Seismicity of Sinai Peninsula, Egypt

The Sinai Peninsula has a triangular shape between the African and Arabian Plates and is bounded from the western and eastern borders by the Gulf of Suez and Gulf of Aqaba–Dead Sea rift systems, respectively. It is affected by strong and destructive earthquakes (e.g., March 31, 1969 and November 22, 1995) and moderate earthquakes (m _b?>?5) throughout its history. After the installation of the Egyptian National Seismic Network (ENSN), a great number of earthquakes has been recorded within and around Sinai. Consequently, the seismogenic source zones and seismotectonic behavior can be clearly identified. Available data, including both historical and instrumental (1900–1997), have been collected from national and international data centers. While the data from 1998 till December 2007 are gathered from ENSN bulletins. The seismogenic source zones that might affect Sinai Peninsula are defined more precisely in this work depending on the distribution of earthquakes, seismicity rate (a value), b value, and fault plane solution of the major earthquakes. In addition, the type of faults prevailed and characterized these zones. It is concluded that the Gulf of Aqaba zone–Dead Sea transform zone, Gulf of Suez rift zone, Cairo–Suez District zone, and Eastern Mediterranean dislocation zone represent the major effective zones for Sinai. Furthermore, there are two local seismic zones passing through Sinai contributing to the earthquake activities of Sinai, these are the Negev shear zone and Central Sinai fault (Themed fault) zone. The source parameters, a and b values, and the maximum expected moment magnitude have been determined for each of these zones. These results will contribute to a great extent in the seismic hazard assessment and risk mitigation studies for Sinai Peninsula to protect the developmental projects.     

Paleoclimate record in the Nubian Sandstone Aquifer,Sinai Peninsula,Egypt

Sixteen groundwater samples collected from production wells tapping Lower Cretaceous Nubian Sandstone and fractured basement aquifers in Sinai were analyzed for their stable isotopic compositions, dissolved noble gas concentrations (recharge temperatures), tritium activities, and ¹⁴C abundances. Results define two groups of samples: Group I has older ages, lower recharge temperatures, and depleted isotopic compositions (adjusted ¹⁴C model age: 24,000–31,000 yr BP; δ¹⁸O: − 9.59‰ to − 6.53‰; δ²H: − 72.9‰ to − 42.9‰; < 1 TU; and recharge T: 17.5–22.0°C) compared to Group II (adjusted ¹⁴C model age: 700–4700 yr BP; δ¹⁸O: − 5.89‰ to − 4.84‰; δ²H: − 34.5‰ to − 24.1‰; < 1 to 2.78 TU; and recharge T: 20.6–26.2°C). Group II samples have isotopic compositions similar to those of average modern rainfall, with larger d-excess values than Group I waters, and locally measurable tritium activity (up to 2.8 TU). These observations are consistent with (1) the Nubian Aquifer being largely recharged prior to and/or during the Last Glacial Maximum (represented by Group I), possibly through the intensification of paleowesterlies; and (2) continued sporadic recharge during the relatively dry and warmer interglacial period (represented by Group II) under conditions similar to those of the present.     

Geochemical and isotopic evolution of groundwater in the Wadi Watir watershed,Sinai Peninsula,Egypt

The Wadi Watir delta in the Wadi Watir watershed is a tourist area in the arid southeastern part of the Sinai Peninsula, Egypt, where development and growth of the community on the delta are constrained by the amount of groundwater that can be withdrawn sustainably. To effectively manage groundwater resources in the Wadi Watir delta, the origin of groundwater recharge, groundwater age, and changes in groundwater chemistry in the watershed needs to be understood. Mineral identification, rock chemistry, water chemistry, and the isotopes of hydrogen, oxygen, and carbon in groundwater were used to identify the sources, mixing, and ages of groundwater in the watershed and the chemical evolution of groundwater as it flows from the upland areas in the watershed to the developed areas at the Wadi Watir delta. Groundwater in the Wadi Watir watershed is primarily from recent recharge while groundwater salinity is controlled by mixing of chemically different waters and dissolution of minerals and salts in the aquifers. The El Shiekh Attia and Wadi El Ain areas in the upper Wadi Watir watershed have different recharge sources, either from recharge from other areas or from different storm events. The downgradient Main Channel area receives groundwater flow primarily from the El Shiekh Attia area. Groundwater in the Main Channel area is the primary source of groundwater supplying the aquifers of the Wadi Watir delta.     

