Virtual Structural Analysis of Jokisivu Open Pit Using ‘Structure-from-Motion’ Unmanned Aerial Vehicles (UAV) Photogrammetry: Implications for Structurally-Controlled Gold Deposits in Southwest Finland

Unmanned aerial vehicles (UAVs) are rapidly growing remote sensing platforms for capturing high-resolution images of exposed rock surfaces. We used a DJI Phantom 3 Professional (P3P) quadcopter to capture aerial images that were used to generate a high-resolution three-dimensional (3-D) model of the Jokisivu open-pit gold deposit that is located in southwestern Finland. 158 overlapping oblique and nadir images were taken and processed with Agisoft Photoscan Pro to generate textured 3-D surface models. In addition, 69 overlapping images were taken from the steep faces of the open pit. We assessed the precision of the 3-D model by deploying ground control points (GCPs) and the average errors were found minimal along X (2.0 cm), Y (1.2 cm), and Z (5.0 cm) axes. The steep faces of the open pit were used for virtual structural measurements and kinematic analyses in CloudCompare and ArcGIS to distinguish the orientation of different fracture sets and statistical categorization, respectively. Three distinct fracture sets were observed. The NW-SE and NE-SW striking fractures form a conjugate geometry, whereas the NNW-SSE striking fractures cut the conjugate fracture set. The orientation of conjugate fractures match well with the resource model of the deposit and NW- and NE-trending segments of regional-scale anastomosing shear zones. Based on the conjugate geometry of fracture sets I and II, and the regional pattern of anastomosing shear system lead us to interpret an origin of gold mineralization in two stages. An early N-S or NNW-SSE crustal shortening, corresponding to the regional D4 (ca. 1.83–1.81 Ga) or pre-D4 (ca. 1.87–1.86 Ga) Svecofennian tectonic event(s) that produced anastomosing shear zones. Subsequent E-W directed D5 contraction (ca. 1.79–1.77 Ga) partly reactivated the anastomosing shear zones with the formation of conjugate system, which controlled the migration of fluids and gold mineralization in SW Finland

Kinematics of subduction in the Ibero-Armorican arc constrained by 3D microstructural analysis of garnet and pseudomorphed lawsonite porphyroblasts from Île de Groix (Variscan belt)

The research was supported by Spanish government project CGL2016-80687-R AEI/FEDER and projects RNM148, P18-RT-3275 and B-RNM-301-UGR18 of the Andalusia Autonomous Government.The first author wishes to thank José Ramón Martínez Catalán for his guidance and friendship during a postdoc in Salamanca (1996–1999). We thank Michel Ballèvre for helping us obtain permission from the Préfecture du Morbihan to collect samples on Île de Groix and for suggesting we include the Pouldu schists in our study. Île de Groix national park guide Catherine Robert (and her dog) provided Domingo Aerden with helpful information and pleasant company during fieldwork. We thank Fátima Linares-Ordoñez for X-ray scanning our samples and Bernhardt Schulz for clarifying various aspects about the petrology of the study area. The authors are very grateful to the two anonymous reviewers, who provided constructive comments, and the handling editors of Solid Earth, Ícaro Dias da Silva and Federico Rossetti.The small island of Groix in southern Brittany, France, is well known for exceptionally well-preserved outcrops of Variscan blueschists, eclogites, and garnetiferous mica schists that mark a Late Devonian suture between Gondwana and Armorica. The kinematics of polyphase deformation in these rocks is reconstructed based on 3D microstructural analysis of inclusion trails within garnet and pseudomorphed lawsonite porphyroblasts using differently oriented thin sections and X-ray tomography. Three sets of inclusion trails striking NE-SW, NNW-SSE, and WNW-ESE are recognized and interpreted to witness a succession of different crustal shortening directions orthogonal to these strikes. The curvature sense of sigmoidal and spiral-shaped inclusion trails of the youngest set is shown to be consistent with northwest and northward subduction of Gondwana under Armorica, provided that these microstructures developed by overgrowth of actively forming crenulations without much porphyroblast rotation. Strongly non-cylindrical folds locally found on the island are reinterpreted as fold-interference structures instead of having formed by progressive shearing and fold-axis reorientation. Six samples of a lower-grade footwall unit of the Groix ophiolitic nappe (Pouldu schists) were also studied. Inclusion trails in these rocks strike E-W, similar to the youngest set recognized on Groix island. They record Carboniferous N-S shortening during continental collision. These new microstructural data from southern Brittany bear a strong resemblance to earlier measured in inclusion-trail orientations in the northwestern Iberia Massif. A best fit between both regions suggests not more than about 15 degrees anticlockwise rotation of Iberia during the Cretaceous opening of the Gulf of Biscay.Spanish Government CGL2016-80687-RAndalusia Autonomous Government RNM148 P18-RT-3275 B-RNM-301-UGR1

