The western termination of the South Pyrenean Triangle Zone; a structural and geophysical characterization.

<p>The presence of multiple evaporite levels strongly influence the structural style and kinematics of fold-and-thrust belts. Particularly (but not exclusively) in their fronts, it is common for these décollements to favor the formation of triangle zones. In the central portion of the Pyrenees, the South Pyrenean Triangle Zone represents the frontal part of this chain, that involves the Oligocene-Miocene Ebro Basin foreland deposits. We have focused on its western termination, characterized by a salt-cored anticline that laterally passes to a backthrust which dies out to the west. These structures are detached on the Upper Eocene-Lower Oligocene syntectonic evaporite Barbastro Formation (and lateral equivalents) that acted as a multidetachment unit. To the north, the south-directed Pyrenean thrust unit detached on Middle-Upper Triassic evaporites to finally glide along the Upper Eocene-Lower Oligocene décollement horizons.</p><p>In this contribution, we present a detailed structural and stratigraphic model of this triangle zone termination, constructed accordingly to two major approaches (1) constraining the geometry and structural architecture based on surface geology, interpretation of seismic lines (>900 km) and wells and, (2) obtaining the 3D density distribution of the detachment level (Barbastro Fm. and lateral equivalents as well as deeper, Triassic evaporites) using gravity stochastic inversion by means of more than 7000 gravity stations and 1500 actual density data from surface rocks. All in all, this multidisciplinary approach allows us to characterize the western termination of the South Pyrenean Triangle zone as the transition from a ramp-dominated and multiple triangle zone to a detachment-dominated one whose geometry, kinematics, and location were controlled by the distribution and heterogeneity of the Upper Eocene-Lower Oligocene syntectonic décollements and the southern pinch-out of the basal detachment of this unit.</p>

The reasons and countermeasures of Bladder Rupture caused by Transurethral Clot Evacuation

Objective: Bladder rupture caused by transurethral clot evacuation is rare in clinic, but an emergency operation is indeed needed in the patient with bladder rupture. We analyzed the reasons of bladder rupture caused by transurethral clot evacuation and provided the countermeasures to guide clinical surgeon to prevent the iatrogenic damage of bladder. Method: We retrospectively reviewed the records of 287 patients in our hospital, who had bladder tamponade resulting from clots of blood for various reasons and underwent transurethral clot evacuation from January 2007 to January 2019. Six male cases, aged from 28 to 76 years (mean 56.67±17.76) had bladder rupture. Four patients whose bladder ruptured intraperitoneally were changed to open surgery to repair bladder and clear the remanent blood clots. Two patients with extraperitoneal bladder rupture and a small bladder crevasse underwent a conservative therapy. Results: We observed that the incidence rate of bladder rupture was not associated with bladder tamponade and the age, but may be associated with gender, bladder paracentesis preoperative and urinary retention preoperative. All six cases were male.. They had different period of urinary retention before operation. No supra-pubis bladder paracentesis was made before operation. The bladder crevasses located in the triangle zone and posterior wall of bladder entirely, and the length of the bladder crevasses ranged from 3 to 7cm (mean 4.83cm). The bladder crevasses were all lengthways, and four cases were of’ bladders ruptured intraperitoneally while another two presented an extraperitoneal bladder rupture. Conclusions: The reasons of bladder rupture caused by transurethral clot evacuation may be related to gender, bladder paracentesis preoperative and urinary retention preoperative. We should decide to use expectant treatment or open surgery immediately according to the extent of the rupture when bladder rupture occurs. doi: https://doi.org/10.12669/pjms.37.3.3911 How to cite this:Liu KL, Wang X, Qu CB, Qi JC. The reasons and countermeasures of Bladder Rupture caused by Transurethral Clot Evacuation. Pak J Med Sci. 2021;37(3):---------. doi: https://doi.org/10.12669/pjms.37.3.3911 This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Active strike-slip faults and an outer frontal thrust in the Himalayan foreland basin

The Himalayan foreland basin formed by flexure of the Indian Plate below the advancing orogen. Motion on major thrusts within the orogen has resulted in damaging historical seismicity, whereas south of the Main Frontal Thrust (MFT), the foreland basin is typically portrayed as undeformed. Using two-dimensional seismic reflection data from eastern Nepal, we present evidence of recent deformation propagating >37 km south of the MFT. A system of tear faults at a high angle to the orogen is spatially localized above the Munger-Saharsa basement ridge. A blind thrust fault is interpreted in the subsurface, above the sub-Cenozoic unconformity, bounded by two tear faults. Deformation zones beneath the Bhadrapur topographic high record an incipient tectonic wedge or triangle zone. The faults record the subsurface propagation of the Main Himalayan Thrust (MHT) into the foreland basin as an outer frontal thrust, and provide a modern snapshot of the development of tectonic wedges and lateral discontinuities preserved in higher thrust sheets of the Himalaya, and in ancient orogens elsewhere. We estimate a cumulative slip of ∼100 m, accumulated in <0.5 Ma, over a minimum slipped area of ∼780 km2. These observations demonstrate that Himalayan ruptures may pass under the present-day trace of the MFT as blind faults inaccessible to trenching, and that paleoseismic studies may underestimate Holocene convergence.

