Calcite Dissolution in Deionized Water from 50℃ to 250℃ at I0 MPa:Rate Equation and Reaction Order

Carbonate minerals and water (or geofiuids) reactions are important for modeling of geochemical processes and have received considerable attention over the past decades. The calcite dissolution rates from 50℃ to 250℃ at 10 Mpa in deionized water with a flow rate varying from 0.2 to 5 mL/min were experimentally measured in a continuous flow column pressure vessel reactor. The dissolution began near the equilibrium with clceq > 0.3 and finally reached the equilibrium at 100℃-250℃, so the corresponding solubility was also determined as 1.87, 2.02, 2.02 and 1.88×10-4"mol/L at 100℃, 150℃, 200~C and 2500C respectively, which was first increasing and then switching to decreasing with temperature and the maximum value might occur between 150℃ and 200℃. The experimental dissolution rate not only increased with temperature, but also had a rapid increase between 150℃ and 200℃ at a constant flow rate of 4 mL/min. The measured dissolution rates can be described using rate equations of R = k(1-c/c<,eq>)<'n> or R = kc<'-n>. In these equations the reaction order n changed with temperature, which indicates that n was a variable rather than a constant, and the activation energy was 13.4 kJ/mol calculated with R = k(1-c/c<,eq>)<'n> or 18.0 kJ/mol with R = kc<'-n>, which is a little lower than the surface controlled values. The varied reaction order and lower activation energy indicates that calcite dissolution in this study is a complex interplay of diffusion controlled and surface controlled processes.     

Calcite Dissolution in Deionized Water from 50°C to 250°C at 10 MPa: Rate Equation and Reaction Order

Carbonate minerals and water （or geofluids） reactions are important for modeling of geochemical processes and have received considerable attention over the past decades. The calcite dissolution rates from 50℃ to 250℃ at 10 MPa in deionized water with a flow rate varying from 0.2 to 5 mL/min were experimentally measured in a continuous flow column pressure vessel reactor. The dissolution began near the equilibrium with c/ceq 〉 0.3 and finally reached the equilibrium at 100℃-250℃, so the corresponding solubility was also determined as 1.87, 2.02, 2.02 and 1.88×10^-4.mol/L at 100℃, 150℃, 200℃ and 250℃ respectively, which was first increasing and then switching to decreasing with temperature and the maximum value might occur between 150℃ and 200℃. The experimental dissolution rate not only increased with temperature, but also had a rapid increase between 150℃ and 200℃ at a constant flow rate of 4 mL/min. The measured dissolution rates can be described using rate equations of R = k（1-c/ceq）n or R = kc-n. In these equations the reaction order n changed with temperature, which indicates that n was a variable rather than a constant, and the activation energy was 13.4 kJ/mol calculated with R = k（1-c/ceq）n or 18.0 kJ/mol with R = kc^-n, which is a little lower than the surface controlled values. The varied reaction order and lower activation energy indicates that calcite dissolution in this study is a complex interplay of diffusion controlled and surface controlled processes.     

A simulation experimental study on oxidative kinetics of sphalerite under hypergene condition

The sphalerite oxidative kinetics under hypergene condition was simulated and studied by means of a mixed flow reactor over a pH range of 1.0 7.8,and at dissolution temperatures from 20 to 55℃,ferric ion concentrations from 1.0×10-5 to 1.0×10-2 mol/L,O 2 flux of 0.5 L/min,and oxidants of ferric ion and O 2.It is indicated that with ferric ion as oxidant,the oxidation rate of sphalerite increases with increasing ferric ion concentration,temperature and decreasing pH value,and under the studied conditions,the dissolution rates of Zn and Cd are approximately identical,with the values of activation energy being 41.75 and 42.51 kJ·mol-1,respectively,suggesting that the oxidation rate of sphalerite is controlled by chemical reactions on mineral surface.However,with O 2 as oxidant,the oxidation mechanism of sphalerite varies with pH value.Oxidation rate decreases with increasing pH value when pH is lower than 5.95,whereas the increase of pH value results in an increase in oxidation rate when pH value is higher than 7.The oxidation rate of sphalerite can be expressed as:R Zn =10 1.1663 [Fe3+] 0 0.154 ·[H+] 0.2659 ·e-41.75/RT or R Cd =10 1.7292 [Fe3+] 0 0.170 ·[H+] 0.2637 ·e-42.51/RT     

