Depletion In Sr Research Articles

Element enrichment/depletion during faulting in shale-rich surface exposures of the 2008 Wenchuan earthquake (Mw 7.9) and implications for coseismic temperature

The coseismic frictional temperature is increasingly recognised as an important factor for the transformation mechanism in shallow crustal faulting. We report changes in the mineralogical and geochemical compositions across the fault zone in the Shaba (SB) exposure of the 2008 Wenchuan earthquake (Mw 7.9), which contained the maximum value of vertical displacement and cut through shale-rich strata by the principal slip surface. Assuming Yb to be an immobile trace element, with respect to those in the adjacent damaged zone and wall rocks, Li, Rb, Cs and most light rare earth elements (LREE) exhibited marked enrichments of 143%, 247%, 475% and >60%, respectively; and a 40% depletion of Sr and <5% depletion of most heavy rare earth elements (HREE) was found, responding to mineralogical transformation such as alteration and dissolution of feldspar and formation of abundant clay minerals. In addition, heterogeneous adsorption of clay minerals could result in fractionation between and within LREE and HREE as well as negative Eu anomalies and positive Ce anomalies. The element enrichment/depletion model of the northern segment of the Yingxiu–Beichuan (YX–BC) fault zone was quite different from the middle/southern segments characterising faults in carbonate and granitic rocks. Through model calculation, the calculated trace element compositions (Li, Rb, Sr, Cs, Ba, La, Sm and Pb) of the fault gouge were obtained at 250 °C, 300 °C and 350 °C, and were produced by frictional heating. By comparing with the observed values, we suggest that high temperatures derived from frictional heating or due to buffering of the slip zone temperature by evaporation of pore water during the earthquake within the principal slip surface in the northern segment of the YX–BC fault zone may not have existed. Mechanical crushing and chemical alteration (not under high-temperature conditions) within the fault zone during the coseismic stage may result in mass removal and element enrichment/depletion. KEY POINTS Mineralogical and geochemical compositions were reported in the Shaba exposure of the 2008 Wenchuan earthquake. Li, Rb, Cs and most LREE exhibited marked enrichments in the fault gouge. Fractionation between and within LREE and HREE, negative Eu anomalies and positive Ce anomalies occur in the fault gouge. High temperatures may not have existed within the principal slip surface of the northern segment of the YX–BC fault zone.

Geochronology, Geochemistry, and Geodynamic Relationship of the Mafic Dykes and Granites in the Qianlishan Complex, South China

The Qianlishan complex, located in Hunan Province of South China, is closely associated with intense W-dominated polymetallic mineralization. The Qianlishan complex is composed of three phases: the main-phase porphyritic and equigranular granites, granite porphyry, and mafic dykes. Geochronologically, the zircon U-Pb dating results show that the porphyritic and equigranular granites have ages of approximately 159 and 158 Ma, respectively, similar to those of mafic dykes (approximately 158 Ma), while the granite porphyry was formed later at approximately 145 Ma. Geochemically, the mafic dykes are characterized by calc-alkaline high-Mg andesite (HMA) with high MgO, TiO2, Mg#, and CA/TH index. They exhibit significantly depleted εNd(t) and εHf(t) with high Ba/La, La/Nb, and (La/Yb)N, indicating that they formed from mixing melts of depleted asthenospheric mantle and metasomatized subcontinental lithospheric mantle (SCLM). The main-phase granites are peraluminous and are characterized by high SiO2, low (La/Yb)N ratios, and relative depletion in Ba, Sr, Ti, and Eu. They also display negative correlations between La, Ce, Y, and Rb contents, suggesting that they are highly fractionated S-type granites. Furthermore, they show high εNd(t) and εHf(t), CaO/Na2O ratios, HREE, and Y contents, indicating that they were produced by parental melting of ancient basement mixed with mantle-derived components. In contrast, the granite porphyry shows A-type signature granites, with higher εNd(t) and εHf(t) and CaO/Na2O ratios than the main-phase granites but similar Zr/Nb and Zr/Hf ratios to the mafic dykes, suggesting that they are the products of partial melting of a hybrid source with ancient basement and the mafic dykes. We thus infer that the slab roll-back led to generation of Qianlishan back-arc basalt and HMA and further triggered the formation of the Qianlishan granite.

Geochronology and textural and compositional complexity of apatite from the mineralization-related granites in the world-class Zhuxi W-Cu skarn deposit: A record of magma evolution and W enrichment in the magmatic system

Apatite is a ubiquitous mineral in granites and crystallizes from the beginning of magma evolution to the latest magma-fluids transitional stage, and thus, is able to record petrogenetic-metallogenic information. In order to figure out the role of granites in the formation of the Zhuxi deposit, textures and compositions of apatites in the Zhuxi granites were investigated. Granites related to the Zhuxi W-Cu deposit include biotite granite, muscovite granite, and granite porphyry. Apatites in these granites are named Group A, Group B (core – Group B1; rim – Group B2), and Group C, respectively. Along this sequence, geochemical characteristics of apatites show gradual enrichment of total rare earth elements (ΣREE), high-field strength elements (HFSE; Th, U, Nb, Ta, Zr, and Hf), as well as ore-forming element W, and depletion of Sr. Meanwhile, Ga content in these apatites consecutively increased, indicating the reduction of oxygen fugacity in the Zhuxi magmatic system. Non-chondritic Y/Ho (mostly > 34) and Zr/Hf (broadly < 5) ratios in Group C apatite reflect the high volume of fluids interacted with the magma of the most evolved granite porphyry. Constant high F contents (3.4–4.4 wt%) in all apatite samples show abundant F in the Zhuxi magmas, which played an important role in the formation of the Zhuxi deposit in terms of facilitating W enrichment in magma and exsolution of W into hydrothermal fluids. The Zhuxi granites formed at ca. 153 Ma when South China Block was in an extensional tectonic setting, and the granite porphyry is the most potential intrusion to cause the mineralization of the Zhuxi deposit.

