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Resurfacing of Procellarum-Imbrium Region by Tectonism and Volcanism: the Role of the Basin-Radial Fracture Zones Around the Imbrium Basin

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Lunar and Planetary Science XLVIII (2017) 1710.pdf RESURFACING OF PROCELLARUM-IMBRIUM REGION BY TECTONISM AND VOLCANISM: THE ROLE OF THE BASIN-RADIAL FRACTURE ZONES AROUND THE IMBRIUM BASIN. F. Zhang and M.-H. Zhu, Space Science Institute, Macau University of Science and Technology, Taipa, Macau ([email protected]). Introduction: The debate regarding to the origin of the Oceanus Procellarum (the largest basalt concen- tration area on the Moon) is still ongoing today. Two formation mechanisms have been proposed: impact [1, 2, 3], and intrusion and crust rifting [4]. But, the de- tailed processes responsible for the resurfacing of Pro- cellarum are yet still unclear. For this purpose, we try to establish a sequence of events accounting for the current surficial state of spatial distribution of volcanic materials in Oceanus Procellarum. Commonly, volcano concentration areas have rift zones underlain by swarms of dikes or other varying scale intrusions. The presence of mantle-derived mafic dikes on the Moon is mainly inferred from associated volcanic morphology and surface deformation [5]. Spatial arrangement of dike-related lineaments reflect the record of fracture system in the lunar crust. Fractures in radial pattern on the Moon are frequently associated with a sufficiently Fig. 1 LROC WAC mosaic for the Procellarum- large basin [6] forming a subset of the Moon's NE-SW Imbrium region. Six large shield volcanos (Rumker, and NW-SE trending grid system [7]. Aristarchus, Prinz, Marius, Kepler, and Hortensius) are Impact-induced faults are nearly ubiquitous over outlined by ellipse. Three basin-radial volcanic belt large areas on the terrestrial planets [8]. These fault zones GM, DPA, and EMK are marked by white systems are preferred sites for late deformation in re- stripes. sponse to lithospheric stresses generated by other pro- Data and Methods: We use data from Lunar Re- cesses. Melosh [6] suggested that faults formed during connaissance Orbiter (LRO) mission to trace surface the Imbrium basin continued to be active for at least expressions of dike segments (structurally controlled 600 Ma on the Moon, inferred from the observation of by large event) to establish the subsurface radial faults cutting mare basalts, ~ 600 Ma after the dike/fracture/fissure systems around the Imbrium basin. formation of Imbrium basin [9]. For the Imbrium basin, Three volcanic belt zones are defined and character- the radial fracture patterns start from the interior [10] ized by abundant surficial dike-related structures. Two and extend further to a distance of ~1 radius beyond relevant volcano-tectonic features characterize the the outmost ring. Subsurface radial dikes detected from three basin-radial fracture zones morphologically: (1) Gravity Recovery and Interior Laboratory (GRAIL) dike-related clusters of aligned eruptive vents (such as data [11] support this interpretation. However, the de- rilles' head depressions, cones and domes) and graben- tection of smaller dikes can not be resolved by the fissures; and (2) sinuous rilles and IMPs, which are GRAIL data due to the limited spatial resolution. Here, commonly related to volcanic structures [12, 5]. These we use linear dike-related surface expressions (linea- volcanic features are spatially associated with the maria ments) to infer the spatial distribution of subsurface around them. All the original data and resulting data dikes/fissures/fractures at the western marginal zone of are processed in ArcGIS software. the Imbrium basin, a transitional region from Mare Results: The Gruithuisen-Mairan (GM) volcanic Imbrium to Oceanus Procellarum (see Fig. 1). This belt zone contains 12 sinuous rilles, 7 non-mare more class of fragmented dike swarms can be recognized as silicic