Liquid-vapor Homogenization Temperatures Research Articles

High MREE-HREE solubility in a carbonatite-derived hydrothermal fluid: Evidence from fluorite-hosted fluid inclusions in the Amba Dongar carbonatite complex, India

Recent experimental works suggest that complexation with alkalis, carbonate, and hydroxyl groups enhances rare earth element (REE) transport and HREE/LREE fractionation, seen in carbonatite-hosted REE deposits. The Amba Dongar carbonatite complex in western India hosts fluorite and REE-fluorcarbonate mineralization occurring as vug/vein fillings or as disseminated ores associated with calcite, dolomite, apatite, baryte, and quartz. In this study, we analyzed the major and trace element composition of fluorite-hosted fluid inclusions, and the trace element chemistry of calcite and fluorite, using laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) to characterize the nature of the hydrothermal fluid and the processes of mineral-fluid interaction. Fluorite contains aqueous bi-phase (liquid + vapor) fluid inclusions of variable size that furnish low salinities (0.4–2.2 wt% NaCl equivalent) and liquid-vapor homogenization temperatures (130 °C–155 °C). The fluid inclusions have high concentrations of alkalis (Na, K), Si, Al, Mg, and Mn, and their chemistry resembles orthomagmatic fluid derived from evolved carbonatite melts. They also have elevated MREE and HREE concentrations relative to the LREE, that is significantly higher than in many other hydrothermal settings. Such fluids with fractionated LREE/HREE were likely derived from residual brines post the LREE-mineralization stage, when the HREE still remained in solution. This report of hydrothermal fluids with elevated MREE and HREE solubility from natural carbonatites supports experimental findings that alkali‑carbonate-hydroxyl complexation helps to mobilize REE and fractionate the LREE from MREE and HREE. Magmatic calcite has LREE-enriched REE patterns while those of hydrothermally-altered calcite is nearly flat. The secondary calcite also has elevated concentrations of Na and K, which suggests that the alkali-rich fluids scavenged the REE from magmatic calcite and redistributed them into more insoluble REE-fluorcarbonates. The REE patterns of fluorite mimic those of its fluid inclusions, with the inclusions containing higher and more variable REE concentrations, suggesting that the REE signals of fluorite are coming from the ablation of fluid inclusions, and not from fluorite themselves.

A Plea for More Skepticism Toward Fluid Inclusions: Part II. Homogenization via Halite Dissolution in Brine Inclusions from Magmatic-Hydrothermal Systems Is Commonly the Result of Postentrapment Modifications

AbstractQuartz-hosted brine inclusions that homogenize via halite dissolution occur in many magmatic-hydrothermal systems. In many cases their calculated minimum entrapment pressures are geologically unrealistically high, which has been interpreted to reflect accidental entrapment of halite crystals, and hence, to indicate halite saturation. Here it is demonstrated based on microthermometric trends and laser ablation-inductively coupled plasma-mass spectrometry analyses of fluid inclusion assemblages from eight different ore deposits that the phenomenon of inclusion homogenization via halite dissolution is commonly caused by postentrapment changes in fluid inclusion volume rather than by cotrapping of halite. Many of the investigated assemblages show highly variable liquid-vapor homogenization temperatures at relatively constant fluid salinity—a trend that cannot be produced by cotrapping of halite or by cotrapping of vapor. Furthermore, in those assemblages that do display variable fluid salinities, the elemental Cl/X concentration ratios (where X denotes any element other than Na) do not increase with increasing fluid salinity. The observed microthermometric and compositional trends are best explained by variable extents of postentrapment reduction in inclusion volume, which increased fluid density and in some cases was accompanied by H2O loss and migration of the inclusions within the host quartz. The fact that such trends can be observed even in seemingly well preserved fluid inclusion assemblages suggests that postentrapment modifications in fluid inclusion volume and H2O contents may be widespread and thus that temperature and pressure estimates from quartz-hosted fluid inclusions should generally be treated with caution. This is particularly true for samples that may have experienced deformation, such as massive quartz veins and rock-forming quartz.

PETROGRAPHIC, FLUID INCLUSION AND OXYGEN ISOTOPE CHARACTERISTICS OF RAMAND AREA, NW IRAN

Ramand mineralization area is located at a distance of about 60 km from the provincial capital of Qazvin province, Iran. The studied area is a part of the Central Iran structural zone in the southern part of Danesfahan geological map. Lithological units in Ramand area are composed of riodacite, rhyolite, tuff riodacite, crystal tuff and riodacite. The presence of clay minerals indicates argillic alteration, which is a good indicator of mineralization. This type of alteration can be detected in volcanic regions which have been severely affected by argillic alteration. Silicification is the most important evidence of precious metal potential in post magmatic environments. According to mineralogical studies, sulfide minerals in the area consist of pyrite and chalcopyrite with supergene minerals such as covellite, malachite, and Fe hydroxides. Based on phase content, the three types of inclusion in Ramand area include vapor, vapor liquid, and liquid rich inclusions. According to fluid inclusion data, the liquid vapor homogenization temperature [TH (L–V)] varied from 73 to 307 °C, and salinity ranged from 1.75 to 4.74 wt% NaCl eq. The calculated δ18O values of water in equilibrium with quartz ranged from 5.8 to 6.9 per ml. Calculated δ18O values of water in equilibrium with calcite ranged from 4.4 to 9.4 per ml. These data suggest that the ores formed most likely originated from magmatic hydrothermal sources along with some meteoric solutions during mineralization processes.