Late Palaeozoic magmatism in the eastern Tseel Terrane of SW Mongolia evidenced by chronological and geochemical data

The eastern Tseel Terrane of SW Mongolia, which is an important part of the Central Asian Orogenic Belt (CAOB), contains a segment of imbricated sheets of Late Palaeozoic granites as well as a bimodal volcanic suite. Late Devonian (380–382 Ma) granites that are enriched in Th, U, and K and depleted in Nb, Ta, P, Ba, Sr, and Ti indicate arc magmatism and are low‐K tholeiitic to medium‐K calc‐alkaline series. Zircon εHf(t) values are of +8.30 to +14.1, with crustal model ages of 0.83–0.48 Ga. The bimodal volcanic suite is composed of N‐MORB basalt and 302 ± 2 Ma rhyolite having A2‐type granite affinities, εHf(t) values ranging from +9.9 to +11.9, and crustal model ages from 0.69 to 0.59 Ga. The rhyolite mighthave originated from partial melting of juvenile lower crust, rather than fractional crystallization of coeval basaltic magma. Late Carboniferous (299–303 Ma) granites are medium‐K to high‐K calc‐alkaline series, cross‐cutting carbonaceous siltstone, emplaced into the deformed volcanic rocks and are characterized by enrichment in K, Th, and U accompanied by depletion in Ba, Nb, Ta, Sr, P, and Ti in a primitive mantle‐normalized diagram with εHf(t) values ranging from +6.05 to +10.6 and crustal model ages from 0.70 to 0.65 Ga. Thus, LA‐ICP‐MS zircon ages in combination with geochemical data document a phase of arc‐related magmatism in the Tseel Terrane at 380–382 Ma. These rocks were subsequently deformed under low‐grade metamorphic conditions and intruded by undeformed granites at c. 299–303 Ma. The coeval 302 Ma rhyolite in bimodal volcanic suite shows typical A2‐type granitic geochemical affinities and probably documents a back‐arc basin extensional environment, which was probably related to the roll‐back of the Palaeo‐Asian Oceanic Plate during the northward subduction under the Central Mongolia microcontinent.

Petrogenesis of early Carboniferous bimodal-type volcanic rocks from the Junggar Basin (NW China) with implications for Phanerozoic crustal growth in Central Asian Orogenic Belt

The Central Asian Orogenic Belt (CAOB) is one of the world's largest and longest-lived accretionary orogens that has been regarded as an important area of crustal growth during the Phanerozoic, yet the growth mechanism is still under debate. A combined study of petrology, geochronology and geochemistry for drilling-sampled early Carboniferous volcanic rocks from the Junggar Basin (NW China), southwestern CAOB, aims to constrain their petrogenesis and implications for Phanerozoic crustal growth. The volcanics show a bimodal-type suite, dominated by basalts, basaltic andesites and subordinate rhyolites, and have consistent zircon U–Pb ages of 334–336 Ma. The mafic rocks exhibit arc-like trace-element distribution patterns characterized by enrichment of LILEs (e.g., Pb) and LREEs but depletion of HFSEs (e.g., Nb, Ta and Ti). They have juvenile isotopic signatures of zircon ɛHf(t) (+11.4 to +15.4) and whole-rock ɛNd(t) (+7.8 to +8.5), with initial (87Sr/86Sr)i of 0.7040–0.7054 and (206Pb/204Pb)i of 17.681–17.817. These geochemical features, together with their variable Ba/La (4.28–44.2) but low (Tb/Yb)N (1.24–1.85) and Sm/Yb (1.65–3.44) ratios, suggest that the mafic volcanics could be derived from a main spinel-bearing mantle source metasomatized by subduction-related fluids. In contrast, the felsic samples are geochemically equivalent to A2-type granite, with high contents of SiO2, Zr, Ga, and show strong depletions in Eu, Sr and Ti. They have zircon Hf (ɛHf(t) = +12.0 to +15.3) and whole-rock Sr-Nd-Pb isotopic compositions ((87Sr/86Sr)i = 0.7032–0.7038; ɛNd(t) = +7.8 to +8.1; (206Pb/204Pb)i = 17.973–18.004) similar to the coeval mafic rocks. These observations, along with the model calculations using MELTS, favor a derivation of felsic rocks from the mafic magma by fractional crystallization. We suggest that the early Carboniferous bimodal-type volcanism formed in a localized back-arc extension within an overall convergent setting, presumably triggered by slab roll-back of the subducting Paleo-Junggar Ocean plate. This bimodal-type magmatism recorded a significant vertical crustal growth event in the Junggar Basin during the Phanerozoic. We propose that oceanic subduction (flare-ups) not only leads to the lateral accretion of arcs, but also results in the vertical growth of mantle-derived materials and subsequent magma differentiation during slab roll-back (flare-lulls); this may considerably change our view of the models of crustal growth in CAOB.

