Magmatic Events Research Articles

Contrasting magma chemistry in the Candelaria IOCG district caused by changing tectonic regimes

Iron oxide-copper-gold (IOCG) deposits are a vital source of copper and critical elements for emerging clean technologies. Andean-type IOCG deposits form in continental arcs undergoing extension, and they have a temporal relationship with magmatism although they do not exhibit a close spatial relation with the causative intrusions. The processes required to form IOCG deposits and their potential connections to iron oxide–apatite (IOA)-type mineralization remain poorly constrained, as well as the characteristics of magmatism linked to both deposit types. Here we combine zircon U–Pb geochronology with zircon trace element geochemistry of intrusive rocks associated with the Candelaria deposit, one of the world’s largest IOCG deposits, to unravel distinctive signatures diagnostic of magmatic fertility. Our results reveal a marked transition in the geochemistry of intrusions in the Candelaria district, characterized by changes in the redox state, water content and temperature of magmas over time. The oldest magmatic stage (~ 128–125 Ma), prior to the formation of the Candelaria deposit, was characterized by zircon Eu/Eu* ratios of 0.20–0.42, and redox conditions of ΔFMQ − 0.4 to + 1.0. The earliest magmatic stage related to the formation of Fe-rich mineralization at Candelaria (118–115 Ma) exhibits low zircon Eu/Eu* ratios (0.09–0.18), low oxygen fugacity values (ΔFMQ ~− 1.8 to + 0.2) and relatively high crystallization temperatures. In contrast, the youngest stage at ~ 111–108 Ma shows higher zircon Eu/Eu* (~ 0.37–0.69), higher oxygen fugacity values (ΔFMQ ~ + 0.4 to + 1.3) and a decrease in crystallization temperatures, conditions that are favorable for the transport and precipitation of sulfur and chalcophile elements. We conclude that Candelaria was formed through two distinct ore-forming stages: the first associated with a reduced, high temperature, water-poor magma developed under a low tectonic stress, followed by a more oxidized, water-rich, and low temperature magmatic event related to a compressional regime. The first event led to Fe-rich and S-poor IOA-type mineralization, while the second event with geochemical signatures similar to those of porphyry copper systems, generated the Cu- and S-rich mineralization. This late stage overprinted preexisting IOA mineralization resulting in the formation of the giant Candelaria IOCG deposit.

Messengers from the Magma Chambers: Petro-Stratigraphic Analysis of Plagioclase-Rich Flood Basalt Lavas in Turkana, Kenya

Abstract Continental large igneous provinces are among the largest magmatic events on Earth, characteristically manifesting at the surface as stacks of monotonous flood basalt lavas that form through a dynamic pattern of eruptive pulses separated by hiatuses. Such dynamic patterns may be difficult to detect from the composition of the lavas. Instead, lava crystal cargoes can be used to study how the eruption cycles inherent to continental large igneous provinces are moderated by episodic recharge and evacuation at multiple crustal levels. Here we present a stratigraphically well-constrained series of 56 flood basalt flows from the Eocene Initial Phase of magmatic activity in East Africa. These flows and their crystal cargo, permit temporal insight into the development of one the youngest and best-preserved continental large igneous provinces. The stratiform mafic lavas exposed in northern Kenya consist of alternating aphyric and plagioclase-phyric lava packages consistent with periods of eruption punctuated by volcanic hiatus, where magmas stall and crystallize plagioclase at medium to shallow crustal levels. Plagioclase compositions (n=541) exhibit little intra-crystal or intra-sample compositional diversity. Intra-crystal equilibrium calculations for Sr and Ti indicate internal chemical equilibrium, requiring storage at high temperature over a prolonged time interval (10,000-100,000 years). Using a series of seven interlinked partial crystal fractionation under equilibrium conditions models, we replicate the observed stratigraphic patterns in plagioclase composition. We find that the balance between recharge and evacuation, and diffusive equilibration within a shallow magmatic system, controls the composition of plagioclase in these flood basalts. We conclude that the shallow fractionation system modulates eruptive cycles and thus constitutes a critical component in studies of continental large igneous provinces.