Glacial–interglacial temperature change in the tropical West Pacific: A comparison of stalagmite-based paleo-thermometers

In the tropics, geochemical records from stalagmites have so far mainly been used to qualitatively reconstruct changes in precipitation, but several new methods to reconstruct past temperatures from stalagmite material have emerged recently: i) liquid–vapor homogenization of fluid inclusion water ii) noble gas concentrations in fluid inclusion water, iii) the partitioning of oxygen isotopes between fluid inclusion water and calcite, and iv) the abundance of the 13C18O16O (‘clumped’) isotopologue in calcite. We present, for the first time, a direct comparison of these four paleo-thermometers by applying them to a fossil stalagmite covering nearly two glacial–interglacial cycles (Marine Isotope Stages (MIS) 12–9) and to two modern stalagmites, all from northern Borneo. The temperature estimates from the different methods agree in most cases within errors for both the old and recent samples; reconstructed formation temperatures of the recent samples match within 2-sigma errors with measured cave temperatures. However, slight but systematic deviations are observed between noble gas and liquid–vapor homogenization temperatures. Whereas the temperature sensitivity of fluid inclusion δ18O and clumped isotopes is currently debated, we find that the calibration of Tremaine et al. (2011) for fluid inclusion δ18O and a synthetic calcite-based clumped isotope calibration (Ziegler et al., in prep.) yield temperature estimates consistent with the other methods. All methods (with the potential exception of clumped isotopes) show excellent agreement on the amplitude of glacial–interglacial temperature change, indicating temperature shifts of 4–5 °C. This amplitude is similar to the amplitude of Mg/Ca-based regional sea surface temperature records, when correcting for sea level driven changes in cave elevation. Our reconstruction of tropical temperature evolution over the time period from 440 to 320 thousand years ago (ka) adds support to the view that climate sensitivity to varying greenhouse forcing is substantial also in the deep tropics.

Garnets in porphyry–skarn systems: A LA–ICP–MS, fluid inclusion, and stable isotope study of garnets from the Hongniu–Hongshan copper deposit, Zhongdian area, NW Yunnan Province, China

The Late Cretaceous Hongniu–Hongshan porphyry–skarn copper deposit is located in the Zhongdian area of northwestern Yunnan Province, China. Garnets from the deposit have compositions that range from Adr14Grs86 to almost pure andradite (Adr98Grs2) and display two different styles of zoning. The garnets are predominantly of magmatic-hydrothermal origin, as is evidenced by their 18Ofluid (5.4–6.9‰) and low Dfluid (−142‰ to −100‰) values, both of which likely result from late-stage magmatic open-system degassing. Three generations of garnet have been identified in this deposit: (1) Al-rich garnets (Grt I; Adr22–57Grs78–43) are anisotropic, have sector dodecahedral twinning, are slightly enriched in light rare earth elements (LREEs) compared with the heavy rare earth elements (HREEs), have negative or negligible Eu anomalies, and contain high concentrations of F. Fluid inclusions within these Al-rich garnets generally have salinities of 12–39wt.% NaCl eq. and have liquid–vapor homogenization temperatures (Th) of 272–331°C. The Grt I are most likely associated with low- to medium-salinity fluids that were generated by the contraction of an ascending vapor phase and that formed during diffusive metasomatism caused by pore fluids equilibrating with the host rocks at low W/R (water/rock) ratios. These garnets formed as a result of the high F activity of the system, which increased the solubility of Al within the magmato-hydrothermal fluids in the system. (2) Fe-rich garnets (Adr75–98Grs25–2) have trapezohedral faces, and are both anisotropic with oscillatory zoning and isotropic. These second-generation Fe-rich garnets (Grt II) have high ΣREE concentrations, are LREE-enriched and HREE-depleted, and generally have positive but variable Eu anomalies. All of the Fe-rich garnets contain high-salinity fluid inclusions with multiple daughter minerals with salinities of 33–80wt.% NaCl eq. Some of them show higher temperatures of halite dissolution (465–591°C) than liquid–vapor homogenization temperatures (319–473°C), and several Fe-rich garnets contain inclusion groups indicative of boiling. The Grt II are associated with high-temperature, hypersaline fluids that were segregated from magma at a depth of at least 5.6km and reacted with carbonates at depths shallower than 2.0km. (3) Al-rich garnet veins (Adr14–60Grs86–40) contain allotriomorphic crystals, have lower HFSE (high field strength element) and REE concentrations than the other garnets, and have HREE-enriched and LREE-depleted patterns with small Eu anomalies that are typical of the majority of garnets. The Grt III most likely formed from residual metasomatic fluids.