Groundwater potentiality mapping in the Sinai Peninsula, Egypt, using remote sensing and GIS-watershed-based modeling

Systematic planning for groundwater exploration using modern techniques is essential for the proper utilization, protection and management of this vital resource. Enhanced Thematic Mapper Plus (ETM+) images, a geographic information system (GIS), a watershed modeling system (WMS) and weighted spatial probability modeling (WSPM) were integrated to identify the groundwater potential areas in the Sinai Peninsula, Egypt. Eight pertinent thematic layers were built in a GIS and assigned appropriate rankings. Layers considered were: rainfall, net groundwater recharge, lithology or infiltration, lineament density, slope, drainage density, depth to groundwater, and water quality. All these themes were assigned weights according to their relative importance to groundwater potentiality and their corresponding normalized weights were obtained based on their effectiveness factors. The groundwater potentiality map was finally produced by WSPM. This map comprises five gradational groundwater potentiality classes ranging from very high to very low. The validity of this unbiased GIS-based model was tested by correlating its results with the published hydrogeological map of Egypt and the actual borehole yields, where a concordant justification was reached. The map declared that the Sinai Peninsula is generally of moderate groundwater potentiality, where this class encompasses an area of 33,120?km² which represents 52% of its total area.     

埃及西奈半岛西南部Um Bogma地区三水铝石体与铀矿化关系

埃及西奈半岛西南部Um Bogma地区是埃及著名的金属与非金属矿产区,区内盛产锰铁矿、铜矿、铀矿、高岭石和石英砂等矿产,铀矿化与三水铝石体关系密切.通过详细的野外地质调查和室内分析鉴定,从三水铝石体和铀矿(化)体的时空分布、结构构造、矿物组成、化学成分、稀土元素及微量元素特征等方面,分析探讨了该地区三水铝石体与铀矿(化)体的内在联系,认为该地区广泛发育于石炭系Um Bogma组中的三水铝石体是红土化作用的结果,铀矿化与三水铝石体的关系十分密切,富含三水铝石、高岭石、蒙脱石等粘土矿物的三水铝石体是铀的良好聚集剂,在长期的表生风化过程中,从岩石活化淋滤出来的铀以微粒及超显微颗粒逐渐被三水铝石体所吸附而形成铀矿(化)体.     

Groundwater quality degradation as a result of overpumping in the delta Wadi El-Arish area,Sinai Peninsula,Egypt

The delta Wadi El-Arish area of the Sinai Peninsula is one of the most important parts of Egypt for industrial and agricultural expansion projects because of its relatively abundant supply of groundwater. This study focuses on the hydrogeology and hydrochemistry of the Quaternary aquifer in the delta Wadi El-Arish area and on the impacts pumping has had on groundwater quality. The objectives were to determine the relationships between groundwater pumping and water levels and water quality, to estimate the hydraulic parameters of the Quaternary aquifer, and to determine the hydrochemistry of groundwater in the Quaternary aquifer and its suitability for irrigation. The conclusions are: (1) potentiometric surface elevations have declined by an average of about 0.5 m since 1981 in response to an increase in pumping, (2) the transmissivity of the lower Pleistocene calcareous sandstone (kurkar) unit is higher than the transmissivity of the upper Pleistocene alluvium, (3) groundwater in the Pleistocene aquifer is augmented with groundwater leaking from the overlying Holocene sand dune deposits through the intervening sandy clay aquitard, (4) groundwater in the kurkar is of lower quality than groundwater in the alluvium, (5) total dissolved solids (TDS) concentrations have increased by an average of about 1500 ppm since 1962, (6) an increase in saltwater intrusion has occurred in the northern part of the study area, and (7) the irrigation suitability of groundwater pumped from wells in much of the area is limited to salt tolerant crops. Our recommendations are: (1) no new pumping wells should be drilled and no increase in pumping rates should be allowed in the delta Wadi El-Arish area, (2) reliable estimates of the quantity of groundwater recharge should be made, (3) flood irrigation systems should be replaced by either drip or sprinkler     

Controls on the formation of stratabound dolostone bodies,Hammam Faraun Fault block,Gulf of Suez

