Fractional Crystallization Processes Research Articles

Origin of silicic rocks of the Deccan Traps continental flood basalt province: Inferences from field observations, petrography, and geochemistry

The origin of silicic rocks (SiO2 > 65 wt%) in Continental Flood Basalt (CFB) provinces could be attributed to complex petrogenetic processes. The 65.5–66 Ma old Deccan Traps CFB contains eight sporadic but significant silicic rock exposures that are studied here in a comprehensive framework using field observations, petrography, major oxides (n = 56), and trace element chemistry. Rhyolite and granophyre, as well as subordinate felsite, ignimbrite, trachyte, pitchstone, and microgranite coexist with volcanic and plutonic mafic rocks such as basalt, basaltic andesite, and gabbro. Multiple isolated and circular/semi-circular hills and linear dykes of silicic rocks are present in the form of lavas with prominent flow folding, rheomorphic ignimbrite, and tuffs. The ‘Rheological Agpaitic Index’ (RAI) indicates that most of the silicic rocks in the Deccan Traps are effusive in nature, except for Rajpipla, Alech, Bombay, and Osham silicic rocks, which are marked by explosive volcanism. Thermodynamic-based Rhyolite-MELTS modelling suggests that the major oxide composition of Pavagadh and Barda basalt is a likely candidate for the parental melt composition of the silicic rocks of the Deccan Traps. Ba, Sr, P, Zr, and Ti anomalies are consistent with the fractionation of K-feldspar, plagioclase, apatite, zircon, and Fe-Ti oxides, respectively. Two broad REE patterns are noticed in the Deccan Traps silicic rocks: a flat pattern for Barda, Alech, and Chogat-Chamardi silicic rocks, and a steep REE pattern for Osham, Rajula, Pavagadh, Rajpipla, and Bombay silicic rocks. Trace element modelling reveals that 5–10 % partial melting of a spinel peridotite source could produce an REE pattern and abundances similar to the associated basalts. Further extensive fractional crystallization (60–90 %) of the parental mafic melt at a deeper depth (where spinel is stable) could produce the REE composition and pattern observed in most silicic rocks except for those of Barda, Alech, and Chogat-Chamardi, which require fractional crystallization of the same parental melt at a shallower depth (where spinel is not stable). The geochemical variability of Deccan Traps silicic rocks reveals an origin from a mantle-derived parental mafic melt that evolved via the assimilation and fractional crystallization (AFC) process to form the silicic exposures, which is typical of silicic volcanism in other global CFBs.

Two million years of evolution of the southern central andes retroarc, Payenia Volcanic Province, Argentina, from the study of the Cerro Nevado Volcanic Complex

New K–Ar ages, major and trace element analyses, and Sr and Nd isotopic data for the Cerro Nevado Volcanic Complex (CNVC) coupled with those previously published allow us to better document the hot thermal anomaly which affected the upper mantle beneath the Andean back-arc Payenia Volcanic Province and generated alkaline magmatism. These data, along with previously published ones from this and neighbor volcanic centers, suggest that this anomaly stagnated there, during at least the last 2 million years. Geochemical features from the CNVC basaltic magmas indicate that they were sourced within an OIB-type mantle with an EMI signature, similar to that underlying the neighboring Auca Mahuida Shield Volcano to the south, and attributed to the rise of a mantle thermal anomaly. We identify at least five events of partial melting and seven eruptive phases from 1.88 to 0.75 Ma. Continental crust contamination in the San Rafael Block crustal basement occurred coupled with fractional crystallization processes, probably in magma chambers and across several cycles, producing the trachybasaltic, trachyandesitic and trachytic magmas of the Cerro Nevado volcanic cone (1.34–1.22 Ma).

Contrasting magmatic evolutions of the Three Sister Volcanoes reflect increased heat flow, crustal melting and silicic magmatism in the Central Oregon Cascade Arc

