Intermediate Volcanic Rocks Research Articles

Age and tectonic setting of Mesozoic extension constrained by the first volcanic events in the Eastern Cordillera and Middle Magdalena Valley, Colombia

Before the rise of the Northern Andes in Cenozoic time, Triassic to Jurassic extensional basins in northwestern South America accommodated predominantly continental strata partly intercalated with volcanic rocks. Coeval plutonism is attributed to a magmatic arc related to the subduction of the Farallon plate beneath South America. The basins later became involved in the Andean orogeny and are now partially exposed in the Eastern Cordillera and Middle Magdalena Valley of Colombia. We have employed (U/Pb) geochronology on zircons from Triassic-Jurassic felsic to intermediate volcanic and volcaniclastic rocks. Most of the ten samples have a substantial proportion of detrital zircons, but only three had no Mesozoic grains. The Mesozoic ages obtained range from ca. 201 Ma to ca. 177 Ma and overlap with published crystallization ages (K/Ar; Ar/Ar; U/Pb) from plutonic bodies. Volcanics from the Jordán and Girón formations are latest Triassic to Early Jurassic and synchronous with major plutonic activity. These ages constrain the early evolution of the extensional basins that formed from about the Triassic-Jurassic transition in an intra-arc position and facilitated the preservation of sediment and arc-derived volcanics. Middle Jurassic ages from the Noreán Fm. are synchronous with sparse plutonism west of the Middle Magdalena Valley. At this time, the magmatic arc had migrated westward, while intrusive activity in the Eastern Cordillera ceased. A geochemical rift signature only appears in scarce Early Cretaceous mafic intrusions that resumed magmatic activity in the Eastern Cordillera. This magmatism, now in a back-arc position, coincides with maximum subsidence of the large Cretaceous basin that extended across the older intra-arc rift basins. Extension and lithospheric thinning ceased by the end of the Early Cretaceous.Graphical abstract

Using compositions of zircon to reveal fertile magmas for the formation of porphyry deposits in the Loei and Truong Son fold belts, northern Laos

The Loei and Truong Son fold belts are well known as being the most geologically important and highly mineralized magmatic arc-related terranes in mainland southeast Asia. Numerous studies have examined the geology, geochemistry, and geochronology but only a few metallogenic and detailed deposit characterizations have been undertaken. This study of zircon geochemical analyses uses laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to provide U-Pb ages and magmatic fertility of felsic to intermediate volcanic and plutonic rocks from ten prospects in the Loei and Truong Son fold belts, in the northwest Laos region. The geochemical and geochronological analyses suggest at least three episodes of magmatism occurred: Silurian-Devonian (434–411 Ma), Early to Middle Permian (299–277 Ma), and Late Permian to Middle Triassic (253–243 Ma). The variable ranges of ɛHf values (−12 to + 12) suggest that mantle-derived and crustal contamination signatures are related to the history of subduction and arc magmatism in this region. Key trace elements and ratios associated with oxygen fugacity of magmas (e.g., Eu/Eu*, Dy/Yb, Ce/Nd, ΔFMQ) imply that the Phu Kham and the west of Vientiane along the Mekong River are likely to be fertile for porphyry copper deposits. In contrast, the Pha Gnai and other suites are less fertile. Using zircon as a fertility indication can be a valuable tool to distinguish between fertile and barren magmatic suites in this area.

Late Jurassic Tethyan igneous records in North Sumatra: Geochronological and geochemical constraints

The Jurassic igneous rocks on Sumatra Island are important for investigating the Mesotethyan evolution and regional correlation in Southeast Asia. This paper presents new laser ablation−multicollector−inductively coupled plasma−mass spectrometry zircon U-Pb-Hf geochronological and isotopic, whole-rock elemental, and Sr-Nd isotopic data for the newly identified Glebruk dolerite and andesite in North Sumatra. New zircon dating results suggest that these mafic−intermediate volcanic rocks, with ages of 150−146 Ma, were formed during the Late Jurassic. The Glebruk dolerite and andesite belong to the calc-alkaline series, are enriched in the light rare earth elements, and exhibit depletion in Nb, Ta, and Ti. Thus, they resemble arc-like volcanic rocks. They have low (87Sr/86Sr)i ratios of 0.7038−0.7048 and strong positive εNd(t) and εHf(t) values of +6.4 to +7.5 and +4.8 to +18.6, respectively. Their geochemical signatures suggest that these Late Jurassic volcanic rocks were derived from a depleted mantle wedge that was metasomatized by the slab-derived melts. The Glebruk volcanic rocks were formed in a continental arc setting in response to the Late Jurassic northward subduction of the Woyla Ocean beneath West Sumatra. Our results and regional geological observations suggest that the Mesotethyan subduction-related igneous rocks could extend from South Qiangtang through West Yunnan to North Sumatra. The Woyla Ocean could represent the southern extension of the Mesotethyan Ocean.

