDES RIFT A1015-33 formation A1015-36 6.4±0.2 V Volcanic belt of El Maiten A1015-40 5.9±0.1 Eocene 34.0±0.5 A1015-22 + granites V Volcanic belt of Pilcaniyeu A1015-38 107.4±1.1 Paleogene + Paleocene granites 7.1±0.1 16.2±0.3 A1015-24 44ºS PAL14-10 113.1±0.6 Unconformity 6.2±0.2 + A1015-31 PAL14-2 V Divisadero group 6.3±0.1 111.4±0.4 + A1015-28 Cretaceous granites (s.l.) A1015-30 Melimoyu volcano 104.4±1.0

15.8±0.2 Cretaceous A1015-29 8.0±0.2 70º W PAL14-7 PAL14-8 Liquiñe-Ofqui fault Reverse faults 100 150 200 250 4.4±0.04 300 23.7±0.5 350 400 450 500 km Distance to the trench

(Baedecker, 1987). Precision for major elements was better than 1% relative. marked by grain size and color index, which usually show transitions. Mag- Analyses of trace elements were performed following the method described matic layered structures are common near the contacts, where accumulation in Bea (1996); the precision was ~2% and 5% error on concentrations of 50 and of mafic minerals and segregation of felsic layers are observed (Figs. 2A and 5 ppm, respectively. Samples for Sr and Nd isotope analyses were digested in a 2B). Mingling zones with dark pillows included into felsic granites are com- clean room using ultraclean reagents and analyzed by thermal ionization mass mon structures, indicating magma behavior during the magma emplacement spectrometry (TIMS) in a Finnigan Mat 262 spectrometer after chromatographic and recharge of subvolcanic magma chambers. Xenoliths from older granitic separation with ion-exchange resins. Normalization values were 86Sr/88Sr = intrusions are also common (Figs. 2C and 2D). Some plutons show subvolca- 0.1194 and 146Nd/144Nd = 0.7219. Isotopic ratios of 87Rb/86Sr and 147Sm/144Nd nic porphyritic textures with a fine-grained matrix and abundant plagioclase were directly determined by ICP-MS (Montero and Bea, 1998) with a precision, phenocrysts. Diorites and quartz-diorites are composed of Pl, Opx, Cpx, Amp, estimated by analyzing 10 replicates of the standard WS-E, better than 1.2% Ox ± Qz, ± Bt (mineral abbreviations after Whitney and Evans, 2010). Tonalites, and 0.9% (2σ), respectively. granodiorites, and monzogranites are mostly composed of Pl, Bt, Kfs, Qz, Amp, Traditional techniques using dense liquids, magnetic separation, and ± Cpx (Table S11). Plagioclase shows the typical complex oscillatory zoning that

handpicking were performed for zircon separation. Zircon crystals of distinct characterizes calc-alkaline granitic rocks. The composition ranges from An51

morphology and size were separated from each sample of igneous rock and (subscript denotes mole %) in diorites and quartz-diorites to An32 in granodio- cast on epoxy mounts that also included three zircon standards used for cali- rites and monzogranites. Clinopyroxene of diorites and quartz-diorites has the

bration procedures. TEMORA (ca. 417 Ma) was used as isotope ratio standard composition Wo44En39Fs16, whereas orthopyroxene is Wo03En54Fs35 (Table S1). zircon (Black et al., 2003), SL13 was used as concentration standard (238 p.m. U) Amphibole compositions range from 6.3 to 7.2 apfu (atoms per formula unit) (Claoue-Long et al., 1995) and GAL (ca. 480 Ma) was used for very high U, Th, of Si and 0.4–0.8 in the Mg/(Mg + Fe) ratio. Most of them are classified as and common Pb content (Montero and Bea, 1998). Before selection of targets, Mg-hornblende, with a very few classified as tschermakitic hornblende and the internal morphology of the zircon crystals was analyzed using cathodolu- actinolite. Biotite is systematically present in most samples, replacing amphi- minescence (CL) images previously obtained through a CL detector coupled bole and with euhedral and interstitial habit. A list of mineral compositions to a scanning electron microscope (SEM). Then, selected zircon crystals were from each sample is given in the Supplemental Material (Table S1). analyzed for U-Th-Pb geochronology using SHRIMP at the IBERSIMS laboratory Figure 2 shows representative textures of diorites and granodiorites of the (University of Granada). Targets were rastered by a primary beam for 120 s prior Aysén region. Descriptions of the Bariloche region were given in Castro et al. to analysis. Then, the selected area was analyzed over six scans by running the (2011). Amphibole is a late phase in the crystallization sequence. Euhedral faces 196 204 204.1 206 207 208 238 248 peak sequence: Zr2O, Pb, background, Pb, Pb, Pb, U, ThO, and are only observed in contact with Qz but not with Pl (Fig. 2E). Plagioclase forms 254 Supplementary Table S1 Secular variations of magma source compositions in the North Patagonian batholith from Jurassic to Tertiary. Is mélange melting involved? Antonio Castro, Carmen Rodríguez, Carlos Fernández, Eugenio Aragón, Manuel Francisco Pereira, J. F. Molina Average of microanalyses or representative analyses from mineral phases performed with electron microprobe UO. Every peak of each scan was measured sequentially 10 times according large euhedral crystals, leaving Kfs and Qz in the interstices. Euhedral Amp

