Occurrence and composition of sphene from eastern fold belt, Mount Isa Inlier, Cloncurry, northwestern Queensland, Australia

Sphene is very common in rocks including albitized granite, dioritic porphyrite, calcsilicate rock and breccia from the eastern fold belt of Mount Isa Inlier, Cloncurry. Two stages of sphenes are present in these rocks. First-staged sphene is relatively fine, euhedral, some grains show round or patchy zoning; second-staged sphene is relatively large, anhedral to subhedral, some grains show patchy zoning;both possibly contain rutile, ilmenite and magnetite inclusions. All sphenes are of low-Al type. The second-staged sphene has lesser Fe apfu than the first-staged sphene. Light-color part of the sphene has bigger Fe apfu than the dark-color part, as observed on one individual grain of sphene with patchy zoning, the average Xro of the sphene with patchy zoning is greater than that of the sphene without patchy zoning. Because the sphenes are taken from different types of rocks, Si, Ti, and Al have variable relations with F OH apfu. Si and Ti are not correlated with OH F in all analyzed samples ; Fe is correlated with OH F in the sphene just from granite and dioritic porphyrite; Al is correlated with OH F in the sphene fromgranite and breccia and is not correlated with OH F in the sphene from the dioritic porphyrite and calcsilicate rocks. The first-staged sphenes were possibly formed in the processes of magmatism and metamorphism. The second-staged sphenes were formed as a result of the breakdown of hornblendes and biotites in the process of Na (Ca) -metasomatism.     

Structures and morphotectonic evolution of the frontal fold–thrust belt,Kameng river section,Arunachal Himalaya,India

The Neogene–Quaternary Siwalik foreland fold and thrust belt is studied for better understanding of tectonics along the Kameng river section of Arunachal Pradesh, India. The Kimi, Dafla, Subansiri, and the Kimin Formation correspond to Lower, Middle and Upper Siwaliks, respectively. The lithology in the foreland basin is dominantly sandstones, siltstones, claystones, carbonaceous shales, and boulder beds in the upper part. The structural style of the sedimentary sequence from the Main Boundary Thrust southward shows first order ramp-flat geometry. The brittle shear transfers slip across glide horizons to shallower depth. Repeated splay generations from a major regional-scale floor transfers slip from one glide horizon to another that shortens and thickens the crust. In the micro-scale, the lithological response in the structural development is well documented as pressure solution seams and other diagenetic deformation signatures. The basement asperity plays a significant role as the moving thrust front produced a major lateral ramp. The differential movement of the mountain front on both sides of the ramp is decipherable. This is especially true at the western part of the SE flowing Kameng river. The tectonic evolution of the area initiated with slip along the MBT \(\sim \)11 Ma ago along with the deposition of the Siwalik sediments. With southward propagation of the mountain front, the foreland basin shifted towards S, produced splay thrusts from the Himalayan Frontal Thrust-1 (HFT-1), which has been uplifting the Kimin and the older terraces.     

Fault-related fold kinematics recorded by terrestrial growth strata,Sant Llorenç de Morunys,Pyrenees Mountains,NE Spain

Foreland basin growth strata are ideal recorders of deformation rates and kinematics in tectonically active regions. This study develops a high-resolution chronostratigraphic age model to determine folding rates in the Eocene-Oligocene terrestrial growth strata of the Berga Conglomerate Group, NE Spain. The Berga Conglomerate Group was sampled for rock magnetic, magnetostratigraphic, and magnetic susceptibility (χ) cyclostratigraphy analyses. Analysis of rock magnetic measurements indicate a mixed mineral assemblage with both paramagnetic and ferromagnetic minerals. A new magnetic reversal stratigraphy constrains the time frame of folding and is in agreement with previous interpretations. Time series analysis of χ variations show statistically significant power at expected orbital frequencies and provides precession-scale (20 kyr) temporal resolution. Strain measurements including anisotropy of magnetic susceptibility (AMS) fabrics and bedding plane strain worm burrow distortion are consistent with fixed hinge, flexural folding kinematics. Fault-related folding was modeled using χ cyclostratigraphy timing and strain measurement kinematic constraints. The onset of folding was at 33.85 Ma and the end of deformation is less constrained but is younger than 31.06 Ma. Deformation and sediment accumulation rates are unsteady at 20 kyr time scales but appear artificially steady at polarity chron time scales.     

