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Plutonic rocks typically have negligible matrix porosity and permeability. However, fractures and mineral alterations create storage space and flow pathways that turn plutonic rocks into fluid reservoirs. Despite significant hydrocarbon discoveries, naturally fractured reservoirs in plutonic rocks have been poorly studied. In most Colombian basins, the crystalline basement has undergone multiple deformational events and is thrust over the Cretaceous to Cenozoic source and reservoir rocks of the conventional petroleum system. This structural configuration is ideal for the migration of oil into a fractured basement. A multiscale fracture analysis, including field, petrographical and petrophysical techniques was conducted on the Permian and Jurassic plutonic basement of Upper Magdalena Basin in order to understand the controls on brittle deformation, the development of fracture networks and their potential to form hydrocarbon reservoirs. The results indicate that protolith textures and structures, including magmatic and mylonitic foliation, favours fracturing. Dykes exhibit higher fracture density (7–48 fractures/m), porosity (mean = 0.4%) and permeability (mean = 125,818.75 mD) than the host rock (2–25 fractures/m; 0.23%; 12,066.09 mD). Intersection zones from regional faults, are characterized by the highest fracture and lineament intensity. Our results suggest that dyke swarms and interacting damage zones can significantly enhance the reservoir quality of plutonic rocks by providing storage in fractures and fluid pathways to the host rock. [ABSTRACT FROM AUTHOR]

Apatite has been recognized as a robust tool for the study of magmatic volatiles in terrestrial and extraterrestrial systems due to its ability to incorporate various volatile components and its common occurrence in igneous rocks. Most previous studies have utilized apatite to study individual magmatic systems or regions. However, volatile systematics in terrestrial magmatic apatite formed under different geological environments has been poorly understood. In this study, we filtered a large compilation of data for apatite in terrestrial igneous rocks (n > 20,000), categorized the data according to tectonic settings, rock types, and bulk-rock compositions, and conducted statistical analyses of the F–Cl–OH–S–CO2 contents (~ 11,000 data for halogen and less for other volatiles). We find that apatite from volcanic arcs preserves a high Cl signature in comparison to other tectonic settings and the median Cl contents differ between arcs. Apatite in various types and compositions of igneous rocks shows overlapping F–Cl–OH compositions and features in some rock groups. Specifically, apatite in kimberlite is characterized as Cl-poor, whereas apatite in plutonic rocks can contain higher F and lower Cl contents than the volcanic counterparts. Calculation using existing partitioning models indicates that apatite with a high OH (or F) content does not necessarily indicate a H2O-rich (or H2O-poor) liquid because it could be a result of high (or low) magma temperature. Our work may provide a new perspective on the use of apatite to investigate volatile behavior in magma genesis and evolution across tectonic settings, volatile recycling at subduction zones, and the volcanic-plutonic connection. [ABSTRACT FROM AUTHOR]

Late Precambrian–Early Paleozoic igneous rocks constitute volumetrically minor components of the Iranian Plateau but preserve important information about the magmatic and tectonic history of the northern Gondwana margin. The Chadormalu intrusions are part of Central Iran, which includes Late Precambrian–Early Paleozoic continental crust that is now embedded in the Alpine-Himalayan orogenic system. New zircon U-Pb and Sr-Nd-Pb isotope data and whole-rock geochemical analyses are presented on gabbroic to granitic rocks of the Chadormalu district to constrain the magmatic history of the Cadomian orogeny in a disrupted fragment of the northern Gondwana margin. The geochemical data identify I-type calc-alkaline magmatism with typical continental-arc features. The laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb zircon ages range from 531.1 ± 1.6 Ma to 539.8 ± 2.2 Ma, consistent with previous data on the Cadomian basement of Central Iran, and document Early Cambrian subduction and extension along northern Gondwana. Whole rock Sr-Nd isotope data for gabbro (ɛNdi= 0.4; i stands for initial; t = 533 Ma) and granites (ɛNdi= -3.6 to -3.0; t = 531–539 Ma) along with radiogenic Pb isotope data attest to melting of older continental crust triggered by mantle melts. The subduction regime was followed by slab retreat ± delamination in an extensional environment which allowed Ediacaran-early Cambrian flare up of magmatism along the northern Gondwana margin at a regional scale. [ABSTRACT FROM AUTHOR]

