Low MgO Research Articles

Origin of low-MgO primitive intraplate alkaline basalts from partial melting of carbonate-bearing eclogite sources

Alkaline basalts occur widely in intraplate settings and carbonate-bearing mantle sources such as carbonated peridotites are increasingly regarded to play a key role in their formation. Carbonated eclogites, most likely the products of subducted carbonate-bearing altered oceanic crust, are probable alternative ingredients in the mantle sources of many intraplate alkaline basalts, highlighting the importance of the subduction-driven deep carbon cycle. However, this widely proposed hypothesis remains enigmatic because the recognition of low-MgO primitive alkaline basalts predicted by experiments is scarce. Here we show that Cenozoic continental intraplate alkaline basalts occurring above the stagnant oceanic slab in the mantle transition zone beneath the Hannuoba region, eastern China, display geochemical features consistent with their origin as low-degree partial melts of carbonate-bearing eclogites. Their MgO contents correlate positively with CaO, Ba/Th and Ti/Eu, but negatively with Dy/Yb and εNd. Remarkably, the most primitive alkaline basalts are characterized by low MgO (<5.25 wt.%), low heavy rare earth elements and Sc contents, low CaO/Al2O3 (<0.41), low Ti/Eu (<3380), but Dy/Yb (>7.1) higher than those of ocean island basalts (OIBs). These features cannot be ascribed to differentiation from high-MgO alkaline basalts because significant amounts of crystallization of clinopyroxene and garnet did not occur during ascent. Differentiation also cannot account for the correlations of time-integrated Sr-Nd isotopes with MgO, Dy/Yb and Ba/Th. Instead, the linear correlations mainly reflect strong interaction between ascending primitive alkaline melts and the lithospheric mantle. The compositions of primitive alkaline basalts reflect the key control of garnet and clinopyroxene in the mantle residue (eclogites), and the Ti, Zr and Hf anomalies further indicate the critical effect of carbonates in the eclogite source. Partial melting of the carbonate-bearing eclogites likely occurred in the uppermost asthenosphere. The production of alkaline basalts with low MgO contents by partial melting of carbonate-bearing eclogite below the peridotite solidus in an intraplate setting has been overlooked and the magmas were instead often considered to be highly evolved. Recycled altered oceanic crust thus may not only cause metasomatism of the deep mantle but may also serve as a direct source of mafic melts. These results on natural rocks support the experiment-based model for subducted altered oceanic crustal material and also indicate its diverse fate in the mantle.

Geochronology and geochemistry of the Late Triassic intrusive rocks in the Liaodong Peninsula, NE China: Petrogenesis and implications for early Mesozoic tectonic evolution

ABSTRACT New whole-rock major and trace element, Sr-Nd isotopic, Zircon U-Pb, and Hf isotopic data for the Late Triassic intermediate-felsic intrusive rocks in the Liaodong Peninsula in the northeastern part of the North China Craton (NCC) were obtained in order to investigate their petrogenesis and provide insights into the Late Triassic tectonic evolution of the eastern segment of the NCC. The laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb ages indicate that they were emplaced at 230–219 Ma. Based on the petrology, petrography, and geochemistry, we divided these intrusions into dioritic rocks and granitic rocks. The dioritic rocks are mainly high-K calk-alkaline to shoshonitic biotite diorite and biotite amphibolite diorite. They are metaluminous, have high MgO contents at low to intermediate silica contents, are depleted in heavy rare earth elements (HREEs) and high field-strength elements (HFSEs), are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs), and have εNd(t) values of −16.99 to −9.78 and εHf(t) values of −15.2 to −6.9, indicating that they were mainly derived from the lithospheric mantle, possibly with a small contribution from ancient continental crust. The granitic rocks mainly include biotite monzogranite and monzogranite. They have low MgO, Yb, and Y concentrations and high Sr/Y, La/Yb, and silica contents. They are high-K calk-alkaline to shoshonitic and metaluminous to weakly peraluminous adakitic I-type granites. They are enriched in LREEs and LILEs, are depleted in HREEs and HFSEs, and have εNd(t) values of −16.95 to −14.21 and εHf(t) values of −18.4 to −10.8, indicating that they were mainly derived from partial melting of a thickened ancient lower continental crust. Combined with the spatial and temporal distributions of the Late Triassic rocks, we conclude that these Late Triassic rocks were formed in an extensional environment resulting from slab break-off of the subducted Yangtze Craton beneath the North China Craton, which also resulted in lithospheric thinning of the North China Craton.

