Geology of the Crüger-Sirsalis Basin: Evidence for prolonged volcanism in the southwestern near side of the Moon

The Pre-Nectarian Crüger-Sirsalis Basin (centered at 16.0°S, 293.0°E; ~ 475 km in diameter) is a primarily degraded and obscured impact basin on the Moon. This study presents the first geological description of the Crüger-Sirsalis Basin using remote sensing datasets from Lunar Reconnaissance Orbiter (LRO), Chandrayaan-1, and Kaguya missions. An inner depression ring (IDR) with a diameter of ~243 km has been identified, besides two of its outer rings with diameters of ~425 km and ~ 475 km. We report two new floor fractured craters, and a new concentric crater, suggesting the presence of shallow magmatic intrusions. A new pyroclastic deposit has been found within the Crüger-Sirsalis Basin. Our spectral assessment of the cryptomaria and mare basalt reveals two different types of cryptomaria in the region. The cryptomare inside the basin possesses similar olivine-pyroxene composition as basalt within the basin. However, the cryptomare outside the Crüger-Sirsalis Basin, towards the Oceanus Procellarum, is predominantly composed of high-Ca pyroxene. The spectral signature of pure anorthosite (PAN) has been found in crater Darwin C, located along the inner ring of the basin. The Byrgius Crater along the outer ring of the basin shows the spectral signature of olivine or Fe-rich glass mixed with orthopyroxene. Crater chronology has revealed that the basin experienced main phase and late phase volcanism, down to ~1.4 Ga. Thus, the Crüger-Sirsalis Basin uniquely experienced prolonged mare volcanism from the pre-cataclysmic stage to the late stage of lunar history.