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Young wrinkle ridges in Mare Imbrium: Evidence for very recent compressional tectonism
Accepted Manuscript Young wrinkle ridges in Mare Imbrium: Evidence for very recent compressional tectonism
Yu Lu, Yunzhao Wu, Gregory G. Michael, Alexander T. Basilevsky, Cui Li PII: DOI: Reference:
S0019-1035(18)30452-4 https://doi.org/10.1016/j.icarus.2019.03.029 YICAR 13252
To appear in:
Icarus
Received date: Revised date: Accepted date:
13 July 2018 8 March 2019 20 March 2019
Please cite this article as: Y. Lu, Y. Wu, G.G. Michael, et al., Young wrinkle ridges in Mare Imbrium: Evidence for very recent compressional tectonism, Icarus, https://doi.org/ 10.1016/j.icarus.2019.03.029
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ACCEPTED MANUSCRIPT Young wrinkle ridges in Mare Imbrium: Evidence for very recent compressional tectonism
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Yu Lu a,b, Yunzhao Wu b,c,*, Gregory G. Michael d, Alexander T. Basilevsky e, Cui Li b,f
School of Geography and Ocean Science, Nanjing University, Nanjing, 210023, China
b
Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of
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a
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Sciences, Nanjing, 210034, China
CAS Center for Excellence in Comparative Planetology, Hefei, China
d
Institute of Geological Sciences, Freie Universitaet Berlin, Berlin, 12249, Germany
e
Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences,
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c
f
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Moscow, 119991, Russia
Jiangsu Center for Collaborative Innovation in Geographical Information Resource
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Development and Application, Nanjing, 210023, China
* Corresponding author.
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E-mail address: [email protected] (Y.Z. Wu).
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ACCEPTED MANUSCRIPT Abstract Wrinkle ridges are common landforms widely distributed in the lunar maria. Many young wrinkle ridges were found inside Mare Imbrium using Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) high-resolution images. They represent very recent
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tectonic activity on the lunar surface. Determining their formation times and morphology is
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important in understanding the Moon’s late evolution. The young ridges were mapped, and they
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have a winding and arched morphology. Based on their small scale and crisp appearance, crosscutting relations with very young small craters whose youth was concluded from spatial
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boulder densities within their ejecta blankets, these young wrinkle ridges were estimated to be as
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young as 10 or a few 10s of Ma, and may still be active today. The young ridges were mainly distributed in the inner region of Imbrium basin, which may suggest that the thermal and
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structural evolution of the inside area of Imbrium basin was protracted.
Keywords: Young wrinkle ridges, Distribution, Morphology, Age determination, Formation
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mechanism
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ACCEPTED MANUSCRIPT 1. Introduction Wrinkle ridges are linear to sinuous landforms on the lunar surface, and widely distributed in the lunar maria. Lunar wrinkle ridges can be hundreds of meters to many kilometers long, and up to hundreds of meters wide. Wrinkle ridges are believed to be asymmetric previously that
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most wrinkle ridges are composed of a broad low relief arch and a superimposed steep ridge
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(Sharpton and Head, 1988; Watters, 1988; Yue et al., 2015). Wrinkle ridges form in
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compressional stress conditions. After long-time controversies about their origin, it is now widely accepted that wrinkle ridges express folded basalt layers overlying thrust faults (Plescia
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and Golombek, 1986; Golombek et al., 1991; Schultz, 2000; Ono et al., 2009; Watters and
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Johnson, 2010).
Recently, lunar wrinkle ridges were globally mapped based on the high resolution images
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from Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) (~100 m/pixel)
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and Narrow Angle Camera (NAC) (~0.5-2 m/pixel) (Robinson et al., 2010), and much more ridges were identified in maria and highlands compared with previous catalog (Wu et al., 2016).
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Through detailed global investigation using LROC NAC data, Wu et al. (2018) classified them
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into three types based on their scales and morphologies: Short, wide and low Type 1, stripe-like Type 2, and braided, winding Type 3. The morphology of these three types of ridges was
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proposed to be the same essentially, i.e., bread twist, and different types only represent different stages of activity of ridges: The large concentric ridges distributed at the periphery of the Imbrium basin stopped the activity earlier, while small ridges, mostly located inside Imbrium basin, stopped the activity later. They also suggest that the old large concentric ridges are actually developed from the bread twist ridge. Lunar wrinkle ridges were considered to be rather old, formed close to emplacement of
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ACCEPTED MANUSCRIPT mare plains (Fagin et al., 1978; Solomon and Head, 1980). A global survey of lunar wrinkle ridge formation times showed that wrinkle ridges formed within 100-650 Ma after mare deposits (Yue et al., 2017). Based on the crosscutting relations with the basalt unit, ejecta blanket, or landslide material, lunar wrinkle ridges were interpreted to be still forming within the past 1.2 Ga (Watters
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and Johnson, 2010), 800 Ma (Xiao et al., 2017), or 100 Ma (Fagin et al., 1978). Recent studies
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have revealed many young wrinkle ridges identified in LROC NAC images (Xiao et al., 2014;
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Zhao et al., 2014; Williams et al., 2016; Clark et al., 2017; Wu et al., 2016; 2018). The crisp morphology and crosscutting relations with fresh craters indicate that wrinkle ridges may be still
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forming within the past 50 Ma (Wu et al., 2018), and suggest that the Moon’s tectonic activity
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probably continues until today (Watters et al., 2012; 2015). This paper aims to better estimate the formation times of these young wrinkle ridges (Fig. 1). They represent very recent tectonic
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activity, and thus are important in understanding the Moon’s late evolution. Here we show the
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distribution, morphologies and formation times of young wrinkle ridges inside Mare Imbrium,
2. Data and method
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and further discuss their possible formation mechanism.
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The low-Sun illumination LROC WAC mosaic (~100 m/pixel), with an incidence angle range of 69o-84o (Wagner et al., 2015), combined with the SLDEM2015 digital elevation model
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(DEM) (~60 m/pixel) (Barker et al., 2016), which was generated by combining Lunar Orbiter Laser Altimeter (LOLA) data and Selenological and Engineering Explorer (SELENE/Kaguya) terrain data, were applied to show the topography and geomorphology of the study area. Images from LROC NAC were calibrated and projected using Integrated Software for Imagers and Spectrometers (ISIS), and were used to detect the distribution of those small young ridges. The young ridges were then mapped with polylines on Kaguya Terrain Camera mosaic (~7.4 m/pixel)
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ACCEPTED MANUSCRIPT (Haruyama et al., 2008) (Fig. 1B). The NAC digital terrain model (DTM) (~5 m/pixel) in the Chang’E-3 (CE-3) landing site, available at the LROC website (http://wms.lroc.asu.edu/), was used to produce profiles for the young ridges. All the images were imported into ArcGIS for subsequent analysis.
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The buffered crater counting method has been applied in several scenarios where the
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conventional counting of superposed craters to date an area is not possible: such as for wrinkle
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ridges (Yue et al., 2017), lobate scarps (Clark et al., 2017; van der Bogert et al., 2018), graben systems (Kneissl et al., 2015), and valleys (Fassett and Head, 2008). Using this method, we need
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to count only craters which unambiguously superpose the ridges, and this can be determined
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unambiguously only where the craters cut steep scarps of the ridge (Yue et al., 2017). However, young wrinkle ridges in this study show no steep scarps (see section 3.1 below). It is difficult to
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tell whether the craters we can see formed before or after the wrinkle ridge, which means no
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timing information is available from crater counting. There are, however, many craters crosscut by young wrinkle ridges in the study area, and the ages of small fresh craters crosscut by the
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ridges could be used to estimate the maximum ages of the ridges.
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The exposure age of ejecta boulders is thought to correspond to the formation age of the crater. Being exposed to the lunar surface environment, boulders are gradually eroded by
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processes, such as the impact of meteoroids or diurnal thermal stresses, and thus degrade with time (Gault and Wedekind, 1969; Rogers and Shoemaker, 1971). Basilevsky et al. (2013) analyzed the boulder abundance at the rims of 12 small (< 1 km) craters with known ages, and concluded that the boulder abundance decreased with exposure time. Li et al. (2018) continued this work and found a quantitative correlation between the ejecta boulder density and crater formation age for mare craters and highland craters separately, and successfully applied this
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ACCEPTED MANUSCRIPT correlation to derive the age of Zi Wei crater. In this study, we used this method to estimate the ages of craters crosscut by the young wrinkle ridges. In order to derive the age of young ridges, four small and fresh-looking craters (named crater A, B, C, D, respectively) crosscut by the young wrinkle ridges were selected to study the
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ejecta boulder abundance and crater ages. The details of these four craters are listed in Table 1.
