High-Mg andesites (HMAs) and related basalts constitute a volumetrically minor, but genetically important occurrence along most convergent plate margins of various ages on Earth. The details of their ...petrogenesis can contain critical information for resolving essential geodynamic and crustal evolutionary issues. This zircon U–Pb dating and geochemical study documents the late Permian metamorphosed high-Mg basaltic to andesitic suite from Kaiyuan of northern Liaoning, North China. These rocks feature SiO2 contents ranging from 48.7 to 63.2wt.%, high Mg# values of 63–75, an enrichment in large-ion lithophile elements (LILE), and depletion in high field strength elements (HFSE). They possess whole-rock initial 87Sr/86Sr ratios of 0.70417–0.70457, εNd(t) values from −0.4 to 5.0, and εHf(t) values from 5.1 to 11, as well as zircon εHf(t) values from −9.4 to 0.4. These features indicate that their petrogenesis most likely involved precursory metasomatism of mantle peridotites by melts from subduction-related sediments, and subsequent partial melting. With a depleted mantle source and possible tectonic link to post-subduction slab break-off, the Kaiyuan suite could present a spatial reference not only for defining the demarcation line between the North China craton (NCC) and the Central Asian Orogenic belt (CAOB) in the region, but also for tracing the final location of the cryptic suturing zone of the Paleo-Asian Ocean. Synthesizing the suite with coeval igneous episodes as well as concomitant metamorphic events along the Solonker–Xra Moron–Changchun zone leads to the characterization of the eventual closure of the Paleo-Asian Ocean within a double-sided subduction system during late Permian–Early Triassic.
•This study documents late Permian high-Mg basaltic to andesitic extrusions from North China.•The suite comes from newly metasomatized lithospheric mantle.•The suite formed in response to post-collisional slab breakoff.•The suite provides a spatial marker for monitoring the craton-orogen boundary.•The rocks record a net crustal growth scenario.
Stable isotopic systematics of Cu and Fe are two important tracers for geological and biological processes. Generally, separation of Cu and Fe from a matrix was achieved by two independent, ...completely different methods. In this study, we report a method for one-step anion-exchange separation of Cu and Fe from a matrix for igneous rocks using strong anion resin AG-MP-1M. Cu and Fe isotopic ratios were measured by multi-collector inductively coupled plasma mass-spectrometry (Neptune plus) using a sample-standard bracketing method. External normalization using Zn to correct for instrumental bias was also adopted for Cu isotopic measurement of some samples. In addition, all parameters that could affect the accuracy and precision of isotopic measurements were examined. Long-term external reproducibility better than ±0.05‰ (2SD) for
δ
65
Cu and ±0.049‰ (2SD) for
δ
56
Fe was routinely obtained. Cu and Fe isotopic compositions of commercially accessible igneous rock standards including basalt, diabase, amphibolite, andesite and granodiorite were measured using this method.
δ
65
Cu values of igneous rock standards vary from −0.01 to +0.39‰ (
n
= 11) with an overall range (0.40‰) that exceeds about 8 times that of the current analytical precision. The improved precisions of stable Cu isotopic analysis thus demonstrate that igneous rocks are not homogeneous in Cu isotopic composition. The procedure for one-step separation of Cu and Fe and high-precision analysis of Cu and Fe isotopic ratios have an important advantage for economical and efficient study of stable Cu and Fe isotopic systematics in geological and biological fields.
A method for single column purification of Cu and Fe for high-precision Cu and Fe isotopic analysis of igneous rocks.
•This study documents one episode of Paleoproterozoic ultramafic–mafic intrusions from the NCC.•The intrusions resemble typical Phanerozoic Alaskan-type complexes.•The intrusions originate from a ...subduction fluid metasomatized lithospheric mantle.•They formed along an active convergent plate margin.•They provide a spatial marker for monitoring the prevalence of subduction in the ZTM.