The Three Sisters stretch, one of the most magmatically active segments of the Oregon Cascade Arc, includes the Three Sisters volcanoes proper (North, Middle and South) as well as the shields and cinder cones of the Mount Bachelor Chain and McKenzie Pass. The Three Sisters record a magmatic transition from fundamentally basaltic andesitic activity in older North Sister products to more diverse activity at Middle Sister, and unusually silicic activity in a Cascade volcano, including rhyolite lava, at South Sister.North Sister magmas reflect magmatic evolution of basaltic andesite through crystal fractionation, mostly of olivine, and incorporation of crustal melts. Middle Sister, although mostly composed of basaltic andesite and andesite, produced dacitic magma through assimilation fractional crystallization processes involving incorporation of silicic melts. South Sister developed a subjacent magma chamber under the southern half of the volcano, where andesitic magmas evolved, dominantly through fractional crystallization, to dacite and rhyolite. A prominent compositional gap at South Sister between dacite and rhyolite and depletion of middle and heavy rare earth elements in rhyolite suggest that amphibole was prominently involved in fractionation processes involving separation of silicic magma from a gabbroic or amphibolitic crystal mush. Silicic magma eventually formed a stagnant cap in the system, where it evolved through small scale fractional crystallization. Rhyolite magma was finally heated to elevated temperatures prior to eruption, presumably through influx of less evolved magma into the base of the stagnant silicic cap and was erupted in late rhyolite lava of Rock Mesa and the Devil's Hill Chain.South Sister lies along strike of the Northwest Rift of Newberry Volcano, which forms the northwestern terminus of the High Lava Plains trend of south-central Oregon. The increased magmatic activity of the Three Sisters stretch and unusual abundance of silicic products, including rhyolite, of South Sister may reflect the arrival and intersection of the High Plains magmatic anomaly with the Cascade Arc.

The off-axis plume–ridge interaction model: Confirmation from the mineral chemistry of Cretaceous basalts of the Ontong Java Plateau

The Ontong Java Plateau (OJP) is the largest known igneous province on Earth. The proposal that its origins involved off-axis plume–ridge interactions remains highly controversial. Here we present new in-situ major (EPMA), trace element (LA-ICP-MS) and Sr isotopic (LA-MC-ICP-MS) characterization of clinopyroxene and plagioclase phases present in OJP tholeiitic basalts from Sites 1183, 1186, 1185, 1187. Site 1187 and Upper Site 1185 have yielded olivine tholeiites containing olivine, Ca-rich augite, Ca-deficient pigeonite, and plagioclase, inferred to be derived from higher degrees of partial melting of dominantly peridotitic mantle and reflecting relatively low crystallization temperatures. Sites 1183 and 1186 and Lower Site 1185 yielded tholeiitic basalts consisting mainly of plagioclase and Ca-rich augite without olivine, interpreted to originate from lower degrees of partial melting of pyroxenite- and peridotite-derived melts with relatively high clinopyroxene and plagioclase crystallization temperatures. Site 1187 and Upper Site 1185 plagioclase, clinopyroxene, and equilibrium melts have much lower REE contents but slightly higher in-situ Sr isotopic ratios compared to those phases at Sites 1183 and 1186 as well as Lower Site 1185. Sites 1186 and 1187 plagioclases and clinopyroxenes display normal zoned textures which are attributed to the process of fractional crystallization and extensive magma mixing beneath the heterogeneous mantle source. In-situ Sr isotopic disequilibrium between plagioclase phenocrysts and plagioclase clusters further indicates an enriched compositional heterogeneity. Due to the strong tensile forces expected at the spreading ridge, the OJP off-axis mantle plume is inferred to be drawn towards the ridge axis, leading to shifts in mineral compositions, degrees of partial melting, and crystallization temperatures inferred for the volcanics of Sites 1183, 1186, 1185, and 1187 as a function of distance from the spreading ridge. The enriched invariability of in-situ Sr isotopic compositions is likely due to the relatively long half-life of the radiogenic elements. These mineral chemistries are consistent with off-axis ridge–plume interaction.

Intrusive Magmatism Strongly Contributed to the Volatile Release Into the Atmosphere of Early Earth

AbstractMagmatic volatile release was crucial for the build‐up and composition of the early atmosphere and thus for the origin and evolution of life. Even though the rate of intrusive to extrusive magma production on Earth is high, intrusive volatile release is commonly neglected in studies modeling the composition of the early atmosphere. This can mainly be attributed to the solubility of volatiles like H2O and CO2. The solubility is increasing with depth and thus is thought to prevent the release of these volatiles. However, due to the accumulation of H2O and CO2 within the melt during fractional crystallization, the solubility can be exceeded even at greater depths. In our study, we developed a novel numeric model to quantify the amount of H2O and CO2 that can be released from an intrusive system if we consider the process of fractional crystallization. Additionally, we take the possibility of melt ascent and the formation of hydrous minerals into account. According to our simulations, the release of H2O and CO2 from an intrusive magma body is possible within the whole lithosphere. However, the release strongly depends on the initial volatile budget, the formation of hydrous phases, the depth of the intrusion and the buoyancy of the melt. Considering all these factors, our study suggests that about 0%–85% H2O and 100% CO2 can be released from mafic intrusions. This renders the incorporation of the intrusive volatile release mandatory in order to determine the volatile fluxes and the composition of early Earth's atmosphere.