The 2014 Earthquake Model of the Middle East: seismogenic sources

The Earthquake Model of Middle East (EMME) project was carried out between 2010 and 2014 to provide a harmonized seismic hazard assessment without country border limitations. The result covers eleven countries: Afghanistan, Armenia, Azerbaijan, Cyprus, Georgia, Iran, Jordan, Lebanon, Pakistan, Syria and Turkey, which span one of the seismically most active regions on Earth in response to complex interactions between four major tectonic plates i.e. Africa, Arabia, India and Eurasia. Destructive earthquakes with great loss of life and property are frequent within this region, as exemplified by the recent events of Izmit (Turkey, 1999), Bam (Iran, 2003), Kashmir (Pakistan, 2005), Van (Turkey, 2011), and Hindu Kush (Afghanistan, 2015). We summarize multidisciplinary data (seismicity, geology, and tectonics) compiled and used to characterize the spatial and temporal distribution of earthquakes over the investigated region. We describe the development process of the model including the delineation of seismogenic sources and the description of methods and parameters of earthquake recurrence models, all representing the current state of knowledge and practice in seismic hazard assessment. The resulting seismogenic source model includes seismic sources defined by geological evidence and active tectonic findings correlated with measured seismicity patterns. A total of 234 area sources fully cross-border-harmonized are combined with 778 seismically active faults along with background-smoothed seismicity. Recorded seismicity (both historical and instrumental) provides the input to estimate rates of earthquakes for area sources and background seismicity while geologic slip-rates are used to characterize fault-specific earthquake recurrences. Ultimately, alternative models of intrinsic uncertainties of data, procedures and models are considered when used for calculation of the seismic hazard. At variance to previous models of the EMME region, we provide a homogeneous seismic source model representing a consistent basis for the next generation of seismic hazard models within the region.Published3465-34966T. Studi di pericolosità sismica e da maremotoJCR Journa

Correlating multiple deformation events across the Mesoproterozoic NE Australia using foliation intersection axes (FIA) preserved within porphyroblasts

Foliation Intersection/Inflection Axes within porphyroblasts (FIAs) allow the chronological and kinematic linking of deformation episodes with associated metamorphism. Measurement of FIAs in the Mesoproterozoic Eastern Fold Belt (EFB) of the Mount Isa Inlier, NE Australia, has revealed phases of deformation and metamorphism that could not previously be distinguished from one another. Both the 'asymmetry switch' and 'FitPitch' FIA measurement techniques have been applied to key localities of polymetamorphosed and multiply deformed EFB, and they yielded the same result. These independent techniques have revealed (1) E–W trending structures that formed during N–S bulk shortening (D1) and associated metamorphism (M1) formed during a period of orogenesis (O1) and N–S oriented structures that formed during E–W bulk shortening (D2) and associated metamorphism (M2) during a period of orogenesis (O2), and (2) the crustal scale tectonic processes associated with polymetamorphism. Middle to upper amphibolite facies metamorphic conditions occurred during O1 with crustal thickening followed by near-isothermal decompression leading to low-pressure/high-temperature (LP/HT) conditions with the emplacement of Williams and Naraku Batholiths around 1550 Ma. This was followed by a second period of middle-to upper-amphibolite facies metamorphism, O2. This history not only correlates better across the EFB, but also with the tectono-metamorphic model recently proposed for the Mesoproterozoic Georgetown Inlier of the north Australian Craton

Microstructural evidence for N–S shortening in the Mount Isa Inlier (NW Queensland, Australia): the preservation of early W–E-trending foliations in porphyroblasts revealed by independent 3D measurement techniques