Mid-Cretaceous intra-oceanic arc-continent collision recorded by the igneous complex in central Myanmar

Magmatic rocks from intra-oceanic arcs are critical for understanding the formation of continental crust and tectonic evolution. The early tectonic evolution of the Neo-Tethyan Ocean before the final Indo-Asia collision remains mysterious, and the geodynamic processes that triggered the Cretaceous magmatism in central Myanmar is still debated. The Cretaceous magmatic complex in the Banmauk-Kawlin area (BKC), west Myanmar terrane (WMT) is composed of the Kanza Chaung granitoid batholith, the Mawgyi Volcanic rocks, and the Pinhinga plutonic complex. Zircon U-Pb dating results of various rocks from the Kanza Chaung batholith suggest magmatism lasted from ca. 110 to ca. 94 Ma, roughly overlapping with new geochronological data for the Mawgyi Volcanics. Mafic rocks, including basalts from the Mawgyi Volcanics and gabbros from the Kanza Chaung Batholith, have geochemical features resembling intra-oceanic arc magmas, characterized by high large-ion-lithophile elements (LILEs) and low high-field-strength elements (HFSEs) and flat trace element patterns. They have depleted Sr (initial 87Sr/86Sr = 0.7035–0.7054) and Nd (εNd(t) = 0.39–6.71) isotopic compositions, with zircon εHf(t) values ranging from +5.8 to +16.1, probably derived from partial melting of the mantle wedge. Diorites formed by differentiation of basaltic magma have similar trace element patterns and Sr-Nd isotopes. The granitic rocks were likely originated from partial melting of juvenile arc lower-crust, indicated by their high SiO2 (>65.0 wt%), low MgO (<2.50 wt%) and depleted Nd and zircon Hf isotopes. The εNd(t) values of the BKC shift markedly (from ~ + 7 to 0) from 105 to 94 Ma, which correlates with a temporal increase of Th/Nb, La/Ta, and La/Sm. Given the juvenile characteristics of the WMT crust, this can be explained by exotic isotopically enriched crustal components subducted into the mantle source, rather than steady-state sediment subduction and crustal contamination. Given the Albian unconformity in the WMT and recent paleomagnetic data, such continent crustal components were likely introduced by collision followed by subduction of Greater India-derived continental sliver beneath the WMT. Thus crust with an Indian continent affinity was possibly accreted to an intra-oceanic arc (WMT) during the mid-Cretaceous.

Petrography, chemical composition, and age constraints of mafic intrusions from the Mesoproterozoic Soisson Intrusive Suite in the southeastern Churchill Province (Canada)

Several kilometre-scale gabbroic intrusions with well-preserved cumulate textures occur over a ∼180 km northwest–southeast strike length area in the Core Zone, within the southeastern Churchill Province. These intrusions (1312–1311 Ma) are devoid of structural and metamorphic overprint and are mainly composed of olivine gabbro. Their overlapping petrographic, geochemical, and mineralogical characteristics suggest that all of these gabbroic intrusions are co-genetic and form the Soisson Intrusive Suite. The Soisson intrusions formed from basaltic parental magmas with low MgO (∼6–7 wt.%) and high Fe–Ti contents. Overall, they are similarly fractionated at the regional scale and incorporated various amounts of upper crustal material, as indicated by field (e.g., xenoliths, hybrid zones) and geochemical (e.g., high HILE/MILE, depletion in Nb±Ta) evidences. The Soisson Intrusive Suite has petrological, geochemical, and mineral chemistry similarities with the troctolite and olivine gabbro cumulates of the Voisey’s Bay and Mushuau intrusions from the ca. 1363 to 1289 Ma Nain Plutonic Suite (NPS), and appears to be contemporaneous with its younger gabbroic–troctolitic intrusion phase, suggesting that the Soisson Intrusive Suite and the gabbroic–troctolitic intrusions of the NPS were formed by similar petrological processes. Furthermore, like many gabbroic–troctolitic intrusions of the NPS (e.g., Voisey’s Bay intrusion), the Soisson intrusions contain Ni–Cu–Co magmatic sulfide mineralization. Among the Soisson intrusions, the Papavoine intrusion located in the southern part of this intrusive suite may be the most prospective intrusion as a Ni, Cu, and Co exploration target. Overall, the Soisson Intrusive Suite’s similarity with the NPS raises questions about their potential genetic link and magmatic connectivity at depth.

Carboniferous to Early Permian magmatism in the Uliastai continental margin (Inner Mongolia) and its correlation with the tectonic evolution of the Hegenshan Ocean

This study presents a comprehensive analysis of zircon U–Pb–Hf isotopic and whole-rock geochemical data of Carboniferous–Early Permian felsic igneous rocks from the Uliastai continental margin (UCM), southeastern Central Asian Orogenic Belt, to constrain the amalgamation of the Inner Mongolia–Daxing'an Orogenic Belt (IMDOB) in the late Paleozoic. Zircon laser ablation inductively coupled plasma mass spectrometry UPb ages of monzogranite, granite porphyry, felsic volcanic rock, and alkali feldspar granite reveal three stages of magmatism in the Early Carboniferous (ca. 336–320 Ma), Late Carboniferous (ca. 311–307 Ma), and Early Permian (ca. 298 Ma). The Early Carboniferous igneous rocks, including monzogranites and later granite porphyries, exhibit affinity with the high-K calc-alkaline highly fractionated I-type granite, and are depleted in high-field-strength elements and enriched in large-ion lithophile elements. Their zircon εHf(t) values of the Early Carboniferous rocks range from +4.6 to +9.1, indicating that they were generated by partial melting of the juvenile crustal materials in a north-dipping subduction-related environment along with the opening of the Hegenshan Ocean. The Late Carboniferous felsic volcanic rocks are highly fractionated high-K calc-alkaline to alkali-calcic I- and A-type granitoids, with relatively strong peraluminous affinities. Considering the zircon εHf(t) values (+6.2 to +10.6) and relatively low Rb/Ba (0.71–3.57) and Rb/Sr (4.18–8.12) ratios, they were likely derived from a juvenile crust and are comparable to partial melts of clay-poor but plagioclase-rich metaigneous rocks. Notably, the A-type granitoids are gradually increasing in the UCM after 311 Ma, and these magmatic rocks have markedly increased zircon saturation temperatures and (K2O + Na2O)/CaO ratios. These changes may result from the slab break-off of the Hegenshan Ocean, and the Late Carboniferous felsic volcanic rocks were formed in a post-collisional setting. The Early Permian alkali feldspar granites are characterized by typical A-type granite geochemistry, with high Ga/Al ratios; low MgO, Cr, Co, and Ni contents; and high zircon saturation temperatures. These rocks have positive εHf(t) values of +10.2 to +12.7 and record an intracontinental extension setting. In combination with the regional geology, the Late Carboniferous post-collisional magmatic rocks suggest that a change from a subduction-related continental margin to a post-collisional tectonic regime might have occurred in the UCM before 311 Ma.