Dolomitization is commonly associated with crustal‐scale faults, but tectonic rejuvenation, diagenetic overprinting and a fluid and Mg mass‐imbalance often makes it difficult to determine the dolomitization mechanism. This study considers differential dolomitization of the Eocene Thebes Formation on the Hammam Faraun Fault block, Gulf of Suez, which has undergone a simple history of burial and exhumation as a result of rifting. Stratabound dolostone bodies occur selectively within remobilized sediments (debrites and turbidites) in the lower Thebes Formation and extend into the footwall of, and for up to 2 km away from, the Hammam Faraun Fault. They are offset by the north–south trending Gebel fault, which was active during the earliest phases of rifting, suggesting that dolomitization occurred between rift initiation (26 Ma) and rift climax (15 Ma). Geochemical data suggest that dolomitization occurred from evaporated (ca 1·43 concentration) seawater at less than ca 80°C. Geothermal convection is interpreted to have occurred as seawater was drawn down surface‐breaching faults into the Nubian sandstone aquifer, convected and discharged into the lower Thebes Formation via the Hammam Faraun Fault. Assuming a ca 10 Myr window for dolomitization, a horizontal velocity of ca 0·7 m year⁻¹ into the Thebes Formation is calculated, with fluid flux and reactivity likely to have been facilitated by fracturing. Although fluids were at least marginally hydrothermal, stratabound dolostone bodies do not contain saddle dolomite and there is no evidence of hydrobrecciation. This highlights how misleading dolostone textures can be as a proxy for the genesis and spatial distribution of such bodies in the subsurface. Overall, this study provides an excellent example of how fluid flux may occur during the earliest phases of rifting, and the importance of crustal‐scale faults on fluid flow from the onset of their growth. Furthermore, this article presents a mechanism for dolomitization from seawater that has none of the inherent mass balance problems of classical, conceptual models of hydrothermal dolomitization.     

胶东半岛洪水岚汤温泉水化学特征与成因分析

胶东半岛蕴藏着丰富的低温地热资源,以温泉为主要出露方式。洪水岚汤温泉位于胶东半岛东部威海市境内,出露在阳泉河北岸的一级阶地,出露标高为66. 83 m,水温约69℃,下伏基岩为侏罗纪二长花岗岩。为查明其水化学特征及成因,本文采用同位素水文地球化学方法进行研究。水化学成分表明:温泉水中主要阳离子为Na~+,主要阴离子为HCO_3~-、SO_4~(2-),水化学类型为HCO_3·SO_4~-Na,pH值为7. 6,总溶解性固体为610. 6 mg/L,F~-含量为4. 2 mg/L,偏硅酸含量为98. 8 mg/L。氢、氧同位素分析结果显示:温泉热水补给来源为大气降水,估算温泉热水补给高程为427～599 m,地下热储温度约为106. 25℃,地下热水循环深度约为2091 m。综合分析洪水岚汤温泉成因模式为:在正棋山山区获得大气降水入渗补给后,沿F1断裂破碎带下渗经历深循环获得大地热流加热后上升,上升过程中混入浅层地下水,在第四系静水压力最小的部位出露成泉。     

Genesis and Tectonic Implications of the Kabr El-BonayaUltramafic Rocks,Sinai Peninsula,Egypt: Constraints fromMineralogical and Geochemical Characteristics