Middle-late Miocene rift-related magmatism in Guaymas, Sonora, Mexico at the eastern margin of the Gulf of California: Petrogenetic implications associated to the Pacific-north American plate boundary

Miocene volcanism in the Guaymas region at the eastern margin of the Gulf of California, in coastal Sonora, NW Mexico, was dominated by arc magmatism. However, the presence of rift-related magmatism is also exposed. Rocks associated with subduction of the Farallon plate beneath North America plate are of Oligocene-Miocene ages, while the magmatic rocks with ages between ca. 12.5 to ca. 6 Ma occur in a post-subduction tectonic setting. This period is sometimes referred to as the proto-Gulf phase. The proto-Gulf magmatic rocks are exposed as part of a volcanic igneous plumbing system, herein named Guaymas Group. The Guaymas Group has an age range between ∼12 and 10 Ma and is defined by two magmatic events: an intermediate compositional pulse (Unit 1) and a felsic pulse (Unit 2).The lithological units from the Guaymas Group have similar geochemical features, exhibiting LILE and LREE enrichment and Nb, Ta and Ti depletion. These rocks show a transitional to tholeiitic composition affinity that differs from the arc magmatism from coastal Sonora. The geochemical data suggest that assimilation and fractional crystallization (AFC) processes played an important role in the geochemical variations observed in volcanic and subvolcanic rocks. The geochemical characteristics of the Guaymas Group rocks also could indicate an origin by decompression melting of a mantle source metasomatized by subduction processes.Finally, considering the geological, geochronological and geochemical study, we suggest that the emplacement of the Guaymas Group rocks is contemporaneous with the oblique rifting environment associated with an incipient Pacific-North American plate boundary.

Revisiting the origin of the Carboniferous Oytag pluton in West Kunlun orogenic belt, northwest China

The Oytag pluton in the West Kunlun orogenic belt of China represents the rare exposed Carboniferous granitoids associated with the early-stage evolution of the Paleo-Tethys Ocean, and its origin is controversial. New zircon U-Pb data suggest an emplacement age of 327–324 Ma for trondhjemite, which slightly predated tonalite (∼314 Ma). These results, along with available published ages, indicate several episodes of magmatism to build the Oytag pluton. Both trondhjemite and tonalite have positive whole-rock Nd isotopic compositions (ε Nd (t) = +4.56 to +8.01 for trondhjemite; ε Nd (t) = +4.68 to +6.15 for tonalite), which positively correlate with whole-rock MgO values. Given the presence of Ordovician inherited zircon grains, variations of whole-rock Nd isotopic compositions are attributed to addition of <10% crustal contaminants during assimilation and fractional crystallization (AFC) processes. Interestingly, trondhjemite and tonalite follow distinct AFC trends, consistent with their different ages. Zircons from two trondhjemite samples have overlapping U-Pb ages but show distinctly different trace elements and internal structures (sector-zoned vs. oscillatory-zoned). The sector-zoned zircons have a less evolved signature of lower Hf contents, higher Eu/Eu* and Th/U ratios than the oscillatory-zoned ones, indicating significant crystal fractionation processes for their parental melts. The more variable Hf contents of the oscillatory-zoned zircons than those of the sector-zoned ones reflect a more dynamic environment where they crystallized. We propose that the sector-zoned zircons were crystallized from locked, interstitial melt in a mush and the oscillatory-zoned zircons from extracted melt. In situ crystal-liquid segregation in a mush chamber thereby could be an efficient approach to the differentiation of Oytag trondhjemite. On the other hand, zircons from tonalite have similar Hf contents to the sector-zoned zircons from trondhjemite, but display slightly higher Eu/Eu* ratios and much higher Th/U ratios. This indicates that tonalite should have experienced much different AFC processes from trondhjemite. Both the episodic magmatism feature and the distinct differentiation processes argue for rises of different batches of magmatism to generate trondhjemite and tonalite in Oytag. Along with the large variations of Hf isotopes (5–6 epsilon units) in zircons, we propose a partial melting of juvenile mafic crust model for the Oytag pluton. Heat from upwelling of asthenosphere may have triggered the partial melting of wet, mafic underplates during the opening of a Paleo-Tethyan back-arc basin. • The Oytag pluton comprises predominant trondhjemite with minor tonalite. • Oytag trondhjemites (327–324 Ma) formed earlier than tonalites (∼314 Ma). • The Oytag pluton was built by different batches of magmas via partial melting.

