High MgO Research Articles

Latest Oligocene adakitic rocks in western Iran: implications for early crustal thickening and tectonic evolution of the Iran Block

Adakitic rocks occur in a variety of tectonic settings and are key to understanding the tectonic evolution and geodynamics of orogenic belts. We investigated latest Oligocene (23.5–22.5 Ma) quartz monzonites and granites from the western segment of the Urumieh–Dokhtar magmatic belt in Iran, which are likely to have formed in response to the early stages of Arabia–Eurasia collision. The studied rocks have the geochemical characteristics of typical adakites, such as high SiO 2 (60.18–68.82 wt%) and Sr (499–793 ppm) contents, low Y (8.90–17.1 ppm) and Yb (0.88–1.58 ppm) contents, and high Sr/Y (26.1‒67.8) and (La/Yb) N (21.9‒32.9) ratios. They have variable K 2 O (3.88–5.09 wt%), MgO (0.44–2.74 wt%; Mg# = 33.7–52.5), Cr (4.27–40.59 ppm), Ni (4.28–35.68 ppm) and Th (9.56–59.59 ppm) contents, and relatively depleted Sr–Nd isotopic compositions [( 87 Sr/ 86 Sr) i = 0.70450–0.70516; ε Nd ( t ) = 2.1–2.7]. These characteristics indicate that the quartz monzonites were derived from the partial melting of delaminated lower crust that interacted with mantle peridotite with high MgO, Cr and Ni contents and depleted Sr–Nd isotopic compositions and suggest that the granites were formed by the fractional crystallization of quartz monzonitic magma. The geochemical features of the studied adakitic rocks could therefore have been affected by magmatic processes (e.g. fractional crystallization), which might be misleading in interpretations of their petrogenesis and related tectonic settings. The geochemical features of the studied rocks indicate that the crust of the western segment of the Urumieh–Dokhtar magmatic belt was thickened to c. 50 ± 4.43 km during the latest Oligocene ( c. 23.5 Ma) as a result of Arabia–Eurasia collision. Supplementary material: Whole rock geochemical and Sr–Nd isotopic compositions, and zircon U–Pb and Lu–Hf isotopic data are available at https://doi.org/10.6084/m9.figshare.c.6188328

Petrogenesis of Alkaline Complex of the Longbaoshan Rare Earth Element Deposit in the Luxi Block, North China Craton, China

The alkaline complex in the southwest region of Luxi Terrane of the North China Craton is spatially correlated with the newly discovered Longbaoshan REE deposit. Its petrogenesis, however, remains ambiguous. In this study, we present an integrated petrology, whole-rock geochemistry, sphene U-Pb and rare earth element data from the Longbaoshan alkaline complex to investigate the petrogenesis, magma source and tectonic evolution. The Longbaoshan alkaline complex consists of mafic to intermediate rocks of hornblende diorite and alkaline hornblende syenite porphyry, biotite monzonite porphyry and aegirine diorite porphyrite. The hornblende diorites show a composition of low SiO2, high MgO, Fe2O3 and moderate Na2O, CaO and are metaluminous and medium-to-high-K calc-alkaline. The hornblende syenite porphyries, biotite monzonites and argirine diorite porphyrites display a relatively higher content of SiO2, Na2O, K2O and Al2O3 and lower contents of MgO, Fe2O3 and CaO and are metaluminous, peralkaline, high-K calcic-alkaline and shoshonite. The sphene U-Pb data shows that the parent magma of the hornblende diorite was emplaced at ca. 120 Ma. All these samples show a common depletion in Th, Nb-Ta and Zr-Hf and enrichment in large ion lithophile elements (e.g., Pb, Ba, Sr) and Light Rare Earth Elements. The magma may have experienced fractionation of pyroxene, amphibole, sphene, apatite and zircon during its evolution. The variable La content, La/Sm, Rb/Sr and (Ta/Th) N ratios indicate that the parent magma may produce by partial melting of a mantle source that was interacted with sediment-derived melts in a subduction setting. Therefore, we propose that the parent magma of the Longbaoshan alkaline complex was derived from a lithospheric mantle which was metasomatized by sediment-derived melt in a prior subduction process. The enriched magma was emplaced through an extension process and experienced subsequent fractionation and assimilation with the continental crust during the rollback of the Paleo Pacific Ocean plate.

Geochronology and geochemistry of the granitoids in the Diancangshan-Ailaoshan fold belt: Implications on the Neoproterozoic subduction and crustal melting along the southwestern Yangtze Block, South China

