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The correct choice of a stone aggregate for railway ballast is directly related to the stability, safety, efficiency, and maintenance costs of the track. The aggregate must meet several criteria to ensure it is the most appropriate material. Thus, the present study aimed to evaluate four distinct stones: two granites, a diabase, and a basalt, all mined in the eastern region of the state of São Paulo, Brazil, regarding their applicability as ballast. Using Brazilian and ASTM procedures for stone samples, the tests were conducted on 55 and 75-mm specimens, in dry and wet conditions. As a result, all stones met the physical properties established by the standards. Among the mechanical properties, uniaxial compressive strength stood out, with all stones where the tested materials advantageously exceeding the 100 MPa required by the Brazilian standard. Regarding the accelerated weathering test with ethylene glycol, only basalt showed more significant changes, although its resistance to weathering was still lower than 10%. Our findings indicate that these stones perform adequately as ballast for railway applications. The study is expected to contribute to revisions of technical standards and the improvement of a database on Brazilian stone materials for use as railway ballast. [ABSTRACT FROM AUTHOR]

The typochemical features of spinels forming continuous series from Al–Cr spinels to ferrispinel and ulvöspinel from basic–ultrabasic rocks of the North Siberian Platform are considered. Their composition features are compared with those of alkali basalts of oceanic islands and lunar marine basalts in the modified Al–Cr–(Fe3+ + 2Ti)–Fe2+ 3D diagram proposed by the author. The identified continuous isomorphous series from Cr-spinel to ulvöspinel is one of the mineralogical indicators of a possible paragenetic relationship between picrite–basalt, alkali olivine–basalt, alkali–ultrabasic, and kimberlite rocks in the North Siberian Platform. The Ballhaus–Berry–Green olivine–Cr-spinel oxythermobarometer used in the rock study in the North Siberian Platform has made it possible to demonstrate that oxygen volatility log fO2 is from two to four orders of magnitude higher than that specified by the fayalite–magnetite–quartz buffer and corresponds to the oxidation state of Pt-bearing dunite–clinopyroxenite rock assemblages of the Ural–Alaskan and Aldan types. [ABSTRACT FROM AUTHOR]

The scarcity of the early Precambrian geological record limits our comprehension of crucial information concerning interactions between the crust and mantle, mechanisms involved in subduction zone arc-continental collisions, as well as patterns of mantle enrichment and crustal growth during this epoch. The Dengfeng terrane in the North China Craton provides significant data on Precambrian crustal evolution, particularly within the Neoarchean magmatic suites. Our study focuses on a variety of basic rocks across several locations in this region. Basic rocks from Huishansi and Sanhuangzhai (2558–2525 Ma) exhibit characteristics such as low SiO2 (45.44–56.54 wt%), K2O (0.77–2.7 wt%), Na2O (1.66–4.51 wt%), and high MgO (4.66–11.22 wt%) and FeOT (8.17–13.77 wt%). Similarly, basic rocks from Shipaihe and Guojiayao (2480 Ma) also display low SiO2 (46.16–52.48 wt%), K2O (0.24–1.28 wt%), and Na2O (1.87–3.75 wt%), with FeOT (1.07–2.31 wt%), but feature higher content of MgO (5.33–8.83 wt%) and Mg# (44–62, averaging 53). Both sets exhibit relatively flat REE patterns and weak negative anomalies in Nb, Ta, and Ti, corresponding to a tholeiitic basalt composition for the protoliths. Analyzing low (Hf/Sm)N, (Nb/La)N, and Th/Yb ratios, coupled with depleted HFSE, suggests potential crustal contamination in the rocks from Huishansi and Sanhuangzhai. Further, based on low V/Sc ratios (5.38–10.27, average 7.02) and depleted zircon ƐHf(t) values, our proposition is that the magma was sourced through partial melting of a depleted and relatively reduced mantle source. These findings offer valuable insights into the tectonic evolution of the Dengfeng terrane, spanning from subduction to post-collisional extension.