The newly discovered ca. 1.35 Ga metamafic rocks in the Oulongbuluke Block, NW China, and its record for transition from the Columbia to Rodinia supercontinent

Abstract The Oulongbuluke Block is an integral part of the Columbia and Rodinia supercontinents, but the lack of rock records from the transitional period between the Columbia and Rodinia supercontinents during the mid–late Mesoproterozoic has impeded our understanding of the tectonic relationship of the Oulongbuluke Block, which lies between the Columbia and Rodinia supercontinents. In this contribution, we present a systematic petrographic, geochemical, and zircon U-Pb-Hf investigation of newly discovered metamafic rocks in the Oulongbuluke Block. The results show that the metamafic rocks have a protolith age of ca. 1.35 Ga and an arcrelated metamorphic age of ca. 1.11–1.09 Ga. The metamafic rock samples are geochemically characterized by relatively high FeOT/MgO and FeOT and low SiO2, MgO, and K2O + Na2O, which shows tholeiitic affinity. These metamafic rocks exhibit slight light rare earth element (LREE) depletion and flat heavy rare earth element (HREE) content with no obvious Eu anomalies and slightly negative Nb, Sr, and Zr anomalies. These conditions are similar to those of enriched midoceanic-ridge basalt (E-MORB) and normal mid-oceanic-ridge basalt (N-MORB). The metamorphic rocks studied also have positive zircon εHf(t) values (2.96–7.04). Hence, the protoliths of the metamafic rocks may have been produced by variable degrees of melting of spinel-phase lherzolite mantle in a mid-oceanic ridge setting that was probably induced by a mantle plume. The presence of metamafic rocks indicates that the Oulongbuluke Block experienced the final breakup of the Columbia supercontinent at ca. 1.35 Ga, and the ca. 1.11–1.09 Ga arc-related metamorphism coincided with the convergence of the Rodinia supercontinent. The tectonic setting of the Oulongbuluke Block changed from a mid-oceanic ridge setting to an arc setting during the mid–late Mesoproterozoic, which was likely a response to the transition from the Columbia supercontinent to Rodinia supercontinent.

Petrology of Koko Rift basalts: Hawai‘i's most recent and atypical rejuvenation stage eruptive sequence

Rejuvenated volcanism is a worldwide phenomena occurring on many volcanic oceanic islands in all of the major ocean basins (e.g., Samoa, Madeira, Mauritius). This plume-related volcanism follows the main edifice-building stage after a hiatus of variable duration (e.g., 0.6–2 Myrs in Hawai‘i). Hawaiian rejuvenated basalts typically have high MgO contents (>10 wt%) and carry upper mantle xenoliths. Thus, these magmas are assumed to have ascended rapidly through the crust. The basalts erupted along the Koko Rift in Honolulu, Hawai‘i are unusual in their large range in MgO (5.4–11.4 wt%), absence of mantle xenoliths and history of magma mixing. The Koko Rift is the youngest area of rejuvenated volcanism in Hawai‘i (67 ± 2 ka) and its best developed rejuvenation-stage rift system (15-km long rift with 12 major and several minor subaerial and submarine eruptive centers). Here we report on the first systematic petrologic investigation of the Koko Rift basalts to better understand this most recent example of Hawaiian rejuvenated volcanism. New textural and mineral chemical evidence indicates magma was stored along the rift and later mixed to produce the subaerial lavas with 10–11 wt% MgO. The lower MgO (5–6 wt%) subaerial lavas were probably byproducts of the initial hybrid magma, subsequent crystal fractionation and then a second magma mixing event. The absence of mantle xenoliths in Koko Rift lavas and the relatively moderate forsterite contents (84–85%) in the higher MgO lavas may be related to the development of a crustal magma system within the rift. The record of crustal magma storage and crystal fractionation, and two magma mixing episodes in the Koko Rift lavas is unique among Hawaiian rejuvenated volcanism.