Geochemical data of the Ediacaran-Cambrian magmatism of Jbel Belkheit and Jbel Bou-Acila as evidence for the Hercynian Cycle Rift-to-Drift events in the Moroccan Central Hercynian Massif

In the eastern sector of the Moroccan Central Hercynian Massif, Ediacaran and Cambrian magmatic rocks outcrop in the anticlines of Jbel Belkheit and Jbel Bou-Acila. These were emplaced between Pan-African deformed-sequences and Lower Palaeozoic levels in two successive volcanic series, separated by confirmed Lower Cambrian limestones: a) a lower series of Ediacaran age composed of felsic and intermediate volcanic rocks (rhyodacites and andesites). The rhyodacites are clearly calc-alkaline in character, comparable to rocks generated in an active margin orogenic context, whereas the andesites are transitional between calc-alkaline and tholeiitic, reflecting a change in the geotectonic context at the end of the Neoproterozoic; and b) an upper series of Cambrian age, composed of anorogenic tholeiitic basalts with massive flows in the bottom and pillow lavas in the top of the sequence. Although structural, petrographic and geochemical data rule out any genetic link between the felsic and the intermediate Ediacaran rocks, a geochemical link between the andesites and Cambrian basalts can be suggested. Both facies are thought to have been generated in an extensional context, although some of the orogenic features of their protolith are still present.In this sense, the Ediacaran andesites would be precursors of the Late Neoproterozoic – Early Cambrian rift rocks, leading to the eventual formation of Cambrian basalts. The latter facies were already emplaced in a clear extensional geodynamic context, and were probably generated by the same source that evolved during progressive crustal extension and thinning. This is confirmed by the evolution of Cambrian basalt morphostructures and geochemical characteristics from: i) massive flow basalts with a geochemical signature of intraplate tholeiites of E-MORB character; to ii) pillow lavas of oceanic tholeiites with a N-MORB character. This transition, therefore, marks the beginning of an oceanization process, which has never been described elsewhere in the Moroccan Cambrian.

The First Discovery of Cambrian Volcanic Rocks and Plagiogranites in the Tekturmas Ophiolite Zone (Central Kazakhstan): Age and Composition

The complex of felsic to intermediate volcanic rocks intruded by plagiogranitic bodies is first revealed in the western part of the Tekturmas ophiolite zone of Central Kazakhstan. The U–Pb (SIMS) geochronological study of one of the plagiogranitic bodies dated back to the Early Cambrian (537 ± 5 Ma) is conducted for the first time. The peculiarities of the volcanic rocks and the composition of plagiogranites indicate their formation in a suprasubduction setting within the Early Cambrian primitive volcanic island arc. The formation of this arc was not related to the evolution of the Ordovician oceanic structures, the complexes of which participate in the structure of the Tekturmas zone.

Formation of Archean greenstone belts: Insights from an assemblage-scale study in the western Superior craton

Archean greenstone belts contain the oldest volcanic rocks on Earth and can provide critical insights into Earth’s early evolution. This study chooses the Sturgeon Lake greenstone belt in the easternmost Western Wabigoon terrane (WWT) of the Superior craton to illustrate an option for better understanding the formation of Archean greenstone belts. Our dataset includes outcrop observations, bulk compositions of 77 mafic to felsic volcanic samples, and in-situ U-Pb, Lu-Hf, and trace elements of zircon from 14 intermediate to felsic volcanic samples. The results revealed that this greenstone belt had broadly continuous volcanism from ca. 2780 to 2725 Ma, followed by a tectonic quiescence prior to a ca. 2707–2703 Ma volcanism at the terrane boundary. The intermediate volcanic rocks are characterized by variable Th/Nb and highly depleted Hf (zircon ƐHf(i) = +3 to + 6), interpreted to be derived from mantle sources ranging from those of normal mid-ocean ridge basalts (N-MORB) to those of enriched MORB (E-MORB), which commonly assimilated various felsic crustal components. The mafic volcanic rocks are dominated by low La/Sm basalts with negligible Nb, Ta anomalies and limited range of Th/Nb, forming a mantle array on the Th/Yb-Nb/Yb plot and consistent with oceanic crust of N-MORB to enriched N-MORB affinities. Some basalts from the ca. 2738–2725 Ma assemblages, however, gave high La/Sm, negative Nb and Ta anomalies, and limited range of Th/Nb plotting above and parallel to the mantle array. These basalts might be associated with passive subcretion and rollback of oceanic crust of the stagnant-lids tectonics or subduction of oceanic lithosphere as in modern-style plate tectonics, both of which are supported by trace element compositions of zircon that indicate hydrous, oxidized, large-ion lithophile element-enriched, and medium- to high-pressure magmas. Identification of three magma-series would not be possible if the data were lumped together, which is commonly seen in terrane- or craton-scale studies that sometimes propose contrasting interpretations of rock origins and Archean geodynamic processes. This detailed approach of distinguishing rock types and zooming into the subunits of a greenstone belt offers a practical solution to more accurately characterize Archean volcanic rocks and to better understand the early Earth.

