Start Of Collision Research Articles

Measurement of Liquid Film Thickness Between Coalescing Twin Air Bubbles in a Water Pool Using a Modified Laser Extinction Method

The objective of this study is to elucidate the mechanisms of bubble coalescence. The coalescence of horizontally contacting twin bubbles is experimentally investigated using an isothermal air–water system. The liquid film thickness formed between the contacting bubbles is measured using an improved laser extinction method. The variation of liquid film thickness between the bubbles at the rupture location and the distribution of the liquid film thickness are evaluated. The experimental parameters are the airflow rate and the measurement position (transmitted laser position). The bubble approach velocity and the time from the start of collision until coalescence were measured. When bubble coalescence occurs rapidly, the liquid film thickness is thinnest near the center, and this position moves toward the periphery from the center with increasing contact duration. The thinnest film thickness appeared just before coalescence and was approximately 1.0 μm. A ring-shaped thinner area in the liquid film emerged and shifted from the center toward the periphery of the liquid film with the increase in the bubble approach velocity and close contact duration. The thinnest liquid film thickness just before the commencement of rupture in the ring-shaped area was approximately 0.3 μm.

Basalts erupted along the Tongan fore arc during subduction initiation: Evidence from geochronology of dredged rocks from the Tonga fore arc and trench

A wide variety of different rock types were dredged from the Tonga fore arc and trench between 8000 and 3000 m water depths by the 1996 Boomerang voyage. 40Ar‐39Ar whole rock and U‐Pb zircon dating suggest that these fore arc rocks were erupted episodically from the Cretaceous to the Pliocene (102 to 2 Ma). The geochemistry suggests that MOR‐type basalts and dolerites were erupted in the Cretaceous, that island arc tholeiites were erupted in the Eocene and that back arc basin and island arc tholeiite and boninite were erupted episodically after this time. The ages generally become younger northward suggesting that fore arc crust was created in the south at around 48–52 Ma and was extended northward between 35 and 28 Ma, between 9 and 15 Ma and continuing to the present‐day. The episodic formation of the fore arc crust suggested by this data is very different to existing models for fore arc formation based on the Bonin‐Marianas arc. The Bonin‐Marianas based models postulate that the basaltic fore arc rocks were created between 52 and 49 Ma at the beginning of subduction above a rapidly foundering west‐dipping slab. Instead a model where the 52 Ma basalts that are presently in a fore arc position were created in the arc‐back arc transition behind the 57–35 Ma Loyalty‐Three Kings arc and placed into a fore arc setting after arc reversal following the start of collision with New Caledonia is proposed for the oldest rocks in Tonga. This is followed by growth of the fore arc northward with continued eruption of back arc and boninitic magmas after that time.

Data Quality Monitoring Display for ATLAS experiment at the LHC

The start of collisions at the LHC brings a new era of particle physics and much improved potential to observe signatures of new physics. Some of these may be evident already from the very beginning of collisions. It's essential at this point in the experiment to be prepared to quickly and efficiently determine the quality of the incoming data. Easy visualization of data for the shift crew and experts is one of the key factors in the data quality assessment process. This paper describes the design and implementation of the Data Quality Monitoring Display and discusses experience from its usage and performance during ATLAS commissioning with cosmic ray and single beam data.

Tectonic processes in the Southern and Middle Urals: an overview

Abstract The tectonic evolution of the Uralide orogen began during the Late Palaeozoic as the continental margin of Baltica entered an east-dipping (today's coordinates) subduction zone beneath the Magnitogorsk and Tagil island arcs. The subsequent arc-continent collision resulted in the development and emplacement of an accretionary complex over the continental margin, the development and deformation of a foreland basin, and the extrusion of high-pressure rocks along the arc-continent suture. There is mounting evidence that, at about the same time as arc-continent collision was occurring along this margin of Baltica, eastward-directed subcontinental subduction of the Uralian oceanic crust was also taking place beneath the Kazakhstan plate. This subcontinental subduction is thought to have resulted in the formation of a continental volcanic arc. The final closure of the Uralian ocean basin and the start of collision between the Baltica and Kazakhstan plates occurred during the Late Carboniferous. This continent-continent collision resulted in development of the Late Carboniferous to Early Triassic western foreland fold and thrust belt and foreland basin of the Uralides. The foreland fold and thrust belt displays a large amount of basement involvement, extensive reactivation of pre-existing faults, and a small amount of shortening. At the same time, widespread strike-slip faulting accompanied by melt generation and granitoid emplacement took place in the interior part of the Uralides, leading to the transfer of material laterally along the strike of the orogen. The final crustal structure of the Uralides that resulted from the combination of all of these tectonic events is bivergent, with a crustal root reaching c. 53 km depth.