Neoarchean to Paleoproterozoic Alaskan-type ultramafic–mafic complexes constitute a rare but genetically important occurrence within the cratonic provinces on Earth and their genesis holds key information for monitoring the evolution of mantle source and the geodynamic processes along ancient convergent plate margins. This geochronological and geochemical study presents one episode of Paleoproterozoic Alaskan-type ultramafic–mafic intrusions from the Zhongtiao Mountain (ZTM) region, North China Craton (NCC), with an emplacement age of ca. 2315Ma. The intrusions consist of a metamorphosed rock assemblage of peridotite, pyroxenite, gabbro, gabbroic diorite, hornblendite and doleritic dykes. They exhibit a compact elliptical geometry as single entity, linear array of stock clusters and crude lithological zonation from cores of peridotites to margins of hornblendites and gabbroic rocks. They are tholeiitic in composition with an SiO2 range from 39.4 to 57.4%, modest enrichment in light rare earth elements (LREE) and depletion in high field strength elements (HFSE). They possess variable whole-rock εNd(t) values from −3.41 to +2.68 and εHf(t) values from −7.23 to +5.11, as well as zircon εHf(t) values from −2.06 to +1.82. These structural and compositional traits bear a close resemblance to those of classic Phanerozoic Alaskan-type complexes. Geochemical and isotopic data indicate that the formation of the present ultramafic–mafic intrusions most likely involved a Mg-rich hydrous parental magma from a subduction fluid-metasomatized lithospheric mantle source and subsequent crystal fractionation–accumulation processes. Besides representing the first recognition of mantle melting events in the ZTM region during the early Paleoproterozoic Siderian interval of ca. 2.45–2.20Ga, this unusual magmatic episode presents a temporal hallmark for indicating the prevalence of continental arc magmatism. Synthesizing these intrusions with the ca. 2.36–2.10 igneous episodes as well as concomitant episodic metamorphic events in the Trans-North China Orogen can lead to the characterization of a possible divergent double subduction system in the final amalgamation of the NCC during the Paleoproterozic.
The Late Mesozoic tectonic evolution of the eastern North China Craton (NCC) remains controversial. In this study, a suite of Early Cretaceous mafic-intermediate dyke swarms found in the same section ...in the Jiaodong Peninsula, eastern NCC, were used to trace the nature of lithospheric mantle and crust-mantle interaction. Zircon U-Pb dating demonstrates that these dykes emplaced into the Jiaodong Peninsula during the same period (112-121 Ma). Diorite dykes have SiO
2
contents of 52.7-54.1 wt.%, Na
2
O+K
2
O contents of 5.77-6.10 wt.%, a limited range of MgO (4.43-5.13 wt.%), Cr (64.8-85.5 ppm) and Ni (23.6-27.7 ppm), and a narrow range of (
87
Sr/
86
Sr)
i
isotopic ratios (0.709240-0.709246), Ɛ
Nd
(t) values (−20.0 to −19.1) and Ɛ
Hf
(t) values (ca. −23.9). Lamprophyre and dolerite dykes have low contents of SiO
2
(50.5-55.4 wt.%) and Na
2
O+K
2
O (4.88-7.28 wt.%), high contents of Al
2
O
3
(14.6-15.8 wt.%), MgO (5.83-8.60 wt.%), Cr (210-292 ppm) and Ni (114-149 ppm), and a narrow range (
87
Sr/
86
Sr)
i
isotopic ratios (0.709134-0.709788), Ɛ
Nd
(t) values (−19.9 to −17.4) and Ɛ
Hf
(t) values (−22.1 to −15.1). Both intermediate and mafic dykes exhibit strong large ion lithophile elements (LILE) enrichment and high field strength element (HFSE) depletion. These geochemical characteristics demonstrate that the magma was primarily derived from relatively low degrees of the partial melting of garnet-lherzolite mantle, which was modified by fluids from a subducting oceanic slab with marine sediments. Both the mafic dykes and intermediate dykes originated from the same magma source and formed in different stages of magma fractionation crystallization. The magma experienced the fractional crystallization of clinopyroxene and more ferromagnesian minerals in a hydrous condition, thus forming mafic dykes. Then, the residual calc-alkaline liquids upwelled into a low-H
2
O and low-pressure environment, in which more plagioclase crystallized from liquid, thus increasing the degree of differentiation and producing the Ca- and Al-rich diorite dyke. Combined with Late Mesozoic mantle-derived mafic-intermediate dykes and crust-derived volcanic rocks in the region, the eastern NCC has experienced considerable lithospheric thinning along with regional extensional tectonics, which was caused by the prolonged thermo-mechanical-chemical erosion on the lithosphere induced by the rollback of the subducted paleo-Pacific plate.