Experimental Study on Water‐rock Reactions with CO2 Fluid in a Deep Sandstone Formation under High Temperature and Pressure

Qiongdongnan Basin has a tectonic geological background of high temperature and high pressure in a deep reservoir setting,with mantle-derived CO2.A water-rock reaction device was used under high temperature and high pressure conditions,in conjunction with scanning electron microscope(SEM)observations,to carry out an experimental study of the diagenetic reaction between sandstone at depth and CO2-rich fluid,which is of great significance for revealing the dissolution of deep clastic rock reservoirs and the developmental mechanism of secondary pores,promoting deep oil and gas exploration.In this study,the experimental scheme of the water-rock reaction system was designed according to the parameters of the diagenetic background of the deep sandstone reservoir in the Qiongdongnan Basin.Three groups of single mineral samples were prepared in this experiment,including K-feldspar samples,albite samples and calcite samples.Using CO2 as a reaction solution,a series of diagenetic reaction simulation experiments were carried out in a semi-closed high temperature and high pressure simulation system.A field emission scanning electron microscope(SEM)was used to observe the microscopic appearance of the mineral samples after the water-rock reaction,the characteristics of dissolution under high temperature and high pressure,as well as the development of secondary pores.The experimental results showed that the CO2-rich fluid has an obvious dissolution effect on K-feldspar,albite and calcite under high temperature and high pressure.For the three minerals,the main temperature and pressure window for dissolution ranged from 150℃to 300℃and 45 MPa to 60 MPa.Scanning electron microscope observations revealed that the dissolution effect of K-feldspar is most obvious under conditions of 150℃and 45 MPa,in contrast to conditions of200℃and 50 MPa for albite and calcite.Through the comparative analysis of experimental conditions and procedures,a coupling effect occurred between the temperature and pressure change and the dissolution strength and calcite.Under high temperature and high pressure,pressure changed the solubility of CO2,furthermore,the dissolution effect and strength of the sandstone components were also affected.The experiment revealed that high temperature and high pressure conditions with CO2-rich fluid has a significant dissolution effect on aluminosilicate minerals and is conducive to the formation of secondary pores and effective reservoirs.Going forward with the above understanding has important implications for the promotion of deep oil and gas exploration.     

http://www.sciencedirect.com/science/article/pii/S167498711400070X

We investigated the relationships among slab geometry,obliquity,and the thermal regime associated with the subduction of oceanic plates using a three-dimensional(3D) parallelepiped thermal convection model.Various models with convex and concave slab shapes were constructed in the numerical simulation,and the temperature and mantle flow distributions were calculated.The results revealed that when the slab dip angle increases,or the obliquity of subduction becomes steeper,the interplate temperature decreases remarkably.Cooler(warmer) zones on the plate interface were identified from the modeling where there was a larger(smaller) subduction angle.Consequently,the interplate temperature distribution is partly controlled by the true subduction angle(TSA),which is a function of the slab dip angle and the obliquity of subduction.The rate of change of the interface temperature for the TSA was10-50 ℃(10°TSA 20°) at depths ranging from(TSA- 10) × 5 km to 60 +(TSA- 10) × 5 km for a flat slab after a subduction history of 7 Myrs.The along-arc slab curvature affects the variation in TSA.The slab radius also appeared to influence the radius of induced mantle flow.     