Geochemistry, petrogenesis, and tectonic setting of the Cúcamo mafic and intermediate volcanic rocks from the Ahualulco Volcanic Complex, San Luis Potosí, Mexico

The Ahualulco Volcanic Complex (AVC) is situated in the north-central part of the San Luis Potosí Volcanic Field (SLPVF) that is found in the southern portion of the Mesa Central (MC). The Cúcamo, AVC is mainly composed of mafic and intermediate volcanic rocks. The present study focuses on understanding the evolution, origin, and magmatic processes and petrogenesis of mafic and intermediate rocks in the Cúcamo, AVC. The Quaternary mafic rocks have porphyritic textures with the mineral assemblage of olivine, and clinopyroxene. These volcanic rocks display high K calc-alkaline basaltic compositions with enrichment in light rare earth elements (LREEs) and incompatible elements. Geochemical modeling reveals that mafic magmas were derived through a partial melting process of a spinel lherzolite source at low degrees of melting (~2 to 15 %) in an extensional regime. The intermediate volcanic rocks show porphyritic and glomeroporphyritic textures with matrix formed by randomly oriented microlites. The main mineral assemblage consists of plagioclase, K-feldspar, and clinopyroxene. These volcanic rocks are characterized by calc-alkaline basaltic andesitic and andesite compositions with enrichment in light rare earth elements and incompatible elements. Geochemical modeling suggests that intermediate rocks were derived from high ratios of assimilation and fractional crystallization processes between mafic melts and continental crust in an extensional environment.

Clay mineralogy and provenance modeling of the Paleoproterozoic Kaladgi shales, Dharwar Craton, Southern India: Implications on paleoweathering and source rock compositions

Proterozoic clastic sediments reveal vast information regarding provenance, depositional conditions, and environmental evolutions. Peninsular India comprising Archean cratons, also have numerous intracratonic Proterozoic sedimentary basins along their margins. The Archean Dharwar craton in southern India has many Proterozoic successions, namely Cuddapah, Kurnool towards the East, and Kaladgi, Badami, and Bhima towards the northern margin. The Paleoproterozoic Kaladgi Basin (∼1.85 Ga) consists of siliciclastic sedimentary rocks with stromatolitic carbonate formations. XRD analysis of shale layers of the Lower Lokapur and Upper Simikere Subgroups have been carried out to understand the primary clay mineral assemblages, weathering history, and provenance. The Lower and Upper shale layers of Lokapur and Simikere Subgroups show a dominance of montmorillonite and kaolinite, respectively. The geochemical affinities and the clay mineral assemblages indicate a more mafic source to the lower shales (Manoli and Hebbal Formations) and increased felsic contribution to the upper shales (Govindakoppa and Daddanhatti Formations). Illite is ubiquitous in all the shales of the Kaladgi Supergroup possibly representing the diagenetic transformation of montmorillonite and kaolinite to illite. Geochemical modeling of provenance has been carried out using (Eu/Eu*)N, (La/Yb)N, (Gd/Yb)N, and (La/Sm)N of all the plausible source rocks and the average compositions of lower and upper shales. The modeling results suggest that the lower shales are derived from a source of mafic rocks – 45 %, K-rich granite – 35 %, and TTG – 20 %. While the upper shales are derived from source characterized by K-rich granites – 61 % and intermediate volcanic rocks – 39 %. These results signify the classical unroofing of TTG-greenstone belts exposing K-rich granites with the progression of sedimentation. Further, a good correlation between K-enrichment (a measure of % difference between CIA and pre-metasomatic CIA) and ƩLREE is attributed to the abundance of kaolinites that fractionate more LREE.