Geochemistry and geochronology of the TTG-sanukitoid suite in the Zhulagou area: Constraints on the Neoarchean crustal evolution of the western North China Craton

The Archean basement in the Yinshan Block of the western North China Craton consists of a variety rock of assemblage, including TTG (tonalite-trondhjemite-granodiorite) rocks and some dioritic gneiss (sanukitoid). Understanding the petrogenesis of these rocks is crucial for comprehending the late Neoarchean crustal evolution of the western North China Craton. This study provides a new geochronological, geochemical, and Sr-Nd-Pb-Hf isotopic data for the TTG-sanukitoid suit that was newly identified in the Zhulagou area. The late Neoarchean TTG gneisses were emplaced around 2.54–2.50 Ga, while dioritic gneiss was emplaced between 2.53 and 2.50 Ga. The TTG gneisses exhibit high SiO2 (64.46–72.24 wt%) and Al2O3 (13.37–16.48 wt%) contents, relatively elevated (La/Yb)N and Sr/Y ratios, as well as low Y and Yb contents. They display variable εHf(t) (+0.94 to +3.57) and εNd(t) (−1.02 to +0.82) values, with relatively low Pb isotopic compositions, suggesting that they were derived from the partial melting of a thickened mafic lower crust. On the other hand, dioritic gneiss shows moderate SiO2 (58.05–61.87 wt%) content, high MgO (2.62–4.06 wt%), Al2O3 (14.42–18.44 wt%) and Cr contents, but relatively low (La/Yb)N values, showing geochemical affinity to the Archean sanukitoids. The dioritic gneiss exhibits variable εHf(t) values (−2.29 to +5.56) and εNd(t) (−2.05 to +2.02), with relatively low Pb isotopic compositions. Furthermore, the presence of amphibolite xenoliths, along with the high Mg# contents (36.84–53.49), indicating the addition of mantle-derived components to its source region. Therefore, the formation of the dioritic gneiss is primarily attributed to partial melting of the thickened (mafic) lower crust and the addition of mantle material. By combining previous studies with the new data presented in this study, we propose that a late Neoarchean tectonic regime involving a mantle plume is the most favorable explanation for the two major magmatic events in the Yinshan Block. Firstly, the earlier pulse/stage of mantle plume resulted in the ~2.7 Ga thickened (mafic) lower crust and a limited amount of TTG rocks. Subsequent pulse/stage of mantle plume triggered partial melting of pre-existing thickened (mafic) lower crust and generated 2.54–2.50 Ga TTG rocks and dioritic gneiss.

The Petrographic Characteristics and U-Pb Zircon Isotope Age of Felsic Extrusive Rocks in the Western Thanh Hoa Area, Song Ma Suture Zone

Felsic extrusive rocks are widely distributed in the western region of Thanh Hoa, primarily comprising rhyolite and rhyolitic tuff formations. They show porphyritic textures, and are composed of 15–25% phenocrysts and 75–85% groundmass. Phenocrysts are mainly euhedral–subhedral plagioclase (5-10 vol.%), K-feldspar (5-10 vol.%) and quartz (5-10 vol.%). The groundmass consists of plagioclase (30-45 vol.%), K-feldspar (25-40 vol.%), quartz (30-40 vol.%), and minor biotite with random distribution. In terms of geological context, these extrusive rocks overlie Silurian-Devonian sequences of sandstone and siltstone interbedded with shale and limestone lenses, and were intruded by the Early Triassic granite of the Song Ma complex. Zircons selected from rhyolite were LA-ICP-MS U-Pb dated, yielding an age of 253 Ma. This age is the timing of the magma crystallization, corresponding to the Late Permian - Early Triassic Indosinian tectonomagmatic event. These findings together with historical study results, prove that the Indosinian magmatic event widely occurred in the Truong Son belt, the Song Ma domain and the Kon Tum area. The eruption of the rhyolite is linked to the amalgamation between the South China and Indochina blocks.

Baddeleyite U-Pb age and whole-rock geochemical characteristics of ∼ 1670 Ma diabase dyke in the Shennongjia area: Implications for the tectonic setting of northern Yangtze Craton during the late Paleoproterozoic

The Shennongjia Group in the northern margin of the Yangtze Craton consists mainly of thick carbonate rocks interlayered with some intervals of volcanic and terrigenous clastic rocks. With the geochronological achievements in recent years, the depositional age of this group can be constrained into the time span of 1400–1000 Ma at present, belonging to the Mesoproterozoic Ectasian period. It is also a potential candidate interval for the “Undefined System/Period” in the Regional Chronostratigraphic Chart of China. According to the 1:200,000-scale conventional regional geological survey in the ‘1960–1970 s’, at the northwest side of the dominant peak of the Mt. Shennongding, it shows a ring-shaped gabbro-diabase dyke intruded in these Ectasian formations. However, due to the lack of comprehensive studies, there are lots of controversy both about the intrusion time and the tectonic setting of the mafic dyke.In this study, by means of the LA-ICP-MS and SHRIMP method successfully, the baddeleyite from the Banbiyan gabbro-diabase dyke yielded gained the weighted average 207Pb/206Pb age 1668.3 ± 5 Ma (MSWD = 1, N = 53) and 1667.8 ± 7 Ma (MSWD = 0.7, N = 23), respectively. It represents an unambiguous late Paleoproterozoic Statherian Period magmatic event in northern Yangtze Craton. Further, for the first time, it indicates the existence of the geological records prior to ∼ 1.67 Ga in the Shennongjia area.In addition, Banbiyan gabbro-diabase samples have relatively concentrated SiO2 (48.33 % to 49.65 %) and high whole iron content (10.25 % to 12.78 %). They show Na2O + K2O ranging from 2.9 % to 4.64 % and TiO2 from 1.36 % to 1.62 %. All samples are enriched in LILE, e.g., Rb, K, and Ba. The REE pattern shows a moderately right-inclined curve between E-MORB and OIB. These geochemiacal characteristics are agreed with contemporaneous magmatic event in the southwestern Yangtze Craton, indicating a within-plate rifting background and should correspond to the rifting of the Columbia Supercontinent.