Phase Position SiO2 TiO2 Al2O3 FeO MgO MnO CaO Na2O K2O P2O5 F Cl Cr2O3 SO3 BaO NiO SrO Total An Ab Or Wo En Fs Ac #Mg #Fe Monzogranite A1015-22 Pl core 58.21 0.01 25.98 0.11 0.01 0.01 7.51 6.98 0.33 0.01 0.01 0.07 0.01 0.01 0.04 0.06 99.34 36.58 61.49 1.93 Pl rim 61.44 23.48 0.13 0.00 0.02 4.61 8.75 0.30 0.01 0.00 0.02 0.02 0.03 98.80 22.16 76.12 1.72 Pl int (n=5) 58.04 0.03 26.22 0.17 0.02 0.01 7.54 7.21 0.30 0.01 0.11 0.01 0.02 0.01 0.08 0.03 0.06 99.86 36.03 62.28 1.69 Am rim 46.43 1.31 6.03 18.97 11.01 0.54 10.75 1.42 0.61 0.41 0.30 0.02 0.04 0.00 97.58 Am int (n=4) 47.23 1.13 5.51 15.80 12.73 0.47 11.40 1.24 0.51 0.00 0.30 0.15 0.02 0.03 0.07 0.02 0.00 96.61 Bt (n=8) 35.81 4.84 13.61 22.01 9.68 0.25 0.02 0.17 9.40 0.01 0.53 0.69 0.09 0.03 0.38 0.03 97.53 0.44 0.56 Tonalite A1015-23 to the total counts per scan: 2 s for mass 196; 5 s for masses 238, 248, and 254; may appear at these interstices together with Qz, denoting the late crystalliza- Pl core (n=7) 56.45 0.04 27.40 0.42 0.02 0.01 9.15 6.49 0.27 0.02 0.07 0.01 0.02 0.01 0.05 0.02 0.06 100.50 43.16 55.31 1.53 Pl rim (n=8) 63.59 0.03 22.78 0.20 0.04 0.01 3.46 9.92 0.24 0.02 0.12 0.01 0.05 0.02 0.03 0.03 0.04 100.32 20.17 78.55 1.28 Pl int (n=16) 56.94 0.05 27.08 0.41 0.03 0.01 8.76 6.48 0.32 0.02 0.11 0.01 0.04 0.01 0.07 0.02 0.07 100.44 42.01 56.14 1.85 Am core (n=2) 54.70 0.15 2.36 9.26 19.99 1.30 8.31 0.21 0.15 0.02 0.23 0.07 0.06 0.01 0.03 0.03 0.04 96.93 Am rim (n=3) 54.39 0.14 1.68 8.16 19.41 0.47 12.06 0.31 0.13 0.01 0.29 0.09 0.07 0.00 0.05 0.04 0.00 97.32 Am int (n=3) 55.06 0.11 1.24 9.16 19.58 0.79 10.82 0.24 0.08 0.02 0.31 0.09 0.04 0.01 0.06 0.03 97.64 Cpx (n=4) 51.36 0.46 1.64 9.00 15.06 0.33 21.28 0.37 0.00 0.02 0.09 0.01 0.05 0.01 0.04 0.01 99.71 42.44 41.81 14.43 1.32 Uvö 0.05 15.63 0.04 73.46 0.01 2.72 0.05 0.03 0.01 0.02 0.00 0.01 0.00 92.02 Monzogranite A1015-24 Pl core (n=10) 56.35 0.04 26.83 0.35 0.01 0.01 8.36 7.11 0.24 0.02 0.09 0.02 0.04 0.01 0.05 0.02 0.07 99.61 38.91 59.77 1.31 15 s for masses 204, 206, and 208; and 20 s for mass 207. The incidence of the tion of a porous residual liquid (Fig. 2F). Resorbed An-rich cores are common Pl rim (n=8) 63.99 0.03 21.83 0.22 0.01 0.03 2.55 10.43 0.34 0.01 0.13 0.00 0.02 0.02 0.05 0.01 0.03 99.69 11.70 86.43 1.87 Pl int (n=21) 59.56 0.03 24.87 0.31 0.02 0.02 6.02 8.41 0.29 0.02 0.11 0.01 0.04 0.02 0.08 0.03 0.06 99.89 27.69 70.70 1.61 Bt (n=11) 36.53 3.10 13.65 17.66 13.36 0.37 0.03 0.12 9.45 0.02 1.42 0.26 0.06 0.03 0.36 0.04 96.46 0.58 0.42 Mt (n=1) 0.15 1.93 0.01 89.98 0.02 0.10 0.05 0.00 0.05 0.14 0.01 0.01 92.44 Ilm (n=1) 0.12 49.08 0.00 40.69 0.10 9.22 0.14 0.02 0.02 0.01 0.01 0.16 99.57 Monzogranite A1015-25 Pl core (n=3) 59.61 0.02 25.44 0.24 0.00 0.01 6.73 7.48 0.43 0.03 0.13 0.00 0.06 0.02 0.05 0.03 0.06 100.34 32.41 65.13 2.46 Pl rim (n=5) 64.38 0.02 22.16 0.26 0.02 0.02 2.67 9.94 0.38 0.03 0.05 0.01 0.05 0.01 0.07 0.05 0.01 100.14 12.71 85.16 2.13 Pl int (n=6) 59.73 0.02 25.25 0.20 0.01 0.01 6.54 7.54 0.52 0.02 0.06 0.01 0.04 0.01 0.07 0.04 0.04 100.11 31.46 65.56 2.97 Bt (n=10) 36.57 4.45 13.75 18.32 12.33 0.42 0.02 0.14 9.62 0.02 0.44 0.22 0.04 0.05 0.46 0.02 96.87 0.55 0.45 Spn inclusion 28.07 30.72 1.89 4.54 0.06 0.29 21.89 0.10 0.00 0.37 0.01 0.04 0.04 87.84 primary beam, with an intensity of 4–5 nA and using a 120 μm Kohler aperture, (Fig. 2G), indicating repeated episodes of crystallization and dissolution. Clin- Monzogranite A1015-26 Pl core (n=2) 54.44 0.03 25.33 0.15 0.02 13.51 5.06 0.11 0.02 0.02 0.02 0.02 0.03 0.01 0.03 98.77 57.24 42.18 0.59 Pl rim (n=1) 59.99 25.98 0.17 0.00 0.01 6.82 7.52 0.12 0.04 0.01 0.01 0.00 0.07 100.74 33.14 66.14 0.72 Pl int (n=12) 58.61 0.03 25.30 0.16 0.01 0.02 7.62 7.32 0.24 0.02 0.07 0.05 0.04 0.01 0.04 0.02 0.03 99.58 34.66 64.01 1.33 Am core (n=4) 46.64 1.21 6.86 16.78 11.45 0.52 11.93 0.99 0.77 0.02 0.37 0.13 0.05 0.02 0.06 0.04 0.04 97.89 Am rim (n=4) 44.66 1.26 8.63 17.01 10.75 0.57 11.73 1.22 1.02 0.04 0.23 0.16 0.07 0.03 0.09 0.02 0.02 97.51 Am int (n=3) 46.77 0.79 6.38 15.94 12.10 0.57 12.06 0.86 0.70 0.04 0.32 0.12 0.03 0.02 0.04 0.02 0.02 96.77 Mt (n=1) 0.04 0.07 0.07 90.56 0.02 0.05 0.02 0.01 0.01 0.01 0.01 0.00 0.16 0.01 0.02 91.05 Bt (n=5) 36.93 2.90 15.18 18.62 11.71 0.41 0.03 0.12 9.81 0.01 0.64 0.12 0.08 0.07 0.04 0.02 96.71 Spn (n=3) 30.13 36.86 1.35 1.39 0.02 0.12 27.74 0.04 0.05 0.04 0.23 0.01 0.02 0.05 0.02 98.06 on the target produced an elliptical crater (17 × 20 μm). A resolution of ~5000 opyroxene appears resorbed and replaced by Amp (Fig. 2H), indicating late Qz-diorite A1015-27 Pl core (n=4) 54.30 0.00 29.23 0.16 0.02 0.04 11.10 5.39 0.26 0.01 0.08 0.02 0.06 0.01 0.05 0.04 100.78 52.46 46.06 1.48 Pl rim (n=4) 56.36 0.03 28.18 0.20 0.01 0.02 9.82 6.03 0.24 0.01 0.09 0.01 0.08 0.01 0.02 0.04 0.09 101.24 46.73 51.91 1.36 Pl int (n=2) 55.34 0.03 28.60 0.19 10.12 5.94 0.29 0.01 0.12 0.00 0.04 0.02 0.05 0.06 100.81 47.71 50.67 1.62 Opx (n=16) 52.18 0.15 0.55 25.64 17.97 1.36 1.11 0.05 0.01 0.02 0.10 0.02 0.04 0.01 0.05 0.04 0.01 99.30 2.26 50.26 47.29 0.20 Cpx (n=17) 51.78 0.18 0.90 10.69 13.11 0.55 22.21 0.28 0.01 0.02 0.10 0.01 0.07 0.01 0.06 0.03 0.01 100.00 43.71 35.91 19.38 0.99 Am core (n=7) 47.08 1.29 6.90 15.94 12.66 0.40 11.46 1.01 0.71 0.02 0.10 0.29 0.06 0.03 0.05 0.02 0.03 98.04 Am rim (n=15) 48.17 0.91 6.30 15.65 13.07 0.43 11.61 0.82 0.57 0.02 0.13 0.22 0.03 0.01 0.05 0.02 0.02 98.02 Am int (n=14) 46.77 1.27 6.94 16.04 12.54 0.41 11.49 0.97 0.72 0.02 0.14 0.27 0.06 0.02 0.03 0.05 0.01 97.74 Bt (n=10) 36.18 4.73 14.40 19.22 11.41 0.19 0.07 0.15 9.49 0.01 0.18 0.40 0.05 0.06 0.29 0.03 96.86 0.52 0.48 AMU (atomic mass units) at 1% peak height was reached by the secondary rehydration of a residual liquid. Mt (n=1) 6.16 0.05 0.39 82.46 2.79 0.24 0.50 0.15 0.04 0.29 0.06 0.12 0.00 0.00 93.25 Qz-diorite A1015-28 Pl core (n=1) 57.45 27.95 0.08 0.00 0.03 9.25 6.34 0.11 0.10 0.03 0.02 101.31 44.37 55.01 0.62 Pl rim (n=4) 57.22 0.03 27.58 0.18 0.11 0.01 9.03 6.46 0.10 0.02 0.02 0.00 0.03 0.01 0.03 0.06 0.11 101.01 43.32 56.10 0.59 Pl int (n=3) 57.26 0.04 27.64 0.08 0.01 0.03 8.96 6.52 0.09 0.02 0.13 0.01 0.02 0.01 0.03 0.02 0.07 100.94 42.94 56.55 0.51 Am core (n=3) 43.57 1.88 10.76 16.29 10.62 0.34 11.63 1.23 1.00 0.01 0.08 0.13 0.03 0.02 0.01 0.01 0.02 97.66 Qz-diorite A1015-29 Pl core (n=7) 55.41 0.01 28.69 0.14 0.02 0.01 10.21 5.80 0.28 0.01 0.08 0.01 0.05 0.02 0.03 0.02 0.04 100.84 48.63 49.77 1.60 Pl rim (n=8) 57.30 0.02 27.15 0.24 0.01 0.01 8.46 6.84 0.35 0.01 0.08 0.00 0.03 0.01 0.05 0.02 0.05 100.63 39.86 58.20 1.95 Pl int (n=11) 58.39 0.03 26.56 0.14 0.01 0.02 7.62 7.27 0.36 0.01 0.08 0.01 0.06 0.02 0.05 0.04 0.05 100.72 36.05 61.91 2.04 beam exit slit set at 80 μm. Mass calibration was performed on the GAL zir- Am (n=11) 43.96 1.67 8.35 20.40 9.17 0.53 11.13 1.47 0.91 0.02 0.08 0.29 0.07 0.02 0.04 0.03 0.02 98.17 Bt (n=4) 35.63 4.11 14.54 21.65 10.17 0.29 0.01 0.17 9.51 0.17 0.29 0.10 0.05 0.09 0.03 96.80 0.46 0.54 Uvö (n=1) 0.06 50.98 0.03 44.96 0.08 4.25 0.07 0.02 0.01 0.01 0.04 0.01 0.05 100.55 Qz-diorite A1015-30 Pl core (n=4) 57.34 0.02 27.47 0.09 0.01 0.01 8.91 6.49 0.19 0.02 0.01 0.05 0.01 0.03 0.04 0.07 100.76 42.75 56.19 1.06 Pl rim (n=5) 59.82 0.01 25.71 0.16 0.01 0.03 6.76 7.83 0.17 0.01 0.09 0.00 0.05 0.00 0.05 0.05 100.76 32.01 67.04 0.95 Pl int (n=12) 58.72 0.02 26.49 0.11 0.01 0.02 7.73 7.18 0.23 0.01 0.06 0.01 0.02 0.01 0.06 0.02 0.05 100.75 36.82 61.90 1.28 Am core (n=3) 44.32 1.08 9.83 17.90 10.00 0.82 11.60 1.20 0.62 0.02 0.02 0.07 0.09 0.02 0.04 0.02 0.02 97.66 Am rim (n=3) 43.56 1.00 10.24 18.24 9.66 0.79 11.61 1.21 0.74 0.02 0.04 0.08 0.04 0.03 0.01 0.02 97.29 Bt (n=3) 36.10 3.20 15.73 19.74 10.97 0.47 0.01 0.13 9.70 0.03 0.21 0.07 0.06 0.04 0.18 0.04 96.68 0.51 0.49 con, analytical sessions initially involved the measurement of the SL13 zircon, Ilm (n=1) 0.06 51.22 0.00 43.35 0.18 5.86 0.00 0.02 0.04 0.02 0.02 0.11 0.01 100.88 Mt (n=1) 0.08 0.17 0.09 90.31 0.22 0.03 0.04 0.02 0.04 0.01 0.07 0.02 91.08 Diorite A1015-31 Pl core (n=8) 48.21 0.04 32.55 0.45 0.09 0.02 15.21 2.25 1.11 0.01 0.09 0.01 0.04 0.01 0.06 0.03 0.06 100.25 74.08 19.79 6.13 Pl rim (n=8) 63.34 0.06 22.95 0.24 0.02 0.02 3.77 9.47 0.40 0.02 0.04 0.01 0.04 0.01 0.07 0.02 0.04 100.52 17.78 80.03 2.19 Pl int (n=6) 52.83 0.04 29.73 0.36 0.06 0.02 11.67 4.99 0.10 0.03 0.04 0.00 0.04 0.01 0.03 0.01 0.10 100.06 56.47 42.98 0.55 Opx (n=2) 52.14 0.29 1.28 24.16 14.77 0.85 2.82 0.52 0.01 0.04 0.15 0.06 0.03 0.01 0.07 0.02 97.22 4.70 46.34 22.90 1.12 Am core (n=4) 46.17 2.01 7.35 14.73 14.18 0.53 9.62 2.32 0.25 0.09 0.19 0.11 0.03 0.02 0.05 0.03 97.65 Am rim (n=3) 47.59 1.99 5.78 14.89 14.08 0.45 9.82 1.98 0.28 0.04 0.22 0.10 0.05 0.01 0.01 0.05 97.34 Am int (n=1) 43.78 2.75 10.20 13.35 13.71 0.38 10.35 2.65 0.30 0.01 0.21 0.08 0.02 0.02 97.70 and TEMORA zircon was used as the isotope ratio standard, measured every Whole-Rock Geochemical Features Diorite A1015-33 Pl core (n=5) 54.69 0.04 29.02 0.14 0.01 0.01 10.74 5.40 0.14 0.02 0.07 0.01 0.03 0.01 0.05 0.02 0.06 100.46 52.00 47.19 0.81 Pl rim (n=4) 57.64 0.03 27.07 0.24 0.02 0.02 8.53 6.64 0.16 0.03 0.00 0.04 0.00 0.02 0.05 0.06 100.56 41.16 57.90 0.94 Pl int (n=7) 53.47 0.03 29.93 0.13 0.01 0.02 11.78 4.87 0.10 0.02 0.11 0.00 0.04 0.02 0.05 0.02 0.05 100.66 56.89 42.53 0.59 Am core (n=1) 46.10 1.36 8.35 16.14 12.04 0.34 11.58 1.16 0.52 0.02 0.09 0.13 0.08 0.02 0.02 0.01 97.89 Am rim (n=4) 46.61 1.17 7.89 15.70 12.45 0.37 11.66 1.01 0.48 0.03 0.11 0.14 0.10 0.01 0.03 0.00 0.01 97.77 Am int (n=1) 52.99 0.29 2.22 12.48 16.38 0.34 11.73 0.25 0.08 0.01 0.03 0.02 0.07 96.89 Bt (n=1) 36.43 4.10 14.83 18.75 12.34 0.15 0.00 0.11 9.51 0.01 0.27 0.04 0.03 0.32 0.01 96.83 0.54 0.46 Diorite A1015-34 Pl core (n=5) 49.90 0.02 32.25 0.19 0.02 0.02 14.55 3.28 0.05 0.02 0.01 0.01 0.05 0.01 0.03 0.02 0.07 100.50 70.84 28.85 0.31 four unknowns. A more detailed description of the analytical procedures and Pl rim (n=5) 59.05 0.04 25.91 0.12 0.01 0.02 7.21 7.43 0.14 0.01 0.05 0.00 0.05 0.01 0.04 0.03 0.06 100.16 34.63 64.55 0.81 Pl int (n=12) 54.97 0.04 28.64 0.32 0.14 0.02 10.38 5.54 0.14 0.02 0.11 0.01 0.04 0.01 0.05 0.03 0.06 100.52 50.49 48.67 0.84 Am core (n=9) 51.60 0.36 4.20 12.02 16.07 0.38 12.12 0.48 0.17 0.01 0.14 0.02 0.06 0.03 0.04 0.02 0.02 97.74 Am rim(n=9) 48.32 0.68 6.95 13.88 14.03 0.35 12.10 0.78 0.34 0.04 0.07 0.05 0.03 0.02 0.04 0.03 0.03 97.73 Am int (n=1) 48.94 0.66 6.67 13.59 14.39 0.37 11.99 0.80 0.35 0.01 0.12 0.05 0.04 0.02 97.97 Bt (n=3) 36.69 3.01 15.37 17.74 12.73 0.12 0.03 0.13 9.70 0.01 0.15 0.11 0.05 0.05 0.24 0.04 96.18 0.56 0.44 Diorite A1015-35 Pl core (n=4) 46.32 0.05 33.14 0.33 0.03 0.01 17.29 1.76 0.03 0.02 0.07 0.01 0.03 0.01 0.04 0.01 0.08 99.23 84.30 15.53 0.17 Pl rim (n=4) 60.84 0.02 24.60 0.17 0.00 0.01 5.77 8.33 0.05 0.02 0.20 0.01 0.07 0.02 0.04 0.04 0.07 100.27 27.61 72.08 0.31 Pl int (n=8) 54.60 0.05 28.71 0.35 0.03 0.02 10.68 5.55 0.03 0.01 0.10 0.01 0.06 0.01 0.04 0.01 0.08 100.36 51.64 48.16 0.20 data reduction can be seen at the site: https://www.ugr.es/~ibersims /ibersims / According to bulk-rock geochemistry, plutonic rocks are separated in two Opx (n=1) 54.58 0.08 0.37 20.69 19.36 1.00 1.13 0.03 0.04 0.04 0.16 0.01 97.41 Am core (n=4) 44.50 2.60 9.31 14.33 13.39 0.38 10.94 1.04 0.26 0.13 0.13 0.07 0.08 0.02 0.02 0.04 0.03 97.29 Am rim (n=3) 49.52 0.54 6.26 12.54 15.29 0.27 11.80 0.69 0.11 0.15 0.05 0.02 0.02 0.11 0.02 0.01 97.41 Am int (n=2) 47.00 1.21 7.95 14.12 14.26 0.33 10.80 0.88 0.20 0.11 0.04 0.06 0.07 0.03 0.03 0.03 0.06 97.19 Bt (n=1) 38.15 1.42 15.82 14.44 16.31 0.09 0.17 0.10 8.03 0.01 0.15 0.09 0.03 0.18 0.06 95.00 Qz-diorite A1015-36 Pl core (n=5) 55.08 0.02 28.61 0.13 0.00 0.02 10.32 5.72 0.12 0.01 0.10 0.01 0.07 0.01 0.06 0.01 0.05 100.36 49.61 49.81 0.59 Pl rim (n=3) 57.44 0.01 27.17 0.20 0.02 0.04 8.43 6.81 0.13 0.01 0.01 0.00 0.01 0.03 0.03 0.03 100.38 40.32 58.96 0.72 Pl int (n=6) 55.09 0.02 28.51 0.13 0.01 0.02 10.16 5.80 0.13 0.01 0.19 0.00 0.06 0.01 0.05 0.02 0.05 100.24 48.83 50.45 0.72 Am core (n=3) 45.67 1.44 8.22 16.44 12.36 0.35 11.05 1.10 0.52 0.02 0.11 0.18 0.07 0.02 0.04 0.02 0.01 97.61 Methods.html. U-Pb data were processed with ISOPLOT software (Ludwig, 2003) groups: (1) a silica-rich (SiO >63 wt%) granitic group ranging in composition Am rim (n=2) 45.98 1.25 8.25 16.89 12.19 0.47 11.07 1.02 0.41 0.02 0.22 0.16 0.04 0.05 0.00 0.01 98.03 2 Am int (n=1) 46.37 1.45 7.79 17.13 12.51 0.51 10.63 0.90 0.46 0.01 0.17 0.17 0.02 0.00 0.06 0.00 98.19 Bt (n=5) 36.10 3.42 15.37 18.30 12.83 0.14 0.17 0.21 8.96 0.01 0.19 0.23 0.08 0.03 0.21 0.03 96.29 0.56 0.44 Diorite A1015-37 Pl core (n=1) 50.13 31.75 0.22 14.02 3.62 0.13 0.06 0.21 0.04 0.01 0.00 0.05 100.14 67.66 31.57 0.76 Pl rim (n=1) 53.32 0.03 29.52 0.19 0.00 11.01 5.30 0.04 0.07 0.01 0.06 0.03 0.01 0.06 99.61 53.34 46.44 0.23 Pl int (n=4) 54.00 0.02 29.18 0.26 0.01 0.02 10.98 5.26 0.13 0.04 0.15 0.01 0.05 0.01 0.01 0.06 100.17 53.17 46.09 0.75 Opx (n=4) 54.39 0.08 0.45 21.01 18.23 1.11 1.75 0.06 0.03 0.10 0.01 0.01 0.01 0.05 0.05 0.02 97.36 3.93 56.49 39.32 0.26 Cpx (n=15) 51.74 0.36 1.43 9.27 14.06 0.28 21.92 0.28 0.02 0.02 0.06 0.01 0.08 0.02 0.04 0.03 0.01 99.63 44.31 39.63 15.04 1.01 Am core (n=3) 52.29 0.43 3.54 11.98 16.42 0.23 11.69 0.39 0.18 0.01 0.07 0.02 0.02 0.05 0.03 97.34 for concordia diagrams and weighted average and concordia age calculations. from tonalites to granodiorites and granites, and (2) a basic to intermediate Am rim (n=11) 50.23 0.69 4.89 12.56 15.91 0.22 11.59 0.52 0.28 0.02 0.09 0.03 0.08 0.02 0.06 0.02 0.01 97.22 Am int (n=3) 49.92 0.76 4.94 12.67 15.71 0.17 11.71 0.52 0.27 0.02 0.12 0.03 0.08 0.00 0.02 0.03 96.97 Diorite A1015-38 Pl core (n=1) 47.84 0.02 33.65 0.30 0.01 16.44 2.25 0.08 0.03 0.01 0.10 0.01 0.02 0.06 100.80 79.77 19.78 0.44 Pl rim (n=1) 52.51 0.00 30.39 0.30 0.03 0.05 12.73 4.47 0.10 0.02 0.03 0.00 0.09 100.70 60.83 38.61 0.56 Pl int (n=11) 52.02 0.05 30.37 0.35 0.02 0.02 12.49 4.54 0.18 0.03 0.15 0.01 0.04 0.02 0.03 0.02 0.06 100.39 59.72 39.27 1.01 Opx (n=15) 53.03 0.23 0.99 20.02 22.85 0.50 1.28 0.04 0.01 0.01 0.05 0.01 0.04 0.02 0.05 0.02 0.01 99.16 2.60 64.63 32.62 0.14 Cpx (n=5) 52.23 0.23 1.02 8.53 14.70 0.25 22.50 0.29 0.01 0.02 0.01 0.03 0.04 0.02 0.01 0.03 99.92 44.73 40.68 13.55 1.05 Am rim (n=7) 47.83 1.34 7.32 11.84 15.54 0.16 11.60 1.03 0.60 0.03 0.10 0.16 0.05 0.03 0.05 0.03 0.02 97.73 Am int (n=6) 46.67 1.79 7.51 11.89 15.14 0.16 11.63 1.03 0.66 0.02 0.13 0.17 0.07 0.03 0.05 0.01 0.02 96.98 group (SiO <63 wt%) formed by hornblende-biotite diorites and quartz-diorites. Diorite A1015-39 2 Pl (n=12) 51.45 0.04 31.13 0.15 0.01 0.02 12.99 4.32 0.03 0.02 0.08 0.01 0.06 0.02 0.04 0.03 0.06 100.47 62.36 37.44 0.20 Am core (n=4) 50.01 0.31 5.54 12.91 15.11 0.36 11.83 0.52 0.11 0.02 0.10 0.08 0.04 0.02 0.02 0.02 0.02 97.03 Am rim (n=3) 50.09 0.24 6.24 13.45 14.77 0.39 11.45 0.52 0.12 0.02 0.05 0.06 0.01 0.03 0.02 97.45 Am int (n=4) 49.51 0.32 6.55 13.40 14.76 0.37 11.73 0.67 0.11 0.02 0.04 0.05 0.03 0.03 0.03 0.01 97.64 Diorite A1015-40 Pl core(n=1) 50.03 0.04 31.77 0.18 0.01 13.59 3.98 0.03 0.03 0.13 0.01 0.03 0.09 99.92 65.25 34.59 0.16 Pl rim (n=2) 50.80 0.03 30.80 0.21 0.00 0.03 12.42 4.63 0.05 0.01 0.03 0.01 0.08 0.05 0.07 0.03 0.06 99.31 59.55 40.16 0.29 Pl int (n=16) 51.99 0.03 30.84 0.20 0.01 0.02 12.33 4.65 0.04 0.02 0.09 0.01 0.03 0.01 0.02 0.02 0.07 100.39 59.42 40.37 0.21 Am core (n=1) 52.93 0.14 2.10 11.97 17.03 0.35 11.71 0.07 0.02 0.01 0.20 0.02 0.11 0.05 0.01 96.65 Am rim (n=1) 46.85 1.61 8.60 13.57 13.92 0.22 11.47 0.71 0.24 0.03 0.03 0.10 0.01 0.03 97.38 In the latter group, we included atypical low-silica rocks (SiO2 <52 wt%) with Am int (n=16) 48.25 1.17 6.42 12.58 14.93 0.30 11.69 0.58 0.20 0.02 0.07 0.03 0.05 0.02 0.03 0.03 0.01 96.37