The Neoproterozoic magmatic and tectonic history of the South China Craton (SCC) is critical for the reconstruction of Rodinia break-up and subsequent Gondwana assembly. Nonetheless, the tectonic attribution of the Neoproterozoic igneous rocks in the southwestern Yangtze is contentious, and the mechanism for crustal anatexis remains unclear. Here, we report mineralogical, whole-rock geochemical and Sr-Nd isotope data, and zircon U-Pb-Hf-O isotope data from the newly found Neoproterozoic trondhjemites and granites in the Diancangshan-Ailaoshan (DCS-ALS) fold belt along the southwestern Yangtze. Both the trondhjemites (ca. 771–762 Ma) and granites (ca. 767 Ma) have high SiO2 and low MgO contents. The trondhjemites have relatively high CaO, Na2O and Sr contents, but low K2O contents and Rb/Sr ratios, and show positive to slightly negative Eu anomalies and heavy rare earth elements (HREEs) depletions, resulting in high Sr/Y and La/Yb ratios. In contrast, the granites have lower CaO, Na2O, and Sr contents, but higher K2O and Rb/Sr, and display negative Eu anomalies and flat HREEs patterns. The trondhjemites have negative εNd(t) (-4.12 to −3.85), positive to negative εHf(t) (-2.50 to + 5.28) and low δ18O (4.37 ‰–7.27 ‰) values. In comparison, the granites have positive εNd(t) (0.09 to 0.26), εHf(t) (+1.24 to + 9.86) and higher δ18O (6.50 ‰–7.24 ‰) values. The distinct elemental and isotopic compositions between the trondhjemite and granite samples reflect two different types of crustal anataxis within different crustal levels. The trondhjemites were formed by water-fluxed melting of the juvenile mafic lower continental arc crust (with addition of ancient Yangtze basement). The granites were derived from dehydration melting of juvenile felsic middle crust. Our results imply that the trondhjemites and granites were formed in a continental arc setting. The melting processes revealed here should be applicable to decipher the widespread Neoproterozoic crustal melting along the southwestern Yangtze, which was most likely fluid-controlled via subduction-induced asthenosphere upwelling. Combined with available regional geological data, we suggest that a long-lived Neoproterozoic (∼880–730 Ma) subduction zone may have extended from the Panxi-Hanna region in the northern/western Yangtze Block to the DCS-ALS fold belt in the southwestern Yangtze. Thus, the SCC may have located on the northwestern margin of Rodinia.

Petrogenesis of Late Devonian I- and A-type granitoids, and associated mafic microgranular enclaves in the northwestern North Qaidam Orogenic Belt, China: Implications for continental crust growth during the post-collisional stage

Post-collisional magmatic intrusions and their mafic microgranular enclaves (MMEs) can provide significant insights into granite petrogenesis, crust-mantle interaction, and the reworking and growth of the continental crust. A combined petrological and geochemical study was carried out on MMEs and their host Niubiziliang I-type felsic composite pluton (granite and granodiorite) and aluminous A 2 -type Datonggou biotite granite from the Niubiziliang batholith in the northwestern segment of the North Qaidam Orogenic Belt (NQOB), China. This study presents whole-rock major- and trace elements and Sr Nd isotopic compositions, electron probe microanalyses of plagioclase, hornblende, and biotite, and zircon U Pb dating and Hf isotopes. Zircon U Pb dating demonstrates that the studied rocks formed during the Late Devonian (ca. 382 Ma). The Niubiziliang composite felsic pluton samples yield a metaluminous calc-alkaline to high-K calc-alkaline I-type granitic composition. The MMEs from Niubiziliang composite felsic pluton have low SiO 2 (52–64 wt%) and high MgO (2.8–4.9 wt%) concentrations. Both MMEs and host granites are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and are depleted in P and high field strength elements (HFSEs). All MMEs and host granitoids samples from Niubiziliang have indistinguishable Sr-Nd-Hf isotopic compositions characterized by initial Sr isotope ratios of 0.70545–0.70633 (MMEs), 0.70555–0.70742 (host rock), whole-rock ε Nd ( 382 Ma ) values of −2.95 to +1.6, −0.25 to +3.5, and zircon ε Hf( 382Ma ) values of +2.2 to +10.2, +1.3 to +10.4, respectively. The Niubiziliang composite felsic pluton is a product of mixing juvenile crust-derived and depleted mantle-derived melts in a 40:60 proportion. MMEs crystallized from the same source as the host granite, and they were formed by self-mixing with the earlier crystallized cumulates when they were affected by the emplacement of subsequent hot magmas. The Datonggou biotite granite has high TFe 2 O 3 /(TFe 2 O 3 + MgO), TiO 2 /MgO, Ga/Al, and Y/Nb ratios, high zircon saturation temperatures (802–846 °C), high HFSE concentrations (e.g., Zr, Nb, and Y), moderate (Na 2 O + K 2 O) concentrations, and low Eu and Sr concentrations. Interstitial biotite has high Fe 2 O 3 but low MgO concentrations, similar to those of aluminous A-type granite. The above-mentioned characteristics imply that the Datonggou biotite granite is an aluminous A 2 -type granite. Considering their high initial Sr isotopic composition (0.72218–0.72652), low ε Nd ( 382 Ma ) (−6.73 to −6.31), and comparatively old two-stage Nd model ages (1640–1674 Ma), we suggest the biotite granite was generated by partial melting of Ordovician-Silurian granitoids with tonalitic compositions at H T -L P conditions. The formation of coeval I- and aluminous A 2 -type granitoids in this region was probably related to the lithospheric mantle delamination and associated asthenospheric upwelling at ca. 390 Ma. The I-type granitoids and MMEs from the Niubiziliang area represent a net addition of juvenile mantle to the crust and, given the wide distribution of contemporaneous I-type granitoids, the post-collisional magmatism has significantly contributed to the growth of the continental crust in the NQOB. • The Niubiziliang granitoids, MMEs, and biotite granite were emplaced at 382 Ma. • Lithospheric delamination occurred at ca. 390 Ma in the North Qaidam belt. • The post-collisional granitoids contribute to the growth of the continental crust.

