3. Methods
3.1. Kinematic analyses
Kinematic analyses of brittle fault planes in the field were performed, following Petit (1987) and Angelier (1994). All structural measurements are expressed as dip direction/dip angle for planar elements and plunge direction/plunge angle for linear features.
3.2. Remote sensing data interpretation
Satellite images to identify sub-vertical linear structures were analyzed. These structures were digitalized using the geographical information system (GIS). Linear features on a satellite image are commonly polygenetic planar elements (fractures, faults, strike-parallel features of resistant strata etc.). For simplification, we term such features on the satellite image as “lineaments“, although they are planar elements. The entire study area (~250 km by 50 km) was analyzed using world satellite imageries at different scales. Linear objects are interpreted as straight segments of valleys or geomorphological alignments related to brittle deformation of rock masses.
The interpretation of remote sensing data, combined with published geological maps of the study area (Béchennec et al., 1986; Villey et al., 1986a, 1986b; Le Métour et al., 1986b; Rabu et al., 1986; Wyns et al., 1992; Roger et al., 1991; Peters et al., 2001, 2005) provided the basis for a brittle deformation model of our study area. More than 10,000 lineaments have been analyzed. The length of these linear features ranges between 100 m and 20 km. The results are summarized with respective rose diagrams for different sectors and for the entire working area, using the GIS extension tool of Jenness (2014).
Comparison of the linear features with geological maps confirms displacement at several places. Remote sensing data interpretation was conducted to see whether the linear features represent geological structures. The interpretation was carried out using the GIS tools (PolarPlots v.1.0.253 of Jenness, 2014) for ArcMap (v. 10.2, Esri ®) for the analysis of satellite imageries for northeastern Oman. The imagery features provided by Esri are WV03_VNIR satellite imagery with resolution of 0.31 m, accuracy of 10.2%, and source Digital Globe.
3.3. LA-SF-ICP-MS U-Pb dating
U-Th-Pb analyses were carried out in the Earthlab at the University of the Witwatersrand. The analytical protocol is similar to Ring and Bolhar (2020) (Supplementary Material S1).
Graphic presentation and calculation of lower intercept ages on a Tera-Wasserburg diagram were carried out using the software ISOPLOT-R (Vermeesch, 2018). Uncertainties of individual and mean/regressed ages are 2 SE (standard error, absolute). Intercept ages were based on individual dates and internal errors (not propagated). Propagated errors on U/Pb ratios can be estimated to be 1.25 times the internal errors for a similar analytical setup as adopted here (Woodhead & Petrus, 2019). Depth-resolution within each analysis is enabled by using a primary carbonate standard (WC-1; Roberts et al., 2017), coupled with downhole-fractionation correction; this further allowed to identify (and exclude) regions of high common Pb, and also to separate time intervals with distinctly variable U/Pb during ablations, sometimes resulting in more than one date for each spot (Woodhead & Petrus, 2019), reflecting age heterogeneity or variable common Pb within the carbonate.
LA-ICPMS data for standards are reported in tables S2 and S3. Sixty-six analyses of Duff Brown carbonate (ID-MC-ICP-MS age: 64.04 ±0.67; 60.5 ±4.6; 66.3 ±3.9 Ma; 2 SE) produce a lower intercept age of 66.16 ±0.5 Ma (MSWD=13; n=66), in excellent agreement with published values (Hill et al., 2016). Fifty-five analyses of the Richard’s Spur speleothem provide an age of 299.96 ±2.36 Ma (MSWD=3; n=55). This age is higher than the accepted ID-TIMS age of 289.2±0.7 Ma (Woodhead et al., 2010) by 3.4 % (relative to accepted value). U-Pb ages for carbonates can be older for LA-based datasets when compared to isotope dilution (ID)-based datasets, possibly reflecting inadequate correction of common Pb in the gas blank (Woodhead & Petrus, 2019), or systematic differences in ablation behavior between carbonates types (speleothems versus micritic carbonates; Nuriel et al., 2017). One in-house standard (“Rio calcite”) provides an accurate age of 56.25 ±0.20 Ma (MSWD=4.7, n=39; C. Lana pers. Comm.). Two unknown samples yield an age of 30.08 ±0.47 and 22.31 ±2.15 Ma (Table S4). Values of MSWD (2.4 and 5.3) are comparable to, or slightly higher than, the range quoted for U-Pb LA-ICP-MS carbonate ages of 2-4 (Woodhead and Petrus, 2019). Three other samples collected from the thrust at site 7a did not produce ages due to low U concntrations and very limited dispersion (Table S5).
3.4. GPlates reconstruction
The relative motions of Arabia and India during the Cenozoic were analyzed by the software GPlates (www.gplates.org). GPlates is based on a large database, including coastlines and seafloor magnetic anomalies (Matthews et al., 2011, 2016; Müller et al., 2016). In our study, Arabia is considerd fixed while the relative translation and rotation of India was observed, allowing for estimation of changing distances between India and the eastern margin of Arabia through time.