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For each crater, several LROC NAC images were chosen according to the criteria described in Li
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et al. (2018). One was selected as the base image for the boulder counting while the other images were used to help to identify and check the boulders. The details of selected images for the
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boulder counting are listed in Table 2. A one-crater-radius wide concentric annulus from the
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crater rim was determined as the counting area for every crater. Due to the relatively poor resolution of LROC NAC images used in this study, only the boulders with size larger than 4 m
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can be identified and mapped in the counting area. Boulders are mapped with rectangles
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according to the method from Krishna and Kumar (2016). The diameter of each boulder is defined as the geometric mean of the long and short axis of the digitized rectangle. The densities
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can be derived from the boulder size and frequency distribution, which are then used to derive
3. Results
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the ages of the craters according to the density to time calibration equation from Li et al. (2018).
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3.1. Location and morphology The landing site of CE-3 (44.1281oN, 19.5110oW) is between two large N-S wrinkle ridges in Mare Imbrium (Fig. 2). The LROC NAC image shows that a small wrinkle ridge, which is several hundred meters long, passes close to the CE-3 landing site (Fig. 3) (Xiao et al., 2014; Wu et al., 2016; 2018). A thorough investigation of young wrinkle ridges was then performed in Mare Imbrium, and Fig. 2C shows the map of them. Some of the young ridges are located to the
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ACCEPTED MANUSCRIPT north of the CE-3 landing site, and display a NS orientation in general, while the others are next to the Eratosthenian lava flow fronts, and mainly show NW-SE orientations. Note that at small scales young ridges can have various directions (Wu et al., 2018) (Fig. 1). They were distributed both on the young Eratosthenian basalts and mainly the old Imbrian basalts (Fig. 2C).
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The young wrinkle ridges are a few hundred meters to tens of kilometers long and usually
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less than 300 m wide. They are sinuous, with a bend every few hundred meters (Fig. 4). The
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bend angles are large, sometimes more than 90o. Several profiles across young wrinkle ridges were made on some flat regions (Fig. 5A), which indicate that these young ridges are dozens of
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meters high, and are arched or domed in some parts (Fig. 4C, 5A), but show no steep ridges or
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scarps. 3.2.Time of formation
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Fig. 6 shows the counting area for each of the study craters and the identified boulders
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within them. The size distributions of boulders are presented in the form of cumulative size-frequency plots with power-law fits and power index (Fig. 7). In general, the cumulative
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number decreases with increasing boulder size. In the diameter range of 4-6 m, the cumulative
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number and the boulder size generally show a linear relationship in log-log form. When the diameter is larger than 6 m, the cumulative number begins to fall off more steeply. In order to use
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the density to time calibration equation from Li et al. (2018), the cumulative boulder density at a size of 3 m should be determined. The data in the range of 4-6 m were fitted with the linear least square method in the log-log coordinates, and the boulder densities at a size of 3 m were derived based on the slope value and intercept value of the linear fitting curve (Fig. 7), which are 4634/km2, 2250/km2, 1403/km2, and 4125/km2 for the four craters respectively. According to the equation in Li et al. (2018), the ages of the four craters are estimated to be - .
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. - .
Ma,
ACCEPTED MANUSCRIPT .
-
. .
Ma,
.
-
. .
Ma, and - .
.
Ma (Fig. 8).
- .
4. Discussion 4.1. The uncertainty of the crater ages The boulder densities of craters A and D are higher than any of those used by Li et al. (2018)
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to construct the calibration function, which leads to ages less than zero. However, Basilevsky et al. (2013; 2015) suggested that higher boulder densities correspond to younger ages, indicating
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that our craters are very young. As the relation from Li et al. (2018) was based on a limited
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number of observations, we may not be surprised that some revision of its form could be needed. In order to get the ages of craters A and D, we tried the
2, and
1 (66.7%) for them.
1 of being in the positive range (Fig. 7). The
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In the Li et al. (2018) model, the ages are within
3,
and D are younger than
.
. - .
.
. - .
Ma,
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and the corresponding ages are
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lower confidence limit of boulder densities at 3 m of these two craters are 3442/km2, 3056/km2,
Ma or
.
.
.
. - .
Ma (Fig. 8), which means that craters A
Ma with a confidence of 66.7%, and the young
- .
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ridges are even younger than 3.2 Ma according to the crosscut relationship. In addition to the
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lobate scarp and graben (Watters et al., 2012), the wrinkle ridge is also one of the youngest structures on the lunar surface.
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The Basilevsky et al. (2013) study, which covers several more craters than the Li et al. (2018) study, albeit with an acknowledged lesser precision in boulder density measurements, strongly suggests an exponential decay behavior in the boulder degradation with a half-life of around 25 Ma (their Fig. 5). If we reconsider the Li et al. (2018) calibration points with this in mind, instead of a linear modelling function representing a constant loss rate, it could have been appropriate to use an exponential function. Such fitted functions are shown in Fig. 9, using the same calibration points as Li et al. (2018), and are expressed in the form 8
-
. As the
ACCEPTED MANUSCRIPT half-life (25 Ma in this study), is 2.77×10-2 Ma-1, and
, relates to the decay rate, , in the following way:
is 829 km-2 for highland and 6530 km-2 for mare craters according to .
the fitting. Such a model yields instead, -
. .
-
. .
Ma,
.
-
. .
Ma,
.
. - .
Ma, and
Ma for craters A, B, C, and D respectively. Errors come from the upper and lower
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.
,
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limits of our cumulative boulder density line fits at 3 m. In either model, some of the features are
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shown to be well under 100 Ma old, and likely in the region of 10 to several 10s of Ma. 4.2. Possible formation mechanism of young wrinkle ridges
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The young ridges inside Mare Imbrium are usually less than 300 m wide, and have a very
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low relief. To generate such folds by thrusting, the thrust was supposed to be a horizontal thrust that flattens into a décollement as indicated by the elastic dislocation modeling in Watters (2004)
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(their Fig. 6 and 8). Possible terrestrial analogs to planetary wrinkle ridges could be found in
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several places on the Earth (Plescia and Golombek, 1986; Watters, 1988; Golombek et al., 1991). The formation of the anticlines in the northern Franklin Mountains, for example, was explained
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as the result of listric thrust faults that flatten into a shallow décollement (Aitkin et al., 1982,
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MAP 1453A; Price, 1986; MacLean and Cook, 1999). The décollement depth (d) could be roughly calculated based on the area-conservation principle (Bulnes and Poblet, 1999), and it
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equals the uplifted area (S) divided by the shortening (l): d = S / l, where S represents the ridge across area, and l equals the curvilinear profile length minus profile horizontal distance (Fig. 1 in Bulnes and Poblet, 1999). The ridge across area and the curvilinear profile length were obtained from the profiles using AutoCAD (Fig. 5A), and the derived depths to décollement are 610 m, 1100 m, 1320 m, 800 m, and 2240 m, respectively, which is quite consistent with the proposal in Watters (2004) that the décollement depth corresponding to small-scale wrinkle ridges may be shallower than that of large-scale wrinkle ridges. Such a shallow décollement suggests that the 9
ACCEPTED MANUSCRIPT thrust faults of the young ridges are shallow-rooted, supporting the thin-skinned deformation model (Watters, 2004). The deformation in the décollement could be associated with the global compression due to the contraction of the Moon, the regional compressional stress that caused by the subsidence of volcanic plains, or the gravitational sliding (Mangold et al., 1998). When
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slumping happened, the dominant orientations of the wrinkle ridges should be orthogonal to the
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slope. Although there seems to be a correlation between the young ridges and the topography
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(Fig. 2D and E), it is self-correlated, i.e., they were distributed on the large ridges (Fig. 5B), which was the process of the development of the wrinkle ridges: Large wrinkle ridges are
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actually developed from small ones (Wu et al., 2018). Besides, there are still many young ridges
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formed at flat regions or even the bottom of craters (e.g., the young ridges around the CE-3 landing site) (Wu et al., 2018) (Fig. 4). All these evidences indicate that the global/regional
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compressional stress should be the dominant stress. Recent studies showed that the global
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distribution of lobate scarps and their low relief and small amount of horizontal shortening suggested a global low-level compressional stress in the upper lunar crust and lithosphere due to
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a small amount of radial contraction of the Moon (Watters et al., 2010; Banks et al., 2012). The
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global compression was considered to be able to initiate shallow-rooted thrust faults on the Moon (Watters et al., 2010; Banks et al., 2012), and thus was widely interpreted to be the main source
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of stress for young tectonism (Williams et al., 2016; Clark et al., 2017). However, young wrinkle ridges in Mare Imbrium are not evenly distributed but concentrated in the inner region of the basin. It seems that global compression is not the only source of stress, and local compressional stress should also be considered. The inside area of Imbrium is located within the Procellarum KREEP Terrane (PKT), which is thought to contain more heat-producing elements. The prolonged cooling of the inner region of Imbrium may produce the regional horizontal
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ACCEPTED MANUSCRIPT compressional stress as suggested by Daket et al. (2016). The real stress to generate these young ridges may be a combination of these global and regional stress caused by various geological processes, and much more evidence is needed to figure it out. For example, if such young ridges were also found in Oceanus Procellarum, another major area in PKT, the supposition of
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prolonged cooling would appear reasonable.