Alteration of Granitoids and Uranium Mineralization in the Blatná Suite of the Central Bohemian Plutonic Complex, Czech Republic

The Bohemian magmatic complex belongs to granitoid plutons of the Central European Variscides. Hydrothermal uranium mineralization evolved in the small uranium deposits Nahošín and Mečichov is associated with N–S shear zones occurring on the SW margin of the Central Bohemian plutonic complex formed by amphibole-bearing biotite granodiorites of the Blatná suite. The purpose of presented study is description of uranium mineralization bounded on brittle shear zones, which is coupled with intense low-temperature hydrothermal alteration of granitic rocks. Uranium mineralization, formed predominantly of coffinite, rare uraninite, and thorite, is accompanied by intense hematitization, albitization, chloritization, and carbonatization of original granitic rocks that could be described as aceites. These alterations are accompanied by the enrichment in U, Ti, Mg, Ca, Na, K, Y, and Zr and depletion in Si, Ba, and Sr. The analyzed coffinite is enriched in Y (up to 3.1 wt % Y2O3). Uraninite is enriched in Th (up to 9.8 wt % ThO2) and thorite is enriched in Zr (up to 5.7 wt % ZrO2). The REE-elements are concentrated in the REE-fluorcarbonate synchysite-(Ce).

Chromitites from an Archean layered intrusion in the Western Dharwar Craton, southern India

Chromite deposits hosted in a layered ultramafic–mafic intrusion in the Archean Chithradurga greenstone belt are part of a suture that divides the Western and Central Dharwar craton blocks in southern India. Serpentinised ultramafic rocks including dunite, peridotite, and phlogopite-rich clinopyroxenite occur with massive chromitite. The olivine compositions show two distinct groups, one with Fo ~91–92 olivines in the massive chromitite, and another group with olivine Fo values of ~95–96, in the serpentinised dunite. The chromite occurs as massive chromitite and as an accessory phase in dunite. The former is characterized by high Cr# (Cr/(Cr + Al) × 100 = 67–70) and moderate to high Mg# (Mg/(Mg + Fe) = 52–66); The latter shows a larger variation in Cr which is likely related to sub-solidus re-equilibration of the chromite during the serpentinization event. In the massive chromitites, sub-solidus re-equilibration of chromite is less significant or absent. Bulk-rock major and trace element analyses of the peridotites reveal a composition less magnesian than depleted mantle rocks, with low TiO2, Na2O, CaO and high Cr, Ni content, a general depletion in Sr and enrichment in Th, U. The chromitites contain variable PGE abundances (ΣPGE = 8-244 ppb) with enrichments of Os, Ir and Ru, relative to Pt and Pd . These features suggest that the chromitites are cumulates formed from a highly magnesian parental magma with komatiitic affinity, derived by large degrees of partial melting, , which underwent crustal contamination. The ReOs isotope data demonstrate a minimum Re-depletion model age (TRD) of 2895 ± 24 Ma for the serpentinized dunite (MY11/3), and a more robust age of 3120 ± 12 Ma for two chromitite samples, which we interpret as the best estimate of the magmatic age of this ultramafic intrusion. Abundant zircon grains also occur within these ultramafic rocks with UPb ages spanning from ca. 2.9 Ga to ca. 2.4 Ga, with a dominant age population in the range 2.8–2.6 Ga. We interpret the upper intercept age at ca. 2.9 Ga to represent the initial crystallization of zircon in the ultramafic rocks, potentially as a result of an early stage of metamorphism and hydrothermal alteration. The 2.5–2.4 Ga zircon ages reflect a late-stage high-grade metamorphic overprint.

Petrogenesis and tectonic implications of Palaeocene (ca. 54 Ma) rhyolites in the western Lhasa Terrane, south Tibet: Constraints from geochemistry and Sr–Nd–Hf isotope compositions

The widespread Linzizong volcanic successions (LVS) in the Lhasa Terrane was a magmatic response to the tectonic transition from Neo‐Tethyan oceanic subduction to the India–Asia collision, which has been the subject of many studies; however, studies on the LVS in the western Lhasa Terrane are scarce compared to those in the east, limiting our understanding of the tectonic transition. Zircon U–Pb ages of two rhyolitic samples from the Shiquanhe region in the west of the Lhasa Terrane indicate that at least part of the Zenong Group, previously thought to have formed during the Early Cretaceous, was actually erupted during the Late Palaeocene (ca. 54 Ma) and belongs to the LVS. The rhyolites are characterized by high SiO2 and Al2O3, moderate K2O and Na2O, and low MgO, CaO, and FeO contents, enrichment in Rb and Th, depletion in Sr, Ba, Eu, Nb, and Ta, and have relatively uniform whole‐rock εNd(t) (−1.90 to −0.89) and zircon εHf(t) (+0.95 to +5.03) values. These geochemical characteristics indicate that they were formed by the partial melting of juvenile continental crust with subsequent plagioclase, biotite, amphibole, and Fe–Ti oxide fractionation. Combined with the results of previous studies, our data show that the western Lhasa Terrane underwent intensive Early Cenozoic crustal growth, similar to what occurred in the east, due to underplating of mantle‐derived magma resulting from the roll‐back and eventual break‐off of the Neo‐Tethys slab after the initial continental collision.