Why do triangle zones exist? Insights from numerical models

&lt;p&gt;Triangle zones in fold and thrust belts are enigmatic structures bound by foreland verging thrust zones and back-thrusts verging towards the hinterland. The geometry as well as kinematic evolution of these structures has been the subject of a wide range of studies over the last few decades. The understanding of triangle zone mechanics is incomplete although different driving mechanisms for their formation have been proposed. So far few &amp;#8211; mostly analogue &amp;#8211; modeling studies have focused on understanding the primary factors controlling their formation. Factors suggested to have a first order control on the formation of triangle zones include the rheological properties of the detachment and overburden rocks, the thickness of the overburden rocks, syn-tectonic erosion and sedimentation rate, fluid over-pressure conditions, and the angle of the detachment. Here we use the arbitrary Lagrangian-Eularian finite element code FANTOM to examine the development of triangle zones. We focus especially on the effect of the angle and rheology of the detachment, the rheology of the overburden strata, and syn-tectonic deposition.&amp;#160;&lt;/p&gt;

A mountain of folds: triangle zone in the fold-and-thrust belt of the External Pamir, Kyrgyzstan

&lt;p&gt;Triangle zones are thrust sheets or stacks of thrust sheets underlain by foreland-directed thrusts and overlain by a kinematically linked &amp;#8220;passive&amp;#8221; roof thrust - a backthrust - directed towards the hinterland. They are not uncommon in thin-skinned fold-and-thrust belts. Most triangle zones are known from seismic data and drilling. We describe a km-scale example exposed on a flank of the Altyn Dara valley near the thrust front of the Pamir mountains in Kyrgyzstan. The External Pamir is a high-level thrust belt built from non-metamorphic strata of Permian to Neogene age. It is bounded on its internal, southern side by the Main Pamir thrust with metamorphic rocks in its hanging-wall and in the north by the Pamir Frontal thrust which juxtaposes it with undeformed foreland strata of the Alai valley.&lt;/p&gt;&lt;p&gt;The triangle zone has formed where the basal detachment of the External Pamir ramps up from Lower Cretaceous redbeds into a succession of Upper Cretaceous marine pelites with a few intercalated limestone horizons. The strongly deformed Upper Cretaceous strata are contained between a north-directed thrust and a south-directed backthrust, both of which carry Lower Cretaceous rocks in their hanging-walls. In stark contrast to classical models, the core of the triangle zone is occupied by a bundle of essentially unfaulted, isoclinal upright folds. The subvertical axial planes diverge slightly upwards and changing elevations of the synclinal troughs suggest an anticlinorium. This structure is exposed over a vertical distance of 1 km in the steep flank of Pik Sverdlova. The folds involve four shaly packages and three limestone horizons. The initial total thickness of this succession was about 500 m. A strong slaty cleavage is developed in the shales, but the limestones do not show marked thickness variations between the long, straight fold limbs and the tight but rounded hinges. Assuming negligible penetrative strain in the limestones, unfolding the sinuous bed length suggests 10 km of horizontal shortening accommodated by folding.&lt;/p&gt;&lt;p&gt;Its overall geometry suggests that the triangle zone originated as a wide zone of detachment folding above a thrust fault propagating at the base of the weak Upper Cretaceous shales. The strong contraction may indicate some kind of buttress towards the foreland such as a syndepositional fault against which the Cenomanian-Turonian succession thinned or terminated, or the backthrust itself if it initiated early on. At any rate, the highly shortened bundle of folds was at some point bypassed along a deeper detachment in Lower Cretaceous strata into which the backthrust merges.&lt;/p&gt;&lt;p&gt;The internal structure of the Pik Sverdlova triangle zone would be difficult to image by conventional seismic techniques. Vertical drilling would also be unlikely to fully reveal the folded architecture. We speculate that in many triangle zones folding may be a more important mechanism than incorporated in the prevailing thrust-stacking models.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

The Durres earthquakes of November 2019: A geological perspective from the Adriatic offshore