Significant variations in the structure and composition of the crust beneath northwestern India: Imprints of magmatism

Northwestern India was affected by the Neoproterozoic Malani and Erinpura magmatism, Cretaceous rifting, and magmatism associated with the Deccan precursors. Receiver function analysis was done using 1704 RFs from 18 stations to image and decipher the imprints of the magmatic events and comprehend the crustal modifications in terms of variations in structure and composition. The H-κ grid search and neighbourhood inversion techniques are used to retrieve the crustal structure and Vp/Vs ratios (κ). The study reveals significant variations in the crustal thickness (H = 34 km to 43 km), composition (κ=1.74 to 1.92) and shear wave velocity structure across northwestern India. The terrains encompassing the Erinpura granite and the Malani igneous suite in the vicinity of the Barmer rift are characterized by a thick (H ≥ 41 km) crust with felsic to intermediate composition (κ ≤ 1.81). The crust beneath the southern part of the Marwar basin is ≈ 38–40 km thick with mafic composition (κ> 1.81). The region around the Barmer rift has a thin crust (H = 34–36 km) with intermediate to mafic composition. The region hosting the Early Cretaceous to Paleogene alkaline complexes exhibits a high Vp/Vs ratio (κ= 1.91) that may be associated with mafic cumulates emplaced by magmatic events that overprint the signatures of the Malani event. The crust is heterogeneous with low/high velocity intracrustal layers that reflect the fractionation of magma at different depths. The mafic residue, together with magmatic intrusions, results in a mafic lowermost crust with high shear velocities of 3.9–4.0 km/s beneath most stations. Overall, northwestern India is characterized by a thick crust with intermediate crustal composition and intracrustal layering resulting from large scale magmatic events linked to the Neoproterozoic reorganization of plates and younger magmatic events.

Testing in-situ apatite Lu–Hf dating in polymetamorphic mafic rocks: a case study from Palaeoproterozoic southern Australia

In mafic systems where primary mineral assemblages have witnessed moderate- to high-temperature hydrous overprinting and deformation, little is known about the retentivity of the Lu–Hf isotopic system in apatite. This study presents apatite laser-ablation Lu–Hf and U–Pb geochronology, zircon geochronology, and detailed petrological information from polymetamorphic mafic intrusions located in the central-western Gawler Craton in southern Australia, which records an extensive tectonometamorphic history spanning the Neoarchaean to the Mesoproterozoic. Zircon records magmatic crystallisation ages of c. 2479–2467 Ma, coinciding with the onset of the c. 2475–2410 Ma granulite-facies Sleafordian Orogeny. The amphibole-dominant hydrous assemblages which extensively overprint the primary magmatic assemblages are hypothesised to post-date the Sleafordian Orogeny. The Lu–Hf and U–Pb isotopic systems in apatite are used to test this hypothesis, with both isotopic systems recording significantly younger ages correlating with the c. 1730–1690 Ma Kimban Orogeny and the c. 1590–1575 Ma Hiltaba magmatic event, respectively. While the early Mesoproterozoic apatite U–Pb ages are attributed to thermal re-equilibration, the older Lu–Hf ages are interpreted to reflect re-equilibration facilitated primarily by dissolution-reprecipitation, but also thermally activated volume diffusion. The mechanisms of Lu–Hf isotopic resetting are distinguished based on microscale textures and trace element abundances in apatite and the integration of apatite-amphibole textural relationships and temperatures determined from the Ti content in amphibole. More broadly, the results indicate that at low to moderate temperatures, apatite hosted in mafic rocks is susceptible to complete recrystallisation in rocks that have weak to moderate foliations. In contrast, at higher temperatures in the absence of strain, the Lu–Hf system in apatite is comparatively robust. Ultimately, the findings from this study advance our understanding of the complex role that both metamorphism and deformation play on the ability of mafic-hosted apatite to retain primary Lu–Hf isotopic signatures.

