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Combined whole-rock geochemistry, zircon U–Pb dating, and Sr–Nd–Pb isotopic analyses were carried out to constrain the petrogenesis and tectonic implications of the “Zaranda Older Granites” (ZOG) and “Younger Granites” (ZYG) in north-central Nigeria. Zircon U–Pb dating yielded 633 ± 3 Ma for the ZOG and 203 ± 1 Ma for the ZYG, corresponding to Late Neoproterozoic and Late Triassic, respectively. The ZOG consists dominantly of biotite granite, which displays a whole-rock ɛNd(t) values of − 3.48 to − 5.00 and Nd model ages of 1620–1720 Ma. Most ZOG samples exhibit elevated Sr/Y (107–128) and La/Yb ratios (36–40), with a positive Eu anomaly (Eu/Eu* = 2.2–2.58), interpreted to reflect magma derivation through partial melting of a thickened lower crust. The ZOG is geochemically and geochronologically similar to the Pan-African granites from Togo–Benin (West Africa) and Northeast Borborema, Sao Paulo (Brazil), suggesting that their emplacement probably marked the initial phase of the Pan-African orogeny during which the Gondwana was amalgamated. The ZYG consists of compositionally diverse alkaline granitoids including aegirine syenites, quartz syenite, and fayalite granite porphyry. These rocks are strongly ferroan, alkalic and show petrographic and geochemical features of classical A-type granites. Substantial depletion in Ba, Sr, P, Ti, and Eu signifies fractionation of felsic and mafic minerals such as feldspar, biotite, amphibole, and Ti-rich augite. The low Y/Nb and Yb/Ta ratios (≤ 2) indicate that the ZYG samples display geochemical features typical of OIB-derived A-type granites. The ɛNd(t) values in the ZYG range from + 4.16 to − 2.76 and the Nd model ages range from 0.6 to 1.2 Ga. Based on these results, we propose that the ZYG samples and by extension, other alkaline granitoids from the Nigerian Younger Granite (NYG) province with similar geochemical compositions were likely generated through extensive differentiation of OIB-type mantle-derived magma. The concentrations of Nb and other HFSEs are much higher in ZYG than ZOG, indicating that the former has higher rare metal mineralization potential.

The effects of melt composition, temperature and pressure on the solubility of fluorite (CaF2), i.e., fluorine concentration in silicate melts in equilibrium with fluorite, are summarized in this paper. The authors present a statistic study based on experimental data in literature and propose a predictive model to estimate F concentration in melt at the saturation of fluorite (C F in melt Fl-sat ). The modeling indicates that the compositional effect of melt cations on the variation in C F in melt Fl-sat can be expressed quantitatively as one parameter FSI (fluorite saturation index): FSI=(3AlNM+Fe2++6Mg+Ca+1.5Na-K)/(Si+Ti+AlNF+Fe3+), in which all cations are in mole, and AlNF and AlNM are Al as network-forming and network-modifying cations, respectively. The dependence of C F in melt Fl-sat on FSI is regressed as: C F in melt Fl-sat =1.130−2.014·exp (1 000/T)+2.747·exp (P/T)+0.111·C melt H2O +17.641·FSI, in which T is temperature in Kelvin, P is pressure in MPa, C melt H2O is melt H2O content in wt.%, and C F in melt Fl-sat is in wt.% (normalized to anhydrous basis). The reference dataset used to establish the expression for conditions within 540–1 010 °C, 50–500 MPa, 0–7 wt.% melt H2O content, 0.4 to 1.7 for A/CNK, 0.3 wt.%–7.0 wt.% for C F in melt Fl-sat . The discrepancy of C F in melt Fl-sat between calculated and measured values is less than ±0.62 wt.% with a confidence interval of 95%. The expression of FSI and its effect on C F in melt Fl-sat indicate that fluorine incorporation in silicate melts is largely controlled by bonding with network-modifying cations, favorably with Mg, AlNM, Na, Ca and Fe2+ in a decreasing order. The proposed model for predicting C F in melt Fl-sat is also supported by our new experiments saturated with magmatic fluorite performed at 100–200 MPa and 800–900 °C. The modeling of magma fractional crystallization emphasizes that the saturation of fluorite is dependent on both the compositions of primary magmas and their initial F contents.

The Nigerian alkaline ring complexes have long been regarded as typical anorogenic A-type granite. However, uncertainty still surrounds many aspects of their petrogenesis and tectonic implication. In this paper, a combined study of whole rock geochemistry, Nd-Pb isotope and zircon U-Pb dating was carried out on the Kudaru ring complex from north-central Nigeria. The complex consists of mildly alkaline fayalite granite porphyry, peralkaline arfvedsonite granite and metaluminous biotite granite, which were emplaced between 176.9 ± 2.5 and 180.55 ± 0.6 Ma. These rocks are characterized by variably high alkalis, HFSEs, Ga/Al ratios, and zircon saturation temperature, typically of A-type granites. Notably, the popular subdivision scheme of A-type granite permits the discrimination of the alkaline-peralkaline granites as typical “A1-type” granites and the metaluminous granite as “A2-type”. These co-existing A1 and A2 granites show distinct isotopic compositions with less negative eNd (t) values and higher 206Pb/204Pb ratios for the former, indicating that the magma which gave rise to the A1 and A2 suites was derived from an enriched mantle source but modified to different extent during ascent. Notably, the coexistence of A1-A2 granites do not indicate discrete tectonic regimes (intraplate setting for A1 and post-orogenic setting for A2), but rather point to a significant role of crustal contamination, as seen also from the differences in Y/Nb ratios.