СТРУКТУРНАЯ ПОЗИЦИЯ, ПЕТРОГЕОХИМИЧЕСКАЯ И ПЕТРОПАЛЕОМАГНИТНАЯ ХАРАКТЕРИСТИКА ВУЛКАНИТОВ НИЛАНСКОГО ТЕРРЕЙНА (ЗОНА СОЧЛЕНЕНИЯ МОНГОЛО-ОХОТСКОГО И СИХОТЭ-АЛИНЬСКОГО ОРОГЕНОВ) И ГЕОДИНАМИЧЕСКИЕ ВЫВОДЫ

The paper presents the results of structural, geochemical, magnetic and paleomagnetic studies on Mesozoic rocks of the Nilan terrane, which from the north flank on the Paleozoic rocks of the Paukan block (52.0°N, 135.6°E). Jurassic and Triassic (?) multiple disturbance deposits of the terrane were found to be fragments of the Middle-Late Jurassic accretionary complex with accumulations of older oceanic rocks varying in thickness and the oceanic plate with completely destroyed stratigraphy. Basic and intermediate volcanic rocks hosted within Jurassic and Triassic (?) sedimentary rocks of the terrane are of oceanic origin. Based on geochemical and paleomagnetic data, it is assumed that the volcanic rocks formed near the equator in geodynamic settings of mid-ocean ridge and intraplate ocean islands.

Tonian–Ediacaran Tectonometamorphic History of the Sa'al Complex, Sinai (Egypt): Implications for the Tectonostratigraphic Framework of the Northern Arabian–Nubian Shield

AbstractThe Sa'al Metamorphic Complex (SMC; southern Sinai) encompasses the oldest arc rocks in the Arabian–Nubian Shield, comprising two non‐consanguineous metavolcanic successions (the Agramiya Group and the Post‐Ra'ayan Formation) separated by the metasediments of the Ra'ayan Formation. It experienced three distinct deformational events (D1–D3) and two low‐medium grade regional metamorphic events (M1–M2). The Agramiya Group and the Ra'ayan Formation experienced all tectonometamorphic events (D1–D3 and M1–M2), whereas the Post‐Ra'ayan volcanic rocks were only affected by the D3 and M2 events. D1 is an extensional event and is connected to the late Rodinia break‐up (∼Tonian; 900–870 Ma). The M1 metamorphism variably affected the older Agramiya Group, the rhyolitic tuffs experiencing lower to upper greenschist facies conditions and the basic and intermediate volcanic rocks undergoing amphibolite facies metamorphism. The Ra'ayan Formation metasediments experienced upper greenschist to amphibolite facies metamorphism. The upper greenschist facies M2 affected the youngest Post‐Ra'ayan volcanic rocks and other stratigraphic successions. The compressive D2 and D3 events were coeval with the accretion of dismembered terranes in the assembly of Gondwana. D2 can be linked to the Tonian–Cryogenian arc‐arc assembly (∼880–760 Ma; in Elat and Sinai), whereas D3 and the accompanying M2 is constrained to 622–600 Ma (Ediacaran).

Petrogenesis of mafic-intermediate magmatism of the Michoacán–Guanajuato volcanic field in Western Mexico. A geochemical review

The Michoacán–Guanajuato volcanic field (MGVF) in the western Trans-Mexican Volcanic Belt is one of the largest and most diverse monogenetic volcanic fields in the world holding more than 1200 volcanic vents. Its eruptive activity goes back to 7 Ma, it is considered an active volcanic field, and the composition of its rocks varies from mafic to silicic. It is essential to understand the geochemical evolution of its products, the complex petrogenetic processes, and the origin of magmas in central Mexico. Although these processes are linked to the subduction of the Cocos plate beneath the North American plate, the magmatic plumbing system of the MGVF remains not completely understood. The MGVF has been studied for decades, focusing in its dominant intermediate magmas. Nevertheless, the origin and evolution of the mafic components and their relation with the intermediate rocks have been poorly discussed. Here, we compile geological and geochemical data of the MGVF to discuss the petrogenesis of mafic magmas along the volcanic field and the role they play in the generation of intermediate melts. We used data published for 429 samples of mafic and intermediate volcanic rocks. Conventional procedures and statistical techniques were used to process the dataset. We propose that MGVF mafic magmas are derived from low degrees (∼1–15%) of partial melting of a spinel-bearing lherzolite source/mantle related to the rapid ascent of the asthenosphere caused by an extensional regime that is present in the area. In contrast, intermediate magmas where divided into two main groups based on the Mg content: high-Mg intermediate rocks, which seems to be derived from different rates of assimilation and fractional crystallization process, and low-Mg intermediate rocks, which can be related to fractional crystallization of mafic magmas. In addition, mafic and intermediate magmas display a chemical diversity which is related to mantle heterogeneity domains in the mantle wedge.