An enhanced chemical maturation of juvenile arc crust recorded by the Urad Houqi intrusive suite in Langshan arc, Central Asia

Continental arc magmatism is crucial in producing juvenile continental crust of andesitic to dacitic composition, yet its impact on the formation of the modern mature continental crust, which is more enriched in potassic and granitic components, remains poorly understood. We examined a suite comprised of norite gabbro, gabbroic diorite, high-Mg diorite, dioritic enclave, and medium-K to high-K granites (the Urad Houqi suite) from the Langshan arc in the southern Central Asian Orogenic Belt (CAOB). Zircon U-Pb geochronology indicates that the Urad Houqi suite was formed ca. 278−268 Ma by a continuous magmatic event, marking the final episode of the late Paleozoic continental arc magmatism in the southern CAOB induced by the subduction of the Paleo-Asian Ocean. The suite exhibits a more potassic and fertile composition compared to typical continental arc magmas, and shows a continuous increasing K2O/Na2O ratio and incompatible element concentrations, including K, Rb, Th, and U, with increasing SiO2 content. The geochemical evolution of the suite offers valuable insights into the maturation process of the juvenile arc crust. By combining zircon Hf and bulk-rock Sr-Nd-Pb isotope studies, we demonstrated that the various lithologies within the Urad Houqi suite recorded a three-stage enhancement of the geochemical fertility of the juvenile Langshan arc crust: (1) generation of the initially fertile primary melt from the mantle wedge metasomatized by the recycled subducted sediments; (2) trans-crustal open-system hybridization processes, including peritectic reaction and magma mixing, that further fertilized the derived melts in addition to fractional crystallization; and (3) diverse petrogenetic processes that contributed to the fertility of the granitic magmas, including polybaric fractionation of the primary magma, anatexis of ancient crust, and extraction of high-silica melts from the shallow mush system. The three-stage maturation of the juvenile Langshan arc crust was typically coupled with the accelerated subduction of the Paleo-Asian Ocean since the earliest Permian. Our study finds that the Urad Houqi suite can serve as an example of modern continental crust maturation at continental arc settings.

Detrital zircon U–Pb geochronology and geochemistry of sandstones in the Siziwang Banner, Central Inner Mongolia: Implication for tectonic evolution

The central Inner Mongolia, located at the intersection of the northern margin of the North China Craton (NCC) and the Central Asian Orogenic Belt, is crucial for deciphering the Late Palaeozoic tectonic evolution associated with the subduction and closure of the Palaeo‐Asian Ocean (PAO). Our study focused on petrology, detrital zircon LA–ICP–MS U–Pb geochronology and whole‐rock geochemistry for the Late Carboniferous to Permian sandstones within the Shuanmazhuang, Dahongshan, Naobaogou, and Laowopu formations in Siziwang Banner, central Inner Mongolia. This comprehensive analysis shed light on the dynamic interplay between the NCC and the South Mongolia Block. Detrital zircon U–Pb ages in investigated samples mainly cluster between 250 and 2650 Ma, with significant peaks at 2.4–2.5 Ga, 1.8–2.0 Ga, 400–430 Ma, and 250–320 Ma, respectively. The geochemistry data are characterized by SiO2 contents (56.29–77.95 wt. %), Na2O / K2O ratios (0.45–1.58) and SiO2/Al2O3 ratios between 4.33 and 7.44. Moreover, they exhibit the slight enrichment in large ion lithophile elements (Rb and Ba) and the depletion in high field strength elements (Nb, Ta, Th, and U). These facts indicate that the sedimentary detritus predominantly originates from felsic sources, probably deriving from the Late Carboniferous–Permian continental island arc‐related intermediate‐acid igneous rocks, the Late Ordovician‐Silurian magmatic rocks in the Bainaimiao arc and the basements of the NCC. Furthermore, our present results also suggest that during the Early–Middle Permian, accelerating oceanic crust subduction triggered significant magmatic events in Siziwang Banner, leading to rapid uplift and the erosion of arc magmatic rocks, as well as the abundant corresponding sediments. Subsequently, the gradual convergence and eventual collision between the NCC and the Southern Mongolian Block took place at the end of the Permian, representing final closure of the PAO.

