S1: Dynamics of igneous processes (Special Session, Joint Session with The Volcanological Society of Japan) [Oral presentations are by invitation only; poster presentations are open to all.]

12:30 PM - 2:00 PM JST(3:30 AM - 5:00 AM UTC)

[S1P-03] Unlocking magma overpressure from partially exposed dykes: A unified fracture-mechanics framework for reconstructing dyke outcrop geometry and emplacement conditions

*Sirshendu Kumar Biswas¹, Anubhab Dey², Tridib Kumar Mondal² (1. Hiroshima University, 2. Geological Studies Unit, Indian Statistical Institute, Kolkata, 203 B.T. Road, Kolkata - 700108, West Bengal, India)

Keywords:

Dyke,Ellipse,Partial exposure,Magma overpressure

Accurate estimation of magma overpressure and dyke dimensions is fundamental to understanding the dynamics of magma transport and the mechanics of magma-driven crustal fracturing. However, natural dykes are rarely completely exposed, posing a major challenge for quantitative estimation of magma overpressure. We therefore develop a unified methodological framework for reconstructing the complete geometry of partially exposed dykes and estimating magma overpressure and emplacement depth using principles of linear elastic fracture mechanics. Exploiting the elliptical geometry of fracture opening, the framework first addresses Mode I dykes with at least one exposed tip, enabling reconstruction of complete dyke geometry from limited field measurements. The methodology is then extended to the more common scenario in which neither dyke tip is exposed by utilizing the differential geometry of elliptical cracks to recover complete dyke dimensions from partial outcrop measurements. Finally, the approach is generalized to partially exposed mixed mode I-III dykes, demonstrating that the relict opening-mode geometry preserved within shear-modified intrusions can be used to estimate magma overpressure under mixed-mode loading conditions. Validation against fully exposed natural dykes across various geodynamic settings, including felsic dykes from the Chotanagpur Granite Gneissic Complex (India), dykes in the caldera walls of Miyake-jima volcano (Japan), and the NE minette dyke of Ship Rock, New Mexico (USA), shows that the methods reliably recover dyke geometry across a range of exposure conditions. Application to partially exposed mafic dykes emplaced within the Archean granites of Dharwar craton, India yields reasonable estimates of magma overpressure and depth of origin. Collectively, these advances provide a robust fracture-mechanics framework for extracting emplacement conditions from partial dyke exposures, substantially expanding the scope of field-based dyke analysis.