Biostratigraphy of the Tethyan cretaceous successions from northwestern Zagros fold–thrust belt,Kurdistan region,NE Iraq

Nineteen benthonic and planktonic foraminiferal zones and their subzones have been recognized in the Tethyan cretaceous successions along the four sections analyzed in the northwestern Zagros fold–thrust belt within the preforeland–foreland basin. A detailed micropaleontological investigation revealed eight benthonic zones from the Qamchuqa Formation (Barremian to Lower Early Cenomanian) including: the Choffatella decipiens interval zone, C. decipiens/Palorbitolina lenticularis total range zone, C. decipiens/Salpingoporella dinarica interval zone, Mesorbitolina texana total range zone, Mesorbitolina subconcava total range zone, Orbitolina qatarica total range zone, Orbitolina sefini total range zone, and the Orbitolina concava partial range zone. The Rotalipora cushmani total range zone was recorded in the Dokan Formation that overlies the Qamchuqa Formation of the Late Cenomanian age. The Gulneri Formation is represented only by the Whitnella archaeocretacea partial range zone/Heterohelix moremani total range subzone and indicates the Late Cenomanian/Early Turonian age. Six planktonic foraminiferal zones were recorded from the Kometan Formation, indicating the Late Cenomanian to Early Campanian age, and are represented by the R. cushmani/H. moremani subzone, Helvetotruncana helvetica total range zone, Marginotruncana sigali partial range zone, Dicarinella primitiva interval range zone, Dicarinella concavata interval zone, Dicarinella assymetrica total range zone, and Globotruncanita elevata partial range zone. Two planktonic foraminferal zones were recorded also and these are related to the Globotruncana (fornicata, stuartiformis, elevata, and ventricosa) assemblage zone, Globotruncana calcarata total range subzone, from the Shiranish Formation, Lower Late Campanian, while the second zone is nominated as the Globotruncana (arca, tricarinata, esnehensis, and bahijae) assemblage zone, Globotruncana gansseri interval subzone, and Globotruncana contusa total range zone of the Late Campanian to basal middle Maastrichtian age. The last zone is related to the Abathomphalus mayaroensis partial range zone (of Late Maastrichtian age) and occasionally intercalated with the Orbitoides–Loftusia benthic zones. An important hiatus, between the Qamchuqa and Kometan formations was proved and manifests Pre-Aruma unconformity, and is occasionally associated with the global Cenomanian–Turonian Oceanic Anoxic Euxinic Event, while the Maastrichtian red bed of the Shiranish Formations mostly points to Tethyan upper Cretaceous Oceanic Red Bed.     

Structural pattern and kinematic framework of deformation in the southern Nallamalai fold–fault belt,Cuddapah district,Andhra Pradesh,Southern India

An association of westerly verging asymmetric folds, easterly dipping cleavages and contractional faults control the pattern and intensity of structures at different scales in the southern Nallamalai fold–fault belt, Cuddapah district of Andhra Pradesh, Southern India. Variation in structural geometry is manifested across the section by the occurrence of relatively low amplitude folds, sometimes only a monocline and by the near absence of contractional faults in the WSW, but tight to isoclinal folds with frequent fold–fault interactions through the central areas towards ENE.The relationships of structural elements in terms of orientation, style, sense of movement and general vergence indicate their development under a progressive contractional deformation. The structures are interpreted to result from a combination of bulk inhomogeneous shortening across the belt and a top-to-west, variable simple shear. Localized developments of crenulation cleavage, rotation of cleavage in the shorter limbs of some mesoscale asymmetric folds and general variation of structural elements in morphology and associations across the belt, indicate partitioning of deformation and a varying degree of non-coaxiality in discrete domains of the bulk deformation.     

Implications of a downward‐facing fold in the Bathurst granite contact aureole,Hill End Synclinorial Zone,New South Wales

A downward‐facing refolded fold in the aureole of the Bathurst Granite displays evidence for three phases of folding. This, and structural anomalies in other Lachlan Fold Belt granitoid aureoles, may be caused by granitoid emplacement. Alternatively they may be records of early deformations, preserved in the granitoid envelopes from the obliterating effects of later deformations. Various causes for the three fold phases are considered, including soft‐sediment deformation, orogenies, and kinking as a result of granitoid emplacement. A unique solution is not yet possible. Unrecognised structural complexities may be widespread in the Hill End Synclinorial Zone.     

