A Laurentian? Grenville-age oceanic arc/back-arc terrane in the Sierra de Pie de Palo, Western Sierras Pampeanas, Argentina

Abstract Whole-rock trace element, field, and petrographical studies indicate that the protoliths of highly deformed metamorphic rocks of the Pie de Palo Complex, Argentina, formed in an oceanic setting like that of SW Pacific supra-subduction complexes (e.g., Lau Basin). Age constraints suggest that this Mesoproterozoic complex, which includes some of the most primitive Grenville-age magmas known on Earth, formed in < 60 million years. Amphibolites (Las Pirquitas/Quemado region) with N-MORB like light-depleted REE patterns and Hf/Ta/Th relations, associated with Fe-rich schists interpreted as hydrothermally altered lavas and gabbros, formed in a back-arc spreading centre. Other ultramafic/mafic units (Quebrada del Gato, Cerros Valdivia/Barboza) formed as arc cumulates, and (central region) as ridge or arc/back-arc lavas (including shoshonite). Intermediate and silicic schists/gneisses are interpreted as arc region greywackes and silicic lavas, and marbles as reef deposits. Quebrada del Gato gneisses with trace elements indicating high pressure residual mineral assemblages are interpreted as younger subduction-related magmas emplaced in a thickened crust. The Pie de Palo Complex probably formed offshore of eastern Laurentia, and subsequently collided with Laurentia east of the Llano uplift, Texas, in Grenvillian times. This block, along with the Precordillera, was rifted from Laurentia in the latest Precambrian, arriving in Gondwana by Ordovician time.

[1]  I. Dalziel,et al.  The Argentine precordillera: A laurentian terrane? , 1996 .

[2]  S. Kay,et al.  Zircon and Whole Rock Nd-Pb Isotopic Evidence for a Grenville Age and a Laurentian Origin for the Basement of the Precordillera in Argentina , 1996, The Journal of Geology.

[3]  R. Astini,et al.  The early Paleozoic evolution of the Argentine Precordillera as a Laurentian rifted, drifted, and collided terrane: A geodynamic model , 1995 .

[4]  I. Dalziel,et al.  Did the Taconic Appalachians continue into southern South America , 1992 .

[5]  E. Ito,et al.  Shoshonitic magmas in nascent arcs: New evidence from submarine volcanoes in the northern Marianas , 1988 .

[6]  S. Kay,et al.  Probing the evolving Andean Lithosphere: Mid‐Late Tertiary magmatism in Chile (29°–30°30′S) over the modern zone of subhorizontal subduction , 1987 .

[7]  R. Allmendinger,et al.  The Sierras Pampeanas of Argentina; a modern analogue of Rocky Mountain foreland deformation , 1986 .

[8]  S. Kay,et al.  Paleozoic terranes of the central Argentine‐Chilean Andes , 1986 .

[9]  D. Wood,et al.  A RE-APPRAISAL OF THE USE OF TRACE ELEMENTS TO CLASSIFY AND DISCRIMINATE BETWEEN MAGMA SERIES ERUPTED IN DIFFERENT TECTONIC SETTINGS , 1979 .

[10]  V. Ramos,et al.  Time constraints on the Early Palaeozoic docking of the Precordillera, central Argentina , 1998, Geological Society, London, Special Publications.

[11]  E. Ruellan,et al.  Tectonics, Magmatism, and Evolution of the New Hebrides Backarc Troughs (Southwest Pacific) , 1995 .

[12]  J. Hawkins.  The Geology of the Lau Basin , 1995 .

[13]  J. Ishibashi,et al.  Hydrothermal Activity Related to Arc-Backarc Magmatism in the Western Pacific , 1995 .

[14]  B. Taylor,et al.  Active margins and marginal basins of the western Pacific , 1995 .

[15]  Ricardo Varela,et al.  Geocronología Rb-Sr de metamorfitas y granitoides del extremo sur de la Sierra Pie de Palo, San Juan , 1993 .

[16]  W. McDonough,et al.  Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes , 1989, Geological Society, London, Special Publications.

[17]  S. Taylor,et al.  The continental crust: Its composition and evolution , 1985 .