Lithospheric-scale 3D configuration of the Central Andes and adjacent forelands: constraints on along- and across-strike variations of density, temperature and strength
There is a great variability in observed crustal deformation style and intensity from the subduction trench across the highest Andes to the foreland lows as well as from the Northern to the Southern Central Andes. Beside the subducting plate that exerts important controls on deformation through its (spatially and temporally) varying dynamics, it is the intrinsic physical properties of the overriding plate that govern the formation of zones of crustal strength and weakness. With this project we want to explore the present-day compositional, thermal and rheological configuration of the Central Andes and adjacent forelands on a lithospheric scale by means of data-driven 3D numerical models. While in the first project phase of StRATEGy this work package focused on the Northern Central Andes, this follow-up project will investigate lithological and related physical heterogeneities of the sediments, the crystalline crust, and the mantle of the Southern Central Andes. For this purpose, geological and geophysical observations such as seismic, seismological, gravity and thermal data will be integrated into consistent 3D models. These static models will be useful to constrain numerical thermo-mechanical experiments (such as planned in project G 3.2) that explore the stress-and-strain relationships across the entire subduction system.
3D lithosphere-scale density and thermal structure of the Central Andean foreland basins
Since the late Oligocene, the intracontinental Chaco-Paraná basin system evolved contemporaneously with the adjacent Andean fold-and-thrust belt. Consequently, four characteristic foreland depozones with different sediment thickness have developed, including (from west to east) wedge-top, foredeep, forebulge, and backbulge depositional environments. In places, very young sedimentary sequences directly overlie basement rocks in the E, while toward the orogen, they cover several kilometres of Paleozoic and Mesozoic sediments. Geophysical data provides local information on the depth to the Moho and the lithosphere-asthenosphere-boundary (LAB); accordingly, the crust and lithosphere thin from ~43 km and ~120 km in the north-eastern parts of the Chaco-Paraná basin to ~35 km and ~80 km, respectively, in the central parts. Towards the Andean orogen in the west, crustal thicknesses increase to more than 60 km and the LAB deepens to more than 150 km. Despite the abundance of geological and geophysical data, there is currently no regionally consistent 3-dimensional representation of the entire lithosphere in the region. Such a model depicting the main compositional heterogeneities of the sediments, the crystalline basement, and the lithospheric mantle has recently been developed for the Central Andes and will be critical for unraveling the long-term evolution of the foreland basin. Based on geological maps, well-logs, and seismic data made available to StRATEGy from industry and our Argentine partner E. Rossello, regional thickness variations of main tectonostratigraphic units will be integrated in a 3D structural model in the framework of PhD project. Subsidence rates and spatiotemporal shifts of depocentres will be cast in terms of phases of increased Andean tectonic loading. The models developed in this project will provide boundary conditions for petroleum-potential assessment in project [G 3.1] and a regional tectonic framework for project [G 3.4]. Furthermore, these models will allow rheological heterogeneities to be distinguished, particularly crustal zones of mechanical weakness, representing important constraints for large-scale numerical thermo-mechanical models developed in projects [G 3.2].