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The shallow décollement also suggests that the sinuous morphology of young wrinkle
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ridges may be associated with the inhomogeneity of the deformed material brought about by impact fracturing of the near-surface. With time more and more impact craters were formed and
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their formation caused small and large near-surface areas of mechanical weakness. When later
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compressional stress arises and deformation leads to thrust faulting, these places of local mechanical weakness are the places where the deformation changes its direction causing the
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sinuous ridge path.
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5. Conclusions
Recently, many young wrinkle ridges were discovered in the inner region of Mare Imbrium
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based on the high resolution LROC NAC images. This study carried out a further research on
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these young ridges, and they were identified and mapped. They show strongly winding morphology, which may be associated with the inhomogeneity of the deformed material through
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impact fracturing. The ages of four small craters crosscut by the young wrinkle ridges were estimated to be < .
. - .
Ma,
.
-
. .
Ma,
.
-
. .
linear calibration function from Li et al. (2018), or and
.
-
. .
Ma, and < .
-
. .
Ma,
.
. - .
.
-
Ma according to the . .
Ma,
.
. - .
Ma,
Ma with the alternative exponential calibration function given in this study. We
interpret these to indicate that the young ridges are possibly as young as 10 or a few 10s of Ma, making them among the youngest structures ever discovered on the Moon. The young ridges 11
ACCEPTED MANUSCRIPT were concentrated in the inner region of Imbrium basin, indicating that the global compression due to the contraction of the Moon is not the only source of stress, and regional compressional stress should also be considered as a possible source. Acknowledgments
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We thank A. Yin, M.E. Banks and an anonymous reviewer for helpful comments and
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suggestions that greatly improved the manuscript. This research was supported by the Key
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Research Program of the Chinese Academy of Sciences, grant XDPB11, the Strategic Priority Research Program on Space Science, the Chinese Academy of Sciences, grant XDA15020302,
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and Minor Planet Foundation of Purple Mountain Observatory. GM was supported by the
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German Space Agency (DLR Bonn), grant 50QM1702 (HRSC on Mars Express) and by the German Research Foundation (DFG) SFB TRR-170 A4. ATB was partly supported by the
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Russian Science Foundation grant 17-17-01149.
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References Aitkin, J.D., Cook, D.G., Yorath, C.J., 1982. Upper Ramparts River (106G) and Sans Sault Rapids (106H) map areas, District of Mackenzie. Geol. Sur. Canada, Mem. 388, 1-48.
T
Banks, M., Watters, T., Robinson, M., Tornabene, L., Tran, T., Ojha, L., Williams, N., 2012.
Orbiter.
J.
Geophys.
Res.
1029/2011JE003907.
Planets
CR
Reconnaissance
IP
Morphometric analysis of small‐ scale lobate scarps on the Moon using data from the Lunar 117,
E00H11.
doi:10.
US
Barker, M.K., Mazarico, E., Neumann, G.A., Zuber, M., Haruyama, J., Smith, D., 2016. A new
AN
lunar digital elevation model from the Lunar Orbiter Laser Altimeter and SELENE terrain camera. Icarus 273, 346-355. doi:10.1016/j.icarus.2015.07.039.
M
Basilevsky, A.T., Head, J.W., Horz, F., 2013. Survival times of meter-sized boulders on the
ED
surface of the Moon. Planet. Space Sci. 89, 118-126. doi: 10.1016/j.pss.2013.07.011. Basilevsky, A.T., Head, J.W., Horz, F., Ramsley, K., 2015. Survival times of meter-sized rock
PT
boulders on the surface of airless bodies. Planet. Space Sci. 117, 312-328.
CE
doi:10.1016/j.pss.2015.07.003.
Bulnes, M., Poblet, J., 1999. Estimating the detachment depth in cross sections involving
AC
detachment folds. Geological Magazine 136, 395-412. Clark, J., van der Bogert, C., Hiesinger, H., Bernhardt, H., 2017. Wrinkle ridge-lobate scarp transition of west Serenitatis: Indications for recent tectonic activity. 48th Lunar Planet. Sci. Conf. Abstract #1001. Daket, Y., Yamaji, A., Sato, K., Haruyama, J., Morota, T., Ohtake, M., Matsunaga, T., 2016. Tectonic evolution of northwestern Imbrium of the Moon that lasted in the Copernican
13
ACCEPTED MANUSCRIPT period. Earth Planets Space 68, 157. doi:10.1186/s40623-016-0531-0. Fagin, S.W., Worrall, D.M., Muehlberger, W.R., 1978. Lunar mare ridge orientations: implications for lunar tectonic models. In 9th Proc. Lunar Planet. Sci. Conf. pp. 3473-3479. Fassett, C.I., Head, J.W., 2008. The timing of martian valley network activity: Constraints from
T
buffered crater counting. Icarus 195, 61-89. doi:10.1016/j.icarus.2007.12.009.
IP
Gault, D.E., Wedekind, J.A., 1969. The destruction of tektites by micrometeoroid impact. J.
CR
Geophys. Res. 74, 6780-6794. doi:10.1029/JB074i027p06780.
Golombek, M.P., Plescia, J.B., Franklin, B.J., 1991. Faulting and folding in the formation of
US
wrinkle ridges. In 21th Proc. Lunar Planet. Sci. Conf. pp. 679-693.
AN
Haruyama, J., Matsunaga, T., Ohtake, M., Morota, T., Honda, C., Yokota, Y., Torii, M., Ogawa, Y., LISM working group., 2008. Global lunar-surface mapping experiment using the Lunar on
SELENE.
Earth
M
Imager/Spectrometer
Space
60,
243-256.
doi:
ED
10.1186/bf03352788.
Planet.
Kneissl, T., Michael, G.G., Platz, T., Walter, S.H.G., 2015. Age determination of linear surface
Fossae
graben
systems
on
Mars.
Icarus
250,
384-394.
doi:
CE
Fortuna
PT
features using the Buffered Crater Counting approach – Case studies of the Sirenum and
10.1016/j.icarus.2014.12.008.
AC
Krishna, N., Kumar, P.S., 2016. Impact spallation processes on the Moon: A case study from the size and shape analysis of ejecta boulders and secondary craters of Censorinus crater. Icarus 264, 274-299. doi:10.1016/j.icarus.2015.09.033. Li, Y., Basilevsky, A.T., Xie, M.G., Ip, W.-H., 2018. Correlations between ejecta boulder spatial density of small lunar craters and the crater age. Planet. Space Sci. 162, 52-61. doi:10.1016/j.pss.2017.08.007.
14
ACCEPTED MANUSCRIPT MacLean, B.C., Cook, D.G., 1999. Salt tectonism in the Fort Norman area, Northwest Territories, Canada. Bull. Can. Petrol. Geol. 47, 104-135. Mangold, N., Allemand, P., Thomas, P.G., 1998. Wrinkle ridges of Mars: Structural analysis and evidence for shallow deformation controlled by ice-rich décollements. Planet. Space. Sci.
T
46, 345-356. doi:10.1016/S0032-0633(97)00195-5.
IP
Ono, T., Kumamoto, A., Nakagawa, H., Yamaguchi, Y., Oshigami, S., Yamaji, A., Kobayashi, T.,
CR
Kasahara, Y., Oya, H., 2009. Lunar radar sounder observations of subsurface layers under the nearside maria of the Moon. Science 323, 909-912. doi:10.1126/science.1165988.
analogs.
Geol.
Soc.
Am.
Bull.