Petrogenesis of the eudialyte-bearing syenite and indication for Nb-Zr-REE mineralization in Bashisuogong, Northwest China

The Bashisuogong alkaline igneous intrusion is located between the South Tianshan Orogenic Belt and the Kepingtage foreland thrust belt at the northern margin of the Tarim Craton and hosts economically significant Nb–Ta–Zr–rare earth element mineralization. Eudialyte has recently been discovered in the syenite unit of this intrusion, which is the primary host mineral for high-field-strength and rare earth elements. Based on detailed petrographic investigations, this study investigated the behavior of trace elements during magma evolution and the enrichment of ore-forming elements using whole-rock geochemical analyses of eudialyte-bearing syenite and compositional analyses of aegirine–augite and different types of eudialyte. We also undertook in situ titanite UPb dating. The Bashisuogong syenite comprises aegirine–augite and aegirine–augite–eudialyte syenite, the latter of which have higher total rare earth element contents. Both types of syenite exhibit slight enrichments in light rare earth elements, significant enrichments in high-field-strength elements (Nb, Ta, Zr, Hf, and Th), depletions in large-ion lithophile elements (Ba and Sr), and large negative Eu anomalies. There are two types (I and II) of eudialyte. Eudialyte I has higher Mn/Fe, Zr/Hf, and Nb/Ta ratios but lower Th/U ratios compared with eudialyte II but similar Y/Ho ratios. Eudialyte II crystallized earlier than eudialyte I, and aegirine–augite, titanite, and apatite crystallized earlier than eudialyte I. Both aegirine–augite and eudialyte have similar trace element characteristics to the host rocks, exhibiting enrichments in highly incompatible high-field-strength and rare earth elements, as well as marked negative Eu anomalies and depletions in Sr. These characteristics suggest that the Bashisuogong alkaline rocks formed by low-degree partial melting of geochemically enriched, metasomatized lithospheric mantle, which formed an alkaline basaltic parental melt that then underwent protracted magma evolution and fractionation in the shallow crust. The eudialyte syenite yield a titanite UPb age of 277.3 ± 1.2 Ma, which is consistent with the ages of different types of alkaline igneous rocks in the study area, indicating they were the products of the same magmatic event. Temporally and spatially, the Bashisuogong ore-bearing alkaline rocks were associated with the Tarim mantle plume, and the mantle plume provided the heat for their formation.

Is the Yermak Plateau a continental fragment from North America? Constraints from Cretaceous and early Eocene magmatic events

The Yermak Plateau (YP) north of Svalbard is a prominent bathymetric feature in the Eurasia Basin of the Arctic Ocean, forming the northwesternmost margin of the Eurasian plate. Seismic data indicate that the YP comprises continental basement; however, little is known about its geology. New petrographic, geochemical, Sr–Nd isotopic, and Ar–Ar geochronological data were obtained on rock fragments, which were previously recovered from basement highs of the northeastern and southwestern YP and are dominantly of magmatic origin. These new data combined with available literature data, and comparisons with volcanic and sedimentary rocks from onshore and offshore areas adjacent to the YP indicate that the northeastern YP and the southwestern YP are different regarding their geological evolution. The southwestern YP comprises an alkaline basaltic suite for which an Ar–Ar biotite age of 51 Ma was previously reported. The suite was formed in a continental extensional regime offshore northern Svalbard. Associated sedimentary rocks (sandstone, several limestones) show petrographic similarity with rocks of the Devonian Old Red Sandstone on Svalbard. From the northeastern YP, in contrast, we recovered mildly alkaline basaltic rocks with mid-Cretaceous Ar–Ar ages (102 ± 3 and 98 ± 3 Ma). The rocks show certain geochemical characteristics (partial enrichments of P, Ba, and Eu), which overlap with similar-aged Cretaceous basaltic rocks from northern Ellesmere Island of Canada and North Greenland. We suggest that the northeastern YP is a continental fragment derived from the North American plate, which was separated from the conjugate Morris Jesup Rise and juxtaposed to the geologically distinct southwestern YP by the propagation of the Gakkel Ridge spreading center since the early Oligocene.Graphical

Seismic evidence of a plume conduit in a metasomatized lithosphere beneath the Barmer rift in northwestern India

Teleseismic tomography was done to investigate the lithosphere beneath northwestern India which was affected by several magmatic episodes since Neoproterozoic times. Broadband stations were deployed in phases at 29 locations in an area of 300 km × 300 km in northwestern India. About 8000 high-quality P phases corresponding to 934 events were used. Relative residuals estimated through adaptive stacking were inverted using the Fast Marching teleseismic tomography to obtain the 3D velocity perturbations. The tomograms revealed an anomalous ≈ 100 km wide, cylindrical zone of low velocities (−2% to −2.3%) extending from a depth of ≈ 60 km to ≈140 km beneath the Barmer rift. A broader zone of low velocities (−1%) encompasses the upper mantle down to a depth of at least 200 km. The anomaly lies beneath the localized, small-volume, eruptive centers of the earliest phase of Deccan volcanism within and on the flanks of the rift which falls on the projected extension of the Reunion hotspot track along the rift system of northwestern India. Explaining such large anomalies requires a significant increase in temperature, presence of melt and/or compositional changes. Geochemical studies indicate that the polychronous (early Cretaceous to Paleogene) alkaline complexes above the anomalous zone are derived from hydrated mantle peridotite and contain an abundance of phlogopites, suggesting a hydrated and metasomatized lithosphere beneath northwestern India. A thermal source impinging from below upon a metasomatized, weak, and rifted lithosphere may result in the observed signature akin to that of a plume conduit that overprints the older signatures of the Neoproterozoic Malani magmatic event.