Coronitic microstructures have been used to interpret the late-stage solidification history of igneous rocks and to constrain the corresponding chemical and/or physical changes. Coronas with three shells were also recognized in the Miaowan olivine norite, Yangtze Craton, South China. In our study, orthopyroxene intergrowth with vermicular magnetite in the inner shell is in optical continuity with magnetite-free orthopyroxene in the middle shell. In the outer shell of brown amphibole remaining magnetite-free orthopyroxene inclusions sporadically occur. Meanwhile Mg# values of orthopyroxene (76–80) in the inner and middle shells are basically consistent with olivine (78–81). In this paper, we propose a multi-stage genetic model for the formation of coronas in the Miaowan olivine norite. In the first stage, the magnetite-free orthopyroxene shell formed through reaction between primocrystal olivine with the residual Si-rich melt at 990–1 053 °C and 6.2–6.5 kbar. In the second stage, the orthopyroxene-magnetite symplectite shell formed when primocrystal olivine reacted with the late-stage residual Fe-rich melt promoted by high oxygen fugacity condition at 927–1 035 °C and 6.0–6.5 kbar. In the third stage, the brown amphibole shell formed as the presence of residual hydrous melt and replaced the middle shell at 821–900 °C and 5.5–6.0 kbar.

We present an analytical approach to determine the Fe2+/ΣFe ratio in amphiboles and biotites using electron probe microanalysis (EPMA). The “flank method” applied in this study is based on the fact that FeL line spectra show different peak position and intensity for Fe2+ and Fe3+, which is associated with a resonant process involving both X-ray absorption and emission. The flank positions for Lα and Lβ, which correspond to sites with minimal Fe3+ L3 absorption and maximal Fe2+ L2 absorption respectively, are determined based on the L-line spectra difference of two Fe-rich ferric and ferrous garnet endmembers, i.e. andradite and almandine. Spectra intensities measured at the Lα and Lβ flank positions for selected amphibole and biotite references can be quantitatively correlated with their Fe2+ weight contents by a linear relation: Lβ/Lα = a + b*Fe2+, in which a and b are constants calibrated upon reference materials. It is emphasized that the constants a and b may vary significantly for different mineral groups and analytical conditions. Thus, a calibration is necessary for each analytical session. Our tests show that the potential beam damage during EPMA that may induce oxidation of the measured material can be minimized by using a large beam size (e.g., 20 μm). The Fe2+/ΣFe ratios determined using the EPMA flank method in collected natural calcic and sodic-calcic amphiboles (FeOT = 2.4–12.7 wt%, Fe2+/ΣFe = 0.45–75) and biotites (FeOT = 4.3-28.2 wt%, Fe2+/ΣFe = 0.67–0.87) are consistent within an error of ±0.1 with the data obtained from the colorimetric wet chemistry method. The EPMA flank method has the potential to be widely applied for accurate in-situ determination of Fe oxidation states in a wide range of minerals, provided that references are available.

In this study, we present systematic petrological, geochemical, LA-ICP-MS zircon U-Pb ages and Nd isotopic data for the A-type granites and syenites from Suizhou-Zaoyang region. The results show that the peralkaline A-type granites and syenites were episodically emplaced in Suizhou-Zaoyang region between 450±3 and 441±7 Ma which corresponds to Late Ordovician and Early Silurian periods, respectively. Petrologically, the syenite-peralkaline granite association comprises of nepheline normative-syenite and alkaline granite in Guanzishan and quartz normative syenite and alkaline granite in Huangyangshan. The syenite-granite associations are ferroan to alkali in composition. They depict characteristics of typical OIB (oceanic island basalts) derived A-type granites in multi-elements primitive normalized diagram and Yb/Ta vs. Y/Nb as well as Ce/Nb vs. Y/Nb binary plots. Significant depletion in Ba, Sr, P, Ti and Eu indicates fractionation of feldspars, biotite, amphiboles and Ti-rich augite. The values of ɛNd(t) in Guanzishan nepheline syenite and alkaline granite are +1.81 and +2.26, respectively and the calculated two-stage model age for these rocks are 1 040 and 1 003 Ma, respectively. On the other hand, the Huangyangshan alkaline granite has ɛNd(t) values ranging from +2.61 to +3.46 and a relatively younger two-stage Nd model age values ranging from 906 to 975 Ma, respectively. Based on these data, we inferred that the Guanzishan nepheline syenites and granites were formed from fractional crystallization of OIB-like basic magmas derived from upwelling of metasomatized lithospheric mantle. The Huangyangshan quartz syenite and granite on the other hand, were formed from similar magmas through fractional crystallization with low input from the ancient crustal rocks. Typically, the rocks exhibit A1-type granite affinity and classified as within plate granites associated with the Ordovician crustal extension and the Silurian rifting.

Source-depleted granites were rarely reported in South China. Hereby we identified such a granitic pluton, the Tiandong pluton, at Northeastern Guangdong province in Southeastern (SE) China. Whole-rock Sr-Nd and zircon Hf isotopes of the Tiandong granites both revealed obviously depleted source signatures, with initial isotopic values of initial 87Sr/86Sr = 0.7032–0.7040, eNd(t) = 1.1–1.5, and eHf(t) = 6–13, respectively. Zircon U-Pb dating implied the granite was intruded in Early Jurassic (188 Ma). The dominant minerals of the Tiandong granite consist of K-feldspar, plagioclase, quartz and biotite, with accessory mineral assemblage of apatite + zircon + magnetite. Based on the mineralogy and the depleted isotopic signature, the granites chemically show I-type affinity such as low Zr + Nb + Ce + Y (131.6 to 212.2), 104 × Ga/Al (2.12–2.27), A/CNK values