Provenance and paleo-weathering of Paleoproterozoic siliciclastic sedimentary rocks of Bijawar Group, Sonrai Basin, Uttar Pradesh, India: using a geochemical approach

Shales and sandstones of the Paleoproterozoic Bijawar Group (India) have been studied to decipher their paleo-weathering conditions and provenance based on geochemistry. Shale samples are composed of k-feldspars, mica, quartz, and fine iron-oxides, whereas sandstones are composed of quartz and k-feldspars. The predominant positive correlation of K2O vs TiO2, Na2O vs Al2O3, and K2O vs Al2O3 indicates that the elements are associated with detrital phases. Trace elements Sc, Rb, Ba,Th, Y, and Zr show a strong positive correlation with Al2O3 and K2O which indicates that the absolute abundances of these elements are controlled mainly by illite. A negative correlation of trace elements Ni, Cu, Co with Al2O3, and K2O represents their presence in iron oxides like magnetite, ilmenite, and hematite. Multi-element Post-Archaean Australian Average Shale (PAAS) normalized spider diagrams show enrichment of V, Pb, Zr, Y, Hf, Th, Rb, and depletion of Ni, Sr, Ba, Nb, U. The depletion of Sr indicates the least enrichment of plagioclase and the same is also supported by negative Eu-anomaly of the samples, though weak. The chondrite normalized rare earth element (REE) plots show a slightly light-REE (LREE) enriched and flat heavy-REE (HREE) pattern with weak negative Eu anomaly. The overall, high values of LaN/SmN (avg. 10.49), CeN/YbN (avg.0.37), LaN/YbN (avg. 34.28) and low values of GdN/YbN (avg. 1.82) and TiO2 (0.27–1.82, average 0.92 < PAAS) in most of the samples, show a relationship with the felsic source rocks. The index of compositional variability (ICV) of the samples is < 0.84 which indicates no enrichment of primary minerals. The chemical index of alteration (CIA) of present samples varies from 48.60 to 81.69, indicating low to moderate intensity of chemical weathering of the source. The plot between SiO2 and Al2O3 + K2O + Na2O depicts that majority of the samples belong to the environment from humid to semi-humid and have attained a high chemical maturity. The high SiO2/Al2O3 values (1.36–20.79) in studied samples indicate relatively high sediment maturity due to the extreme sorting of sediments in a stable cratonic regime. A stable cratonic regime, with a low upliftment rate that has allowed strong chemical weathering of protoliths, is further indicated by low CaO, Na2O, and Sr contents of the studied samples. The overall geochemical characteristics of the present samples—high SiO2, Al2O3 and K2O and low TiO2, MgO, Na2O, and CaO contents—suggest a felsic provenance. The felsic nature of the source rocks is also supported by the trace element ratios like (La/Lu)N (7.72–76.89), La/Sc (1.50–7.40), La/Co (0.39–11.48), Th/Co (0.80–15.90), and Cr/Th (0.08–5.10). Since the Bijawar Group is sited over the Bundelkhand Granite Gneiss Complex (BGGC), it is, therefore, plausible that the main source components of Bijawar Group siliciclastic rocks are the BGGC felsic rocks.

Discovery of Neoproterozoic highly fractionated syenogranite in the southwestern part of the Erguna Massif in NE China and its geological implication

ABSTRACT Earlier studies of the Neoproterozoic magmatism and tectonic evolution in Erguna Massif of NE China are spatially confined to the central and northern parts of the area, but the southwestern part of the massif is poorly studied. This contribution documents new zircon U-Pb geochronology, Lu-Hf isotopic systematics, and whole-rock geochemistry from Neoproterozoic granites in the southwestern part of the area. The aim of this study is to determine the petrogenesis of the granites and further elucidate on the geodynamic setting of Neoproterozoic magmatism in the massif and their geological implications. Syenogranite samples from the region yield LA-ICP-MS U-Pb zircon weighted mean ages of 853 ± 5 Ma and 824 ± 3 Ma, and both dates are evidence for Neoproterozoic magmatism in the southwestern part of the massif. Both syenogranite samples are peraluminous (A/CNK = 1.06–1.43), calc-alkaline with high-K values, and assay 76.06–76.52 wt% SiO2, 1.98–3.20 wt% Na2O, and 4.63–4.77% wt% K2O. The syenogranites’ Chondrite-normalized REE pattern display a ‘gull-wing’ shape, with low (La/Yb)N ratios of 2.28–4.29 and significant negative Eu anomalies of δEu = 0.09–0.19. The syenogranites are characterized by depletion in Ba, Nb, Ta, Sr, P, and Ti and enrichment in Rb, Th, U and K compared to the N-MORB and non-fractionated granites elsewhere in the massif. These geochemical characteristics show that the Neoproterozoic syenogranite plutons in SW Erguna Massif are highly fractionated. Zircons from the granites also have εHf(t) values of +7.68 to −1.48 with corresponding two-stage model ages of ca. 1828 to 1258 Ma, indicating that they formed from the partial melting of a Palaeo- and Mesoproterozoic igneous source in the middle crust. In combination with previously published geological data, it is proposed that the Neoproterozoic granites in the southwestern study area were emplaced in an extensional environment before or during the initial stages of the break-up of the Rodinia.