Metallogeny of the state of Oaxaca, southern Mexico: A review

The state of Oaxaca is one of the most geologically complex and diverse in Mexico. It comprises five tectonostratigraphic terranes of contrasting nature that form a sort of tectonic collage where several magmatic pulses were developed. The different lithological assemblages of Oaxaca favored the generation of a variety of ore deposit types, some of which have been a prime source of several commodities for centuries. This paper addresses the time-space relationship between ore deposits and tectono-magmatic events, based upon the available descriptions and radiometric ages. Most Meso-to Neoproterozoic ore deposits of Mexico occur in this region, and were formed during the regional granulite-facies metamorphic stage(s) recorded in the Oaxacan Complex. Such deposits are rare element-bearing pegmatites, nelsonites (ilmenite-apatite rich rocks), Ti-rich anorthosites, and pegmatites. The Oaxacan Complex also hosts a number of orogenic gold lodes that were likely formed in more than a single metamorphic episode and still require additional research to clarify their age and geological affiliation.The onset of arc-related magmatism in the Late Carboniferous-Permian is recorded by the intrusion of the calc-alkaline Zaniza, Cuanana and Honduras batholiths, along with several minor deformed and undeformed bodies enclosed in the Oaxacan Complex. Little is known about the metallogeny associated with such magmatism. Although supra-subduction magmatism re-initiated in the Jurassic and is probably responsible for the San Juan Mazatlán Cu porphyry, most of the metallogeny of Oaxaca is tightly linked to the Sierra Madre del Sur (SMS) igneous province, which began in Jalisco by the Late Cretaceous and migrated to the SE until it reached the Isthmus of Tehuantepec by the Middle Miocene. In Oaxaca, the Oligocene-Miocene coastal belt of granitic-granodioritic intrusions accounts for some IOCG deposits, especially in its easternmost portion, which then continues to the Coastal Chiapanecan Neogene batholithic belt.In W-NW Oaxaca, the intracontinental igneous province of the SMS marked the beginning of Cenozoic magmatism and is represented by thick volcanic-hypabyssal successions along with minor intrusions, with which copious magmatic-hydrothermal deposits are associated. Early Eocene and mid-Oligocene volcanism is restricted to the western half of the state, where basic-to intermediate-composition effusive products occur in the Mixteca and western Oaxaca tectonostratigraphic terranes. During this time span, many low-to intermediate-sulfidation epithermal, Fe-rich (IOCG) and polymetallic skarn deposits were produced. However, the “boom” in magmatic-hydrothermal mineralizations occurred during the terminal pulses of the SMS volcanism (Miocene), which comprise profuse intermediate volcanic rocks capped by the outburst of silicic magmatism. The early-to mid-Miocene event constitutes the most prominent in terms of metal endowment and diversity of ore deposit types, accounting for about 250 deposits and occurrences in the central and near-eastern portions of the state, which are ascribed to low-to intermediate-sulfidation epithermal, sulfide skarns, IOCG “clan” and Cu(–Mo) porphyry types. Among these, epithermal deposits are, by far, the most abundant type.Recent Ti-rich beach deposits and Au alluvial placers are present in southern and easternmost Oaxaca, respectively. In addition, supergene enrichment zones and uneconomic laterites occurrences are found in some localities.Oaxacan ore deposits can be grouped into five major metallogenic epochs: 1) Meso-Neoproterozoic REE-Th-U-Ti deposits and, possibly, orogenic gold lodes during the Olmecan-Zapotecan events (assembly of Rodinia); 2) feasible late Carboniferous-Permian (?) orogenic gold deposits; 3) early Eocene Ag–Au–Pb–Zn–Fe deposits during the onset of the SMS volcanic activity; 4) mid-Oligocene Ag–Pb–Zn–Sb–Hg–Fe(-Au) deposits during effusive-dominated pulses of the SMS volcanism; and 5) early-to mid-Miocene Au–Ag–Pb–Zn–Cu–Fe(-Mo-Sb) deposits during the termination of the SMS magmatism. The existence of a wealth of ore deposits with varying features underlines the economic potential of metallogenetic provinces and epochs in Oaxaca and exalts the necessity to expand the knowledge regarding the tectonic-magmatic-metallogenic evolution of the state.