Oman as a fragment of Ediacaran eastern Gondwana

Comprehensive U-Pb detrital zircon geochronology of Ediacaran sandstones from Oman indicates that they originated from Neoproterozoic basement with a peak magmatic age of ca. 850−780 Ma (Tonian), with lesser Paleoproterozoic and Ediacaran sources and renewed magmatic input starting at ca. 550 Ma. Comparison with detrital zircons from the Arabian-Nubian and NW Indian Shields supports an eastern Gondwana affinity for the Ediacaran succession of Oman. Tonian basement sediment sources are present in Oman. Sources for older Paleoproterozoic zircons (ca. 2500 and 1800 Ma) are not found in Oman but are known from the cratonic Indian Shield. The signal of the main magmatic events of the juvenile Arabian-Nubian Shield, peaking at ca. 640−620 Ma, is rare or absent in the Ediacaran rock succession of Oman. However, deformed Ediacaran clastic units with an Arabian-Nubian Shield affinity occur in western Oman. Influx of latest Ediacaran−early Cambrian zircons (550−525 Ma) is interpreted as due to final Cambrian Angudan/Malagasy orogeny-related magmatism. These results, together with new ages for volcano-sedimentary terranes in the subsurface of SW Oman and seismic observations, support the interpretation that the Ediacaran succession of Oman was deposited along the western, passive margin of the Greater Indian Shield, on the eastern (east and west in this paper refer to present-day coordinates) side of the Mozambique Ocean. Oman then collided with the Arabian-Nubian Shield in the early Cambrian, when the Angudan/Malagasy orogeny led to final consolidation of Gondwana. Our data support the inference that the youngest and final suture between the Indian and Arabian Shields lies in the subsurface of Oman along the early Cambrian western deformation front.

Oligocene–Miocene arc magmatic activities associated with the giant Reko Diq porphyry Cu–Au deposit, western Chagai arc, Balochistan, Pakistan

The Chagai belt to the north of the Afghan block and the east of the Iranian block in the western part of Pakistan is known for occurrence of Oligocene to Miocene calc‐alkaline magmatic belt. The present study discusses the characteristics of episodic magmatic activities that contributed to mineralization for the Reko Diq porphyry complex in the western part of the Chagai belt. U–Pb dating of zircons from volcanic rocks of the Reko Diq porphyry complex yielded ages of 25.8 ± 1.8 and 12.29 ± 0.44 Ma for two phases of magmatic crystallization. Geochemical analyses of whole‐rock rhyolite and dacite indicate that the rock units are peraluminous calc‐alkaline, derived from Andean‐type subduction. The magma was formed due to partial melting of the thickened mafic lower crust in a continental arc setting in relation to the subduction of the Neotethys along the Makran subduction zone. The abundance of zircons, Hf, REE, U/Pb and Th indicates high degrees of magmatic evolution. Moreover, the Sr and Nd isotopic data indicate the fractional contribution of depleted N‐MORB mantle to the Reko Diq magmas through bulk mixing with magmas derived from the lower continental crust. Short‐lived magmatic systems repeated magma injection, and various episodes of hydrothermal fluid flow have led to the formation of porphyry mineralization. Emplacement of the Reko Diq porphyry complex and related Cu–Au mineralization is associated with a series of tectonic–magmatic events at different episodes of the Oligocene–Miocene times.

Deciphering Iberian Variscan Orogen Magmatism Using the Anisotropy of Magnetic Susceptibility from Granites

In this paper, we have synthesized the information derived from more than 20 papers and PhD theses on the anisotropy of the magnetic susceptibility (AMS) of 19 Variscan granite plutons, spanning the period between 320 Ma and 296 Ma. The AMS data are obtained from 876 sampling sites with more than 7080 AMS measurements and a re-interpretation is proposed. The studied granites exhibit a magnetic susceptibility (Km) ranging from 30 to 10,436 × 10−6 SI units. Most granites typically exhibit Km values below 1000 × 10−6 SI, indicative of paramagnetic behavior. Biotite serves as the main carrier of iron (Fe), emphasizing the reduced conditions prevalent during the formation of granite melts in the Variscan orogeny. The AMS fabrics of the studied granite plutons record the magma strain, expressing the chronologic evolution of the stress field during the orogeny. This chronologic approach highlights the magmatic events between around 330 and 315 Ma, occurring in an extensional regime, in which the Borralha pluton is an example of a suite that recorded this extensional AMS fabric. Plutons with ages between 315 and 305 Ma show AMS fabrics, pointing out their emplacement in a compressional tectonic regime related to the Variscan collision. The plutons, younger than 305 Ma, record AMS fabrics indicating that the tectonic setting for emplacement changes from a wrench regime to an extensional one at the end of the collision stage. This is evident as there is a chronological overlap between the granites that exhibit AMS fabrics indicating extension and the ones that have AMS fabrics indicating a wrench regime.