Geochemistry of a lateritic mantle developed on basalt in the Cameroon Western Highlands (Cameroon Volcanic Line)

Although lateritic mantles have been strongly documented, there is need to continuously characterise and update information at site-scale so as to optimize exploration and exploitation operations in various industrial domains. In this paper, four soil profiles developed on basalt are described in detail to appreciate their morphology, mineralogy, geochemistry, pedogenesis and ore potential. The basalt is composed of olivine, plagioclase feldspars and pyroxenes and accessory magnetite, sphene and apatite. The basalt shows high levels of Ba, Cr, V, Sr, Ni, Zn and Zr; meanwhile total REEs range from 185.03 to 199.45 mg kg−1. The weathering indices reveal an extreme weathering intensity of the parent rock. Newly formed minerals are kaolinite (15–48%), haematite (13–40%), Goethite (10.5–19%) and gibbsite (10–12%), magnetite (4–9.56%), feldspars (4.67–6.10), apatite (2.8–3.9) and sphene (1.77–2.46%). The weathered materials show high levels of Cr (40–850 mg kg−1), V (145–582 mg kg−1), Zr (300–583 mg kg−1) and Ce (24.2–510 mg kg−1). The total REEs of the weathered materials range from 126.52 to 1267.69 mg kg−1, with the predominance of LREE. The REE basalt-normalized patterns revealed slight LREE depletion, more pronounced for the B horizons relative to the underlying C horizons as well as HREE enrichment that increase with depth and altitude. In these soils, mass balance calculations reveal depletion of Si, Ca, Mg, Ba, K, Na, Mn, P, Rb, Sr, La and Lu, enrichment of Al, Fe, Ti, Ga, U, Zr, Dy, Hf, U, Tm and Yb meanwhile Cr, Cs, Sn, Ta, Th, Tl, V, W, Y, Nb, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Ho are either depleted or enriched from one profile to the other. Apart from Cr, V, Zr and Ce whose concentrations respectively attain 850 mg kg−1, 582 mg kg−1, 487 and 510 mg kg−1, the mining potential of the studied lateritic mantle is low.

The Neoproterozoic alkaline rocks from Fangcheng area, East Qinling (China) and their implications for regional Nb mineralization and tectonic evolution

An integrated study was carried out on samples from the Fangcheng alkaline complex so as to establish the origin and evolution of the Nb-rich alkaline felsic magmas. The Fangcheng complex is composed of nepheline syenites, biotite syenites, alkali-feldspar syenites, quartz syenites and syenogranites. Titanite and zircon U-Pb dating reveals that these rocks were simultaneously emplaced between 867 and 833 Ma. They are strongly enriched in HFSEs (e.g., Nb and Zr) and LREEs, with obvious depletions of Ba, Sr and Eu. Notably, all Fangcheng alkaline rocks are enriched in Nb, and this is particularly true for the nepheline syenites (Nb = 161–461 ppm). The nepheline syenites and biotite syenites yield relatively high εNd(t) values (−0.7 to −1.5) and initial 208Pb/204Pb ratios (36.12–37.61) as compared to the quartz syenites and syenogranites (−4.5 to −4.9 and 23.40–36.72, respectively). Likewise, lower zircon εHf(t) values (−4.2 to −6.9) are recorded by the quartz syenites and syenogranites. Based on our results, we suggest that the Fangcheng alkaline rocks were generated via low degrees of partial melting of an enriched mantle during which the fractionation of an alkali basaltic melt generated a nepheline syenite magma. An ongoing segregation of sodic minerals caused the parent melt to evolve towards a potassium-rich composition, leading to the generation of the biotite syenites and alkali-feldspar syenites. Ultimately, the quartz syenites and syenogranites represent the end products of a highly evolved alkaline magma containing a significant degree of contamination by siliceous-rich crustal materials. The enrichment of Nb in all lithologies was controlled by both magmatic and hydrothermal processes. In an initial F- and HFSE-rich magmatic system, prolonged fractionation of Nb-poor minerals led to the concentration of both F and Nb in the residual melts, as is recorded by the Nb-rich titanite. Hydrothermal metasomatism by Na- and F-rich fluids induced further remobilization and subsequent precipitation of Nb to form secondary titanite, pyrochlore, euxenite and rutile in a post-magmatic stage. We infer that the Neoproterozoic Fangcheng alkaline rocks were emplaced in a post-collisional extensional regime, implying that the assembly of the Rodinia supercontinent might have been completed prior to ca. 833 Ma.

Multi-Phase Manganese Mineralization in the Noamundi Synclinorium, East Indian Shield

Manganese mineralization associated with phyllites in and around Joda, Odisha belongs to the Iron Ore Group of Noamundi basin and is a part of Jamda-Koira belt of East Indian Shield. The present study area comprises low to medium grade tectonites containing economic resources of both iron and manganese. Present study is concentrated on Manganese mineralization. Field study and petro-mineralogical observations reveal syngenetic character of manganese ores comprising lowT higher oxides viz. pyrolusite, cryptomelane, manganite as major Mn-minerals along with highT lower oxides viz. jacobsite, bixbyite, braunite and hausmannite as minor Mn-minerals. The Mn-ore bodies and associated phyllites have undergone multiple phases of deformation and metamorphism followed by hydrothermal and supergene processes. Four deformational phases have been deciphered during field study. Geochemical analyses of ores and phyllitic host rocks show high values of Al2O3, TiO2, Ba, Co, Ni, Cr, Cu, Sc, V, As, Zn but depletion of Sr, Yb, Sm, Nb. Geochemical data infer ores to be a recycling product originally derived from a mafic crustal source of tholeiitic character. Age data obtained from Sm-Nd ratio of two rock samples are 3.46 Ga and 2.79 Ga. Present work provides a critical assessment on the multiphase mineralization of manganese ores.

