Along-strike variation in structural styles and hydrocarbon occurrences, Subandean fold-and-thrust belt and inner foreland, Colombia to Argentina

Abstract

The approximately N-S-trending Andean retroarc fold-and-thrust belt is the locus of up to 300 km of Cenozoic shortening at the convergent plate boundary where the Nazca plate subducts beneath South America. Inherited pre-Cenozoic differences in the overriding plate are largely responsible for the highly segmented distribution of hydrocarbon resources in the fold-and-thrust belt. We use an ~7500-km-long, orogenparallel ("strike") structural cross section drawn near the eastern terminus of the fold belt between the Colombia-Venezuela border and the south end of the Neuquén Basin, Argentina, to illustrate the control these inherited crustal elements have on structural styles and the distribution of petroleum resources. Three pre-Andean tectonic events are chiefl y responsible for segmentation of subbasins along the trend. First, the Late Ordovician "Ocloyic" tectonic event, recording terrane accretion from the southwest onto the margin of South America (present-day northern Argentina and Chile), resulted in the formation of a NNW-trending crustal welt oriented obliquely to the modern-day Andes. This paleohigh infl uenced the distribution of multiple petroleum system elements in post-Ordovician time. Second, the mid-Carboniferous "Chañic" event was a less profound event that created modest structural relief. Basin segmentation and localized structural collapse during this period set the stage for deposition of important Carboniferous and Permian source rocks in the Madre de Dios and Ucayali Basins in Peru. Third, protracted rifting that lasted throughout the Mesozoic provided the framework for deposition of many of the source rocks in the Subandean belt, but most are not as widely distributed as the Paleozoic sources in Bolivia and Peru. We attribute variations in the style of Andean deformation and distribution of oil versus gas in the Subandes largely to differences in pre-Cenozoic structure along

Extension and Dynamics of the Andes Inferred From the 2016 Parina (Huarichancara) Earthquake

“…Within 300 km of the Andes range front the top ∼5-8 km of the crust consists of sedimentary basins that contain no earthquakes (McGroder et al, 2015; Figure 11c) and that we assume support negligible force. Outside of the sedimentary basins, earthquakes occur throughout the thickness of the crust (Assumpção, 1992;Assumpção & Suarez, 1988; this study; Figure 11c), and therefore, we assume that stresses in the basement crust are supported by frictional resistance on faults given by equation (2).…”

“…We construct one-dimensional yield stress profiles that reflect the stress state as a function of depth to the east of the sub-Andean belt in the bending and nonbending part of the South American foreland and integrate the yield stress to estimate the force the lithosphere can support in these different regions (F fl = ∫ Δ xx dz; e.g., ; Brace & Kohlstedt, 1980;Goetze & Evans, 1979). We then compare these estimates of foreland strength Thermal expansivity a , crust 3 × 10 −5 K −1 Turcotte and Schubert (2002) Thermal expansivity a , mantle 3-4.5 ×10 −5 K −1 Bouhifd et al (1996) Asthenosphere density ( a , 0 ∘ C) 3,330 kg/m 3 Turcotte and Schubert (2002) Lithospheric Mantle density (0 ∘ C) a − 50 kg/m 3 Lucassen et al (2005) and McKenzie and Priestley (2016) Crustal density (0 ∘ C) 2,800 kg/m 3 Lucassen et al (1999) Foreland fault dips 30-50 ∘ This study Activation energy (E) 540 kJ/mol Karato and Wu (1993) Activation volume (V) 2 0 c m 3 /mol Karato and Wu (1993) Stress exponent (n) 3 Karato and Wu (1993) Seismogenic thickness 40-45 km Assumpção and Suarez (1988) Foreland sediment thickness 5-8 km McGroder et al (2015) Neutral fiber depth 13-28 km See section 3.4…”

“…The spatial relationship between normal faulting and foreland deformation style is suggestive of a causal link. Late Miocene to recent normal faulting in the high Andes correlates along strike with regions of wide thin‐skinned fold‐thrust belts (Kley et al, ), the locations of low‐angle thrust‐faulting earthquakes (Devlin et al, ), and thick Paleozoic and Mesozoic sediments in the adjacent foreland basin (McGroder et al, ; supporting information Figure S17). In contrast, in regions where the active foreland deformation style comprises predominantly reverse faulting emerging at the front of steep topography (e.g., Shira Uplift of Peru, Kley et al, ; Sierra Pampeanas of Argentina, Alvarado & Beck, ; Oriente of Ecuador, Kley et al, ) the style of faulting in the adjacent high Andes is dominantly compressional (Figure ).…”

“…Reverse-faulting earthquakes in regions >300 km from the Andes range front (Figure 9a) indicate the South American foreland crust is breaking in response to compressional forces acting through the lithosphere (Assumpção, 1992). However, within 300 km of the Andes range front, asymmetrical sedimentary basins (McGroder et al, 2015), long-wavelength, negative free-air gravity anomalies (Lyon-Caen et al, 1985), and shallow extensional faulting overlying compressional faulting at the base of the crust (Figures 10, 11a, and 11c) imply that the forelands are bending in response to the load of the Andes (e.g., Lyon-Caen et al, 1985;Watts et al, 1995).…”

Orogenic Wedge Evolution of the Central Andes, Bolivia (21°S): Implications for Cordilleran Cyclicity

“…The stratigraphy in the central Andean fold‐thrust belt consists of an ~8‐ to 15‐km‐thick package of Phanerozoic, predominantly siliciclastic sedimentary rocks (Sempere, ). However, stratigraphic thicknesses differ by several kilometers both along and across strike due in part to pre‐Andean tectonism (McGroder et al, ; Starck, ; Tankard et al, ), as well as variations in accommodation space during development of the Cenozoic foreland basin (e.g., Cardozo & Jordan, ; Horton, ; Horton & DeCelles, ). The across‐strike variability in the stratigraphic section at ~21°S is documented from field observations and a restored cross section (e.g., Anderson et al, ).…”