Geodynamic controls on the contamination of Cenozoic arc magmas in the southern Central Andes: Insights from the O and Hf isotopic composition of zircon

Abstract

Subduction zones, such as the Andean convergent margin of South America, are sites of active continental growth and crustal recycling. The composition of arc magmas, and therefore new continental crust, reflects variable contributions from mantle, crustal and subducted reservoirs. Temporal (Ma) and spatial (km) variations in these contributions to southern Central Andean arc magmas are investigated in relation to the changing plate geometry and geodynamic setting of the southern Central Andes (28-32°S) during the Cenozoic. The in-situ analysis of O and Hf isotopes in zircon, from both intrusive (granitoids) and extrusive (basaltic andesites to rhyolites) Late Cretaceous -Late Miocene arc magmatic rocks, combined with high resolution U-Pb dating, demonstrates distinct across-arc variations. Mantle-like d 18 O (zircon) values (+5.4& to +5.7& (±0.4 (2r))) and juvenile initial eHf (zircon) values (+8.3 (±0.8 (2r)) to +10.0 (±0.9 (2r))), combined with a lack of zircon inheritance suggests that the Late Cretaceous ($73 Ma) to Eocene ($39 Ma) granitoids emplaced in the Principal Cordillera of Chile formed from mantle-derived melts with very limited interaction with continental crustal material, therefore representing a sustained period of upper crustal growth. Late Eocene ($36 Ma) to Early Miocene ($17 Ma) volcanic arc rocks present in the Frontal Cordillera have 'mantle-like' d 18 O (zircon) values (+4.8& (±0.2 (2r) to +5.8& (±0.5 (2r))), but less radiogenic initial eHf (zircon) values (+1.0 (±1.1 (2r)) to +4.0 (±0.6 (2r))) providing evidence for mixing of mantle-derived melts with the Late Paleozoic -Early Mesozoic basement (up to $20%). The assimilation of both Late Paleozoic -Early Mesozoic Andean crust and a Grenville-aged basement is required to produce the higher than 'mantle-like' d 18 O (zircon) values (+5.5& (±0.6 (2r) to +7.2& (±0.4 (2r))) and unradiogenic, initial eHf (zircon) values (À3.9 (±1.0 (2r)) to +1.6 (±4.4 (2r))), obtained for the Late Oligocene ($23 Ma) to Late Miocene ($9 Ma) magmatic rocks located in the Argentinean Precordillera, and the Late Miocene ($6 Ma) volcanic rocks present in the Frontal Cordillera. The observed isotopic variability demonstrates that the assimilation of pre-existing continental crust, which varies in both age and composition over the Andean Cordillera, plays a dominant role in modifying the isotopic composition of Late Eocene ScienceDirect Geochimica et Cosmochimica Acta 164 (2015) [386][387][388][389][390][391][392][393][394][395][396][397][398][399][400][401][402] to Late Miocene mantle-derived magmas, implying significant crustal recycling. The interaction of arc magmas with distinct basement terranes is controlled by the migration of the magmatic arc due to the changing geodynamic setting, as well as by the tectonic shortening and thickening of the Central Andean crust over the latter part of the Cenozoic.

Fluvial and Eolian Sediment Mixing During Changing Climate Conditions Recorded in Holocene Andean Foreland Deposits From Argentina (31–33°S)