Modern-style plate tectonics manifested by the late Neoarchean TTG-sanukitoid suite from the Datong-Huai'an Complex, Trans-North China Orogen

When modern-style plate tectonics started and operated on a specific old craton has been a key point involving the early Earth's evolution. In order to address this issue on the evolution of the Neoarchean North China Craton (NCC), we investigated a representative successive magmatic rock suite of tonalite-trondhjemite-granodiorite (TTG) and sanukitoid in the Datong-Huai'an Complex. Geochemically, TTG gneisses in the Datong-Huai'an Complex can be divided into high-pressure (HP) and low-pressure (LP) TTG rocks. The HP TTGs emplaced at ∼2538–2497 Ma and 2441 Ma, respectively. Geochemical data shows that they are characterized by steep rare earth element (REE) patterns, obvious negative Nb, Ta, Ti anomalies and positive δEu anomalies, high Sr/Y, Nb/Ta and (La/Yb) N ratios, and positive ɛ Hf (t) (+2.1 to +9.1) and δ 18 O values (avg. 5.5‰ to 6.0‰). Their protolith is interpreted as the consequence of partial melting of a subducted oceanic slab with garnet and minor rutile as residual phases. In contrast, the LP TTGs emplaced at ∼2518 Ma. They display flat REE patterns, slightly negative Nb, Ta, Ti anomalies and negative δEu anomalies, low Sr/Y, Nb/Ta and (La/Yb) N ratios, positive ɛ Hf (t) (+3.4 to +5.9) and high δ 18 O values (avg. 5.9‰ to 6.1‰). They were most likely generated by partial melting of the mafic lower crust with residual plagioclase and amphibolite in the source region. The sanukitoid rocks emplaced at 2517–2485 Ma and show high MgO, Cr and Ni concentrations but relatively low (La/Yb) N values, positive ɛ Hf ( t ) values (+1.5 to +5.4), and higher δ 18 O values (avg. 6.8‰ to 7.5‰), suggesting that they were originated from partial melting of the mantle peridotite that was previously modified by slab-derived or sediment-derived melts. Combined with previous petrological, geochronological and geochemical data, we propose that the Datong-Huai'an Complex recorded the prolonged magmatism through ca. 2.56 Ga to 2.44 Ga, which was characterized by the high-angle subduction of oceanic lithosphere, leading to the opening of a mantle wedge, slab rollback and back-arc extension. All these lines of evidence manifested that a modern-style plate tectonics regime started along the western margin of the NCC Eastern Block during the late Neoarchean, though the interior Eastern Block was still dominated by the mantle plume-induced crustal growth and vertical tectonism. • Coeval TTGs and sanukitoids were recognized in the Datong-Huai’an Complex. • They recorded the prolonged high-angle subduction with rollback and back-arc extension. • Modern-style plate tectonics started along the margin of NCC Eastern Block in late Neoarchean.

A spectral approach on mineralogy and geochemistry of garnet skarns in Arc-Type granitoids

Garnets that common constituent of skarn type iron deposits are wide ranges of chemical compositions, and they are also important as a semi-gemstone mineral. This study has been investigated garnets and inclusions of its formed in contacts of Pertek granitoid and Keban marble by using a combination of multiple techniques including Raman spectrum, electron microprobe, petrography and LA-ICP-MS. The main mineral assemblage observed in the skarn formation is diopside, garnet, quartz, magnetite, calcite and pyrite. The garnets are in size between 1 and 7 cm and have reddish, greenish and light–dark brown colour. The compositions of the garnets are mainly grossular-andradite, andradite-grossular, less grossular and andradite. Increased porosity and horizontal flow of hydrothermal fluids during metasomatism resulted in the formation of garnets of different sizes. Raman spectroscopy studies on garnets show to be that the idiomorphic and semi-idiomorphic garnets are predominantly grosular, andradite and uvarovite in the core. Raman spectroscopy studies on garnets showed to have predominantly grossular, andradite and uvarovite composition in the core of the idiomorphic and semi-idiomorphic garnets. As for the rare earth element (REE) analysis and distribution model, the chondrite-normalized REE patterns of all garnets in the study area have similar trends and generally in the right-slopping shape depleted in HREE and enriched in LREE, mostly controlled by adsorption. High Fe2O3, CaO and MgO contents may cause to high mobility during skarn formation associated with contact metamorphism and cation exchange via hydrothermal fluids (eg uvarovite in the core). All garnets have generally positive Ce and positive Eu anomalies. These results suggest that the garnets in the studya area formed in conditions showing increase in pH and high oxygen fugacity or decrease in temperature in the source of the hydrothermal fluids.

Paleoproterozoic (ca. 2.1–1.9 Ga) dioritic-granitic magmatism in the Dunhuang Terrane, Northwestern China: Implications for petrogenesis and tectonic evolution