The Kabr El-Bonaya mafic–ultramafic intrusion is exposed along the southeastern border of the Sinai Peninsula and the northernmost segment of the Arabian-Nubian Shield(ANS). It occurs as an elliptical intrusive body that is located along the major NE–SW trending fracture zones that prevail in the Kid metamorphic complex. The ultramafic rocks in the complex comprise ultramafic cumulates of peridotites(dunite, harzburgite and wehrlite) and pyroxenite. These rocks are generally unmetamorphosed and have intrusive contacts with the country rock. Mineral chemistry and whole-rock chemical compositions of these ultramafic rocks are mostly consistent with those of residual mantle peridotites from refractory suprasubduction tectonic settings. Based on the variations of the major elements, the studied ultramafic rocks are consistent with those of a supra-subduction zone mantle, as it seems to have melted at 1–2 GPa and 1300–1450°C. Linear variations of Al2 O3, CaO, V and Ni with MgO, coupled with incompatible and rare-earth-element depletion and mineral compositions,suggest prior events of partial melting in both wehrlites and harzburgites. The LREE enrichment in the harzburgite, as well as the development of Cr-rich spinel, is consistent with a history of melt–peridotite interaction. The calculated(Sm/Yb)N variations for the studied peridotites indicate a general increase in the addition of fluids with an increasing degree of melting from the wehrlite(～13–15 wt% of fluid) in the source, after initial spinel peridotite melting to the harzburgite(～20–25 wt% of fluid) in the same source, which is contrary to normal abyssal peridotites. The estimated equilibration temperature ranges from 1214 to 1321°C for the studied wehrlites and from 1297 to 1374°C for harzburgites. The Mg-rich nature of the analysed olivines from the studied ultramafic rocks(Fo = 81.41 to 91.77) reflect their primary composition and are similar to olivines in Alaskan-type ultramafic rocks. The Fo content of the analyzed olivines decrease slightly from the dunite to the harzburgite to the wehrlite and to pyroxenite, reflecting a fractional crystallization trend. The high Cr# and very low TiO2 contents(0.03–0.12 wt%) of the Cr-spinels from the studied peridotites are mostly consistent with modern highly refractory fore-arc peridotites, indicating that these peridotites developed in a supra-subduction zone environment.     

Normal faulting as a control on the stratigraphic development of shallow marine syn-rift sequences: the Nukhul and Lower Rudeis Formations, Hammam Faraun fault block, Suez Rift, Egypt

Tectono-stratigraphic analysis of the East Tanka fault zone (ETFZ), Suez Rift, indicates that the evolution of normal fault segments was an important control on syn-rift depositional patterns and sequence stratigraphy. Sedimentological and stratigraphic analysis of the Nukhul Formation indicates that it was deposited in a narrow (ca 1–2 km), elongate (ca 5 km), fault-bounded, tidally influenced embayment during the low subsidence rift-initiation phase. The Nukhul Formation is composed of transgressive (TST) and highstand (HST) systems tract couplets interpreted as reflecting fault-driven subsidence and the continuous creation of accommodation in the hangingwall to the ETFZ. The overlying Lower Rudeis Formation was deposited during the high subsidence rift-climax phase, and is composed of forced regressive systems tract (FRST) shallow marine sandbodies, and TST to HST offshore mudstones. Activity on the ETFZ led to marked spatial variability in stratal stacking patterns, systems tracts and key stratal surfaces, as footwall uplift, coupled with regressive marine erosion during deposition of FRST sandbodies, led to the removal of intervening TST–HST mudstone-dominated units, and the amalgamation of FRST sandbodies and the stratal surfaces bounding these units in the footwall. This study indicates that the evolution of normal fault segments over relatively short (i.e. <1 km) length-scales has the potential to enhance or suppress a eustatic sea-level signal, leading to marked spatial variations in stratal stacking patterns, systems tracts and key stratal surfaces. Crucially, these variations in sequence stratigraphic evolution may occur within time-equivalent stratal units, thus caution must be exercised when attempting to correlate syn-rift depositional units based solely on stratal stacking patterns. Furthermore, local, tectonically controlled variations in relative sea level can give rise to syn-rift stacking patterns which are counterintuitive in the context of the structural setting and perceived regional subsidence rates.     

A Pan-African core complex in the Sinai,Egypt

In the late Precambrian history of the Wadi Kid area in the Sinai, Egypt, two deformation phases are clearly recognized. The first phase, D₁ (pre-620 Ma), produced a steep regional foliation, axial planar to upright F₁ folds, in rocks of a lower-greenschist grade. This compressional phase of deformation is interpreted in terms of subduction in an island-arc setting. The second phase, D₁ (post-620 Ma), is mainly expressed by the widespread development of sub-horizontal mylonitic zones with a total thickness of 1.5 km. Shear sense indicators give a consistent regional transport direction to the northwest, with local indications of reversal to the southeast. This event is associated with regional LP/HT metamorphism, indicative of high thermal gradients. Because of the LP/HT metamorphism, the change in geochemical nature of the granitoids, and the orientation of the dykes, we interpret the mylonitic zones as low-angle normal shear zones related to core-complex development during an extensional event with the transport reversal being induced by doming. We postulate that orogenic collapse was responsible for the transition from the D₁ compressional phase to the D₁ extensional phase.     