Spatially associated A- and I- type granites and mafic dyke rocks from the Jiuhuashan region (South China) have been geochemically studied with a special emphasis on their halogen (F, Cl, Br, I) contents to better understand the role of halogens during their genesis. The A-type granites and mafic dyke rocks (125–130 Ma) intruded later than the I-type rocks (140–143 Ma) and whole-rock Nb/Ta ratios increase from I-type granites (12–14) via A-type granites (14–18) to mafic dykes (19–20). The eNd(t) values for the two rock series are indistinguishable (about − 4 to − 8), whereas mafic dykes reach eNd(t) values of up to + 2. We suggest that I- and A-type granites generate from a common source dominated by lower crust, whereas the associated mafic dykes representing mantle-derived magma. We propose that the I-type rocks were emplaced during subduction of the paleo-Pacific slab, whereas subsequent tectonic extension triggered upwelling of mantle-derived magmas that provided sufficient heat to re-melt the residual lower crust, and crystallized to the A-type granites. Relative to I-type granites, the A-type rocks are F-rich (mean of 1230 ppm vs. 540 ppm) but poor in Cl (mean of 25 ppm vs. 50 ppm) and Br (mean of 130 ppb vs. 200 ppb), with indistinguishable I contents (from

Adakites and adakitic rocks are pivotal in understanding the formation and evolution of the early continental crust. However, there remain controversies about the origin of these rocks. This paper reports petrological, mineralogical and geochemical data for the newly identified Neoproterozoic (ca. 819 Ma) adakitic dacite porphyries in the Kongling area, Yangtze Craton, with the aim of constraining their petrogenesis and elucidating the role of magmatic processes in generating the adakitic melts. The dacite porphyries are characterized by high SiO2 (62.2–64.8 wt%), Mg# (52–60), Sr/Y and (La/Yb)N ratios, as well as depleted Nd-isotope compositions (ƐNd (819 Ma) = 0.1–1.6), geochemically comparable to high-Mg# adakitic rocks. Core-rim zoned amphibole and plagioclase phenocrysts are common. Overall, the amphibole cores show lower MgO, FeO, Sr, but higher Al2O3 concentrations than the rims. Similarly, the plagioclase cores exhibit lower An [Ca/(Ca + Na + K), atomic ratios] but more enriched 87Sr/86Sr(i) than the rims. Geochemical modeling demonstrates that the melts in equilibrium with the amphibole cores have high SiO2, low MgO, CaO, Fe2O3T and TiO2 as well as flat REE patterns and low Sr/Y ratios. Such felsic melts were likely generated by low-degree dehydration melting of the Paleo- to Meso-proterozoic amphibolites of the Kongling Complex. On the contrary, the melts in equilibrium with the amphibole rims possess lower SiO2 and higher MgO with elevated (La/Yb)N and Sr/Y ratios, suggesting involvement of more mafic melt components. In combination with regional geology, we propose that this mafic endmember possibly formed through fractional crystallization of original subduction-related basaltic magmas that are geochemically equivalent to the Neoproterozoic Panxi-Hannan arc-type basaltic rocks. Mass-balance calculation further reveals that the Kongling dacite porphyries could form by mixing of the above two geochemically distinct endmembers in ratios of ca.50: 50. Importantly, the adakitic signature of these rocks (i.e., high Sr/Y and (La/Yb)N ratios) was inherited from the fractionated arc-type mafic melts, highlighting the significant role of magma mixing in generating the adakitic melts. We propose that this mechanism may have been much more common than as previously thought and contributes significantly to continental growth and evolution.

Series of trachytic rocks, containing significantly high Nb contents, were identified in the Zhuxi region of South Qinling Orogenic Belt (SQB). An integrated investigation, mainly focusing on Nb variations in rocks and minerals, was conducted to constrain the enrichment mechanism of niobium. The Zhuxi trachytic rocks are predominantly composed of trachyte ignimbrites and trachytes, with pronounced Nb contents of 213–627 ppm and 116–384 ppm, respectively. Apatite U–Pb dating has revealed that the rocks were formed during the Silurian (434 ± 10 Ma), consistent with the associated alkali basaltic rocks. The trachytic rocks are chemically characterized by high total alkali, HFSEs (Nb, Ta, Zr, and Hf), and LREE, along with a marked depletion of Ba, Sr, P, and Ti, similar to the oceanic island basalt (OIB)-type series. The Zhuxi trachytic rocks are most probably generated by partial melting of a metasomatic lithospheric mantle followed by extensive fractional crystallization. The whole rock fluorine contents gradually decreased with decreasing Nb contents from trachyte ignimbrites (F = 123–3090 ppm) to trachytes (F = 90–1820 ppm), indicating that substantial quantities of halogen played an important role in Nb enrichment. The major mineral reservoirs of niobium in Zhuxi trachytic rocks are columbite, titanite, and aeschynite of magmatic and hydrothermal origins. The magmatic titanite generally contains lower Nb2O5 (0.71–1.68 wt%) than the hydrothermal titanite (0.67–7.27 wt%). In contrast, the Nb2O5 contents are indistinguishable in magmatic and hydrothermal columbites (70.16–74.44 wt%). Aeschynite is essentially a hydrothermal product, comprising high Nb2O5 contents (25.64–39.67 wt%). The high Nb contents in early-crystallized magmatic columbites and titanites indicate that the parental magma was initially Nb-enriched. The pronounced Nb contents in hydrothermal mineral phases (such as titanite) reveal that hydrothermal processes likely led to further Nb enrichment.

This paper presents geochronological, mineralogical, geochemical, and Sr-Nd isotopic data for recently identified Upper Triassic appinite dyke swarms in the East Kunlun orogenic belt (EKOB), northern Tibetan Plateau. Zircon U-Pb isotopic analyses using SHRIMP and LA-ICP-MS techniques yield 206 Pb/ 238 U ages of 226.1 ± 1.9 Ma and 226.4 ± 3.5 Ma, which can be interpreted as the crystallization ages of the appinite dykes. All the samples are characterized by high Al 2 O 3 contents, enrichments in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and strong depletions in Nb, Ta, Ti and P. These characteristics are comparable to those of subduction-related calc-alkaline high-Al basalts. Delayed plagioclase nucleation caused by relatively high-pressure conditions and high H 2 O contents is the most likely interpretation of the high Al contents. The geochemical and isotopic variations suggest that the appinite dykes were derived from partial melting of a mixed mantle source consisting of enriched lithospheric mantle and MORB-type asthenospheric mantle and had experienced some degree of crustal contamination during migration through continental crust. The appinite dykes are associated with previously documented, contemporaneous high-Ba-Sr and/or high-Sr/Y granites (225–223 Ma) derived from thickened mafic lower crust. These rocks provide important constraints on the compositional variations in the orogenic lithospheric mantle during the Late Triassic and provide evidence of a post-collisional environment associated with lithospheric delamination or slab break-off.

