Igneous sill and finger emplacement mechanism in shaledominated formations: a field study at Cuesta del Chihuido, Neuquén Basin, Argentina

J. SPACAPAN; SVERRE PLANKE; OLIVIER GALLAND; HECTOR LEANZA

JOURNAL OF THE GEOLOGICAL SOCIETY

GEOLOGICAL SOC PUBL HOUSE

Lugar: Londres; Año: 2016 vol. 174 p. 1 - 12

0016-7649

Abstract: Seismic reflection data and field observations have revealed the presence of voluminous igneous sill complexesemplaced into organic-rich shale formations in sedimentary basins worldwide. Damage and structures associated with sills havemajor implications for fluid flow through basins. Constraining the distribution of these structures requires a good understandingof the sill emplacement mechanism. However, most mechanical models of sill emplacement assume elastic host behaviour,whereas shale is expected to deform inelastically. This contradiction calls for new field observations to better constrain sillemplacement mechanisms. In this paper, we report on detailed field observations of spectacularly exposed fingers and a sillemplaced in shale at Cuesta del Chihuido, in the Neuquén Basin, Argentina. Exceptional outcrop conditions allow detaileddescriptions of both (1) the entire cross-section of the intrusions, and (2) the deformation structures accommodating intrusionpropagation in the host rock. All intrusions exhibit irregular, blunt or rectangular tips. The structures accommodating the tippropagation are systematically compressional, including reverse faults, folding and imbricate thrust system. Our observationssuggest that the studied intrusions have propagated by pushing the host rock ahead, as a viscous indenter. Our observationssuggest that the viscous indenter model is probably a dominant mechanism of sill emplacement in shale.