Determining gypsum growth temperatures using monophase fluid inclusions—Application to the giant gypsum crystals of Naica, Mexico

Determining the formation temperature of minerals using fluid inclusions is a crucial step in understanding rock-forming scenarios. Unfortunately, fluid inclusions in minerals formed at low temperature, such as gypsum, are commonly in a metastable monophase liquid state. To overcome this problem, ultra-short laser pulses can be used to induce vapor bubble nucleation, thus creating a stable two-phase fluid inclusion appropriate for subsequent measurements of the liquid-vapor homogenization temperature, T-h. In this study we evaluate the applicability of T-h data to accurately determine gypsum formation temperatures. We used fluid inclusions in synthetic gypsum crystals grown in the laboratory at different temperatures between 40 degrees C and 80 degrees C under atmospheric pressure conditions. We found an asymmetric distribution of the T-h values, which are systematically lower than the actual crystal growth temperatures, T-g; this is due to (1) the effect of surface tension on liquid-vapor homogenization, and (2) plastic deformation of the inclusion walls due to internal tensile stress occurring in the metastable state of the inclusions. Based on this understanding, we have determined growth temperatures of natural giant gypsum crystals from Naica (Mexico), yielding 47 +/- 1.5 degrees C for crystals grown in the Cave of Swords (120 m below surface) and 54.5 +/- 2 degrees C for giant crystals grown in the Cave of Crystals (290 m below surface). These results support the earlier hypothesis that the population and the size of the Naica crystals were controlled by temperature. In addition, this experimental method opens a door to determining the growth temperature of minerals forming in low-temperature environments.

A numerical model to estimate trapping conditions of fluid inclusions that homogenize by halite disappearance

Fluid inclusions (FI) that homogenize by halite disappearance are common in some geological environments, and interpretation of microthermometric data from these inclusions has been limited by the lack of a model describing the PVTX relationships over the complete range of PTX conditions found in nature. In this study, a system of equations has been developed that can be used to estimate salinity, pressure and density of FI that homogenize by halite disappearance. The salinity, pressure, density and dP/dT slope of the FI isochore are calculated as functions of liquid–vapor homogenization temperature (Th) and halite dissolution temperature (Tm). The equations are based on a numerical model describing the isochoric pressure–temperature trajectory followed by halite-saturated fluids during heating. The model is valid for Th and Tm from 100 to 600°C, and for pressures along the liquid–vapor–halite curve to 300MPa.

Synthetic Fluid Inclusions. XVII. PVTX Properties of High Salinity H2O-NaCl Solutions (>30 wt % NaCl): Application to Fluid Inclusions that Homogenize by Halite Disappearance from Porphyry Copper and Other Hydrothermal Ore Deposits

Fluid inclusions that homogenize by disappearance of the halite crystal after the vapor bubble has disappeared have been reported from a wide range of ore-forming systems. While this inclusion type is most commonly observed in porphyry copper and similar magmatichydrothermal ore deposits, they have also been reported from iron oxide copper-gold (IOCG), Mississippi Valley-type, orogenic (lode, greenstone) gold, massive sulfide, unconformity U, and mantotype deposits, as well as from non-ore associated granitoids and oceanic crust. The lack of experimental data to interpret microthermometric data from these inclusions, combined with poor petrographic characterization of inclusion origin, has led to a wide range of inferred PT trapping conditions for the inclusions. The relationship between liquid-vapor homogenization temperature (ThL-V), halite dissolution temperature (Tmhalite) and pressure has been determined using synthetic H2O-NaCl fluid inclusions that homogenize by halite disappearance. The experimental data cover the range ThL-V ≈ 150° to 500°C and Tmhalite ≈ 275° to 550°C. An empirical equation describing the relationship between pressure, ThL-V, and Tmhalite has been developed to estimate formation pressures from microthermometric data and is valid from pressures along the liquid + vapor + halite curve to 300 MPa. A detailed literature review reveals that the results of this study cannot be applied retroactively to estimate pressures of previously reported inclusions that homogenize by halite dissolution for several reasons. First, most workers have not collected and reported the data in a manner that allows one to determine if the inclusions have trapped a single, homogeneous phase and have not leaked or changed volume following trapping. Thus, it is not possible to determine if the inclusions show consistent microthermometric behavior within a group of coeval inclusions. Additionally, many published studies provide only summaries of results from numerous samples or present the data graphically, precluding application of our results to individual inclusions. However, based on our review, it appears that much of the published data for inclusions that homogenize by halite dissolution represent inclusions that have either trapped a halite crystal along with the liquid or have reequilibrated by necking and/or stretching. Results from this study have been used to estimate minimum formation pressures for inclusions from the Ditrau Alkaline Massif, Transylvania, Romania, the Musoshi stratiform copper deposit, Zaire, the Bismark skarn deposit, northern Mexico, the Naica chimneymanto deposit, Mexico, the Questa porphyry molybdenum deposit, New Mexico, and the Bingham Canyon porphyry Cu-Mo deposit, Utah. In each case, pressures estimated using results from the present study are in good agreement with previous pressure estimates. However, in some cases estimated pressures (both our estimates as well as those of other authors) appear to be unreasonably high, based on the geologic setting at the time of formation. These results highlight the currently limited understanding concerning pressures (depths) of ore formation.