3D microstructural analyses of porphyroblast inclusion trails using both the ‘asymmetry switch’ method for determining foliation intersection axes preserved in porphyroblasts (FIAs) and the recently developed ‘FitPitch’ method, reveal W–E- and N–S-trending FIA sets in the White Blow Formation of the Mount Isa Inlier. Each method reveals two subsets of FIAs centered on each of these major trends. These were distinguished based on the relative timing, trend, and orientation of inclusion trail patterns. Thirty-six samples were analyzed using both techniques and produced very similar results. Pitches of the inclusion trails preserved within the porphyroblasts in vertically oriented thin-sections and trends in horizontal sections yield distinct near-orthogonal modal orientations from all the analyzed samples. This indicates that the porphyroblasts host successive fabrics as crenulation foliations and did not rotate with respect to geographical axes. W–E- and N–S-trending FIAs have been obtained from both garnet and staurolite porphyroblasts hosting differentiated crenulation cleavages. Garnet and staurolite growth during bulk north–south shortening recorded the development of multiple foliations and an associated succession of metamorphic events at middle-amphibolite facies conditions that predates the metamorphic history generally recognized in this terrain. This period of bulk shortening and associated metamorphism formed during a period of orogenesis called O1. W–E shortening formed N–S striking foliations that preserve a period of orogenesis (O2), and another succession of metamorphism involving more phases of porphyroblast growth preserving N–S-trending FIAs. Overprinting of successive FIA trends (WSW–ENE, WNW–ESE, NNW–SSE, and SSW–NNE) suggests a relative clockwise rotation of the bulk shortening direction through time as it switches from N–S to W–E overall, with a major ‘tectonic break’ or decompression between O1 and O2. The porphyroblast inclusion trail patterns preserving W–E-trending FIAs provide a window into the lengthy period of earlier deformation and metamorphism that is no longer preserved within the matrix foliations

N-S shortening during orogenesis in the Mt Isa Inlier: the preservation of W-E structures and their tectonic and metamorphic significance

Mesoproterozoic Mt Isa inlier of NW Queensland exhibits complex tectonometamorphic history that is generally considered to result from low-pressure/high-temperature (LP/HT) metamorphism with an anticlockwise pressure-temperature-deformation path. Yet studies regarding the nature of the P-T history and tectonic regime that led to such a LP/HT signature have been quite limited. A detailed FIA (Foliation Intersection/Inflection Axes preserved in the porphyroblasts) analysis combined with textural relationships and P-T pseudosections, using key localities across the Eastern Fold Belt of the Mt Isa Inlier, has resolved the cause of the LP/HT signature. Measurement of FIAs in the Eastern Fold Belt has revealed phases of deformation and metamorphism that could not previously be distinguished from one another. Both the ‘asymmetry switch’ and ‘FitPitch’ FIA measurement techniques have been applied to key localities of polymetamorphosed and multiply deformed Eastern Fold Belt, and they yielded the same result. These independent techniques have revealed (1) W-E trending structures that formed during N-S bulk shortening (O1) and N-S oriented structures that formed during W-E bulk shortening (O2) in the Eastern Fold Belt, (2) the presence of separate periods of metamorphism associated with each direction of bulk shortening, and (3) the crustal scale tectonic processes associated with polymetamorphism. The structural overprinting relationships do not support previously suggested non-coaxial west vergent, nappe-style folding in the region. A progressive succession of overprinted FIA trends reveals a clockwise rotation of the principal direction of bulk shortening with time. This requires a radical shift of relative plate movement from N-S to W-E during development of the north Australian craton in the Mesoproterozoic (ca 1.60 and 1.50Ga). Significantly, O1 porphyroblasts preserving W-E FIAs exhibit mineral textures of Barrovian style, whereas O2 formed porphyroblasts preserving N-S FIAs are Buchan in style. This supports the emplacement of the Williams/Naraku Batholiths after O1 around the onset of O2. Higher-pressure garnet cores, modeled in MnNCKFMASH P-T pseudosections preserved early W-E FIAs and formed during O1. This was followed by decompression and then low pressure – high temperature (LP/HT) metamorphism when N-S FIAs were preserved within porphyroblasts. This is further supported by the presences of at least two distinctive generations of staurolite and kyanite that grew both before and after andalusite/cordierite. Middle to upper amphibolite facies metamorphic conditions occurred during O1 with crustal thickening followed by fast erosion and near-isothermal decompression leading to LP/HT conditions. This was followed by O2 and a second period of middle- to upper- amphibolite facies metamorphism that obliterated and/or obscured the tectonometamorphic signature of primitive O1 in the matrix of most rocks. This history appears to correlate better with that observed in the southwest United States, which may have been located against the NE of the Australia at this period in time

Tectonic significance of structural successions preserved within low-strain pods: implications for thin- to thick-skinned tectonics vs. multiple near-orthogonal folding events in the Palaeo-Mesoproterozoic Mount Isa Inlier (NE Australia)