Geochronology, geochemistry, and Hf isotopic compositions of Triassic igneous rocks in the easternmost segment of the East Kunlun Orogenic Belt, NW China: implications for magmatism and tectonic evolution

ABSTRACT The voluminous Triassic igneous rocks in the East Kunlun Orogenic Belt (EKOB) are important for investigations of the tectonic evolution of the Paleo-Tethys Ocean. This study focused on the geochronology and petrogenesis of igneous rocks in the Elashan area with the aim of constraining the regional tectonic evolution. The 238 Ma syenogranites are characterized by high SiO2 contents and marked depletions in Sr and Eu. We conclude that they are highly fractionated I-type granites derived from partial melting of Mesoproterozoic lower crust with significant fractional crystallization. Comparing with contemporaneous granites and mafic rocks, the 236 Ma quartz monzodiorites have moderate MgO (1.5–1.6 wt.%) and SiO2 (61.0–61.9 wt.%) contents and εHf(t) values (–1.2 to +1.9). They were probably generated by the mixing of Mesoproterozoic lower-crust-derived and enriched lithospheric mantle-derived melts. The 230 Ma appinites have high MgO contents (3.8–6.1 wt.%) and enriched Hf isotopic compositions, and were likely derived from partial melting of lithospheric mantle that had been metasomatized by subduction fluids. We infer that these rocks were emplaced in syn-collisional slab break-off and the later initial post-collisional extensional setting between the BayanHar-Songpan Ganze and East Kunlun terranes. The basement composition, magmatism, and tectonic evolution of the Elashan area are similar to those of the eastern EKOB.

Petrogenesis of the early Permian A-type granites in the Halajun region, southwest Tianshan, western Xinjiang, NW China: implications for geodynamics of Tarim large igneous province

ABSTRACT Formation of a large igneous province, an explosive magmatic event in earth, is intimately related to geodynamic processes. The Tarim large igneous province, a famous representative in China, contains A-type granites. However, the petrogenesis of the A-type granites is debated. Some researchers think that the A-type granites are developed through extensive fractionation of magma derived from partial melting of newly underplated or gabbroic rocks. Others insist that the A-type granites are developed through intensive fractional crystallization of plume-derived mafic magma. Here, we present zircon U–Pb ages and whole-rock geochemical and Sr–Nd isotopic data for the Kezilekezitage, Keziertuo, Tamu, and Halajun II intrusions in northwest Tarim to elucidate their petrogenesis and geodynamic implications. Zircon U–Pb dating yielded crystallization ages of the Kezilekezitage, Keziertuo, and Halajun II intrusions of 275.1 ± 3.1 Ma (MSWD = 1.14), 274.8 ± 1.8 (MSWD = 0.46) and 275.6 ± 0.7 (MSWD = 1.04), respectively. The whole-rock geochemistry of the four intrusions is characterized by REE and HFSE enrichment, Ba, Sr, P, Ti, and Eu depletion, εNd (t) values of – 1.2 to +0.3, two-stage Nd model ages (T2DM) of 1.14–1.02 Ga, and an A1-type granite affinity. Whole-rock zircon geothermometry indicates a high formation temperature of 721–924°C. It is concluded that these A-type granites were generated by partial melting of Neoproterozoic OIB-like rocks, coupled with extensive fractional crystallization and minor crustal contamination. The production of the A-type granites at ca. 275 Ma represented the termination and greatest degree of lithospheric thinning during large igneous province formation.

Europium and barium enrichments in compositionally zoned felsic tuffs: A smoking gun for the origin of chemical and physical gradients by cumulate melting

Felsic pyroclastic deposits of overall low crystallinity erupted from caldera volcanoes frequently display internal gradients in composition and crystal content. The chemical gradients in the melt phase are consistent with differentiation paths and mineral/melt element partitioning predicted from the observed phenocryst assemblage. The same units typically show crystal-scale evidence for generation of eruptible magma by thermal rejuvenation of initially static, high-crystallinity (>50%) mush. Deposit-scale zoning can be reconciled with system rejuvenation by a model in which a high-crystallinity cumulate mush beneath its cognate supernatant liquid is melted by more mafic recharge to produce denser, remobilized magma of accumulative composition. In this model, zoning is a symptom of thermal rejuvenation, but requires a fusible cumulate, as provided by alkali feldspar-rich assemblages. We review existing data and present new whole-rock, glass and mineral compositions for nine examples of zoned felsic units, across the spectrum of alumina- and silica-saturation. We show that whole rocks and glasses in the late-erupted or least-evolved parts of these examples are strongly enriched in Ba (and, less consistently, Sr), and exhibit positive Eu anomalies, providing unequivocal evidence for the production of eruptible magma through melting of alkali feldspar cumulate mush. Hence, felsic volcanic rocks of low to moderate crystallinity may nonetheless have chemical signatures characteristic of cumulates. However, many other zoned tuffs show more subdued Ba-Eu enrichment and lack positive Eu anomalies. Enrichment of Eu and Ba in the melt is modulated by the extent and degree of equilibration during melting, and may be a transient signal that is quickly suppressed by new feldspar growth occurring between melting and eruption. In cases of very highly evolved rhyolites, the prior depletion of Ba, Sr and Eu by extensive alkali feldspar fractionation precludes development of any strong enrichment, although the patterns of relative variation are similar to those in the examples discussed here.