The implications of petrogenesis and tectonics of Paleoproterozoic (ca. 2.1–1.9 Ga) granitoid rocks in Dunhuang Terrane have hitherto received less attention. According to data from zircon UPb dating, the ages of dioritic gneiss, granodioritic gneiss and potassic granite are 2045 ± 44 Ma, 1998 ± 15 Ma and 1950 ± 38 Ma, respectively. The dioritic gneiss has MgO = 1.87–2.93 wt% (Mg# = 46.8–50.9), Yb ≤ 1.9 ppm and Y ≤ 18 ppm, with variable εHf(t) (−2.8 − +5.5) and εNd(t) (−5.6 − +1.3) values, indicating that the mantle wedge source above the subducted slab contributed with subduction fluids and ocean sediment melt in an arc setting. The granodioritic gneiss has relatively high MgO (3.00–1.83 wt%), variable Cr (13.5–106 ppm) and Ni (12.2–72.9 ppm), negative εHf(t) (−20.4 to −10.1) and εNd(t) (−15.2 to −12.8) values, and high P2O5 and TiO2 saturation temperatures (∼800 °C). These data indicate magma source of late Paleo- to early Mesoarchean (∼3.2–3.1 Ga) continental crust rocks. The potassic granite has high K2O (5.52–6.79 wt%) and low MgO (0.10–0.19 wt%) concentrations, low Mg# (37.7–44.6) values, and negative εHf(t) (−12.8 to −2.5) and εNd(t) (−10.6 to −4.8) values. These results suggest that pre-existing Neoarchean crustal rocks were partially melted possibly under transitional stage from syn- to post-collision. Compared with the adjacent areas, Paleoproterozoic (ca. 2.1–1.8 Ga) evolutionary period related to assembly of Columbia supercontinent in Dunhuang Terrane is comparable with that in northeastern Tarim Craton and southwestern Alxa Block, but terminated ∼100 Ma later than that in southeastern Tarim Craton (Aketashtage Terrane).

Characteristics of the Tectonic Background and Sedimentary Paleoenvironment of Coal-Bearing Strata from the Yan’an Formation in the Ordos Basin: Evidence from the Geochemistry of Major and Trace Elements

The coal-bearing strata of the Jurassic Yan’an Formation in the Ordos Basin, China, contain various energy sources, including coal, oil, and gas. However, due to the complex geological conditions of the coexistence of multiple energy sources, it is difficult to explore coal, oil, and gas. Geochemical features record important geological information about rock formations at that time. Therefore, it is of great significance to study the characteristics of major and trace elements and the paleoenvironment of the coal-bearing strata of the Jurassic Yan’an Formation in the Huangling area for the subsequent smooth mining of coal mines and other energy sources. An X-ray fluorescence spectrometer and inductively coupled plasma mass spectrometer were used to determine the major and trace elements of the Yan’an Formation, respectively, and the coal-bearing strata of the Yan’an Formation were comprehensively analyzed from the vertical and different lithology aspects: the paleoweathering characteristics, provenance environment, sediment source, and tectonic background. At the same time, the paleosedimentary environment characteristics of coal-bearing strata were recovered through a series of environmental discrimination indicators, including Sr/Cu, Sr/ppm, Sr/Ba, Th/U, U/Th, V/Cr, V/(V + Ni), V/Sc, and V/Ni. The results show that the sedimentary mode of the Yan’an Formation in the Ordos Basin is mainly fine-grained deposition, and tight sand-mud interbeds and mudstone layers are developed in fine-grained sandstone deposits. The sedimentary rocks are dominated by granite (obvious negative Eu anomaly), mixed with some basement volcanic rocks and ancient sedimentary rocks, and the parent rocks have many geneses (high SiO2, low MgO, and low CaO). The degree of weathering is generally stable but has not experienced complete weathering. Among them, the lower clastic particles have undergone moderate weathering from the source area to the sedimentary basin, and the sandstone is slightly higher than the mudstone. The paleoclimate of the Yan’an Formation was warm and humid in the early stage and tended to be dry and hot. The overall paleowater depth was less than 10 m, and the local area showed a shallow lake subfacies. It experienced a transition from a saline lake facies to a freshwater environment. It is typical brackish–brackish water with a partially oxidized environment (i.e., a sub-rich oxygen environment).

Forearc and back-arc mantle characteristics of the mafic-ultramafic rocks of Simlipal complex, Singhbhum Craton, India

The Simlipal complex of Singhbhum Craton is enigmatic in terms of its shape, stratigraphy, age and geodynamic setting. The circular-shaped Simlipal complex has predominant mafic volcanic rocks and quartzites associated with komatiites, komatiitic basalts, picrites, boninites, andesites and other ultramafic rocks. The mafic rocks are subalkaline tholeiitic basalts to basaltic andesites with moderate SiO2 (45.94–54.26 wt%), MgO (6.09–12.21 wt%), Fe2O3 (10.02–16.44 wt%), CaO (8.33–12.12 wt%), Mg # (32–58), low TiO2 (0.4–1.02 wt%), P2O5 (0.08–0.34 wt%), Ni (112–241 ppm) and Cr (104–506 ppm). The chondrite normalized rare earth element (REE) patterns are slightly fractionated [(La/Yb)N = 2.97–5.44] with slight negative to positive Eu anomalies (Eu/Eu* = 0.84–1.46). Their primitive mantle normalized multielement patterns exhibit negative Th, Nb, Ta and positive to negative Ti anomalies. The ultramafic rocks characterized as harzburgites, have high MgO (34.77–38.11 wt%), Ni (1974–2453 ppm), Cr (3875–4610 ppm) and Mg# (80–85), low SiO2 (40.61–44.18 wt%), TiO2 (0.08–0.14 wt%), Al2O3 (2.24–3.79 wt%), Fe2O3 (7.24–9.77 wt%) and P2O5 (∼0.05 wt%). Their chondrite normalized REE patterns exhibit fractionated LREE [(La/Sm)N = 2.07–2.37], depleted MREE, almost flat HREE [(Gd/Yb)N = 0.99–1.14] and a pronounced trough at Nb-Ta; ZrHf and Ti on the primitive mantle normalized multielement patterns. The basalt gave a zircon UPb age of 2843 ± 16 Ma (MSWD = 0.72) which is the crystallization age. HFSE relationship of the basalts indicates back-arc nature and their melting in the spinel-lherzolite field. The peridotites are arc cumulates, exhibiting boninitic characteristics and forearc affinity. Their PGE systematics indicate retention of sulphides in the residue during the partial melting and fractionation of the mantle. These peridotites and basalts were generated in forearc and back-arc environments during the Neoarchean time, subsequently juxtaposed with plume-derived volcanic sequences and the passive margin sediments as the arc progressed towards the continent. The plume-arc accretion model (PAA) is a viable tectonic setting with the presence of komatiites, komatitic basalts, picrites, tholeiitic basalts and peridotites. Further, the metasediments from the passive continental margin accreted with PAA products in the Simlipal complex. The above findings also support the existence of Archean smaller plate configuration and the proximity of the arc to the continental margin. After the formation of the volcano-sedimentary sequences, the meteoritic impact appears to have obliterated the accretionary imprints in the Simlipal complex.