Kinetics of Hydrothermal Reactions of Minerals in Near-critical and Supercritical Water

This work presents new experimental results on the kinetics of mineral dissolution in near-critical and supercritical water in a temperature range (T) from 25 to 400℃ and a constant pressure of 23 MPa. Kinetic experiments were carried out by using a flow reactor (packed bed reactor) of an open system. The dissolution rates of albite and magnetite were measured under these experimental conditions. Na, Al and Si release rates for albite dissolution in water were measured as a function of the temperature and flow velocity in the reaction system. The maximum release rates of Na, AI and Si of albite dissolution in the hydrothermal flow systems under different flow velocities were always obtained at 300℃, that is to say, the maximum albite dissolution rates in the flow systems, regardless of different flow rates, were repeatedly measured at 300℃. Results indicate a wide fluctuation in albite dissolution rates occurring close to the critical point of water. The dissolution rates increased when the temperatu     

Hydrothermal Alteration Zoning and Kinetic Process of Mineral-Water Interactions

This study reports the kinetic experimental results of albite in water and in KCI solution at 22 MPa in the temperature range of 25 to 400℃. Kinetic experiments have been carried out in an open flow-through reaction system (packed bed reactor). Albite dissolution is always incongruent in water at most temperatures, but becomes congruent at 300℃ (close to the critical point 374℃). At temperatures from 25 to 300℃, the incongruent dissolution of albite is reflected by the fact that sodium and aluminum are easily dissolved into water; from 300 to 400℃ it is reflected by silicon being more easily dissolved in water than Al and Na. Maximum albite dissolution rates in the flow hydrothermal systems have been repeatedly observed at 300℃, independent of flow rates.The kinetic experiments of albite dissolution in a KCl aqueous solution (0.1 mol KCl) indicate that the dissolution rate of albite increases with increasing temperature. Maximum silicon release rates of albite have been observed at 400℃, while ma     

Metallogenic Mechanism of the Tianbaoshan Pb—Zn Deposit,Sichuan

The Tianbaoshan Pb-Zn deposit in Sichuan Province,exhibiting open-space-filling and /or replacement textures,occurs as being of vine style in the Sinian(Late Proterozoic) carbonate rocks,and is simple in ore composition.A systematic study of lead isotope and rareearth elements reveals that the ore-forming materials were derived from multiple sources.The ultimate source of the sulfur in all stages in seawater sulfate but the reducing mechanisms are different,The carbon was derved from marine carbonate and organic matter,The ore-forming fluid,meteoric in origin,belongs to a Ca^2 -Mg^2 -Cl^--Hco3^- type of weak acidic to alkalic solutions with a salinity of about 5wt% NaCl.The ore was formed at the depth of about 1 km from 150 to 250℃ during the main stage of ore deposition.The heated meteoric water,after extracting ore materials from wall rocks,evolved into ore-forming solution with a low salinity, in which metals were trasported as chloride complexes such as PbCl,ZnCl and ZnCl.The metal-bearing solution moved upward along deep faults to low-pressure zones,where the metal ions reacted with reduced sulfur and were precipitated as sulfied minerals.The textures of the minerals were controlled by the rate at which the reduced sulfur was supplied.     

The mechanism of surface chemical kinetics of dissolution of minerals

This paper deals with the mechanism of dissolution reaction kinetics of minerals in aqueous solution based on the theory of surface chemistry.Surface chemical catalysis would lead to an obvous decrease in active energy of dissolution reaction of minerals.The dissolution rate of minerals is controlled by suface adsorption,surface exchange reaction and desorption,depending on pH of the solution and is directly proportional to δH^n0 ,When controlled by surface adsorption,i.e.,nθ=1,the dissolution rate will decrease with increasing pH;when controlled by surface exchane reaction,i.e.,nθ=0,the dissolution rate is independent of pH;when controlled by desorption,nθis a positive decimal between 0 and 1 in acidic solution and a negative decimal between-1 and 0 in alkaline solution.Dissolution of many minerals is controlled by surface adsorption and/or surface exchange reactions under acid conditions and by desorption under alkaline conditions.     