Petrogenesis and tectonic setting of A-type granites in the Babouri-Figuil Magmatic Complex (North Cameroon): Constraints from whole rock geochemistry, zircon U[sbnd]Pb geochronology and Sr-Nd-Hf isotopes

The tectonics of the Central Africa Orogenic Belt (CAOB, in Cameroon, Chad, and the Central Africa Republic) is poorly constrained. For this reason, a study was carried out at the Cameroon-Chad border from biotite granite and hornblende-biotite massifs that intruded a gneiss-amphibolites basement of the NW Cameroon domain. Together, we report data on the whole-rock major and trace element compositions, mineral chemistry, and zircon U/Pb ages, supported by Nd-Sr-Hf isotopes. Both rocks are calc-alkaline, except for one sample with a Rittmann Serial Index (σ) > 3.5 (alkaline), high-K, and marginally peraluminous. The biotite granite is alkalic-calcic, whereas hornblende-biotite granite is alkalic. These rocks are characterized by high contents in SiO2 (> 69.85 wt%), Fe-number [FeOt/(FeOt+MgO)] (ferroan), TiO2/MgO, and low CaO, MgO, and P2O5 contents. Their petrological and geochemical features, such as early formed sodic and iron-rich amphibole, late crystallized biotite, and high Ga/Al ratios, are consistent with A-type granite formed from F and Cl enriched melts. Biotites compositions are close to those of annite, and amphiboles to ferro-amphibole, ferro-edenite, and ferro-gedrite types. The correlation for some major elements against SiO2 is consistent with fractionation of K-feldspar, plagioclase, apatite, amphibole, biotite, FeTi oxides, and MnO-rich phases under 882 to 967 °C, < 5 kb, and low ƒO2 (∆QFM = −0.55) at shallow crustal levels between <1 and 7 Km. Zircon U/Pb geochronology indicates two magmatic episodes for the biotite granite (RBO-27 and SMO-8) 602 ± 1.6 Ma, 602 ± 1.8 Ma, and (DBE-9) 707 ± 2.5, whereas hornblende-biotite granite (HRI-23) yielded 604 ± 1.0 Ma, respectively. The younger group yielded moderately to notably depleted initial Hf and Nd values [εHf(t) = − 3.4 to +1.8, av. = − 1.80; εNd(t) = − 2.46 to - 0.95, at 1.34 to 1.51 Ga], and low to moderate calculated initial Sr values (87Sr/86Sr(i) = 0.66781–0.70287). The older A-type granite yielded highly depleted initial Hf values (εHf(t) = + 7.74 to +9.30). The strong positive Pb anomaly for these granites indicates involvement of either crustal component or melt from the subducted slab. Given that the obtained initial Hf and Nd values are enriched relative to the depleted mantle (εHf(t) ~ +14; εNd(t) ~ +6.5), it therefore, suggest that these granites could be derived from low-degree partial melting of a juvenile crust extracted from the mantle.

Age and genesis of the Jinshan gold deposit in the Chinese North Tianshan: A link to large-scale strike–slip shearing events

Large-scale transcrustal strike–slip shearing, orogenic gold deposits, and magmatic Ni–Cu sulfide deposits are prominent features in the Chinese North Tianshan in the northeastern segment of the Tianshan Orogenic Belt. Therelationshipbetween the shearing events and the different styles of mineralization, however, remains ambiguous. Here, structural data, zircon U–Pb–Hf isotopes, bulk-rock geochemistry, muscovite 40Ar/39Ar age dating, and S–Pb isotopes of pyrite from the Jinshan gold deposit are utilized in conjunction with the Pb isotope composition of mineralized mafic–ultramafic rocks of the Huangshandong Ni–Cu sulfide deposit to characterize thelinkbetweenstrike–slipshearing events, andorogenicAuandmagmaticNi–Cu sulfidemineralization. The new zircon U–Pb age results indicate that the host diorite of the gold orebodies formed at ca. 335 Ma. These diorites are enriched in light rare earth elements and large ion lithophile elements (e.g., Ba, U, K, and Pb), but depleted in high field strength elements (e.g., Nb, Ta, and Ti), and have low MgO (4.45–5.17 wt%) contents, Mg# (0.32–0.36), and (La/Yb)CN ratios (4.81–6.90). Based on the lack of ancient crustal basement rocks in the Qoltag Arc, the depleted Nd–Hf isotope composition (εHf(t) = 10.82–15.38; εNd(t) = 6.17–6.67), the juvenile Hf depleted-mantle model ages (350–530 Ma), and the enrichment in Na2O (4.45–5.17 wt%) relative to K2O (1.05–2.20 wt%) of the diorite, it is inferred that the primary magma from which the diorite crystallized was derived from partial melting of metasomatized mantle wedge in an oceanic arc environment. Two muscovite samples separated from an auriferous quartz lode yield 40Ar/39Ar plateau ages of 248.6 ± 0.8 Ma and 249.6 ± 0.9 Ma, representing the age of the gold mineralization event. The similarity in S–Pb isotope composition of pyrite in the Jinshan gold deposit and pyroxenite in the Huangshandong Ni–Cu sulfide deposit suggests that the auriferous fluids required for the formation of the Jinshan gold deposit could represent a mixture of deuteric fluids with limited upper crustal metamorphic fluids from the Kanggur–Huangshan Shear Zone.