The Hucunnan ore deposit is a representative skarn Cu–Mo deposit in the Tongling district, an important ore district of the renowned Middle–Lower Yangtze River metallogenic belt of China. The deposit ...shows distinct zonation of metals, with Cu mineralization distributed mainly in the exoskarn zone at shallow depths, and Mo mineralization occurring chiefly in the endoskarn zone located at deeper depths. Field evidence and petrographic observations indicate that the ore-forming processes can be divided into the skarn, quartz–molybdenite, quartz–chalcopyrite, and carbonate stages. Five types of fluid inclusions (FIs) are present in the deposit: solid-bearing (type 1), liquid-rich (type 2), vapor-rich (type 3), pure vapor (type 4), and CO2-bearing (type 5). The skarn stage contains mainly type 1 and 2, but also minor type 3 and 4 FIs; the FIs display homogenization temperatures of 434–570°C and salinities of 2.07–66.0wt.% NaCl equiv. The existence of hematite daughter minerals in the type 1 inclusions, together with the presence of magnetite in skarn, implies that the skarn-stage fluid was oxidizing. The skarnization of the granodiorite porphyry is commonly accompanied by potassic alteration, suggesting that the fluids were rich in alkali. Similar to the skarn stage, the quartz–molybdenite stage contains type 1 and 2, and minor type 3 and 4 FIs, which yield homogenization temperatures of 280–458°C and salinities of 1.40–54.2wt.% NaCl equiv. The presence of sulfide instead of hematite daughter minerals in the type 1 inclusions in quartz–molybdenite veins associated with sericitization indicates that the fluids of the quartz–molybdenite stage were more reducing and more acidic than the fluids in the skarn stage. The decrease in oxygen fugacity and increase in acidity could have resulted from magnetite crystallization and the consumption of alkali cations and OH−, respectively, during the skarn stage. The quartz–chalcopyrite stage contains all types of FIs, which show homogenization temperatures of 203–392°C and salinities of 1.22–46.6wt.% NaCl equiv. Observations of hematite-bearing type 1 FIs in quartz–chalcopyrite veins containing anhydrite associated with biotitization suggest that the fluids of the quartz–chalcopyrite stage were oxidizing and alkali-rich, probably on account of the inflow of meteoric water and boiling in an open system. In the carbonate stage, only type 2 FIs are present; these FIs yield the lowest homogenization temperatures of 156–276°C and the lowest salinities of 1.05–12.3wt.% NaCl equiv. Microthermometry and H–O isotope data indicate that the ore-forming fluids were dominated by magmatic water in the early stages (skarn and quartz–molybdenite stages), and that the magmatic water gradually mixed with circulating meteoric water during the late stages (quartz–chalcopyrite and carbonate stages). The coexistence of saline and vapor-rich FIs as internal trails or clusters within individual crystals, with similar homogenization temperatures but contrasting salinities and homogenization modes (to the liquid and vapor, respectively), in the first three stages strongly suggests that three episodes of fluid boiling occurred in these stages, as further supported by the hydrogen isotopic compositions of the fluids, which are lower than those of magmatic water. Based on the above data, we conclude that temporal changes in redox conditions, acidity, and temperature in the mineralizing fluids resulted in the temporal separation of Cu and Mo by selective sulfide precipitation in the Hucunnan skarn deposit. The competition among metals (e.g., Mo and Cu) for sulfur in magmatic fluids, along with vapor–brine immiscibility (fluid boiling), are major factors that contributed to the spatial separation of Cu and Mo in the deposit.
Display omitted
•The deposit shows a clear separation of Mo and Cu mineralization in both space and time.•The fluids changed to more oxidizing and alkali-rich conditions from Mo- to Cu- mineralization stages.•The changes in fo2, pH, and temperature resulted in the temporal separation of Cu and Mo.•The competition among metals for sulfur and boiling led to the spatial separation of Cu and Mo.