Event-wise structural successions and their regional correlation across the orogenic belts are always been problematic, resulting in construction of conflicting tectonic models. However, in recent years, it has been demonstrated that complex deformation and metamorphic overprinting relationships and their correlation across large regions can be resolved through careful quantitative analysis of fabrics preserved within low-strain pods at different scales. In this study, integrated macro, meso and microstructural analyses of the southern Selwyn Range of the Palaeo-Mesoproterozoic Mount Isa Inlier, NE Australia, have revealed that the tectonic evolution involved four dominant fabric-generating events. These differ from those reported previously based on interpretation of the Mount Isa deep seismic section. D1 is preserved in low-strain zones as outcrop-scale recumbent folds (S1 subparallel S0) with E–W trending fold axes. D2 is characterized by upright to inclined N–S trending folds with a pervasive regional foliation (S2), subparallel to S0/S1. D3 was very heterogeneously developed in the region and appears to be controlled by rheological contrast. Three structural domains are recognized. The Eastern Domain (ED) and Central Domain (CD) are characterized by shallow dipping S3 foliation. S3 foliation is rare in the Western Domain (WD). Deformation during D4 was intense in the WD and produced complex overprinting patterns. All these observations from macro to microscopic scale suggest that the regional S2 initially formed as a steep foliation and was deflected to shallow to moderate dips due to the effect of subvertical shortening (D3). These observations are difficult to reconcile with previously suggested thin- to thick-skinned nappestyle tectonics in the region. Metamorphic field gradient is higher (sillimanite zone) in the ED, which represents deeper crustal levels than the rocks exposed in theCDandWDseparated by pre-existing faults. Andalusite porphyroblasts in the WD preserve steeply dipping S2, whereas staurolite porphyroblasts preserve gently dipping S3, suggesting staurolite grew after andalusite. This interpretation is consistent with the appearance of mineral phases in the KFMASH system along a prograde P–T path (M2) for D2 and D3. An earlier higher pressure P–T path (M1) is proposed for D1 based on the metamorphic mineral assemblages in the MnNCKFMASH system

Orthogonal switching of AMS axes during type-2 fold interference : Insights from integrated X-ray computed tomography, AMS and 3D petrography

We applied X-ray computed microtomography (μ-CT) in combination with anisotropy of magnetic susceptibility (AMS) analysis to study metamorphic rock fabrics in an oriented drill core sample of pyrite-pyrrhotite-quartz-mica schist. The sample is extracted from the Paleoproterozoic Martimo metasedimentary belt of northern Finland. The μ-CT resolves the spatial distribution, shape and orientation of 25,920 pyrrhotite and 153 pyrite grains localized in mm-thick metapelitic laminae. Together with microstructural analysis, the μ-CT allows us to interpret the prolate symmetry of the AMS ellipsoid and its relationship to the deformation history. AMS of the sample is controlled by pyrrhotite porphyroblasts that grew syntectonically during D1 in subhorizontal microlithons. The short and intermediate axes (K3 and K2) of the AMS ellipsoid interchanged positions during a subsequent deformation (D2) that intensely crenulated S1 and deformed pyrrhotite, while the long axes (K1) maintained a constant position parallel to the maximum stretching direction. However, it is likely that all the three AMS axes switched, similar to the three principal axes of the shape ellipsoid of pyrite porphyroblasts from D1 to D2. The superposition of D1 and D2 produced a type-2 fold interference pattern.peerReviewe

The 2014 seismic hazard model of the Middle East: overview and results

The Earthquake Model of Middle East (EMME) Project aimed to develop regional scale seismic hazard and risk models uniformly throughout a region extending from the Eastern Mediterranean in the west to the Himalayas in the east and from the Gulf of Oman in the south to the Greater Caucasus in the North; a region which has been continuously devastated by large earthquakes throughout the history. The 2014 Seismic Hazard Model of Middle East (EMME-SHM14) was developed with the contribution of several institutions from ten countries. The present paper summarizes the efforts towards building a homogeneous seismic hazard model of the region and highlights some of the main results of this model. An important aim of the project was to transparently communicate the data and methods used and to obtain reproducible results. By doing so, the use of the model and results will be accessible by a wide community, further support the mitigation of seismic risks in the region and facilitate future improvements to the seismic hazard model. To this end all data, results and methods used are made available through the web-portal of the European Facilities for Earthquake Hazard and Risk (www.efehr.org)