Temporal variations in the geochemistry of Mesozoic mafic–intermediate volcanic rocks in the northern Great Xing'an Range, Northeast China, and implications for deep lithospheric mantle processes

Identifying the composition of the recycled materials in the lithospheric mantle is crucial for establishing links between mantle geochemical ‘reservoirs’ and deep mantle geodynamic processes. However, studies that focus on deep mantle processes under multiple subduction tectonic regimes have been absent. In this paper, we present 40 Ar/ 39 Ar age, whole-rock geochemical, and Sr–Nd–Pb–Hf isotope, zircon Hf-O isotope, and in situ plagioclase Pb isotope data for Mesozoic mafic–intermediate volcanic rocks in the northern Great Xing'an Range, northeast China. These and published data are used to constrain the deep processes that occurred in the lithospheric mantle during the Mesozoic, in the context of the evolution of the Mongol–Okhotsk Ocean and whether subduction of the Paleo-Pacific Plate affected the formation of volcanic rocks in the western part of northeast China. The Mesozoic mafic–intermediate volcanic rocks in the northern Great Xing'an Range can be divided into three stages: Early Jurassic (~180 Ma), Late Jurassic (~155 Ma), and late Early Cretaceous (~120 Ma). These rocks are mainly basalt, basaltic andesite, andesite, and trachyandesite. The Mesozoic mafic–intermediate volcanic rocks have SiO 2 = 47.34–60.00 wt%, TFe 2 O 3 = 4.73–11.63 wt%, and Mg # = 26–66, belong to the medium- to high-K calc-alkaline series, exhibit enrichment in light rare earth elements and large-ion lithophile elements, exhibit depletions in heavy rare earth elements and high-field-strength elements (e.g., Nb and Ta), and have no obvious Eu anomalies. These geochemical features are similar to those of arc igneous rocks. Relative to mid-ocean ridge basalts, these mafic–intermediate volcanic rocks exhibit more radiogenic Sr-Pb and less radiogenic Nd-Hf isotopic compositions. The Th/Yb (1.47–3.43) and (Hf/Sm) PM (0.80–1.15) ratios of the Early Jurassic mafic–intermediate volcanic rocks are much lower than those of the Late Jurassic mafic–intermediate volcanic rocks (Th/Yb = 4.31–5.25; (Hf/Sm) PM = 1.49–2.60), whereas the late Early Cretaceous igneous rocks exhibit large variations in these ratios (Th/Yb = 0.37–14.8; (Hf/Sm) PM = 0.59–2.14). The above features show that: (1) the primary magmas of the mafic–intermediate volcanic rocks were mainly derived by partial melting of depleted lithospheric mantle; (2) the lithospheric mantle was mainly metasomatized by sediment-derived fluids related to subduction of the Mongol–Okhotsk oceanic plate during the Early Jurassic, whereas the mantle source was mainly modified by sediment-derived melts triggered by the collapse of thickened lithosphere after closure of the Mongol–Okhotsk Ocean in the Late Jurassic; and (3) sediment-derived fluids associated with subduction of the Paleo-Pacific Plate caused further enrichment of the lithospheric mantle in the western part of northeast China during the late Early Cretaceous. • J 1 , J 3 and K 1 mafic magmas were derived by melting of depleted lithospheric mantle. • J 1 lithospheric mantle was modified by the Mongol-Okhotsk slab-derived fluid. • J 3 lithospheric mantle was modified by the Mongol-Okhotsk slab sediment-derived melt. • K 1 lithospheric mantle was re-modified by the Paleo-Pacific slab-derived fluid.

Geochemistry of the Permian–Triassic boundary strata in the southwest margin of the North China Craton: Provenance and tectonic implications

The Late Permian Sunjiagou Formation and Early Triassic Liujiagou Formation were studied to understand the palaeoclimatic and palaeoenvironmental changes in the southwest margin of the North China Craton across the Permian–Triassic boundary, as well as the tectonic evolution of their provenance sediment. Major, trace, and rare earth elements in 20 clastic rock samples from the strata above and below the boundary were analysed. Overall, the Sunjiagou Formation samples showed an average index of compositional variability (ICV) and chemical index of alteration (CIA) of 1.53 and 73.59, respectively, indicating high‐maturity sediments in a warm and humid environment with moderate chemical weathering, whereas Liujiagou Formation samples had an average ICV and CIA of 2.40 and 70.1, respectively, indicating low‐maturity sediments in a cold and dry environment with mild chemical weathering. These strata were composed of first‐cycle sediments in a tectonically active area. The provenance of the Sunjiagou Formation was dominated by quartz‐rich sedimentary rocks, whereas that of Liujiagou Formation had both quartz‐rich sedimentary rocks and intermediate volcanic rocks. The provenance tectonic settings were mainly the continental island arc and active continental margin. Thus, the study area was in a terrestrial, freshwater sedimentary environment from the Late Permian to Early Triassic, and the climate gradually changed from warm and humid to dry and hot, with multiple small‐scale periodic evolutions. Taken together, these findings further confirm that the entire study area was in an oxidizing environment and the oxidation degree in the Early Triassic was higher than that in the Late Permian.