Concurrent magma mixing and crystallization processes revealed by clinopyroxene macrocrysts from Lamont guyot lavas in NW Pacific

Minerals in volcanic rocks have been commonly used to reconstruct the physicochemical conditions of crystallization and magma chamber processes (magma mixing and recharge) prior to eruption which are fundamental to deduce the petrogenesis of volcanic rocks. Here we present mineral chemistry including in situ major-trace element and Sr isotopic data for clinopyroxene (Cpx) and plagioclase macrocrysts from lavas collected from Lamont guyot in the Wake seamount group, NW Pacific. The Cpx macrocrysts display normal and reverse zoning or complex zoning (e.g., combination of reverse, normal, sector and/or patchy zoning). The normally-zoned Cpx macrocrysts are euhedral and in Fe Mg equilibrium with the host rock compositions. In contrast, the cores of reversely- and complexly-zoned Cpx macrocrysts are in textural (e.g., resorption texture) and chemical (very low Mg#) disequilibrium with their host rock compositions. These reversed cores, however, form coherent compositional trends with and display parallel trace element patterns to the normally zoned Cpx crystals, suggesting that these resorbed cores are most likely antecrysts which crystallized from progenitor melts. The continuously changing major-trace element contents with Cpx Mg# values can be explained by crystallization of these Cpx crystals from melts that progressively fractionate Cpx, plagioclase and Fe Ti oxides. Together with those of the complexly-zoned plagioclase, the complex zoning patterns and large ranges of La/Yb and Sm/Yb ratios at a restricted Cpx Mg# range record magmatic processes of fractional crystallization and mixing in the magma plumbing system. The Cpx crystals from a single lava sample have various 87 Sr/ 86 Sr ratios (0.7025–0.7042) extending from HIMU (high μ = 238 U/ 204 Pb) to FOZO (focal zone) mantle components suggesting that the large 87 Sr/ 86 Sr variation in Cpx could be explained by mixing between HIMU and FOZO components. Our data suggest that frequent recharging of melts derived from different mantle sources and concurrent mixing and crystallization are important processes that shape the currently observed compositional variation of Lamont guyot lavas. • Textural and compositional zoning of Cpx from Lamont seamount lavas, NW Pacific • Cpx shows large trace element and 87 Sr/ 86 Sr variations at a restricted Mg# range. • Reverse and complex zoning textures of Cpx record magma recharge and mixing. • Mixing of multiple batches of HIMU- and FOZO-derived melts. • Concurrent mixing and crystallization played a key role in forming the Cpx crystals.

Petrogenesis of Chang’E-5 mare basalts: Clues from the trace elements in plagioclase

AbstractThis study focuses on using the chemical compositions of plagioclase to further investigate the petrogenesis of Chang’E-5 young mare basalts and constrain its parental melt composition. Together with previously published data, our results show that the plagioclase in mare basalts overall displays large variations in major and trace element concentrations. Inversion of the plagioclase data indicates that the melt compositions parental to Chang’E-5 basalts have high rare earth elements (REE) concentrations similar to the high-K KREEP rocks (potassium, rare earth elements, and phosphorus). Such a signature is unlikely to result from the assimilation of KREEP components, because the estimated melt Sr shows positive correlations with other trace elements (e.g., Ba, La), which are far from the KREEP end-member. Instead, the nearly parallel REE distributions and a high degree of trace element enrichment in plagioclase indicate an extensive fractional crystallization process. Furthermore, the estimated melt REE concentrations from plagioclase are slightly higher than those from clinopyroxene, consistent with its relatively later crystallization. Using the Ti partition coefficient between plagioclase and melt, we estimated the parental melt TiO2 content from the earliest crystallized plagioclase to be ~3.3 ± 0.4 wt%, thus providing robust evidence for a low-Ti and non-KREEP origin for the Chang’E-5 young basalts in the Procellarum KREEP terrane.

