Integrative Interpretation of Thermochronometric Data: Application to Inversion Tectonics Settings

Ketcham, Richard A.¹; Mora, Andres; Almendral, Ariel; Parra, Mauricio; Casallas, Wilson; and Robles, Wilmer
¹[email protected]

Thermochronometric data provide a powerful way to build reliable time-temperature (t-T) histories in petroleum basins. Integrating information from multiple samples into a single modelling framework is a challenge, but is likewise a necessary step forward for providing refined and robust t-T histories. The challenges are particularly severe in inversion terranes where erosion has erased all synkinematic strata. Here we apply two new computational tools for interpreting thermochronometric data that facilitate the joint use of multiple samples, to obtain a continuous history of heating and cooling that would be extremely difficult to obtain using other tools. The first, Fetmove, is a finite element solver that takes as input a series of detailed balanced cross sections, and solves the heat flow equation in 2D along with predicted thermochronometric ages that can be compared against measured data. The key feature of Fetmove is a workflow that allows the interpreter to engage in successive refinements of the structural model using the inferences provided by thermochronometric data. The second is new functionality in the HeFTy software for inverse modelling of thermochronometric data that permits simultaneous modelling of samples down a well or borehole. This extension forces attention on issues that have previously been relatively neglected in thermochronometry-based modelling, in particular that of multiple provenance. The rewards in doing so include more robust modelling and interpretation and, in some cases, insights concerning the unroofing histories of the source rocks that contributed to a given sedimentary unit.

Our pilot cases show that Fetmove applied in the deeply exhumed inversion faults of the Cordillera is ideal for getting high resolution t-T histories along a 2d cross section, and the times at which potential petroleum source rocks were in the oil generation window. In contrast, the improved HeFTy fits more to the case of structures displaying only moderate inversion and post-inversion unconformities and quiescence based on borehole data. This is the case for the buried inverted half-grabens in the Magdalena Valley. In the first case we found that oil generation stopped after the Oligocene whereas in the second case there might be generation even today.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013