Variation of plagioclase shape with size in intermediate magmas: a window into incipient plagioclase crystallisation

Volcanic rocks commonly display complex textures acquired both in the magma reservoir and during ascent to the surface. While variations in mineral compositions, sizes and number densities are routinely analysed to reconstruct pre-eruptive magmatic histories, crystal shapes are often assumed to be constant, despite experimental evidence for the sensitivity of crystal habit to magmatic conditions. Here, we develop a new program (ShapeCalc) to calculate 3D shapes from 2D crystal intersection data and apply it to study variations of crystal shape with size for plagioclase microlites (l < 100 µm) in intermediate volcanic rocks. The smallest crystals tend to exhibit prismatic 3D shapes, whereas larger crystals (l > 5–10 µm) show progressively more tabular habits. Crystal growth modelling and experimental constraints indicate that this trend reflects shape evolution during plagioclase growth, with initial growth as prismatic rods and subsequent preferential overgrowth of the intermediate dimension to form tabular shapes. Because overgrowth of very small crystals can strongly affect the external morphology, plagioclase microlite shapes are dependent on the available growth volume per crystal, which decreases during decompression-driven crystallisation as crystal number density increases. Our proposed growth model suggests that the range of crystal shapes developed in a magma is controlled by the temporal evolution of undercooling and total crystal numbers, i.e., distinct cooling/decompression paths. For example, in cases of slow to moderate magma ascent rates and quasi-continuous nucleation, early-formed crystals grow larger and develop tabular shapes, whereas late-stage nucleation produces smaller, prismatic crystals. In contrast, rapid magma ascent may suppress nucleation entirely or, if stalled at shallow depth, may produce a single nucleation burst associated with tabular crystal shapes. Such variation in crystal shapes have diagnostic value and are also an important factor to consider when constructing CSDs and models involving magma rheology.

Hydrogeochemistry characterization of an overexploited municipal, agricultural, and industrial aquifer, central Mexico

The Valley of Celaya aquifer, located in one of the most important agricultural and industrial areas in central Mexico, has been extremely overexploited for several decades for agricultural, industrial, and municipal uses. The Celaya aquifer is a multilayer, composed of an open upper alluvial (sedimentary deposit) aquifer with inter-layers of late tertiary acid tuffs and basalts (medium semi-confined aquifer) and a downward recharge from River La Laja. The groundwater follows a natural hydrogeochemical evolution, producing low total dissolved solids (TDS) carbonate-type to medium TDS Na-enriched carbonate-type water. The average water temperature is 33 °C, with three thermal groups (low temperature: 16–29 °C, medium temperature: 30–30 °C, and high temperature: 46–60 °C). The electrical conductivity ranges from 645 to 805 μS/cm. Isotopic data (δ2H and δ18O) indicates an evaporation and mixing line with a regression equation of δ2H = 5.48 xδ18O-20.67; R2 = 0.9827. Saturation index geothermometric calculations for the bottom of the well indicate temperatures ranging from 98 to 135 °C. The Cl vs. B relationships indicate the water chemistry is mostly due to local water-rock interaction with a minor magmatic contribution (deep igneous rock). The arsenic and fluoride concentrations are above the limits of the standard on the eastern part of the study area (As = 0.54 mg/L and F = 3.2 mg/L). The arsenic concentration may be due to groundwater residence time, while the fluoride concentration is generally associated with acid and intermediate volcanic rocks. Inverse geochemical modeling indicates a normal evolution of groundwater from meteoric water with some influence from meteoric water to rock-water interactions with sediments and volcanic rock to a deep regional aquifer. This aquifer is considered a low-temperature system (≤150 °C), conductive, and non-magmatic with extensional dominance where local faults produced by overexploitation play an important role in transporting water, and potentially toxic elements to the surface. The hydrogeochemical characterization in this study will help improve the sustainable management of groundwater resource.