Occurrences of Ore Minerals and Fluid Inclusion Study on the Kingking Porphyry Copper–Gold Deposit, Eastern Mindanao, Philippines

AbstractThe Kingking deposit is a gold‐rich porphyry copper deposit and the southernmost deposit at the eastern Mindanao mineralized belt, Philippines. It is underlain by Cretaceous–Paleogene sedimentary and volcanic rocks that are intruded by mineralized Miocene diorite porphyries and by barren Miocene–Pliocene dacite and diorite porphyries. The main alteration zones in the deposit are the inner potassic zone and the outer propylitic zone. The biotite‐bearing diorite and hornblende diorite porphyries are the primary host rocks of mineralization. Two dominant copper minerals, bornite and chalcopyrite, which usually occur as fracture fillings, are associated with fine crystalline quartz veinlet stockworks in the mineralized diorites. Minor secondary covellite, chalcocite and digenite are also observed. The primary Cu‐Fe sulfide phases initially deposited from ore fluids consisted of bornite solid solution (bnss) and intermediate solid solution (iss), which decomposed to form the bornite and chalcopyrite. Peculiar bornite pods that are different from dissemination and are associated with volcanic rock xenoliths in biotite‐bearing diorite porphyry are noted in a drill hole. These pods of bornite are not associated with quartz veinlet stockworks. Fluid inclusion analyses show three types of inclusions contained in Kingking samples: two‐phase fluid‐rich and vapor‐rich inclusions and polyphase hypersaline inclusions from porphyry‐type quartz veinlet stockworks. The liquid–vapor homogenization temperatures (TH) and the dissolution temperature of halite daughter crystals (TM) from the polyphase hypersaline inclusions predominantly range from 400°C up to >500°C. The wide range of TH and TM may be due to heterogeneous trapping of variable ratios of vapor and brine. For some inclusions, TH > TM and in some cases, TH < TM, indicating that some of the brine was supersaturated or saturated with NaCl at the time of entrapment. Calculated salinity of the polyphase hypersaline inclusions ranges from 40 to 60% NaCl equivalent. Temperature and vapor pressure of mineralized fluid were estimated to be 400°C and 16 MPa.

Primary Ore Mineral Assemblage and Fluid Inclusion Study of the Batu Hijau Porphyry Cu-Au Deposit, Sumbawa, Indonesia

Abstract. The Batu Hijau porphyry Cu-Au deposit, Sumbawa Island, Indonesia, is associated with a tonalitic intrusive complex. The temperature-pressure condition of mineralization at the Batu Hijau deposit is discussed on the basis of fluid inclusion microthermometry. Then, the initial Cu-Fe sulfide mineral assemblage is discussed. Bornite and chalcopyrite are major copper ore minerals associated with quartz veinlets. The quartz veinlets have been classified into ‘A’ veinlets associated with bornite, digenite, chalcocite and chalcopyrite, ‘B’ veinlets having chalcopyrite bornite along vuggy center-line, rare ‘C’ chalcopyrite-quartz veinlets, and late ‘D’ veinlets consisting of massive pyrite and quartz (Clode et al., 1999). Copper and gold mineralization is associated with abundant ‘A’ quartz veinlets. Abundant fluid inclusions are found in veinlet quartz consisting mainly of gas-rich inclusions and polyphase inclusions throughout the veinlet types. The hydrothermal activity occurred in temperature-pressure conditions of aqueous fluid immiscibility into hypersaline brine and dilute vapor. The halite dissolution (Tm[halite]) and liquid-vapor homogenization (Th) temperatures of the polyphase inclusions in veinlet quartz range from 270 to 472d̀C and from 280 to 454d̀C, respectively. The estimated salinity ranges from 36 to 47 wt% (NaCl equiv.). The apparent pressures lower than 300 bars are estimated to have been along the liquid-vapor-halite curve for the fluid inclusions having the Th lower than the Tm that trapped the brine saturated with halite, or at slightly higher pressure relative to liquid-vapor-halite curve for the fluid inclusions having the Th higher than the Tm that trapped the brine unsaturated with halite. The actual temperature and pressure during the hydrothermal activity at the Batu Hijau deposit are estimated to have been around 300d̀C and 50 bars. At such temperature-pressure conditions, the principal and initial Cu-Fe sulfide mineral assemblages are thought to be chalcopyrite + bornite solid solution (bnss) for the chalcopyrite-bearing assemblage, and chalcocite-digenite solid solution and bnss for the chalcopyrite-free assemblage.

Evolution of Hydrothermal System at the Dizon Porphyry Cu-Au Deposit, Zambales, Philippines

