Supporting Information (SI) for Volcanic history of the Imbrium basin: A close-up view from the lunar rover Yutu Jinhai Zhang, Wei Yang, Sen Hu, Yangting Lin, Guangyou Fang, Chunlai Li, Wenxi Peng，Sanyuan Zhu, Zhiping He, Bin Zhou, Hongyu Lin, Jianfeng Yang, Enhai Liu, Yuchen Xu, Jianyu Wang, Zhenxing Yao, Yongliao Zou, Jun Yan, Ziyuan Ouyang S1. Topographical features of the Chang’e-3 landing site .................................2 S2. APXS experimental method ........................................................................3 S3. Geochemical features of Chang’e-3 landing site.........................................8 S4. VNIS spectra decoding method....................................................................9 S5. Lunar Penetrating Radar data processing....................................................15 S6. SI References...............................................................................................29 ● Supplementary Figures S1 to S21 ● Supplementary Tables S1 to S3 1 S1. Topographical Features of the Chang’e-3 Landing Site Figure S1 shows the landing site of Chang’e-3 in the northeastern Imbrium basin. It locates on the young and high-Fe, high-Ti lava flow that overlying on the old and low-Ti basalt unit emerging about 10 km north. The young lava was dateed 2.0-2.3 Ga (1), and the old unit was dated 3.5 Ga (2). Another basalt unit, with intermediate FeO and TiO2 contents (3) or referred to as higgh-Al (4), can be recognized (Fig. S1c). However, age of this intermediate basalt unit is indistinguishable from the old low-Ti basalt. From Apollo orbital photography, Schaber (5) outlined three main lava flows extended about 1200 km, 600 km, 400 km from the venting region near the Euleer crater 700 km southwest to the landing site, and they overlie on the old low-Ti basalt unit (Fig. S1b). Chang’e-3 landed on the youngest lava flow that extended 1200 km. The landing site has abundant rocky ejecta (Fig. S2), which cover about 5.7% of the surface. Fig. S1. The geological map of Mare Imbrium, showing Chang’e-3 landed on the young high-Ti basalt unit that probably overlies on other two units. (a) The image of Mare Imbrium, taken by Chang’e-1; (b) Disstribution of three main lava flows originated from a venting area near the crater Euler, modified from (5); (c) Compositional map of basalt units, after (3); (d) Modal age map after (1), except for 3.5 Ga from (2). 2 Fig. S2. Typical landscape at the Chang’e-3 landing site, showing abundant rocky ejecta. S2. APXS Experimental Method The Active Particle-induced X-ray Spectrometer (APXS) was equipped on the robotic arm of Yutu, and it consists of a dual radioactive source of 55Fe (half-life of 2.73 year, 470 mCi) and 109Cd (half-life of 1.27 years, 45 mCi) and a Si-drift detector with an energy resolution of 135 [email protected] keV (6). The surfaces of targets were irradiated by the X-ray from decay of both 55Fe and 109Cd, and the fluorescent X-ray spectrum was counted by the Si-drift detector. The data used in this study are 2B level, which have been corrected for energy calibration, working distance, effect of temperature and dead time (6). Twelve elements, including Mg, Al, Si, Ca, Ti, K, Cr, Fe, Sr, Y, Zr and Nb, have been detected in the lunar soil at the landing site (Fig. S3). The K and K lines of Cu were from the device material, and K lines of Mn and Fe overlapped by Compton scattering peaks of the 55Fe source. Two APXS analyses of the lunar soil have been carried out, together with the measurements of the onboard basaltic working reference. All analyses have been corrected for background and peak overlapping. The compositions of the lunar soil were calculated from the net counts, calibrated with the onboard basalt reference and a set of standards that were measured in laboratory. S2.1 Measurements of the standards and working references in laboratory In order to calibrate the in-situ analyses of the lunar soil at the landing site, a total of 10 standard materials and working references have been measured in laboratory within a period from April 24, 2013 to July 2, 2014. These analyses were carried out in three 3 analysis sessions, using the onboard APXS or its duplicate (Table S1). The standards used in this study include one China National Standards basalt (GBW07105, also labeled as GSR-3 (7)), 2 Lunar Soil Simullants (CLRS-1, CLRS-2), 2 rock chips of lunar meteorites (NWA 2995, NWA 4734) and 5 terrestrial basalts (DC13-16R, NAO rock, DC13-08, 03JG-2, HBJ4-3). These standards and working references cover the compositional ranges of the lunar soil. The powder sample surfaces (60 mm in diameter) were strickled flat, and the measurements were carried out in a vacuum chamber. The