scholarly journals Deeply subducted continental fragments: II. Insight from petrochronology in the central Sesia Zone (Western Italian Alps)

2017 ◽  
Author(s):  
Francesco Giuntoli ◽  
Pierre Lanari ◽  
Marco Burn ◽  
Barbara Eva Kunz ◽  
Martin Engi
Keyword(s):  
High Pressure ◽  
Vertical Velocity ◽  
Lower Pressure ◽  
Italian Alps ◽  
Mineral Growth ◽  
Internal Complex ◽  
Volcanic Suite ◽  
Pressure Peak ◽  
Eclogite Facies ◽  
Nw Italy

Abstract. Continental granulite terrains subducted to mantle depths commonly show only partial and localized eclogitization. The Sesia Zone (NW Italy) is exceptional as eclogitic micaschists predominate in large parts of this terrane, and Alpine high-pressure (HP) assemblages almost completely replaced the Permian granulite protoliths. This study documents when and at what conditions this extensive HP-equilibration took place. Results constrain the main stages of mineral growth and deformation, associated with fluid influx that occured during continental subduction. Our study comprises both main complexes of the Sesia terrane and covers some of the recently recognized tectonic subunits involved in its assembly, hence our data constrain the HP-tectonics that formed the Sesia Zone. In the Internal Complex (IC), pulses of fluid percolated at eclogite facies conditions, between 77 and 55 Ma with the HP-conditions reaching ~ 2 GPa and 600–670 °C. By contrast the External Complex (EC) records a lower pressure peak of ~ 0.8 GPa for 500 °C, at ~ 63 Ma. The juxtaposition of the two complexes occurred during exhumation, at ~ 0.8 GPa and 350 °C; the timing is constrained between 46 and 38 Ma. Mean vertical exhumation velocities are constrained between 0.9 and 5.1 mm/year for the IC, up to its juxtaposition with the EC. Exhumation to the surface occurred before 32 Ma, as constrained by the overlying Biella Volcanic Suite, at a mean vertical velocity between 1.6 and 4 mm/year. These findings constrain the processes responsible for the exhumation and assembly of high pressure continental units.

scholarly journals Deeply subducted continental fragments – Part 2: Insight from petrochronology in the central Sesia Zone (western Italian Alps)

Solid Earth ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 191-222 ◽  
Author(s):  
Francesco Giuntoli ◽  
Pierre Lanari ◽  
Marco Burn ◽  
Barbara Eva Kunz ◽  
Martin Engi
Keyword(s):  
High Pressure ◽  
Subduction Zone ◽  
Driving Forces ◽  
Microstructural Analysis ◽  
Age Dating ◽  
Subduction Channel ◽  
Mineral Growth ◽  
Pressure Peak ◽  
Nw Italy ◽  
Temperature Time

Abstract. Subducted continental terranes commonly comprise an assembly of subunits that reflect the different tectono-metamorphic histories they experienced in the subduction zone. Our challenge is to unravel how, when, and in which part of the subduction zone these subunits were juxtaposed. Petrochronology offers powerful tools to decipher pressure–temperature–time (P–T–t) histories of metamorphic rocks that preserve a record of several stages of transformation. A major issue is that the driving forces for re-equilibration at high pressure are not well understood. For example, continental granulite terrains subducted to mantle depths frequently show only partial and localized eclogitization. The Sesia Zone (NW Italy) is exceptional because it comprises several continental subunits in which eclogitic rocks predominate and high-pressure (HP) assemblages almost completely replaced the Permian granulite protoliths. This field-based study comprises both main complexes of the Sesia terrane, covering some of the recently recognized tectonic subunits involved in its assembly; hence our data constrain the HP tectonics that formed the Sesia Zone. We used a petrochronological approach consisting of petrographic and microstructural analysis linked with thermodynamic modelling and U–Th–Pb age dating to reconstruct the P–T–t trajectories of these tectonic subunits. Our study documents when and under what conditions re-equilibration took place. Results constrain the main stages of mineral growth and deformation, associated with fluid influx that occurred in the subduction channel. In the Internal Complex (IC), pulses of fluid percolated at eclogite facies conditions between 77 and 55 Ma with the HP conditions reaching  ∼  2 GPa and 600–670 °C. By contrast, the External Complex (EC) records a lower pressure peak of  ∼  0.8 GPa for 500 °C at  ∼  63 Ma. The juxtaposition of the two complexes occurred during exhumation, probably at  ∼  0.8 GPa and 350 °C; the timing is constrained between 46 and 38 Ma. Mean vertical exhumation velocities are constrained between 0.9 and 5.1 mm year−1 for the IC, up to its juxtaposition with the EC. Exhumation to the surface occurred before 32 Ma, as constrained by the overlying Biella Volcanic Suite, at a mean vertical velocity between 1.6 and 4 mm year−1. These findings constrain the processes responsible for the assembly and exhumation of HP continental subunits, thus adding to our understanding of how continental terranes behave during subduction.

