New field and remote sensing data constrain the size and geometry of the Dhala impact structure, India

Abstract The Dhala structure in India, one of the oldest and most deeply eroded impact structures known on Earth, exhibits distinct morphological features. Despite decades of investigation, two fundamental attributes of the Dhala structure, its shape (variously described as rectangular, elliptical, to circular) and diameter (2.96 to ~25 km) have remained unresolved. Here, we report extensive new data pertaining to the spatial disposition of different lithounits with pre‐, syn‐ and post‐impact fabric data, and the occurrence within target granitoids of overturned fold structures related to the collapse of the central uplift, and provide an updated estimate of the current impact‐melt breccia volume of ~2 km 3 . We propose a firm constraint on the size of the transient crater based on the extent of shock effects within target rocks and drill cores of the crater floor and below. We also provide compelling evidence for the presence of a collapsed structural uplift in the region of the Central Elevated Area (CEA), which is surrounded by a ring of monomict impact breccia exposures. Diagnostic shock deformation features in target granitoid, Giant Quartz Veins (GQVs), and samples from the breccia ring are also reported. Multispectral remote sensing, combined with digital elevation model analysis using sunshading and radial derivative techniques, reveals multiple elliptical to ovoid features around the CEA. These features, along with structural and fabric data, indicate a strong control of pre‐impact basement anisotropies on the final crater geometry. We propose a revised diameter of ~10–12 km for the transient cavity and ~25 km for the final structure based on the integrated field and remote sensing data sets. The Dhala structure exhibits a distinctly elliptical morphology, with its major axis oriented in the southwest‐northeast direction. The age of the Dhala impact is revised by ~400 Ma, constraining it now to the 1700 to 2100 Ma interval. The revised age constraint is derived from shock‐metamorphic features identified within GQVs of approximately 2.1 Ga age, indicating the pre‐impact emplacement of these reefs.