Showing papers on "Petrography published in 2022"

An olivine cumulate outcrop on the floor of Jezero crater, Mars

Abstract: The geological units on the floor of Jezero crater, Mars, are part of a wider regional stratigraphy of olivine-rich rocks, which extends well beyond the crater. We investigated the petrology of olivine and carbonate-bearing rocks of the Séítah formation in the floor of Jezero. Using multispectral images and x-ray fluorescence data, acquired by the Perseverance rover, we performed a petrographic analysis of the Bastide and Brac outcrops within this unit. We found that these outcrops are composed of igneous rock, moderately altered by aqueous fluid. The igneous rocks are mainly made of coarse-grained olivine, similar to some martian meteorites. We interpret them as an olivine cumulate, formed by settling and enrichment of olivine through multistage cooling of a thick magma body. Description Igneous rocks in Jezero crater The Perseverance rover landed in Jezero crater on Mars in February 2021. Farley et al. describe the geologic units investigated by the rover as it began to traverse the crater floor, based on images and spectroscopy. The authors found that the rocks are of igneous origin, later modified by reactions with liquid water. They also describe the collection of drilled samples for potential return to Earth by another spacecraft. Liu et al. present compositional data for these igneous rocks based on x-ray fluorescence measurements. They found similarities with some Martian meteorites and conclude that the igneous rocks formed from crystals that sank in a thick sheet of magma. Together, these studies constrain the history of Jezero crater and provide geological context for analysis of the drill samples. —KTS X-ray fluorescence measurements of rocks on the floor of Jezero crater on Mars show that they formed from a thick magma.

Rapid response petrology for the opening eruptive phase of the 2021 Cumbre Vieja eruption, La Palma, Canary Islands

Abstract: How and why magmatic systems reactivate and evolve is a critical question for monitoring and hazard mitigation efforts during initial response and ongoing volcanic crisis management. Here we report the first integrated petrological results and interpretation provided to monitoring authorities during the ongoing eruption of Cumbre Vieja, La Palma, Canary Islands, Spain. The first eruptive products comprised simultaneous Strombolian fountain-fed lava flows and tephra fall from near-continuous eruption plumes. From combined field, petrographic and geochemical analyses conducted in the 10 days following sample collection, we infer low percentage mantle melts with a variably equilibrated multimineralic crystal-cargo and compositional fractionation by winnowing during eruptive processes. Hence ‘rapid response’ petrology can untangle complex magmatic and volcanic processes for this eruption, which combined with further study and methodological improvement can increasingly assist in active decision making.

Relationship of Mineralogical Composition to Thermal Expansion, Spectral Reflectance, and Physico-Mechanical Aspects of Commercial Ornamental Granitic Rocks

Abstract: The aim of the present study is to link the thermal expansion, spectral reflectance, and physico-mechanical aspects of different types of commercial granitic rocks with their mineralogical and chemical composition. The granitic rock types were characterized using several analyses, including petrography, chemical, mineralogical, and thermo-gravimetrical analysis using XRF, XRD, and TG/DTG/DSC techniques. The rock types were subjected to several performance tests, such as tests of their thermal expansion, spectral reflectance, and physico-mechanical properties. The results revealed that quartz, albite, and potash feldspar with minor amounts of mica (biotite/muscovite/annite) are the main mineralogical constitutes, in addition to some alteration minerals, such as kaolinite, saussorite, and prehnite. The studied granitic rocks were classified as monzogranite/syenogranite of high K-calc-alkaline and peraluminous characters and are related to late- to post-collisional settings. The thermogravimetrical analysis revealed that the overall mass loss over the whole temperature range up to 978 °C did not exceed 3% of the initial weight for all studied rocks. The results of thermal expansion revealed that the maximum change in linear thermal expansion for all rock types did not exceed 0.015% of their initial lengths at an unusual air temperature of 50 °C. The spectral analysis revealed that iron and hydroxyl ions are the main spectral absorption features that appeared in the VIS-NIR and SWIR regions, in addition to the appearance of the common and distinctive absorption peaks of the main mineral composition. Furthermore, the spectral reflectance demonstrated that the granitic rock types of low iron oxide content achieved a high reflectivity percent in the VIS-NIR and SWIR spectral regions compared with those of high iron content. As a general trend, the granitic rock types of high iron content and/or lower quartz content exhibited a high performance regarding their physical and mechanical properties, such as water absorption, apparent porosity, bulk density, compressive strength, and abrasion resistance. The results of water absorption, density, strength, and abrasion resistance of the studied granitic rocks are in the range of 0.14–0.31%, 2582–2644 kg/m3, 77.85–222.75 MPa, and 26.27–55.91 Ha, respectively, conforming to the requirements of ornamental stones according to the ASTM standard.

