Search Results (100)

The Mazenod Lake region of the southern Great Bear Magmatic Zone (GBMZ) of the Northwest Territories, Canada, comprises the north-central portion of the Faber volcano-plutonic belt. Widespread and abundant surface exposure of several coalescing hydrothermal systems enables this paper to document, without ambiguity, the relationships between geology, structure, alteration, and mineralization in this well exposed iron-oxide–copper–gold (IOCG) mineral system. Mazenod geology comprises rhyodacite to basaltic-andesite ignimbrite sheets with interlayered volcaniclastic sedimentary rocks dominated by fine-grained laminated tuff sequences. Much of the intermediate to mafic nature of volcanic rocks is masked by low-intensity but pervasive metasomatism. The region is affected by a series of coalescing magmatic–hydrothermal systems that host the Sue–Dianne magnetite–hematite IOCG deposit and several related showings including magnetite, skarn, and iron oxide apatite (IOA) styles of alteration ± mineralization. The mid to upper levels of these systems are exposed at surface, with underlying batholith, pluton and stocks exposed along the periphery, as well as locally within volcanic rocks associated with more intense alteration and mineralization. Widespread alteration includes potassic and sodic metasomatism, and silicification with structurally controlled giant quartz complexes. Localized tourmaline, skarn, magnetite–actinolite, and iron-oxide alteration occur within structural breccias, and where most intense formed the Sue–Dianne Cu-Ag-Au diatreme-like breccia deposit. Magmatism, volcanism, hydrothermal alteration, and mineralization formed during a negative tectonic inversion within the Wopmay Orogen. This generated a series of oblique offset rifted basins with continental style arc magmatism and extensional structures unique to GBMZ rifting. All significant hydrothermal centers in the Mazenod region occur along and at the intersections of crustal faults either unique to or put under tension during the GBMZ inversion. Full article

The Aptian–Albian interval represents a significant cooling phase within the Cretaceous “hothouse” climate, marked by dynamic climatic fluctuations. High-resolution continental records are essential for reconstructing terrestrial climate and ecosystem evolution during this period. This study examines a lacustrine-dominated succession of the Shahezi Formation (Lishu Rift Depression, Songliao Basin, NE Asia) to access paleo-weathering intensity and paleoclimate variability between the Middle Aptian and Early Albian (c. 118.2–112.3 Ma). Multiple geochemical proxies, including the Chemical Index of Alteration (CIA), were applied within a sequence stratigraphic framework covering four stages of lake evolution. Our results indicate that a hot and humid subtropical climate predominated in the Lishu paleo-lake, punctuated by transient cooling and drying events. Periods of lake expansion corresponded to episodes of intense chemical weathering, while two distinct intervals of aridity and cooling coincided with phases of a reduced lake level and fan delta progradation. To address the impact of potassium enrichment on CIA values, we introduced a rectangular coordinate system on A(Al₂O₃)-CN(CaO* + Na₂O)-K(K₂O) ternary diagrams, enabling more accurate weathering trends and CIA corrections (CIA_corr). Uncertainties in CIA correction were evaluated by integrating geochemical and petrographic evidence from deposits affected by hydrothermal fluids and external potassium addition. Importantly, our results show that metasomatic potassium addition cannot be reliably inferred solely from deviations in A-CN-K diagrams or the presence of authigenic illite and altered plagioclase. Calculations of “excess K₂O” and CIA_corr values should only be made when supported by robust geochemical and petrographic evidence for external potassium enrichment. This work advances lacustrine paleoclimate reconstruction methodology and highlights the need for careful interpretation of weathering proxies in complex sedimentary systems. Full article

