Implications of Magmatic Events on Hydrocarbon Generation: Occurrences of Gabbroic Rocks in the Orito Field, Putumayo Basin, SW Colombia
Abstract
Mafic dikes and sills intruded the sedimentary succession in the Orito Oil Field, located in the Putumayo Basin, SW Colombia. One sample from the Orito-4 well yields a Late Miocene to Pliocene age (40K/40Ar on amphibole 6.1 ± 0.7 Ma) for the igneous event in the basin. This coincides with the widely recognized regional Andean orogenic uplift that affected most of sub-Andean Peru, Ecuador, and Colombia. Furthermore, the uplift consequently coincides with a second pulse of hydrocarbon generation and expulsion in the Putumayo Basin. This second pulse was thermally more evolved than the first one (Late Oligocene - Miocene). The high content of CO2 in the gas budget recovered in different wells along the basin may be related to the heat flux of the mafic intrusions. There are four geological events that coincide with this large scale evolution during the late Miocene to early Pliocene (13 - 3 Ma): regional orogenic uplift, persistent igneous intrusions, CO2 formation, and a second pulse of hydrocarbon generation and expulsion. The Late Miocene - Pliocene age of the intrusion is the key to formulate a hypothesis where these four events are joined together. Regional uplift and intrusions: The mafic rocks of the Orito Oil Field show Sr-Nd-Pb isotopic compositions that suggest derivation from a mantle source below the western edge of the South American continent. The geochemical signature of these rocks that form part of the Northern Volcanic Zone (NVZ) reflects subduction-related magmatism. Thus, they record subduction and start of the last pervasive uplift episode that took place during the Late Neogene. Intrusions and second migration phase: The Late Miocene pulse of hydrocarbon generation and migration coincides closely with the estimated age of the intrusions; therefore, a causal link with the geothermal anomaly induced by the mafic igneous rocks is likely. The temperature of a mafic magma reaching 1000 to 1200°C is sufficient to heat the host rocks, where the abundance of dikes eventually changed the regional heat flux. Intrusions and CO2: The presence of CO2 in the basin can be explained as the result of carbonate breakdown associated with igneous intrusions in carbonate sequences. Moreover, since the carbonates are part of the source and reservoir formations of the basin, this gas represents a fundamental factor when assessing the economic risk during various exploration phases. These gabbroic intrusions played an important role in the paleo-heat flow scenario. The magmatic input led to an increase of the maturity of the source rock. The combination of the four elements mentioned above from middle Miocene to Pliocene favored the formation of thermally more-evolved hydrocarbons, but also promoted the generation of major contents of CO2 accumulating in the same traps as the hydrocarbons.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFM.V13E0585V
- Keywords:
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- 1031 Subduction zone processes (3060;
- 3613;
- 8170;
- 8413);
- 1040 Radiogenic isotope geochemistry;
- 1065 Major and trace element geochemistry;
- 3640 Igneous petrology