Pre-Orientale Southwest Peak-Ring Basin: Gravity Structure, Geologic Characteristics, and Influence on Orientale Basin Ring Formation and Ejecta Emplacement

Jinzhu Ji,James W Head,Jianzhong Liu

doi:10.3390/rs13132635

Abstract

The Orientale impact basin is the youngest and most well-preserved of the lunar multi-ring basins. The generally well-preserved ring structures and basin facies are distinctly anomalous in the southwestern quadrant; the outer Cordillera ring extends significantly outward, the Outer and Inner Rook mountain rings are more poorly developed and show anomalous characteristics, and the Montes Rook Formation varies widely from its characteristics elsewhere in the basin interior. Based on the gravity, image, and topography data, we confirmed that the southwest region of the Orientale basin represents the location of a pre-existing ~320 km rim–crest diameter peak–ring basin centered at 108.8°W, 28.4°S, and characterized by an ~170 km peak–ring diameter. We model the structure and morphology of this large pre-Orientale peak–ring basin (about one-third the diameter of Orientale) and show that its presence and negative relief had a distinctive influence on the development of the basin rings (disrupting the otherwise generally circular continuity and causing radial excursions in their locations) and the emplacement of ejecta (causing filling of the low region represented by the peak–ring basin, creating anomalous surface textures, and resulting in late stage ejecta movement in response to the pre-existing peak–ring basin topography. The location and preservation of the peak–ring basin Bouguer anomaly strongly suggest that the rim crest of the Orientale basin excavation cavity lies at or within the Outer Rook Mountain ring.

Highlights

The Orientale basin is the youngest multi-ring basin and preserved the origin characteristics of the impact basin well [1,2,3,4,5] displaying four distinct concentric rings, Inner Depression (~320 km), Inner Rook ring (~480 km), Outer Rook ring (~620 km), and Cordillera ring (~930 km), respectively
The southwestern region of the Orientale basin is topographically complex, where the Cordillera ring is an outward excursion of ring structures and the Outer Rook ring is likewise distorted with wider ring massifs
In this study, based on multiple datasets, including the Gravity Recovery and Interior Laboratory (GRAIL) Bouguer gravity anomaly, SLDEM2015, and Wide Angle Camera (WAC) mosaic images, combining the statistical and empirical formulas [13,23,25,26,27], we confirmed that the southwestern region of Orientale basin is a pre-existing peak–ring basin, whose center is 108.8◦ W, 28.4◦ S with ~320 km rim–crest diameter and ~170 km peak–ring diameter

Summary

Introduction

The Orientale basin is the youngest multi-ring basin and preserved the origin characteristics of the impact basin well [1,2,3,4,5] displaying four distinct concentric rings, Inner Depression (~320 km), Inner Rook ring (~480 km), Outer Rook ring (~620 km), and Cordillera ring (~930 km), respectively. Based on previous research results and topographical features, we have initially drawn different ring structures of the Orientale basin (Figure 1). The. Cordillera ring is continuous and well-preserved in all directions around the basin except the southwestern region (Figure 1), where the massifs most extensively developed and ring structures are difficult to distinguish and several previous mapping efforts have noted an outward excursion of massifs and ring structures in this region [3,4,6,7].

Methods

Results

Discussion

Conclusion