The dike-gabbro transition zone of mid-ocean ridges (MORs) is a critical site for the accretion of oceanic crusts as it is the main zone of interactions between the hydrothermal and magmatic systems. In this study, volatiles contents of CO2, S, F, Cl and Br for a variety of lithologies from the dike-gabbro transition zone of an intact oceanic crust were investigated in order to examine the magmatic imprint versus hydrothermal influence. The studied samples include plutonic rocks (gabbros, diorites and tonalites), hornfelses (i.e. granoblastic dikes), an amphibole-rich vein and albitites. These rocks were recently sampled by the IODP (Integrated Ocean Drilling Program) at Site 1256, representing parts of an oceanic crust that formed at the fast-spreading ridge of the East Pacific Rise. The bulk CO2 contents (500–10,000 ppm) show no lithological dependence and are similar to those of fresh lavas. Highly variable bulk S concentrations (3–900 ppm) show significant depletions compared to undegassed MORB melts, which might be caused by exsolution of magmatic fluids during crystallization. The plutonic samples have Cl concentrations of 500–1000 ppm, remarkably higher than the hornfelses (200–600 ppm Cl) and erupted lavas (average ~ 200 ppm Cl). Except for the albitites that contain very low F (20–30 ppm) and the hydrothermal amphibole-rich vein that contains extremely high F (~ 1000 ppm), the other lithologies have similar F concentrations within 100–350 ppm. The Br concentrations of different lithologies are largely overlapping within 0.5–3.5 ppm. Petrological and mineralogical evidence indicates that bulk F concentrations are dominated by the presence of amphibole and apatite, whereas Cl and Br are mainly hosted in fluid inclusions rather than in hydrous minerals. The variation of F/Cl and Br/Cl ratios may trace the mixing between MORB magmas and seawater-derived fluids, crystallization of apatite and amphibole, and/or extraction of magmatic fluids. Our data support the current S budget of oceanic crust, but indicate that the budgets of C and Cl may have been underestimated.

The formation time and origin of the Neoproterozoic alkaline-peralkaline rocks from the SW Arabian-Nubian Shield (ANS) are poorly constrained. An assessment of petrography, whole-rock geochemistry, incorporated with zircon U–Pb dating, trace element, and Hf isotope, has been done on the El Dair granitic complex, NE Nuba Mountains, Sudan. LA-ICPMS U–Pb zircon ages from two granite samples yield a weighted mean of 567.3 ± 2.5 Ma and 598.3 ± 21 Ma, respectively, signifying that the El Dair complex was formed at ca. 560–600 Ma. The El Dair granite samples exhibit alkaline-peralkaline affinity (A.I. = 1.04–1.17) and are classified as high-K calc-alkaline series. The samples display similar composition with typical A-type granite: e.g., elevated Na2O + K2O contents, Ga/Al, FeOT/MgO, TiO2/MgO, ratios, and HFSEs (i.e., Zr, Ta, Nb, and Y) with negative Ba, Sr, and Ti anomalies and depleted contents of CaO, MgO, and P2O5. The El Dair granite samples illustrate high Zr (563–1163 ppm) contents, yielding high magma temperatures of 884–966 °C. The zircon trace elements investigations show HREE enrichment and positive Ce but negative Eu anomaly, characteristic of igneous zircons. The initial eHf(t) of + 4.2 − +5.8 and eNd isotopic values of + 1.83 − +1.92 from El Dair A-type granite samples are rather enriched than the values of depleted mantle (eHf ~ + 14 and eNd ~ + 6.5). Whole-rock elemental and isotopic data from the El Dair complex apparently denote that the magmas were produced via low degrees partial melting of juvenile crust through the assemblage of ANS during Neoproterozoic time.

Appinites are commonly derived from a mantle source and are potentially significant in constraining the tectonic nature and evolution of ancient orogens, yet they have received little attention because of their limited outcrop. Here we investigate the newly identified appinitic rocks from the Laoniushan complex in the eastern Qinling Orogen. The appinites are composed of coarse-grained hornblendite, medium- and fine-grained hornblende-gabbro, and diorite porphyrite in the field occurrence. Winthin the appinitic rocks, the hornblendite displays features of cumulates. This study presents LA-ICP-MS zircon U-Pb data, mineral chemistry and whole rock geochemistry of the appinites. Zircons in the mafic to ultramafic rocks yield a U-Pb age of 152 ± 1Ma. The geochemistry of the rocks displays: lower SiO2, higher Fe2O3T and MgO contents, relatively flat chondrite normalized REE patterns with slight enrichment in light REE and a minor negative Eu anomaly; enrichment in large-ion lithophile elements(LILE, e.g. Rb, Ba, Sr and P), and depletion in high field strength elements(HFSE, e.g. Nb, Zr, Hf and Ti). Such geochemical features, together with crust-like bulk Sr-Nd isotopic compositions(initial 87Sr/86Sr ratios of 0.7057–0.7072, eNd(t) = −17.2 to −9), suggest that the Laoniushan appinites likely originated from an ancient metasomatised mantle, followed by fractional crystallization in the petrogenetic process. The studied appinites were most likely generated in an intracontinental extensional environment in the Late Mesozoic.