working distance is about 10 mm. Each sample was counted for 30 minutes. Fig. S3. The X-ray spectra of the lunar soil and the onboard basaltic reference analyzed by APXS on the rover Yutu. Ka and Kb lines of Cu are from the device itself, and Ka lines of Mn and Fe overlapped by Compton scattering peaks of the 55Fe source. S2.2 Data processing Background of the X-ray spectra: The APXS data were processed using PyMca software (8). The continuum background was fitted using a linear function. For the dual radioactive sourrce, it is difficult to evaluate the spectral background theoretically, which is mainly contributed from elastic and inelastic peaks of the Fe and Cd sources, Compton scattering in the targets and the detector, and fluorescence of the major elements of the targeets. In order to find the smooth and best fitting background, sseveral empirical functions including none background, constant background, linear function, linear polynomial function and exponential polynomial function were applied, and the results are compared in Fig. S4. The major elements, including Al, Si, K, Ca, Ti and Cr, show nearly the same results for the different modes of background; whereas, Mg shows differences between the connstant or none background and the other background functions. 4 In order to assess the fitting of background, we plotted the net peak areas of the elements versus the recommended concentrations of the standards and working references. It is found that the data can be best fitted by the linear model of background (Fig. S5). Table S1. The information of the standards and working references. Chemical Analysis Sample Name Rock Type Form Composition session GBW07105 Basalt Powder (1) (a)(c) NAO powder Basalt Powder (2) (a) NAO rock Basalt Rock Chip (2) (a) NWA2995 Lunar Breccia Rock Chip (3) (b) NWA4734 Lunar Basalt Rock Chip (3) (b) DC13-16R Basalt Rock Chip (4) (b) DC13-16P Basalt Powder (4) (c) DC13-08 Basalt Powder (4) (c) 03JG-3 Basalt Powder (5) (c) HBJ4-3 Basalt Powder (5) (c) CLRS-1 Lunar Soil Simulant Powder (6) (c) CLRS-2 Lunar Soil Simulant Powder (7) (c) The experiments were carried out in 3 analysis sessions in ground laboratory: (a) April 24, 2013, with the onboard APXS; (b) December 20, 2013, with the duplicated APXS, and (c) July 2, 2014, with the duplicated APXS. (1) GBW07105 is a basalt of China National Standards; (2) NAO powder and NAO rock are the same basalt in different form, which was collected from Hannuoba, northeastern China, by National Astronomical Observatory (Report for CE-3 APXS scientific verification experiments, File Number: CE3-GRAS-CSSY-004-F2); (3) NWA2995 is a lunar feldspathic breccia, and NWA4734 is a lunar basalt (9); (4) DC13-08 and DC13-16 are low-Ti and high-Ti Emeishan flood basalts, respectively, collected from Dongchuan, southwestern China. DC13-16P and DC13-16R are powder and rock chip of DC13-16, respectively; (5) 03JG-3 and HBJ4-3 are Cenozoic basalts from western Liaoning, northeastern China (10); (6) CRLS-1 is China low-Ti Lunar Soil Simulant standard (Report for low-Ti basaltic lunar soil simulant standard CLRS-1); (7) CRLS-2 is the China high-Ti Lunar Soil Simulant standard (Report for high-Ti basaltic lunar soil simulant standard CLRS-2). Peak overlapping correction: After background removal, the peak area fitting was performed within the range of channel 50 and channel 1300 (corresponding to energy from 0.70 keV to 16.80 keV) with Pseudo-Viogt functions. The peak area of each element was determined from the deconvolved peak. The uncertainties of the peak areas were estimated < 1-3% for Si, K, Ca, Ti and Fe, <6% for Al, <15% for Mg, < 10% for Sr, Zr and Cr, < 30-50% for Nb and Y. Calibration of decay of the radioactive sources: Since 109Cd source (half-life of 1.27 years) decays quickly than 55Fe source (half-life of 2.73 year), the relative peak counting rates of Fe, Sr, Y, Zr and Nb to those of other elements (the X-ray energy lower 5 than K line of Fe) vary with time. Therefore, the peak area of each element was calibrated to the same intensity of the radioactive source on April 24, 2013, assuming that the low energy X-ray lines of Mg, Al, Si, K, Caa, Ti and Cr were excited only by 55Fe source. Calibration by the standards and working references: After calibration of decay of the radioactive source, the net peak areas of the elements were normalized to the internal reference element, i.e., Mg, Al, K, Ca, Ti, Fe and Cr normalized to Si, whereas Sr, Zr, Y and Nb normalized to Fe. Figure S5 plots the abundance ratios versus the peak area ratios of these elements of the standards and working references. All of the elements show linear correlations, with the regression lines through the origin of coordinates.