97,
1289-1299.
AN
terrestrial
US
Plescia, J.B., Golombek, M.P., 1986. Origin of planetary wrinkle ridges based on the study of
doi:10.1130/0016-7606(1986)97<1289:OOPWRB>2.0.CO;2.
of
the
lithosphere.
J.
Struct.
Geol.
8,
239-254.
doi:
ED
delamination
M
Price, R.A., 1986. The southeastern Canadian Cordillera: thrust faulting, tectonic wedging, and
10.1016/0191-8141(86)90046-5.
PT
Robinson, M.S., Brylow, S.M., Tschimmel, M., Humm, D., Lawrence, S.J., Thomas, P.C.,
CE
Denevi, B.W., Bowman-Cisneros, E., Zerr, J., Ravine, M.A., Caplinger, M.A., Ghaemi, F.T., Schaffner, J.A., Malin, M.C., Mahanti, P., Bartels, A., Anderson, J., Tran, T.N., Eliason,
AC
E.M., McEwen, A.S., Turtle, E., Jolliff, B.L., Hiesinger, H., 2010. Lunar Reconnaissance Orbiter Camera (LROC) Instrument Overview. Space Sci. Rev. 150, 81-124. doi:10.1007/s11214-010-9634-2. Rogers, E.M., Shoemaker, F.F., 1971. Communication of Innovations; A Cross-Cultural Approach. Schultz, R.A. 2000. Localization of bedding-plane slip and backthrust faults above blind thrust
15
ACCEPTED MANUSCRIPT faults: Keys to wrinkle ridge structure. J. Geophys. Res. 105, 12035-12052. doi:10.1029/1999JE001212. Sharpton, V.L., Head, J.W., 1988. Lunar mare ridges-Analysis of ridge-crater intersections and implications for the tectonic origin of mare ridges. In 19th Proc. Lunar Planet. Sci. Conf. pp.
T
307-317.
IP
Solomon, S.C., Head, J.W., 1980. Lunar mascon basins: Lava filling, tectonics, and evolution of
CR
the lithosphere. Rev. Geophys. 18, 107-141. doi:10.1029/RG018i001p00107. van der Bogert, C.H., Clark, J.D., Hiesinger, H., Banks, M.E., Watters, T.R., Robinson, M.S.,
US
2018. How old are lunar lobate scarps? 1. Seismic resetting of crater size-frequency
AN
distributions. Icarus 306, 225-242. doi:10.1016/j.icarus.2018.01.019. Wagner, R.V., Speyerer, E.J., Robinson, M.S., Team, L., 2015. New mosaicked data products
M
from the LROC team. 44th Lunar Planet. Sci. Conf. Abstract # 1473.
ED
Watkins, J.A., Ehlmann, B.L., Yin, A., 2015. Long-runout landslides and the long-lasting effects of early water activity on Mars. Geology 43, 107-110. doi:10.1130/G36215.1
PT
Watters, T.R., 1988. Wrinkle ridges assemblages on the terrestrial planets. J. Geophys. Res. 93,
CE
10236-10254. doi:10.1029/JB093iB09p10236. Watters, T.R., 2004. Elastic dislocation modeling of wrinkle ridges on Mars. Icarus 171, 284-294.
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doi:10.1016/j.icarus.2004.05.024. Watters, T.R., Johnson, C., 2010. Lunar tectonics. In: Watters, T.R., Schultz, R.A. (Eds.), Planetary tectonics. Cambridge University Press, New York, pp. 121-182. Watters, T.R., Robinson, M.S., Banks, M.E., Tran, T., Denevi, B.W., 2012. Recent extensional tectonics on the Moon revealed by the Lunar Reconnaissance Orbiter Camera. Nat. Geosci. 5, 181-185. doi:10.1038/ngeo1387.
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ACCEPTED MANUSCRIPT Watters, T.R., Robinson, M.S., Beyer, R.A., Banks, M.E., Bell, J.F., 3rd, Pritchard, M.E., Hiesinger, H., van der Bogert, C.H., Thomas, P.C., Turtle, E.P., Williams, N.R., 2010. Evidence of recent thrust faulting on the Moon revealed by the Lunar Reconnaissance Orbiter Camera. Science 329, 936-940. doi:10.1126/science.1189590.
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Watters, T.R., Robinson, M.S., Collins, G.C., Banks, M.E., Daud, K., Williams, N.R., Selvans,
IP
M.M., 2015. Global thrust faulting on the Moon and the influence of tidal stresses. Geology
CR
43, 851-854. doi:10.1130/G37120.1.
Williams, N., Bell, J., Shirzaei, M., Watters, T., Banks, M., Daud, K., French, R., 2016. Evidence
US
for active tectonism at the lunar surface. 47th Lunar Planet. Sci. Conf. Abstract #2808.
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Wu, Y.Z., Li, L., Luo, X.X., Lu, Y., Chen, Y., Pieters, C.M., Basilevsky, A.T., Head, J.W., 2018.
doi:10.1016/j.icarus.2017.12.029.
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Geology, tectonism and composition of the northwest Imbrium region. Icarus 303, 67-90.
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Wu, Y.Z., Tang, X., Zhang, X.M., Chen, Y., Cai, W., 2016. An unusual geology of Mare Imbrium and implication to the global evolution. 47th Lunar Planet. Sci. Conf. Abstract #1406.
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Xiao, Z., Huang, Q., Zeng, Z., Xiao, L., 2017. Small graben in the southeastern ejecta blanket of
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the lunar Copernicus crater: Implications for recent shallow igneous intrusion on the Moon. Icarus 298, 89-97. doi:10.1016/j.icarus.2017.02.014.
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Xiao, Z., Zeng, Z., Fa, W., Li, Z., Xiao, L., Li, H., 2014. Wrinkle ridges at the landing site of Chang'E-3: Potential targets to reveal the nature of thrust faults on the Moon. 45th Lunar Planet. Sci. Conf. Abstract #1719. Yue, Z., Li, W., Di, K., Liu, Z., Liu, J., 2015. Global mapping and analysis of lunar wrinkle ridges. J. Geophys. Res. Planets 120, 978-994. doi:10.1002/2014JE004777. Yue, Z., Michael, G., Di, K., Liu, J., 2017. Global survey of lunar wrinkle ridge formation times.
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ACCEPTED MANUSCRIPT Earth Planet. Sci. Lett. 477, 14-20. doi:10.1016/j.epsl.2017.07.048. Zhao, J.N., Huang, J., Qiao, L., Xiao, Z.Y., Huang, Q., Wang, J., He, Q., and Xiao, L., 2014. Geologic characteristics of the Chang’E-3 exploration region. Sci. China-Phys. Mech.
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Astron. 57, 569-576. doi:10.1007/s11433-014-5399-z.
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Tables and Figures: Table 1. The parameters of the craters studied in this work, including location and size. Location (Lat., Lon.)
Size
A
38.76° N, 14.19° W
186 m
B
38.34° N, 13.99° W
C
39.14° N, 14.46° W
D
38.93° N, 14.32° W
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Name
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CE
PT
ED
M
AN
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CR
IP
215 m
19
305 m 227 m
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Table 2. The parameters of the LROC NAC images used in this study.
Image ID
Pixel scale (m/pixel)
Local solar time (24-hour clock)
Incidence angle (degree)
A
M1195501480RE
1.29
11.06
40.76
M1236712255LE
1.27
14.63
M1149609994RE
1.45
11.16
M1208474485RE
1.29
12.93
39.93
M1236712255RE
1.27
14.65
51.41
M1103651966LE
1.15
M1149609994LE
1.45
M1195501480LE
1.29
M1167255092LE
1.39
M1129574084RE M1219040214RE M1208474485LE
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M1208474485LE M1147254408LE
IP
CR
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39.21
11.08
40.71
/
52.93
1.47
14.83
56.28
1.26
16.26
71.41
1.29
12.91
39.86
1.29
11.06
40.76
1.29
12.91
39.86
1.44
13.03
40.53
AN
11.18
PT
M1195501480RE
41.27
AC
D
39.3
11.12
M
C
51.25
ED
B
T
Name
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ACCEPTED MANUSCRIPT Highlights: 1. Many young wrinkle ridges were found inside Mare Imbrium. 2. The youngest ridges were estimated to be as young as 10 Ma.
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3. Young ridges are concentrated in the inner region of the Imbrium basin.