Synthesis and characterization of plate like high surface area MgO nanoparticles for their antibacterial activity against Bacillus cereus (MTCC 430) and Pseudomonas aeruginosa (MTCC 424) bacterias

• A high surface area and plate like MgO were synthesized by simple precipitation method. • MgO showed good antibacterial activity against both Bacillus cereus and Pseudomonas aeruginosa bacterias. • Pseudomonas aeruginosa (MTCC 424) was slightly resistant compared to Bacillus cereus (MTCC 430). • The effect of morphology, surface area, and particle size on antibacterial activity was analysed. In the present work high surface area MgO nanoparticles were synthesized by simple precipitation method without using any directing agent or capping agent. In this regard various experimental conditions required to achieve high surface area MgO nanoparticles have been addressed in this work. The experimental conditions namely, pH, calcination temperature, digestion temperature, digestion temperature and nature of precursor and precipitating agent, collectively produce high surface area MgO nanoparticles. The optical bandgap, functional group identification, the crystalline phase, surface morphology of MgO nanoparticles were obtained from UV– Vis, FTIR, XRD, SEM, and HRTEM techniques. The optical bandgap was found to be 5.8 eV. With the help of BET technique both specific surface area and the average pore diameter values were obtained and were found to be 246.95 g/m 2 and 6.721 nm respectively. The antibacterial activity of MgO nanoparticles was tested against Bacillus cereus (MTCC 430) and Pseudomonas aeruginosa (MTCC 424) bacterias. The material exhibited good antibacterial activity against both bacterias. A dosage concentration of 80 mg/ml concentration was sufficient to inhibit the bacterial growth. Further analysed the effect of particles size, surface area, optical bandgap, and morphology on antibacterial activity of MgO nanoparticles.

Asthenospheric mantle metasomatized by subducted marine sediments: Li isotopic evidence from Dagze mafic rocks, southern Tibet

Lithium (Li) isotopes show large isotopic fractionation during low temperature processes and have been widely used to trace subduction components at convergent margins. To identify recycled subducting components in the asthenospheric mantle, we report the lithium concentrations and isotopic compositions of the ca. 90 Ma Dagze mafic rocks from the eastern Gangdese Arc, southern Tibet, along with their corresponding whole-rock analyses and Sr-Nd-Pb isotope data. They mainly comprise basalts and diabases with high MgO (7.2–8.3 wt%) and low K 2 O (0.02–0.68 wt%) contents. These rocks show slightly variable initial 87 Sr/ 86 Sr ratios (0.7048 to 0.7057), relatively low and homogeneous Pb isotope ratios ( 206 Pb/ 204 Pb = 18.2948–18.6462, 207 Pb/ 204 Pb = 15.5587–15.6132, 208 Pb/ 204 Pb = 38.3843–38.8352) and positive ε Nd (t) values (3.0–4.9), similar to ophiolites from the Indus-Yarlung Tsangpo suture (IYTS). However, they are remarkably depleted in high field strength elements (HFSE; such as Nb and Ta) and slightly enriched in light rare earth elements (LREE) [(La/Yb) N = 2.8–4.4], both of which imply their mantle affinities with distinctive arc signatures. The δ 7 Li values of these rocks range from −2.0 to +2.0‰ (average = −0.7‰), with the majority of samples falling outside the depleted mantle range (+3.4 ± 1.4‰). They exhibit high Li contents (13.2 to 34.1 ppm) and Li/Y ratios (0.8 to 2.2), which are comparable with marine sediments. The negative correlation between Li/Y ratios and δ 7 Li values also suggests the addition of subducted marine sediments. The modeling of δ 7 Li values in combination with Pb-Sr-Nd isotopic ratios suggests that ~1 to 5% of marine sediments have been added into the mantle source of the Dagze mafic rocks. Combined with a previous study, we suggest that the Dagze mafic rocks were derived from the upwelling asthenospheric mantle metasomatized by subducted marine sediments. • Reporting the negative δ 7 Li values of the Dagze mafic rocks. • Demonstrating the lithium isotopic heterogeneities in the asthenospheric mantle. • Modeling ~1 to 5% of marine sediments to the mantle source of the Dagze mafic rocks.