The intrusive body in the south of Vineh, located in the north of Karaj city, is one of the several late Eocene plutons that intruded into the volcano-sedimentary Karaj Formation in the south of Central Alborz. This intrusive body comprises monzogabbro, monzodiorite, monzonite, and syenite with an alkaline shoshonitic nature and geochemically is cogenetic, evolved through fractional crystallization. The rocks are medium to coarse-grained with a dominant hypidiomorphic granular texture and consist of plagioclase, olivine, clinopyroxene, amphibole, orthoclase, and quartz. Titanite, apatite, biotite, and opaque occur as accessory minerals, whereas, epidote, chlorite, calcite, and iddingsite as secondary minerals. Geochemical data such as LREE enrichment relative to HREE, Pb positive anomaly, and depletion of Nb, Ta, Zr, Ti, as well as major, minor, and trace element data indicate that primary magma of these rocks formed in an active continental margin under the influence of Neo-Thetys subduction components beneath Central Iranian microplate. Alternatively, based on tectonic discrimination diagrams, the study of plutonic rocks is mainly attributed to the post-collision tectonic regime. Therefore, it seems that the magma originated from a low degree of partial melting (3 to 5 percent) of phlogopite-spinel peridotite source at a depth of about 60 to 65 km in an extensional back-arc basin as a result of slab rollback in the late Eocene, following the subduction of Neo-Thetys in Central Iran. The generated melt during the ascent underwent assimilation and fractional crystallization in lower depth magma chamber. [ABSTRACT FROM AUTHOR]

The accurate estimation of temperature distribution in the earth's crust and modelling of heat-related processes in geodynamics requires knowledge of the thermal conductivity of plutonic rocks. This study compiled an extensive data set of 530 representative plutonic rock samples, including thermal conductivity, major oxide composition and (for two subsets of data) modal mineralogy. For the first time, three machine learning algorithms (ML; i.e. support vector regression, random forest and extreme gradient boosting) were employed to estimate the thermal conductivity of plutonic rocks using the major oxide composition feature as input variables. The performance of these ML-based models was evaluated against a geochemically compositional model and eight mineral-driven physically based empirical mixing models. Results show that the means of predicted thermal conductivity by the ML-based models and the geochemically compositional model are not significantly different from the measured thermal conductivity at a significance level of 5 per cent. However, the ML-based models outperformed the best-performing non-ML model, the geochemically compositional model. The highest prediction accuracy was achieved by extreme gradient boosting, which reduced the mean absolute percentage error and root mean square error by more than 50 per cent. Furthermore, SiO2 is confirmed as the most important independent variable, followed by Al2O3, TiO2, CaO and K2O. The turning point observed in the thermal conductivity trend with SiO2 wt per cent may be primarily attributed to variations in mineral composition within the subgroup of igneous rock types classified based on SiO2 wt per cent. This study explores, for the first time, the use of ML algorithms to estimate the thermal conductivity of plutonic rocks from their major oxide composition. [ABSTRACT FROM AUTHOR]

Zhob Ophiolite complex is composed of three detached blocks named Omzha, Ali Khanzai and Naweoba blocks. The crustal plutonic section of the Naweoba block is mapped and divided into gabbro and granite. Based on petrographical studies, the gabbros fell in the domain of gabbro, gabbronorite, and hornblende gabbro while granitic rocks fell in the vicinity of quartz-rich granitic rocks, granodiorite, plagiogranite and tonalite. Gabbroic rocks cover the maximum area of the crustal plutonic section and are usually medium-grained while at many places the grain size is quite large to be seen with naked eyes. Minerlogically gabbroic rocks consist of orthopyroxene, clinopyroxene, amphibole and plagioclase. These rocks maybe the fragments of main crustal plutonic section of the Zhob ophiolite. The granitic rocks having mafic minerals dominted in the eastern portion, while the felsic minerals dominted ones are in the west. The eastern side of the granitic body is compact and massive compared to western portion which is quite altered and shattered. Granitic rocks are composed of plagioclase, alkali feldspar and quartz where rutile and Cr-spinel exist in trace amounts. The gabbros of Naweoba block may have formed in a magma chamber as a result of fractional crystallization. While the granites maybe a late magmatic differentiate from the same magma chamber. The close correlation of gabbroic and granitic rocks of Naweoba block with Muslim Bagh, Khanozai and Bela ophiolites suggests their formation in supra subduction zone setting.