domes (Gruithuisen and Mairan domes), 1 mare the signature of major magmatic events, in many in- dome, 2 cones, and more than 50 gas-release erup- stances linked to the Imbrium impact-induced faults tion/deposit related depressions (IMPs). Similar to that may have persisted as zones of lithospheric weak- these dome locations, some source depressions of sinu- ness. The purpose of this work is to provide much ous rilles have elongated forms displaying the preferen- needed constraint for the major magmatic and tectonic tial direction radial to the Imbrium basin. events responsible for the long-term resurfacing of The Delisle-Prinz-Aristarchus (DPA) volcanic belt Procellarum-Imbrium region over geologic time scales. zone is a positive-relief region of ~100 km in width Lunar and Planetary Science XLVIII (2017) 1710.pdf and extends from northeast of Delisle crater to the Ar- the maximum stress within the lithosphere may be istarchus Plateau. The main features in DPA region switched to a direction parallel to a meridian from a include: (1) a pre-mare highland plateau-Aristarchus direction perpendicular to a meridian [20]. Conse- [5], (2) highland crater Prinz and mountains Harbinger, quently, with time and cooling of lithosphere, the ori- remnants of outer Imbrium rims, (3) basin-radial linear entations of linear tectonic structures show a wide- rille (graben) segments, (4) distinctive alignment of spread pattern of concentric and radial to the Imbrium vents, and (5) some IMPs within or around two source basin, such as a large-scale Imbrium pattern of graben vents at the Prinz site. The observation of sinuous rilles [6], many of which are underlain by a dike wider than at the end of some linear rille (graben) segments indi- 100 m that likely penetrate the lunar crust down to cates the direct evidence for the volcanic origin of the depth of ~20 km [13]. rille (graben) underlain by subsurface dike [13] or be- Conclusions: This study has identified three vol- ing a collapsed lava tube or a fissure vent. Caldera-like canic belt zones at the western margin of the Imbrium pit and vent area near the Prinz [14] would be the erup- basin. These belts represent basin-related rift and frac- tive center feeding the surrounding mare plains of Oce- ture zones characterised by radiating lineament systems anus Procellarum and Mare Imbrium. or volcanic features arranged in linear distribution. Euler-Mayer-Kepler (EMK) rift and fracture zones Imbrium basin-radial dike related volcanic eruptions are highly fractured areas allowing multiple pathways are most likely to be responsible for the long history of for magma to the surface. In the areas numerous linear emplacement of mare basalts in the Procellarum- volcanic features are radial to the Imbrium basin and Imbrium region. Imbrium impact event play a signifi- shape the surface tectonically and volcanologically cantly important role in reshaping the nearside crust of across about half of a million square kilometers. These the Moon. The fractured lunar crust provides direct volcanic lineaments (17 cone rows (line of spatter pathways for magma ascending to the surface as the cones along fissure vent), 15 linear rilles (graben), 5 pit Imbrium basin evolves. The unique thermal setting and (crater) chains, and 4 fissure vents) represent subparal- a thin lunar crust of the region allow the post-Imbrium lel dikes over a broad area displaying elliptical bounda- volcanism to be extended within a prolonged duration ry. The long axis of both elliptical fracture zones ex- in lunar history. hibit the Imbrium basin-radial pattern. Many cones Acknowledgments: This work was supported by display elongated summit vents oriented radially with the Science and Technology Development Fund of respect to the Imbrium basin. Macau (075/2014/A2 and 039/2013/A2). Discussion: The basin-concentric and basin-radial References: [1] Cadogan P. (1974) Nature, 250, orientations of dike-related lineaments around the basin 315–316. [2] Whitaker E. (1980) In: