CIG   05423
CENTRO DE INVESTIGACIONES GEOLOGICAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
An Ediacarian carbonate platform in the Eastern Sierras Pampeanas of Argentina: Sr isotopic relations in marbles of the Sierra de Ancasti
Autor/es:
BALDO, E.G; RAPELA, C.W.; MURRA, J.A.; GALINDO, C.; PANKHURST, R.J; DAHLQUIST, J.A.; CASQUET, C.; STOESSEL, N.
Lugar:
Santiago de Chile
Reunión:
Simposio; GEOSUR 2007: An International Congress on the Geology and Geophysics of the Southern Hemisphere; 2007
Resumen:
A sequence of quartzite, calcite and calcite-dolomite marbles, quartz-mica schist, biotite gneiss and metabasite crops out in the eastern flank of the Sierra de Ancasti. In the central part of the sierra the sequence is represented by the Ancasti Formation, an important succession of rhythmically banded psammo-pelitic schists without marble. Metamorphic grade increases westwards, culminating in a gneiss–migmatite complex. U-Pb SHRIMP zircon data limit sedimentation to less than 600 – 570 Ma (Rapela et al. 2007 in press). The main tectono-thermal event affecting the metasedimentary rocks is assigned to the Pampean orogeny (Early to Middle Cambrian (Knüver, 1983). Meta-carbonate rocks in the eastern border of the sierra are subdivided into: (a) a northern group ("La Calera", "Ancaján" and "Albigasta" quarries) of calcite marble at low to medium metamorphic grade (Cal + Ms + Phl + Qtz + Gr + Py), and (b) a southern group ("La Montosa", "Hermanos Moya" and "El Cerrito" quarries) of calcite and calcite-dolomite marbles metamorphosed at the high grade (Cal ± Qtz and Cal + Dol + Fo + Spl + Chu). Twenty-three marble samples from eastern Ancasti were analysed for Sr isotopes and Rb, Mn, Mg and Ca contents. Ten yielded Sr = 977–3644 ppm, Mn/Sr < 0.2, Mg/Ca < 0.01 and 87Sr/86Sr ratios in the range 0.7075–0.7078 (mean 0.7077 ± 0.00020), whereas the remainder yielded 87Sr/86Sr ratios of 0.7084–0.7086, lower Sr contents and higher Mn/Sr and Mg/Ca ratios, i.e., altered from original marine compositions. An apparent Ediacarian depositional age (580–570 Ma) is assigned to the marbles by referring the lowest observed 87Sr/86Sr ratios to secular trends in seawater isotopic compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. lower Sr contents and higher Mn/Sr and Mg/Ca ratios, i.e., altered from original marine compositions. An apparent Ediacarian depositional age (580–570 Ma) is assigned to the marbles by referring the lowest observed 87Sr/86Sr ratios to secular trends in seawater isotopic compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. 0.7077 ± 0.00020), whereas the remainder yielded 87Sr/86Sr ratios of 0.7084–0.7086, lower Sr contents and higher Mn/Sr and Mg/Ca ratios, i.e., altered from original marine compositions. An apparent Ediacarian depositional age (580–570 Ma) is assigned to the marbles by referring the lowest observed 87Sr/86Sr ratios to secular trends in seawater isotopic compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. lower Sr contents and higher Mn/Sr and Mg/Ca ratios, i.e., altered from original marine compositions. An apparent Ediacarian depositional age (580–570 Ma) is assigned to the marbles by referring the lowest observed 87Sr/86Sr ratios to secular trends in seawater isotopic compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. 87Sr/86Sr ratios in the range 0.7075–0.7078 (mean 0.7077 ± 0.00020), whereas the remainder yielded 87Sr/86Sr ratios of 0.7084–0.7086, lower Sr contents and higher Mn/Sr and Mg/Ca ratios, i.e., altered from original marine compositions. An apparent Ediacarian depositional age (580–570 Ma) is assigned to the marbles by referring the lowest observed 87Sr/86Sr ratios to secular trends in seawater isotopic compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. lower Sr contents and higher Mn/Sr and Mg/Ca ratios, i.e., altered from original marine compositions. An apparent Ediacarian depositional age (580–570 Ma) is assigned to the marbles by referring the lowest observed 87Sr/86Sr ratios to secular trends in seawater isotopic compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. 87Sr/86Sr ratios of 0.7084–0.7086, lower Sr contents and higher Mn/Sr and Mg/Ca ratios, i.e., altered from original marine compositions. An apparent Ediacarian depositional age (580–570 Ma) is assigned to the marbles by referring the lowest observed 87Sr/86Sr ratios to secular trends in seawater isotopic compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. 87Sr/86Sr ratios to secular trends in seawater isotopic compositions. This is compatible with the age constrained by detrital zircons in the Ancasti Formation and agrees with that of Puncoviscana basin limestone interpreted as a subtidal–supratidal sediment near the platform margin (Omarini et al., 1999). Similar 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin. 87Sr/86Sr ratios and depositional age have been reported for limestones of the Loma Negra Formation (Sierras Bayas Group, Tandilia system), the Arroyo del Soldado Group (Uruguay), and the Corumbá Formation (Brazil) (Misi et al., 2007). However, according to a recent paleogeographic model (Rapela et al., 2007), these approximately coeval carbonate deposits were not necessarily deposited in the same basin.