Petrography and Provenance of the Sub-Himalayan Kuldana Formation: Implications for Tectonic Setting and Palaeoclimatic Conditions

Abstract: In this paper, the depositional environment, age, and tectonic context of the Sub-Himalayan Kuldana Formation are discussed in detail. To determine the Kuldana Formation’s depositional environment, age, and tectonic setting, sedimentological, palaeontological, and petrographic investigations have been conducted accordingly. The Kuldana Formation lithologically consists of both siliciclastic and carbonate rocks. Petrographically, the Kuldana Formation’s sandstone is divided into litharenite and feldspathic litharenite petrofacies. The sandstone plots on the QtFL and QmFLt suggest that the sandstone of the Kuldana Formation derived from a recycled orogen provenance field that developed during the collision of the Indian and Eurasian plates in the Lesser and Higher Himalayas. The plots in the diamond diagram further demonstrate that the detritus of the Kuldana Formation was derived from low and middle-to-upper rank metamorphic rocks of the Himalayas. Throughout the deposition of sandstone, paleo-climate conditions were semi-humid to semiarid. Dolostone and limestone are the two main types of carbonate rocks found in the Kuldana Formation. According to Dunham’s Classification, the Kuldana Formation limestone is classified as mudstone, wackstone, and packstone. These petrofacies suggest that the limestone was deposited in an inner-outer ramp setting. The bioclasts include bivalves, brachiopods, crinoid, gastropods, Globigerinoides spp, Lockhartia pustulosa, miliolids, Nummulites atacicus, Nummulites discorbina, Nummulites mamillatus, Nummulites djodjokartae, Nummulites vascus, and ostracods suggesting that the age of Kuldana Formation is Middle Eocene- early Oligocene. The Kuldana Formation was deposited during the initial stages of the Himalayan Orogeny as a result of the Ceno-Tethys Ocean’s regression and transgression, as revealed by a succession of siliciclastic and non-clastic rocks.

Hydrocarbon prospectivity of the miocene-pliocene clastic reservoirs, Northern Taranaki basin, New Zealand: integration of petrographic and geophysical studies

