Fast sediment underplating and essentially coeval juvenile magmatism in the Ordovician margin of Gondwana, Western Sierras Pampeanas, Argentina

Abstract

Keywords:Famatinian magmatic arc Juvenile magmatismMetasedimentary high-pressure upper amphibolite fades gneisses (1.2 ± 0.1 ePa and 780± 45 QC) at Las Chacras, Sierra de Valle Fertil, are tectonically juxtaposed to thewesternmost parts (outboard) of the Famatinian (Early Ordovician) magmatic arc, which underwent syn-plutonic middle crust high-grade metamorphism at lower pressure. U-Pb SHRIMP zircon data suggest that the gneisses contain Famatinian igneous detritus, so that their sedimentary protoliths were probably deposited in a forearc basin and then rapidly underthrust and accreted to the lower crust of the arc, essentiallycoevallywith arc magmatism at468 ± 4 Ma Chemically and isotopically juvenile garnetiferous amphibolites within the gneisses are recognised as representing the most primitive magmas so far obselVed in this belt, which has often been considered to be a continental arc derived from isotopically mature sources. This is consistent with the idea that at least part of the dominant Famatinian magmatism originated in depleted mantle but was heavily contaminated by crustal components. U-Pb SHRIMP zircon geochronology Gondwana Sierras Pampeanas

The Gondwana connections of northern Patagonia

“…However, in terms of Sm-Nd isotope systematics (Fig. 9) the Patagonian samples compare well with the I-type Ordovician plutonic rocks from the Sierras Pampeanas Dahlquist et al 2013), especially the later Famatinian granitoids of Sierra de Valle Fértil (Casquet et al 2012).…”

“…7). Casquet et al (2012) demonstrated the presence of juvenile mafic magmas in the Early Ordovician suites of the Sierras Pampeanas, which thus may be bimodal in both composition and origin, but the Patagonian granites are mostly comparable to the evolved Famatinian I-types.…”

The evolution of a mid-crustal thermal aureole at Cerro Toro, Sierra de Famatina, NW Argentina

“…Only a few Famatinian igneous rocks have positive values of εNdt, such as a few gabbros in the Sierra de Valle Fértil (εNdt = +0.25, +0.9, n=2, Otamendi et al, 2009Otamendi et al, , 2012, subordinate Na-rich granites of the TTG associations in the Pampean foreland (εNdt = +1.6 to −0. 2, Pankhurst et al, 2000) and amphibolites (metabasaltic dykes) of the Loma de Las Chacras (εNdt = +1.8 to +4.8, Casquet et al, 2012a), suggesting more primitive input to Famatinian magmatism.…”

The Capilla del Monte pluton, Sierras de Córdoba, Argentina: the easternmost Early Carboniferous magmatism in the pre-Andean SW Gondwana margin

“…Including main references only, these are Pampean magmatism, 555-515 Ma (Rapela et al , 2007Sims et al 1998;Schwartz et al 2008); Famatinian magmatism, 484-463 Ma (Pankhurst et al , 2000Rapela et al 2008b;Dahlquist et al 2008;Dahlquist and Alasino 2012;Ducea et al 2010;Casquet et al 2012); Achalian magmatism, 393-366 Ma (Dorais et al 1997;Sims et al 1998;StuartSmith et al 1999;); Rapela et al 2008a;Dahlquist et al 2014b); and Early Carboniferous magmatism, 357-322 Ma (Dahlquist et al 2006(Dahlquist et al , 2010Grosse et al 2009;Alasino et al 2012). The last group is hereinafter referred to as Early Gondwana magmatism following Rapela and Llambías (1999).…”