INSIGHTS INTO THE ORIGIN OF SHALLOW MARINE DOLOSTONES, LONGWANGMIAO FORMATION (LOWER CAMBRIAN), NORTHEAST SICHUAN BASIN, CHINA: PETROGRAPHIC AND GEOCHEMICAL CONSTRAINTS

For a better understanding of the origin of Early Cambrian dolomites in the Sichuan Basin, which serve as valuable oil and gas reservoirs, we present and interpret complex multiparameter petrographic and geochemical analyses of dolomites in the Cambrian Longwangmiao Formation at the Yangsiqiao section. Our data show that these dolomites mainly occur in the middle and upper parts of the Longwangmiao Formation, and we identify two types of dolomites: micrite and fine-medium crystalline dolomites. The micritic dolomites, occasionally coupled with quartz and mica minerals, show dirty crystal surfaces, nonautogenous crystal shapes, and dark cathodoluminescence and mainly occur in pure micrite and granular dolostones, which retain the original sedimentary texture. Contrarily the fine-medium crystalline dolomites, mainly developed in crystalline and grain dolostones and generally coupled with residual calcites and altered sedimentary textures, have a dark heart-bright boundary texture under a polarized microscope and occasional zonal texture under cathode luminescence. Furthermore, the micritic dolomites have CaO and MgO contents approximately similar to those of the ideal stoichiometric dolomite, relatively high Sr concentration, Σ rare-earth element (REE) +Y concentrations, and δ13C and δ18O values located in the corresponding range of dolomite deposited from Early Cambrian marine water. However, light-REE enrichment (LREE), heavy-REE (HREE) depletion patterns, and high Al2O3 and SiO2 contents distinguish these micritic dolomites from typical marine carbonate deposits. Notably, the fine-medium crystalline dolomites have higher CaO content and lower MgO, Al2O3 and SiO2 contents, lower Sr and higher Fe and Mn concentrations than those of micritic dolomites. The ΣREE+Y concentrations and REE patterns of these fine-medium crystalline dolomites belong to the typical marine carbonate deposits. These features indicate considerable differences in origins between micrite and fine-medium crystalline dolomites. The micritic dolomites show a significant genetic response to the precipitation of seawater in shallow marine with the injection of terrestrial water during the syngenetic period, while the fine-medium crystalline dolomites have a typical response to the secondary metasomatism products of original calcites at the shallow burial stage.

Catalytic preparation of carbon nanotube/SiC whisker bonded low carbon MgO–C refractories and their high-temperature mechanical properties

The effects of Co, Fe and Ni catalysts generated from their nitrate precursors on the formation of carbon nanotubes (CNTs) from pyrolysis of phenolic resin were investigated, and the former two performed the best at 873 K, and 1073–1273 K, respectively. Density functional theory calculations indicate that a Co nanocluster requires the lowest energy for forming the five-membered carbon ring (the controlling step in the CNT generation), making Co the best catalyst for the formation of CNTs at relatively low temperatures. On the other hand, molecular dynamics calculations show that an Fe nanocluster has the highest melting point among the three nanoclusters and can retain its integrity at 1280 K, making Fe the best catalyst for the formation of CNTs at relatively high temperatures. Hot modulus of rupture of the CNT (along with additionally formed SiC whisker) reinforced low-carbon MgO–C refractory sample containing 0.25 wt% Fe catalyst was about 20% higher than that of its catalyst-free counterpart.

Paleoproterozoic tectonic evolution of the Khondalite Belt in the North China Craton: Constraints from the geochronology and geochemistry of 1.9–2.3 Ga felsic and basic intrusive rocks in the Jining area

Although the Paleoproterozoic Khondalite Belt is one of the most important delineation boundaries in the North China Craton, its tectonic evolution remains controversial. Here, we present new geochronological and geochemical data for Paleoproterozoic granodiorite gneiss, amphibolite, and gabbro and monzogranite dykes in the Jining area in order to constrain the tectonic evolution of the Khondalite Belt. Zircon U–Pb dating indicates that the granodiorite gneiss, amphibolite and monzogranite were emplaced at ca 2.3 Ga, 2.0 Ga and 1.9 Ga, respectively. The 2.3 Ga granodiorite gneisses have positive εNd(t) values (+0.6 to +1.3) and high zircon saturation temperatures (864–873 °C), and show geochemical characteristics of A2-type granites, probably indicating extension background related to subduction. The 2.0 Ga amphibolites have high Nb contents and their protoliths display geochemical features of Nb-enriched basalts. The low MgO, Cr, Ni, LREE-enriched patterns, and negative εNd(t) values (−5.5 to −6.3) with relatively old Nd model ages suggest that the protoliths were derived from a fertile mantle source metasomatized by slab-derived melts. The distinct geochemical characteristics suggest that the formation of the amphibolites were attributed to the upwelling asthenosphere triggered by the opening of slab window. Based on the U-Pb ages of zircons and the contact relationship in the outcrops, the intrusive age of the gabbros was constrained to be 2.0–1.9 Ga. These gabbro dykes have high Mg#, Cr, and Ni contents, and show E-MORB-like REE patterns with high contents of large ion lithophile elements and negative Nb-Ta anomalies, indicating a subducting tectonic setting. Their high Ba/Th and Rb/Y ratios, low Th/Ta and Nb/Y ratios imply a mantle source metasomatized by slab-derived fluids. The 1.9 Ga monzogranite dykes have high Sr and Sr/Y ratios, low Yb and HREE, similar to those of typical adakitic rocks. Their low MgO, Cr, Ni, Mg# and negative εNd(t) suggest that the dykes were generated by partial melting of thickened lower continental crust. These different rocks, therefore, indicate a convergent margin occurred along the Khondalite Belt before the collision between the Yinshan Block and the Ordos Block, followed by extension event at ca. 2.3 Ga and closed with a collision at ca. 2.0–1.9 Ga, and then changed to post-collisional tectonic setting with the adakitic monzogranite dykes formed at ca. 1.9 Ga.

