Structural parameters of the late Ediacaran dyke swarm in the Saghro Massif (Eastern Anti-Atlas, Morocco): Implications for the depth of magma origin, paleo stress reconstruction and emplacement models

Abstract

The study of dyke swarms is crucial for understanding the processes of magma intrusion and the tectonic environments that influence volcanic activity. Dyke swarms are essential records of tectonic and magmatic events, offering insights into magma ascent, chamber dynamics, and stress conditions during emplacement. In this context, the dyke swarm of the central part of the Saghro Massif (Eastern Anti-Atlas) is investigated for the first time, using structural aspects of the dykes and paleo stress inversion to constrain magma overpressure, the depth of magma reservoir, the state of stress during emplacement, and the tectonic regime responsible for emplacement. We selected seventy-eight mafic and intermediate dykes in the swarm of the Central Part of the Saghro Massif (CPSM), characterized by different orientations N-S to NNE-SSW, NE-SW, E-W and NW-SE. In addition, the size distribution of thicknesses and lengths follows a power-law and a log-normal distribution respectively. We calculate magmatic overpressure using selected dyke aspect ratios to estimate the depth of the magma reservoir. This study suggests that the CPSM dykes form mainly due to the injection of magma from a deep magma reservoir at depths >31 km, hence close to the Moho crust-mantle boundary (31-33 km). Paleo stress reconstruction shows that the CPSM dyke swarm was emplaced when the minimum principal compressive stress (63) was oriented WNW-ESE, and the maximum principal compressive stress (61) was vertical. The reconstruction also shows that the emplacement of the CPSM swarm occurred during a transtensional tectonic regime, associated with the WACadomian orogeny.