■■ RESULTS MgO <8 wt% (many at ~6 wt% MgO), variable TiO2, and K2O <1 wt%. Most of these atypical diorites have Mg# within the range 0.5–0.6, where Mg# = 1 Supplemental Material. Geochemical and geochro- Mineral and Petrographic Features molar MgO/(MgO + FeOT), and T stands for total iron as FeO. Similar to other nologic data. Please visit https://doi.org/10.1130 Andean-type batholiths (Castro, 2020), plutonic rocks of the North Patago- /GEOS.S.13705915 to access the supplemental material, and contact [email protected] with any Plutons of the North Patagonian batholith are composed of homogeneous nian batholith are magnesian, plotting below Miyashiro’s line separating questions. diorites, tonalites, granodiorites, and monzogranites. Textural variations are tholeiitic (ferroan) from calc-alkaline (magnesian) series on the basis of the

Figure 2. Representative structures and petrographic relations of rocks from the North Patagonian batholith in the Aysén region. (A, B) Magmatic layering with concentrations B of mafic minerals (Bt and Amp) alternating with granitic layers (San Nicolás bridge). (C, D) Mingling relations of diorites (dark) and granites with inclusions of xenoliths from a tonalite (To) host (area between Melimoyu and Correntoso creeks, Chile). (E–H) Back- scattered electron images (atomic number Z-contrast) showing representative relations of diorites and granodiorites of the Aysén region. Abbreviations of mineral names are after Whitney and Evans (2010). See text for details.