The Thermal History of the Huangmeijian Granite Intrusion in Anhui and Its Relation to Mineralization: Isotopic Evidence

Whole-rock Rb-Sr, zircon U-Pb and hornblende, biotite and K-feldspar K-Ar ages areused to reconstruct the cooling history of the Huangmeijian intrusion in the Anqing-Lujiangquartz-syenite belt in Anhui. Oxygen isotope geothermometry of mineral pairs demonstrates thatdiffusion is a dominant factor controlling the closure of isotopic systems. Assuming the coolingof the intrusion is synchronous with a dicrease in local geothermal gradients, an emplacementdepth of about 8 km and the magma crystallization temperature of 800±50℃ are estimated. TheHuangmeijian intrusion experienced a rapid cooling process and uplifted after its emplacementand crystallization at 133 Ma B.P. with a cooling rate of 34.5℃/Ma and an uplifting rate of 0.35mm/a. The intrusion was rising until it rested at a depth of 3km at a temperature of 300±50℃about 14 Ma later. Then the intrusion was in slow cooling and uplifting with a cooling rate of4.4℃/Ma and an uplifting rate of 0.04 mm/a. U-Pb dating of pitchblende is done for the hydrothermal uranium deposit formed in thecontact zone of the Huangmeijian intrusion. The result shows that the mineralization age is closeto the closing time of the K-Ar system in biotite. The fluid inclusion thermometry indicates thatthe mineralization temperature is in agreement with the closure temperature of the biotite K-Arsystem. This suggests a close relationship between the slow cooling of the intrusion and thehydrothermal uranium mineralization process.     

Hydrothermally induced diagenesis: Evidence from shallow marine-deltaic sediments,Wilhelmøya,Svalbard

Sedimentary basins containing igneous intrusions within sedimentary reservoir units represent an important risk in petroleum exploration. The Upper Triassic to Lower Jurassic sediments at Wilhelm?ya(Svalbard) contains reservoir heterogeneity as a result of sill emplacement and represent a unique case study to better understand the effect of magmatic intrusions on the general burial diagenesis of siliciclastic sediments. Sills develop contact metamorphic aureoles by conduction as presented in many earlier studies. However, there is significant impact of localized hydrothermal circulation systems affecting reservoir sediments at considerable distance from the sill intrusions. Dolerite sill intrusions in the studied area are of limited vertical extent(～12 m thick), but created localized hydrothermal convection cells affecting sediments at considerable distance(more than five times the thickness of the sill)from the intrusions. We present evidence that the sedimentary sequence can be divided into two units:(1) the bulk poorly lithified sediment with a maximum burial temperature much lower than 60-70 ℃,and(2) thinner intervals outside the contact zone that have experienced hydrothermal temperatures(around 140 ℃). The main diagenetic alteration associated with normal burial diagenesis is minor mechanical plastic deformation of ductile grains such as mica. Mineral grain contacts show no evidence of pressure dissolution and the vitrinite reflectance suggests a maximum temperature of ～40 ℃. Contrary to this, part of the sediment, preferentially along calcite cemented flow baffles, show evidence of hydrothermal alteration. These hydrothermally altered sediment sections are characterized by recrystallized carbonate cemented intervals. Further, the hydrothermal solutions have resulted in localized sericitization(illitization) of feldspars, albitization of both K-feldspar and plagioclase and the formation of fibrous illite nucleated on kaolinite. These observations suggest hydrothermal alteration at T 120-140 ℃ at distances considerably further away than expected from sill heat dissipation by conduction only, which commonly affect sediments about twice the thickness of the sill intrusion. We propose that carbonate-cemented sections acted as flow baffles already during the hydrothermal fluid mobility and controlled the migration pathways of the buoyant hot fluids. Significant hydrothermally induced diagenetic alterations affecting the porosity and hence reservoir quality was not noted in the noncarbonate-cemented reservoir intervals.     

Thermal Behavior and Determination of the Heated Structure of 11Å Anomalous Tobermorite by in situ X-ray Diffraction

This article presents the thermal transitions of a tobermorite-bearing sample when heated from 30°C up to 1200°C,both in vacuum and in static air,including tobermorite transforming to wollastonite,aragonite to calcite and calcite to lime.Characteristics obtained by in situ high temperature X-ray diffraction,field emission scanning electron microscopy and scanning transmission electron microscopy analyses jointly indicate that the investigated tobermorite is anomalous.The variations along the a,b,c axes and the volume changes of tobermorite with increasing temperature are described,and its thermal shrinkage coefficients therefore determined.The comparison between the refined structures at 30°C and 800°C demonstrates that the shrinkage degree (Δa/a_0) along the a axis is higher than those (Δb/b_0,Δc/c_0) along the b and c axes.The wollastonite is formed in two ways:Tobermorite converting to wollastonite and lime reacting with quartz to form wollastonite.     