The Esquinzo Ultra-Alkaline Rock Suite of Fuerteventura Basal Complex (Canary Islands): Evidence for Origin of Carbonatites by Fractional Crystallization

The origin of the carbonatites that appear on Earth is one of the most controversial current topics in the petrogenesis of igneous rocks. Situated in the northern sector of the Basal Complex of Fuerteventura (Canary Islands), the Miocene Esquinzo ultra-alkaline plutonic rock complex is composed of pyroxenites, melteigites-ijolites-urtites, malignites-nepheline syenites, carbonatites, silicocarbonatites, nephelinites and nepheline phonolites. This work tries to establish the genesis of this massif of ultra-alkaline rocks with associated carbonatites from Fuerteventura (which are very rare in the oceans). The geochemical characteristics of these rocks and the minerals that are included in them have allowed us to establish their origin. This complex was generated by three successive magmatic events associated with differentiation of melanephelinite magmas emplaced in the oceanic crust. Silicocarbonatite and calciocarbonatite (sövites) dykes are related to the first magmatic event and were formed by fractional crystallization of H2O- and CO2-rich ijolite magmas. The melanephelinite magmas that formed these plutonic ultra-alkaline rocks were apparently generated as partial melts of asthenospheric mantle, which assimilated enriched lithospheric mantle material as they ascended. The upwelling of this large body of anomalous asthenospheric Miocene material exceeded the deformation associated with plate motions and led to an oceanic rifting event in Fuerteventura.

Magmatically driven hydrocarbon generation and fluid flow in the Namibe Basin of Angola

Abstract Magmatic activity can severely alter the thermal structure of a sedimentary basin, with variable effects on the petroleum system. The Namibe Basin of Angola (Cretaceous South Atlantic rift) contains well-exposed magmatic and petroleum system elements and allows integrated assessment of how magmatic activity can modify the petroleum system. The basin was affected by syn-rift and post-rift magmatic events, and bitumen is observed within both the Pre- and Post-Salt stratigraphical sections. In the Pre-Salt, fluorescent bitumen has a lacustrine signature and is associated with calcite and quartz cements. Onshore Pre-Salt units are thermally immature, and therefore the source rock that generated the Pre-Salt bitumen is likely located offshore. Hydrocarbons migrated or re-migrated via magmatically driven fluids, reaching the present-day onshore. Closer to magmatic units, non-fluorescent pyrobitumen was instead observed, evidencing hydrocarbon cracking processes following emplacement. In the Post-Salt, bitumen is in situ and shows marine-like signatures compatible with an immediate Post-Salt source rock depositional environment. In the immediate Post-Salt, units with very high total organic carbon values (TOC; up to 13.8%) and excellent source rock properties (hydrogen index >600 mgHC g −1 TOC) have reached thermal maturation. Within the Namibe Basin these Post-Salt source units lie in proximity to major Turonian–Coniacian–Santonian volcanic centres and associated shallow intrusions, which are likely to have caused thermally forced maturation processes and generation of the Post-Salt hydrocarbons. This paper demonstrates the importance of an integrated field, petrographic and geochemical approach in unravelling the influence of magmatic activity on basin thermal structure and petroleum systems.

The role of polyphase deformation in the formation of iron deposits and gold mineralization in the paleoproterozoic nyong complex greenstone belt (Southwestern Cameroon)

The Toko-Nlonkeng area is situated in the Nyong Complex of the northwestern Congo craton. In this study, airborne geophysical data (radiometric and magnetic) and structural data (outcrops and core samples) were used to investigate the relationship between structural evolution, iron formation (IFs)-hosted iron ore deposits, and gold mineralization in the Paleoproterozoic Nyong complex greenstone belt in southwestern Cameroon. Magnetic and radiometric trends, combined with field data, show general NE-SW, NW-SE, and E-W directions that correlate with the main gold-bearing structures. The study area has undergone four (04) deformation phases relating to polycyclic metamorphic and magmatic events. The D1 and D2 phases are the result of progressive ductile and transpressional deformation; D3 is a brittle-ductile deformation; and D4 is essentially brittle with various types of fracture networks late to post-orogenic. The D3 deformation phase is characterized by constrictive deformation with C3 shears and meso‑ to mega-P3-folds, and the main stress axes show φσ2 > φσ1> φσ3, reflecting a shearing tectonic regime with a maximum E-W shortening. This polyphase deformation is derived from the Eburnean/Trans-Amazonian deformation related to the collision between the Congo and São Francisco cratons. The main strain in the structural style of the Nyong Complex appears to be transpressive tectonics. This study reveals that iron ore and gold mineralization were mostly found on the hinges of folds and confirms that folding shear zones controlled the iron ore and gold target in the Nyong Complex and Northeast Brazil. The study proposes an approach to optimize future exploration activity based on the integration of the data.