La Queglia carbonatitic melnöite: a notable example of an ultra-alkaline rock variant in Italy

Very primitive ultramafic igneous rocks occur at Mt. La Queglia (Abruzzo, Italy). They form a strongly deformed sill–dyke system now tilted vertically. These rocks were initially classified as alnöite and, subsequently, have been suggested to be a carbonatitic olivine melilitite. However, further investigation and interpretation of these rocks is needed due to the presence of hand-specimen-scale textural variation suggesting a complex petrogenesis. We study the texture, mineral chemistry, and whole-rock geochemistry to define three main rock-types. (1) A brecciated rock with an ocellar texture composed of calcite pseudomorphs after olivine and melilite, plus fresh diopside in a groundmass of mica, aegirine, garnet, calcite, apatite, perovskite, titanate and chlorite. Zoned ocelli in this rock show an amoeboid shape, agglutination, and menisci typical of a plastic state. (2) A quenched rock showing a spinifex texture containing long feathery phenocrysts of cpx and mica suspended in a groundmass of nepheline, aegirine, apatite, Ti–rich magnetite, plus abundant calcite and some K-feldspar and zeolites. (3) A coarse-grained rock is composed of calcite plus intergranular glauconite, a mixture of spinel mineral group and Ti–rich magnetite, accessory barite, pyrite, and chabazite-K. The igneous rocks at Mt. La Queglia show extreme SiO2-undersaturation (33.5–37.3 wt% SiO2), high MgO contents and TiO2/Al2O3 ratios. Rock-type 1 has a lower Mg number Mg# = 100 × [Mg/(Mg + Fe2+)], higher Ca number Ca# = 100 × [Ca/(Ca + Mg)], high Cr (up to 720 ppm) Ni (up to 379 ppm), higher rare earth elements (REE) contents as well as La/Lu ratio, compared to rock-type 2. Perovskite and chromite accumulation seems an important agent during rock differentiation. Rock-type 3 shows REE cross-over with rock-type 2 suggesting light (L)REE concentration in a carbothermal residuum. Mt. La Queglia rocks are an end-member compared to other Upper Cretaceous and Paleogene Italian lamprophyres, suggesting a low degree of melting of a HIMU (a colloquialism for “high-μ”; referring to mantle domains with high 238U/ 204Pb) garnet-bearing mantle source.

Petrogenesis of newly identified Neoarchean granitoids in the Qingyuan of NE China: Implications on crustal growth and reworking of the North China Craton

• A new ca. 2.7–2.5 Ga granitoid suite was identified in the Qingyuan, NE China. • The 2.68 Ga TTG was derived from ancient lower crust as well as juvenile crust. • Qingyuan granitoids record two periods of crustal growth and reworking events. Discovery of ca. 2.7 Ga tonalite-trondhjemite-granodiorite (TTG) in the North China Craton (NCC) can provide the key clue to understanding the Neoarchean crustal evolution. Most recently, we mapped out ca. 2.7 Ga TTGs from the northern Qingyuan at the northeastern margin of NCC. Together with the associated ca. 2.6–2.5 Ga high-K granites and high-Mg diorites, this study provides new constraints on crustal growth and reworking during the Neoarchean. Zircon U–Pb dating indicates that the TTGs, high-K granites and high-Mg diorites were formed at ca. 2.68 Ga, ca. 2.56 Ga and ca. 2.54 Ga, respectively. All of these lithologies exhibit enrichments in large ion lithophile elements (e.g., Rb and Ba) but depletions in high field strength elements (e.g., Nb and Ta), with positive εHf(t) and εNd(t) values. The TTGs have moderate SiO 2 , low Al 2 O 3 and variable MgO contents with high Sr/Y and (La/Yb) N ratios. They were likely derived from partial melting of mafic lower crust. High SiO 2 and K 2 O but low MgO and Cr contents as well as high Sr/Y and (La/Yb) N ratios reflect an origin of recycling of ancient crustal rocks (e.g., pre-existing TTGs) for the high-K granites. The high-Mg diorites have high MgO and Cr contents but low Sr/Y and (La/Yb) N ratios, which indicate that they could be sourced from partial melting of metasomatized mantle peridotite. Combined with previous studies, the northeastern NCC experienced two major periods of ca. 2.7 Ga and ca. 2.6–2.5 Ga crustal growth and reworking events.

Geodynamic evolution of lithospheric removal of the North China Craton: Constraints from late Mesozoic volcanic rocks in the Bohai Bay Basin, East China

The subduction history of Paleo-Pacific Plate (PPP) related to lithospheric removal in the North China Craton (NCC) still poorly constrained. To address this issue, we report a detailed investigation of LA-ICP–MS zircon U–Pb chronology, geochemistry, and Sr-Nd isotope compositions of a set of late Mesozoic volcanic rocks collected from boreholes in the Bohai Bay Basin. Late Jurassic (150.6 Ma) adakitic rocks are trachyandesites with high MgO (1.41–5.78 wt%), Mg# (46–64), Cr (25.1–110 ppm) and Ni (12.4–34.0 ppm) contents similar to those of high-Mg adakitic rocks. These samples were probably the result of partial melting of a delaminated region of thickened lower continental crust. Early Cretaceous samples are basalt and trachyandesite. Trachyandesites (ca. 115 Ma) exhibit low εNd(t) values (-15.9 to −12.9) and older TDM2 ages (2.19–1.96 Ga), indicating that they originated in the ancient lower crust. Hornblende may have been the main residual phase in the source, suggesting that these samples were likely formed by partial melting of the lower crust at depths of 30–40 km. The coeval basalts are OIB-like series with depleted Sr-Nd isotopes, depleted Pb and no depleted Nb, implying that they were derived from a depleted mantle source metasomatized by recycled oceanic crust. Combined with those of previous studies, our findings show that subducted PPP beneath the NCC experienced local slab rollback and fast slab rollback during late Mesozoic, resulting in lithospheric removal and destruction of the NCC. Finally, the magmatic activity that marked the large-scale lithosphere removal ended after ca. 115 Ma.