“…Reported dates and percent discordance for grains younger than 850 Ma are 206 (Ramos, 2004(Ramos, , 2009Bahlburg et al, 2009;Rapela et al, 2016); (2) The Eastern Sierras Pampeanas (725-520 Ma) age group are recycled from Carboniferous to Permian sedimentary sequences found in the Precordillera fold-thrust belt (Fosdick et al, 2015;Capaldi et al, 2017 (Rapela et al, 2007;Schwartz et al, 2008); 3 (Mpodozis and Kay, 1992;Dahlquist et al, 2013) and minor recycled sources from Triassic sedimentary deposits in the Sierras Pampeanas and Neogene deposits throughout the Frontal Cordillera, and Precordillera (Fosdick et al, 2015(Fosdick et al, , 2017; (5) Permian Triassic 280-205 Ma age group includes dominant Choiyoi Igneous Complex and subsequent Triassic plutons exposed in the Frontal Cordillera ( Figure 2B; Mpodozis and Kay, 1992;del Rey et al, 2016). Additional sources of Permian Triassic 280-205 Ma age components include recycled Jurassic to Cretaceous sedimentary deposits in the High Andes and Neogene deposits across the Precordillera (Capaldi et al, 2017;Mackaman-Lofland et al, 2019); (6) Andean Arc 120-0 Ma Cretaceous to Neogene Andean arc volcanic and volcaniclastic rocks of the Principal Cordillera, Frontal Cordillera, Precordillera, and Sierras Pampeanas, and recycled from Neogene basin fill (Kay and Mpodozis, 2002;Jones et al, 2015).…”

Neogene Retroarc Foreland Basin Evolution, Sediment Provenance, and Magmatism in Response to Flat Slab Subduction, Western Argentina

“…Carboniferous-Permian arc rocks (350-280 Ma), Choiyoi igneous rocks (280-240 Ma), and Triassic plutons are the main rock units in the Frontal Cordillera (del Rey et al, 2016;Mpodozis & Kay, 1992). Miocene to Quaternary (23-0 Ma) zircons from Andean arc rocks and recycled volcaniclastic rocks across the Frontal Cordillera (Figure 2a; Jones et al, 2015;Kay et al, 1991;Kay & Mpodozis, 2001). Predicted provenance variations associated with orogenic unroofing along Frontal Cordillera structures involves initial erosion of Neogene volcanic and volcaniclastic cover 10.1029/2019TC005958 Tectonics (RBLA01) followed by increased contributions from Carboniferous to Triassic igneous rocks (RMDZ01) (Figure 6b; Mackaman-Lofland et al, 2020;Pinto et al, 2018).…”

“…Erosion of the Frontal Cordilleran further expressed in middle-Miocene deposits to the southwest (Manantiales basin; Mackaman-Lofland et al, 2020: Pinto et al, 2018, southeast (Cachueta basin: Buelow et al, 2018), northern Bermejo basin (Fosdick et al, 2015;Jordan et al, 1996), and northeastern Bermejo basin (Ischigualasto-Villa Unión basin: Lemos-Santos et al, 2019). Igneous geochemical signatures suggest increased crustal contributions related to continued crustal thickening (>50 km) (Litvak et al, 2018;Jones et al, 2015;Kay et al, 1991). Diminished arc activity from 15 to 12 Ma overlaps with a reported shift to enhanced strike-slip conditions in the Andean hinterland at 30°S (Giambiagi et al, 2017), possibly linked to increased gravitational potential energy in thickened orogenic crust .…”

Geochronology and Geochemistry of Archean TTG and Tremolite Schist Xenoliths in Yemadong Complex: Evidence for ≥3.0 Ga Archean Continental Crust in Kongling High-Grade Metamorphic Terrane, Yangtze Craton, China

“…The >3.2 Ga T DM2 ages and the small number of 3.2 Ga inherited zircons in the 3.0-2.9 Ga TTG gneisses [23] indicate a vital role was played by an ancient crystalline basement in the genesis of these rocks, which actually fits a continental arc setting. In continental arcs, due to the melting and/or contamination of the overriding thick ancient continental crust above the subduction zone, the granitoid magmas therein are commonly imprinted by less radiogenic Hf features and characterized by lower εHf(t) values [64][65][66]. Therefore, the tectonic environment of the Kongling Terrane during the period 3.0-2.9 Ga may have been like a modern continental arc, indicating that plate tectonics in the Yangtze Craton commenced before 2.9 Ga.…”