3-dimensional trapdoor structure of laccolith-induced doming and implications for laccolith emplacement, Pampa Amarilla, Mendoza Province, Argentina

Laccolith emplacement and growth are controlled by doming of overburden rocks. Understanding the mechanics and structural evolution of laccolith-induced doming is therefore essential for revealing the emplacement dynamics and growth of laccoliths. In this paper, we present a 3D reconstruction of a subsurface laccolithic intrusion through the structural reconstruction of a well-exposed dome at Pampa Amarilla, Neuquen Basin, southern Mendoza province, Argentina. The 3D reconstruction was made possible by the unique integration of surface geological data and subsurface 3D seismic and borehole data. We estimate that the Pampa Amarilla laccolith is similar to 400 m thick, similar to 3 km and 2 km long in the E-W and N-S directions, respectively. Along an E-W cross section, the laccolith exhibits a wedge shape with maximum thickness near its western edge and gradual thinning toward the east. The structure of the dome is typical of a trapdoor, with faulting along the western, northwestern and southwestern edges, and tilting of the overburden to the east. The trapdoor tilting of the laccolith's overburden was the main mechanism controlling the thickening and growth of the Pampa Amarilla laccolith, which exhibits a relatively high thickness-to-length ratio T/D similar to 0.13. Numerous laccolithic intrusions exhibit similar values of T/D, and our study suggests that faulting commonly controls emplacement of laccoliths with T/D > 0.1; conversely, our study suggests that the established mechanical models of laccolith emplacement based on elastic bending of the overburden applies only to thin laccoliths. Finally, our study highlights the necessity and value of integrating field geological measurements with subsurface 3D seismic and borehole data for structural reconstructions of subsurface laccolith intrusions.

Automated summary

Understanding the mechanics and structural evolution of dome formation caused by laccolith emplacement is crucial for the understanding of laccolith dynamics and growth. In this study, a 3D reconstruction of a subsurface laccolithic intrusion in Pampa Amarilla, Argentina, was achieved through the integration of surface geological data and subsurface 3D seismic and borehole data. The results show that trapdoor tilting of the laccolith's overburden is the main mechanism controlling the thickening and growth of the laccolith, suggesting faulting commonly controls emplacement of laccoliths with a high thickness-to-length ratio. The study highlights the importance of integrating field geological measurements with subsurface data for structural reconstructions of laccolith intrusions.