Abstract. Evolution of hydrothermal system from initial porphyry Cu mineralization to overlapping epithermal system at the Dizon porphyry Cu-Au deposit in western central Luzon, Zambales, Philippines, is documented in terms of mineral paragen-esis, fluid inclusion petrography and microthermometry, and sulfur isotope systematics. The paragenetic stages throughout the deposit are summarized as follows; 1) stockwork amethystic quartz veinlets associated with chalcopyrite, bornite, magnetite and Au enveloped by chlorite alteration overprinting biotite alteration, 2) stockwork quartz veinlets with chalcopyrite and pyrite associated with Au and chalcopyrite and pyrite stringers in sericite alteration, 3) stringer quartz veinlets associated with molybdenite in sericite alteration, and 4) WNW-trending quartz veins associated with sphalerite and galena at deeper part, while enargite and stibnite at shallower levels associated with advanced argillic alteration. Chalcopyrite and bornite associated with magnetite in quartz veinlet stockwork (stage 1) have precipitated initially as intermediate solid solution (iss) and bornite solid solution (bnss), respectively. Fluid inclusions in the stockwork veinlet quartz consist of gas-rich inclusions and polyphase inclusions. Halite in polyphase inclusions dissolves at temperatures ranging from 360dC to >500dC but liquid (brine) and gas (vapor) do not homogenize at <500dC. The maximum pressure and minimum temperature during the deposition of iss and bnss with stockwork quartz veinlets are estimated to be 460 bars and 500dC. Fluid inclusions in veinlet stockwork quartz enveloped in sericite alteration (stage 2) consist mainly of gas-rich inclusions and polyphase inclusions. In addition to the possible presence of saturated NaCl crystals at the time of entrapment of fluid inclusions that exhibit the liquid-vapor homogenization temperatures lower than the halite dissolution temperatures in some samples, wide range of temperatures of halite dissolution and liquid-vapor homogenization of polyphase inclusions from 230dC to >500dC and from 270dC to >500dC, respectively, suggests heterogeneous entrapment of gaseous vapor and hypersaline brine. The minimum pressure and temperature are estimated to be about 25 bars and 245dC. Fluid inclusions in veinlet quartz associated with molybdenite (stage 3) are dominated by gas-rich inclusions accompanied with minor liquid-rich inclusions that homogenize at temperatures between 350dC and 490dC. Fluid inclusions in vuggy veinlet quartz associated with stibnite (stage 4) consist mainly of gas-rich inclusions with subordinate polyphase inclusions that do not homogenize below 500dC. Fluid inclusions in veinlet quartz associated with galena and sphalerite (stage 4) are composed of liquid-rich two-phase inclusions, and they homogenize into liquid phase at temperatures ranging widely from 190dC to 300dC (suggesting boiling) and the salinity ranges from 1.0 wt% to 3.4 wt% NaCl equivalent. A pressure of about 15 bars is estimated for the dilute aqueous solution of 190dC from which veinlet quartz associated with galena and sphalerite precipitated. In addition to a change in temperature-pressure regime from lithostatic pressure during the deposition of iss and bnss with stockwork quartz veinlets to hydrostatic pressure during fracture-controlled quartz veinlet associated with galena and sphalerite, a decrease in pressure is supposed to have occurred due to unroofing or removal of the overlying piles during the temperature decrease in the evolution of hydrothermal system. The majority of the sulfur isotopic composition of sulfides ranges from ±0 % to +5 %. Sulfur originated from an iso-topically uniform and homogeneous source, and the mineralization occurred in a single hydrothermal system.

Fluid inclusion studies in quartz veinlets in the porphyry copper deposit at Sungun, East-Azarbaidjan, Iran

The porphyry copper deposit (PCD) at Sungun is located in East Azarbaidjan, in the NW of Iran.The Sungun porphyries occur as stocks and dikes ranging in composition from quartz monzodiorite through quartz monzonite and granodiorite to granite. The stocks are divided into two groups (1) Porphyry Stocks I and (2) Porphyry Stock II. Porphyry Stock II, hosting the copper ore, experienced intense hydro-fracturing leading to the formation of stockwork-type and anastomozing veinlets and micro-veinlets of quartz, sulfides, carbonates, and sulfates. Three distinct types of hydrothermal alteration and sulfide mineralization are recognized at Sungun (1) hypogene, (2) contact metasomatic (skarn), and (3) supergene. Four types of hypogene alteration are developed at Sungun, potassic, propylitic, potassic–phyllic, and phyllic. Four types of inclusion are common at Sungun based upon their phase content (1) mono-phase vapor, (2) vapor-rich 2-phase, (3) liquid-rich 2-phase, and (4) multi-phase solid. Halite is the principal solid phase. The distribution pattern, shape, and phase contents of fluid inclusions in quartz veinlets at Sungun are analogous to those from Bingham and Globe-Miami in western USA. The fluid inclusion data at Sungun showed that the liquid–vapor homogenization temperature [ T H(L–V)] values for liquid-rich 2-phase, vapor-rich 2-phase, and halite-bearing inclusions vary from 160 to 580 °C, from 200 to 600 °C, and from 160 to 580 °C, respectively. The ascending unboiled fluid at the onset of the phyllic alteration episode had temperatures ∼580 °C and was moderately saline (∼15 wt%). With the gradual decrease in temperature, the salinity of this fluid gradually decreased, so that its salinity at temperatures of ∼370 and <270 °C were ∼7 and <2 wt%, respectively. Multiple boiling events occurred in Porphyry Stock II during phyllic alteration. With each boiling event the salinity of the residual fluid increased substantially. The first boiling event occurred at temperatures 540–560 °C, and increased the salinity of the residual fluid up to ∼50 wt%. At temperatures >350 °C the residual fluid remained undersaturated (with respect to NaCl) however, at temperatures <350 °C they became saturated. The minimum internal pressures calculated for the inclusions having T s (NaCl)≈ T H(L–V) showed that they were developed under the maximum hydrostatic pressure head of ∼1500 m during the boiling events.