The appinite–granite association has been found in various tectonic regimes related to recent subduction, arc-continent or continent–continent collision and post-collision (orogen), and appinites generally originate from recently subduction-modified lithospheric mantle. We conducted a study on a rarely reported appinite–granite association formed in an intracontinental regime, the Zhangjiafang–Qinglongshan complex (ZQC), in which the appinites were derived from an ancient sub-continental lithospheric mantle (SCLM). The ZQC is located in the western Wugongshan domain, and consists of basaltic to intermediate appinites and granitoids. Ten dated samples (including massive and gneissoid granitoids, hornblende gabbro, and diorite) give zircon 206Pb/238U ages ranging from 444 ± 3 Ma to 452 ± 4 Ma, indicating that these various lithologies were emplaced synchronously. The basaltic appinites show radiogenic 87Sr/86Sri (0.71016–0.71431) and negative eNd(t) (− 6.1 to − 8.9) and zircon eHf(t) (− 4.2 to − 7.5) values. Combined with regional geological background, an origin from the Neoproterozoic metasomatised SCLM can be inferred for the appinites in the Wugongshan domain. The granitoids are peraluminous and almost high-K calc–alkaline to shoshonitic. They exhibit a wide range of isotopic compositions (87Sr/86Sri = 0.70828–0.71857, eNd(t) = − 6.2 to − 10.5, zircon eHf(t) = − 9.5 to − 26.6). Some of the granitoids display the most evolved Sr–Nd isotopic signatures among all the studied lithologies, which are consistent with those of the middle to upper crust, suggesting a pure crustal origin. Other granitoids show relatively mafic composition and less evolved isotopic signature. The intermediate appinites have intermediate chemical compositions between those of the basaltic appinites and granitoids, and similar Sr–Nd isotopic compositions to those of the basaltic appinites that have relatively evolved composition and isotopic signature. The petrographical and the geochemical studies, as well as magma mixing and mingling between mafic magma and felsic magma observed in field work, indicate that the ZQC was formed by several complex magmatic processes including assimilation and fractional crystallization (AFC) of a basaltic magma derived from an enriched mantle, magma mixing and mingling, fractional crystallization of a crust-derived felsic magma. The contribution of the Neopreoterozoic subduction-modified lithospheric mantle to the early Paleozoic granitoids in South China has been poorly constrained due to its evolved isotopic signatures (such as negative eNd(t) and eHf(t) values, high initial ratio of 87Sr/86Sr) and few studies on the early Paleozoic basaltic–felsic rock association. Our work here suggests that the Wugongshan appinite–granite association was formed in an intracontinental orogen, and the ancient enriched mantle may have had a significant chemical contribution to the formation of some of the Paleozoic peraluminous granites in South China.

Halogen abundances in apatite, biotite, amphibole, titanite, and other halogen-rich minerals (sodalite and eudialyte) from ultramafic pyroxenites and glimmerites, shonkinites, and gabbroic, monzonitic, and syenitic rocks of the alkaline to peralkaline Tamazeght complex (Morocco) are presented. Apatite, biotite, and amphibole show the highest F contents in the most evolved rocks, which also contain interstitial fluorite (restricted in syenites). The Cl contents of apatite, biotite, and amphibole are highest in the intermediate rocks. Sodalite (Cl-rich) is equally common in the evolved rocks, although Cl contents of apatite, biotite, and amphibole are low. We suggest that the early magmatic crystallization of sodalite causes a strong depletion of Cl in the remaining melt, resulting in the subsequent crystallization of Cl-poor apatite, biotite, and amphibole. Late-magmatic eudialyte in some of the rocks may indicate a late-stage re-enrichment of Cl. The Br contents of biotite, amphibole, eudialyte, and sodalite reveal that Cl-rich minerals generally contain high Br. The Cl/Br ratios of individual minerals are, however, highly variable. This suggests that besides melt composition, other factors, such as crystal-melt partitioning and fluid mobility, may influence Cl/Br ratios in igneous minerals, resulting in potentially strong fractionation of Cl from Br in minerals. Estimation of F and Cl contents in alkaline melts suggests that primitive ultramafic melts are poorer in Cl than evolved melts, whereas their F contents are relatively similar. The low apparent Cl contents of the syenitic melts, calculated based on apatite compositions, may reflect the halogen abundance during late-magmatic conditions, as the presence of early magmatic sodalite indicates Cl-rich syenitic melt compositions.

The Miaoya syenite and carbonatite complex is located in the southern margin of the South Qinling belt, central China. LA-ICP-MS zircon U–Pb dating reveals that the syenite and carbonatite have crystallization ages of 445.2 ± 2.6 Ma (MSWD = 0.66) and 434.3 ± 3.2 Ma (MSWD = 1.08), respectively. Both syenite and carbonatite display low ISr values (0.7004 to 0.7053) and depleted eNd(t) values of +1.1 to +5.5, with one-stage Nd model ages of 0.65 to 0.94 Ga. Their zircon eHf(t) values are also similarly positive (+3.1 to +8.9), and one-stage Hf model ages range from 0.71 to 0.92 Ga. Whole-rock geochemistry suggests that the syenite belongs to the shoshonitic series and both syenite and carbonatite show identical REE and trace element patterns. The coeval intrusive ages, similar geochemical and Sr–Nd–Hf isotopic compositions suggest that the Miaoya carbonatite and associated syenite are genetically related to each other. We consider that the carbonatite could be a final product by protracted fractionation of a CO2-rich alkaline melt. The depleted eNd(t) and zircon eHf(t) isotopes also indicate that the associated syenite and carbonatite could be originated from a mantle-derived magma. The sources are likely composed of dominated HIMU mantle and minor EMI mantle. We propose that the Silurian Miaoya Complex was formed in the extensional rifting setting, associated with the mantle upwelling. Copyright © 2016 John Wiley & Sons, Ltd.