Diagenesis and Fluid Flow History in Sandstones of the Upper Permian Black Jack Formation, Gunnedah Basin, Eastern Australia

The fluid flow history during diagenesis of sandstones in the Upper Permian Black Jack Formation of the Gunnedah Basin has been investigated through integrated petrographic observations, fluid inclusion investigations and stable isotope analyses. The early precipitation of mixed-layer illite/smectite, siderite, calcite, ankerite and kaolin proceeded at the presence of Late Permian connate meteoric waters at temperatures of up to 60℃. These evolved connate pore waters were also parental to quartz, which formed at temperatures of up to 87℃. The phase of maximum burial was characterized by development of filamentous illite and late calcite at temperatures of up to -90℃. Subsequent uplifting and cooling led to deep meteoric influx from surface, which in turn resulted in dissolution of labile grains and carbonate cements, and formation of second generation of kaolin. Dawsonite was the last diagenetic mineral precipitated and its formation is genetically related to deep-seated mamagtic sourced CO2.     

Macro‐and Microstructural,Textural Fabrics and Deformation Mechanism of Calcite Mylonites from Xar Moron‐Changchun Dextral Shear Zone,Northeast China

The calcite mylonites in the Xar Moron-Changchun shear zone show a significance dextral shearing characteristics. The asymmetric(σ-structure) calcite/quartz grains or aggregates, asymmetry of calcite c-axes fabric diagrams and the oblique foliation of recrystallized calcite grains correspond to a top-to-E shearing. Mineral deformation behaviors, twin morphology, C-axis EBSD fabrics, and quartz grain size-frequency diagrams demonstrate that the ductile shear zone was developed under conditions of greenschist facies, with the range of deformation temperatures from 200 to 300°C. These subgrains of host grains and surrounding recrystallized grains, strong undulose extinction, and slightly curved grain boundaries are probably results of intracrystalline deformation and dynamic recrystallization implying that the deformation took place within the dislocation-creep regime at shallow crustal levels. The calculated paleo-strain rates are between 10~(–7.87)s~(–1) and 10~(–11.49)s~(–1) with differential stresses of 32.63–63.94 MPa lying at the higher bound of typical strain rates in shear zones at crustal levels, and may indicate a relatively rapid deformation. The S-L-calcite tectonites have undergone a component of uplift which led to subhorizontal lifting in an already non-coaxial compressional deformation regime with a bulk pure shear-dominated general shear. This E-W large-scale dextral strike-slip movement is a consequence of the eastward extrusion of the Xing'an-Mongolian Orogenic Belt, and results from far-field forces associated with Late Triassic convergence domains after the final closure of the Paleo-Asian Ocean.     

Research for time-temperature equivalence effect of rock (I):Theory research

In order to know about the rheological properties of rock in a long range of the time scale,method of increasing temperature was brought forward to accelerate the rheological process of rock,which could extend the time scale of experimental test data.Firstly,based on the generalized linear viscoelastic constitutive equation with temperature variable,the creep behavior of rock was divided into three types according to the different strain dependences of the time,that is,Hookean deformation,Newtonian flow,and retarded elasticity.Then the general equivalence relationship between time parameter and temperature parameter was derived for each type of strain.Finally,the relation between time parameter and temperature parameter in the whole creep was considered and the general theory of time-temperature equivalence effect(TTEE) of rock was established.This research reveals: ①The temperature effect on the instantaneous strain could be modified through vertical shift.②The key point of the TTEE of Newtonian flow depends on whether in the study of linear viscoelastic behavior of rock change of temperature is completely equivalent to a shift of the logarithmic time scale or not.③By plotting the results of a creep experiment performed at different temperatures and comparing the curves obtained,one can decide whether the rock considered have TTEE.④The TTEE of the whole creep should satisfy that the horizontal shift function of Newtonian flow and retarded elasticity is consentaneous.     