&lt;p&gt;At 3:54 night time on November the 26th the city of Durres in Albania was hit by an earthquake of Mw 6.2, followed in the next 4 hours by three additional earthquakes with Mb &gt; 5.0. These earthquakes, part of a sequence that continued with much reduced intensity until mid December, caused severe damages in Durres and the adjacent region, counting a final human toll of about 50 casualties and over 2000 injuried. The historical catalogues show that Albania has been affected by over 10 relatively strong earthquakes (Mw&gt; = 6.0) in the last 200 years (Kiratzi and Dimakis 2013), testifying to an important seismic history.&lt;/p&gt;&lt;p&gt;The focal mechanisms of the Durres earthquakes show compressive fault planes placed at ca. 10 km depth. These earthquakes are part of a belt of compressional earthquakes that borders to the east the southern Adriatic, including the strong Montenegro earthquake (Mw 7.1) of April 1979, indicating that shortening is currently ongoing at the front of the southern Dinarides and Hellenides.&lt;/p&gt;&lt;p&gt;The geological structure of Albania, at the junction between the Dinarides and the Hellenides, shows structural complexities that have their roots in the Mesozoic paleogeography of the region (Argnani, 2013). The front of the Albanian fold-and-thrust belt extends to the sea, where it has been studied thanks to some seismic acquisition campaigns aimed at investigating the geology of the Adriatic Sea (Argnani 2013). This sector of the thrust front is characterized by the presence of important back thrusts, which are correlated to the spatial distribution of the Mesozoic domains of carbonate platforms and pelagic basins. In the sector facing the southern Adriatic basin the presence of a large thickness of Oligocene-Quaternary clastic sediments filling the foredeep promotes the development of triangle zones and backtrusts. The basal thrust of the triangle zone system affects Mesozoic carbonates at an estimated depth of 10-15 km (Fantoni and Franciosi, 2010) and appears to be the source of the Durres earthquakes. A similar structural setting can be envisaged for the Montenegro earthquake of 1979, as the offshore structures show a continuity, although a substantial change in strike occurs across the trend of the Shkoder-Peja line. A large lateral displacement of the internal units occurs along the Shkoder-Peja transversal line, which marks the junction between the Hellenides and the Dinarides. The shallow water limestones of the more external Kruja domain, however, are not laterally offset. Palaeomagnetic results indicate that the Miocene-Pliocene clock-wise rotation of the western arm of the Aegean opening was accomplished just south of the Shkoder-Peja line; these rotations impose an overall change in strike of the outer thrusts, although the frontal structures are specifically affected by the nature of the Mesozoic domains entering the thrust system.&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;Argnani A. (2013) -. Ital. J. Geosci., 132, 175-185.&lt;/p&gt;&lt;p&gt;Fantoni R., Franciosi R. (2010) - Rend. Fis. Acc. Lincei 21, S197&amp;#8211;S209.&lt;/p&gt;&lt;p&gt;Kiratzi A., Dimakis E. (2013) - Ital. J. Geosci., 132, 186-193.&lt;/p&gt;

Growth of triangle zone fold-thrusts within the NW Borneo deep-water fold belt, offshore Sabah, southern South China Sea

The NW Borneo deep-water fold-and-thrust belt, offshore Sabah, southern South China Sea, contains a structurally complex region of three to four seafloor ridges outboard of the shelf-slope break. Previous studies have suggested the seafloor ridges formed either above shale diapirs produced by mass movement of overpressured shales (i.e., mobile shale) or above an imbricate fold-and-thrust array. Here, we performed tectonostratigraphic analyses on a petroleum industry three-dimensional (3-D) seismic volume that imaged the full growth stratal record. We show fold growth history, deformation styles, along-strike structural variabilities, and synkinematic sedimentation during triangle zone–style fold growth. Nine seismic horizons within growth strata were mapped and correlated to petroleum industry seismostratigraphy. Synkinematic sedimentation interactions with growing folds and near-surface strains were analyzed from seismic attribute maps. We interpret that the seafloor structures were formed by imbricate thrusts above multiple detachments. We estimate ∼8 km minimum shortening since the late Miocene ca. 10 Ma. The folds show oversteepened fold forelimbs, back-rotated backlimbs, and forward-vergent (NW to NNW) “blind” thrust ramps that terminate within the growth strata. Fold cores show evidence of internal shear. Immature folds show detachment fold geometries, whereas mature folds show forelimb break thrusts, type I triangle zones, and rotated forward-vergent roof thrusts. Thrust linkages spaced ∼10 km apart were exploited as thrust top synkinematic sedimentation pathways; the linkages also partition near-surface strains. Our comprehensive, three-dimensional documentation of triangle zone fold growth and sedimentation in a deep-water fold belt highlights internal shear, multiple detachments, and opposite thrust vergence; mobile shales are not required to explain the deformation.