FeO/(FeOT + MgO) ratio (Frost et al., 2001; Miyashiro, 1974), and calc-alkalic according to the alkali-lime Peacock index. They are metaluminous to weakly

peraluminous at silica values of >70 wt% SiO2 and show linear variations in Harker variation diagrams, which are compatible with magmatic differentiation (Fig. 3). Trace elements show depletion in Nb, compared with the neighbors D K and La, in the MORB-normalized diagrams (Fig. 4A), and enrichment in large ion lithophile elements (LILEs), mostly following the pattern of continen-

tal andesites. Granites (SiO2 >63 wt%), as the most fractionated rocks, show depletions in elements such as Sr, P, Zr, Hf, and Ti, which are partitioned to To the coexisting solid assemblage. Differences in chondrite-normalized REEs between diorites and granites (Figs. 4B–4E) occur irrespective of the age of generation. Mesozoic and Tertiary diorites display gentle slope patterns with positive Eu anomalies in some samples and slightly negative or no anomaly in others. Granites display more fractionated patterns with higher light REE/ heavy REE ratios. Those relations are compatible with fractionation of granites from diorites and, in both cases, in the absence of heavy REE fractionating phases such as garnet. A complete list of isotopic ratios is given in Table 1. With the exception of E A101529 A101531 two samples (PAL14–7 and PAL14–8), the rest of the dated samples were ana- Amp Kfs lyzed for Sr-Nd isotopes. Strontium isotopic initial ratios varied within a narrow Amp Qz Pl 87 86 143 144 range of ( Sr/ Sr)i = 0.7037–0.7065. Neodymium initial ratios ( Nd/ Nd) were normalized to bulk earth ratios and are given in epsilon (ε) notation, ranging Qz from −2.66 to +3.19 ε units. The most primitive ratios were displayed by the Pl youngest plutons of the Aysén region. Isotopic mixing curves were calculated using the general mass balance equations for Sr and Nd (in mg/kg; ppm in the equations) and the respective initial isotopic ratios of end members involved:

Mix B CC 87Sr 87Sr 87Sr A101533 A101527 = Sr B X + Sr CC (1 X ) , (1) G H 86 86 ppm B 86 ppm B Amp Bt Sr Sr Sr Pl and Qz Amp 143 Mix 143 B 143 CC Nd Nd B Nd CC 144 = 144 Ndppm X B + 144 Ndppm (1 X B ) , (2) Pl Nd Nd Nd Cpx

where XB refers to the fraction of oceanic crust in the mixture, and the super- scripts Mix, B, and CC refer to the isotopic ratios of mixture, oceanic crust, and continental crust, respectively. For the end-member B, the average composition

SiO 2 (wt%) 1000 45 50 55 60 65 70 75 80 2 100

1 10

TiO 2 (wt%)

20 Rock/MORB 1 0 15 Al2O3 (wt%) 0 i K P Y T Zr Sr Hf Th Tb La Ba Yb Rb Tm Nb Nd Sm 12 Ce 10 1000 Aysén Mesozoic Aysén Mesozoic 8 B (Diorites) (Granites s.l.) 8 FeO (wt%) 4 100 0 4 MgO (wt%)

12 0 10

Rock/chondrite CaO (wt%) 8 4 Ce Nd Eu Tb Ho Tm Lu Ce Nd Eu Tb Ho Tm Lu 1 La Pr Sm Gd Dy Er Yb La Pr Sm Gd Dy Er Yb 6 Na2O (wt%) 0 1000 Bariloche 4 D Aysén Tertiary E (Diorites) Mesozoic 2 5 granites/tonalites

0 4 100

K2O (wt%) 1 10

0 45 50 55 60 65 70 75 80 Qz-diorites

SiO 2 (wt%) Rock/chondrite Aysén plutons Bariloche plutons Ce Nd Eu Tb Ho Tm Lu Ce Nd Eu Tb Ho Tm Lu 1 Diorite/Qz-diorite (Mesozoic) Diorite/Qz-diorite La Pr Sm Gd Dy Er Yb La Pr Sm Gd Dy Er Yb Granites (Mesozoic) Granites Diorite/Qz-diorite (Tertiary) Figure 4. Trace-element diagrams of samples from the North Patagonian ba- No age available tholith. (A) Mid-ocean-ridge basalt (MORB)–normalized (Thompson et al., 1984) spider diagram. (B–E) Chondrite-normalized (Nakamura, 1974) plots of rare Figure 3. Silica variation diagrams (Harker) showing the trend of earth elements (REEs) comparing patterns of dioritic and granitic rocks from representative samples from the North Patagonian batholith in the Bariloche and Aysén regions. In all diagrams, the average composition of the regions of Aysén and Bariloche. Qz—quartz. continental andesites (Kelemen et al., 2003) is shown (purple line). Qz—quartz.

TABE 1. Sr AND Nd ISOTOPES OF SAMPES FROM NORTH PATAGONIAN BATHOITH

87 86 87 86 87 86 17 1 13 1 Sample SiO2 Age Rb Sr Rb/ Sr Sr/ Sr 2SD Sr/ Sri Sm Nd Sm/ Nd Nd/ Nd 2SD εNdt TDM t Ma ppm ppm ppm ppm Ga A1015‑36 5.33 5. 0.1 2.8 380.7 0.2267 0.702 0.002 0.702 .067 16.5515 0.186 0.512728 0.003 1.80 0.71 pal1‑10 5.5 6.2 0.1 2. 305.2 0.065 0.702 0.002 0.7020 3.78 16.1671 0.185 0.51278 0.002 2.8 0.57 A1015‑31 8.25 6. 0.2 15. 50.3 0.015 0.701 0.003 0.7018 3.53 13.6627 0.1555 0.512800 0.002 3.1 0.5 A1015‑33 53.3 6. 0.2 23. 303.5 0.223 0.7023 0.003 0.7021 3.101 12.0061 0.1562 0.512658 0.003 0.2 0.76 A1015‑2 60.01 8 0.2 60.5 301. 0.5803 0.7073 0.002 0.7066 5.652 23.60631 0.18 0.512722 0.001 1.6 0.66 A1015‑30 60.5 15.8 0.2 3. 337. 0.3760 0.7002 0.003 0.7033 3.32 1.53171 0.1383 0.512756 0.003 2.2 0.61 A1015‑38 51.5 15. 0.1 5.3 68.7 0.0326 0.7026 0.00 0.7025 5.58 5.57 0.606 0.51265 0.003 –0.52 0.8 core: 16.1 0.2 A1015‑0 7.80 33. 0. .2 500.8 0.023 0.7018 0.003 0.7017 1.83 6.7278 0.1702 0.512775 0.002 2.7 0.60 A1015‑21 55.27 0 1. 31.2 502.1 0.17 0.707 0.002 0.702 .577 17.52201 0.157 0.51272 0.002 2.22 0.68 A1015‑28 55.6 10. 0.8 .7 08.8 0.3166 0.708 0.003 0.702 6.023 26.3500 0.1382 0.512628 0.003 0.58 0.82 A1015‑22 67. 107 1 130. 21. 1.232 0.70630 0.003 0.703 .717 22.605 0.125 0.51261 0.002 1.02 0.7 A1015‑2 72.83 113 0.6 81.6 222.0 1.0631 0.70566 0.003 0.7035 .672 1.032 0.156 0.512686 0.003 1.67 0.75 A1015‑25 72.12 11.7 1.6 10.1 183.6 1.617 0.70637 0.00 0.7036 3.3 1.071 0.108 0.512703 0.00 2.56 0.68 A1015‑27 57.1 121.7 0.7 36.1 35.3 0.3028 0.7056 0.002 0.700 .26 17.2306 0.1502 0.512617 0.00 0.31 0.86 A1015‑26 6.15 123.7 0.5 105. 16. 1.8651 0.7075 0.003 0.7025 .338 20.2888 0.123 0.51268 0.002 2.2 0.71 pal1‑15 8.6 12.8 0.8 3.6 32.1 0.0238 0.70567 0.003 0.70562 3.002 11.050 0.151 0.512565 0.002 –0.7 0.6 A‑208‑6 71.32 1. 1. 38.7 273. 0.085 0.7052 0.003 0.70505 2.777 11.65600 0.10 0.51260 0.002 2.02 0.75 A‑208‑8 50.71 15.5 1.8 51.0 31.2 0.322 0.70577 0.003 0.7082 3.18 13.0100 0.152 0.512608 0.002 0.25 0.8 A‑208‑33 7.50 156.8 2.5 116.2 1.7 2.271 0.71020 0.003 0.7051 2.803 1.0100 0.1137 0.512527 0.003 –0.50 0.5 A‑208‑11 62.8 161.7 2.6 3.0 31.6 0.353 0.70560 0.003 0.706 5.07 2.100 0.133 0.512650 0.002 1.3 0.81 A‑208‑1 75.66 163.5 2.7 18.5 3.7 6.10 0.7132 0.003 0.7050 5.0 28.71800 0.12 0.51250 0.002 –2.16 1.0 A‑208‑22 6.7 166.7 2.2 61.2 2.1 0.6027 0.70725 0.003 0.70581 3.528 20.100 0.105 0.51203 0.002 –2.6 1.13 A‑208‑13 71.80 168. 2.3 155.0 161.0 2.787 0.7118 0.003 0.7051 6.36 2.07100 0.1330 0.5128 0.002 –1.36 1.03 A‑208‑1 60.8 171 5 7.1 378.3 0.5673 0.70720 0.003 0.70582 6.60 30.2300 0.128 0.51225 0.002 –2.66 1.13 A‑208‑31 7.30 171 3 2.0 187.8 1.17 0.7085 0.003 0.7051 5.553 2.50000 0.1138 0.512528 0.002 –0.3 0.5 A‑208‑20 71.6 171.6 2.6 170.2 15.8 3.378 0.7130 0.003 0.7080 8.312 3.5300 0.127 0.51238 0.002 –2.38 1.11 A‑208‑2 56.1 172.5 3.1 50.6 73.0 0.303 0.70525 0.003 0.70 6.123 25.500 0.152 0.512500 0.002 –1.56 1.05 A‑208‑8 77.55 173.2 2.7 86.3 7.0 5.328 0.715 0.003 0.7068 6.3 30.5100 0.1276 0.51257 0.002 –0.25 0. Note: SDstandard deviation; TDMdepleted mantle model. ‑Pb zircon ages ere taken from Castro et al. 2011.