Abstract: Abstract In this study, it is aimed to characterize the Early pliocene sandstone (EP-SD) and the Late Miocene-Early Pliocene Mangaa sandstone reservoirs and the efficiency of their sealing cap rocks using the petrographical and petrophysical data of these sandstone zones in northern Taranaki basin, New Zealand. The prospective potential reservoirs were studied using impregnated thin sections, XRD data analysis, and well log data (self-potential, gamma-ray, sonic, density, neutron, shallow\deep resistivity and PEF) to characterize the reservoir zones, in addition to Mercury intrusion capillary pressure data (MICP) to check the efficiency of some potential seals. The EP-SD and the Mangaa sandstone units are typically poorly consolidated very fine sandstone to siltstone, with porosities averaging 25%. The sands are composed of quartz (38.3–57.4%), with common feldspars (9.9–15.2% plagioclase, and 2.7–6.3% K-feldspars) and up to 31.8% mica. In Albacore-1 well to the north of the Taranaki Basin, the Mangaa formation includes three separate for each of the EP-SD zones (EP-SD1, EP-SD2, and EP-SD3), and the Mangaa sequence (Mangaa-0, Mangaa-1, and Mangaa-2). The thin section studies indicate that, the studied samples are grouped into greywackes, arenites and siltstone microfacies with much lithic fragments and feldspars, sometimes with glauconite pellets. From the XRD data, it is achieved that the mineral composition is dominated by quartz, mica/illite, feldspars, and chlorite. The petrophysical investigation revealed absence of pay zones in the EP-SD zones, and presence of thin pay zone with net thickness 5.79 m and hydrocarbon saturation of about 25.6%. The effective porosities vary between 23.6 and 27.7%, while the shale volume lies between 12.3 and 16.9%. Although the shale content is relatively low, the relatively high API (50–112 API of average 75 API) is contributed by the relatively high K-feldspar content and intercalations with thin siltstone and muddy siltstone beds. Sealing units include the intra-formational seals within the Mangaa sequence, mudstones and fine grained units overlying the Mangaa and further intra-formational mudstones, within the shallower EP-SD units. The efficiency of these seals indicates the capability to trap 16.4–40.6 m gas or 17.4–43.0 m oil which is relatively low in correlation with their efficiency in the central parts of the Taranaki Basin Overlying the primary seals, mudstones of the Giant Foresets Formation provide additional regional seal.

830-million-year-old microorganisms in primary fluid inclusions in halite

Abstract: Primary fluid inclusions in bedded halite from the 830-m.y.-old Browne Formation of central Australia contain organic solids and liquids, as documented with transmitted light and ultraviolet–visible (UV-vis) petrography. These objects are consistent in size, shape, and fluorescent response with cells of prokaryotes and eukaryotes and with organic compounds. This discovery shows that microorganisms from saline depositional environments can remain well preserved in halite for hundreds of millions of years and can be detected in situ with optical methods alone. This study has implications for the search for life in both terrestrial and extraterrestrial chemical sedimentary rocks.

Extensive recrystallization of Cenozoic dolomite during shallow burial: A case study from the Palaeocene–Eocene Umm er Radhuma formation and a global meta‐analysis

Abstract: Recrystallization of dolomite can alter textural, mineralogical and geochemical attributes used to infer environmental conditions of initial dolomitization. A meta‐analysis of the published literature shows that extensive recrystallization is most common in old and deeply buried dolomites, but data from the Palaeocene–Eocene Umm er Radhuma Formation in Qatar show that this can also happen in geologically young carbonates that have never been deeply buried. Evidence of extensive recrystallization comes from a principal component analysis of published mineralogical and geochemical data that are integrated with new clumped isotope (∆47) measurements and cathodoluminescence petrography. The observations indicate that dolomite stoichiometry and cation ordering correlate with dolomite texture and depth: shallow mimetic dolomites are less stoichiometric and poorly‐ordered whereas coarser and deeper planar‐e and planar‐s to nonplanar dolomites with mottled cathodoluminescence signatures are more stoichiometric and well‐ordered, suggesting they have recrystallized. Dolomite δ18O data (Vienna Pee Dee Belemnite) also covary with texture, as mimetic dolomites have the narrowest range (−0.45‰ to +0.38‰), planar‐e dolomites are generally ≤0‰ (−2.4‰ to +0.68‰) and planar‐s to nonplanar dolomites exhibit the widest range (−2.3‰ to +1.4‰). The principal component analysis results indicate one component with positive loadings for dolomite stoichiometry (+0.752) and cation ordering (+0.813), and negative loading for δ18O (−0.833), trends predicted in recrystallized dolomites. The ∆47‐derived temperatures (32 to 46°C) and δ18Ow (+0.18 to +2.6‰ Vienna Standard Mean Ocean Water) reflect recrystallization by warm, slightly evaporated seawater at shallow depths. In the context of a meta‐analysis of recrystallized dolomites in the literature, this study implies that extensive dolomite recrystallization in Cenozoic dolomites and shallow‐burial conditions is an under‐appreciated phenomenon. The results of this study also demonstrate that initial petrological attributes can be significantly altered after dolomitization, hindering interpretations of past seawater chemistry and environmental conditions of dolomitization.