Role of MgO in lowering glass transition temperature and increasing hardness of lithium silicate glass and glass-ceramics

The effect of variation of MgO (1.5, 4.5 and 7.5 mol%) content on glass structure, crystallization behavior, microstructure and mechanical properties in a Li2O–K2O–Na2O–CaO–MgO–ZrO2–Al2O3–P2O5–SiO2 glass system has been reported here. Increased amount of MgO enhanced the participation of Al2O3 as a glass network former along with [SiO4] tetrahedra, reducing the amount of non-bridging oxygen (NBO) and increasing bridging oxygen (BO) amount in glass. The increased BO in glass resulted in a polymerized glass structure which suppressed the crystallization and subsequently increased the crystallization temperature, bulk density, nano hardness, elastic modulus in the glasses as well as the corresponding glass-ceramics. MgO addition caused phase separation in higher MgO (7.5 mol%) containing glass system which resulted in larger crystals. The nano hardness (∼10 GPa) and elastic modulus (∼127 GPa) values were found to be on a much higher side in 7.5 mol% MgO containing glass-ceramics as compared to lower MgO containing glass-ceramics.

Middle–Late Triassic southward-younging granitoids: Tectonic transition from subduction to collision in the Eastern Tianshan–Beishan Orogen, NW China

Abstract To constrain the closure mechanism and time of the Paleo-Asian Ocean, we report new geochronological and geochemical data for Triassic granites along a NW–SE corridor from Eastern Tianshan to Beishan, NW China. Seven granites have U-Pb ages that young southwards from 245 Ma to 234 Ma in the Kanguer accretionary complex, to 237 Ma to 234 Ma in the eastern Central Tianshan block, to 229 Ma to 223 Ma in the Liuyuan accretionary complex. Granites in the Kanguer accretionary complex formed by fractional crystallization and are peraluminous, high-K, calc-alkaline, and crust-derived. They have very low MgO (Mg# = 6–9), Cr, and Ni contents, and their high εNd(t) (+3.40) and εHf(t) (+4.49 to +11.91) isotopes indicate that the Dananhu arc crust was juvenile. The Huaniushan pluton in the Liuyuan accretionary complex displays the geochemical signatures of both A1- and A2-type granites (Y/Nb = 0.32–3.39). All other granites in the Central Tianshan block and Liuyuan accretionary complex are aluminous A2-types with high K2O + Na2O, Al, rare earth elements (REE), Zr + Nb + Y, Ga, Fe/Mg, and Y/Nb and remarkable depletions of Eu, Ba, Nb, Ta, Sr, P, and Ti. They have a broad range of MgO (Mg# = 9–59), Cr, and Ni contents, Isr (0.70741–0.70945) values, negative εNd (t) (−2.98 to −1.14), and low to moderate εHf(t) (−1.22 to +7.78), which suggests a mixture of mantle and crustal components. These 245–223 Ma granitoids show marked Nb-Ta depletions that point to a subduction origin. Notable enrichments in Nd-Hf isotopes of Late Triassic granites are likely an indication of collision. Integration with previous data enables us to conclude that the delamination of an oceanic slab and mantle upwelling induced partial melting of thickened arc crust during a tectonic transition from a multiple supra-subduction margin to a collisional setting in the Late Triassic.

Early Jurassic high εNd(t)-εHf(t) granites in the Southeastern South China Block: Early Jurassic crustal growth or crustal reworking?

Granites that have high εNd(t) and zircon εHf(t) (here phrased as ‘HNHGs’) can offer significant insights into the processes of crustal growth and reworking. This study investigates Early Jurassic HNHGs in the Southeastern (SE) South China Block (SCB) to determine whether they reflect crustal growth or reworking processes, which has implication for understanding the tectonic setting of the SE SCB. We presented new zircon geochronological and Hf-O isotopic, and geochemical analyses on these HNHGs to assess the fundamental crustal processes. Zircon U-Pb geochronological analyses yield the crystallization ages of 192.9 ± 0.8 Ma, 186.7 ± 2.5 Ma and 188.6 ± 1.3 Ma for the Wengong, Gaokeng and Chabei granites, respectively. These HNHGs display high SiO2 (69.75–77.50 wt%), low MgO (0.07–0.83 wt%) and Rb/Sr (0.74–14.3), belonging to unfractionated granites. They have low (87Sr/86Sr)i and zircon δ18O, high εNd(t) and zircon εHf(t), originating from partial melting of a juvenile crust. The HNHGs show a spatial distribution that overlaps with Early Paleozoic lithospheric mantle-derived mafic igneous rocks in the SE SCB. Isotope modeling results imply that the juvenile crust was likely a consequence of mixing among depleted mantle, subordinate enriched lithospheric mantle and SCB basement rocks during Early Paleozoic. These HNHGs record crustal reworking, rather than crustal growth during Early Jurassic, and formed in a continental extension setting.

