Close this window to return to the Tectonic Analysis Limited website

Title Fission track ages and sedimentary provenance studies in Peru, and their implications for Andean paleogeographic evolution, stratigraphy and hydrocarbon systems
Author Lorcan Kennan
Source Technical Papers, VI INGEPET Conference, October 13-17 2008, Lima, Peru
Abstract Reconnaissance fission track dating was carried of 33 samples collected from the Bagua-Santiago, Huallaga, Urubamba-Camisea and Alto Manu areas. We present preliminary results and conclusions, pending further data analysis. Track length distributions suggest that many samples underwent prolonged residence in the partial annealing zone, with long cooling histories, and only some samples pass a Chi2 test, so in most cases a "fission track age" does not date a particular geological event. In these samples, discrete age populations can be distinguished which indicate differing grain resistance to track annealing, a function of grain chemistry Cooling history modeling of grain ages and track lengths and, possibly, data on the chemistry (e.g. Cl/Fl/OH content) of apatite grains is required. Preliminary interpretation of the data is possible, even in the absence of thermal modeling. In particular the zircon grain ages which have generally not been deeply enough buried to have been reset, and we can distinguish inherited and syn-deposition (airfall or reworked young volcanic) components which give us several new absolute ages, including a new 68.5 Ma direct age for the "Vivian sandstone" at Pongo de Mainique Oligocene and Early Miocene ages for strata about 2.5 km above the Cretaceous. The apatite data suggest a 25 Ma age for initial uplift at the rear of the Santiago and Huallaga Basins, Late Miocene rejuvenation of uplift between the Bagua and Santiago Basins, coincident with formation of the frontal Campanquiz Anticline, and a slightly older age for the unroofing of the frontal thrusts in the Huallaga Basin. Apatite data from the Machu Picchu area indicate rapid unroofing at ca. 1 km/Ma since the Late Pliocene, younger than the thin-skinned thrusting in the Camisea area and probably driven by the same post-thrusting thick-skinned deformation which caused the uplift of the Shira and Vilcabamba Cordilleras. Thrusting in the Camisea area is dated as Late Miocene to Pliocene in age. Apatite ages in the Mipaya and Coņec areas are mostly detrital and partially annealed but still reveal an influx of volcanic material coincident with the Middle Oligocene volcanic flare-up in the arc to the west, consistent with changes in sediment provenance from sedimentary to mixed metamorphic/volcanic. The data provide valuable insights into the timing of deposition, burial, deformation and uplift, and can be used to improve our understanding of petroleum systems in the Peruvian foreland basins.
PDF Full Text and Figures, 1 Mb
Contact Please email if you would like to know more about this work and associated projects.

Close this window to return to the Tectonic Analysis Limited website