Multi-ring Basins: can be ascribed to the stress differences in the lunar Formation and Evolution, 414, p.101. [3] Wilhelms, D. crust as the Imbrium basin evolves. The Imbrium im- (1987) US Geol. Surv. Prof. Pap., 1348, 1–302. [4] pact site was a long-lived hotspot [15] with a thin crust Andrews-Hanna J. et al. (2014) Nature, 514 (7520) [16]. The initiation of the radial tensional fractures or 68–71. [5] Head J. and Wilson L. (2016) Icarus, 283, faults is believed to occur at the time of the Imbrium 176–223. [6] Melosh H. (1976) LPS VII, 2967–2982. event due to a broad domal uplift of the region around [7] Strom R. (1964) Commun. Lunar Planet Lab, 2, the basin resulting from stress relief (stress relaxation) 205–216. [8] Solomon S. and Duxbury E. (1987) JGR, at depth [17, 6]. The domical topography formed at the 92 (B4). [9] Taylor S. (1975) New York, Pergamon surface due to the shallow emplacement of magma Press, Inc., p.390. [10] Zhang F. et al. (2016) EPSL, and/or lava accumulation on the top and flanks has 445, 13–27. [11] Andrew-Hanna J. et al. (2013) Sci- been clearly identified as large shield volcanos on the ence 339 (6120), 675–678. [12] Braden S. et al. (2014) Moon [14]. Early in the major period of mare volcan- Nat. Geosci., 7 (11), 787–791. [13] Klimczak C. (2014) ism (~3.9-3.1 Ga ago, [18]), the extension state of the Geology, 42 (11), 963–966. [14] Spudis P. et al. (2013) Moon [19], regional extensional stresses caused by JGR, 118 (5), 1063–1081. [15] Wieczorek M. and post-Imbrium-impact uplift and viscous relaxation (fa- Phillips R. (2000) JGR, 105 (E8), 20417–20430. [16] cilitate dike intrusion), and the viscoelastic nature of Wieczorek M. et al. (2013) Science, 339 (6120), 671– the lithosphere would allow regional deformation to 675. [17] Mason R. (1976) Proc. Geol. Assoc., 87 (2), take place over a long period of time [20], in accord- 161–168. [18] Hiesinger H. (2011) Spec. Pap. Geol. ance with the elevated heat flux in this region (always Soc. Am, 477, 1–51.
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  • GRAIL-Identified Gravity Anomalies in Oceanus Procellarum: Insight Into 2 Subsurface Impact and Magmatic Structures on the Moon 3 4 Ariel N

    GRAIL-Identified Gravity Anomalies in Oceanus Procellarum: Insight Into 2 Subsurface Impact and Magmatic Structures on the Moon 3 4 Ariel N

    1 GRAIL-identified gravity anomalies in Oceanus Procellarum: Insight into 2 subsurface impact and magmatic structures on the Moon 3 4 Ariel N. Deutscha, Gregory A. Neumannb, James W. Heada, Lionel Wilsona,c 5 6 aDepartment of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 7 02912, USA 8 bNASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 9 cLancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK 10 11 Corresponding author: Ariel N. Deutsch 12 Corresponding email: [email protected] 13 14 Date of re-submission: 5 April 2019 15 16 Re-submitted to: Icarus 17 Manuscript number: ICARUS_2018_549 18 19 Highlights: 20 • Four positive Bouguer gravity anomalies are analyzed on the Moon’s nearside. 21 • The amplitudes of the anomalies require a deep density contrast. 22 • One 190-km anomaly with crater-related topography is suggestive of mantle uplift. 23 • Marius Hills anomalies are consistent with intruded dike swarms. 24 • An anomaly south of Aristarchus has a crater rim and possibly magmatic intrusions. 25 26 Key words: 27 Moon; gravity; impact cratering; volcanism 1 28 Abstract 29 30 Four, quasi-circular, positive Bouguer gravity anomalies (PBGAs) that are similar in diameter 31 (~90–190 km) and gravitational amplitude (>140 mGal contrast) are identified within the central 32 Oceanus Procellarum region of the Moon. These spatially associated PBGAs are located south of 33 Aristarchus Plateau, north of Flamsteed crater, and two are within the Marius Hills volcanic 34 complex (north and south). Each is characterized by distinct surface geologic features suggestive 35 of ancient impact craters and/or volcanic/plutonic activity.