Opposite vergent synclines on the flanks of a large-scale box fold in the Chamba–Lahaul region, northwest Himalaya, India

This article focuses on two regional-scale synclines of the Chamba Thrust Sheet, northwest Himalaya. These synclines were explained by two different tectonic events. Earlier studies ascribe the NE vergent Tandi syncline and the SW vergent Chamba syncline to the older NE-directed nappe stacking and the younger SW-directed Himalayan deformation events, respectively. The new field data and structural analysis reveal that these synclines define the flanks of a large-scale asymmetric box fold referred to here as the Hadsar–Chobia box fold and to a common phase of deformation. The box fold in the Chamba Thrust Sheet has developed over a ductile–brittle substrate referred to here as the Chamba Thrust. This thrust has translated a portion of the Tethys Himalaya over both the Higher Himalayan Crystallines and the Lesser Himalaya. Structural analysis, particularly the parallelism between the trends of hinge lines of the Hadsar–Chobia box fold and the strike of the regional thrust planes indicate that the folding and translation may have occurred simultaneously during the D₁ deformation episode.     

Pressure–temperature-deformation history for a part of the Mesoproterozoic fold belt in North Singhbhum,Eastern India

The supracrustal rocks in the easternmost part of the Proterozoic fold belt of North Singhbhum, eastern India, are folded into a series of large upright folds with variable plunges. The regional schistosity is axial–planar to the folds. The folds were produced by a second phase of deformation (D2) and were preceded by D1 deformation, which gave rise to isoclinal folds (mapped outside the study area) and the locally preserved, bedding-parallel schistosity. A shearing deformation during D2 was responsible for the sheath-like geometry of a major fold. The axial planes were curved by D3 warping. The first metamorphic episode (M1) of low-pressure type produced andalusite porphyroblasts prior to, or in the early stage of, D1 deformation. The main metamorphism (M2), responsible for the formation of chloritoid, kyanite, garnet and staurolite porphyroblasts, was late- to post-D2 in occurrence. The Staurolite isograd separates two zonal assemblages recorded in the high-alumina and the low-alumina pelitic schists. Geothermobarometric calculations indicate the peak metamorphic temperature to be 550 °C at 5.5 kb. Fluid composition in the rocks before and during M2 metamorphism was buffered and fluid influx, if any, was not extensive enough to overcome the buffering capacity of the rocks. From M1 to M2, the P–T path is found to have a clockwise trajectory, that is consistent with a tectonic model involving initial asthenospheric upwelling and rifting, followed by compressional deformation leading to loading and heating.     

An example of the use of veins to establish a cover fold history—irregully formation,western Australia

Structural correlation using fold overprinting and style, plus the timing and orientation of possible syntectonic veins, are used to interpret three minor folding events in part of the Irregully Formation. The formation lies near the base of the Middle Proterozoic Bangemall Group in the Bangemall Basin of Western Australia. It comprises interbedded well-laminated dolostones and orthoquartzites, metamorphosed under lower greenschist-facies conditions. Bedding in the formation is folded about a gently NW-plunging axis. Most mesofolds are consistent with the bedding distribution, exhibiting a fold-axis maximum plunging gently NW and vertical axial planes. Folds with NE-, E- and NNE-trending axial planes are common in the area, but most cannot be explained by reorientation of the dominant NW-trending folds.A deformation history accounting for different fold geometries is established using fold overprinting in conjunction with dilational offsets between fold-related quartz and dolomite veins. A number of approaches to determine the history of folding are possible. Fold overprinting is the most valuable criterion, but in weakly deformed terrains it may not be easily recognised, so that alternative methods should be examined. Fold directions in the Irregully Formation are parallel to trends in the underlying Ashburton Formation, suggesting a degree of basement reactivation. As a fold chronology in the cover has been established accounting for mesofolds and macrofolds, the interpreted reactivation is believed to have involved compression rather than passive drape over earlier structures. In the Irregully Formation differently oriented folds probably developed through a degree of cover shortening, associated with reactivation of basement faults or folds.     