The South China Block is characterized by the large-scale emplacement of felsic magmas and giant ore deposits during the Yanshanian. We present zircon Hf isotopic compositions, whole-rock major and trace element compositions of the Fengshun complex, located in eastern Guangdong Province, South China. The Fengshun complex is a multi-stage magmatic intrusion. It is composed of two main units, i.e., the Mantoushan (MTS) syeno-monzogranites, alkali feldspar granites and the Hulutian (HLT) alkali feldspar granites. LA-ICPMS zircon dating shows that the complex emplaced in 166–161 and 139±2 Ma, respectively. Geochemically, the MTS granites show relatively various geochemical compositions with low REE contents (87.76×10-6–249.71×10-6), Rb/Sr ratios (1.19–58.93), pronounced Eu negative anomaly (0.01–0.37) and low Nb/Ta ratios (2.40–6.82). In contrast, the HLT granites exhibit relatively stable geochemical characteristics with high REE contents (147.35×10-6–282.17×10-6), Rb/Sr ratios (2.05–10.30) and relatively high Nb/Ta ratios (4.45–13.00). The isotopic data of the MTS granites display relatively enriched values, with I Sr varying from 0.708 2 to 0.709 7, e Nd(t) from -7.8 to -6.9 and e Hf(t) from -7.4 to -3.2, in comparison with those of the HLT which are ISr=0.703 05–0.704 77, e Nd(t)=-5–-3.4 and e Hf(t)=-0.7–1.8). The two-stage model ages of the MTS granites (T 2DM(Nd)=1.51–1.59 Ga and T 2DM(Hf)=1.26–1.48 Ga) are also higher than those of the HLT granites (T 2DM(Nd)=1.21–1.34 Ga and T 2DM(Hf)=0.96–1.10 Ga). Thus the MTS and HLT granites might originate from different sources. The former is more likely derived from partial melting of Meso-Proterozoic basement triggered by upwelling of asthenosphere and/or underplate of the basaltic magma and then extensive fractional crystallisation, similar to the genesis of Early Yanshanian granitoids of the EW-trending tectono-magmatism belt in the Nanling range. In comparison, the latter might have involved with asthenosphere component, similar to the Early Cretaceous granitoids of NE-NNE-trending granitoid-volcanic belt in coastal region, southeastern China. We propose that the MTS granites were mainly formed in Paleo-Tethyan post-orogenic extensional tectonic setting whereas the HLT granites were formed in the back-arc extensional tectonic setting. The period at 139 Ma represents the initial time of roll-back of the paleo-Pacific Plate in SE-trending.

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 eNd(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 eHf(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.

A series of magmatic syenites containing extremely high K2O contents (up to 15 wt%, mean of 12 wt%) have been identified in the Songxian region of Qinling Orogenic Belt (Central China). An integrated investigation, combining mineral composition, whole-rock elemental and Sr Nd isotopic geochemistry and zircon U–Pb geochronology, was conducted to track the origin and evolution of the ultrapotassic intermediate magma. The Songxian syenites mainly consist of alkali-feldspar syenite and aegirine-augite syenite, which outcrop as five independent stocks or dykes in the field. Zircon U–Pb dating of the Songxian syenites yields emplacement ages of 233–237 Ma. Alkali feldspar is the dominant mineral for both rock types, while aegirine-augite, aegirine and subordinate riebeckite are characteristic of the aegirine-augite syenite. Both the alkali-feldspar syenite and the aegirine-augite syenite belong to a weakly peraluminous to peralkaline series, and are characterized by extreme enrichment in K and large ion lithophile elements (LILEs; e.g., Rb, Ba, Sr) and prominent negative anomalies of high field strength elements (HFSEs; e.g., Nb, Ta). In comparison to the alkali-feldspar syenites, the aegirine-augite syenites have higher CaO and Na2O contents and Mg# values, but lower Al2O3 and K2O contents. All the syenites show relatively homogeneous and enriched initial Sr Nd isotopic compositions with initial 87Sr/86Sr = 0.7069–0.7090 and eNd (t) = −14.5 to −22.0, similar to the regional mafic rocks and indicative of an enriched lithospheric mantle source. The composition of clinopyroxene records a prolonged fractional crystallization process of the syenitic magma, which has a key role in promoting K enrichment in the residual melt. The Songxian syenites and the other analogous Early Mesozoic alkaline rocks and carbonatites in the southern margin of North China Craton were generated in a post-collisional extensional regime and represented a regional geodynamic transition from convergence to extension.

A-type granites were emplaced in Zaranda at 203 ± 1 Ma corresponding to Late Triassic. Petrologically, the A-type granite association includes syenite, quartz syenite and alkali granite of ferroan-alkalic composition. In Yb/Ta versus Y/Nb binary plots, they display certain characteristics typical of OIB derived A-type granites. The depletion in Ba, Sr, Ti and Eu indicates fractionation of feldspars, biotite, amphiboles and augite. The isotopic analysis of Zaranda, as drawn from a previously conducted study yielded lower 87Rb/86Sr values of 0.7048 and positive ɛNd(t) + 0.9. Overall, the above data proved to reveal that the Zaranda A-type granites were formed from assimilation fractional crystallization of OIB-like magmas, as derived from lithospheric mantle. Late Triassic crustal extension, preceding the opening of the Atlantic Ocean in Early Jurassic, was most probably the main trigger for the emplacement of such A-type granite suites, which ranks them within plate A-type granite sensu stricto.