Microthermometric analysis of synthetic fluid inclusions in the hydrothermal diamond-anvil cell

The hydrothermal diamond-anvil cell (HDAC) was employed as a pressurized fluid inclusion heating stage to determine temperatures of phase transitions in synthetic fluid inclusions in quartz. Using this technique, the common problem of decrepitation or stretching of inclusions having high internal pressures was eliminated. Homogenization temperatures of pure H 2 O synthetic inclusions determined in the HDAC are inversely related to the confining pressure exerted on the sample, suggesting a decrease in inclusion volume with increasing confining pressure. The very good reproducibility and reversibility of these experiments indicate that volume changes during heating under confining pressure in the HDAC are elastic in nature. However, results of microthermometric experiments in the HDAC indicate that the change in homogenization temperature is significantly larger than would be predicted by the equations of state for quartz and water. This difference reflects an additional component of volume change related to stress within the quartz host, causing displacement of the inclusion walls into the inclusion cavity, as predicted by theoretical models describing the behavior of inclusions in minerals. Liquid-vapor homogenization temperatures [Th(L-V)] and halite dissolution temperatures (Tm halite) were determined for synthetic fluid inclusions in the ternary H 2 O-NaCl- CO 2 . The measured homogenization temperatures were regressed as a function of confining pressure at Th(L-V). The intersection of the Th(L-V)-confining pressure curve with an independently obtained P-T curve for the solvus of the same ternary composition provides the ‘‘correct’’ homogenization temperature, that is, the homogenization temperature corresponding to a confining pressure equal to the pressure on the solvus at that same temperature. This method for determining corrected Th(L-V) is based on the assumption that the effect of elastic stress on Th(L-V) approaches zero as the confining pressure approaches the internal pressure in the inclusion at homogenization. The Th(L-V) values at these intersection points were used to calculate lines of constant homogenization temperature (iso-Th lines). For a composition of H 2 O + 40 wt% NaCl + 10 mol% CO 2 , the iso-Th slopes decrease from about 53 bar/°C at Th(L-V) = 500 °C to 8.5 bar/°C for Th(L-V) = 650 °C. The halite dissolution temperature (in the presence of liquid and vapor) averages 342 °C (range ±6 °C) without recognizable pressure dependence. The slopes of iso-Th lines for a composition of H 2 O + 20 wt% NaCl + 20 mol% CO 2 decrease from approximately 23 bar/°C at Th(L-V) = 475 °C to 6 bar/°C for Th(L-V) = 600 °C. Using the HDAC technique, the high-pressure portion of the halite liquidus was redetermined for an H 2 O-NaCl solution containing 40 wt% NaCl. These new measurements confirm the data of Bodnar (1994), which were obtained using a gas-flow heating stage at 1 atm confining pressure. This indicates that Bodnar’s (1994) observation of an essentially pressure independent liquidus at pressures ≳2 kbar is real and not a result of inclusion stretching

Activation of microglia and expression of heat shock protein during kainic acid-induced hippocampal seizure in the rat

The Late Cretaceous Hongniu–Hongshan porphyry–skarn copper deposit is located in the Zhongdian area of northwestern Yunnan Province, China. Garnets from the deposit have compositions that range from Adr14Grs86 to almost pure andradite (Adr98Grs2) and display two different styles of zoning. The garnets are predominantly of magmatic-hydrothermal origin, as is evidenced by their 18Ofluid (5.4–6.9‰) and low Dfluid (−142‰ to −100‰) values, both of which likely result from late-stage magmatic open-system degassing. Three generations of garnet have been identified in this deposit: (1) Al-rich garnets (Grt I; Adr22–57Grs78–43) are anisotropic, have sector dodecahedral twinning, are slightly enriched in light rare earth elements (LREEs) compared with the heavy rare earth elements (HREEs), have negative or negligible Eu anomalies, and contain high concentrations of F. Fluid inclusions within these Al-rich garnets generally have salinities of 12–39 wt.% NaCl eq. and have liquid–vapor homogenization temperatures (Th) of 272–331 °C. The Grt I are most likely associated with low- to medium-salinity fluids that were generated by the contraction of an ascending vapor phase and that formed during diffusive metasomatism caused by pore fluids equilibrating with the host rocks at low W/R (water/rock) ratios. These garnets formed as a result of the high F activity of the system, which increased the solubility of Al within the magmato-hydrothermal fluids in the system. (2) Fe-rich garnets (Adr75–98Grs25–2) have trapezohedral faces, and are both anisotropic with oscillatory zoning and isotropic. These second-generation Fe-rich garnets (Grt II) have high ΣREE concentrations, are LREE-enriched and HREE-depleted, and generally have positive but variable Eu anomalies. All of the Fe-rich garnets contain high-salinity fluid inclusions with multiple daughter minerals with salinities of 33–80 wt.% NaCl eq. Some of them show higher temperatures of halite dissolution (465–591 °C) than liquid–vapor homogenization temperatures (319–473 °C), and several Fe-rich garnets contain inclusion groups indicative of boiling. The Grt II are associated with high-temperature, hypersaline fluids that were segregated from magma at a depth of at least 5.6 km and reacted with carbonates at depths shallower than 2.0 km. (3) Al-rich garnet veins (Adr14–60Grs86–40) contain allotriomorphic crystals, have lower HFSE (high field strength element) and REE concentrations than the other garnets, and have HREE-enriched and LREE-depleted patterns with small Eu anomalies that are typical of the majority of garnets. The Grt III most likely formed from residual metasomatic fluids.