scholarly journals Deeply subducted continental fragments – Part 1: Fracturing, dissolution–precipitation, and diffusion processes recorded by garnet textures of the central Sesia Zone (western Italian Alps)

Solid Earth ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 167-189 ◽  
Author(s):  
Francesco Giuntoli ◽  
Pierre Lanari ◽  
Martin Engi
Keyword(s):  
High Pressure ◽  
Diffusion Processes ◽  
Shear Zones ◽  
Granulite Facies ◽  
Thermodynamic Modelling ◽  
Italian Alps ◽  
Eclogite Facies ◽  
Compositional Patterns ◽  
And Diffusion ◽  
Insight Into

Abstract. Contiguous continental high-pressure terranes in orogens offer insight into deep recycling and transformation processes that occur in subduction zones. These remain poorly understood, and currently debated ideas need testing. The approach we chose is to investigate, in detail, the record in suitable rock samples that preserve textures and robust mineral assemblages that withstood overprinting during exhumation. We document complex garnet zoning in eclogitic mica schists from the Sesia Zone (western Italian Alps). These retain evidence of two orogenic cycles and provide detailed insight into resorption, growth, and diffusion processes induced by fluid pulses in high-pressure conditions. We analysed local textures and garnet compositional patterns, which turned out remarkably complex. By combining these with thermodynamic modelling, we could unravel and quantify repeated fluid–rock interaction processes. Garnet shows low-Ca porphyroclastic cores that were stable under (Permian) granulite facies conditions. The series of rims that surround these cores provide insight into the subsequent evolution: the first garnet rim that surrounds the pre-Alpine granulite facies core in one sample indicates that pre-Alpine amphibolite facies metamorphism followed the granulite facies event. In all samples documented, cores show lobate edges and preserve inner fractures, which are sealed by high-Ca garnet that reflects high-pressure Alpine conditions. These observations suggest that during early stages of subduction, before hydration of the granulites, brittle failure of garnet occurred, indicating high strain rates that may be due to seismic failure. Several Alpine rims show conspicuous textures indicative of interaction with hydrous fluid: (a) resorption-dominated textures produced lobate edges, at the expense of the outer part of the granulite core; (b) peninsulas and atoll garnet are the result of replacement reactions; and (c) spatially limited resorption and enhanced transport of elements due to the fluid phase are evident along brittle fractures and in their immediate proximity. Thermodynamic modelling shows that all of these Alpine rims formed under eclogite facies conditions. Structurally controlled samples allow these fluid–garnet interaction phenomena to be traced across a portion of the Sesia Zone, with a general decrease in fluid–garnet interaction observed towards the external, structurally lower parts of the terrane. Replacement of the Permian HT assemblages by hydrate-rich Alpine assemblages can reach nearly 100 % of the rock volume. Since we found no clear relationship between discrete deformation structures (e.g. shear zones) observed in the field and the fluid pulses that triggered the transformation to eclogite facies assemblages, we conclude that disperse fluid flow was responsible for the hydration.