Continental rifts represent one of the most important settings geologically and economically. The Suez Rift represents more than 74% of the Egyptian crude oil. It represents the northern end of the Red Sea, which understanding is vital to reconstructing the tectonics, dynamics, and time–temperature history of the whole region. An effective method to reveal rift-related history is by studying its flanks, which are represented here by the Arabian-Nubian Shield Neoproterozoic basement rocks. We applied an approach integrating new fission-track thermochronology data, new time–temperature modeling, stratigraphic information, and geological knowledge, which has proven its effectiveness in such geological settings. The collected samples from the Wadi Hebran area on the eastern flank of the Suez rift showed two differentiated cooling histories: The first has a Carboniferous zircon fission-track and a Cretaceous apatite fission-track age, and the second has a Triassic zircon fission-track and an Oligocene–Miocene apatite fission-track age. The time–temperature history modeling supported four distinct cooling events activated through the Neoproterozoic post-accretion erosional event, Variscan tectonic event, Gondwana disintegration, and the Suez Rift initiation. The rock uplift that accompanied the Suez Rift reaches up to 4 km, explaining the extraordinary elevations of the Catherina region, and supports an active rift component in the southern segment of the Suez Rift eastern flank. Full article

Continental rifting is the process by which land masses separate and create new ocean basins. The emplacement of large igneous provinces (LIPs) is thought to have played a key role in (super) continental rifting; however, this relationship remains controversial due to the lack of a clearly established mechanism linking LIP emplacement to continental fragmentation. Here, we show that plume flow links LIP magmatism to continental rifting quantitatively. Our findings are further supported by the sedimentary record, as well as by the mineralogy and petrology of the rocks. This study analyzes the early Cretaceous separation of West Gondwana into South America and Africa. Prior to rifting, Jurassic hiatuses in the stratigraphic record of continental sediments from both continents indicate plume ascent and the resulting dynamic topography. Cretaceous mafic dyke swarms and sill intrusions are products of major magmatic events that coincided with continental rifting, leading to the formation of large igneous provinces in South America and Africa, including the Central Atlantic Magmatic Province, Equatorial Magmatic Province, Paraná–Etendeka, and Karoo. It has been suggested that dyke intrusions may weaken the lithosphere by reducing its mechanical strength, creating structural weaknesses that localize extensional deformation and facilitate rift initiation. The sedimentary analysis and petrological evidence from flood basalt magmas indicate that plumes may have migrated from the depths toward the surface during the Jurassic and erupted during the Cretaceous. It is thought that the resulting fast plume flow, induced by one or more mantle plumes, generated a dynamic force that, in combination with lithospheric weakening from dyke intrusion, eventually rifted the lithosphere of West Gondwana. Full article

The Luanchuan Neoproterozoic gabbroic intrusions are located at the southern margin of the North China Craton (NCC), intruding into the marble and schist from the Nannihu and Meiyaogou Formations of the Neoproterozoic Luanchuan Group. The gabbroic rocks consist of plagioclase (30%–50%) and amphibole (40%–60%), with minor ilmenite (2%–5%), biotite (1%–3%), and titanite (~1%). Based on the occurrence and mineral chemistry, two types of biotites were identified. The first type of biotite (Bt I) is brown, with a fine- to micro-grained anhedral texture, occurring around the magmatic ilmenite and coexisting with titanite. Bt I is characterized by high TiO₂ and FeO contents, with TiO₂ > 2 wt% (2.03 wt%–3.15 wt%) and FeO ranging from 19.94 wt% to 22.08 wt%. The other type of biotite (Bt II) is light grayish-brown to dark reddish-brown, with a medium- to coarse-grained euhedral texture, coexisting with grayish-green amphibole. Bt II exhibits lower TiO₂ (1.40 wt%–1.90 wt%) and FeO contents (18.03 wt%–21.42 wt%). The K₂O (7.56 wt%–9.32 wt%) and SiO₂ (34.49 wt%–37.04 wt%) contents of Bt I are slightly lower than those of Bt II (8.28 wt%–9.73 wt% and 35.18 wt%–37.52 wt%, respectively). Despite the low Ti content in biotites, the mineral occurrence indicates that both types of biotite yield a magmatic origin, resulting from the reactions between early crystallized minerals and residual magma. Bt I originated from the reaction between ilmenite and residual magma, while Bt II resulted from the production of the reaction between clinopyroxne and residual magma. Ilmenite exhibits low MgO and Fe₂O₃ contents but high FeO and MnO contents, suggesting genetic similarities to the Skaergaard and Panzhihua intrusions. Both types of biotites record consistent temperatures (T = 766 to 818 °C), pressures (P = 5.30–8.80 kbar), and oxygen fugacities (log fO₂ = −12.35 to −14.06), aligning with those of the Fanshan complex and the Falcon Island intrusion. The mineralogy of ilmenite and biotite indicates that the Luanchuan gabbroic intrusions formed in a continental rift setting, which is considered to be associated with the breakup of the Rodinia supercontinent. Full article