Anisotropic thermal expansion of calcite at high pressures; an in situ X-ray diffraction study in a hydrothermal diamond-anvil cell

Lattice parameters of calcite were measured at simultaneous high pressures and temperatures up to 10 kbar and 500°C. Samples of Solnhofen limestone and distilled, deionized water were loaded in a hydrothermal diamond-anvil cell. In situ energy-dispersive X-ray diffraction was used to determine lattice parameters along five H20 isochores with densities of 1.040, 0.964, 0.760, 0.670, and 0.595 glcm3from 30 to 500°C; these densities correspond to the ice-melting temperature of -7.7 °C and the liquid-vapor homogenization temperatures 92.4,274.5, 318.9, and 344.6 °C, respectively. In addition, data along the P axis were collected by hydrostatic compression at room temperature and along the T axis by heating at atmospheric pressure. Our results show that anisotropic thermal expansion of calcite continues up to 10 kbar, therefore making it a good double internal X-ray standard. Both a and c lattice parameters are fitted to second-order polynomials of pressure, temperature, and a cross term.

Synthetic fluid inclusions: XII. The system H 2ONaCl. Experimental determination of the halite liquidus and isochores for a 40 wt% NaCl solution

The slopes of the liquidus and lines of constant liquid-vapor homogenization temperature (iso-Th) in P- T space for a 40 wt% NaCl bulk composition in the H 2O-NaCl system were determined using synthetic fluid inclusions. Inclusions were synthesized in the one-phase field at 350°–800°C and 1–6 kbar, and the temperatures of liquid-vapor homogenization and halite dissolution were determined on a heating/cooling stage. The pressure along the liquidus corresponding to a measured halite dissolution temperature [Tm (halite)] was determined from the intersection of the inclusion iso-Th line in the one-phase field with the measured Tm (halite). The P- T position of the iso-Th line in the one-phase field was determined from the measured liquid-vapor homogenization temperature [Th ( L- V)] of a given inclusion and the known experimental formation temperature and pressure for that same inclusion. The slope of the 40 wt% halite liquidus determined from synthetic fluid inclusions is −5.5°C/kbar. This value is in good agreement with an extrapolation of the data of Gunter et al. (1983) and cooling data of Koster van Groos (1991) to lower salinities, but shows considerable disagreement with the extrapolated heating data of Koster van Groos (1991). Over the salinity range 27–100 wt% NaCl, the slope of the halite liquidus predicted by the results from this study combined with data of Milne (1978), Gunter et al. (1983), and cooling data of Koster Van Groos (1991) is given by dT dP (°C/kbar) = − 38.38 + 0.90S − 0.0029S 2 , where “ S” is the salinity in wt% NaCl. Microthermometric data combined with the known temperatures and pressures of formation were used to construct lines of constant liquid-vapor homogenization temperature (iso-Th) for fluid inclusions with a salinity of 40 wt% NaCl. The slopes of the iso-Th lines for inclusions which homogenize by vapor-bubble disappearance decrease smoothly with increasing Th, from 14.1 bars/°C for inclusions which homogenize at 323°C to 5.52 bars/°C for inclusions with homogenization temperatures of 650°C. For inclusions which homogenize by halite dissolution (Th < 323°C), the slopes of the iso-Th lines within the one-phase liquid field decrease with increasing Th ( L- V) from 21.5 bars/°C (150°C) to 14.1 bars/ °C (323°C). The average slopes of the iso-Th lines within the liquid + halite field are much steeper than those in the one phase field, and decrease from 24.8 bars/°C at 150°C to 20.3 bars/°C at 300°C.

Distribution of fluid inclusions in igneous quartz of the Capitan pluton, New Mexico, USA