Pharmacological Targeting of SERCA in Breast Cancer

About 12% of U.S. woman develop breast cancer at some time during their lifetime. In addition to surgery and radiation therapy, chemotherapy is a key part of treatment following diagnosis. However, current drugs have variable success due to challenging disease subtypes that exhibit drug resistance. As a result, over 40,000 women die every year from intractable metastatic breast cancer. Thus, various new targets against breast cancer cells are currently under study. Aberrant intracellular Ca2+ homeostasis is observed in most cancer cells, hence, proteins that modulate Ca2+ levels may serve as a potential therapeutic target. Thapsigargin (TG) and cyclopiazonic acid (CPA) are agents known to potently inhibit the endoplasmic/sarcoplasmic reticulum (ER/SR) Ca2+‐ATPase (SERCA) and have shown high efficacy for impairing cancer cell growth. However, TG and CPZ are highly cytotoxic for normal cells. In recent years, our lab used spectrometry UV‐visible Ca2+ loading and ATPase activity assays in SR microsomes to identify novel drugs that target SERCA in striated muscle via an inhibitory, calcium‐dependent mechanism. These include drugs of the benzothiazepine (BZT) family (K201, CGP, PH00095) and antiepileptic drugs (sipatrigin, pimozide). The action of these new agents would cause partial SR depletion in cells by affecting Ca2+ sequestration at low cytosolic Ca2+. Interestingly, some of these drugs have been found to be cytoprotective under various stressful conditions. It is possible that these drugs prevent damaging SR Ca2+ overload under pathological conditions, including ischemia, via its action on SERCA. These findings contrast with the cytotoxicity associated with TG and CPZ. We compared the efficacy of these new SERCA inhibitors versus TG/CPZ on cell viability of breast cancer cell lines MCF‐7 and MDA‐MB‐231. MTS assay revealed TG and CPZ were more efficacious than our new compounds to decrease MCF‐7 viability. However, none of the agents tested significantly affected MDA‐MB‐231, a more metastatic breast cancer cell line. When paired with chemotherapeutics, K201, TG and CPZ synergistically reduce MCF‐7 viability. Still, the effects of chemotherapeutics on MDA‐MD‐231 was not significantly changed. Based on our studies, targeting intracellular Ca2+ homeostasis may serve as a potential therapeutic target for some breast cancer cell types but not all. Here, we find that drugs of the BZT family, as well as some antiepileptics, reduce MCF‐7 cell viability and potentially synergize with the action of chemotherapeutics. However, MDA‐MB‐231 remain largely unaffected by these agents. In principle, we thought that MDA‐MB‐231 may not have significant intracellular Ca2+ stores; yet immunoblot analysis reveal comparable levels of SERCA1/2 protein expression in both cell lines. Still, MDA‐MB‐231 seems to preferentially utilize Ca2+ entry from the extracellular space for cell survival. Further studies of plasma membrane Ca2+ transporters are required to elucidate the dependence of intracellular Ca2+ signaling among these breast cancer cell lines.Support or Funding InformationCT Moy Endowed Fund, Eskridge Foundation Grant, SIUSOM ‐ Team Development Grant

Tonalite-Dominated Magmatism in the Abitibi Subprovince, Canada, and Significance for Cu-Au Magmatic-Hydrothermal Systems

In Archean greenstone belts, magmatism is dominated by intrusive and volcanic rocks with tholeiitic affinities, as well as tonalite- and granodiorite-dominated large-volume batholiths, i.e., tonalite–trondhjemite–granodiorite (TTG) suites. These intrusions are associated with poorly documented mineralization (Cu-Au porphyries) that, in the Neoarchean Abitibi Subprovince (&gt;2.79 to ~2.65 Ga), Superior Province, Canada, are associated with diorite bearing plutons, i.e., tonalite–trondhjemite–diorite (TTD) suites. The importance of TTG versus TTD suites in the evolution of greenstone belts and of their magmatic-hydrothermal systems and related mineralization is unconstrained. The aim of this study was to portray the chemistry and distribution of these suites in the Abitibi Subprovince. The study used data compiled by the geological surveys of Québec and Ontario to evaluate the chemistry of TTG and TTD suites and uncovered two coeval magmas that significantly differentiated (fractional crystallization mostly): 1) a heavy rare earth elements (HREE)-depleted tonalitic magma from high pressure melting of an hydrated basalt source; and 2) a hybrid HREE-undepleted magma that may be a mixture of mantle-derived (tholeiite) and tonalitic melts. The HREE-depleted rocks (mostly tonalite and granodiorite) display chemical characteristics of TTG suites (HREE, Ti, Nb, Ta, Y, and Sr depletion, lack of mafic unit, Na-rich), while the other rocks (tonalite and diorite) formed TTD suites. Tonalite-dominated magmatism, in the Abitibi Subprovince, comprises crustal melts as well as a significant proportion of mantle-derived magmas and this may be essential for Cu-Au magmatic-hydrothermal mineralizing systems.