Metallogenetic epoch and material source of Be-pegmatite differentiated from biotite granite in Mufushan complex

The Mufushan Complex (MFSC) is a significant rare metal mineralized in the central China district and is renowned for its marked economic value of rare metal deposits. While the main rare metal mineralization (RMM) stage in the MFSC relates to the magmatic event of two-mica monzogranite, the mineralization event related to biotite monzogranite remains unknown. To fill this gap, this study focuses on porphyritic biotite monzogranite and adjacent Be-rich pegmatite samples obtained from Changqing Pegmatite No. 1, which is situated in the southeastern part of the MFSC. We subjected these samples to zircon U–Pb dating and Hf isotope analysis using laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) and utilized an electron probe X-ray microanalyzer (EPMA) and LA–ICP–MS to examine the major and trace elements present in the muscovite samples. Our findings revealed precise chronological data for the geological history of Changqing, pinpointing the intrusion age of biotite monzogranite to 145.8 ± 1.1 Ma and the crystallization age of Be-rich pegmatite to 144.9 ± 1.1 Ma, firmly situating these events within the Late Jurassic to Early Cretaceous epoch. Regarding isotopic composition, zircon εHf (t) for granite ranged from −9.29 to −5.09, and their corresponding TDM2 ranged from 1788 to 1520 Ma. Similarly, zircon εHf (t) for pegmatite ranged from −7.89 to −5.47, and their corresponding TDM2 ranged from 1699 to 1544 Ma. These isotopic signatures strongly indicate a shared origin for the initial magma of granite and pegmatite. The partial melting of the thick Lengjiaxi Group tasedimentary strata serves as a material source for RMM. The transition from granite to pegmatite exhibits remarkable constancy in the primary components of muscovite. By examining its geochemical attributes, we observed synchronous decreases in FeO, MgO, SiO2, MnO, Be, Rb, and Cs, coupled with synchronous increases in Nb and Ta contents, along with Ta/Nb values. These findings strongly imply that the Changqing biotite monzogranite and Be-rich pegmatite originate from the continuous differentiation and evolution of a common magmatic source, establishing a clear genetic relationship between them. The MFSC has its origins in three distinct stages of magmatic activity and RMM spanning from 160 Ma to 120 Ma. Considering the distribution patterns of similar pegmatite veins, the metallogenic potential observed during the biotite granite stage may serve as an external indicator of marked mineralization within large batholiths.

Crystal mush rejuvenation in the formation of Triassic dacites in Mengku, SE Tibetan Plateau

The tectono-magmatic event of the Changning-Menglian Paleo-Tethys orogen is an important process for understanding the tectonic evolution of the SE Tibetan Plateau. This orogen is composed of Changning-Menglian suture, Lancang group, Lincang batholith, and Yunxian volcanics. The Lincang batholith and its volcanic counterparts are part of Triassic magmatism in this orogen. The botholith is composed of biotite monzogranite, granodiorite and diorite. The Middle to Late Triassic volcanics include Manghuai rhyolite, Xiaodingxi basalt and Mengku dacite. The Mengku dacite is volcanic dome in west of the batholith. Lincang biotite monzogranite and Mengku dacite have similar geochemistry and are characterized by negative εHf (t) values (–13.2 to –5.2) and εNd (t) values (–14.7 to –8.8), whereas diorite dikes within the Lincang batholith have slightly high εHf (t) values (–8.3 to –4.9) and εNd (t) values (–6.9 to –6.7). Manifestations of resorption textures in quartz and reverse compositional zoning in feldspars are recognized from Mengku dacite. We consider that Mengku dacites resemble the erupted Lincang biotite monzogranite as they occur in the same tectonic settings and have similar geochemical features and mineral assemblages dominated by plagioclase, alkali-feldspar, quartz, and biotite. The evolution of the Mengku dacite magma is characterized by the rejuvenation of crystal mush represented by the Lincang batholith. The required thermal input was supplied by mafic magma, represented by diorite dikes and enclaves within the Lincang batholith. The Middle to Late Triassic magmatic event in this orogen likely resulted from lithospheric delamination and upwelling of the asthenosphere in a post-collisional environment.