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Figure 1
Figure 2ac
Figure 2de
Figure 3
Figure 4
Figure 5r1
Figure 5r2
Figure 6
Figure 7
Figure 8
Figure 9
Yu Lu, Yunzhao Wu, Gregory G. Michael, Alexander T. Basilevsky, Cui Li PII: DOI: Reference:
S0019-1035(18)30452-4 https://doi.org/10.1016/j.icarus.2019.03.029 YICAR 13252
To appear in:
Icarus
Received date: Revised date: Accepted date:
13 July 2018 8 March 2019 20 March 2019
Please cite this article as: Y. Lu, Y. Wu, G.G. Michael, et al., Young wrinkle ridges in Mare Imbrium: Evidence for very recent compressional tectonism, Icarus, https://doi.org/ 10.1016/j.icarus.2019.03.029
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ACCEPTED MANUSCRIPT Young wrinkle ridges in Mare Imbrium: Evidence for very recent compressional tectonism
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Yu Lu a,b, Yunzhao Wu b,c,*, Gregory G. Michael d, Alexander T. Basilevsky e, Cui Li b,f
School of Geography and Ocean Science, Nanjing University, Nanjing, 210023, China
b
Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of
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a
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Sciences, Nanjing, 210034, China
CAS Center for Excellence in Comparative Planetology, Hefei, China
d
Institute of Geological Sciences, Freie Universitaet Berlin, Berlin, 12249, Germany
e
Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences,
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c
f
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Moscow, 119991, Russia
Jiangsu Center for Collaborative Innovation in Geographical Information Resource
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Development and Application, Nanjing, 210023, China
* Corresponding author.
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E-mail address: [email protected] (Y.Z. Wu).
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ACCEPTED MANUSCRIPT Abstract Wrinkle ridges are common landforms widely distributed in the lunar maria. Many young wrinkle ridges were found inside Mare Imbrium using Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) high-resolution images. They represent very recent
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tectonic activity on the lunar surface. Determining their formation times and morphology is
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important in understanding the Moon’s late evolution. The young ridges were mapped, and they
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have a winding and arched morphology. Based on their small scale and crisp appearance, crosscutting relations with very young small craters whose youth was concluded from spatial
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boulder densities within their ejecta blankets, these young wrinkle ridges were estimated to be as
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young as 10 or a few 10s of Ma, and may still be active today. The young ridges were mainly distributed in the inner region of Imbrium basin, which may suggest that the thermal and
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structural evolution of the inside area of Imbrium basin was protracted.
Keywords: Young wrinkle ridges, Distribution, Morphology, Age determination, Formation
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mechanism
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ACCEPTED MANUSCRIPT 1. Introduction Wrinkle ridges are linear to sinuous landforms on the lunar surface, and widely distributed in the lunar maria. Lunar wrinkle ridges can be hundreds of meters to many kilometers long, and up to hundreds of meters wide. Wrinkle ridges are believed to be asymmetric previously that
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most wrinkle ridges are composed of a broad low relief arch and a superimposed steep ridge
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(Sharpton and Head, 1988; Watters, 1988; Yue et al., 2015). Wrinkle ridges form in
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compressional stress conditions. After long-time controversies about their origin, it is now widely accepted that wrinkle ridges express folded basalt layers overlying thrust faults (Plescia
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and Golombek, 1986; Golombek et al., 1991; Schultz, 2000; Ono et al., 2009; Watters and
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Johnson, 2010).
Recently, lunar wrinkle ridges were globally mapped based on the high resolution images
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from Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) (~100 m/pixel)
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and Narrow Angle Camera (NAC) (~0.5-2 m/pixel) (Robinson et al., 2010), and much more ridges were identified in maria and highlands compared with previous catalog (Wu et al., 2016).
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Through detailed global investigation using LROC NAC data, Wu et al. (2018) classified them
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into three types based on their scales and morphologies: Short, wide and low Type 1, stripe-like Type 2, and braided, winding Type 3. The morphology of these three types of ridges was
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proposed to be the same essentially, i.e., bread twist, and different types only represent different stages of activity of ridges: The large concentric ridges distributed at the periphery of the Imbrium basin stopped the activity earlier, while small ridges, mostly located inside Imbrium basin, stopped the activity later. They also suggest that the old large concentric ridges are actually developed from the bread twist ridge. Lunar wrinkle ridges were considered to be rather old, formed close to emplacement of
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ACCEPTED MANUSCRIPT mare plains (Fagin et al., 1978; Solomon and Head, 1980). A global survey of lunar wrinkle ridge formation times showed that wrinkle ridges formed within 100-650 Ma after mare deposits (Yue et al., 2017). Based on the crosscutting relations with the basalt unit, ejecta blanket, or landslide material, lunar wrinkle ridges were interpreted to be still forming within the past 1.2 Ga (Watters
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and Johnson, 2010), 800 Ma (Xiao et al., 2017), or 100 Ma (Fagin et al., 1978). Recent studies
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have revealed many young wrinkle ridges identified in LROC NAC images (Xiao et al., 2014;
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Zhao et al., 2014; Williams et al., 2016; Clark et al., 2017; Wu et al., 2016; 2018). The crisp morphology and crosscutting relations with fresh craters indicate that wrinkle ridges may be still
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forming within the past 50 Ma (Wu et al., 2018), and suggest that the Moon’s tectonic activity
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probably continues until today (Watters et al., 2012; 2015). This paper aims to better estimate the formation times of these young wrinkle ridges (Fig. 1). They represent very recent tectonic
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activity, and thus are important in understanding the Moon’s late evolution. Here we show the
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distribution, morphologies and formation times of young wrinkle ridges inside Mare Imbrium,
2. Data and method
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and further discuss their possible formation mechanism.
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The low-Sun illumination LROC WAC mosaic (~100 m/pixel), with an incidence angle range of 69o-84o (Wagner et al., 2015), combined with the SLDEM2015 digital elevation model
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(DEM) (~60 m/pixel) (Barker et al., 2016), which was generated by combining Lunar Orbiter Laser Altimeter (LOLA) data and Selenological and Engineering Explorer (SELENE/Kaguya) terrain data, were applied to show the topography and geomorphology of the study area. Images from LROC NAC were calibrated and projected using Integrated Software for Imagers and Spectrometers (ISIS), and were used to detect the distribution of those small young ridges. The young ridges were then mapped with polylines on Kaguya Terrain Camera mosaic (~7.4 m/pixel)
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ACCEPTED MANUSCRIPT (Haruyama et al., 2008) (Fig. 1B). The NAC digital terrain model (DTM) (~5 m/pixel) in the Chang’E-3 (CE-3) landing site, available at the LROC website (http://wms.lroc.asu.edu/), was used to produce profiles for the young ridges. All the images were imported into ArcGIS for subsequent analysis.
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The buffered crater counting method has been applied in several scenarios where the
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conventional counting of superposed craters to date an area is not possible: such as for wrinkle
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ridges (Yue et al., 2017), lobate scarps (Clark et al., 2017; van der Bogert et al., 2018), graben systems (Kneissl et al., 2015), and valleys (Fassett and Head, 2008). Using this method, we need
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to count only craters which unambiguously superpose the ridges, and this can be determined
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unambiguously only where the craters cut steep scarps of the ridge (Yue et al., 2017). However, young wrinkle ridges in this study show no steep scarps (see section 3.1 below). It is difficult to
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tell whether the craters we can see formed before or after the wrinkle ridge, which means no
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timing information is available from crater counting. There are, however, many craters crosscut by young wrinkle ridges in the study area, and the ages of small fresh craters crosscut by the
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ridges could be used to estimate the maximum ages of the ridges.
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The exposure age of ejecta boulders is thought to correspond to the formation age of the crater. Being exposed to the lunar surface environment, boulders are gradually eroded by
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processes, such as the impact of meteoroids or diurnal thermal stresses, and thus degrade with time (Gault and Wedekind, 1969; Rogers and Shoemaker, 1971). Basilevsky et al. (2013) analyzed the boulder abundance at the rims of 12 small (< 1 km) craters with known ages, and concluded that the boulder abundance decreased with exposure time. Li et al. (2018) continued this work and found a quantitative correlation between the ejecta boulder density and crater formation age for mare craters and highland craters separately, and successfully applied this
5
ACCEPTED MANUSCRIPT correlation to derive the age of Zi Wei crater. In this study, we used this method to estimate the ages of craters crosscut by the young wrinkle ridges. In order to derive the age of young ridges, four small and fresh-looking craters (named crater A, B, C, D, respectively) crosscut by the young wrinkle ridges were selected to study the
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ejecta boulder abundance and crater ages. The details of these four craters are listed in Table 1.