Experimental investigation of trace element partitioning between amphibole and alkali basaltic melt: Toward a more general partitioning model with implications for amphibole fractionation at deep crustal levels

Abstract Time-series experiments were carried out in a piston-cylinder apparatus at 0.8 GPa and 1030–1080 °C using a hydrous K-basalt melt as the starting material to determine the element partition coefficients between amphibole and silicate glass. Major, minor, and trace element compositions of amphibole and glass were determined with a combination of electron microprobe and laser ablation inductively coupled plasma mass spectrometry. Results show that the main mineral phase is calcic amphibole, and the coexisting glass compositions range from basaltic trachyandesite to andesite. We estimated the ideal radius, the maximum partition coefficient and the apparent Young’s modulus of the A, M1-M2-M3, and M4-M4′ sites of amphibole. The influence of melt and amphibole composition, temperature, and pressure on the partition coefficients between amphiboles and glasses has also been investigated by comparing our data with a literature data set spanning a wide range of pressures (0.6–2.5 GPa), temperatures (780–1100 °C), and compositions (from basanite to rhyolite). Finally, we modeled a deep fractional crystallization process using the amphibole-melt partition coefficients determined in this study, observing that significant amounts of amphibole crystallization (&amp;gt;30 wt%) well reproduce the composition of an andesitic melt similar to that of the calc-alkaline volcanic products found in Parete and Castelvolturno boreholes (NW of Campi Flegrei, Italy).

A snapshot of the transition from monogenetic volcanoes to composite volcanoes: case study on the Wulanhada Volcanic Field (northern China)

Abstract. The transition processes from monogenetic volcanoes to composite volcanoes are poorly understood. The Late Pleistocene to Holocene intraplate monogenetic Wulanhada Volcanic Field (WVF) in northern China provides a snapshot of such a transition. Here we present petrographic observations, mineral chemistry, bulk rock major and trace element data, thermobarometry, and a partial melting model for the WVF to evaluate the lithology and partial melting degree of the mantle source, the crystallization conditions, and pre-eruptive magmatic processes occurring within the magma plumbing system. The far-field effect of India–Eurasia collision resulted in a relatively high degree (10 %–20 %) of partial melting of a carbonate-bearing eclogite (∼ 3 wt % carbonate; Gt/Cpx ≈ 2 : 8, where Gt denotes garnet and Cpx denotes clinopyroxene) followed by interaction with ambient peridotite. The primary melts ascended to the depth of the Moho (∼ 33–36 km depth), crystallized olivine, clinopyroxene and plagioclase at the temperature of 1100–1160 ∘C with the melt water contents of 1.1 wt %–2.3 wt %. Part of the primary melt interacted with the lithospheric mantle during ascent, resulting in an increase in the MgO contents and a decrease in the alkaline contents. The modified magma was subsequently directly emplaced into the middle crust (∼ 23–26 km depth) and crystallized olivine, clinopyroxene and plagioclase at the temperature of 1100–1160 ∘C. The primary melts from the same mantle sources migrated upward to the two-level magma reservoirs to form minerals with complex textures (including reverse and oscillatory zoning and sieve texture). Magma erupted along the NE–SW-striking basement fault and the NW–SE-striking Wulanhada–Gaowusu fault in response to the combined effects of regional tectonic stress and magma replenishment. The crustal magma reservoir in the WVF may represent a snapshot of the transition from monogenetic volcanoes to composite volcanoes. It is possible to form a composite volcano with large magma volumes and complex compositions if the magma is continuously supplied from the source and experiences assimilation and fractional crystallization processes in the magma plumbing system at crustal depth.

Geochemical signals of coexisting magma mixing and fractional crystallization processes in the arc setting: Case study of Wulan intrusive suite in the NE Tibet Plateau

To understand the fundamental processes for the generation of granitic plutons and compositional diversity of continental crust, we investigate the Wulan intrusive suite in the North Wulan terrane (NWT) along the NE Tibet Plateau. The intrusive suite consists of three-stage igneous rocks including stage I gabbro and granite emplaced at 258–254 Ma, stage II gabbro, diorite, and tonalite emplaced at 250–245 Ma, and stage III gabbro, granodiorite, and leucogranite emplaced at 242–241 Ma. Geochemical analyses and thermodynamic modeling suggest that gabbros were derived from partial melting of heterogeneous lithospheric mantle domains, and they were involved in the formation of coeval intermediate to granitic pluton/batholith. MMEs with variable compositions hosted in granitic pluton do not always represent the products that were generated by magma mixing between injected mafic melts and host granite. In contrast, some low-Si varieties may be generated by crystal fractionation of injected mafic magmas. The hybrid compositions of diorite also indicate a complex petrogenetic process characterized by fractionation of basaltic magmas followed by replenishment of mantle-derived mafic melts. These lines of evidence suggest that both fractional crystallization and magma mixing may concurrently occur in the construction of hybrid intermediate to granitic rocks. In addition, the injected mafic melts, together with newly formed MMEs, would induce compaction and convection of granitic crystal mush, thereby promoting melt extraction to form highly evolved leucogranites. These complex petrogenetic processes and their different combinations play an important role in the construction of the hybrid continental crust in the arc setting.