Age of initiation of collision between India and Asia: A review of stratigraphic data

The collision of India with Asia is perhaps the most profound tectonic event to have occurred in past 100 Ma. It is responsible for the uplift of the Himalayas and Tibetan Plateau and has been argued to have been responsible for geological, geochemical, and climatological consequences of global extent. Yet the age of initiation of this collision remains poorly constrained. The literature is replete with estimates that range from the Late Cretaceous (> 65 Ma) to latest Eocene (< 40 Ma) with little consensus in between. This paper reviews the available stratigraphic evidence from the Himalayan region, and concludes that only in the western Zanskar-Hazara region is the age well constrained as starting in the Late Ypresian (∼ < 52 Ma). To the east only in the Malla Johar region of the Tethyan Himalayas have potentially syn-collisional sediments been recognized south of the Indus Yarlung Zangbo suture. However, here the correlation of the upper part of the Sangchamalla Flysch is contentious, with correlations ranging from Late Cretaceous to Middle Eocene (Lutetian). In the most eastern sections of Tertiary rocks thus far recognized within the Tethyan Himalayas north and east of Everest (Mount Qomolangma) normal, shallow shelf-type carbonates extend into the Lutetian, without evidence of a change in sedimentation to the top of the section, so the start of collision must be still younger. Along-strike of the Indus Yarlung Zangbo suture thick submarine delta-fan complexes derived from erosion of the Himalayan-Tibet system provide independent estimates that agree with a diachronous collision initiating in the late Ypresian in the west and progressing into and perhaps through the Lutetian in the east. The stratigraphic and magmatic history along the north side of the suture are compatible with such a diachronous history. This diachroneity has important implications for estimates of the accommodation of strain within this orogenic system.

Thrusting and backthrusting in the Briançonnais domain of the western Alps

Summary The Briançonnais domain comprises the deformed remnants of a semi-independent microcontinental strip that lay close to the European margin of the Mesozoic Tethys. A Triassic carbonate platform of south-Alpine type was broken up by extension in Early to Middle Jurassic time, producing a syn-rift sequence characterized by small basins with marginal breccia wedges, internal unconformities, and local terrestrial sediments. The pre-Triassic basement was probably reduced to about half its original thickness during this extensional phase. Late Jurassic and Cretaceous subsidence was accompanied by pelagic sedimentation. Flysch sedimentation began shortly before the onset of compressional tectonics in late Palaeocene or Eocene time. Underthrusting and accretion of the Briançonnais domain to the developing Alpine thrust wedge caused an early phase of thrusting, producing antiformal stacks of kilometrescale thrust sheets in parts of the external Briançonnais. The internal margin of the domain was underplated at depths of up to 40 km, and was affected by high-P low-T metamorphism and regional ductile deformation. Stretching lineations and slip-vectors related to this stage trend NW in the northern French Alps, but swing to WSW in the S. Backthrusting in Oligocene time was probably associated with the start of collision with the European margin proper. Families of back thrusts and associated recumbent folds cut, deform or reactivate older structures. The members of each family appear to have been activated in sequence towards the internal margin of the Alps, forming large-scale duplexes, the floor and roof thrusts of which are in part reactivated early thrusts. The trend of stretching lineations and slip-vectors in the Briançonnais domain vary in both space (NW in the N, SW in the S), and time (later trends lie consistently anticlockwise of early ones). These trends and their changes are incompatible with calculated Africa/Europe plate motions for the Tertiary. Independent NW to WNW motion of Adria relative to Europe is probably required. Anticlockwise rotation and bending of the internal Alps during collision could explain the radial pattern of the early vectors. The radial pattern of the later backthrusting matches the radial pattern of coeval forethrusting in the external zones, however; this is therefore unlikely to be a result of later rotations, and may reflect the dominance of gravitational body forces during the later stages of mountain-building.

Volcanic rocks of the 1985 Tibet Geotraverse: Lhasa to Golmud

Volcanic rocks encountered during the Tibet Geotraverse have been studied in the field, in thin section and by major and trace element geochemistry in order to determine their most probable original eruptive environment. Rocks from a total of eleven distinct volcanic provinces were studied in this way. They provide evidence for: an active continental margin or post-collision province of probable Devonian/early Carboniferous age in the northern Kunlun mountains; an active continental margin of late Carboniferous age in the southern Lhasa Terrane; Permian continental rifts in the central Qiangtang and central Kunlun Terranes; Triassic volcanic arcs in the southern Lhasa and northern Qiangtang Terranes; a Triassic active continental margin dyke swarm in the northern Kunlun mountains; a Jurassic post-collision or back-arc rifting province in the southern Qiangtang Terrane; a Jurassic island arc in the northern Lhasa Terrane; a Cretaceous post-collision province in the northern Lhasa Terrane possibly extending in to the southern Qiangtang Terrane; and a Palaeogene active continental margin in the southern Lhasa Terrane. An Oligocene trachyte plug in the northern Qiangtang Terrane was the only evidence encountered during the Geotraverse of volcanism post-dating the Palaeogene India-Eurasia collision. However, the composition of this plug, coupled with new and published analyses from Miocene volcanics in the southern Lhasa terrane and from the Pliocene-Recent volcanic province of northwest Tibet, places important constraints on models for post-collision underplating of Tibet by continental lithosphere: any underplating is likely to have been (a ) much later than the start of collision, ( b ) directed beneath Tibet from the north as well as the south, and ( c ) limited in extent.