scholarly journals Deeply subducted continental fragments: I. Fracturing, dissolution-precipitation and diffusion processes recorded by garnet textures of the central Sesia Zone (Western Italian Alps)

2017 ◽  
Author(s):  
Francesco Giuntoli ◽  
Pierre Lanari ◽  
Martin Engi
Keyword(s):  
High Pressure ◽  
Diffusion Processes ◽  
Outer Part ◽  
Fluid Phase ◽  
Granulite Facies ◽  
Thermodynamic Modelling ◽  
Italian Alps ◽  
Facies Metamorphism ◽  
Eclogite Facies ◽  
And Diffusion

Abstract. Complex zoning in garnet from micaschists of the Sesia Zone (Western Italian Alps) preserves evidence of two orogenic cycles and provides detailed insights into resorption, growth and diffusion processes induced by fluid pulses at high pressure. Data on local textures and mineral chemistry are combined with data derived from thermodynamic modelling to understand and quantify these processes. Garnet shows low-Ca porphyroclastic cores that are stable at (Permian) granulite facies conditions. In one sample, the first garnet rim that surrounds the pre-Alpine granulite facies core indicates that pre-Alpine amphibolite facies metamorphism followed the granulite facies event. The cores show lobate edges and preserve inner fractures, which are sealed by high pressure Alpine garnet. This observation suggests that during the first stages of subduction, before hydration of these high temperature rocks, brittle failure of the garnet occurred, implying high strain rates. Several Alpine rims show different textures indicative of interaction with hydrous fluid: (a) resorption-dominated textures produced lobate edges, at the expense of the outer part of the granulite core; (b) peninsulas and atoll garnets are produced by replacement reactions; (c) spatially limited resorption and enhanced transport of elements due the fluid phase is evident along brittle fractures and their immediate proximity. Thermodynamic modelling shows that all of these Alpine rims formed at eclogite facies conditions. Structurally controlled samples allow these fluid-garnet interaction phenomena to be traced across a portion of the Sesia Zone, with decreasing in fluid-garnet interaction toward external areas (NW). Replacement of the Permian HT assemblages by hydrate-rich Alpine assemblages can reach nearly 100%. However, no clear relationship is visible between deformation structures and fluids that triggered eclogite facies metamorphism; suggesting disperse fluid flow.

scholarly journals Harvesting the Potential of CO2 before it is Injected into Geological Reservoirs

2021 ◽  
Vol 3 (4) ◽  
pp. 1-1
Author(s):  
Tran X Phuoc ◽  
◽  
Mehrdad Massoudi ◽  
Keyword(s):  
High Pressure ◽  
Mechanical Work ◽  
Lower Pressure ◽  
Co2 Injection ◽  
Gas Temperature ◽  
Expansion Valve ◽  
Useful Power ◽  
Turbine Disks ◽  
Pressure Transport ◽  
The Cost

To store CO2 in geological reservoirs, expansion valves have been used to intentionally release supercritical CO2 from high-pressure containers at a source point to lower-pressure pipelines and transport to a selected injection site. Using expansion valves, however, has some shortcomings: (i) the fluid potential, in the form of kinetic energy and pressure which can produce mechanical work or electricity, is wasted, and (ii) due to the Joule-Thomson cooling effect, the reduction in the temperature of the released CO2 stream might be so dramatic that it can induce thermal contraction of the injection well causing fracture instability in the storage formation. To avoid these problems, it has been suggested that before injection, CO2, should be heated to a temperature slightly higher than that of the reservoir. However, heating could increase the cost of CO2 injection. This work explores the use of a Tesla Turbine, instead of an expansion valve, to harvest the potential of CO2, in the form of its pressure and kinetics, to generate mechanical work when it is released from a high-pressure container to a lower-pressure transport pipeline. The goal is to avoid throttling losses and to produce useful power because of the expansion process. In addition, due to the friction between the gas and the turbine disks, the expanded gas temperature reduction is not as dramatic as in the case when an expansion valve is used. Thus, as far as CO2 injection is concerned, the need for preheating can be minimized.