Fluid inclusions in granites have been used extensively in studies of magmatic-hydrothermal processes, but few studies have documented the distribution of secondary fluid inclusions within the nonmineralized main body of an intrusion. Previous work on fluid inclusions in Th-U-REE quartz/ fluorite vein deposits in the Capitan pluton suggests that these veins resulted from high-temperature, high-salinity, magmatic fluids in fractured and brecciated zones in the cooled outer carapace of the pluton. Petrographic examination of phenocryst quartz in forty-four thin sections of granite from the Capitan pluton reveals that these same fluids are found in secondary fluid inclusions. Fluid inclusions with daughter minerals commonly occur in the outer granophyre and aplite zones, but are usually absent in the porphyritic core. Microthermometric data and calculated salinities from fifty-eight fluid inclusions in phenocryst quartz and thirty-one fluid inclusions in miarolitic quartz (both samples taken from the granophyre zone) also correlate fairly well with the data from the Th-U-REE quartz/fluorite vein deposits, and similar types of fluid inclusions are found in all three occurrences of quartz. A major difference, however, is that vapor-rich inclusions, abundant as secondary inclusions in igneous phenocryst quartz, are extremely scarce in the vein quartz. Liquid-vapor homogenization temperatures of high-salinity inclusions in phenocryst quartz range from 204–509°C with an average of 384°C. Halite dissolution temperatures of high salinity inclusions range from 442–583°C with an average of 525°C. Total homogenization temperatures are not as well documented due to decrepitation of many of the high salinity inclusions before total homogenization. Samples of miarolitic quartz appear to contain more low-salinity fluid inclusions than the phenocryst quartz, but high-salinity inclusions are present as well. These observations suggest that the magmatic-hydrothermal fluids responsible for vein mineralization were not only concentrated in the vein systems, but were also widely dispersed within the outer portions of the pluton. Furthermore, the greater abundance of fluid inclusions in the outer textural zones of the pluton suggests that the interior of the pluton had not yet fully crystallized when these fluids exsolved from the magma.

Migration of orogenic fluids through the Siluro-Devonian Helderberg Group during late Paleozoic deformation: constraints on fluid sources and implications for thermal histories of sedimentary basins

Fluid inclusion data and fracture-filling cement fabrics in deformed, but non-overthrusted, carbonate and siliciclastic rocks of the Siluro-Devonian Helderberg Group, central Appalachians, indicate post-cementation, late Paleozoic migration of high pressure, high temperature fluids. Void-filling quartz and calcite cements contain secondary, two-phase fluid inclusions (liquid + vapor) which occur in annealed microfractures. Most melting temperatures (last occurrence of ice) are −20° to −25° C, which correspond to salinities of greater than 22 equivalent wt.% NaCl. Pressure-corrected liquid-vapor homogenization temperatures are 200° to 300 + °C and greatly exceed maximum paleotemperatures (≈150°C) given by conodont CAI values, vitrinite reflectance, illite crystallinity, or temperatures calculated from known sedimentary overburden. Completely cemented sandstone and limestone also have multiple crosscutting trains of secondary hydrocarbon inclusions. Hydrocarbon inclusions occur along deformation microstructures in cements. Some hydrocarbon inclusion trains crosscut cement-filled fractures. The nature of occurrence of the secondary inclusions suggests that fluids moved along intracrystalline deformation microstructures either during or after late Paleozoic deformation. Rare fractures contain transported skeletal grains, “exotic” clasts (lithologies different from wall rock), recemented clasts of fracture-filling cement, and mud. Cement clasts contain solid inclusions of mud and skeletal fragments, and indicate several episodes of particle transport, cementation, and refracturing prior to final fracture filling and cementation. These fracture fills locally crosscut stylolites. Coarse-grained, poorly sorted, “clastic fracture fills” suggest migration of rapidly moving fluids which were capable of transporting clasts through fracture conduits under deep burial conditions. Conduction calculations place upper limits on size and duration of thermal anomalies which were caused by extrabasinal fluids. These calculations indicate that hot fluid migration events most likely were short-lived. Heat transfer by extraformational fluids moving along faults and fractures may have been the mechanism by which thermal anomalies developed in the Helderberg Group. Stratigraphic constraints suggest that likely sources for the hot brines are overthrusted terranes to the east of the study area. Possible stratigraphic horizons which were sources for the overpressured, hot fluids may have been thick Cambrian shales which are important detachment horizons for major, late Paleozoic thrust sheets in the eastern Valley and Ridge province (east of the study area). Fluids may have migrated during thrusting, along thrust faults which ramp upwards from east to west into stratigraphically higher units; thrust faults ultimately die out in Devonian units. Some of the dissolved ions in the secondary two-phase inclusions may have been incorporated when shale-derived fluids moved through Silurian evaporites or Cambro-Ordovician carbonates which contain evidence of cryptic evaporites. Potential source rocks for secondary hydrocarbon inclusions may have been Lower Silurian through Lower Devonian strata, based on Lopatin modeling and assuming that migration occurred during late Paleozoic deformation. This study may help to explain many apparently anomalous geologic phenomena in deformed foreland basin sediments. It also has implications for tracking migration pathways for fluids which facilitate regional scale deformation in fold-and-thrust belts and how “tectonic fluids” may affect the rocks through which they move.

Post-metamorphic CO2-rich fluid inclusions in granulites

In granulite-facies samples from the Adirondack Mountains, NY, estimates of peak-metamorphic CO2 fugacities based on mineral equilibria are not consistent with estimates based on data for high-density, CO2-rich fluid inclusions. Of the 21 Adirondack samples investigated for this study, all contain CO2-rich inclusions. Inclusions occur in quartz, apatite, and garnet. They range in size from 3 to 50 μm and are without visible H2O. In a few of the inclusions, freezing point determinations and preliminary Laser Raman spectroscopy show the presence of small amounts (<3%) of other fluids (N2 and H2S). CO2 liquid-vapor homogenization temperatures are between −46 and +31° C, corresponding to densities between 1.14 and 0.5 gm/cc. Some of these densities are consistent with peak-metamorphic entrapment (1.06 to 1.1 gm/cc).