Ankerite

About: Ankerite is a research topic. Over the lifetime, 859 publications have been published within this topic receiving 23960 citations.

Open versus closed mesogenetic systems in Cretaceous fluvial and tidal sandstones, Sirt Basin, Libya

Abstract: This study constrains factors controlling the distribution of diagenetic alteration and their impact on reservoir quality of the Cretaceous sandstones from the Al- Bayda Platform, located in the southern Sirt Basin (Libya). These factors include the presence of early cements as well as the influx of hot basinal brines. The studied samples come from two blocks in the Khalifa Field, which are dislocated by a major normal fault. The deep-burial (mesogenetic) alteration includes the partial to pervasive replacement of early (eogenetic) dolomite and calcite cements by ferroan-dolomite, ankerite and siderite, precipitation of grain-coating chlorite, and cementation by quartz overgrowths, barite and anhydrite, particularly in the downthrown block. The association of quartz overgrowths with barite suggests that deep burial was influenced by the influx of hot basinal brines through faults. Conversely, deep-burial alteration in braided fluvial deposits of the Nubian sandstones of the upthrown block include: illitization of eogenetic smectite, quartz cementation and formation of chlorite. This study shows that deep burial of the studied sandstones did not occur in a closed system, but was affected by the influx of hot basinal brines through faults, which formed during basin rifting. This interpretation is supported by the relatively high homogenization temperatures (100–110°C; corrected to 110–125°C) of primary fluid inclusions within quartz overgrowths, which exceed the maximum burial temperatures experienced by the Cretaceous succession, and by the high salinity of these inclusions.

Experimental Modeling of Silicate and Carbonate Sulfidation under Lithospheric Mantle P,T-Parameters

Abstract: Interactions of mantle silicates with subducted carbonates, sulfides, and sulfur-rich fluids are experimentally simulated in the olivine-ankerite-sulfur and olivine-ankerite-pyrite systems using a multi-anvil high-pressure split-sphere apparatus at 6.3 GPa and range of 1050–1550 °C. Recrystallization of Fe,Ni-bearing olivine and ankerite in a sulfur melt was found to be accompanied by sulfidation of olivine and carbonate, involving partial extraction of metals, carbon, and oxygen into the melt, followed by the formation of pyrite (±pyrrhotite), diopside, and Fe-free carbonates. The main features of metasomatic alteration of Fe,Ni-olivine by a reduced sulfur fluid include: (i) a zonal structure of crystals (Fe-rich core, Mg-rich rim); (ii) inclusions of pyrite and pyrrhotite in olivine; (iii) certain Raman spectral characteristics of olivine. At T > 1350 °C, two immiscible melts, a predominantly sulfur melt with dissolved components (or a Fe–Ni–S–O melt) and a predominantly carbonate one, are generated. The redox interaction of these melts leads to the formation of metastable graphite (1350–1550 °C) and diamond growth (1550 °C). The studied olivine-ankerite-sulfur and olivine-ankerite-pyrite interactions may be considered as the basis for simulation of metasomatic processes accompanied by the formation of mantle sulfides during subduction of crustal material to the silicate mantle.

Petrology, Geochemistry and Stable Isotope Studies of Carbonate-Rich Dyke-Like Bodies, Chhaktalao Area, Madhya Pradesh

Abstract: Carbonate-rich rocks occur as E-W trending dyke-like bodies in the Deccan 'basalts at Chhaktalao area in the lower Narmada valley and show a structurally controlled mode of emplacement. Modal composition shows calcite as the dominent mineral (∼90%). Ankerite, apatite, altered olivine, augite and opaques account for the remaining percentage. Geochemically, these rocks show high CaO (>50%) with low SiO 2 , TiO 2 , FeO* and K 2 O. Trace element concentrations are low compared to average carbonatites. Stable isotope studies show that δ 13 C(-1.74‰ to -2.8‰) and δ 18 O(+12.75‰ to +13.35‰) values do not compare with those of "primary igneous carbonatites" eventhough they fall within the wide range of "igneous carbonatites". These rocks can be considered only as carbonate-rich rocks and not as true carbonatites.

Diagenesis of Dawsonite-bearing Tuffite in Beier Sag,Hailar Basin

Abstract: The dawsonite-bearing pyroclastic rock from Damoguaihe-Yimin Formation in Beier Sag of Hailar Basin was taken as the research objectPolarization microscope,Scanning Electron Microscope,Energy Disperse Spectroscope,alizarin red-S staining,Cathode Luminescence and X-ray Diffractomer are used in this research to study its rock type,types of authigenic minerals and paragenetic sequencesIt is ascertained that the host rock type of dawsonite is tuffite and carbonates are the main authigenic mineral such as dawsonite,ankerite and sideriteContent of dawsonite is up to 25%The paragenetic sequence is shown as sideriteⅠ→ kaolinite,overgrowth quartz → dawsonite → microcrystalline quartz → calcite → ankerite → sidriteⅡ→ bitumenDawsonite is characterized by replacing feldspar,quartz,debris and kaolinite matrix,which is different from pore-filling dawsonite found in other field,implicating that these mass in tuffite could provide origin of metal ions,and reacting with diagenetic fluid under the participation of CO2 which results in precipitation of dawsoniteLarge amount of carbonates(15%~44%) developed proves that pyroclastic rock owns a relatively well capacity of CO2 fixation