Processes Associated with Multiphase Dolomitization and Other Related Diagenetic Events in the Jurassic Samana Suk Formation, Himalayan Foreland Basin, NW Pakistan

Abstract: Foreland fold and thrust belts always represent a complex diagenetic history of carbonate succession, particularly multiphase dolomitization, due to the multi-sourcing nature of fluids affecting syn-to post-depositional successions. The present work documents a comprehensive study on the diagenetic changes, particularly dolomitization patterns in the Jurassic carbonates (Samana Suk Fm) in the Lesser Himalayan fold and thrust belt, NW Pakistan. To better understand the processes involved, integrated field/petrographic, geochemical, isotopic, and micro-thermometric studies were carried out. Field observations indicate that dolostones appear as light grey to brown stratabound and patchy units within the formation. Petrographic analysis reveals that fabric destructive matrix dolomite (RD-I) and fabric preserving replacive dolomite (RD-II) phases are present as distinct units. In addition, saddle dolomite cement (SD) and fracture-filling calcite (CC) are also observed in association with replacive dolomite cement. Geochemical analysis (EPMA) showed that Fe, Mn, and Ba concentrations in matrix dolomite are relatively less than those of replacive/saddle dolomite and fracture-filling calcite, suggesting a hydrothermal source of replacive/saddle dolomite in reducing conditions. Furthermore, stable isotope studies of RD-I showed non-depleted δ18O values, which represent coeval seawater signatures of Jurassic carbonates. RD shows depleted δ18O values and non-depleted δ13C, respectively, indicating burial or elevated temperature of dolomitization. Fracture-filled calcite represents lighter δ18O values and δ13C, indicative of relatively high temperatures. 87Sr/86Sr ratios of all diagenetic phases range from 0.707718 to 0.710747, showing more radiogenic values indicates interaction fluids with more radiogenic sources. Fluid inclusion micro-thermometry data of saddle dolomite shows TH ranging from 102.8 to 186 ̊C, and salinity ranging from 11.7 to 19.4 eq. wt.% NaCl, suggesting hot saline brines are responsible for the dolomitization. Fracture-filling calcite shows TH ranging from 68.0 to 98.4 °C and salinity ranging from 6.9 to 13.1 eq. wt.%. NaCl suggests moderately hot and saline solutions are responsible for their formation. In conclusion, the above-mentioned studies indicate two distinct processes of dolomitization are involved in the formation of matrix and replacive/saddle-type dolomites. RD-I has formed in the evaporative setting, whereas RD has formed due to the interaction of hydrothermal fluids during burial. Fracture-filling calcite is produced from hot subsurface solutions during uplift related to the Himalayan orogeny.

Implementation of Petrographical and Aeromagnetic Data to Determine Depth and Structural Trend of Homrit Waggat Area, Central Eastern Desert, Egypt

Abstract: In the current study, we conducted petrographic investigation combined with aeromagnetic data in order to classify variable granitic rocks, delineate structural trends and deduce depth of the basement rocks cropping out in Homrit Waggat area, Central Eastern Desert, Egypt. Field and petrographic investigations revealed that the granitic Homrit Waggat rocks include two groups. The first group includes the older granitic rocks, comprising tonalites and granodiorites. In contrast, the second one includes younger granitic rocks, involving alkali-feldspar granites, syenogranites and albitized granites. Depth as well as subsurface structures can be identified using magnetic method. Two tectonic maps representing the deep-seated and the shallow-seated structural features were constructed to show the structural history of the study area. The major tectonic trends indicate that the regional structures are controlled by deeper structures which have NW–SE, NNE–SSW—NE–SW and N–S directions. On the other hand, we find that the local structure trends are controlled by the local shallow structures that have NNE–SSW, NNW–SSE, ESE–WNW and N–S directions. Depth levels of the economic rare metal-bearing rocks range from 0 km to 1.2 km (Euler deconvolution technique) and from 0 km to 2.3 km (the analytical signal profiles) by using the aeromagnetic data, reflecting large resources of rare metal-bearing rocks.