scholarly journals Assessment of Severe Accident Management for Small IPWR under an ESBO Scenario

2019 ◽  
Vol 2019 ◽  
pp. 1-10 ◽  
Author(s):  
Hao Yu ◽  
Minjun Peng
Keyword(s):  
High Pressure ◽  
Low Pressure ◽  
Lower Pressure ◽  
Severe Accident ◽  
Maximum Temperature ◽  
Pressurized Water ◽  
The Core ◽  
Severe Accidents ◽  
Accident Management ◽  
Degradation Studies

Interest in evaluation of severe accidents induced by extended station blackout (ESBO) has significantly increased after Fukushima. In this paper, the severe accident process under the high and low pressure induced by an ESBO for a small integrated pressurized water reactor (IPWR)-IP200 is simulated with the SCDAP/RELAP5 code. For both types of selected scenarios, the IP200 thermal hydraulic behavior and core meltdown are analyzed without operator actions. Core degradation studies firstly focus on the changes in the core water level and temperature. Then, the inhibition of natural circulation in the reactor pressure vessel (RPV) on core temperature rise is studied. In addition, the phenomena of core oxidation and hydrogen generation and the reaction mechanism of zirconium with the water and steam during core degradation are analyzed. The temperature distribution and time point of the core melting process are obtained. And the IP200 severe accident management guideline (SAMG) entry condition is determined. Finally, it is compared with other core degradation studies of large distributed reactors to discuss the influence of the inherent design characteristics of IP200. Furthermore, through the comparison of four sets of scenarios, the effects of the passive safety system (PSS) on the mitigation of severe accidents are evaluated. Detailed results show that, for the quantitative conclusions, the low coolant storage of IP200 makes the core degradation very fast. The duration from core oxidation to corium relocation in the lower-pressure scenario is 53% faster than that of in the high-pressure scenario. The maximum temperature of liquid corium in the lower-pressure scenario is 134 K higher than that of the high-pressure scenario. Besides, the core forms a molten pool 2.8 h earlier in the lower-pressure scenario. The hydrogen generated in the high-pressure scenario is higher when compared to the low-pressure scenario due to the slower degradation of the core. After the reactor reaches the SAMG entry conditions, the PSS input can effectively alleviate the accident and prevent the core from being damaged and melted. There is more time to alleviate the accident. This study is aimed at providing a reference to improve the existing IPWR SAMGs.

Case Study on the Effect of Mean Stress on Ground Storage Vessels for Fuelling

2019 ◽  
Author(s):  
Daniel T. Peters ◽  
Myles Parr ◽  
Matthew Naugle
Keyword(s):  
High Pressure ◽  
Natural Gas ◽  
Gas Storage ◽  
Pressure Vessels ◽  
Lower Pressure ◽  
Mean Stress ◽  
Gaseous Fuels ◽  
Design Pressure

Abstract The use of high-pressure vessels for the purpose of storing gaseous fuels for land based transportation application is becoming common. Fuels such as natural gas and hydrogen are currently being stored at high pressure for use in fueling stations. This paper will investigate the use of autofrettage in high pressure cylinders and its effects on the life of a vessel used for gas storage. Unlike many high-pressure vessels, the life is controlled by fatigue when cycled between a high pressure near the design pressure and a lower pressure due to the emptying of the content of the vessels.