Post‐collisional alkaline lamprophyre magmatism in northern Iran: Implications from whole‐rock geochemistry and mineral compositions

AbstractThe Shanderman lamprophyre dykes crop out in the western part of the Alborz Mountains (Talesh). These rocks are classified as camptonites, composed of primary olivine, Ti‐rich diopside, kaersutite, biotite, plagioclase, K–feldspar, and minor Ti–rich spinels, magnetite, pentlandite–pyrrhotite/chalcopyrite, and powellite–scheelite. Secondary analcime–wairakite, serpentines, and prehnite are common minor minerals within the studied rocks. Olivine, Ti‐rich diopside, spinel, and amphibole show distinct chemical zoning. Spinels display a core‐to‐rim decrease in Cr2O3, MgO, and Al2O3 concentrations and an increase in TiO2 and FeOT (total Fe as FeO), reflecting the oxidation state increase due to hydrothermal fluid influx. Low SiO2 contents (&lt;42 wt%), high MgO (12.44 to 13.98 wt%), and Fe2O3T (12.76 to 13.43 wt%), Cr (318–537 μg/g) and Ni (231–327 μg/g) contents indicate the ultrabasic nature of the rocks. The samples show potassic character (2.1–2.8 wt% K2O), along with elevated LREE and LILE, and also exhibit minor positive Eu anomalies (Eu/Eu* = 1.09 to 1.20). Olivine–spinel geothermometry indicates a maximum crystallization temperature of 1227 °C (ave. 988 °C ± 65 °C). Exsolution of pentlandite–pyrrhotite/chalcopyrite solid solutions occurred during magma cooling and crystallization. At lower temperatures, analcime–wairakite and prehnite partially replaced plagioclases. The geochemical modeling of the rocks indicates the Shanderman lamprophyre magmas were derived from low‐grade melting (&lt;5%) of amphibole–bearing garnet lherzolite source without or with very few phlogopites. The primary magma of Shanderman lamprophyres was derived from a depth of ~135 km by partial melting of a metasomatized mantle source in a post‐collisional environment.

Development of Magnesium Fertilizer Replacing Kieserite from Bio-Physico-Chemical Activated Dolomite

All plants, especially cocoa and oil palm, require magnesium (Mg) along with other macro- and micro-nutrients. Kieserite as the most common Mg-supplying fertilizer for crops is still imported for Indonesia due to lack of natural deposits in the country. On the other hand, dolomites (CaMgCO3) are found abundantly and mostly used as liming material due to low MgO content and solubility as well. Many efforts have been carried out since a century ago to convert dolomite into Mg fertilizer substituting kieserite. However, there are no efficient processes available yet and therefore it is the objective of this study to develop a potentially efficient process by employing bio-physico-chemical activation approach in converting dolomite into kieserite-like product. A series of experiments were conducted by using a calcinated dolomite from Sidayu, Gresik, East Java, reacting with H2SO4, and inoculating with Mg-solubilizing microbes. An 80-mesh calcined dolomite powder was reacted with water at 1:3 ratio (% w/v) and after one hour stirring added with technical grade H2SO4 improving 27.7% MgO content from 18% to 23%. The formula was then tested its effectiveness for cocoa and oil palm seedlings in the greenhouse for three and six months, respectively. By combining NPK fertilizer at standard dosage with the formula of Mg-fertilizer at 75% of kieserite rate yielded the highest performances by six-month-old oil palm seedlings in a greenhouse experiment. To obtain conclusive results under field conditions, the formula was tested at field experiments using immature and mature oil palm trees. At 0.9 kg/tree/year dosage, the Mg-fertilizer formula was superior to conventional kieserite at 1.6 kg/tree/year rate in supporting vegetative growth of immature oil palm. From the mature oil palm trial, it can be concluded that the use of the new formulated Mg-fertilizer at 50% rate of conventional kieserite (2 kg/tree/year) resulted in an insignificant different yield of fresh fruit bunches (FFB) compared to standard kieserite dosage.

Age and petrogenesis of late Mesozoic intrusions in the Huoluotai porphyry Cu-(Mo) deposit, northeast China: Implications for regional tectonic evolution

Multi-stage igneous rocks developed in the recently discovered Huoluotai Cu-(Mo) deposit provide new insights into the controversial late Mesozoic geodynamic evolution of the northern segment of the Great Xing’an Range (NSGXR). Zircon U-Pb dating suggests that the monzogranite, ore-bearing granodiorite porphyry, diorite porphyry, and granite porphyry in the deposit were emplaced at 179.5 ± 1.6, 148.9 ± 0.9, 146.1 ± 1.3, and 142.2 ± 1.5 Ma, respectively. The Re-Os dating of molybdenite yielded an isochron age of 146.9 ± 2.3 Ma (MSWD = 0.27). The Jurassic adakitic monzogranite and granodiorite porphyry are characterized by high SiO2 and Na2O contents, low K2O/Na2O ratios, low MgO, Cr, and Ni contents, low zircon εHf(t) values relative to depleted mantle, and relatively high Th contents. They were produced by partial melting of a subducted oceanic slab, with involvement of marine sediments in the magma source and limited interaction with mantle peridotites during magma ascent. The Late Jurassic diorite porphyry is characterized by moderate SiO2 contents, high MgO, Cr, and Ni contents, and positive dominated εHf(t) values, indicating it was produced by partial melting of a subduction-modified lithospheric mantle wedge and underwent limited crustal contamination during magma ascent. The early Early Cretaceous adakitic granite porphyry shows high SiO2 and K2O contents and K2O/Na2O ratios, low MgO, Cr, and Ni contents, enriched Sr–Nd isotopic compositions, and slightly positive zircon εHf(t) values, suggesting it was produced by partial melting of thickened mafic lower crust. The NSGXR experienced a tectonic history that involved flat-slab subduction (200–160 Ma), and tearing and collapse (150–145 Ma) of the Mongol–Okhotsk oceanic lithosphere. The period of magmatic quiescence from ca. 160 to 150 Ma was a response to flat-slab subduction of the Mongol–Okhotsk oceanic lithosphere. Crustal thickening in the NSGXR (145–133 Ma) was due to the collision between the Amuria Block and the Siberian Craton.