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For each crater, several LROC NAC images were chosen according to the criteria described in Li
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et al. (2018). One was selected as the base image for the boulder counting while the other images were used to help to identify and check the boulders. The details of selected images for the
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boulder counting are listed in Table 2. A one-crater-radius wide concentric annulus from the
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crater rim was determined as the counting area for every crater. Due to the relatively poor resolution of LROC NAC images used in this study, only the boulders with size larger than 4 m
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can be identified and mapped in the counting area. Boulders are mapped with rectangles
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according to the method from Krishna and Kumar (2016). The diameter of each boulder is defined as the geometric mean of the long and short axis of the digitized rectangle. The densities
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can be derived from the boulder size and frequency distribution, which are then used to derive
3. Results
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the ages of the craters according to the density to time calibration equation from Li et al. (2018).
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3.1. Location and morphology The landing site of CE-3 (44.1281oN, 19.5110oW) is between two large N-S wrinkle ridges in Mare Imbrium (Fig. 2). The LROC NAC image shows that a small wrinkle ridge, which is several hundred meters long, passes close to the CE-3 landing site (Fig. 3) (Xiao et al., 2014; Wu et al., 2016; 2018). A thorough investigation of young wrinkle ridges was then performed in Mare Imbrium, and Fig. 2C shows the map of them. Some of the young ridges are located to the
6
ACCEPTED MANUSCRIPT north of the CE-3 landing site, and display a NS orientation in general, while the others are next to the Eratosthenian lava flow fronts, and mainly show NW-SE orientations. Note that at small scales young ridges can have various directions (Wu et al., 2018) (Fig. 1). They were distributed both on the young Eratosthenian basalts and mainly the old Imbrian basalts (Fig. 2C).
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The young wrinkle ridges are a few hundred meters to tens of kilometers long and usually
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less than 300 m wide. They are sinuous, with a bend every few hundred meters (Fig. 4). The
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bend angles are large, sometimes more than 90o. Several profiles across young wrinkle ridges were made on some flat regions (Fig. 5A), which indicate that these young ridges are dozens of
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meters high, and are arched or domed in some parts (Fig. 4C, 5A), but show no steep ridges or
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scarps. 3.2.Time of formation
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Fig. 6 shows the counting area for each of the study craters and the identified boulders
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within them. The size distributions of boulders are presented in the form of cumulative size-frequency plots with power-law fits and power index (Fig. 7). In general, the cumulative
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number decreases with increasing boulder size. In the diameter range of 4-6 m, the cumulative
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number and the boulder size generally show a linear relationship in log-log form. When the diameter is larger than 6 m, the cumulative number begins to fall off more steeply. In order to use
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the density to time calibration equation from Li et al. (2018), the cumulative boulder density at a size of 3 m should be determined. The data in the range of 4-6 m were fitted with the linear least square method in the log-log coordinates, and the boulder densities at a size of 3 m were derived based on the slope value and intercept value of the linear fitting curve (Fig. 7), which are 4634/km2, 2250/km2, 1403/km2, and 4125/km2 for the four craters respectively. According to the equation in Li et al. (2018), the ages of the four craters are estimated to be - .
7
. - .
Ma,
ACCEPTED MANUSCRIPT .
-
. .
Ma,
.
-
. .
Ma, and - .
.
Ma (Fig. 8).
- .
4. Discussion 4.1. The uncertainty of the crater ages The boulder densities of craters A and D are higher than any of those used by Li et al. (2018)
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to construct the calibration function, which leads to ages less than zero. However, Basilevsky et al. (2013; 2015) suggested that higher boulder densities correspond to younger ages, indicating
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that our craters are very young. As the relation from Li et al. (2018) was based on a limited
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number of observations, we may not be surprised that some revision of its form could be needed. In order to get the ages of craters A and D, we tried the
2, and
1 (66.7%) for them.
1 of being in the positive range (Fig. 7). The
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In the Li et al. (2018) model, the ages are within
3,
and D are younger than
.
. - .
.
. - .
Ma,
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and the corresponding ages are
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lower confidence limit of boulder densities at 3 m of these two craters are 3442/km2, 3056/km2,
Ma or
.
.
.
. - .
Ma (Fig. 8), which means that craters A
Ma with a confidence of 66.7%, and the young
- .
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ridges are even younger than 3.2 Ma according to the crosscut relationship. In addition to the
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lobate scarp and graben (Watters et al., 2012), the wrinkle ridge is also one of the youngest structures on the lunar surface.
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The Basilevsky et al. (2013) study, which covers several more craters than the Li et al. (2018) study, albeit with an acknowledged lesser precision in boulder density measurements, strongly suggests an exponential decay behavior in the boulder degradation with a half-life of around 25 Ma (their Fig. 5). If we reconsider the Li et al. (2018) calibration points with this in mind, instead of a linear modelling function representing a constant loss rate, it could have been appropriate to use an exponential function. Such fitted functions are shown in Fig. 9, using the same calibration points as Li et al. (2018), and are expressed in the form 8
-
. As the
ACCEPTED MANUSCRIPT half-life (25 Ma in this study), is 2.77×10-2 Ma-1, and
, relates to the decay rate, , in the following way:
is 829 km-2 for highland and 6530 km-2 for mare craters according to .
the fitting. Such a model yields instead, -
. .
-
. .
Ma,
.
-
. .
Ma,
.
. - .
Ma, and
Ma for craters A, B, C, and D respectively. Errors come from the upper and lower
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.
,
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limits of our cumulative boulder density line fits at 3 m. In either model, some of the features are
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shown to be well under 100 Ma old, and likely in the region of 10 to several 10s of Ma. 4.2. Possible formation mechanism of young wrinkle ridges
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The young ridges inside Mare Imbrium are usually less than 300 m wide, and have a very
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low relief. To generate such folds by thrusting, the thrust was supposed to be a horizontal thrust that flattens into a décollement as indicated by the elastic dislocation modeling in Watters (2004)
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(their Fig. 6 and 8). Possible terrestrial analogs to planetary wrinkle ridges could be found in
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several places on the Earth (Plescia and Golombek, 1986; Watters, 1988; Golombek et al., 1991). The formation of the anticlines in the northern Franklin Mountains, for example, was explained
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as the result of listric thrust faults that flatten into a shallow décollement (Aitkin et al., 1982,
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MAP 1453A; Price, 1986; MacLean and Cook, 1999). The décollement depth (d) could be roughly calculated based on the area-conservation principle (Bulnes and Poblet, 1999), and it
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equals the uplifted area (S) divided by the shortening (l): d = S / l, where S represents the ridge across area, and l equals the curvilinear profile length minus profile horizontal distance (Fig. 1 in Bulnes and Poblet, 1999). The ridge across area and the curvilinear profile length were obtained from the profiles using AutoCAD (Fig. 5A), and the derived depths to décollement are 610 m, 1100 m, 1320 m, 800 m, and 2240 m, respectively, which is quite consistent with the proposal in Watters (2004) that the décollement depth corresponding to small-scale wrinkle ridges may be shallower than that of large-scale wrinkle ridges. Such a shallow décollement suggests that the 9
ACCEPTED MANUSCRIPT thrust faults of the young ridges are shallow-rooted, supporting the thin-skinned deformation model (Watters, 2004). The deformation in the décollement could be associated with the global compression due to the contraction of the Moon, the regional compressional stress that caused by the subsidence of volcanic plains, or the gravitational sliding (Mangold et al., 1998). When
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slumping happened, the dominant orientations of the wrinkle ridges should be orthogonal to the
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slope. Although there seems to be a correlation between the young ridges and the topography
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(Fig. 2D and E), it is self-correlated, i.e., they were distributed on the large ridges (Fig. 5B), which was the process of the development of the wrinkle ridges: Large wrinkle ridges are
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actually developed from small ones (Wu et al., 2018). Besides, there are still many young ridges
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formed at flat regions or even the bottom of craters (e.g., the young ridges around the CE-3 landing site) (Wu et al., 2018) (Fig. 4). All these evidences indicate that the global/regional
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compressional stress should be the dominant stress. Recent studies showed that the global
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distribution of lobate scarps and their low relief and small amount of horizontal shortening suggested a global low-level compressional stress in the upper lunar crust and lithosphere due to
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a small amount of radial contraction of the Moon (Watters et al., 2010; Banks et al., 2012). The
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global compression was considered to be able to initiate shallow-rooted thrust faults on the Moon (Watters et al., 2010; Banks et al., 2012), and thus was widely interpreted to be the main source
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of stress for young tectonism (Williams et al., 2016; Clark et al., 2017). However, young wrinkle ridges in Mare Imbrium are not evenly distributed but concentrated in the inner region of the basin. It seems that global compression is not the only source of stress, and local compressional stress should also be considered. The inside area of Imbrium is located within the Procellarum KREEP Terrane (PKT), which is thought to contain more heat-producing elements. The prolonged cooling of the inner region of Imbrium may produce the regional horizontal
10
ACCEPTED MANUSCRIPT compressional stress as suggested by Daket et al. (2016). The real stress to generate these young ridges may be a combination of these global and regional stress caused by various geological processes, and much more evidence is needed to figure it out. For example, if such young ridges were also found in Oceanus Procellarum, another major area in PKT, the supposition of
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prolonged cooling would appear reasonable.
