Compositional and morphological variations of effusive lava flows and
explosive pyroclastic deposits at the caldera forming Gardner shield
volcano on the Moon
Abstract
We estimated the mineralogy of the effusive and explosive units at the
Gardner shield volcano using Chandrayaan-1 Moon Mineralogy Mapper (M3)
data and Lunar Reconnaissance Orbiter (LRO) Diviner data. We present a
high-resolution 3D morphological map of the shield based on LRO Camera
(LROC) Narrow Angle Camera (NAC) and Wide Angle Camera (WAC) images and
LOLA SLDEM data. The shield shows evidence of caldera subsidence with
downsag and possible trapdoor style subsidence, including a central
normal fault, partially developed fault-ring structure, resurgence, and
subsidence blocks, two sinuous rilles, graben, lineaments, a parasitic
cone SE of the central caldera. The shield comprises 5 prominent
voluminous and 10 thinner effusive basaltic flow units, and one
explosive unit displaying pyroclastic material at the center of the
caldera. North of the caldera is Gardner crater, which is a simple
bowl-shaped impact crater, formed after the shield, revealing fresh
mineralogy from the shield and highlands, including high calcium
pyroxene, olivine, and Fe-spinel. The crater has a dark debris flow on
its eastern wall, landslides, a boulder cluster, boulder tracs, and
lineaments. The shield presents a unique lava river channel originating
from a secondary oblique fault ~ 5 km wide and spreading
tens of kilometers at the northern part of Mare Tranquillitatis. Our
volcano-tectonic study indicates that the Gardner shield is a science
rich site with exploration potential to study basaltic caldera-forming
volcanoes with in-situ pyroclastic resources as it comprises almost all
the major compositional and structural aspects to understand lunar
thermal, tectonic, and geological evolution.