Fluorine plays an important role in magmatic and hydrothermal processes, but due to its low abundance in geological samples determining F is difficult by electron probe microanalysis. By using a W-Si multi-layered pseudocrystal as the diffraction crystal instead of thallium acid phthalate (TAP), count rates were considerably higher, which however introduced spectral interferences between FKα and FeLα and MgKβ lines when normal integral mode is applied. In this study, we developed a protocol using a W-Si multi-layered pseudocrystal for measuring accurately trace level F in both minerals and glasses. First, we used differential mode with an optimised PHA (pulse height analysis) setting in signal processing, instead of normal integral mode, which completely eliminated the second-order MgKβ line. Second, the overlap of the first-order FeLα on FKα peak, which cannot be filtered by modifying the PHA setting, was calibrated quantitatively using F-free minerals and silicate glasses. Applying this two-step method, F was determined in a number of reference glasses, as well as in glasses synthesised from powders of the rock reference materials AC-E, GS-N and DR-N. Our data are consistent within error with F concentrations determined by other methods, demonstrating the reliability of this method.

A comprehensive study on zircon U-Pb age dating, whole-rock geochemistry and Sr-Nd isotope data has been conducted on the mafic rocks of the Xiazhuang uranium ore district and adjacent regions in South China. Based on field work and petrographic features, three rock types (the Kuzhukeng gabbro, the WNW-trending dolerite dykes and the NNE-trending lamprophyre dykes) are distinguished. Early Jurassic SHRIMP and LA-ICPMS ages of zircon for the Kuzhukeng gabbro (198 ± 1 Ma) and WNW-trending dolerite dykes (193 ± 4 Ma) have been obtained, which are 50 Ma older than previously thought (being Cretaceous). These geochronologic data provide new evidence for the rarely identified Early Jurassic magmatisms in South China. Whole-rock geochemical data for the Kuzhukeng gabbro and WNW-trending dolerite dykes are similar, both of which being higher in FeO and TiO 2 but lower in SiO 2 and K 2 O than the NNE-trending lamprophyre dykes. Trace element characteristics and Sr-Nd isotope data indicate arc-like signatures similar to the Cretaceous southeast coast basalts of China for the lamprophyre dykes, but an OIB-like geochemical affinity for the high-TiO 2 mafic rocks similar to the Permo/Triassic Emeishan flood basalts and the Middle Jurassic Ningyuan alkaline basalts. We propose that the lamprophyre dykes formed in an arc volcanic system driven by the subduction of the paleo-Pacific plate. In contrast, the Kuzhukeng gabbro and associated dolerite dykes record the post-orogenic (Indosinian) extension event in the Tethyan tectonic regime. This further implies that the Indosinian extension may have lasted until the Early Jurassic, and therefore, the subduction of the paleo-Pacific plate in south China was probably later than this period. Most U deposits of the Xiazhuang area are located at the intersection between the WNW-trending dolerite dykes and the NNE-trending faults within the Triassic granites of eastern Guidong complex, South China. Previous metallogenesis studies assumed that intrusion of the WNW-trending mafic dykes induced upward migration of mantle-derived CO 2 -rich fluids, which leached U from the Triassic granite and subsequently precipitated at the intersection between mafic dykes and NEE-trending faults. Our new age data for the WNW-trending dolerite dykes reveal an age gap with respect to the associated U deposits (85–135 Ma) of at least 50 Ma, arguing against this model. Here, we propose that the role played by the dolerite dykes for U mineralizations is more likely to provide a favorable physicochemical environment promoting the precipitation of U from oxidized fluids. The fluids themselves, however, are probably related to the NNE-trending fault system and associated lamprophyre dykes rather than to the dolerites.

To better understand the Neoproterozoic tectonic evolution along the northern margin of Yangtze Block, we have determined the geochronological and geochemical compositions of newly recognized bimodal volcanic suite and coeval granites from the western Dabie terrain. LA-ICP-MS zircon U-Pb dating reveals that the felsic and mafic volcanics from the Hong’an unit have crystallization ages of 730 ± 4Ma and 735 ± 5Ma, respectively, indicating that the bimodal suite was erupted during the Neoproterozoic. The Xuantan, Xiaoluoshan, and Wuchenhe granites yield U-Pb ages of 742 ± 4 Ma, 738 ± 4 Ma, and 736 ± 4 Ma, respectively. The felsic volcanic rocks show peraluminous characteristics, and have a close affinity to S-type granite. The mafic volcanic rocks are basalt in compositions, and are likely generated from a depleted mantle source. The granites belong to high-K calc-alkaline and calc-alkaline series, display metaluminous to peraluminous, and are mainly highly fractionated I-type and A-type granite. The granites and felsic volcanics have zircon εHf(t) values of −16.4 to + 5.6 and two-stage Hf model ages (TDM2) of 1.28 to 2.40 Ga, suggesting that they were partial melting of varying Mesoproterozoic–early-Neoproterozoic crust. The granites have εNd(t) of -14.7 to -1.5, and the two-stage Nd model ages (TDM2) values of 1.54 to 2.61 Ga, also implying the Yangtze crustal contribution. These Neoproterozoic bimodal suite and coeval granites were most likely generated in a rifting extensional setting, triggered by the mantle upwelling, associated with crust–mantle interaction. Intensive magmatic rocks are widespread throughout the South Qingling, Suizhao, western Dabie and eastern Dabie areas during 810–720 Ma, and show peak ages at ~ 740 Ma. Combining regional geology, we support a continental rifting extensional setting for the north margin of the Yangtze Block during the break-up of the supercontinent Rodinia.