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The shallow décollement also suggests that the sinuous morphology of young wrinkle
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ridges may be associated with the inhomogeneity of the deformed material brought about by impact fracturing of the near-surface. With time more and more impact craters were formed and
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their formation caused small and large near-surface areas of mechanical weakness. When later
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compressional stress arises and deformation leads to thrust faulting, these places of local mechanical weakness are the places where the deformation changes its direction causing the
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sinuous ridge path.
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5. Conclusions
Recently, many young wrinkle ridges were discovered in the inner region of Mare Imbrium
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based on the high resolution LROC NAC images. This study carried out a further research on
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these young ridges, and they were identified and mapped. They show strongly winding morphology, which may be associated with the inhomogeneity of the deformed material through
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impact fracturing. The ages of four small craters crosscut by the young wrinkle ridges were estimated to be < .
. - .
Ma,
.
-
. .
Ma,
.
-
. .
linear calibration function from Li et al. (2018), or and
.
-
. .
Ma, and < .
-
. .
Ma,
.
. - .
.
-
Ma according to the . .
Ma,
.
. - .
Ma,
Ma with the alternative exponential calibration function given in this study. We
interpret these to indicate that the young ridges are possibly as young as 10 or a few 10s of Ma, making them among the youngest structures ever discovered on the Moon. The young ridges 11
ACCEPTED MANUSCRIPT were concentrated in the inner region of Imbrium basin, indicating that the global compression due to the contraction of the Moon is not the only source of stress, and regional compressional stress should also be considered as a possible source. Acknowledgments
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We thank A. Yin, M.E. Banks and an anonymous reviewer for helpful comments and
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suggestions that greatly improved the manuscript. This research was supported by the Key
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Research Program of the Chinese Academy of Sciences, grant XDPB11, the Strategic Priority Research Program on Space Science, the Chinese Academy of Sciences, grant XDA15020302,
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and Minor Planet Foundation of Purple Mountain Observatory. GM was supported by the
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German Space Agency (DLR Bonn), grant 50QM1702 (HRSC on Mars Express) and by the German Research Foundation (DFG) SFB TRR-170 A4. ATB was partly supported by the
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Russian Science Foundation grant 17-17-01149.
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References Aitkin, J.D., Cook, D.G., Yorath, C.J., 1982. Upper Ramparts River (106G) and Sans Sault Rapids (106H) map areas, District of Mackenzie. Geol. Sur. Canada, Mem. 388, 1-48.
T
Banks, M., Watters, T., Robinson, M., Tornabene, L., Tran, T., Ojha, L., Williams, N., 2012.
Orbiter.
J.
Geophys.
Res.
1029/2011JE003907.
Planets
CR
Reconnaissance
IP
Morphometric analysis of small‐ scale lobate scarps on the Moon using data from the Lunar 117,
E00H11.
doi:10.
US
Barker, M.K., Mazarico, E., Neumann, G.A., Zuber, M., Haruyama, J., Smith, D., 2016. A new
AN
lunar digital elevation model from the Lunar Orbiter Laser Altimeter and SELENE terrain camera. Icarus 273, 346-355. doi:10.1016/j.icarus.2015.07.039.
M
Basilevsky, A.T., Head, J.W., Horz, F., 2013. Survival times of meter-sized boulders on the
ED
surface of the Moon. Planet. Space Sci. 89, 118-126. doi: 10.1016/j.pss.2013.07.011. Basilevsky, A.T., Head, J.W., Horz, F., Ramsley, K., 2015. Survival times of meter-sized rock
PT
boulders on the surface of airless bodies. Planet. Space Sci. 117, 312-328.
CE
doi:10.1016/j.pss.2015.07.003.
Bulnes, M., Poblet, J., 1999. Estimating the detachment depth in cross sections involving
AC
detachment folds. Geological Magazine 136, 395-412. Clark, J., van der Bogert, C., Hiesinger, H., Bernhardt, H., 2017. Wrinkle ridge-lobate scarp transition of west Serenitatis: Indications for recent tectonic activity. 48th Lunar Planet. Sci. Conf. Abstract #1001. Daket, Y., Yamaji, A., Sato, K., Haruyama, J., Morota, T., Ohtake, M., Matsunaga, T., 2016. Tectonic evolution of northwestern Imbrium of the Moon that lasted in the Copernican
13
ACCEPTED MANUSCRIPT period. Earth Planets Space 68, 157. doi:10.1186/s40623-016-0531-0. Fagin, S.W., Worrall, D.M., Muehlberger, W.R., 1978. Lunar mare ridge orientations: implications for lunar tectonic models. In 9th Proc. Lunar Planet. Sci. Conf. pp. 3473-3479. Fassett, C.I., Head, J.W., 2008. The timing of martian valley network activity: Constraints from
T
buffered crater counting. Icarus 195, 61-89. doi:10.1016/j.icarus.2007.12.009.
IP
Gault, D.E., Wedekind, J.A., 1969. The destruction of tektites by micrometeoroid impact. J.
CR
Geophys. Res. 74, 6780-6794. doi:10.1029/JB074i027p06780.
Golombek, M.P., Plescia, J.B., Franklin, B.J., 1991. Faulting and folding in the formation of
US
wrinkle ridges. In 21th Proc. Lunar Planet. Sci. Conf. pp. 679-693.
AN
Haruyama, J., Matsunaga, T., Ohtake, M., Morota, T., Honda, C., Yokota, Y., Torii, M., Ogawa, Y., LISM working group., 2008. Global lunar-surface mapping experiment using the Lunar on
SELENE.
Earth
M
Imager/Spectrometer
Space
60,
243-256.
doi:
ED
10.1186/bf03352788.
Planet.
Kneissl, T., Michael, G.G., Platz, T., Walter, S.H.G., 2015. Age determination of linear surface
Fossae
graben
systems
on
Mars.
Icarus
250,
384-394.
doi:
CE
Fortuna
PT
features using the Buffered Crater Counting approach – Case studies of the Sirenum and
10.1016/j.icarus.2014.12.008.
AC
Krishna, N., Kumar, P.S., 2016. Impact spallation processes on the Moon: A case study from the size and shape analysis of ejecta boulders and secondary craters of Censorinus crater. Icarus 264, 274-299. doi:10.1016/j.icarus.2015.09.033. Li, Y., Basilevsky, A.T., Xie, M.G., Ip, W.-H., 2018. Correlations between ejecta boulder spatial density of small lunar craters and the crater age. Planet. Space Sci. 162, 52-61. doi:10.1016/j.pss.2017.08.007.
14
ACCEPTED MANUSCRIPT MacLean, B.C., Cook, D.G., 1999. Salt tectonism in the Fort Norman area, Northwest Territories, Canada. Bull. Can. Petrol. Geol. 47, 104-135. Mangold, N., Allemand, P., Thomas, P.G., 1998. Wrinkle ridges of Mars: Structural analysis and evidence for shallow deformation controlled by ice-rich décollements. Planet. Space. Sci.
T
46, 345-356. doi:10.1016/S0032-0633(97)00195-5.
IP
Ono, T., Kumamoto, A., Nakagawa, H., Yamaguchi, Y., Oshigami, S., Yamaji, A., Kobayashi, T.,
CR
Kasahara, Y., Oya, H., 2009. Lunar radar sounder observations of subsurface layers under the nearside maria of the Moon. Science 323, 909-912. doi:10.1126/science.1165988.
analogs.
Geol.
Soc.
Am.
Bull.
97,
1289-1299.