The analysis of sand distribution in a marine–continental rift basin is of practical value for hydrocarbon prediction. The primary objective of this study is to investigate the correlation between Paleoproterozoic sand development and paleomorphology in the Nanpu sag, and to focus on identifying the key factors controlling sand deposition in the marine–continental rift basin. Correspondence between the development of the Paleoproterozoic sand in the Nanpu sag and the paleogeomorphology shows that the gully limited the deposition of the sand into the lake. The differentiation and aggregation of the sand in the lake basin were influenced by two kinds of slope break zones (the syn-sedimentary fracture tectonic slope break zone and the paleo-topographic flexural depositional slope break zone). Due to tectonic movements in the marine–continental rift basin, as well as provenance supply and weather during chasmic stages, the impact of valley and syndeposit slope break zone on sand development varies. In areas where allocation is better as valley–syndeposit slope break zone, basal slope and its vicinity usually are favorable for delta (braided channel) and fan delta sand development, which extend basinward through hydraulic transport. Meanwhile, under the influence of syntectonic and gravitational disequilibrium, gravity flow sand can be seen sporadically distributed in the deep end of fan fronts. This study is of great significance for oil and gas exploration in the Bohai Bay Basin region and contributes to a better understanding of depositional processes in similar marine–continental rift basins around the globe. Full article

Archean craton comprises ancient and stable continental lithosphere, lacking significant seismic activity, magmatic activity, and tectonic deformation. Typically, its lithospheric mantle exhibits high electrical resistivity. However, within the Archean Tanzanian cratonic mantle, a high conductivity layer has been discovered, with an electrical conductivity of approximately 0.1 S/m. We conducted the electrical conductivity experiments on olivine aggregates containing sodium carbonate at the pressure of 3 GPa and the temperature ranging from 600 to 1200 °C. It was found that a very small amount of alkali-carbonate melt can significantly increase the electrical conductivity of dunite. The mass fraction of alkali-carbonate melt is less than 2.0 wt% in the highly conductive layer of the Tanzanian cratonic mantle. The permeability barriers made the melts preserve within the depth range of 80 to 120 km. Therefore, the presence of alkali-rich carbonate melts may be the best mechanism to explain the high conductivity anomaly in the lithospheric mantle of the Tanzanian craton. In contrast, the carbonate melts with high mobility migrated directly to shallow depths along fractures in the mobile belt/rift zone, leaving a dry and resistive residual mantle. Full article