Structural style of the Chos Malal fold and thrust belt,Neuquén basin,Argentina: Relationship between thick- and thin-skinned tectonics

The Chos Malal fold and thrust belt (FTB) is a thick-skinned mountain belt formed by Mesozoic deposits of the Neuquén Basin during the Andean orogeny. Four structural cross-sections in the entire deformed area, supported by field and subsurface data, suggest a strong link between thick and thin-skinned structures. Major Andean thrusts branching from a detachment placed 12 km into the crust created large basement wedges, which were inserted in the cover producing minor order structures. The westernmost of these wedges is exposed forming the Cordillera del Viento, while others basement slices at depth were interpreted from seismic lines. These thick-skinned structures transferred deformation to the cover along the Auquilco Formation and contributed to create all thin-skinned structures surveyed in the Chos Malal FTB. We recognized half-graben geometries in the seismic lines, preserving their extensional configuration, which suggests that the main normal faults were not inverted. Shortenings calculated from the restoration of the four cross-sections are 16.9 km (29.7%), 16.9 km (29.7%), 14.7 km (26.9%) and 14.15 km (26.3%), which evidence a slight diminution of the contraction toward the south probably associated with the plunge of the Cordillera del Viento structure in this segment of the Chos Malal FTB.     

Age of the Ust’-Gilyui sequence in the Stanovoi Complex of the Selenga-Stanovoi Superterrain, Central Asian fold belt

According to the results of U-Pb geochronological investigations, the age of the amphibolite protoliths (metabasalts) in the Ust??-Gilyui sequence within the Stanovoi Complex of the Amazar-Gilyui structural and formational zone in the Selenga-Stanovoi Superterrain of the Central Asian fold belt can be estimated at 193 ± 1 Ma. The Nd model age of the Ust??-Gilyui metasedimentary rocks is in the interval of t _Nd(DM) = 1.1?C3.1 Ga. This information along with the previously obtained geochronological data are indicative of the fact that the Ust??-Gilyui sequence consists of metasedimentary and metavolcanic rocks of various ages: (1) volcanic rocks with the age of 193 ± 1 Ma; (2) metasedimentary and metavolcanic rocks broken through by the Paleozoic granitoids dated to 370 Ma and characterized by minimum estimations of t _Nd(DM) = 1.1 Ga, i.e., rocks with an age of 1.1?C0.4 Ga. In addition, it is quite possible that this sequence also includes more ancient rocks. The SSS Amazar-Gilyui structural and formational zone is likely to be a tectonic mélange composed of the metasedimentary and metavolcanic rocks of the Mesozoic and, probably, Paleozoic and Early Precambrian ages. The studied zone was formed in the Mesozoic, most likely, in the course of the collision processes initiated by the closing up of the Mongol-Okhotsk Ocean.     

Recent large fold nucleation in the upper crust: Insight from gravity,magnetic, magnetotelluric and seismicity data (Sierra de Los Filabres–Sierra de Las Estancias,Internal Zones,Betic Cordillera)

Rheological heterogeneities in the upper-crust have a close relationship with the fold position where rigid bodies could constitute initial perturbations that allow the nucleation of folds. Consequently, establish the position and geometry of anomalous rocks located in the upper-crust by geophysical studies help to understand the folded structure observed on surface. New geological observations in the field, along with gravity, magnetic, magnetotelluric and seismicity data, reveal the subsurface structure in the Sierra de Los Filabres–Sierra de Las Estancias folded region part of the Alpine belt in southern Spain. The geometry of the upper crust is determined by geological field data, 2D gravity models, 2D magnetic models and 2D MT resistivity model, while seismicity evidences the location of the deep active structures. These results allow us to propose that a basic rock body at 4 to 9 km depth has determined the nucleation and development of the Sierra de Los Filabres kilometric antiform. N-vergent large late folds are subjected to a variable present-day stress field. Earthquake focal mechanisms suggest the presence in depth of a regional NW–SE compressive stress field. However, most of the seismogenetic structures do not extend up to the surface, where NW–SE and WNW–ESE outcropping active normal faults are observed, thus indicating a NE–SW extension in the upper crust simultaneous to orthogonal NW–SE compression related to reverse faults and minor folds developed in the Eastern Almanzora Corridor and in the nearby Huércal–Overa Basin. The recent and active tectonic studies of cordilleras hinterland subjected to late folding greatly benefits from the integration of surface observations together with geophysical data.     

