ALBERT

Beschreibung: The Amik Basin is an asymmetrical composite transtensional basin developed between the seismically active left-lateral Dead Sea Fault (DSF) splays and the left-lateral oblique-slip Karasu Fault segment during neotectonic period. The relationship between the DSF and the East Anatolian Fault Zone is important as it represents a triple junction between Arabian Plate, African Plate and Anatolian Block in which the Amik Basin developed. The basin was formed on a pre-Miocene basement consisting of two rock series: Paleozoic crustal units with a Mesozoic allochthonous ophiolitic complex and ~1300 m thick Upper Miocene-Lower Pliocene sedimentary sequence. Plio-Quaternary sediments and Quaternary volcanics unconformably overlie the deformed and folded Miocene beds. Quaternary alkali-basaltic volcanism, derived from a metasomatized asthenospheric or lithospheric mantle, is most probably related to the syn-collisional transtensional strike-slip deformation in the area. Active faults in the region have the potential to generate catastrophic earthquakes (M〉7). Nineteen samples of cold and thermal groundwaters have been collected over the Amik Basin area for dissolved gas analyses as well as two samples from the gas seeps, and one bubbling gas from a thermal spring Samples were analysed for their chemical and isotopic (He, C) composition. On the basis of their chemical composition, three main groups can be recognized. Most of the dissolved gases (16; Group I) collected from springs or shallow wells (〈 150 m depth), contain mainly atmospheric gasses with very limited H2 (〈 80 ppm) and CH4 (1– 2700 ppm) contents and minor concentrations of CO2 (0.5–11.2 %). The isotopic composition of Total Dissolved Carbon evidences a prevailing organic contribution with possible dissolution of carbonate rocks. However the CO2-richest sample shows a small but significant deep (probably mantle) contribution which is also evidenced by its He isotopic composition. Further three samples, taken from the northern part of the basin close to Quaternary volcanic outcrops and main tectonic structures, also exhibit a small mantle He contribution (Fig. 1). The two dissolved gases (Group II) collected from deep boreholes (〉 1200 m depth) are typical of hydrocarbon reservoirs being very rich in CH4 (〉 78 %) and N2 (〉 13%). The water composition of these samples is also distinctive of saline connate waters (Cl- and B-rich, SO4-poor). Isotopic composition of methane (δ13C ~ -65‰) indicates a biogenic origin while He-isotopic composition points to a prevailing crustal signature for one (R/Ra 0.16) of the sites and a small mantle contribution for the other (R/Ra 0.98) (Fig. 1). The three free gas samples (Group III), taken at two sites within the ophiolitic basement west of the basin, have the typical composition of gas generated by low temperature serpentinisation processes with high hydrogen (37–50 %) and methane (10–61 %) concentrations. While all three gases show an almost identical δD-H2 of ~ -750‰, two of them display an isotopic composition of methane (δ13C ~ -5‰; δD ~ -105‰) and a C1/[C2+C3] ratio (~100) typical of abiogenic hydrocarbons and a significant contribution of mantle-type helium (R/Ra: 1.33). The composition of these two gasses is comparable to that of the gasses issuing in similar geologic conditions (Chimera-Turkey, Zambales-Philippine and Oman ophiolites). The gas composition of the other site evidences a contribution of a crustal (thermogenic) component (δ13C-CH4 ~ -30‰; δD-CH4 ~ -325‰; C1/[C2+C3] ~ 3000). Such crustal contribution is also supported by higher N2 contents (40% instead of 2%) and lower He-isotopic composition (R/Ra 0.07) (Fig. 1). These first results highlight contributions of mantle-derived volatiles possibly drained towards shallow levels by the DSF and other parallel structures crossing the basin showing a tectonic control of the fluids circulating within the Basin .

Beschreibung: Published

Beschreibung: Patras, Greece

Beschreibung: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Beschreibung: open

