Paper No. 341-7
Presentation Time: 3:10 PM
WAS THE AREQUIPA MASSIF THE CONJUGATE RIFTED MARGIN OF EASTERN LAURENTIA?
Previous Neoproterozoic tectonic reconstructions have placed the Arequipa Massif (AM) and the Eastern Cordillera (EC) of southern Peru between Newfoundland’s Humber margin of Laurentia and Amazonia after Mesoproterozoic accretion of an allochthonous AM. An alternative model places the AM on Amazonia’s western margin throughout the Neoproterozoic. New metamorphic, geochronological and geochemical constraints from these terranes inspire a reinterpretation of the tectonic history of the AM. Evidence for late Cambrian accretion is found in the EC with metamorphic titanite from the metasedimentary Choquequirao Fm and arc magmatism in orthogneiss of the Iscaybamba Fm. We also dated the late Early Ordovician San Nicolas coastal batholith, which intrudes the AM, and confirms contemporaneity with other plutons intruding the AM in southern Peru and northern Chile. If Arequipa accreted onto Amazonia in the late-Cambrian, then its post-Mesoproterozoic rift history should have a conjugate margin in the northern Appalachians, Amazonia, or another continental margin. Inherited cores from the San Nicolas granodiorite reflect the same peaks found in detrital zircon samples from the AM’s Ediacaran San Juan Fm. cover sequence at 2.0-1.7, 1.4-0.9, and 0.8-0.7 Ga. While 2.0-1.7 and 1.4-0.9 Ga ages are common in the northern Appalachians, 0.95-0.55 Ga ages are rare. Alternatively, a 0.8-0.7 Ga peak is broadly similar in age to A-type granitoids and orthogneisses in the EC of Peru and NW Argentina dated at 691, 751, and 774 Ma, in support of a para-autochthonous Amazonian origin. Furthermore, the ~3km thick carbonate-dominated Ediacaran succession of the San Juan Fm can be correlated with many similar Amazonian successions, while no counterparts are known from northeastern Laurentia. TIMS ages of San Juan Fm. detrital zircons are closer matches to rift volcanics from the Mount Rogers Volcanic Complex of Virginia and the Rosh Pinah Volcanic Complex of the Gariep Belt in southern Namibia, opening up potential correlations with the Kalahari and the southern Appalachians, where similar basins occur. In conclusion, a more complex tectonic history in the AM is recognized that is consistent with a Neoproterozoic rift event. Instead of finding its conjugate margin in the northern Appalachians, we favor a parautochthonous origin of the AM.