Effect of Curing Temperature on the Properties of a MgO-SiO2-H2O System Prepared Using Dead-Burned MgO.

The hydration of M-S-H prepared using silica fume (SF) and dead-burned MgO cured at 20 °C, 50 °C, and 80 °C was investigated, and the properties and performance of this M-S-H were measured. The formation of M-S-H was characterized using XRD, FTIR, TGA, and 29Si MAS-NMR. Results show that the compressive strength of paste prepared using MgO calcined at 1450 °C for 2 h reached 25 MPa after 28 d. The shrinkage of mortar made with low reactivity MgO was lower than that made with high reactivity MgO. The pH value of MgO/SF paste mixed with dead-burned MgO did not exceed 10.4 at room temperature. The shrinkage of M-S-H prepared using dead-burned MgO was less than that prepared using more active MgO, and its strength did not decrease over time. No (or only a small amount of) Mg(OH)2 was formed, which is why the strength of M-S-H prepared with dead-burned MgO continually increased, without decreasing. The promotion of curing temperature favor process of MgO hydration and is beneficial for degree of silica polymerization. The sample cured in 50 °C water showed the highest relative degree of reaction.

Effect of the Timing Addition of Ferrosilicon with Al and Ca Impurities on Inclusion Formation in Al‐Killed Automobile Gear Steel SCr420H

The current study investigates the effect of the timing of the addition of ferrosilicon with Al and Ca impurities on the inclusion evolution during the refining process of Al‐killed gear steel SCr420H. To achieve this aim, laboratory experiments and thermodynamic calculations are conducted. The process sample, the ingot sample, and ferrosilicon are polished and analyzed by scanning electron microscope‐energy dispersive spectrometer. The results show that Ca and Al impurities mainly exist as intermetallic compounds or are segregated on the phase boundary between FeSi2and Si in the ferrosilicon. The Ca content of the ingot increased with the delay of adding the ferrosilicon with Al and Ca impurities. In case the ferrosilicon is added at the end of the refining process, many liquid calcium aluminate inclusions can be observed in the ingot, which indicates that changing the timing of adding ferrosilicon with Al and Ca impurities is a promising way to modify inclusion to liquid inclusion. Based on the thermodynamic calculation, MgO‐saturated spinel is more easily modified into CaO–Al2O3inclusion than spinel with low MgO content. When ferrosilicon is added in steel containing enough Mg, inclusions are transformed into spinel with high MgO content first, and afterward are modified into liquid calcium aluminate inclusions.

Petrogenesis of the late Cretaceous Budongla Mg-rich monzodiorite pluton in the central Lhasa subterrane, Tibet, China: Whole-rock geochemistry, zircon U-Pb dating, and zircon Lu-Hf isotopes

Mg-rich monzodiorite are found in the Budongla gold ore district, Zhongba County, Xizang (Tibet) Autonomous Region, P.R. China. Studying the petrogenesis of this intermediate pluton can provide effective information to explore the geological evolution of the Lhasa terrane. One monzodiorite sample yielded a weighted mean 206Pb/238U age of 92.7 ± 1.1 Ma (mean square weighted deviation=0.33) using LA-ICP-MS zircon U-Pb dating, which represents the late phase of Late Cretaceous magmatism. The rock-forming minerals in the Budongla Mg-rich monzodiorite mainly include K-feldspar, plagioclase, quartz, biotite augite, and amphibole, and its accessory minerals mainly include magnetite, titanite, zircon, and apatite. The rocks are rich in K2O+Na2O and K2O with medium contents of SiO2, CaO, and A12O3,, suggesting these rocks belong to the high-K calc-alkaline series. These rocks have high MgO, Fe2O3, and FeO, with high Mg# values and low DI, which implies they are Mg-rich intermediate intrusive rocks. The rocks are enriched in LREEs and LILEs and depleted in HREEs and HFSEs. They have negative Eu anomalies, no obvious negative Ce anomalies, and slightly negative εHf(t). We infer that the Budongla pluton is a high-K calc-alkaline metaluminous Mg-rich monzodiorite and intruded during the post-collisional period of the Lhasa and Qiangtang terranes.