Deciphering the brittle failure of eclogites at high-pressures: hydrofractures as fluid-escape pathways

2020 ◽  
Author(s):  
Michał Bukała ◽  
Károly Hidas ◽  
Carlos J. Garrido ◽  
Christopher Barnes ◽  
Iwona Klonowska ◽  
...  
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Outer Zone ◽  
Passive Margin ◽  
National Agency ◽  
Vein Formation ◽  
Iapetus Ocean ◽  
Eclogite Facies ◽  
Textural Relationship ◽  
Opening And Closing

<p>The Tsäkkok lens (northern Scandinavian Caledonides) represents the outermost part of the rifted Baltica passive margin and consists of sediments and pillow basalts of MORB affinity that were metamorphosed in eclogite facies. The Tsäkkok eclogites underwent metamorphism in a cold subduction regime (~8 °C/km) at the onset of the Iapetus Ocean closure. These rocks record pervasive high-pressure, fracturing during prograde dehydration at eclogite-facies conditions reaching up to 2.2 GPa and 590 ºC. Locally, the omphacite-dominated groundmass is transected by fractures sealed either by omphacitite or garnetite veins. Garnetite veins form a dense network that disrupt intact eclogite blocks, whereas omphacitite is found in rare, single veins. The garnetite veins are dominated by dense, poikiloblastic garnet clusters and display two chemically different zones, i.e., a high-Mn inner zone and a low-Mn outer zone. Detailed microstructural and geochemical mapping by EDS-EBSD SEM revealed that the high-Mn inner zone is disrupted and sealed by the low-Mn garnet zone. Garnets in the vein usually show little elongation and moderate intracrystalline substructure that is dominated by slightly changing misorientations without clear subgrain boundaries. By contrast, garnets of the sealed domain display an abrupt grain size reduction and anomalously high density of sharp intracrystalline misorientations in equant grains. The interstitial space between garnet grains in both of the inner and outer zones of the vein is infilled by omphacite + rutile + quartz + phengite + glaucophane.</p><p>The textural relationship between the inner- and outer zones of the garnetite vein implies syn-deformation growth of the outer zone, while the mineral assemblage attests for high-pressure conditions of the vein formation. Considering the lack of significant offset along the vein, we interpret the observed microstructures as formed during the sudden opening and closing of a brittle fracture, typical of hydrofracturing, and fast crystal growth assisted by high-pressure fluids. Presumably, these fractures constitute a fluid escape pathway during dehydration at prograde/peak conditions.</p><p>Research funded by NCN project no. 2019/33/N/ST10/01479 (M.Bukała) and no. 2014/14/E/ST10/00321 (J.Majka), as well as the The Polish National Agency for the Academic Exchange scholarship no. PPN/IWA/2018/1/00046/U/0001 given to M.Bukała.</p><p> </p>

Practical Considerations When Conducting a Transient Analysis of a Heat Exchanger Tube Rupture

2012 ◽  
Author(s):  
David R. Thornton ◽  
Robert A. Sadowski ◽  
Philip A. Henry
Keyword(s):  
High Pressure ◽  
Heat Exchanger ◽  
Transient Analysis ◽  
Low Pressure ◽  
Lower Pressure ◽  
Pressure Side ◽  
Analysis Methodology ◽  
Large Pressure ◽  
Process Plants ◽  
Shell And Tube

As part of operations, petrochemical and process plants sometimes require the exchange of heat between a high pressure fluid and a lower pressure fluid in shell-and-tube heat exchangers. In most cases, the high pressure fluid exists on the tubeside and the lower pressure is on the shellside. While rare, it is possible for a tube inside the exchanger shell to rupture suddenly, releasing the high pressure fluid into the shellside. If the pressure of the high pressure fluid exceeds the design pressure of the low pressure shell or its attached piping, it might be possible for the resulting pressure in the low pressure side to exceed permitted values. In such cases, API 521 provides guidance on assuring that sufficient pressure relief is available to limit the pressures on the heat exchanger(s)’ low pressure side. An overpressure analysis per API 521 can include both steady-state and transient analysis methods for determining that the pressures remain within acceptable levels. In situations where a large pressure differential exists between the high and low pressure sides of the exchanger, the transient, hydraulic analysis of the tube rupture event can be used as a tool to help mitigate over pressure. After briefly discussing the analysis methodology, this paper discusses some of the practical considerations and decisions that normally go into conducting the analysis.

Sign in / Sign up

Export Citation Format

Share Document