Correlations among large igneous provinces related to the West Gondwana breakup: A geochemical database reappraisal of Early Cretaceous plumbing systems

The opening and spreading of the Atlantic Ocean between Africa and South America evolved during the Early Cretaceous and were preceded by dramatic tholeiitic (mafic) magmatism and minor silicic and alkaline volcanism. These features are presently recognized from the equatorial regions of Brazil and Africa to the Falklands and South Africa. In southeastern South America, continental flood basalts and related plumbing systems constitute the Paraná Magmatic Province (PMP), whose African counterpart is the Etendeka Magmatic Province (EMP). In northeastern Brazil, dike swarms and sill complexes compose the Equatorial Atlantic Magmatic Province (EQUAMP). As a common feature, these provinces are chemically represented by two prevalent magma types: (1) tholeiitic basalts and basaltic andesites with low Ti (TiO2 < ∼2 wt.%), also including transitional Ti tholeiites with TiO2 ∼ 2.7–1.7 wt.%, and low incompatible element contents. This type is predominantly found in the southern PMP and EMP, with minor occurrences in the EQUAMP. (2) Tholeiitic basalts and basaltic andesites with high Ti (TiO2 > ∼2 wt.%) and incompatible element contents. High Ti tholeiites are relevant in the northern PMP and EMP, and dominant in EQUAMP. Evolved rocks (SiO2 = 57–65 wt.%) interpreted as byproducts of assimilation and/or fractional crystallization (AFC) processes from high Ti tholeiitic magmas, are scarce (but present) in all three provinces. An accurate analysis of multivariable databases collected from the literature for dikes and sills, including major and trace element and radiogenic isotope data, reveals close similarities in their geochemical signatures. In a paleogeographic reconstruction of West Gondwana, the intrusive remnants of the PMP, EMP and EQUAMP are spread over an area of nearly 10 × 106 km2, forming perhaps the most extensive set of plumbing systems on Earth, with a relatively consistent chronology based on a vast collection of K–Ar and 40Ar/39Ar data available in the literature. This work provides the first comprehensive data comparison to support the existence of what may have been a single intercontinental-scale magmatic province of West Gondwana.

Exploration of process optimization for recovery of sodium and ammonium sulfate crystals from vanadium precipitation wastewater

In this paper, we have studied vanadium precipitation wastewater in two stages of the fractional crystallization process. In order to extract sodium sulfate and ammonium sulfate products with large particle size and uniform particle size distribution from the rear end vanadium precipitation wastewater and to realize the resource reuse of vanadium precipitation wastewater, the effects of various operating parameters (seeding amount, evaporation rate, stirring rate, growing time) on the particle size and particle size distribution of sodium sulfate and ammonium sulfate products were investigated. Better separation and crystallization conditions of sodium sulfate and ammonium sulfate were obtained. The optimized crystallization conditions of sodium sulfate are: the addition amount of ammonium sulfate seeding with a particle size of 40 μm is 1.17 %, the evaporation rate is 100 mL/h, the stirring rate is 80 rpm, the crystal growth time is 60 min, and the main particle size M.S. value of sodium sulfate crystals is 242.23 μm; The optimized crystallization conditions of ammonium sulfate were as follows: the addition amount of sodium sulfate seeding with a particle size of 80 μm was 0.68 %, the evaporation rate was 160 mL/h, the stirring rate was 150 rpm, and the crystal growth time was 30 min. The M.S. value of the final ammonium sulfate crystal was 880 μm.

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.