Fragment of the Early Paleozoic (∼500 Ma) island arc in the structure of the Olkhon Terrane,Central Asian fold belt

The volcanic (basaltic, basalt andesitic, andesitic, and rhyolitic) porphyric rocks of the Tsagan-Zaba complex are studied in the Olkhon composite terrane of the Central Asian foldbelt. The concordant U-Pb (SHRIMP-II) age of single zircon grains from rhyolites (492 ± 5 Ma) may be interpreted as the period of formation of the Tsagan-Zaba complex. The volcanic rocks of this complex are characterized by clear suprasubduction geochemical features and positive ?_Nd(t) values. The similar ages, compositions, and ?_Nd(t) values of the studied volcanic rocks and gabbroic rocks of the Birkhin pluton allow us to combine them into a common Birkhin volcano-plutonic association, which may be considered as a fragment of a section of the mature island arc of ～500 Ma in age. The gabbroic rocks may be interpreted as the middle part of this section, whereas the volcanic and volcanosedimentary rocks belong to its upper part. The section was disintegrated 470–460 Ma ago, when the Early Paleozoic island arc was accreted to the southern flank of the Siberian craton in the course of the oblique collision and became a part of the Olkhon composite terrane.     

Geochemistry and provenances of the Jurassic terrigenous rocks of the Upper Amur and Zeya–Dep troughs,eastern Central Asian fold belt

This paper reports the results of complex geochemical and Sm–Nd isotope-geochemical studies of terrigenous rocks of the Upper Amur and Zeya–Dep troughs, as well as U–Pb geochronological studies of detrital zircons. It is established that the studied troughs have orogenic nature, which is of key significance for understanding the geodynamic evolution of East Asia in the Mesozoic. Such interpretation is consistent with structural features of the troughs (migration of basin axis inward the continent with time, stratigraphic rejuvenation in the same direction), which are typical of foreland basins regarded as analogues of foreland (marginal) troughs. Obtained data indicate that orogenic processes responsible for the formation of the Mongol-Okhotsk fold belt began in the Early Jurassic.     

Reconstructing the Cryogenian–Ediacaran evolution of the Porongos fold and thrust belt,Southern Brasiliano Orogen,based on Zircon U–Pb–Hf–O isotopes

The Neoproterozoic geotectonic triad of the Brasiliano Orogen is reconstructed in southern Brazil from studies focused on the Porongos fold and thrust belt. We integrate field geology with isotopic studies of zircon U–Pb SHRIMP and Lu–Hf–O laser determinations in seven metasedimentary and three metavolcanic rock samples. The results indicate that the Porongos palaeo-basin was derived from mixed sources (3200–550 Ma), with major contributions from Rhyacian (2170 Ma) and Ediacaran (608 Ma) sources. Minor contributions from Archaean to Tonian sources are also registered. The maximum depositional age of the Porongos palaeo-basin is established by the age range of 650–550 Ma with T_DM model ages between 2.5 and 1.3 Ga. The reworked signature (ε_Hf values = ?34 to ?4) and the characteristic crustal magma reservoirs (δ¹⁸O ≥5.3 ‰) indicate that these sediments are equivalent to Neoproterozoic granites of the Dom Feliciano Belt. The episodic depositional history started in the Cryogenian (650 Ma) and lasted until the Ediacaran (most likely 570 Ma). A magmatic event of Tonian age is recorded in rhyodacite samples interleaved with the metasedimentary rocks and dated at 773, 801, and 809 Ma. The crustal evolution of the Sul-Riograndense Shield included mountain building, folding and thrusting and flexural subsidence in the foreland. An orogenic triad is revealed as the Pelotas Batholith, the Porongos fold and thrust belt and the Camaquã Basin, all part of the Dom Feliciano Belt.     