Classification of rocks is one of the basic parts of geological research and is a difficult task due to the heterogeneous properties of rocks. This process is time consuming and requires sufficiently knowledgeable and experienced specialists in the field of petrography. This paper has a novelty in classifying plutonic rock types for the first time using thin section images; and proposes an approach that uses the deep learning method for automatic classification of 12 types of plutonic rocks. Convolutional neural network based DenseNet121, which is one of the deep learning architectures, is used to extract the features from thin section images of rocks; and the classification process is carried out with a single layer fully connected neural network. The deep learning model is trained and tested on 2400 images. AUC, accuracy, precision, recall and f1-score are used as performance measure. The proposed approach classifies plutonic rock images on the test set with an average accuracy of 97.52% and a maximum of 98.19%. Thus, the applied deep transfer learning is promising in geosciences and can be used to identify rock types quickly and accurately. [ABSTRACT FROM AUTHOR]

Igneous rocks form when molten magma is cooled and solidified, either within the Earth’s crust (plutonic rocks), or from lava extruded onto the Earth’s surface in the atmosphere or underwater (volcanic rocks). The classification of igneous rocks can be done using data from different instrumental techniques. However, these approaches tend to be expensive and time-consuming. In this research work, several models for the classification of granitoids, which are the most abundant plutonic rocks in the Earth’s crust, were created with a convolutional neural network developed with TensorFlow. Specifically, several combinations of gabbro, diorite, tonalite, granodiorite, monzodiorite, and granite image samples were used in the experiments. The best result was obtained in the model that classifies images of gabbro, diorite, granodiorite, and granite with an accuracy value of 95%, an average precision value of 96%, an average recall value of 95%, and an average F1 score value of 95%.

The study aimed to determine the natural radioactivity levels of 226Ra, 232Th, and 40K by the Gamma-Ray spectrometry method, and radiological hazard parameters of the plutonic rocks in the Western and Central Sakarya Zone and to analyze the data using multivariate statistical methods. The average radiological values of samples were determined as 40K (1295.3 Bq kg−1) > 232Th (132.1 Bq kg−1) > 226Ra (119.7 Bq kg−1). According to the skewness values of the distributions of the examined radionuclides, 226Ra (2.1) and 232Th (0.7) seemed to be positively right-skewed while 40K (−0.2) had a negatively right-skewed histogram. On the other hand, the following kurtosis values were calculated for the distributions: 226Ra (5.8 > 3), 232Th (−0.7), and 40K (−0.8). Kolmogorov–Smirnov and Shapiro–Wilk tests were applied to the data to test their normality. Therefore, Spearman’s correlation coefficient method was performed. The radionuclides of 226Ra and 232Th were found to have a positive correlation with radiological hazard parameters of the samples. 2 (two)-related factors identified, and the cumulative value was calculated to be 98.7% on the basis of the Scree Plot. According to the hierarchical cluster analysis, the samples that are grouped with those from Camlik region are prominent. The average radioactivity values of Camlik, Sogukpinar, Karacabey, and Sogut (except for 232Th) regions were detected to be higher than the world averages while the value of 40K was also found to be higher than the average values of various countries in the world.

