Discriminating rapid exhumation from syndepositional volcanism using detrital zircon double dating: Implications for the tectonic history of the Eastern Cordillera, Colombia

Abstract

Lag time is the difference between the closure age of a thermochronologic system and the depositional age of host strata. Lag-time analysis of sedimentary basin fi ll provides insight into the exhumation history of adjacent eroded orogens. In a case study of the Paleogene Floresta basin in the Eastern Cordillera fold-thrust belt of Colombia, variations in lag time refl ect changes in both sediment source areas and exhumation patterns. However, near-zero lag times can be produced by either syndepositional volcanism or rapid exhumation. We applied U-Pb geochronology and (U-Th)/He (ZHe) thermochronology to individual zircon grains and identifi ed zircons of volcanic origin as those for which the U-Pb age is within the 2σ uncertainty of their ZHe age. Consistent discrimination of young ZHe ages as the products of either rapid exhumation or volcanism reveals three stages in the history of the northern Andean hinterland. (1) Early to late Paleocene: The appearance of syndepositional and Mesozoic volcanic zircons marks the initial infl ux of magmatic arc detritus. (2) Middle to late Eocene: Near-zero lag times point to rapid, regionally extensive exhumation attributable to thrust-induced uplift of the Magdalena Valley basement. (3) Late Eocene to late Oligocene: Increased lag time is interpreted as recycling of shallowly buried foreland-basin strata possibly due to movement on basinbounding thrust systems. The presence of volcanic zircons with ZHe ages younger than or indistinguishable from the youngest exhumationally cooled zircons underscores the need for double dating to reliably identify volcanic infl uence in detrital thermochronology datasets. These data highlight the utility of double-dated ZHe results for extracting tectonic histories and reliably excluding volcanic zircons from lag-time analysis.

Hyperspectral imaging for the determination of bitumen content in Athabasca oil sands core samples

“…After the upper Eocene, lag time increases again. Saylor et al (2012a) interpret, as we do, the presence of a new source area to the west due to the advance of a new thrust sheet. This is in line with the deduced eastward advance of the Pesca-Soapaga thrust system (Figure 2) based on AFT modeling (Figures 7, 10).…”

“…Bedrock thermochronology for deformed belts of the Andean retroarc system included apatite and zircon fission track analysis (AFT and ZFT, respectively; Parra et al, 2009b;Silva et al, 2013 and Table 2, data from this work) as well as apatite and zircon (U-Th)/ He analysis (AHe and ZHe, respectively) combined with vitrinite reflectance data Parra et al, 2012;Caballero et al, 2013a, b, Table 3). Detrital thermo-and geochronology of intermontane and foreland basin fill included (U-Th)/He analysis of zircons (ZHe) Bande et al, 2012;Saylor et al, 2012a) and zircon U-Pb geochronology Nie et al, 2010Nie et al, , 2012Saylor et al, 2011;Bande et al, 2012;Caballero et al, 2013a, b;Silva et al, 2013).…”

“…Starting in the Late Cretaceous-Paleocene, punctuated eastward migration of the contractional deformation front ultimately inverted the rift basin (Gómez et al, 2005a;Parra et al, 2009a, b;Saylor et al, 2011). In the late Eocene-early Oligocene, the advancing thrust front broke the previously continuous foreland basin into the eastern Llanos and western Middle Magdalena Valley basins (Gómez et al, 2005a;Moreno et al, 2011;Saylor et al, 2011Saylor et al, , 2012aSánchez et al, 2012). The sedimentary record of the Llanos foreland basin is the product of these tectonic, climatic, and erosional processes in the hinterland.…”

“…In addition, locating the axis for changing provenance based on detrital U-Pb is complicated due to recycling of Paleocene strata originally sourced in the Central Cordillera (e.g., Saylor et al, 2012a). However, we argue that the location of a northnortheast-trending reentrant of lacustrine or shallow marine shaly facies marks the geographic location of the basin axis (i.e., the topographically lowest area, the axis of which separates regions of Eastern Cordilleran-derived sediments from craton-derived sediments).…”

U-PB zircon tuff geochronology from the Karoo Basin, South Africa: implications of zircon recycling on stratigraphic age controls

“…Lanci et al (2013) suggested that the robust single crystal age data presented by Fildani et al (2007Fildani et al ( , 2009) were erroneously young due to Pb-loss. The ages presented in this study are based on zircon age populations (n ≥ 3) to estimate ash ages, greatly minimizing the chances of the age being affected by Pb-loss (Saylor et al 2012), but corroborate, support, and reproduced the age estimates produced by Fildani et al (2007Fildani et al ( , 2009, Coney et al (2007), Weislogel et al (2011), Lanci et al (2013), and Rubidge et al (2013). It is not likely that the zircon ages presented in this study have been affected by Pb-loss because (1) only concordant analyses were considered; (2) ash ages are based on concordant age populations and weighted averages; (3) individual results are repeatable (Fildani et al 2007(Fildani et al , 2009Lanci et al 2013;Rubidge et al 2013); and (4) the observed age inversion is present in both this study and previous studies (Fildani et al 2007(Fildani et al , 2009Coney et al 2007;Weislogel et al 2011;Lanci et al 2013;Rubidge et al 2013) using a variety of analytical techniques (SHRIMP, TIMS, LA-ICPMS) and consistently occurs across the basin directly above the proposed tuff gap.…”