Petrology of Mafic Dykes from the Njimom Area (West-Cameroon): A Contribution to the Characterization of Late Paleozoic and Mesozoic Magmatism in the Southern Continental Part of the Cameroon Volcanic Line

In the western Cameroon, crop out several dyke swarms of Paleozoic–Mesozoic age. These dykes intrude the Precambrian basement in the southern continental part of the Cretaceous Cameroon Volcanic Line. In the Njimom area, two groups of mafic dykes that crosscut the Neoproterozoic basement rocks have been observed. A first group intrudes the mylonites whereas the second group intrudes the granites. The dykes are alkaline basalts and hawaiites. The mineralogical assemblage of both groups of dykes consists of plagioclase, clinopyroxene, altered olivine, and opaque oxides. The dykes that cross-cut the Precambrian mylonitic gneisses show moderate TiO2 (1.7–2.0 wt.%), low MgO (4.4–7.1 wt.%), and compatible trace element concentrations (e.g., Cr = 70–180 ppm; Ni = 30–110 ppm). The dykes that intrude the granites have TiO2 contents between 2.3 and 2.5 wt.% and moderate compatible trace element concentrations (e.g., Cr = 260–280 ppm; Ni = 170–230 ppm). MgO varies from 5.9 to 9.2 wt.%. All mafic dykes are enriched in light lanthanide element and show moderate Zr/Nb and high Zr/Y, Nb/Yb, and Ti/V ratios similar to those of average ocean island basalt (OIB)-type magmas. Some dykes that intrude the mylonites show evidence of contamination by continental crust. The composition of the clinopyroxenes of the dykes that intrude the mylonites clearly indicate different and unrelated parental magmas from dykes that intrude the granites. Contents and fractionation of the least and the most incompatible elements suggest low degrees of partial melting (3–5%) of heterogeneous source slightly enriched in incompatible elements in the spinel stability field. The geochemical features of Njimom dykes (in particular the dykes that intrude the granites) are similar to those of Paleozoic and Mesozoic dykes recorded in the southern continental part of the Cameroon Volcanic Line, suggesting multiple reactivations of pre-existing fractures that resulted in the fragmentation of western Gondwana and the opening of the South Atlantic Ocean.

Mesoproterozoic (∼1.3 Ga) S–type granites in Shangdu area, Inner Mongolia of the North China Craton (NCC): Implications for breakup of the NCC from the Columbia supercontinent

Mesoproterozoic (∼1.3 Ga) magmatism in the North China Craton (NCC) was characterized by diabase sills, while contemporary granitic magmatism was relatively rare, limiting our understanding of the NCC’s evolution during this period. In this manuscript, we report newly identified ∼1.3 Ga S–type granitic plutons in the Shangdu area, the western part of the northern NCC. Based on the results of geochemical, geochronological and zircon in–situ Lu–Hf isotope analyses, we discussed the petrogenesis, tectonic setting of the granitic plutons and the regime that drove the break–up of the NCC from the Columbia supercontinent. The zircon laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb dating results indicate that these granites were emplaced at some time between 1315 ± 21 Ma and 1307 ± 32 Ma. Moreover, the geochemical results show that they have high contents of SiO2 (75.34–76.97 wt%), Al2O3 (12.90–13.61 wt%) and Na2O + K2O (6.21–8.31 wt%), but low MgO (0.09–0.25 wt%) and Mg# (14–34). The A/CNK ratios varied between 1.10 and 1.28, indicating that the granites belong to the peraluminous series. Furthermore, the existence of Al–rich minerals (e.g., muscovite and garnet) suggests that they are the S–type granites. The ∼1.3 Ga zircon display negative to slightly positive εHf(t) values (−9.28–3.1) and old two–stage model ages (TDM2) (3.3–2.1 Ga). The ages of the inherited zircon and Lu–Hf isotope compositions of the ∼1.3 Ga zircon in the granite are consistent with those of the detrital zircon from Jining complex, the eastern part of the Khondalite Belt. Based on these facts, we infer that the granites in this study derived from the partial melting of the Jining complex. The coeval mafic dykes (in the Yanliao large igneous province) and the Shangdu granite in the north margin of the NCC strongly suggest an extensional setting, which was related to the break–up of the NCC from the Columbia supercontinent. A mantle plume was likely the dominant driver of the break–up and it should have provided heat for the partial melting of Jining complex.