of Sr-rich altered oceanic crust from Ocean Drilling Program (ODP) Site 801 Supplemental Material (Table S4). Thermobarometric and hygrometric data was used (Kelley et al., 2003), and the isotopic initial ratios from the mean were obtained with the equations of Ridolfi and Renzulli (2012) and are shown

composition of ocean-ridge basalts were used (Gale et al., 2013). An analysis in pressure-temperature (P-T) and temperature-water (T-H2O) diagrams (Fig. 5). of secular variations of isotopic ratios is given in the Discussion. Equation 1b of Ridolfi and Renzulli (2012) was used for pressure calculations. All samples were equilibrated at low pressure (300–100 MPa), and most of them below 200 MPa. With exception of a Tertiary diorite from Aysén (A1015–38) that Amphibole Thermobarometry yielded the highest temperature at ~900 °C, the rest of the samples clustered at 800 °C (840 °C at maximum). Amphibole was present in nearly all studied rocks in the Aysén and Bari- Furthermore, P-T conditions of magma emplacement were also estimated loche regions. It was analyzed with an electron microprobe, together with with the new calibrations of the amphibole-plagioclase NaSi-CaAl exchange associated plagioclase and occasionally pyroxene, in samples analyzed for thermometer (Molina et al., 2020) using the expressions A1, A2, and B2 (preci- zircon dating and isotopic relations. The aim was to obtain the temperature, sion ~±50 °C), and the Si/Al amphibole-plagioclase partitioning barometer from pressure, and water content data of magmas at the time of crystallization. Molina et al. (2015) (Fig. 5; Table S5). Calculations were done with expressions A complete list of amphibole analyses and calculations is given in the A1 and A2 at 0.1 and 1.5 GPa, as these show a negligible pressure dependence,

Tertiary samples from Aysén Molina et al. 2015, 2020 Ridolfi and Renzulli, 2012 thermobarometry thermobarometry

29 (8 Ma; 60.01 wt% SiO2) 29 (8 Ma; 60.01 wt% SiO ) 300 2 30 (15.8 Ma; 60.95 wt% SiO2) 31 (6.4 Ma; 48.25 wt% SiO2) 33 (6.4 Ma; 53.34 wt% SiO ) 31 (6.4 Ma; 48.25 wt% SiO2) 2 36 (5.9 Ma; 54.33 wt% SiO ) P error 2 33 (6.4 Ma; 53.34 wt% SiO2) 38 (7.12/16 Ma; 51.54 wt% SiO2) 8 40 (32.5 Ma; 47.8 wt% SiO2)

36 (5.9 Ma; 54.33 wt% SiO2) T error 200 38 (7.12/16 Ma; 51.54 wt% SiO2) 6

i T error o r i O (wt %) 4 t

e 2 Pressure (MPa)

H >

Intensity 6 W 0 100 e w 2 t g t% ra n it c e ry so s lid ta us ls 700 800 900 T (°C) 0 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 2000 Temperature (ºC) Figure 5. Pressure-temperature plots showing the results of amphibole B Mesozoic samples from Aysén thermobarometric and hygrometric calculations (Ridolfi and Renzulli, 2012) Ridolfi and Renzulli, 2012 with samples from Aysén (A, B) and 300 Molina et al. 2015, 2020 thermobarometry Bariloche (C). Pl-Amp-Pl thermobarom- thermobarometry 26 (124 Ma; 69.15 wt% SiO2) etry results (Molina et al., 2015, 2020) 27 (122 Ma; 57.41 wt% SiO ) 26 (124 Ma; 69.15 wt% SiO2) 2 are shown for Aysén samples for a con-

22 (107.3 Ma; 67.44 wt% SiO ) D 27 (122 Ma; 57.41 wt% SiO ) 2 stant pressure of 100 MPa, considered

2 i 8 o

28 (104.7 Ma; 55.46 wt% SiO ) r

28 (104.7 Ma; 55.46 wt% SiO ) 2 i 200 2 t as a subvolcanic pressure. Error bars

> 6 are displayed below the legend for each

6 0 method. Amphibole hygrometric results

t % are shown as Kernel density plots at the

O (wt %) 4 Intensity 2 Pressure (MPa) c ry H right of pressure-temperature diagrams. 100 s ta Wet granite solidus are after Johannes ls 2 and Holtz (1996). The curve of 60 wt% W et crystals is traced by thermodynamic gr ani te so lidus 700 800 900 modeling with Rhyolite-MELTS (Gualda 0 T (°C) 350 400 450 500 550 600 650 700 750 800 850 900 950 et al., 2012). Analyzed samples are labeled indicating the silica content. Temperature (ºC) Samples from Bariloche

A2018-8 (154.5 Ma; 50.71 wt% SiO2)

A208-7 (56.92 wt% SiO2) 300 A208-14 (171 Ma; 60.98 wt% SiO2)

AN04-110 (62.15 wt% SiO2)

A208-21 (64.52 wt% SiO2)

AN04-102 (64.93 wt% SiO2) D 8 i A208-10 (69.88 wt% SiO ) o 2 r

200 t

> 6

6 0

w Intensity

t % O (wt %) 4 2

c H r

Pressure (MPa) 100 y s ta 2 ls

W et gr ani te so lidus 700 800 900 0 T (°C) 600 650 700 750 800 850 900 950 Temperature (ºC)

and with expression B2, which is not pressure related (Molina et al., 2020). line of points located along the Chile Trench in the segment between 38°S Average values of temperatures were used for the barometric calculations. and 55°S, at 1° intervals and taking South America as the fixed plate. Special Temperature estimates were even lower than those calculated by the equations emphasis was placed on the zone corresponding to the North Patagonian of Ridolfi and Renzulli (2012). Temperatures for diorites, considering the three batholith (39°S to 46°S). The relative angular velocity vectors of the involved expressions together, are 724–761 °C at the cores of amphibole and plagioclase, plates were obtained from distinct sources from the literature (see references decreasing to 642–703 °C at the rims. In quartz-diorites, temperature estimates in the caption to Fig. 6). Determination of the 3 × 3 matrices of total recon- are more homogeneous, ranging from 667 °C to 707 °C. Pressure estimates struction rotations was directly derived from the compiled data. Following for both diorites and quartz-diorites cluster around zero, thus being consistent the rules of finite rotations (Cox and Hart, 1986), the matrices of forward with magma crystallization in a shallow environment. motion stage rotation were determined. For each stage, the angular velocity These temperatures were compared (Fig. 5) with the position of the vector from 70 Ma to 0 Ma, with intervals of 5 m.y., was obtained. From that water-saturated granite minimum (Johannes and Holtz, 1996) and the curve information, standard procedures allowed computation of the relative linear for 60 wt% crystals of diorite A1015–36 with 2 wt% initial water, calculated velocity vectors at each studied site along the Chile Trench. In the case of with the Rhyolite–MELTS thermodynamic model (Gualda et al., 2012). Melt the displacement of Aluk relative to South America, finite rotation matrices water content in equilibrium with amphibole was estimated by amphibole describing the relative displacement of these two plates are not available. hygrometry (Ridolfi and Renzulli, 2012). Therefore, it was necessary to use the “absolute” motions of Aluk and South America relative to a hotspot reference frame (HS) for the period between 64 Ma and 0 Ma to obtain the total reconstruction rotations of Aluk relative to U-Pb Zircon Geochronology South America. The rest of the procedure matches the one used for the rotation of Farallon/Nazca versus South American plates. The period between 180 In total, 492 spots from 19 North Patagonian batholith plutonic rocks in and 85 Ma lacked data for some time intervals (Engebretson et al., 1985). The the Aysén area were analyzed for U-Pb SHRIMP zircon geochronology. Zircon need to obtain information every 5 m.y. forced us to determine those rotations crystals showed a wide range in size and morphology, from rounded (sub- by calculating the intermediate rotation matrices. The remaining procedure hedral) to prismatic (euhedral), including simple crystals, composite cores was identical to that explained for the period 64–0 Ma. No information was with simple concentric zoning, banded zoning, one or more overgrowths, and found for the period 85–60 Ma. unzoned sectors. Descriptions of analyzed zircons, concordia diagrams, and The kinematic analysis presented here does not differ from previous studies CL images are shown in the Supplemental Material and Figure S1. Isotopic regarding the nature of the methodology used to obtain the relative velocity data are given in the Supplementary Material (Table S3). The U-Pb ages of vectors of the different subducting plates with respect to the South American igneous zircon defined two sequential age groups: (1) a Cretaceous group, plate. However, there are two aspects that make the approach presented in including diorite, granodiorite, tonalite, and granite plutons, ranging from ca. this work novel. First, a long period of time was modeled (the last 180 m.y.), 142 to 90 Ma and displaying a wide range of Th/U (0.2–2.38), and (2) a Tertiary while previous studies tended to focus on specific stages of the evolution group, comprising diorite, tonalite, and gabbro plutons ranging from ca. 34 of the Andean margin. Second, the variation in the relative velocity vectors to 4 Ma and with a wide range of Th/U (0.12–2.19). Only 2% of analyses repre- between the plates over a large segment of the margin (between 38°S and sented inherited zircon crystals distributed in a diorite (ca. 608, 607, 497, 123, 55°S) was analyzed in great detail (1° intervals). In previous studies, the inter- 120 Ma), a gabbro (ca. 120, 119 Ma), and a granodiorite-tonalite (ca. 366, 362, est had focused on the determination of vectors of average relative velocity 356 Ma), indicating recycling of Neoproterozoic, Paleozoic, and Cretaceous or in much less extensive areas, without the coverage that has been given in sources. After integrating the ages from the Aysén and Bariloche sections this work. Because both the methodology and the databases used here and (Figs. 1A and 1B), three main peaks of plutonic activity at 168, 121, and 12 Ma in other works are the same, the results for specific points of the margin and were identified in the North Patagonian batholith. for specific periods of time are very similar to those previously published by other authors (e.g., Haschke et al., 2006a; Pardo-Casas and Molnar, 1987; Somoza, 1998; Somoza and Ghidella, 2012). However, the approach presented ■■ KINEMATIC ANALYSIS OF LITHOSPHERIC PLATES in this work is the only one that allows a detailed comparison between the tectonic setting in terms of relative plate motions and the geochemical and Determination of the linear velocities of the Farallon-Nazca (breakup of Far- geochronological evolution of the North Patagonian batholith, which was the allon to Cocos and Nazca plates took place at around 25–23 Ma), Phoenix-Aluk objective of this study. (hereafter called Aluk), and Antarctic plates relative to the South American The kinematic evolution of lithospheric plates that were involved in the plate during the last 180 m.y. was performed following standard procedures generation of the North Patagonian batholith is shown in Figure 6 for the of plate kinematic analysis. Relative velocity vectors were determined at a four main periods of magmatic activity. Starting with the oldest stages of