Geochemistry of impact glasses in the Chang’e-5 regolith: Constraints on impact melting and the petrogenesis of local basalt

Lunar impact glasses can provide important information on the bulk compositions of their sources and the impact history of the Moon. Here, we report the chemical composition of fifty-four clean glass spherules containing neither relict clasts nor crystals from the Chang’e-5 (CE5) regolith. They can be subdivided into three compositional groups: (1) mid-Ti basaltic (TiO2 = 4.1 ∼ 6.5 wt%), (2) low-Ti basaltic (TiO2 = 1.3 ∼ 3.9 wt%), and (3) high-Al (Al2O3 > 15 wt%). Fifty-one glasses (∼94 %) are mid-Ti basaltic, which form a loose compositional cluster for most major and trace elements. These glasses exhibit considerable variations in SiO2 (35.3 ∼ 45.3 wt%). Their TiO2, Al2O3, MgO and CaO show negative correlations with SiO2, while the Na2O, K2O and P2O5 positively correlate with SiO2, also yielding a positive correlation between the CIPW normative plagioclase and olivine. These variations likely result from differential vaporization of SiO2, strongly suggesting an impact origin of these glasses. Their major and trace element compositions are averagely similar to the bulk-rock, in turn indicating that they were formed from the local regolith. The remaining three glasses, including two low-Ti basaltic and one high-Al variety, exhibit distinct major and trace elements from the regolith, indicating an exotic source. In addition, the mid-Ti basaltic glasses provide another approach for estimating the average composition of the CE5 basalt other than directly measuring the small basalt fragments assuming that the exotic materials in the CE5 regolith were limited. This estimation reveals critical trace element characteristics of the CE5 basalt, e.g., it has higher La/Yb (3.71), Sm/Yb (1.76), Sr/Yb (31.6), and (Eu/Eu*)N (0.45) than KREEP, indicating that CE5 basalt must derive from a non-KREEP source. Chemical modeling indicates that the contribution of KREEP-rich materials in the mantle source should be less than 0.3 %. The trace element characteristics of the CE5 basalt can be reproduced by extensive (80 %) fractional crystallization after low-degree (2 %) melting. We propose that this fractional crystallization process might occur at depth, implying vast igneous underplating (7,250 ∼ 11,750 km3) beneath the CE5 landing area. This study also suggests that the high Th concentration (5.43 ppm) is an inherent property of the CE5 basalt resulting from extensive fractional crystallization. Thus, high Th detected by remote sensing may not be associated directly with a KREEP component but rather with highly fractionated basalts.

Geochronology and geochemistry of the Miocene volcanics from the Kütahya area: Constraints for post-collisional magmatism in western Anatolia, Turkey

The first geochronological and geochemical data are presented for the Kütahya area volcanics in western Turkey to study mantle sources and magmatic processes. Petrographically, the studied volcanics are composed primarily of olivine augite basalt and augite basalt, with minor basaltic andesites/trachyandesites, and show porphyric, hyalo-microlithic porphyric and rarely glomeroporphyric textures. The rock samples contain plagioclase as phenocrysts and microlites, olivine, augite and biotite as phenocrysts, sanidine, opaques, and volcanic glass. Whole-rock K–Ar dating of the studied volcanics yielded cooling ages between 20.1 ± 0.7 and 17 ± 0.5 Ma (Early Miocene). The volcanics indicate magma evolution from shoshonitic to medium-high-K character. High contents of LILEs and LREEs, and low amounts of Nb, Ta, Zr and Ti indicate that fractional crystallization and assimilation processes had a role in the evolution of these volcanics. The studied volcanics also have moderate to high 87Sr/86Sr (0.70719–0.70971), negative εNd values (−6.27 to −4.63), and high 206Pb/204Pb (18.93–19.05), 207Pb/204Pb (15.69–15.76) and 208Pb/204Pb (38.99–39.32) ratios. Integrated trace element geochemical and Sr-Nd-Pb-O isotopic data suggest that the Kütahya area volcanics evolved via AFC processes from parental magma(s) that originated from a subcontinental veined lithospheric mantle source metasomatized by subduction-related fluids and melts.

Petrogenetic evolution of Lichi volcanics from Arunachal Himalaya, Northeast India: Insights from geochemical modelling

