Kőzetdeformáció mechanikai és geokémiai folyamatok határán üledékes medencékben: Rock deformation at the interaction of mechanical and geochemical processes in sedimentary basins

Attesting deformation, natural fractures and faults are pervasive in low-porosity rocks in sedimentary basins. In the diagenetic realm fractures in rocks locally affect the flow of hot, reactive fluids and rock strength. Hot fluids cause dissolution, cement precipitation, and other chemical reactions, which can profoundly modify where fracture porosity, and as a consequence, connectivity exists. Although fractures may form in different settings at different locations, and at different times throughout a basin evolution history, they can potentially show similar patterns and geometric attributes, such as their position relative to bedding, shapes, aperture sizes, and cement infill types and textures. The similarity of patterns and geometric shapes impedes interpretation of intrinsically limited subsurface fracture data. Cement infills and textures, fluid inclusions trapped within, and cement isotopic compositions, on the other hand, can provide powerful evidence useful for unraveling the origin and timing of fracture formation. This presentation offers a glimpse into how geochemical analysis of fracture cements is revolutionizing fracture description and interpretation, and shows how the complexity of cement deposits are the key to unlocking the otherwise difficult-to-interpret simple patterns and geometric shapes of opening-mode fractures

Mezozóos alkáli magmatizmus a Kárpát régióban: a Ditrói Alkáli Masszívum petrogenezise = Mesozoic alkaline magmatism in Carpathian region: petrogenesis of the Ditró Alkaline Massif

A Ditrói Alkáli Masszívum a Keleti-Kárpátok központi kristályos kőzettömegébe nyomult be, és ezekkel a metamorf kőzetekkel együtt vett részt az alpi tektonikai eseményekben. Szerkezetileg a Bukovinai takaróhoz tartozik, annak négy prekambriumi, kora paleozóos litológiai egységével érintkezik. A terepi (térképezési), petrográfiai, geokémiai, izotóp-geokémiai, cirkonmorfológiai, fluidzárvány és mikrotermometriai, raman spektroszkópiai valamint kormeghatározási vizsgálatok és adatok alapján a Ditrói Alkáli Masszívum kialakulása egy kontinentális autonom magmás aktivizációhoz köthető. A magmatizmus a kontinentális kéreg kialakulása utáni, az intruzó a platform alapzatát átszelő mélytörések mentén alakult ki. Ez a magmatizmus sokféle alkáli (miaszkitos) kőzetegyüttest produkált. A Tarnica Komplexum Kőzetei (peridotitok, gabbrók), a nefelinszienitek és gránitok közel azonos időben keletkezett, komagmás kőzetek. Ez a magmás tevékenység a középső-triász extenziós tektonikai környezetben, a dél-európai passzív kontinentális szegélyen, köpenyeredetű magma felemelkedésével indult. A Bukovinai-Géta mikrokontinensnek az európai platformtól a jurában történő elszakadásával, a Civcin - Severin riftrendszer mentén egy újabb, köpeny eredetű, intrúzió jött létre. Az így keletkezett szienitek az első magmás folyamat kogenetikus kőzeteivel keveredve egy sor hibrid kőzetet eredményeztek (dioritok, monzonitok). | The formation of the Ditró Alkaline Massif can be related to continental magmatic activation. The process started in the Middle Triassic at the Southern passive edge of the European continent in an extensional tectonic environment by the uplift of mantle origin magma, producing various types of petrologic associations. The rocks of the Tarnica Complex (nepheline syenites and granites) are comagmatic as they were formed almost simultaneously. By the Jurassic detachment of the Bukovina-Géta microcontinent from the European platform a new, mantle origin intrusion developed. The mixing of syenites of this formation with the rocks of the first magmatic phase resulted various hybrid rocks

Fracture, Dissolution, and Cementation Events in Ordovician Carbonate Reservoirs, Tarim Basin, NW China

Ordovician carbonate rocks of the Yijianfang Formation in the Tabei Uplift, Tarim Basin, contain deeply buried (>6000 m), highly productive oil and gas reservoirs associated with large cavities (>10 m). Previous workers inferred that large cavities are paleocaves (paleokarst) formed near the surface and subsequently buried. Alternately, caves may have formed by dissolution at depth along faults. Using 227 samples from 16 cores, we document textures and cement compositions bearing on cavity histories with petrographic, high-resolution scanning electron microscopy (SEM), isotopic, and fluid inclusion microthermometric observations. Results show that dissolution occurred at depth and was caused by (1) acidic fluids derived from Middle-Late Silurian and/or Devonian-Permian hydrocarbon generation and maturation, (2) high-temperature fluids, of which some were associated with Late Permian igneous activity, and (3) Mg-rich fluids that accompanied Jurassic-Cretaceous deformation and the formation of partially open fractures and stylobreccias (fault breccias). The relative paragenetic sequence of the structure-related diagenesis suggests seven stages of fracturing, dissolution, and cementation. Mottle fabrics in the Yijianfang Formation contain argillaceous carbonate-rich silt and are bioturbation features formed within the marine environment. Those mottled fabrics differ from clearly karstic features in the overlying Lianglitage Formation, which formed by near-surface dissolution and subsequent infilling of cavities by allochthonous sediment. Mottle fabrics are crosscut by compacted fractures filled with phreatic-vadose marine cements and followed by subsequent generations of cement-filled fractures and vugs indicating that some fractures and vugs became cement filled prior to later dissolution events. Calcite cements in fractures and vugs show progressively depleted values of δ18O documenting cement precipitation within the shallow (~220 m), intermediate (~625 m), and deep (~2000 m) diagenetic environments. Deep (mesogenetic) dissolution associated with fractures is therefore the principal source of the high porosity-permeability in the reservoir, consistent with other pieces of evidence for cavities localized near faults