Water quality implications of the neutralization of acid mine drainage with coal fly ash from India and the United States

Subsurface coal mining often induces the formation of acid mine drainage (AMD) in active and abandoned coal mines while coal combustion generates coal combustion residuals (CCR), including fly ash (FA), with elevated levels of toxic metals. Decades of AMD and CCR production have caused major environmental and human health impacts. Given the typically elevated level of oxides in FA, previous studies have examined its potential to neutralize AMD and remove the associated metals. While the neutralization of AMD through reaction with FA has been demonstrated to successfully remove cationic metals, the fate of oxyanion forming elements are less well studied and is the focus of this study. Here we conducted 49 different experiments in which simulated AMD solutions were interacted with representative U.S. (n = 7) and Indian (n = 6) FA samples through controlled liquid to solid ratios in short-term (24 h) and long-term (up to 5 weeks) lab-scale experiments. We show that Class-F FA, originating from Gondwana and Northeastern Tertiary coals in India, has limited neutralization capacity, while Class-C FA, with high CaO and MgO contents from Powder River coals in the U.S. has the greatest AMD neutralization capacity among the studied fly ashes. The neutralization experiments show that AMD-FA reactions cause the removal of cationic elements (i.e., Fe, Mn, and Al) from solution, while at the same time, leaching oxyanion forming elements (i.e., As, Se, Mo, Cr, B, Tl, and Sb) from the FA, increasing the potential environmental risks from the treated leachates. The magnitude of mobilization of these elements depends on their concentrations in the FA and the pH conditions. We show that using FA from the Appalachian and Illinois coals efficiently neutralizes AMD, but also results in secondary contamination of the treated effluents with oxyanion forming elements to levels exceeding drinking water and ecological standards, which could contaminate the ambient environment, whereas neuralization with Powder River Basin Class-C FA induces only limited contamination.

The Early Cretaceous Granitoids and Microgranular Mafic Enclaves of Sanguliu Pluton, the Liaodong Peninsula: Implications for Magma Mixing and Decratonic Gold Mineralization in the Eastern North China Craton

Some Early Cretaceous granitoids characterized by abundant mafic microgranular enclaves (MMEs) formed by magma mixing have been associated with gold deposits in the eastern North China Craton (NCC). However, the genetic connection of magma mixing with gold mineralization remains unclear. The zircon U–Pb ages and in situ Lu-Hf isotopic compositions, whole-rock major- and trace-element and Sr–Nd–Pb isotopic compositions, as well as EPMA biotite compositions, were presented for the Sanguliu granodiorite and enclaves in the Liaodong Peninsula in order to obtain insights into the spatial and temporal distribution, and internal connection of magma mixing with the decratonic gold deposits in the eastern NCC. The Sanguliu granodiorite yielded coeval formation ages with the enclaves (~123 Ma), and their acicular apatites and plagioclase megacrysts suggest that the enclaves were formed by mixing between mafic and felsic magmas. Geochemically, the Sanguliu granodiorite is high-K calc-alkaline I-type granite, with an initial 87Sr/86Sr ratio of 0.70552 to 0.71470 and strongly negative εNd(t) (−11.4 to −21.3) and zircon in situ εHf(t) values (−15.1 to −25.4), indicating that the felsic magmas were ancient lower crust with the involvement of mantle-derived materials. Meanwhile, the enclaves have high MgO (4.18 to 6.17 wt.%), Cr (45.91 to 290.04 ppm), and Ni (19.65 to 88.18 ppm) contents, with high Mg# values of 50 to 57 at intermediate SiO2 contents (53.68 to 55.78 wt.%), highly negative εNd(t) values (mostly −18.42 to −22.03), and in situ zircon εHf(t) values (−18.6 to −22.7), indicating that the mafic magma was mainly derived from the enriched lithospheric mantle. Furthermore, the biotites from the Sanguliu granodiorite clustered between the MH and NNO buffers in the Fe2+–Fe3+–Mg diagram. This, combined with the high Ce/Ce* ratios (1.30 to 107.18) of the zircons, indicates that the primary magmas forming the Sanguliu granodiorite had a high oxygen fugacity, which is favorable for gold mineralization. These findings, together with previous studies of the Early Cretaceous granitoids with enclaves in the eastern NCC, suggest that magma mixing commonly occurred during 110–130 Ma and is temporally, spatially, and genetically related to decratonic gold systems in eastern NCC.

Petrogenesis and Tectonic Implication of the Hongtaiping High-Mg Diorite in the Wangqing Area, NE China: Constraints from Geochronology, Geochemistry and Hf Isotopes

This study presents new data from zircon U–Pb dating and Hf isotope analysis, as well as whole-rock major- and trace-element compositions of the Hongtaiping high-Mg diorite in the Wangqing area of Yanbian, NE China. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) zircon U–Pb dating gives an eruption age of ca. 267 Ma for the high-Mg diorite. These samples have MgO contents of 13.30% to 16.58% and high transition metal element concentrations, classified as sanukite. Their rare earth element (REE) contents range from 45.2 to 68.4 ppm and are characterized by slightly positive Eu anomalies (Eu/Eu* = 1.08–1.17). They show enrichment in light REEs (LREEs) and depletion in heavy REEs (HREEs), with LREE/HREE ratios = 6.54–6.97 and (La/Yb)N values = 7.24–8.08. The Hongtaiping high-Mg diorite is enriched in Rb, U, K, and Sr, but depleted in Th, Nb, and Ta. High MgO contents, Mg# values, and transition metal element concentrations imply that the magma experienced insignificant crystallization fractionation and crustal contamination. Relatively homogenous positive Hf isotopic values indicate that the original magma was generated by the partial melting of a depleted mantle wedge that was metasomatized by subducting slab fluids. The magma was generated by the moderate degree partial melting (20%–30%) of a garnet lherzolite source. Combined with previous studies, this shows that the high-Mg diorite was formed by the northward subduction of the Paleo-Asian oceanic plate during the Middle Permian.