[Display omitted] • 474–512 Ma ages of zircons are in line with the Cadomian basement in Iran. • Sr-Nd-Pb isotopes indicate variable degree of crustal contribution. • Continental rifting happened in a pre-collisional back-arc setting in the Ordovician. The late Proterozoic - early Paleozoic tectono-magmatic evolution of Central Iran is considered to be a result of subduction of the Proto-Tethys Ocean and the amalgamation of Gondwana continental fragments. Here, we present whole-rock geochemistry, Sr-Nd-Pb isotopes and zircon U-Pb-Hf data for monzonite to quartz monzonite from deep drill core in the area of the Iron Anomaly 21-A, Bafq metallogenic province of Central Iran, to decipher the petrogenetic evolution of the mantle during late Proterozoic–early Paleozoic times. The plutonic rocks display enrichment in large-ion lithophile elements (Rb, Ba, K, and Cs), and depletion in high-field-strength elements (Nb, Ta, Ti), typical of continental arcs. Zircon U-Pb ages of the studied rocks are in the range of 474–512 Ma, which is consistent with the general consensus on the age of the Cadomian basement of Central Iran, and the culmination of subduction along northern Gondwana in the early Paleozoic. The isotopic signatures of the samples, e.g., (87Sr/86Sr) i = 0.706 to 0.718, εNd (t) = − 3.3 to + 1.8, (206Pb/204Pb) i = 18.87 to 20.32, (207Pb/204Pb) i = 15.72 to 15.84, (208Pb/204Pb) i = 40.74 to 42.32, and εHf (t) = -4.7 to + 11.6, cover a compositional range of mantle-derived melts with variable degree of contamination by Neoproterozoic continental crust. A setting of back-arc continental rifting is envisaged for the late Neoproterozoic to early Paleozoic magmatism in the Bafq province. [ABSTRACT FROM AUTHOR]

The south Ardestan plutonic rocks constitute major outcrops in the central part of Iran’s Cenozoic magmatic belt and encompass a wide compositional spectrum from gabbro to granodiorite. U–Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) dating of zircon three granodiorites yielded ages of 24.6 ± 0.1, 24.6 ± 0.1, and 24.5 ± 0.1 Ma. For tonalitic rocks, internal Rb–Sr isochron ages (biotite, feldspars) indicate cooling ages of 20.4 ± 0.1, 20.5 ± 0.1, and 22.3 ± 0.1 Ma, which are slightly younger than the zircons’ ages. The limited variations in their Sr–Nd isotope ratios indicate derivation from an asthenospheric mantle source. A geodynamic model is presented in which late Oligocene–Miocene rollback of the Neotethyan subducting slab triggered asthenospheric upwelling and partial melting in the south Ardestan. These melts were subsequently modified through fractional crystallization and minor crustal contamination en-route to the surface. Plagioclase + orthopyroxene-dominated fractional crystallization accounts for differentiation of gabbro to gabbroic diorite, whereas fractionation of clinopyroxene, titanomagnetite, and orthopyroxene led to differentiation of gabbroic diorite to diorite. Amphibole fractionation at deeper levels led to the development of tonalites. [ABSTRACT FROM PUBLISHER]

New whole-rock geochemical analyses (major and trace elements) of three tonalite plutons and high Mg/Fe granodiorites and diorites, termed sanukitoid suites, are presented from Neoarchaean Kuhmo district, eastern Finland. The 2.83 Ga and 2.78 Ga tonalites display only moderate fractionation of LREE/HREE thus demanding only minor or no residual garnet in their respective source regions. However, the more prominent HREE depletion in the 2.75 Ga tonalites requires more significant garnet residue. The relatively wide compositional variation in the tonalites implies that Archaean TTG (tonalite-trondhjemite-granodiorite) magmatism was derived in general from sources that exhibited considerable mineralogical heterogeneity. The ~2.70 – 2.74 Ga high-Mg/Fe granodiorites and diorites are characterised by strong fractionation of LREE/HREE, relatively high Ba and Sr, and elevated abundances of Cr and Ni as well systematic depletions in P and Ti, which are all typical features of Archaean sanukitoid suites. Some of the granodiorite plutons contain compositionally intermediate high-K enclaves, which share these geochemical characteristics, implying a contribution of mafic-intermediate LILE- and LREE- enriched source for the magma. The geochemical characteristics of the studied plutonic rocks demonstrate the role of contrasting sources for the tonalites and sanukitoid suites in the Kuhmo district.