tectonic evolution (ca. 180 Ma), subduction velocities of the Aluk plate were On one hand, isotopically evolved components (e.g., older crust and sedi- high (>>140–150 km m.y.–1) and predominantly normal to the trench (α = 60°– ments) may be introduced into the mantle by subduction (Stern, 1991a, 1991b). 70°, where α is the obliquity angle, i.e., the angle between the velocity vector On the other hand, pristine mantle magmas may acquire evolved components and the azimuth of the trench) in the period 180–140 Ma (Fig. 6, stage 1). At in the continental crust by processes of magma assimilation, storage, and 140–130 Ma, a strong decrease down to 90–100 km m.y.–1 (Fig. 6, stage 2) in the hybridization (MASH; Hildreth and Moorbath, 1988). The two processes are convergence velocity coincided with similar to slightly lower α values (50°–70°). discussed in this section in light of geochemical and geochronological data Velocity values progressively increased during the period 130–100 Ma, while obtained from the North Patagonian batholith. the obliquity angle attained 80°. A new change took place between 100 and 85 Ma, with very low relative velocities (<40 km m.y.–1) of nearly orthogonal convergence. Kinematic information is lacking for the period 85–60 Ma. The Crustal Origin: Melting, Assimilation, and MASH last segment of Aluk was subducted below the South America plate between 60 and 50 Ma, with velocities of 70–80 km m.y.–1 and moderate obliquity angles The systematic presence of isotopically evolved features in Andean-type (50°–60°). The available information suggests that the Farallon–Aluk–South batholiths, and in arc magmas in general (DePaolo, 1981a), is traditionally America triple junction quickly migrated from north to south along the North attributed to crustal assimilation. The correlation between the thickness of the Patagonian batholith between ca. 50 and 45 Ma (during stage 3, Fig. 6). Sub- crust and the evolved isotopic ratios (high 87Sr/86Sr and low 143Nd/144Nd) in vol- duction of the Farallon plate started at ca. 45 Ma in the studied area, with canic rocks of central Chile was the basis for the MASH (melting, assimilation, convergence velocities and angles similar to, albeit slightly lower than, that of storage, and hybridization) hypothesis (Hildreth and Moorbath, 1988). However, the last stage of subduction of Aluk (Fig. 6, initial stage 4). A marked increase the application of the MASH model to account for the geochemical variability (up to 140 km m.y.–1) of subduction velocity happened during the Oligocene of plutons entails serious difficulties. First, the secular geochemical varia- at around 30 Ma, also with a high obliquity angle of >80° (Fig. 6, plain stage tions observed for long periods of time are not compatible with the expected 4). The kinematic history during the last 20 m.y. (Fig. 6, 15 and 0 Ma) shows a decrease of crustal contaminants in a protracted process of assimilation. Sec- progressive decrease of the relative velocity (70–80 km m.y.–1 currently) and ond, there is no clear correlation between major-element compositions and of the obliquity angle (present values are α = 80°). The Nazca–Antarctic–South evolved isotopic ratios (Nielsen and Marschall, 2017; Stern, 2020). Although America triple junction is slowly migrating northward, and it is currently located a positive correlation between silica and the Sr isotopic ratio has been found at the contact between the South and North Patagonian batholiths. Therefore, in some lavas of the Andean Central volcanic zone (Davidson et al., 1991), neither the triple junction nor the subduction of the Antarctic plate has affected other Andean volcanic centers show a scattered distribution or a constant Sr the studied zone. initial ratio for a wide range of silica content in lavas (Davidson et al., 1991). In sum, four main tectonic stages can be identified according to the Moreover, constant Nd initial ratios have been reported in Andean plutonic kinematic regime (Figs. 6 and 7): (1) Jurassic, (2) Early Cretaceous, (3) Late and volcanic rocks covering a wide range of silica from 50 to 75 wt% (Stern, Cretaceous–Paleogene, and (4) Neogene–Quaternary. Interestingly, we report 2020, his fig. 11). A process of assimilation and fractional crystallization (AFC) clear differences in the rate of magma production (volume addition rate per will produce a trend with changing initial isotopic ratios with magma com- arc length; Fig. 7A): ~4 km3 m.y.–1 km–1 for the older stages 1 and 2 (Jurassic position (DePaolo, 1981b). Third, the geochemical trends (major elements) of to Early Cretaceous), ~10 km3 m.y.–1 km–1 in stage 4 (Neogene), and very low plutons closely follow the differentiation cotectic lines and not the assimila- values during stage 3 (Late Cretaceous–Paleogene, ~0.5 km3 m.y.–1 km–1), which tion trends (see review in Castro, 2013). In the case of the North Patagonian was characterized by episodes of null magmatic activity. These tectonic stages batholith, assimilation trends pointing to metasediments are not observed, were checked for changes in the source compositions of magmas identified and the radiogenic ratios for Sr and Nd isotopes are equally found in diorites on the basis of their Sr-Nd initial isotopic fingerprints. and granites. Moreover, the lack of inherited cores in most samples implies a single magmatic cycle for the origin of zircon and the absence of local assimilation in the crust during ascent and emplacement of plutons. ■■ DISCUSSION Andean-type batholiths could have been generated by melting of a hybridized lower crust (Hammerli et al., 2018). Although this mechanism can In Andean (= Cordilleran) batholiths, the origin of granites is a controversial account for hybrid isotopic features, high melt fractions are required to pro- matter. The melting of the lower crust and fractionation from a basic magma duce tonalites and granodiorites from a hybrid crustal source, implying very precursor followed by crustal assimilation are in principle able to produce high temperatures around 1000–1100 °C at lower-crustal pressures (1–1.5 GPa) granitic magmas. The two opposite hypotheses account for the hybrid (crust + according to experimental data (Castro et al., 2010). These temperatures are mantle) composition of granitic batholiths. However, the way magmas acquire higher than those predicted by thermal models, even when high proportions these crustal components is debated. of basaltic sills were emplaced at the lower crust (Annen and Sparks, 2002).

80ºW 75ºW 70ºW 65ºW 80ºW 75ºW 70ºW 65ºW 80ºW 75ºW 70ºW 65ºW 175 Ma 150 Ma 130 Ma 40ºS 40ºS 40ºS 40ºS

45ºS 45ºS 45ºS 45ºS

Stage 1 Stage 1 Stage 2

50ºS 50ºS 50ºS 50ºS

55ºS 55ºS 55ºS 55ºS

80ºW 75ºW 70ºW 65ºW 80ºW 75ºW 70ºW 65ºW 80ºW 75ºW 70ºW 65ºW 110 Ma 90 Ma 60 Ma 40ºS 40ºS 40ºS 40ºS

Figure 6. Reconstructed Aluk, Nazca, and Antarctic 45ºS 45ºS 45ºS 45ºS plate motions relative to a fixed South American plate. Although the entire time period spanning Stage 2 Stage 3 Stage 3 from 180 Ma to 0 Ma has been studied, only 12 selected snapshots are shown here, representative of 50ºS 50ºS 50ºS 50ºS the four evolution stages mentioned in the main text. The maps show, using Universal Transverse Mercator (UTM) projection, the present-day Chilean and Argentinian coastlines and the trench contour. The triple junctions are represented when it is required. The computed velocity vectors are plotted 55ºS 55ºS 55ºS 55ºS at scale on the moving plates and located along the trench, with 1° spacing. The data sources are 80ºW 75ºW 70ºW 65ºW 80ºW 75ºW 70ºW 65ºW 80ºW 75ºW 70ºW 65ºW as follows: displacement of Nazca relative to South Nazca America (DeMets et al., 2010; Somoza and Ghidella, 50 Ma plate 45 Ma 30 Ma 2012); displacement of the Antarctic plate relative 40ºS 40ºS 40ºS 40ºS to South America (Cande and Leslie, 1986; DeMets et al., 2010); displacement of Aluk relative to South America (Engebretson et al., 1985; Gordon and Jurdy, 1986); displacement of triple junctions relative to 45ºS 45ºS 45ºS 45ºS South America (Cande and Leslie, 1986; Somoza and Ghidella, 2012). Computation of the relative velocity vectors followed the rules of finite rotations Stage 3 Stage 3 Stage 4 (Cox and Hart, 1986). Concerning the novelty of the convergence directions relative to those calculated 50ºS 50ºS 50ºS 50ºS elsewhere, see the main text.

Aluk 55ºS 55ºS plate 55ºS 55ºS

80ºW 75ºW 70ºW 65ºW 80ºW 75ºW 70ºW 65ºW 80ºW 75ºW 70ºW 65ºW 20 Ma 15 Ma Nazca 0 Ma plate Chile Argentina 40ºS 40ºS 40ºS 40ºS North 50 km m.y.-1 Patagonian Batholith

45ºS 45ºS 45ºS South 45ºS American plate Stage 4 Stage 4 South Patagonian 50ºS 50ºS 50ºS Batholith 50ºS

N Antarctic 55ºS 55ºS 55ºS plate Chile 55ºS trench 80ºW 75ºW 70ºW 65ºW 80ºW 75ºW 70ºW 65ºW 80ºW 75ºW 70ºW 65ºW

Neogene Quaternary Paleogene Cretaceous Jurassic

M O E P Upper Lower U M L per arc-length (Ays é n) Pl Volume addition rate 160 38ºS 10 (km

) 42ºS 120 8 3 -1 46ºS m.y. 80 6 m.y. -1

4 km

(km 40

4 3 2 1 2 -1 )

Relative velocity 0 0 90°

Figure 7. Summary of plate kinematics data and

α correlations with Sr and Nd initial isotopic ratios N dextral of plutons. (A) Time variation of plate velocities 0° + sinistral - computed for the displacement of the Aluk (before

Angle 50–40 Ma) and Nazca (after 50–40 Ma) plates relative to the South American plate at three selected latitudes, corresponding to the northern (38°S) and -90° southern (46°S) boundaries of the North Patagonian 0 50 100 150 batholith and its central line (42°S). Angle α is con- Arc narrowing Time (Ma) before present vergence obliquity (α = 0° for parallel and α = 90° Flat subduction for orthogonal relative displacement). Positive/neg- Mountain building Contraction ative values refer to dextral/sinistral convergence. Subduction erosion Extension Approximate volume addition rate per arc-length Subduction of Triple of plutonic rocks at Aysén was calculated based on junction Farallon/Nazca plate Subduction of Aluk plate map relative surfaces, a N-S length of 200 km, and Breakup Opening southern Karoo mantle considering an average depth of 10 km for the ba- Farallon plate South Atlantic ocean plume tholith according to models (Cruden et al., 2018). Age bins are large due to the scarce number of available ? ? age determinations at the studied zone. Values are Main apparently lower than typical arc magma production unconformities rates (e.g., Wörner et al., 2018), first, because of the bin size and, second, due to the fact that the volcanic B rocks and the lower-crust intrusions have not been considered. In any case, the time variations of the Aysén addition rate shown by the upper-crust batholith +5.0 Bariloche have a very clear expression, regardless of similar variations in the contemporary volcanism or magma emplacement at the lower crust. Relevant tectonic events in the South American plate (Echaurren et al., 0.0 2017; Folguera and Iannizzotto, 2004; Haschke et al., 2006b; Orts et al., 2012) are also shown. Numbers 1 Nd(t) to 4, separated by thick, vertical, dashed gray lines, mark the four evolutionary stages identified in this -5.0 work. U—Upper; M—Middle; L—Lower. (B) Initial isotopic ratios of 87Sr/86Sr and 143Nd/144Nd, the latter in epsilon notation, for dated samples of the North Patagonian batholith, calculated at the time (t) of magma generation. Numbers 1 to 4, separated by thick, vertical, hashed gray lines, mark the four evo- Bariloche lutionary stages identified in this study. M—Miocene, O—Oligocene, E—Eocene, P—Paleocene. 0.7060

