Y. Hervouet et al., Interaction between an intracutaneous thrust wedge and a transcurrent zone: the northwestern flank of the Venezuela Andes, B SOC GEOL, 172(2), 2001, pp. 159-175
Geological setting
The Venezuela Andes or Merida Andes (fig. 1) extend from the Colombian bord
er in the SW to Barquisimeto in the NE, and constitute a basement uplift ex
ceeding 5,000 m near Merida (Pico Bolivar). This young chain is bordered to
the W by the Maracaibo foredeep basin, and to the E by the Barinas-Apure f
oreland basin. The Bocono fault divides the Andean Belt in two parts along
a NE-SW direction. This shows that the uplift of the Andes is contemporaneo
us with an oblique translation.
In the study area, located on the northwestern flank near Maracaibo basin,
three major structures are present: in the E, the N-S senestral strike slip
Valera-Rio Momboy fault, in the S the E-W dextral strike slip Pinango faul
t and, in the center, the SW-NE striking Las Virtudes thrust verging toward
NW.
Lithologic and stratigraphic formations (fig. 4).
The Las Virtudes Fault separates two different structural zones. In the SE,
overthrust units are made of crystalline basement, Paleozoic substratum an
d preorogenic sedimentary formations (Cretaceous-Eocene). The foredeep flex
ural basin, located NW, is filled by synorogenic molasses (Neogene and Quat
ernary), largely developed within the Betijoque Fm. (Upper Miocene to Plioc
ene in age) which reaches a thickness of 5 000 m.
Structure of the northwestern Andean flank
Las Virtudes Fault and ifs thrust slice zone
Near Las Virtudes village (fig. 5, 6-2), this thrust is systematically asso
ciated with a narrow overturned foredeep depo belt (Cretaceous to Neogene i
n age). These slices are unknown elsewhere in the Andean Chain and represen
t the terminal faulted part of the thrust drag. However, where this slice z
one is missing (central and northeastern part of the study area), the Las V
irtudes Fault is not clearly documented : its throw decreases rapidly and i
t is possible that the fault disappears northeastward.