Zonal Metamorphic Complex in the Tongulack Mountain Ridge, Altai, Russia, and Explanation of Its Origin with the Help of Thermal Modelling

A moderate pressure / high temperature zonal metamorphic complex in the Tongulack Mountain Ridge, Altai, Russia, is described, and the applicability of the models of magmatic intrusion and fluid flow to explanation of its origin discussed. The Precambrian complex was formed at 500-700℃ and 3.0-5.5 kbars; it is a linear, 25-30 km wide, thermal anticline with a curved axis showing symmetric metamorphic zoning. The metamorphism was isochemical by its nature, as is corroborated by the chemical compositions of the rocks. Four zones can be recognized within the metamorphic complex: chloritic (on the peripheries), cordieritic, sillimanitic and staurolite-out (in the centre). The zones are separated by successive isograds: cordierite, staurolite-in or sillimanite and staurolite-out. It is argued that the origin of the metamorphic zoning can be explained best by a combined fluid-magmatic model; conductive heat flow from the intrusion predominated considerably over the fluid flux in heat transfer: the fluid flow     

Diagenetic Evolution and Formation Mechanisms of High-Quality Reservoirs under Multiple Diagenetic Environmental Constraints: An Example from the Paleogene Beach-Bar Sandstone Reservoirs in the Dongying Depression, Bohai Bay Basin

The diagenetic environment, diagenetic responses, diagenetic transformation model and formation mechanisms of high-quality reservoirs (beach-bar sandstones of the Paleogene fourth member) in the Dongying depression were studied through the analysis of fluid inclusions, thin section and burial evolution history. The diagenetic fluids of the beach-bar sandstone reservoirs evolved from early high salinity and weak alkalinity to low salinity and strong acidity, late high salinity and strong alkalinity and late low salinity and acidity, which were accompanied by two stages of oil and gas filling. The fluids at the margins of the sandbodies were continuously highly saline and strongly alkaline. The western (eastern) reservoirs experienced early open (closed), middle open, and late closed diagenetic environments during their burial history. The flow pattern was characterized by upwelling during the majority of the diagenesis (in the east, a non-circulating pattern transitioned into an upwelling current). Due to the evolution of the diagenetic fluids, the diagenetic sequence of the beach-bar reservoirs was as follows: early weak carbonate cementation; feldspar and carbonate cement dissolution and authigenic quartz cementation; late carbonate and anhydrite cementation, authigenic feldspar cementation, and late quartz dissolution; and late carbonate cementation, feldspar dissolution, and authigenic quartz cementation. The diagenetic strength during these stages varied or was absent altogether in different parts of the reservoirs. Due to the closeness of the diagenetic environment and the flow pattern of the diagenetic fluids, the diagenetic products are variably distributed in the sandstones interbedded with mudstones and in the fault blocks. The evolution of multiple alternating alkaline and acidic diagenetic environments controlled the distribution patterns of the reservoir diagenesis and reservoir space, and the reservoir quality index, RQI, increased gradually from the margins to the centers of the sandstones. The closeness of the diagenetic environment and the flow patterns of the diagenetic fluids controlled the differences in the reservoir properties among the fault blocks. With increasing distance from the oil-source faults, the RQI values in the west gradually decreased and in the east initially increased and then decreased.     