The Kekebieketi mining area is located on the southern margin of the Altai Mountains in Northern Xinjiang and is at the junction of the Siberia and Kazakhstan‐Junggar plates. Faults and magmatic rocks are well developed, and the main stratum is the Middle Devonian Kaxiweng Formation. The Kekebieketi‐Kalatongke‐Xibodu basic to ultrabasic mixed rock strip is an appropriate area for mineral resources and a good target to study the crustal and mantle evolution. This study explored the tectonic age and setting of basic rocks in the Kekebieketi mining area and provides a basis for the study of basic rocks and discrimination of the wider formation. The basic rocks were mainly gabbro, pyroxenolite, basic subvolcano rock, and diabase. They have all been altered to different degrees through amphibolization, sub‐amphibolization, actinolitization, chloritization, epidotization, zoisitization, uralitization, and serpentinization. Similar rare earth element compositions of the different rock types suggest that they are homologous. Enrichment of large ion lithophile elements (Cs, Rb, Sr, and U) and depletion of high field strength elements (Nb, Ta, Zr, and Hf) showed that the basic rocks have the characteristics of island arc magmatic rocks. A single zircon U–Pb age of 321 ± 2.5 Ma was obtained from a hornblende gabbro. Based on the petrological and geochemical features, we concluded that the basic rocks in the study area were formed during the post‐collision period in East Junggar. The parental magma is mainly composed of metasomatic mantle wedge material and upwelling asthenosphere, which is why it showed geochemical characteristics of subduction. [ABSTRACT FROM AUTHOR]

Analysis of borehole samples offers the potential to investigate the chemostratigraphic variations of a large igneous province in subsurface. New geochemical data based on multielement analyses of 829 chip samples that were obtained during the drilling of seven deep boreholes is presented for the central area of the Paraná Igneous Province (PIP). In order to detail the compositional variations found within the two main types from the Central-Northern Subprovince (CNSP), simple statistical treatment was carried out for part this database. Thus, the combination of low (L) and high (H) contents of Th, Nb, La and Yb was used as a means to create 16 geochemical subtypes for the Type 4 (LSi-LZr-HTi-HP) sequence. Likewise, other four elements (Cr, Ni, Cu and Pd) were selected with the same intention for the Type 1 ( Central-Northern ) (LSi-LZr-LTi-LP) sequence. When subtypes are plotted in the cross section, it is possible to observe that those with similar characteristics tend to be associated in groups ( cycles ). This analysis showed that the volcanic pile can be divided into at least eleven different cycles and also that they are laterally continuous throughout the section. The compositional changes observed in these volcanic cycles also display correlations with Mg#, Zr, Ti/Y and La/Sm N ratios, for example. Therefore, since the reservoir is marked by periods of injection of more differentiated or more mafic magmas, it could be suggested that it was periodically recharged with batches of magma from the parental source. [ABSTRACT FROM AUTHOR]

The concentrations of 26 trace elements have been determined by laser ablation ICP-MS in zircons from four samples of basic rocks of the Korosten anorthosite-mangerite-charnockite-granite plutonic complex, the Ukrainian Shield. Zircons from the Fedorivka and Torchyn gabbroic intrusions and Volynsky anorthosite massif have distinctive abundances of many trace elements (REE, Sr, Y, Mn, Th). Zircons from the gabbroic massifs are unusually enriched in trace elements, while zircons from pegmatites in anorthosite are relatively depleted in trace elements. High concentrations of trace elements in zircons from gabbroic intrusions can be explained by their crystallization from residual interstitial melts enriched in incompatible elements. The zircons studied demonstrate a wide range of Ti concentrations, which reflects their temperature of crystallization: the zircons most enriched in Ti, from mafic pegmatites of the Horbuliv quarry (20-40 ppm), have the highest temperature of crystallization (845 ± 40 °C). Lower (720-770 °C) temperatures of zircon crystallization in gabbroic rocks are explained by its crystallization from the latest portions of the interstitial melt or by simultaneous crystallization of ilmenite. The Ce anomaly in zircons correlates with the degree of oxidation of the coexisting ilmenite. [ABSTRACT FROM AUTHOR]