The Beishan Orogenic Belt, situated along the southern margin of the Central Asian Orogenic Belt, represents a critical tectonic domain that archives the prolonged subduction–accretion processes and Paleo-Asian Ocean closure from the Early Paleozoic to the Mesozoic. Early Permian magmatism, exhibiting the most extensive spatial-temporal distribution in this belt, remains controversial in its geodynamic context: whether it formed in a persistent subduction regime or was associated with mantle plume activity or post-collisional extension within a rift setting. This study presents an integrated analysis of petrology, zircon U-Pb geochronology, in situ Hf isotopes, and whole-rock geochemistry of Early Permian granites from the Tiancang area in the southern Beishan Orogenic Belt, complemented by regional comparative studies. Tiancang granites comprise biotite monzogranite, monzogranite, and syenogranite. Zircon U-Pb dating of four samples yields crystallization ages of 279.3–274.1 Ma. These granites are classified as high-K calc-alkaline to calc-alkaline, metaluminous to weakly peraluminous I-type granites. Geochemical signatures reveal the following: (1) low total rare earth element (REE) concentrations with light REE enrichment ((La/Yb)_N = 3.26–11.39); (2) pronounced negative Eu anomalies (Eu/Eu* = 0.47–0.71) and subordinate Ce anomalies; (3) enrichment in large-ion lithophile elements (LILEs: Rb, Th, U, K) coupled with depletion in high-field-strength elements (HFSEs: Nb, Ta, P, Zr, Ti); (4) zircon ε_Hf(t) values ranging from −10.5 to −0.1, corresponding to Hf crustal model ages (T_DMC) of 1.96–1.30 Ga. These features collectively indicate that the Tiancang granites originated predominantly from partial melting of Paleoproterozoic–Mesoproterozoic crustal sources with variable mantle contributions, followed by extensive fractional crystallization. Regional correlations demonstrate near-synchronous magmatic activity across the southern/northern Beishan and eastern Tianshan Orogenic belts. The widespread Permian granitoids, combined with post-collisional magmatic suites and rift-related stratigraphic sequences, provide compelling evidence for a continental rift setting in the southern Beishan during the Early Permian. This tectonic regime transition likely began with lithospheric delamination after the Late Carboniferous–Early Permian collisional orogeny, which triggered asthenospheric upwelling and crustal thinning. These processes ultimately led to the terminal closure of the Paleo-Asian Ocean’s southern branch, followed by intracontinental evolution. Full article

Recently published marine geophysical and seafloor drilling data permit a substantive reappraisal of the rifting and spreading that formed the South China Sea (SCS). The SCS rifted margins are different from those of the Atlantic type, having higher strain rates, younger orogenic crust, and distributed syn-rift magmatism. Rifting ~66–11 Ma and spreading 30–14 Ma split a Cretaceous Andean arc and forearc, producing >700 km of seafloor spreading in the east and a ~2000-km-wide rifted margin in the west. Luconia Shoals–Dangerous Grounds–Reed Bank–north Palawan–SW Mindoro were separated from China when the SCS opened. Brittle faulting of the upper crust was decoupled from ductile flow and magmatic intrusion of the lower crust, producing wide rifting with thin spots held together by less extended surrounds. Sediments accumulated in inter-montane lakes. Transform faults formed at/after breakup to link offset spreading segments. Spreading in the eastern subbasin from C11n to C5AD was at rates averaging 62 mm/yr, 30–24 Ma, decreasing to 38.5 mm/yr younger than 23 Ma. Spreading reorganization was common as margin segments broke up to the SW and spreading directions changed from ~N-S before 23 Ma to NW-SE after 17 Ma. Full article

Seismic sedimentology and sequence stratigraphy, as emerging interdisciplinary fields, demonstrate unique advantages in characterizing seismic geomorphological responses of various system tracts within the stratigraphic frameworks of rift lacustrine basins. Focusing on the Paleogene Dainan Formation in the Gaoyou Sag of the Subei Basin, eastern China, this study integrates seismic termination patterns, sedimentary cyclicity analysis, and well-to-seismic calibration to subdivide the formation into three third-order sequences containing lowstand (LST), transgressive (TST), and highstand (HST) system tracts. The distribution of five distinct sedimentary facies exhibits pronounced sub-tectonic zonations controlled by the basin’s architecture and structural evolution, with steep slope zones dominated by nearshore subaqueous fan–fan delta complexes, gentle slopes developing normal deltaic systems, and deep-semi-deep lacustrine facies with slump turbidite fans concentrated in depositional centers. Through a novel application of 90° phase adjustment, spectral decomposition, and multi-attribute fusion techniques, the relationship between seismic amplitude attributes and lithologies are established via seismic lithology calibration. Detailed sequence evolution analyses and seismic geomorphological interpretation systematically elucidate the spatio-temporal evolution of depositional systems within different system tracts in rift lacustrine basins, providing a novel methodological framework for sequence stratigraphic analysis in continental rift settings. Full article