Beschreibung: The study area is a 130 km long fast spreading graben in Central Greece bordered by active faults. Its complex geodynamical setting includes the presence at depth of a subduction slab responsible for the recent (Quaternary) volcanic activity in the area which possibly represents the northward continuation of the South Aegean active volcanic arc. To the area belongs also the western termination of the North-Anatolian fault a tectonic lineament of regional importance. The high geothermal gradient of the area is evidenced by the presence of many thermal springs with temperatures from 19 to 82 °C, issuing along the normal faults bordering the graben. In the period 2004-2012 more than 60 gas and water samples have been collected and their chemical and isotopic analysis revealed a wide range of compositions. Going from west to east the gas composition changes (Fig. 1) from CH4- to CO2-dominated passing through mixed N2-CH4 and N2-CO2 compositions, while at the same time the He isotopic composition goes from typical crustal values (0.02 R/Ra) up to 0.87 R/Ra (corrected for air contamination), showing in the easternmost sites a small but significant mantle input (up to ~ 10%). Isotopic composition of CH4-C indicates a thermogenic origin for the CH4-rich samples (δ13C from -50 to -37 ‰) and hydrothermal origin for the remaining samples (〉 -25‰). Positive δ15N values (around +2 ‰) indicate a contribution of crustal derived nitrogen for the N2-rich samples. The most pristine values of δ13C(CO2) refer to the most CO2-rich samples. These values (~ -3 ‰) point to a mixed mantle-marine carbonate source. Lower δ13C values (-10 ÷ -5 ‰) of the other sites can be explained by loss of CO2 due to dissolution processes. Also temperature and salinity of the waters shows differences along the graben increasing from west to east (Fig. 2). Two main groups can be separated on the basis of the total dissolved salts (TDS). The first, represented by dilute waters (TDS 〈 500 mg/l), is found in the westernmost sites characterised by the presence of CH4-rich and mixed N2-CH4 gases. The remaining waters display higher salinities (TDS from 9 to 35 g/l) due to the mixing with high salinity waters. The water composition can be explained by mixing of two end-members, one with low salinity of meteoric origin and the other with high salinity of marine origin. The mixing can be evidenced in Fig. 2. Low salinity waters show low chloride contents and their light water isotope composition overlaps the field of the cold groundwaters of the area confirming their meteoric origin. High salinity waters are aligned along the mixing line between the cold groundwaters and the seawater confirming the contribution of marine component. Most of the water compositions in the triangular graph of Giggenbach fall in the field of the non equilibrated waters being therefore unsuitable for geothermometric estimations. Only the easternmost sites (Gialtra, Ilion and Edipsos) falling the field of the partially equilibrated waters yield estimated temperatures in the range 150-170 °C. Silica geothermometers confirm these estimations. This study revealed that the complex geodynamic setting of the area is clearly reflected in the wide compositional range of the gases collected in the area that evidence contributions from different end-members (atmosphere, crust, mantle and hydrothermal systems). Water chemistry can be explained mainly from the mixing of a meteoric low-salinity end-member with a high-salinity marine end-member partially modified by hydrothermal water-rock interactions. The highest estimated temperatures in the hydrothermal reservoirs are in the range 150-170 °C.

Beschreibung: Published

Beschreibung: Patras, Greece

Beschreibung: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Beschreibung: open

Beschreibung: Etna volcano, Italy, hosts one of the major groundwater systems of the island of Sicily. Waters circulate within highly permeable fractured, mainly hawaiitic, volcanic rocks. Aquifers are limited downwards by the underlying impermeable sedimentary terrains. Thickness of the volcanic rocks generally does not exceed some 300 m, preventing the waters to reach great depths. This is faced by short travel times (years to tens of years) and low thermalisation of the Etnean groundwaters. Measured temperatures are, in fact, generally lower than 25 °C. But the huge annual meteoric recharge (about 0.97 kmˆ3) with a high actual infiltration coefficient (0.75) implies a great underground circulation. During their travel from the summit area to the periphery of the volcano, waters acquire magmatic heat together with volcanic gases and solutes through water-rock interaction processes. In the last 20 years the Etnean aquifers has been extensively studied. Their waters were analysed for dissolved major, minor and trace element, O, H, C, S, B, Sr and He isotopes, and dissolved gas composition. These data have been published in several articles. Here, after a summary of the obtained results, the estimation of the magmatic heat flux through the aquifer will be discussed. To calculate heat uptake during subsurface circulation, for each sampling point (spring, well or drainage gallery) the following data have been considered: flow rate, water temperature, and oxygen isotopic composition. The latter was used to calculate the mean recharge altitude through the measured local isotopic lapse rate. Mean recharge temperatures, weighted for rain amount throughout the year, were obtained from the local weather station network. Calculations were made for a representative number of sampling points (216) including all major issues and corresponding to a total water flow of about 0.315 kmˆ3/a, which is 40% of the effective meteoric recharge. Results gave a total energy output of about 140 MW/a the half of which is ascribable to only 13 sampling points. These correspond to the highest flow drainage galleries with fluxes ranging from 50 to 1000 l/s and wells with pumping rates from 70 to 250 l/s. Geographical distribution indicates that, like magmatic gas leakage, heat flow is influenced by structural features of the volcanic edifice. The major heat discharge through groundwater are all tightly connected either to the major regional tectonic systems or to the major volcanic rift zones along which the most important flank eruptions take place. But rift zones are much more important for heat upraise due to the frequent dikes injection than for gas escape because generally when dikes have been emplaced the structure is no more permeable to gases because it becomes sealed by the cooling magma.

Beschreibung: Published

Beschreibung: Vienna, Austria

Beschreibung: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive

Beschreibung: open