Geochronological and geochemical features of the Xiaowulangou complex plutons, Xilinhot, Inner Mongolia, and their geological significance

The southern margin of the Central Asian Orogenic Belt (CAOB) is pivotal to understanding the ultimate closure process of the Palaeo‐Asian Ocean; however, controversial issues regarding the petrogenesis and tectonic setting of its Late Palaeozoic igneous rocks have caused uncertainty regarding the Late Palaeozoic oceanic and continental evolution of the area. Herein, the Xiaowulangou complex plutons near Xilinhot, Inner Mongolia, were considered as a case study for the southern margin of the CAOB, and they were analysed via multiple geological methods, including field geology, petrology, zircon U–Pb isotopic geochronology, and geochemistry to achieve greater clarity on these issues. Lithologically, the plutons consist of diorite, quartz diorite, granodiorite, and monzonitic granite. Zircon U–Pb dating gives weighted mean ages of the diorite, quartz diorite, and granodiorite plutons as 329 ± 1 (mean squared weighted deviation [MSWD] = 0.22) and 306 ± 1 (MSWD = 0.83), 310 ± 1 (MSWD = 0.23), and 328 ± 1 (MSWD = 0.40) and 300 ± 1 Ma (MSWD = 1.4), respectively, corresponding to the late Early Carboniferous to the Late Carboniferous. The diorites and the quartz diorites constitute a suite of low‐K tholeiitic calc‐alkaline I‐type granitoids. They have low rare earth element (REE) content with a flat distribution pattern lacking pronounced negative Eu anomalies (δEu = 0.74–1.06). Geochemically, they are more enriched in large‐ion lithophile elements (LILEs) such as Rb, Th, K, and Sr than in high‐field‐strength elements (HFSEs) such as Nb, Ta, Ti, and P, indicating that these rocks were formed in a subduction setting as a result of partial melting of a mantle wedge that had been metasomatized by subduction fluids. The granodiorites and monzonitic granites belong to the peraluminous and calc‐alkaline to high‐K calc‐alkaline series and feature high silicon and alkali content; low P2O5 and CaO content; enrichment in Rb, Th, K, Zr, and Hf; depletion in Nb, Ta, Sr, P, and Ti; and significant negative Eu anomalies (δEu = 0.66–0.95 and 0.06–0.46, respectively). The granodiorites and monzonitic granites show the characteristics of I‐type granite that were mainly derived from partial melting of the crust. The petrological and geochemical characteristics of the rocks indicate that the plutonic complex is a result of superposed injection of a mixture of mantle‐ and crust‐derived magmas with different degrees of evolution. This was probably triggered by underplating of mantle magmas that originated from the partial melting of a wedge mantle metasomatized by hydrous fluids from the subducted slab. The diorites and quartz diorites were produced by fractional crystallization of mantle‐derived magma. The granodiorites and monzonitic granites crystallized from magma formed by mixing of the intermediate to basic magma and crust‐derived acidic magma. Considering their petrological and geological features, the Xiaowulangou complex plutons were formed in an active continental margin setting related to the northward subduction of the Palaeo‐Asian Ocean from the Early Carboniferous to the Late Carboniferous. Furthermore, consequently, a tectonic evolution model was established from the Late Palaeozoic to the Early Mesozoic in the Xilinhot–Xi Ujimqin Banner regions based on these new data and the regional geology.

Late Silurian-Early Devonian slab break-off beneath the Canadian Appalachians: Insights from the Nashwaak Granite, west-central New Brunswick, Canada

Late Silurian-Early Devonian granites are widespread in the Miramichi Highlands of New Brunswick, but their petrogenesis is controversial and hinders an understanding of the geological evolution of the Canadian Appalachians. Here we present a detailed geochemical and geochronological study of the Nashwaak Granite, and compare it with coeval granites in this region to indicate a Late Silurian-Early Devonian slab break-off regime in the Canadian Appalachians. The Nashwaak Granite consists of two-mica granite, biotite granite, and biotite granite dyke swarms. These rocks intruded at ca. 420 Ma and their compositions show a highly siliceous, calc-alkaline, and peraluminous characteristic. They show similar REE distribution patterns, similar depletion of Ba, Sr, Nb, P, and Ti, and similar Nd isotopes as contemporaneous granites inboard of the Salinic suture zone (Bamford Brook Fault). Together, these data suggest that Late Silurian-Early Devonian granites in the Miramichi Highlands may be derived from partial melting of the Neoproterozoic to lower Cambrian Ganderian basement resembling the Brookville terrane. Enriched subcontinental lithospheric mantle may have also been involved in the magma system (where coeval gabbro occurs within the Granite), but a contribution from asthenospheric mantle is absent. These linearly-distributed and post-collisional granites are most likely formed by Salinic slab break-off, with corresponding uplift and extension recorded by 422-419 Ma bimodal volcanic rocks, unconformities in sedimentary rocks, and extensional deformation (D3) in the Brunswick subduction complex of northern New Brunswick.