The effects of a synthetic M 7.1 strike lateral earthquake are evaluated at five sites in Michoacan state, western Mexico. In this work, the ground motion simulation was applied using the empirical Green’s function method proposed by Irikura (1986) by scaling the recordings of an M 5.1 left-lateral event to a hypothetical M 7.1 event assuming the same source mechanism. An M 4.3 was used as a Green’s function to generate an M 5.1 synthetic earthquake. Comparing the observed and synthetic M 5.1 earthquake, parameters were adjusted in order to scale the M 7.1 earthquake. Seven scenarios were tested for which the corresponding PGA and PGV were calculated. The results show that the maximum intensities at each station depend on the proposed rupture starting point. The highest Peak Ground Acceleration was 74.1 cm/s² corresponding to an intensity MMI of V at FMIR station located 60 km from the epicenter. The synthetic results constitute a useful input for seismic hazard studies in a state with poor instrumental deployment, such as Michoacan, and for technical standards for earthquake design that could be considered in the corresponding construction regulations. Full article

The Mesoproterozoic alkaline Grønnedal-Íka complex (1325 ± 6 Ma) is intruded into old Archean gneissic bedrock between Ikka Fjord and Kangilinnguit (Grønnedal) by Arsuk Fjord in Southwestern Greenland. This 8 × 2.8 km oval-shaped complex constitutes the oldest part of the Gardar Province, representing a failed continental rift across southern Greenland. It comprises outer rings of mainly nepheline syenites with a central plug of Fe- and Ca-rich carbonatites. Here, we present petrological data on the syenites and carbonatites combined with geochemical modelling of groundwater percolating through the Grønnedal-Íka complex and the secondary minerals and fluid chemistry arising from these fluid–rock reactions. The results show that modelling using input data of (1) meteoric water in a closed system with respect to atmospheric CO₂ can (2) dissolve the primary minerals of the syenites and carbonatites and (3) simulate the fluid chemistry of the natural sodium carbonate springs of 3–4 °C and pH 10–11 seeping up through fractures at the bottom of Ikka Fjord, which (4) leads to the deposition of nearly a thousand tufa columns of the cold carbonate mineral ikaite (CaCO₃•6H₂O). Our results thereby support the geochemical relationship between fluid–rock reactions inside the Grønnedal-Íka alkaline complex and the precipitation of ikaite in the shape of submarine tufa columns in Ikka Fjord. The modelling indicates that the groundwater itself can be supersaturated with respect to ikaite and provide the seed crystals that lead to the columnar growth of ikaite up to 20 m tall in the seawater of Ikka Fjord. Full article