Late Palaeozoic arc flank and fore‐arc basin sequence of the New England fold belt in the stanage bay region,central Queensland

Devonian and Carboniferous (Yarrol terrane) rocks, Early Permian strata, and Permian‐(?)Triassic plutons outcrop in the Stanage Bay region of the northern New England Fold Belt. The Early‐(?)Middle Devonian Mt Holly Formation consists mainly of coarse volcaniclastic rocks of intermediate‐silicic provenance, and mafic, intermediate and silicic volcanics. Limestone is abundant in the Duke Island, along with a significant component of quartz sandstone on Hunter Island. Most Carboniferous rocks can be placed in two units, the late Tournaisian‐Namurian Campwyn Volcanics, composed of coarse volcaniclastic sedimentary rocks, silicic ash flow tuff and widespread oolitic limestone, and the conformably overlying Neerkol Formation dominated by volcaniclastic sandstone and siltstone with uncommon pebble conglomerate and scattered silicic ash fall tuff. Strata of uncertain stratigraphic affinity are mapped as ‘undifferentiated Carboniferous’. The Early Permian Youlambie Conglomerate unconformably overlies Carboniferous rocks. It consists of mudstone, sandstone and conglomerate, the last containing clasts of Carboniferous sedimentary rocks, diverse volcanics and rare granitic rocks. Intrusive bodies include the altered and variably strained Tynemouth Diorite of possible Devonian age, and a quartz monzonite mass of likely Late Permian or Triassic age.

The rocks of the Yarrol terrane accumulated in shallow (Mt Holly, Campwyn) and deeper (Neerkol) marine conditions proximal to an active magmatic arc which was probably of continental margin type. The Youlambie Conglomerate was deposited unconformably above the Yarrol terrane in a rift basin. Late Permian regional deformation, which involved east‐west horizontal shortening achieved by folding, cleavage formation and east‐over‐west thrusting, increases in intensity towards the east.     

Structural geometry of a thick‐skinned fold‐thrust belt termination: The Olary Block in the Adelaide Fold Belt,South Australia

The Olary Block comprises a set of Palaeoproterozoic to Mesoproterozoic basement inliers that were deformed together with the Neoproterozoic sedimentary cover of the Adelaide Geosyncline during the ca 500 Ma Cambro‐Ordovician Delamerian Orogeny. Balanced and restored structural sections across this region show shortening of less than 20%. These basement inliers represent the interface between a region of thick‐skinned deformation bordering the Curnamona Craton to the north and a region of thin‐skinned deformation to the south and west in the Nackara Arc. The basement inliers represent upthrust segments of the subsided basin margin with the sedimentary package thickening to the south and to the west. Earlier formed extensional faults provided the major strain guides during Delamerian shortening. An early phase of east‐west shortening is interpreted to be synchronous with dextral strike‐slip deformation along basement‐relay structures (e.g. Darling River lineament). During progressive shortening the tectonic transport direction rotated into a northwest to north direction, coeval with the onset of the main phase of thin‐skinned fold deformation in the adjacent Nackara Arc.     

Rainfall-induced landslide in the active frontal fold–thrust belt of Northwestern Himalaya,Jammu: dynamics inferred by geological evidences and Ground Penetrating Radar

Landslides are the most established geological hazards in the frontal fold–thrust belt of Northwestern Himalaya comprising of Siwaliks and Murree strata. The continuous rainfall from 2 to 6 September, 2014 caused a massive landslide at village Sadal in Udhampur district of Jammu and Kashmir state. The landslide occurred in the early morning of September 6, 2014, destroying entire Sadal habitation comprising 45 houses, and killing 41 people and more than 500 domestic animals. Google earth images of pre and post-landslide events along with the field measurements show the kinematics of upper and lower parts of the slide. Horizontal and vertical components of displacement and mode of failure suggest the landslide as of complex nature. The shallow subsurface geophysical imaging through Ground Penetrating Radar (GPR) survey shows the failure plane composed of friable mudstone bed underlain by massive mudstone and overlain by cross-bedded sandstone. The depth of debris material above the failure plane ranges from 6 m at Site S1a-b to 10 m at Site-S2b and 20 m at Site S3a. The velocity analysis of Site-3 shows four thick layers represented from bottom to surface by L1—sandstone (V?=?0.16 m/ns, travel time?=?356.36 ns), L2—mudstone (V?=?0.17 m/ns, travel time?=?288.48 ns), L3—massive mudstone (V?=?0.19 m/ns, travel time 220.68 ns), and L4—cross-laminated sandstone (V?=?0.20 m/ns, travel time?=?77.58 ns) overlaying the failure plane. The study shows the landslide occur along the western limb of a fold identified during the present work. We mapped an old landslide on the same limb which shows 5–6 m-thick subsurface debris material with thick rock fragments involved in the landslide process. The detailed geological and geophysical investigations suggest that both the landslides were triggered by extreme rain fall events.