The Lichi volcanic rocks crop out along the Main Boundary Thrust (MBT) of the Arunachal Himalaya, northeast India are comprised primarily of sub‐alkaline basalt (SiO2 ranges from 48.66 to 50.62 wt%), with minor trachy‐andesite (SiO2 ranges from 57% to 61.42 wt%). The distribution of incompatible trace elements, low concentrations of large‐ion lithophile elements, and REE behaviour suggests an enriched nature of the studied rocks and limited influence of the crustal contamination during their evolution. Linear distribution trends of major oxide, consistent patterns of trace elements, and REEs on primitive mantle‐ and chondrite‐normalized diagrams suggest the cogenetic nature of mafic basaltic rocks and intermediate trachy‐andesite. The variation in Ti/Y (256.00–469.95) and Zr/Y (7.65–36.96) ratios indicates that garnet was present in the source. The well‐defined geochemical trends on variation diagram and the sub‐parallel trends on the chondrite‐normalized REE patterns suggest that fractional crystallization processes have played a major role in the evolution of parental magma. Petrogenetic modelling implies that the sub‐alkaline basalts and intermediate rocks were derived from low‐degree partial melting (1%–5%) of a garnet bearing peridotite source. The melt further evolved by fractional crystallization. We conclude that the geochemical attributes of the Lichi volcanics of the Arunachal Himalaya imply their emplacement in a continental extensional regime and possibly resulted from the Cretaceous Kerguelen plume activities.

Late Permian rift-related volcanic rocks from the Zhongba Terrane, Southern Tibet: implications for the opening of the Neotethys

ABSTRACT The questions of how and when the Neotethys Ocean opened are crucial for understanding the evolution of the Tethys Realm and the break-up of Gondwana. However, the evolution of the Neotethys remains controversial. Herein, we report the zircon U–Pb ages, whole-rock major as well as trace elements, and Sr–Nd isotopic data for the basaltic volcanic rocks from the Zhongba Terrane in the western Yalung–Zangbo Suture Zone. The results demonstrate that the Saga basalts were extruded during the Late Permian (257–258 Ma). All samples are characterized based on the low SiO2 content (44.03–50.33 wt%) and belong to the high-K calc-alkaline series. Furthermore, they exhibit light rare earth element enrichment ((La/Yb)N = 12.7–26.7); slightly positive Eu anomaly(Eu/Eu* = 1.01–1.14); prominent Nb and Ta positive anomalies; slightly negative Zr, Hf, and Ti anomalies and exhibit high ratios of Ta/Hf (0.93–1.21), Zr/Y (8.68–10.63), and Nb/Zr (0.39–0.45). The (87Sr/86Sr)i ratio varied from 0.7050 to 0.7063, with relatively constant and depleted εNd(t) values ranging from 0.52 to 1.08. The rocks were probably sourced from a low-degree partial melting of the asthenospheric mantle in a rift environment and had undergone the process of fractional crystallization. These characteristics indicate that the Saga basalts differ from the rift-related magmatic rocks produced by the Panjal Traps. Consequently, combined with the recently reported detailed fieldwork, the Zhongba Terrane disintegrated from the northern margin of Gondwana during the Late Permian, promoting the opening of the Neotethys Ocean, which is most likely caused by the northward subduction of the Paleotethys Ocean.

Petrogenesis and Tectonic Setting of the Gold-Bearing Magmatic Rocks of the North-Western Melfi Massif, Central Chad

This paper presents petrographic and geochemical data on magmatic rocks of the north-western Melfi massif (part of the Gera Massif at the center of Chad) in the Adamawa-Yadé domain. The study area consists of syenite and granite, all crosscut by minor dykes and quartz veins. Syenite and granite show porphyritic texture and are dominated by K-feldspar and plagioclase phenocrysts, biotite, a variable proportion of quartz, and often few amphiboles. These rocks are characterized by low Mg#, Ni and Co, high K2O, Na2O, LREE/HREE ratio, I-type geochemistry as well as positive Eu anomaly, suggesting an origin from partial melting of crustal rocks (here garnet-amphibolite) and metasomatized mantle-derived component with the input of sediments. The compositional evolution from syenites to granite raises the fractional crystallization process in their petrogenesis and involves the fractionation of amphibole, biotite, plagioclase, apatite, magnetite, and ilmenite. Studied samples are affected by the post-magmatic hydrothermal alteration with an assemblage made of epidote, biotite, sericite, and opaques minerals. In addition, they are characterized by considerable gold concentration (Au = 0.6-3.8 ppm) suggesting that the north-western part of the Melfi massif in the center of Chad is a preferential site of gold mineralization. The K-rich calc-alkaline to shoshonitic geochemistry and the pronounced Nb, Ta, and Ti negative anomalies of these rocks, combined with their high Nb/Ta (7.55-32.10), La/Nb (1.80-11.73), and La/Ta (21.53-376.60) ratios but low Rb (57.60-138.30 ppm) indicate that they are subduction-related or arc-related magmas belonging to the Great Central Gondwana Arc (GCGA) formed further to east-directed subduction direction.