The tectonic setting of the late mesozoic of South China is in a debate between two schools of thought: an intra-continental rift zone along a passive continental margin or active rifting associated with subduction of the paleo-Pacific Plate. In this study, we present new sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon ages, along with geochemical data of three basic dikes that cross-cut the Dexing porphyry copper deposit. The deposit is the largest of its kind in eastern China and part of large scale mineralization associated with Mesozoic magmatic activity in the area. Our results indicate that the dikes were emplaced in the Late Jurassic with an average U-Pb age of 153.5 ± 2.4 Ma. The intrusions have bulk εNd(t) of ca +0.7 and zircon εHf(t) value of +1.54 to +6.92. Based on relatively enriched light rare earth elements (LREE) and depleted high-field-strength elements (HFSE) abundances with pronounced negative Ta-Nb, Hf-Zr and Ti anomalies in multi-element diagrams, we propose that these dikes were derived from a subduction-modified lithospheric mantle source. The variability in Hf isotopes identifies some degree of crustal contaminations. Our data support a scenario with a back-arc extensional setting or an intra-arc rift environment associated with the westward subduction of the paleo-Pacific Plate at or prior to the late Jurassic as the most likely cause for these subduction signatures. [ABSTRACT FROM AUTHOR]

New geochemical and geochronological U–Pb and Sm–Nd data from amphibolites of the Alto Tererê Group, which are of Palaeoproterozoic age, are presented. The amphibolites are exposed in the central-eastern portion of the Rio Apa Block, southern Amazonian Craton, Mato Grosso do Sul, Brazil, and are composed of hornblende, plagioclase, quartz, biotite, cummingtonite and epidote. The amphibolites are subdivided into three lithofacies: (i) thinly banded amphibolites (metabasalts), (ii) coarse- and medium-grained amphibolites with relic subophitic texture (metagabbros), and (iii) amphibolites with relic cumulate texture (metapyroxenites). Chemical data also suggest the subdivision of the amphibolites into three different types. These rocks yield a U–Pb zircon age of 1768 ± 6 Ma and are therefore older than rocks of part of the Rio Apa Complex. Their Sm–Nd model ages range between 2.89 and 1.88 Ga, and their εNd (T) values range between −3.40 and + 3.74. Chemical analyses of these rocks indicate SiO 2 concentrations between 45.23 and 50.65 wt.%, MgO concentrations between 4.34 and 8.01 wt.%, TiO 2 concentrations between 0.91 and 1.74 wt.%, weakly fractionated rare-earth element (REE) patterns with mild depletion in heavy REEs, enrichment in large-ion lithophile elements (LILEs) and high-field-strength element (HFSEs), negative Nb, Ta and Co anomalies, positive Ba and Pb anomalies, low Ce concentrations, high Rb/Y ratios and low Th/La and Hf/Sm ratios. These features reflect metasomatism of the mantle wedge produced by sediments from the subducted plate. Various degrees of melting mark the evolution of the parent basic magmas, although subordinate crustal contamination may also have occurred. The geochemical signature of the amphibolites corresponds to that of tholeiitic basalts generated in an extensional back-arc-basin environment. The deposition in the basin apparently ceased during the first episode of compression and deformation at approximately 1.68 Ga, and the main deformation was most likely related to the San Ignácio Orogeny, which dates to approximately 1.3 Ga. [ABSTRACT FROM AUTHOR]

This paper highlights the geodynamic evolution of the early Precambrian rock associations in the northwestern part of the Russian Arctic where the rocks are exposed in the Kola region (northeastern Baltic Shield). The evolution is shown to predetermine the metallogenic potential of the area. It is emphasized that the Earth's evolution is a non-linear process. Thus, we cannot draw direct analogies with Phanerozoic time or purely apply the principle of actualism, which is still widely used by experts in Precambrian geology to study the premetamorphic history of ancient deposits. In both cases, the principles should be adjusted. This article provides a novel technique for reconstructing geodynamic regimes of protolith formation in the early Precambrian. The technique identifies changing trends in geodynamic regimes during the formation of the Archean structural and compositional complexes in the Kola region. These trends fit into the earlier suggested general scheme of their formation, thus enhancing its reliability. The metallogeny of the ore areas is specified. The results of the geodynamic reconstructions explain most of the location patterns of minerals within the Kola region. Thus, the authors consider the metallogenic forecast based on geodynamic reconstructions to be a promising trend for further research. [ABSTRACT FROM AUTHOR]