Double-dating applied to provenance study in actual rivers in the
foothills of the Eastern Cordillera Colombia
Abstract
The combination of different thermochronologic techniques on the same
samples or even the same grains has become in a useful tool, to
establish a complete history of the geological process that has
controlled a rock, and for gaining information on sediment provenance
and the exhumation of sediment source areas. Determination of
crystallization and cooling ages of detrital zircon from modern river
sediments is a powerful method for tracing sediment provenance and
exhumation of orogenic mountain belts. In this work we explain with new
examples of modern river samples from the Colombian Andes how zircon
fission-track (ZFT) and U-Pb dating can be used in provenance studies to
better understand the temporal association between source and
depositional site and how the evolution of orogenic mountain belts from
such data in a setting where large amounts of sediment are recycled from
sedimentary source rocks and volcanic input may complicate the
exhumational signal. Whereas the ZFT data provide information about the
most recent thermal history and exhumation of the source rocks, they are
complementary to U-Pb data which reflect the original zircon
crystallization age and its ultimate provenance. The study contains data
of detrital zircon U-Pb and zircon fission-track dating from modern
river sediments of the Guatiquia and Guayuriba rivers in the eastern
foothills of the EC, and the Magdalena River at Girardot on the western
flank of the EC. Each individual dating technique offers unique
information with respect to provenance and exhumation. We use our data
to highlight certain advantages and limitations of using zircon U-Pb and
FT dating in provenance studies, including the identification of
original source areas, sediment recycling and the difficulty of
detecting amagmatic orogens in the detrital zircon record. The data
obtained in this study allows us to better understand the association
between exhumation of sources and their detrital zircon signatures in
modern rivers that drain a part of the EC The results obtained allowing
us to make first-order observations about the provenance signal in
modern rivers on the east flank of the Eastern Cordillera, our data
clearly show that the zircon U-Pb age spectra of the Paleozoic through
Mesozoic sedimentary section being eroded is related to sources in the
Amazon Craton, the magmatic Paleozoic basement of the same EC, and
exhumation of proximal Precambrian basement blocks. On the other hand,
the Magdalena River sample indicates the presence of these same EC
sources plus the addition of younger Permo-Triassic and Jurassic zircons
derived from reworking of Upper Magdalena Valley sedimentary units
and/or the crystalline basement of the CC. The ZFT data presented here
complements the existing record of recent exhumation for the EC and the
Magdalena River at Girardot on the western flank of the EC. Each
individual dating technique offers unique information with respect to
provenance and exhumation.