Abstract
Two tectono-thermal metamorphic events, M1-D1 (S1, with associated white mica and chlorite: WM1-Chl1) and M2-D2 (S2, with development of WM2-Chl2), are established from polyphase white mica growth for low-grade units from the Ordovician metasedimentary successions of La Cebila Metamorphic Complex in the Famatinian belt (western-central Argentina). The thermobarometric characterization of the M1 main event was carried out by means of clay-mineral analysis and crystallo-chemical parameter measurements. Epizonal (temperatures between 300 and 400ºC) and low-pressure conditions are suggested for M1 event, based in Kübler index values ranging from 0.23 to 0.17 Δº2θ, white mica b parameter values between 9.004 and 9.022 Å (mean of 9.014 Å, n=16) and Si contents between 3.13-3.29 a.p.f.u. Temperatures of ~180-270ºC are estimated for the M2 event, with Kübler index values ranging from 0.31 to 0.46 Δº2θ. The M1-D1 event of La Cebila could be linked to highstrain heating tectono-metamorphic Ordovician regime recorded in others complexes from Famatinian foreland region of Sierras Pampeanas.
Highlights
The Early Cambrian to Late Ordovician record of South American Central Andes comprises widespread igneous, metamorphic and sedimentary complexes forming the southwestern margin of Gondwana in the Early Paleozoic (e.g., Pankhurst and Rapela, 1998; Chew et al, 2007; Ramos, 2008)
In the central and northwestern regions of Argentina, the Ordovician record is represented by the Famatinian orogenic belt (Aceñolaza and Toselli, 1976), with the main outcrops situated within the Puna, Cordillera Oriental and the eastern Sierras Pampeanas (Fig. 1a)
As the WM1 is the dominant phase, we considered the measured b parameter values as representative of the conditions reached by the sequence during the M1 event
Summary
The Early Cambrian to Late Ordovician record of South American Central Andes comprises widespread igneous, metamorphic and sedimentary complexes forming the southwestern margin of Gondwana in the Early Paleozoic (e.g., Pankhurst and Rapela, 1998; Chew et al, 2007; Ramos, 2008). Cébila Metamorphic Complex (previously named La Cébila Formation, González Bonorino, 1951), located within the Famatinian belt is composed of a variety of metamorphic and igneous rocks (Espizúa and Caminos, 1979; Fig. 1b), including low- to high-grade metasedimentary rocks metamorphosed under low-pressure conditions (Verdecchia, 2009). An Early Ordovician depositional age has been recently constrained for this complex (Verdecchia et al, 2007), which makes its previously assumed association with the Neoproterozoic to Early Cambrian Pampean Orogeny (e.g., Zimmermann, 2005) unlikely. The tectono-metamorphic events with their associated thermobarometric conditions, as well as some retrograde diagenetic processes, have been established in order to understand the post-depositional history of this complex
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