http://www.sciencedirect.com/science/article/pii/S1674987111000387

Fluid flow is an integral part of hydrothermal mineralization,and its analysis and characterization constitute an important part of a mineralization model.The hydrodynamic study of mineralization deals with analyzing the driving forces,fluid pressure regimes,fluid flow rate and direction,and their relationships with localization of mineralization.This paper reviews the principles and methods of hydrodynamic studies of mineralization,and discusses their significance and limitations for ore deposit studies and mineral exploration. The driving forces of fluid flow may be related to fluid overpressure,topographic relief,tectonic deformation, and fluid density change due to heating or salinity variation,depending on specific geologic environments and mineralization processes.The study methods may be classified into three types,megascopic(field) observations, microscopic analyses,and numerical modeling.Megascopic features indicative of significantly overpressured (especially lithostatic or supralithostatic) fluid systems include horizontal veins,sand injection dikes,and hydraulic breccias.Microscopic studies,especially microthermometry of fluid inclusions and combined stress analysis and microthermometry of fluid inclusion planes(FIPs) can provide important information about fluid temperature,pressure,and fluid-structural relationships,thus constraining fluid flow models.Numerical modeling can be carried out to solve partial differential equations governing fluid flow, heat transfer,rock deformation and chemical reactions,in order to simulate the distribution of fluid pressure, temperature,fluid flow rate and direction,and mineral precipitation or dissolution in 2D or 3D space and through time.The results of hydrodynamic studies of mineralization can enhance our understanding of the formation processes of hydrothermal deposits,and can be used directly or indirectly in mineral exploration.     

Tectono–Thermal Evolution, Hydrocarbon Filling and Accumulation Phases of the Hari Sag, in the Yingen–Ejinaqi Basin, Inner Mongolia, Northern China

This work restored the erosion thickness of the top surface of each Cretaceous formations penetrated by the typical well in the Hari sag, and simulated the subsidence burial history of this well with software BasinMod. It is firstly pointed out that the tectonic subsidence evolution of the Hari sag since the Cretaceous can be divided into four phases: initial subsidence phase, rapid subsidence phase,uplift and erosion phase, and stable slow subsidence phase. A detailed reconstruction of the tectonothermal evolution and hydrocarbon generation histories of typical well was undertaken using the EASY R_0% model, which is constrained by vitrinite reflectance(R_0) and homogenization temperatures of fluid inclusions. In the rapid subsidence phase, the peak period of hydrocarbon generation was reached at c.a.105.59 Ma with the increasing thermal evolution degree. A concomitant rapid increase in paleotemperatures occurred and reached a maximum geothermal gradient of about 43-45℃/km. The main hydrocarbon generation period ensued around 105.59-80.00 Ma and the greatest buried depth of the Hari sag was reached at c.a. 80.00 Ma, when the maximum paleo-temperature was over 180℃.Subsequently, the sag entered an uplift and erosion phase followed by a stable slow subsidence phase during which the temperature gradient, thermal evolution, and hydrocarbon generation decreased gradually. The hydrocarbon accumulation period was discussed based on homogenization temperatures of inclusions and it is believed that two periods of rapid hydrocarbon accumulation events occurred during the Cretaceous rapid subsidence phase. The first accumulation period observed in the Bayingebi Formation(K_1 b) occurred primarily around 105.59-103.50 Ma with temperatures of 125-150℃. The second accumulation period observed in the Suhongtu Formation(K_1 s) occurred primarily around84.00-80.00 Ma with temperatures of 120-130℃. The second is the major accumulation period, and the accumulation mainly occurred in the Late Cretaceous. The hydrocarbon accumulation process was comprehensively controlled by tectono-thermal evolution and hydrocarbon generation history. During the rapid subsidence phase, the paleo temperature and geothermal gradient increased rapidly and resulted in increasing thermal evolution extending into the peak period of hydrocarbon generation,which is the key reason for hydrocarbon filling and accumulation.     

Efficiency of a re-usable Carius tube for determination of platinum group elements in ultramafic rocks

Digestion with aqua regia in Carius tube is commonly employed for determination of PGEs in geological samples. However, silicates cannot be completely dissolved by aqua regia and PGEs might partially remain in silicate residue. In this study, an ultramafic reference material was used to investigate the efficiencies of a new re-usable Carius tube after digestion at 220 and 240℃, and an autoclave-lined Carius tube at 260 and 280℃. The results show that about 10% of PGEs retained in the silicate residues at 220 and 5% still r℃ emains even digestion temperature increases to 280℃. These results agree with previous works that increasing the digestion pressure and temperature can achieve more effective dissolution. Thus, a modified digestion procedure for determination of PGEs in ultramafic rocks by the re-usable Carius tube was proposed in this study.