НИЖНЕСИЛУРИЙСКИЕ ОТЛОЖЕНИЯ ЮГО-ЗАПАДНОГО ПРИМОРЬЯ: СОСТАВ И ПРОИСХОЖДЕНИЕ

The authors present the results of studying the material composition of terrigenous rocks at the early Silurian Cordonkà formation of the South-Western Primorye. In terms of their parameters, the rocks correspond to petrogenic graywackes formed due to mechanical destruction of rocks of demolition sources. They are characterized by a low degree of the material maturity, weak processing of it, high burial speed. Interpretation of the results showed that sediments accumulated in the basin associated with the oceanic island arc. The sources area was the arc itself, composed of the basic and intermediate volcanic rocks, as well as the igneous and sedimentary formations of its basement.

The ore prospecting prediction model for the Huili copper orefield in Sichuan Province, China

The prediction theory and methodology of ore prospecting were developed from an in-depth study of 129 typical deposits in China. It has been verified to be an effective method that is particularly suitable for the initial ore prospecting. In this method, the internal and external factors of metallogenesis are combined together to construct a geological model of prospecting prediction, which consists of metallogenic geological body, metallogenic structure, metallogenic structural plane and metallogenic characteristics. The Huili area is located in the western margin of the Yangtze Plate, where the regional metallogenic geological conditions are superior, and a series of unique iron-copper deposits were formed. In recent years, great breakthroughs and progress have been made in the deep and peripheral areas of the Huili copper orefield. Herein, we take the Huili copper orefield as a typical example to illustrate the specific application of this method in deep ore prospecting of hydrothermal deposits. The metallogenic geological body is the ore-hosting volcanic rocks (albitite in the Hekou Group), and the main metallogenic structure and structural planes are interfaces between basic (intermediate) volcanic rocks and sedimentary rocks and the possible volcanic vent. Combined with the summary of metallogenic characteristics, we constructed a geological model for ore prospecting in the Huili copper orefield.

Petrography And Field Study Of Andesitic Ignimbrite In Temangan, Kelantan

The volcanic rocks in Temangan, Kelantan consist of felsic to intermediate volcanic rocks, that is mainly of pyroclastic with rhyolitic, dacitic, and andesitic tuff. A geological review has been carried out in Kampung Bukit Besi, Temangan, in Kelantan, Malaysia, which is composed of schist, shale, andesite, and ignimbrite. In Temangan, andesite and ignimbrite show an intimate relationship, as the ignimbrite exists as the fragments and andesite as the matrix. The methodology used in this study are petrography and X-ray Diffraction (XRD) analyses, to determine the mineralogical composition of andesitic ignimbrite. Andesite shows aphenitic and porphyritic textures and consist of pyroxene, plagioclase, alkali feldspar, quartz, biotite and iron oxides. A range of plagioclase textures indicate imperfect equilibrium condition from andesite, reflecting plagioclase dissolution and regrowth. The structural analysis suggest that thrust fault occurred in the study area. Andesite and ignimbrite of the two stages are suggested to have derived from the andesite magma eruption which produced pyroclastic flow eruptions in small amount in most caldera volcanoes at high temperature gradient.

Magmatism in the Siang window of the Eastern Himalayan Syntaxis, NE India: a vestige of Kerguelen mantle plume activity

Abstract We report new U–Pb zircon ages for mafic plutonic (gabbro) and volcanic (andesite) rocks, along with the whole-rock chemistry of a mafic–felsic suite of volcanic rocks from the Siang window of the Eastern Himalayan Syntaxis, NE India. Field relationships, and mineralogical and geochemical characteristics, of the studied mafic–intermediate–felsic rocks suggest their co-magmatic linkage that was generated in an extensional tectonic environment. Incompatible trace elements and low concentrations of large ion lithophile elements (LILEs) and REE behaviour reflect both the enriched nature of the mafic rocks and the limited influence of crustal contamination in their genesis. Partial melting and fractional crystallization processes have played a major role during the genesis of these felsic volcanics from the parental mafic magma. The laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb ages suggest that the mafic plutonic rock was emplaced at c. 121.18 ± 1 Ma and intermediate volcanic rock was emplaced at c. 135.48 ± 0.50 Ma during the Early Cretaceous period. The new ages are consistent with earlier reported zircon U–Pb ages (133.0 ± 1.9–130.7 ± 1.8 Ma) of felsic volcanic rocks from the present study area. Our new field observations, and mineralogical and geochemical characteristics, in conjunction with the U–Pb isotopic database suggest that the major magmatic event in the core of the Siang window of the Eastern Himalaya is coeval with the Rajmahal–Sylhet–Mikir–Shillong flood basalts of eastern and northeastern India, and the Comei–Bunbury Large Igneous Province of southeastern Tibet and SW Australia. These events are related to the break-up of eastern Gondwana and outbreak of the Kerguelen plume.