0.7050 Aysén

0.7040

0.7030

0 50 100 150 200 Time (Ma) before present

Water-assisted melting of lower-crust sources (Qian and Hermann, 2013) may Aysén plutons Bariloche plutons proceed at lower temperatures, giving rise to water-saturated granitic liquids. Diorite/Qz-diorite (Mesozoic) Diorite/Qz-diorite Granites (Mesozoic) Granites This is in contradiction with the characteristic water-undersaturated condi- Diorite/Qz-diorite (Tertiary) tions that prevail during crystallization of magmas in the upper crust. In sum, No age available although crustal signatures are implicit in Andean-type batholiths, a crustal 12 origin for magmas is very unlikely. Experimental residues 10 (Pl, Px) Fractionation from a Dioritic (Andesitic) Parental Magma 8 Experimental A plausible interpretation, as an alternative to crustal melting and assim- cotectic ilation, is fractionation from a mafic magma precursor coming from the 6 array

subduction system and carrying crustal signatures. The composition of this CaO (wt%) Diorites & gabbros Mostly cumulates mafic precursor has been widely debated. Models based on a basaltic composi- 4 tion have failed to explain the geochemical features of magmas and the scarcity

of ultramafic residues in the lower (arc) crust. By contrast, the “andesite model,” 2 Fractionated which was introduced by S.R. Taylor years ago (Taylor, 1967), accounts for liq- Tonalites/granodiorites/granites uid compositions (diorites and granodiorites) in Cordilleran batholiths (Castro, 0 2013, 2020; Castro et al., 2010, 2013). Moreover, major-element trends of arc 0 2 4 6 volcanics and calc-alkaline batholiths follow curved linear patterns (for review, MgO (wt%) see Castro, 2020), which are compatible with liquid lines of descent relating to intermediate (andesitic) parental compositions as the precursors of batholiths. Figure 8. CaO-MgO diagram (wt%) showing the North Patagonian batholith samples compared with the low-water cotectic array and their Accordingly, proxy diagrams (Fig. 8) plotting major oxides, for which corresponding plagioclase-pyroxene (Pl-Px) solid residues (details on this variations are controlled by phase relations, were used here to reveal the array are given in Fig. 9). Yellow star marks the composition of model main process responsible for geochemical variations in the North Patagonian parental magmas for calc-alkaline batholiths (Castro, 2020) (see text for batholith. Rock compositions plot along the low-water main cotectic array of additional explanation). Qz—quartz. calc-alkaline systems, which was traced from experiments using a modeled parental intermediate magma (Castro, 2020, 2021). This parental magma has

a dioritic composition (with SiO2 = 58.6 wt%, FeO = 7.3 wt%, MgO = 3.2 wt%, 1 GPa and 1100–800 °C (Fig. 9B) using a modeled diorite composition as the

CaO = 6.5 wt%, K2O = 1.5 wt%), and it was determined by two independent starting material (yellow star in Fig. 9A). Diorites and gabbros with higher approaches: (1) near-solidus experiments on lower-crust granulites, assumed MgO and CaO contents may represent cumulates. In fact, many of these to be cumulates formed in the course of fractionation to granitic melts; and diorites and gabbros often overlap lower-crust granulitic compositions. This (2) the composition of the gap observed in the Patagonian batholith. The fol- supports the inference that diorites-gabbros are related by a fractionation lowing observations arise from the comparison between the experiments and process similar to that connecting granites and granulites on a wider scale. North Patagonian batholith samples (Fig. 8): (1) Those rocks richer in silica Furthermore, liquid and bulk solid compositions are very similar at 0.3 and

(SiO2 >63 wt%) follow a pattern that is on average very similar to the low-water 1 GPa (Fig. 9), implying that lower- and upper-crust differentiation processes

cotectic array. (2) Diorites and quartz-diorites (SiO2 <63 wt%) plot in an area can give similar results. There is a significant gap along the cotectic, also overlapping Pl-Px solid residues, which belong to the same experiments that reproduced by experiments, that supports fractionation as the main process yielded the cotectic liquids. relating granitic rocks (mostly granodiorites) and quartz-diorites. The two These comparisons extend to the whole Patagonian batholith to empha- groups are marked by two kernel density maxima in the CaO-MgO diagram size that interpretations from the Aysén and Bariloche regions of this study (Fig. 9B) and coincide with experimental liquids at 1050 °C and 1000 °C, at are not local and can be of general applicability. The low-water cotectic array, 0.3 GPa. A big jump in composition within a 50 °C margin is parallel to an mentioned above, is compared with the composition of the whole Patagonian increase in liquid percentage from 38 wt% at 1000 °C to ~60 wt% at 1050 °C batholith in Figure 9. Other cotectic trends resulting from high-water exper- (see inset in Fig. 9B), a phenomenon considered intrinsic to fractionation of iments are also shown for comparison (Fig. 9A). It is clear that low initial arc magmas (Reubi and Blundy, 2009).

water conditions prevailed in the batholith parental magmas. The low-water These data support the interpretation that granitic rocks (SiO2 >63 wt%) cotectic line was traced from experimental liquids at conditions of 0.3 and of the Aysén and Bariloche regions represent fractionated liquids from a

common parental intermediate magma of dioritic composition. Most diorites and some scarce gabbros with low silica and low MgO contents (Fig. 8) 14 may represent cumulates, i.e., crystal mushes that lost a residual granitic liquid during crystallization. A discussion on the mechanism of crystal/liquid 12 separation is out of the scope of this paper. Separation of a crystal-rich mush and a fractionated liquid (magmatic splitting) is intrinsic to crystallization at the thermal boundary layers of ascent conduits (Rodríguez and Castro, 10 2017). Crystallization experiments and the mechanical behavior of magmas in conduits, where mafic microgranular enclaves are generated (Fernández 8 and Castro, 2018), support magma splitting as a mechanism responsible for U18 crystal/liquid segregation. Such magmatic enclaves are common features to AP09 QH13

all Andean batholiths, and their presence proves two essential aspects that 6 must be considered in addressing petrogenetic interpretations of batholiths.

First, they represent early magma pulses that quenched against the ascent CaO (wt%) 4 conduits, which supports a near-liquid state of the magmas. Second, they are

indicators of magmatic fractionation leading to differentiation during ascent MCA Liquids Cumulates and emplacement of plutons. Trace elements also support magma fractionation 2 as the process linking diorites and granites in the North Patagonian batholith (Castro et al., 2011). Fractionation of REEs is compatible with fractionation of 0 solid assemblages dominated by clinopyroxene and plagioclase. 0 2 4 6 8 10 12 Amphibole thermometry and hygrometry (measurement of the liquid water MgO (wt%) content in equilibrium with amphibole) constitute relevant data because they B can be used to constrain the origin of magmas. In accordance with textures, 5 1100 ºC which reveal amphibole crystallization in late magmatic stages in dioritic and 1050 ºC granitic rocks (Figs. 2E–2H), amphibole temperatures yielded values below 4 800 °C (Fig. 5). These temperatures are near-solidus in diorites, implying that amphibole started to precipitate in dioritic magmas when the crystal content 3 300 MPa was higher than 60 wt%, which is in total agreement with textural observa- 60

tions. A comparison was made with the curve at 60 wt% of crystals, calculated 40 with Rhyolite-MELTS from a diorite with 2 wt% initial water content (Fig. 5). 2 Intensity 1000 ºC The results were consistent with hygrometric estimates, which clustered at CaO (wt%) 20 900 ºC % of liquid ~5–6 wt% water and 780–810 °C, supporting the supposition that an initial 1 0 water content of ~2 wt% would have been sufficient to reach the necessary 900 ºC 600 800 1000 800 ºC T (°C) conditions for amphibole crystallization at later stages. Amphibole crystals 0 formed at lower temperatures yield higher melt water contents (Fig. 5), which 0 1 2 3 4 is compatible with water enrichment in the residual melt of a crystallizing MgO (wt%)

magma. In our case, low-temperature amphiboles formed near the solidus Figure 9. Diagrams showing the comparison of experimental data with the overall compo- of the water-saturated granite minimum (Fig. 5), with some of them being sition of the Patagonian batholith. (A) Kernel density plot of the Patagonian batholith (238 subsolidus actinolites. In the case of the Bariloche area, where granitic rocks samples) compiled from the literature (see Castro, 2020). Cotectic arrays from high-wa- are dominant, amphibole temperatures were also near the solidus, which ter-content and low-water-content experiments are also shown. These are: U18 (Ulmer et al., 2018); AP09 (Alonso Perez et al., 2009); QH13 (Qian and Hermann, 2013); MCA (main implies low initial water content in the magmas. Near-solidus crystallization of cotectic array; Castro, 2021). The region of cumulates overlaps with many lower-crust amphibole, which is a characteristic feature of Andean-type batholiths (Castro, granulites (blue squares). (B) Detail of the granitic (sensu lato) region of the former di- 2013), is also supported by the common pyroxene-to-amphibole replacement agram showing the 1 wt% water cotectic array (MCA) traced after the compositions of textures as a consequence of rehydration of the residual liquid (Beard et al., experimental liquids at 300 MPa (yellow triangles) and 1 GPa (orange diamonds; Castro, 2021). The compositional jump between the two maxima takes place within the range 2004). Also, the presence of polycrystalline amphibole aggregates (clots) proof 50 °C at 300 MPa and corresponds with the jump in liquid fraction (inset in B). Yellow vides evidence of late magmatic (near-solidus) pyroxene destabilization and star in A represents the dioritic parental composition. Kernel density values were com- replacement (Castro and Stephens, 1992). puted using the generic function density in R code. For further explanation, see main text.

Magma Sources 7 12 Ma

} Bariloche A parental intermediate magma was identified by experimental constraints. 6 Next, we addressed the problem of the source of the magmas by means of 168 Ma Sr and Nd systematics. In the North Patagonian batholith, a wide range of 5 Aysén } isotopic ratios is found in plutons, irrespective of whole-rock compositions. Initial isotopic ratios for 87Sr/86Sr and 143Nd/144Nd of selected samples from the 4 North Patagonian batholith were normalized to the age of generation in three 121 Ma Figure 10. Age-frequency histo-

groups, 168, 121, and 12 Ma, according to the three main peaks of magmatic } gram showing the three main peaks of plutonic activity in the activity (Fig. 10). 3 North Patagonian batholith at