The tectonic evolution of Hainan Island during the Late Permian–Early Triassic period is still unclear. This study identified two types of basalts on the island and presented detailed geochronology, whole-rock geochemistry, and Hf isotope data of the Late Permian–Early Triassic basalts. U-Pb dating results indicated that baddeleyites and zircons of one sample from Group 1 basalts had formation ages of 256 ± 3 Ma and 255 ± 3 Ma, respectively, and two samples from Group 2 gave formation ages of 241 ± 2 Ma and 240 ± 3 Ma, respectively. Both groups are characterized by negative anomalies of Nb, Ta, and Ti, and enrichment in Ba, Th, U, and K. Group 1 belongs to sub-alkaline basalt and exhibited SiO₂ contents ranging from 50.50% to 51.05%, with ΣREE concentration of 136–148 ppm. Hf isotope analysis showed that the ε_Hf(t) values of baddeleyites and zircons were −10.56 to −4.70 and −14.94 to −6.95, respectively. Group 2 belongs to alkaline basalt and had a higher SiO₂ content of 52.48%–55.49% and ΣREE concentration of 168–298 ppm. They showed more depleted Hf isotopic composition with ε_Hf(t) values ranging from −2.82 to +4.74. These data indicate that the source area of Group 1 was an enriched mantle, likely derived from partial melting of spinel lherzolite mantle, and was modified by subduction-derived fluids. Group 2 was derived from depleted mantle, most likely originating from partial melting of garnet + spinel lherzolite mantle. They were contaminated by crustal materials and metasomatized by subduction-derived fluids with a certain degree of fractional crystallization. Comprehensive analysis suggests that Group 1 samples likely formed in an island arc tectonic setting, while Group 2 formed in a continental intraplate extensional (or initial rift) tectonic setting. Their formation was mainly controlled by the Paleo-Tethys tectonic domain. Group 1 basalts implied that subduction of the Paleo-Tethys oceanic crust lasted at least in the late Permian (ca. 255 Ma). Group 2 basalts revealed that the intra-plate extensional (or initial rift) stage occurred in the middle Triassic (ca. 240 Ma). Full article

The widespread occurrence of Mesozoic ocean island basalt (OIB)-like igneous rocks in the Southern Tibetan Himalayan Belt provides important constraints on the rifting of East Gondwana. This study undertook a petrological, geochronological, and geochemical investigation of mafic intrusive rocks in the Cuona area of the eastern Tethyan Himalayan Belt. The mafic intrusions have OIB-type geochemical signatures, including diabase porphyrite, gabbro, and diabase. Zircon U–Pb dating indicates that the diabase porphyrite formed at 135.0 ± 1.6 Ma. The diabase porphyrite and gabbro are enriched in high-field-strength elements (Nb and Ti) and large-ion lithophile elements (Sr and Pb) and experienced negligible lithospheric mantle or crustal contamination. The diabase is enriched in large-ion lithophile elements (LILEs, e.g., La and Ce) and depleted in high-field-strength elements (HFSEs, e.g., Ru, Zr and Ti). In general, the mafic intrusions exhibit significant light REE enrichment and heavy REE depletion and have no Eu anomalies. Whole-rock neodymium (ε_Nd(t) = 1.55) and zircon Hf (ε_Hf(t) = 0.60–3.73) isotopic compositions indicate derivation of the magma from enriched type I mantle. We propose that the diabase porphyrite and diabase formed in a continental margin rift setting, influenced by the Kerguelen mantle plume, and represent magmatism related to the breakup of East Gondwana. However, the gabbro formed in a relatively stable continental intraplate environment, likely derived from deep magmatic processes associated with the Kerguelen mantle plume. Our results provide new constraints on the early activity of the Kerguelen mantle plume and offer insights into the breakup and tectonic evolution of East Gondwana. Full article

Continental rift zones on the early Earth provided essential conditions for the emergence of the first cells. These conditions included an abundant supply of raw materials, cyclic fluctuations in pressure and temperature over millions of years, and transitions of gases between supercritical and subcritical phases. While evidence supports vesicle formation and the chemical evolution of peptides, the mechanism by which information was stored remains unresolved. This study proposes a model illustrating how interactions among organic molecules may have enabled the encoding of amino acid sequences in RNA. The model highlights the interplay between three key molecular components: a proto-tRNA, the vesicle membrane, and short peptides. The vesicle membrane acted as a reservoir for hydrophobic amino acids and facilitated their attachment to proto-tRNA. As a single strand, proto-tRNA also served as proto-mRNA, enabling it to be read by charged tRNAs. By replicating this information and arranging RNA strands, the first functional peptides such as pore-forming proteins may have formed, thus improving the long-term stability of the vesicles. This model further outlines how these vesicles may have evolved into the earliest cells, with enzymes and larger RNA molecules giving rise to tRNA and ribosomal structures. Shearing forces may have facilitated the first cellular divisions, representing a pre-LUCA stage. Full article