The Middle–Lower Yangtze Region (MLYR) is one of the most important metallogenic belts in China that hosts numerous Cu–Fe–Au–S deposits. The Hucunnan deposit in the central part of MLYR is a newly ...discovered porphyry–skarn‐type copper–molybdenum deposit during recent drilling exploration. Laser ablation ICP–MS analysis carried out in this study yields U–Pb isotopic ages of 137.5 ± 1.2 Ma for the Cu–Mo bearing granodiorite rock and 125.0 ± 1.5 Ma for the Cu‐bearing quartz diorites. The Re–Os isotopic dating of seven molybdenite samples gave an isochron age of 139.5 ± 1.1 Ma, suggesting a syn‐magma mineralization of molybdenite in the Hucunnan deposit. Since porphyry‐type molybdenum deposits are rare in central MLYR, the discovery of the Hucunnan deposit suggests possible molybdenite mineralizations in the deep places of the Cu–Mo bearing granitoids. In addition, the U–Pb isotopic age of 125 Ma for the Cu‐bearing quartz diorites implies a new Cu mineralization period for the MLYR that was rarely reported by previous studies.
The Hucunnan deposit in the central part of The Middle‐Lower Yangtze Region is a newly discovered copper‐molybdenum deposit during recent drilling exploration. In this study, Two episodes of magma activates have been recognized. The first episode (137.5±1.2) Ma formed the Cu‐Mo bearing granodiorite rock, while the second (125.0±1.5 Ma) generated the Cu‐bearing quartz diorites.
We examined the coprecipitation behavior of Ti, Mo, Sn and Sb in Ca–Al–Mg fluorides under two different fluoride forming conditions: at <
70 °C in an ultrasonic bath (denoted as the ultrasonic ...method) and at 245 °C using a Teflon bomb (denoted as the bomb method). In the ultrasonic method, small amounts of Ti, Mo and Sn coprecipitation were observed with 100% Ca and 100% Mg fluorides. No coprecipitation of Ti, Mo, Sn and Sb in Ca–Al–Mg fluorides occurred when the sample was decomposed by the bomb method except for 100% Ca fluoride. Based on our coprecipitation observations, we have developed a simultaneous determination method for B, Ti, Zr, Nb, Mo, Sn, Sb, Hf and Ta by Q-pole type ICP-MS (ICP-QMS) and sector field type ICP-MS (ICP-SFMS). 9–50 mg of samples with Zr–Mo–Sn–Sb–Hf spikes were decomposed by HF using the bomb method and the ultrasonic method with B spike. The sample was then evaporated and re-dissolved into 0.5 mol l
−
1
HF, followed by the removal of fluorides by centrifuging. B, Zr, Mo, Sn, Sb and Hf were measured by ID method. Nb and Ta were measured by the ID-internal standardization method, based on Nb/Mo and Ta/Mo ratios using ICP-QMS, for which pseudo-FI was developed and applied. When 100% recovery yields of Zr and Hf are expected, Nb/Zr and Ta/Hf ratios may also be used. Ti was determined by the ID-internal standardization method, based on the Ti/Nb ratio from ICP-SFMS. Only 0.053 ml sample solution was required for measurement of all 9 elements. Dilution factors of ≤
340 were aspirated without matrix effects. To demonstrate the applicability of our method, 4 carbonaceous chondrites (Ivuna, Orgueil, Cold Bokkeveld and Allende) as well as GSJ and USGS silicate reference materials of basalts, andesites and peridotites were analyzed. Our analytical results are consistent with previous studies, and the mean reproducibility of each element is 1.0–4.6% for basalts and andesites, and 6.7–11% for peridotites except for TiO
2.
Contrary to what is currently known, archetypal zircon samples from gneisses and intrusive leucogranites in the Palaeoproterozoic Suhum Basin, SE Ghana, suggest the involvement of Neoarchean crustal ...material in the formation of the Palaeoproterozoic juvenile crust of the Birimian terranes in Ghana. The zircons dated using U–Pb dating methods and subjected to Lu–Hf isotopic analysis suggest that crustal‐forming events from different contemporaneous magmatic episodes within the Suhum Basin took place over a time interval of 139 Ma from 2224 to 2085 Ma. Whole‐rock Lu–Hf data obtained for the gneissic and leucogranitic rocks gave model ages (T
DM2
) ranging from 2789 to 2456 Ma with ɛHf(t) values ranging from −1.1 to +5.4. These model ages imply that the magmas that formed these rocks were sourced from the early Palaeoproterozoic juvenile mantle with substantial Neoarchean crustal reworking.
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