The two end members of crustal components in the mélange (Fig. 11) cor- Number of samples 168, 121, and 12 Ma. respond to the midpoints on the fields of the Chilean accretionary complex 2 and the North Patagonian massif (Pankhurst et al., 1999). These two midpoints were recalculated in accordance with the three peaks of magmatic activity 1 at 168, 121, and 12 Ma (Fig. 11), assuming the modeled compositions for Rb, Sr, Sm, and Nd of the bulk continental crust (Rudnick and Gao, 2003) for the 0 North Patagonian massif, and global subducting sediment (GLOSS; Plank and 0 40 80 120 160 Langmuir, 1998) for the Chilean Trench sediments. Age (Ma) Whatever the nature of crustal sources involved (sediments or Neopro- terozoic basement), recycled isotopic fingerprints are present in both diorites and granites, indistinctively. For instance, the most primitive diorite [sample Schumacher, 2012), where conditions favorable for melting existed. Experi- 87 86 A208–11: εNd = 1.34; ( Sr/ Sr)i = 0.70469] from Bariloche (Fig. 11A) is richer in mental works on mélange melting (Castro et al., 2010; Cruz-Uribe et al., 2018)

silica (62 wt%; Table 1) than the less primitive diorite [sample A208–14: εNd = showed that temperatures >1000 °C are required to satisfy melt compositions 87 86 −2.66; ( Sr/ Sr)i = 0.70582]. Because crustal assimilation will tend to increase and involved phase equilibria. About 50 vol% liquid of granodioritic composi- the silica content of the most contaminated magma, the observed decoupling tion can be formed at T = 1050–1100 °C and P = 1.5–2.0 GPa (Castro et al., 2010) is likely to be compatible with variable proportions of sediments in the source from an amphibolite-pelite mélange. The production of less silicic magmas, like (Vogt et al., 2013). It has been experimentally shown (Castro et al., 2010) that the diorites forming large plutons in the North Patagonian batholith, requires magma composition can be buffered over a wide range of end members in a either the incorporation of crystals from the source or an increase in the melt composite source (mélange). fraction by raising the temperature to near-liquidus conditions (>>1200 °C). These are features of premelting mixing of subducted mélanges (Nielsen In the latter case, a complete reaction of the mélange with the peridotite is and Marschall, 2017). All plutons, felsic and mafic, plot along mixing lines the most suitable scenario leading to the generation of wet dioritic liquids in (Fig. 11) linking the altered oceanic crust and the two crustal sources available in equilibrium with forsteritic olivine (Castro et al., 2013). the region, namely, the inferred Mesoproterozoic basement of the North Pata- gonian massif and sediments of the Chilean accretionary complex (Pankhurst et al., 1999). The magma source in Bariloche was a mélange composed of Geodynamic Implications basement and altered oceanic crust, with the fraction of altered oceanic crust

(XB) ranging from 0.6 to 0.3 (Fig. 11A). In the Aysén region, the altered oceanic According to thermomechanical models (Gerya and Meilick, 2011; Vogt

crust fraction of plutons is higher, i.e., XB = 0.8–0.6 (Figs. 11B and 11C), and the et al., 2012), the proportions of end members in the mélange are dictated continental component is in part represented by sediments of the accretionary by tectonic parameters such as the subduction angle, convergence rate and complex. The youngest plutons (12 Ma) plot between the two mixing curves, obliquity, and the thermal-mechanical state of the lithosphere. In this way, the supporting the implication of a mélange formed by trench sediments, altered correlation between tectonic processes and magma isotope composition can oceanic crust, and old crustal basement in the source region of the magmas. be found, which supplies an additional proof for the mélange diapir model The three end members could have been introduced via subduction erosion (MDM). Such correlation is found in the North Patagonian batholith as follows: (von Huene and Schöll, 1991) and sediment subduction into the subduction (1) High relative linear velocities (~140 km m.y.–1) and obliquity angles channel (Cloos and Shreve, 1988), where they mixed mechanically and evolved (60°–70°) predominated in the age interval ca. 180–140 Ma (stage 1, Fig. 12A) into Rayleigh-Taylor instabilities and diapiric structures intruding into the hot due to the subduction of Aluk below South America. The Jurassic kinematics neighboring mantle (Gerya and Yuen, 2003; Gerya et al., 2004; Marschall and were dominated by the extensional tectonic regime in the South America

(AOC) Figure 11. (A–C) Mixing models of initial isotopic ratios of Sr and Nd (Nd in epsilon 10 ε 168 Ma notation), showing possible mélange source compositions using a juvenile end member, 8 represented by the altered oceanic crust (AOC), and two evolved end members, represented by the North Patagonian massif and the Chilean accretionary complex. These are 6 compared with isotopic ratios of plutons normalized to the three peaks of plutonic activity Bariloche plutons 4 at 168, 121, and 12 Ma. Squares along the mixing lines represent 10% increments of end members involved. Qz—quartz. 2 0.704 0.706 0.708 0.710 0.712 0.714 0.716 87 86 -2 ( Sr/ Sr)initial

–1 -4 plate (Echaurren et al., 2017), fast plate convergence (~140 km m.y. ), and εNd sparse sediment supply, which are all considered to be favorable conditions -6 Chilean accretionary for subduction erosion (Clift and Vannucchi, 2004; Keppie et al., 2009), leading -8 complex to the entrainment into the mantle of materials from the upper-plate basement North Patagonian -10 massif (Stern, 2011). Plutons of the North Patagonian batholith (diorites and their Legend derivative granites) that formed during stage 1 record old crustal signatures Aysén plutons (high initial 87Sr/86Sr and very negative ; Figs. 7B and 11A) compatible with εNd (AOC) 10 Diorite/Qz-diorite (Mesozoic) the implication of a Mesoproterozoic basement in the source. B 121 Ma Granites (Mesozoic) 8 Diorite/Qz-diorite (Tertiary) (2) A sudden drop in the relative velocities of Aluk (down to 90–100 km Bariloche plutons m.y.–1) marks the Jurassic-Cretaceous transition. The Early Cretaceous (stage 2; 6 Granites Diorite/Qz-diorite Figs. 6, 7A, and 11B) was characterized in the region by a progressive increase 4 Aysén plutons (Mesozoic) in the velocity of convergence, triggered by the opening of the southern South 2 Atlantic Ocean (Franke, 2013; Larson and Ladd, 1973). Obliquity angles attained 0.706 0.708 0.710 0.712 0.714 0.716 80°, giving rise to a period of plate coupling that favored subduction of trench Bariloche plutons (87Sr/86Sr) sediments (Vogt et al., 2012, 2013), formed by denudation of the previously -2 at 121 Ma initial formed arc. Subduction erosion of the Proterozoic basement may have con- ε -4 tinued during this stage, giving rise to a three-component mélange. Some Nd -6 Chilean plutons of the North Patagonian batholith plot between the two mixing curves accretionary -8 complex in Figure 11A, denoting the influence of subducted sediments in the source of North Patagonian magmas (see also Fig. 7B). -10 massif (3) Relatively slow convergence velocities (around 60 km m.y.–1), low obliquity angles (40°–60°), and extensional or transtensional tectonic conditions (e.g., (AOC) 10 Folguera and Iannizzotto, 2004; Haschke et al., 2006b) characterized the Late 12 Ma Cretaceous and Paleocene (stage 3; Figs. 6, 7A, and 11C). The low convergence 8

rates, typical of stage 3, together with the switch to extensional conditions and 6 low rates of sediment arrival to the trench are conditions favoring the absence 4 of subduction erosion (Clift and Vannucchi, 2004). These features explain the Aysén plutons (Tertiary) Aysén plutons (Mesozoic) at 12 Ma low magmatic productivity of this period (~0.5 km3 m.y.–1 km–1; Fig. 7A). 2 2 (4) The last tectonic episode (stage 4, Fig. 12D) commenced upon the 0.706 0.708 0.710 0.712 0.714 0.716 breakup of the Farallon plate (Lonsdale, 2005) at ca. 25–23 Ma and the abrupt 87 86 -2 ( Sr/ Sr)initial increase in the velocity of Nazca relative to South America, restoring values –1 -4 of around 140 km m.y. at nearly orthogonal convergence (>80°). Accordingly, εNd a contractional regime dominated this stage along with arc narrowing and -6 Bariloche plutons at 12 Ma

mountain building (Haschke, et al., 2006a; Orts et al., 2012). -8 (5) The most recent kinematic evolution shows a progressive decrease -10 –1 Chilean in the convergence velocities down to around 80 km m.y. , which coincides accretionary complex with current values (DeMets et al., 2010). The tectono-magmatic conditions North Patagonian were similar during stages 2 and 4 (Figs. 6, 7, and 11). Therefore, Miocene to massif

140 km m.y.-1 > 140 Ma Magmatic Stage 1 Trench Forearc arc Retroarc 0 km ? ? Continental crust I a a- Permo-Triassic accretionary wedge 50 Aluk South Oceanic crust America Lithospheric mantle 100 Asthenospheric mantle Liquiñe-Ofqui fault system and ancestors 150 0 100 200 300 400 km Mélange (partially molten) diapir Accretionary prism and subduction channel 130 km m.y.-1 Magmatic B 140-100 Ma arc Stage 2 Hydrated mantle Trench II Forearc III Retroarc 0 km IV ? ? I Volcanic rocks North Patagonian batholith 50 Aluk V South Sediment transport America Figure 12. (A–D) Plate profiles depicting the VI Normal velocity relative to SA lithosphere sections for the main evolution- 100 Contractional overriding plate ary stages during the generation of the North Extensional overriding plate Patagonian batholith. The sections integrate 150 magma sources according to isotopic ratios 0 100 200 300 400 km of plutons and plate-tectonic evolution over I: Tectonic erosion of Proterozoic basement the period ca. 180–10 Ma. The location of -1 60 km m.y. II: Uplift and relief formation mélange diapirs and plate geometry follow 100-30 Ma Magmatic III: Sediment transport to the trench Stage 3 results of thermomechanical numerical mod- Trench Forearc arc Retroarc IV: Generation of the accretionary prism V: Sediment subduction els (Gerya and Meilick, 2011; Gerya and Yuen, 0 km VI: Tectonic erosion of basement and 2003; Vogt et al., 2012, 2013). SA—South sediment subduction America; PH—Phoenix plate. Farallon 50 South America

100 Lithospheric slab-window PH 60 km m.y.-1 150 0 100 200 300 400 km 140 km m.y.-1 Magmatic D < 30 Ma arc Stage 4 Trench II Forearc III Retroarc 0 km I 50 V Nazca South VI America Relative plate 100 velocity scale: 50 km m.y.-1 150 0 100 200 300 400 km

recent magmas show juvenile isotopic ratios (Fig. 7B), with more than 80% generation based on melting of subducted mélanges. According to isotopic altered oceanic crust and coupled participation of the two continental reser- ratios, a large proportion (>50%) of oceanic crust, representing juvenile mate- voirs, namely, the inferred Proterozoic basement and subducted sediments. rial in batholiths, is recycled into new arc crust in subduction zones. Taking into account the results of this study and experimental constraints, We propose that the parental mafic to intermediate magmas that gave it follows that secular changes in magma source compositions are fairly well rise to the plutons and batholiths were rooted below the lithosphere of the correlated with changes in tectonic processes during subduction and justified overriding plate. In this model, distinct isotopic reservoirs, depending on the by models and on geophysical grounds. For instance, coupling periods of tectonic regime and available materials, can be incorporated via subduction subduction enhance subduction erosion of the upper plate (von Huene and and subduction erosion. Schöll, 1991) and introduce low-density portions of the continental crust into the subduction channel (Gerya and Yuen, 2003). Thermomechanical models of subduction zones (Gerya et al., 2004; Vogt et al., 2012) predict an alterna- ACKNOWLEDGMENTS tion between coupling and decoupling stages over periods of several million This research was funded by the Spanish Agency of Science and Technology (Projects CGL2013– 48408–C3–1–P and PGC2018–096534-B-I00) and the University of Huelva. Rodriguez is grateful for years, which are recorded by changes in the isotopic signatures of magmas a Juan de la Cierva postdoctoral research grant. This is IBERSIMS publication 49. (Vogt et al., 2013). Another prediction of the models is the secular change in the proportions of end members incorporated into the subduction channel

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