Petrography and geochemistry of the Middle Jurassic Fort Member Sandstone, Jaisalmer Formation, Western India: Implications for weathering, provenance, and tectonic setting

Abstract: Detrital mineralogy, major oxides, trace, and rare earth elements (REE) were examined in the Middle Jurassic Fort Member Sandstone (FMS) of the Jaisalmer Formation in Western India to understand palaeoweathering, provenance of sediments, and to decipher the tectonic setting. The sandstones are classified as arkose to sub‐litharenite types according to their relative percentages of quartz, feldspar, and lithic fragments, and major elemental ratios. The values of Chemical Index of Alteration (67–85), Plagioclase Index of Alteration (78–97) and Chemical Index of Weathering (83–97) along with A‐CN‐K diagram suggest moderate to intense chemical weathering in the source region. Presence of fresh feldspars and dominance of monocrystalline quartz, showing both parallel and undulose extinction, indicate plutonic and volcanic felsic igneous provenance. Contribution from metamorphic orogen sources is indicated by the lithic fragment population. Various geochemical parameters such as Th/Sc, Cr/Th, Ti/Zr, and Eu/Eu* support a dominant felsic provenance. Higher Zr/Sc ratios relative to the magmatic Zr/Sc‐Th/Sc trend, higher Zr and Hf concentrations in the FMS indicate some extent of sedimentary recycling and zircon sorting. LREE enrichment, flat HREE pattern, negative Eu anomaly and trace element ratios, in conjunction with palaeocurrent data, indicate a likely sediment contribution from basement source terrains including Erinpura‐Mount Abu‐Sirohi granites, Malani Igneous Suite, and Aravalli‐Delhi orogens. The major and trace element tectonic setting discrimination diagrams for the FMS indicate a passive margin setting.

Mineral Composition and Grain Size Effects on the Fracture and Acoustic Emission (AE) Characteristics of Rocks Under Compressive and Tensile Stress

Abstract: Abstract The influence of rock mineral composition and mineral grain size on basic rock strength performance and AE characteristics have been studied, 13 different rocks microstructures are analyzed in an optical microscope thin section using petrographic image analysis, making it possible to determine the mineral composition and mineral texture characteristics of rocks. Then, the basic strength parameters of rock and AE signals generated during fracture propagation were obtained by UCT (uniaxial compression test) and BIT (Brazilian intension test). Finally, the relationship between basic strength parameters and AE characteristics of rock with mineral composition and grain size was analyzed. The results showed that different mineral constituents have significant effects on rock strength. The positive influence of plagioclase content on igneous strength was obtained. Sedimentary rocks strength increases initially and then decreases with the increase of plagioclase content. Besides, with the increase in quartz and K-feldspar content, the strength of the rock was weakened obviously. It is also found that the greater the dimensional deviation of mineral grain, the greater the strength of the rock. The strength of igneous rocks was inversely proportional to the mineral grain size, but there is no correlation between the sedimentary rocks strength and the mineral grain size. Furthermore, the tension–shear crack propagation of rock can effectively distinguish by judging that the data set of the AF–RA density graph was nearby the AF axis or RA axis and the peak frequency data sets of below 100 kHz or more than. Alterations in the rock nature are the main key reasons for the differences between AE hit rate, AE count rate, AE energy, and cumulative energy. The plagioclase content and grain size play a decisive role in AE signal characteristics and failure mode.