We present major and trace elemental geochemical data, Sr–Nd–Hf isotopes and zircon U–Pb ages for igneous rocks of the Mufushan complex (~ 2400 km 2 outcrop area) in South China. The complex intruded episodically from late Jurassic (ca.154 Ma) to early Cretaceous (ca. 146 Ma) with a compositional evolution from diorite through granodiorite and biotite-bearing monzogranite to two-mica leucogranite and garnet-bearing leucogranite dykes. Diorites have high Mg# (up to 71), low SiO 2 and high siderophile elements (e.g. Cr, Ni and V) resembling sanukite or high-Mg diorite. They display isotopic characteristics similar to those of incident enriched mantle-derived mafic rocks, such as low I Sr (t) (0.7080–0.7085), high eNd(t) (− 4.3 to − 4.8) and eHf(t) (− 2.41 to 0.59). In contrast, felsic rocks show a common crustal signature with higher I Sr (t) (0.7115–0.7184), lower eNd(t) (− 7.9 to − 10.2) and eHf(t) values (− 7.73 to − 4.04). These felsic rocks display decreasing Al 2 O 3 , CaO, FeO tot , MgO contents and gradually enhanced depletions in Sr, Ba and Ti and Eu with increasing SiO 2 and decreasing zircon U–Pb age, which implies continuous magmatic evolution towards leucogranites dominated by fractional crystallization. The most evolved SiO 2 -rich rocks (two-mica leucogranites) are compositionally similar to the Himalaya leucogranites, indicating that prolonged fractional crystallization of metaluminous granitic magma is a feasible mechanism to form peraluminous leucogranitic magma. The differentiation process of the felsic magma lasted from 152 to 146 Ma as indicated by zircon U–Pb dating, which implies that magma differentiation, emplacement and subsequent solidification in giant batholiths may proceed on a timescale of several million years.

Apatites from carbonatites, related alkaline silicate rocks, a carbonate-bearing melilititic dyke rock (bergalite), and a diatreme breccia (containing both carbonate and silicate fragments) of the Miocene Kaiserstuhl Volcanic Complex, SW Germany, are used to reconstruct the petrogenetic relationship among these rocks. Apatites from carbonatites reach higher Sr and Nb contents but are generally lower in Fe, Mn, Th, U, Si, S, Cl and Br compared to apatites from associated silicate rocks, whilst Na, REE and F contents are overlapping. Apatites from bergalite show a systematic and discontinuous core-rim zonation, with the core being compositionally similar to apatites from silicate rocks and the rim corresponding to carbonatitic apatites. These observations imply that the bergalite apatites nucleated in a silicate melt and continued to crystallize from an evolving CO 2 -enriched melt probably with carbonatitic affinity. Apatites from a diatreme breccia comprise three populations: (1) similar to the apatites from silicate rocks, (2) similar to the carbonatitic apatites, and (3) resembling apatite population (1) partially replaced by apatite (2). We infer that apatite (1) was derived from silicate-rock fragments and apatite (2) crystallized from a later intruding carbonatitic melt, which metasomatized the silicate-rock fragments and caused the replacement textures as observed in apatite population (3). We conclude that apatites from the Kaiserstuhl complex preserve important information on the petrogenetic relationship between carbonatitic and silicate melts. The carbonatitic melts at the Kaiserstuhl complex are probably the products of protracted fractionation of a CO 2 -rich nephelinitic melt.

We present halogen compositions in a series of alkaline rocks from the Kaiserstuhl, Hegau and Urach areas of the Upper Rhine Graben region (South Germany). Most primitive rocks (olivine melilitites and olivine nephelinites) have lower Cl and Br concentrations (generally below 100 μg/g and below 0.3 μg/g, respectively) compared to more evolved tephrites, phonolites and related rocks (up to 7600 μg/g Cl and 34 μg/g Br). However, the Cl/Br ratios of the majority of the investigated samples are relatively uniform (371 ± 120), regardless of rock type and sample locality, suggesting that partial melting, fractional crystallization, and degassing have limited effects on the fractionation of Cl from Br. The mean value of the Cl/Br ratio is similar to previous estimates for basaltic rocks representing MORB and OIB mantle signatures. Fluorine concentrations of the primitive rocks show limited variations (900–1100 μg/g) and are within the range defined by the evolved rocks (400–2100 μg/g), but are much higher than previous estimates for the MORB and OIB mantle (50–135 μg/g). This may indicate a relatively F-rich mantle source beneath the Rhine Graben region. In contrast to Cl/Br ratios, the F/Cl ratios vary significantly over three orders of magnitudes (from Positive correlations between F, Cl and Br contents in a series of tephritic rocks from Kaiserstuhl probably record degassing processes, since these samples have similar geochemical and isotopic signatures with the only difference being textural: they vary from glassy to phanerocrystalline. Simplified calculations imply that about 50% F and 90% Cl and Br were released during the crystallization process, resulting in increasing F/Cl, but relatively constant Cl/Br ratios.

The Huashanguan rapakivi pluton in Zhongxiang, Hubei Province, China, is the first discovered Proterozoic rapakivi pluton in the Yangtze block. Based on field and petrographical observations, a typical rapakivi texture was found in the northern portion of the Huashanguan granitic pluton. Almost all the K-feldspar phenocrysts were round to oval in shape and most had plagioclase coatings known as rapakivi phenocrysts. Alkali feldspars and quartz had two or more generations. Petrochemically, the Huashanguan rapakivi granites were characterized as having high values of Si, K, Fe, Th, U, La, Ga, Ce, Sm and LREE, low values of Ca, Mg, Sr, Nb, Y and HREE, and a negative Eu anomaly. These geochemical characteristics of the Huashanguan granites were concordant with typical rapakivi granites, and had an affinity to A-type granites. LA-ICP-MS U-Pb zircon dating also was conducted. The dating yielded a 207Pb/206Pb weighted mean age of 1851±18 Ma (MSWD =1.2), which represents the age of the pluton emplacement. The age of 803±170 Ma at the lower intercept in the concordia diagram corresponds to the age of a later deformation event which affected the pluton, and suggests that the Huashanguan pluton was influenced by Neoproterozoic thermo-tectonic events after its formation. The discovery of Paleoproterozoic Huashanguan rapakivi granites indicates continental rifting or a post-orogenic extensional event that took place in the Paleoproterozoic in the Yangtze block. These events may be related to the breakup of the Paleoproterozoic Columbia supercontinent.