AN
terrestrial
US
Plescia, J.B., Golombek, M.P., 1986. Origin of planetary wrinkle ridges based on the study of
doi:10.1130/0016-7606(1986)97<1289:OOPWRB>2.0.CO;2.
of
the
lithosphere.
J.
Struct.
Geol.
8,
239-254.
doi:
ED
delamination
M
Price, R.A., 1986. The southeastern Canadian Cordillera: thrust faulting, tectonic wedging, and
10.1016/0191-8141(86)90046-5.
PT
Robinson, M.S., Brylow, S.M., Tschimmel, M., Humm, D., Lawrence, S.J., Thomas, P.C.,
CE
Denevi, B.W., Bowman-Cisneros, E., Zerr, J., Ravine, M.A., Caplinger, M.A., Ghaemi, F.T., Schaffner, J.A., Malin, M.C., Mahanti, P., Bartels, A., Anderson, J., Tran, T.N., Eliason,
AC
E.M., McEwen, A.S., Turtle, E., Jolliff, B.L., Hiesinger, H., 2010. Lunar Reconnaissance Orbiter Camera (LROC) Instrument Overview. Space Sci. Rev. 150, 81-124. doi:10.1007/s11214-010-9634-2. Rogers, E.M., Shoemaker, F.F., 1971. Communication of Innovations; A Cross-Cultural Approach. Schultz, R.A. 2000. Localization of bedding-plane slip and backthrust faults above blind thrust
15
ACCEPTED MANUSCRIPT faults: Keys to wrinkle ridge structure. J. Geophys. Res. 105, 12035-12052. doi:10.1029/1999JE001212. Sharpton, V.L., Head, J.W., 1988. Lunar mare ridges-Analysis of ridge-crater intersections and implications for the tectonic origin of mare ridges. In 19th Proc. Lunar Planet. Sci. Conf. pp.
T
307-317.
IP
Solomon, S.C., Head, J.W., 1980. Lunar mascon basins: Lava filling, tectonics, and evolution of
CR
the lithosphere. Rev. Geophys. 18, 107-141. doi:10.1029/RG018i001p00107. van der Bogert, C.H., Clark, J.D., Hiesinger, H., Banks, M.E., Watters, T.R., Robinson, M.S.,
US
2018. How old are lunar lobate scarps? 1. Seismic resetting of crater size-frequency
AN
distributions. Icarus 306, 225-242. doi:10.1016/j.icarus.2018.01.019. Wagner, R.V., Speyerer, E.J., Robinson, M.S., Team, L., 2015. New mosaicked data products
M
from the LROC team. 44th Lunar Planet. Sci. Conf. Abstract # 1473.
ED
Watkins, J.A., Ehlmann, B.L., Yin, A., 2015. Long-runout landslides and the long-lasting effects of early water activity on Mars. Geology 43, 107-110. doi:10.1130/G36215.1
PT
Watters, T.R., 1988. Wrinkle ridges assemblages on the terrestrial planets. J. Geophys. Res. 93,
CE
10236-10254. doi:10.1029/JB093iB09p10236. Watters, T.R., 2004. Elastic dislocation modeling of wrinkle ridges on Mars. Icarus 171, 284-294.
AC
doi:10.1016/j.icarus.2004.05.024. Watters, T.R., Johnson, C., 2010. Lunar tectonics. In: Watters, T.R., Schultz, R.A. (Eds.), Planetary tectonics. Cambridge University Press, New York, pp. 121-182. Watters, T.R., Robinson, M.S., Banks, M.E., Tran, T., Denevi, B.W., 2012. Recent extensional tectonics on the Moon revealed by the Lunar Reconnaissance Orbiter Camera. Nat. Geosci. 5, 181-185. doi:10.1038/ngeo1387.
16
ACCEPTED MANUSCRIPT Watters, T.R., Robinson, M.S., Beyer, R.A., Banks, M.E., Bell, J.F., 3rd, Pritchard, M.E., Hiesinger, H., van der Bogert, C.H., Thomas, P.C., Turtle, E.P., Williams, N.R., 2010. Evidence of recent thrust faulting on the Moon revealed by the Lunar Reconnaissance Orbiter Camera. Science 329, 936-940. doi:10.1126/science.1189590.
T
Watters, T.R., Robinson, M.S., Collins, G.C., Banks, M.E., Daud, K., Williams, N.R., Selvans,
IP
M.M., 2015. Global thrust faulting on the Moon and the influence of tidal stresses. Geology
CR
43, 851-854. doi:10.1130/G37120.1.
Williams, N., Bell, J., Shirzaei, M., Watters, T., Banks, M., Daud, K., French, R., 2016. Evidence
US
for active tectonism at the lunar surface. 47th Lunar Planet. Sci. Conf. Abstract #2808.
AN
Wu, Y.Z., Li, L., Luo, X.X., Lu, Y., Chen, Y., Pieters, C.M., Basilevsky, A.T., Head, J.W., 2018.
doi:10.1016/j.icarus.2017.12.029.
M
Geology, tectonism and composition of the northwest Imbrium region. Icarus 303, 67-90.
ED
Wu, Y.Z., Tang, X., Zhang, X.M., Chen, Y., Cai, W., 2016. An unusual geology of Mare Imbrium and implication to the global evolution. 47th Lunar Planet. Sci. Conf. Abstract #1406.
PT
Xiao, Z., Huang, Q., Zeng, Z., Xiao, L., 2017. Small graben in the southeastern ejecta blanket of
CE
the lunar Copernicus crater: Implications for recent shallow igneous intrusion on the Moon. Icarus 298, 89-97. doi:10.1016/j.icarus.2017.02.014.
AC
Xiao, Z., Zeng, Z., Fa, W., Li, Z., Xiao, L., Li, H., 2014. Wrinkle ridges at the landing site of Chang'E-3: Potential targets to reveal the nature of thrust faults on the Moon. 45th Lunar Planet. Sci. Conf. Abstract #1719. Yue, Z., Li, W., Di, K., Liu, Z., Liu, J., 2015. Global mapping and analysis of lunar wrinkle ridges. J. Geophys. Res. Planets 120, 978-994. doi:10.1002/2014JE004777. Yue, Z., Michael, G., Di, K., Liu, J., 2017. Global survey of lunar wrinkle ridge formation times.
17
ACCEPTED MANUSCRIPT Earth Planet. Sci. Lett. 477, 14-20. doi:10.1016/j.epsl.2017.07.048. Zhao, J.N., Huang, J., Qiao, L., Xiao, Z.Y., Huang, Q., Wang, J., He, Q., and Xiao, L., 2014. Geologic characteristics of the Chang’E-3 exploration region. Sci. China-Phys. Mech.
AC
CE
PT
ED
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US
CR
IP
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Astron. 57, 569-576. doi:10.1007/s11433-014-5399-z.
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Tables and Figures: Table 1. The parameters of the craters studied in this work, including location and size. Location (Lat., Lon.)
Size
A
38.76° N, 14.19° W
186 m
B
38.34° N, 13.99° W
C
39.14° N, 14.46° W
D
38.93° N, 14.32° W
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Name
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M
AN
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215 m
19
305 m 227 m
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Table 2. The parameters of the LROC NAC images used in this study.
Image ID
Pixel scale (m/pixel)
Local solar time (24-hour clock)
Incidence angle (degree)
A
M1195501480RE
1.29
11.06
40.76
M1236712255LE
1.27
14.63
M1149609994RE
1.45
11.16
M1208474485RE
1.29
12.93
39.93
M1236712255RE
1.27
14.65
51.41
M1103651966LE
1.15
M1149609994LE
1.45
M1195501480LE
1.29
M1167255092LE
1.39
M1129574084RE M1219040214RE M1208474485LE
CE
M1208474485LE M1147254408LE
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CR
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39.21
11.08
40.71
/
52.93
1.47
14.83
56.28
1.26
16.26
71.41
1.29
12.91
39.86
1.29
11.06
40.76
1.29
12.91
39.86
1.44
13.03
40.53
AN
11.18
PT
M1195501480RE
41.27
AC
D
39.3
11.12
M
C
51.25
ED
B
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Name
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ACCEPTED MANUSCRIPT Highlights: 1. Many young wrinkle ridges were found inside Mare Imbrium. 2. The youngest ridges were estimated to be as young as 10 Ma.
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3. Young ridges are concentrated in the inner region of the Imbrium basin.
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Figure 1
Figure 2ac
Figure 2de
Figure 3
Figure 4
Figure 5r1
Figure 5r2
Figure 6
Figure 7
Figure 8
Figure 9