Triggering upstream channel incision in the fluvial systems of the trunk valley of Wadi Watir drainage basin, South Sinai Peninsula, Egypt

Dredging the alluvial fans for repaving the international road located in the bottom of the Wadi Watir valley produced vertical cliff faces of different heights, and at different locations of the fans. The heights of the cliff faces resulted in considerable elevation differences between the surface of the dredged alluvial fans and the local base level provided by the Watir trunk valley. The principal geomorphic response to this anthropogenic intervention is triggering upstream channel incision waves at different intensities in the fluvial systems of the downstream reaches of the Watir drainage basin. The channel incision processes resulted in subsequent geomorphic adjustment scenarios that vary from widening the active channels on the surface of the dredged fans, triggering rockfalls from the adjacent hillslopes, and transporting coarse alluvial deposits from the main sediment sources of the fluvial systems, and eventually re-depositing them as sheetform gravel, channelform gravel, and new fan lobes. The major outcome of the various geomorphic adjustment processes was changing the role of the alluvial fans within the fluvial systems from buffer zones where fan aggradation was dominant into dynamic coupled zones. Being coupled zones, the dredged alluvial fans allowed high potential of mass transmission from the feeder catchment areas into the Watir trunk valley. Under such conditions, it could be stipulated that considerable changes in the morphology of landscapes are highly anticipated in response to flash flood events that intermittently occur in the Watir drainage basin.     

The effect of uniaxial compression in the behaviour of remanent and induced magnetizations for basaltic rocks from the western Sinai Peninsula, Egypt

Seventy oriented basaltic samples were collected from six sites from the Wadi Budra and Farsh El Azraq areas of the west-central part of Sinai. Rock magnetic properties such as Curie temperatures and hysteresis parameters, as well as microscopic observations, point to magnetite as the main carrier of the remanent magnetization. The stress sensitivity of basaltic rocks is relatively low. High stress produces an increase in the remanent and induced magnetizations perpendicular to the applied stress axis and a decrease parallel to it. The change of magnetization during stress action ranges from 1.1% to 3.5% for a stress of 100?bar. The differential total magnetic intensity field with time (within 2?years) was observed through 80 magnetic observation points set up on both sites of the basaltic sheet at the studied area. The observed temporal variations of magnetization can be interpreted as stress loading parallel to the regional stress field in the order of 50?±?20?bar, according to the stress sensitivity of the precursor basalt.     

Fluid-mineral equilibria in a hydrothermal system,Roosevelt hot springs,Utah

The availability of fluids and drill cuttings from the active hydrothermal system at Roosevelt Hot Springs allows a quantitative comparison between the observed and predicted alteration mineralogy, calculated from fluid-mineral equilibria relationships. Comparison of all wells and springs in the thermal area indicates a common reservoir source, and geothermometer calculations predict its temperature to be higher ($\text{288°C ± 10°}$) than the maximum measured temperature of 268°C.The composition of the deep reservoir fluid was estimated from surface well samples, allowing for steam loss, gas release, mineral precipitation and ground-water mixing in the well bore. This deep fluid is sodium chloride in character, with approximately 9700 ppm dissolved solids, a pH of 6.0, and gas partial pressures of O₂ ranging from 10^?32 to 10^?35 atm, CO₂ of 11 atm, H₂S of 0.020 atm and CH₄ of 0.001 atm.Comparison of the alteration mineralogy from producing and nonproducing wells allowed delineation of an alteration pattern characteristic of the reservoir rock. Theoretical alteration mineral assemblages in equilibrium with the deep reservoir fluid, between 150° and 300°C, in the system Na₂O-K₂O-CaO-MgO-FeO-Fe₂O₃-Al₂O₃-H₄SiO₄-H₂O-H₂S-CO₂-HCl, were calculated. Minerals theoretically in equilibrium with the calculated reservoir fluid at $\text{>240°C}$ include sericite, K-feldspar, quartz, chalcedony, hematite, magnetite and pyrite. This assemblage corresponds with observed higher-temperature ($\text{>210°C}$) alteration assemblage in the deeper parts of the producing wells. The presence of montmorillonite and mixed-layer clays with the above assemblage observed at temperatures <210°C corresponds with minerals predicted to be in equilibrium with the fluid below 240°C.Alteration minerals present in the reservoir rock that do not exhibit equilibrium with respect to the reservoir fluid include epidote, anhydrite, calcite and chlorite. These may be products of an earlier hydrothermal event, or processes such as boiling and mixing, or a result of errors in the equilibrium calculations as a result of inadequate thermochemical data.     

Tectonic evolution of kid metamorphic complex and the recognition of Najd fault system in South East Sinai,Egypt

International Journal of Earth Sciences - A low-to medium-grade metamorphic belt of a volcano-sedimentary succession occurs in the eastern side of South Sinai as a part of the northernmost...     

Geochemistry and petrogenesis of post-collisional alkaline and peralkaline granites of the Arabian-Nubian Shield: a case study from the southern tip of Sinai Peninsula,Egypt

The southern Sinai Peninsula, underlain by the northernmost extension of the Arabian-Nubian Shield, exposes post-collisional calc-alkaline and alkaline granites that represent the youngest phase of late Neoproterozoic igneous activity. We report a petrographic, mineralogical and geochemical investigation of post-collisional plutons of alkaline and, in some cases, peralkaline granite. These granites intrude metamorphosed country rocks as well as syn- and post-collisional calc-alkaline granitoids. The alkaline and peralkaline granites of the southern tip of Sinai divide into three subgroups: syenogranite, alkali feldspar granite and riebeckite granite. The rocks of these subgroups essentially consist of alkali feldspar and quartz with variable amounts of plagioclase and mafic minerals. The syenogranite and alkali feldspar granite contain small amounts of calcic amphibole and biotite, often less than 3%, while the riebeckite granite is distinguished by sodic amphibole (5–10%). These plutons have geochemical signatures typical of post-collisional A-type granites and were most likely emplaced during a transition between orogenic and anorogenic settings. The parental mafic magma may be linked to lithospheric delamination and upwelling of asthenospheric mantle material. Differentiation of the underplated basaltic magma with contributions from the juvenile crust eventually yielded the post-collisional alkaline granites. Petrogenetic modelling of the studied granitic suite shows that pure fractional crystallization cannot quantitatively explain chemical variations with the observed suite, with both major oxides and several trace elements displaying trends opposite to those required by the equilibrium phase assemblage. Instead, we show that compositional variation from syenogranite through alkali feldspar granite to riebeckite granite is dominated by mixing between a low-SiO₂ liquid as primitive or more primitive than the lowest-SiO₂ syenogranite and an evolved, high-SiO₂ liquid that might be a high-degree partial melt of lower crust.     

Carbon and oxygen isotopes in epigenetic hydrothermal rocks from Hamam-el-Farun,Sinai

Rock samples from an Eocene cliff above the thermal spring of Hamam-el-Farun (west coast of Sinai) show various degrees of dolomitization and calcitization ${}^{18}\text{O}{}^{16}\text{O}$ and ${}^{13}\text{C}{}^{12}\text{C}$ ratios indicate that dolomite and secondary calcite precipitated from hot brines.     

Opaque mineralogy and magnetic investigation of some basaltic occurrences, Sinai, Egypt

Ore microscopic investigation of the Fe?CTi oxide minerals was carried out on samples from three Oligo-Miocene basaltic occurrences from Sinai, Egypt. These occurrences are Gebel Maghara (north Sinai), Rageibet Naama (central Sinai), and Wadi Matulla (west Sinai). The results and correlations of magnetic parameters such as NRM intensity and susceptibility, coercive force H _c, and the ratio M _r/M _s, H _c and Q value, the ratio M _r/M _s, saturation magnetization M _s, and K are discussed in light of opaque mineralogical studies. It has been found that the variations in the magnetic properties of the basaltic occurrences are strongly dependent on the crystallite size and nature and style of exsolution textures and fabrics. The latter are controlled by the cooling conditions, being most sensitive to the partial pressure of oxygen in the melt.     

Geochemistry and mineral chemistry of Pan-African amphibolites of South Sinai,Egypt

In the Wadi Feiran area, amphibolites occur as inclusions, bands, linear bodies of variable thickness and irregular lenses in para-geneisses. Chemical evidence indicates that these amphibolites display an igneous origin and were derived from magma essentially of tholelitic rather than alkaline composition; transitional in character between continental and island-arc. The chemistry of amphiboles, related to pressure and temperature conditions of meta-morphism, showed that they were formed under low pressure and high temperature conditions.