The North China Craton (NCC) experienced strong destruction (i.e., decratonization) during the Mesozoic, which triggered intensive magmatism, tectonism and thermal events and formed large-scale gold ...and other metal deposits in the eastern part of the craton. However, how the decratonization controls the formation and distribution of large-scale of gold and other metal deposits is not very clear. Based on a large number of published data and new results, this paper systematically summarizes all the data for the rock assemblages, chronology, geochemistry and petrogenesis of Mesozoic magmatic rocks, as well as for the mineralizing ages of gold and other metal deposits and the evolution of the Mesozoic basins in the eastern NCC. The results are used to restore the extensional rates of Mesozoic to Cenozoic basins and the strike-slip distance of the Tanlu Fault, to ascertain the location of the Paleo-Pacific plate subduction zones during the Mesozoic to Cenozoic, and to reconstruct the temporal and spatial distribution of Mesozoic gold and other metal deposits and magmatic rocks in the eastern NCC. It is obtained that the magmatism and mineralization in the eastern NCC westward migrate from east to west during the Early to Middle Jurassic, but they eastward migrate from west to east during the Early Cretaceous. The metallogenesis of these deposits is genetically related to magmatism, and the magmas provided some ore-forming materials and fluids for the generation of metal deposits. The geodynamic mechanism of decratonization and related magmatism and mineralization is proposed, i.e., the westward low-angle subduction of the Paleo-Pacific slab beneath the NCC formed continental magmatic arc with plenty of porphyry Cu-Mo-Au deposits in the Jurassic, similar to the Andean continental arc in South America. The mantle wedge was metasomatized by the fluids/melts derived from the subducting slab, laying a material foundation for hydrothermal mineralization in the Early Cretaceous. While the rollback of the subducting slab with gradually increasing subduction angle and the retreat of the subduction zones during the Early Cretaceous induced strong destruction of the craton and the formation of extensive magmatic rocks and large-scale gold and other metal deposits.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We report the first U–Pb geochronological investigation of schorlomite garnet from carbonatite and alkaline complexes and demonstrate its applicability for U–Pb age determination using laser ablation ...inductively coupled plasma mass spectrometry (LA-ICP-MS) due to its relatively high U and Th abundances and negligible common Pb content. The comparative matrix effects of laser ablation of zircon and schorlomite are investigated and demonstrate the necessity of a suitable matrix-matched reference material for schorlomite geochronology. Laser-induced elemental fractional and instrumental mass discrimination were externally-corrected using an in house schorlomite reference material (WS20) for U–Pb geochronology. In order to validate the effectiveness and robustness of our analytical protocol, we demonstrate the veracity of U–Pb age determination for five schorlomite samples from: the Magnet Cove complex, Arkansas (USA); the Fanshan ultrapotassic complex, Hebei (China); the Ozernaya alkaline ultramafic complex, Kola Peninsula (Russia); the Alnö alkaline–rock carbonatite complex (Sweden); and the Prairie Lake carbonatite complex, Ontario (Canada). The schorlomite U–Pb ages range from 96 Ma to 1160 Ma, and are almost identical to ages determined from other accessory minerals in these complexes and support the reliability of our analytical protocol. Schorlomite garnet U–Pb geochronology is considered to be a promising new technique for understanding the genesis of carbonatites, alkaline rocks, and related rare-metal deposits.
An improved chemical method is developed to accurately measure the W isotopic compositions of silicate samples with a precision of better than ±0.05
ε
on
ε
182
W. Compared with the conventional ...method, two developments of this method mainly include the sample digestion process that is modified to better W dissolution from the co-precipitations and the W separation procedure. The optimized extraction chromatography using TEVA resin is designed to more efficiently separate W from Ti, Zr and Hf after the first-stage cation-exchange procedure with the percent recovery of W more than 85%. The blank during the whole procedure is less than 0.3 ng and is negligible for W isotopic analysis. The W isotopic ratios of Alfa Aesar W standard solution and a variety of silicate reference materials,
i.e.
, RGM-2, GSP-2, AGV-2, JB-3, BCR-2 and BHVO-2, are measured by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). RGM-2, GSP-2, AGV-2, JB-3 and BCR-2 have normal
ε
182
W values, identical to that of the terrestrial Alfa Aesar W standard, whereas BHVO-2 has a negative
ε
182
W value of −0.09 ± 0.05 (2SD,
N
= 10). The duplicate measurements of Alfa Aesar W standard solution RGM-2 and BHVO-2 show that the external reproducibility of
ε
182
W is usually better than 5 ppm (2SD), which is the most precise among the published data measured by MC-ICPMS and can be comparable to the precision acquired by negative thermal ionization mass spectrometry (N-TIMS) (about 5 ppm). All these results show that our new method provides an efficient way to precisely measure W isotopic compositions of silicate materials. It provides a widely useful tool to reveal the earliest history of the silicate earth and offers the ability to resolve sub-million-year age differences in meteorites.
Titanite is a common accessory mineral that preferentially incorporates considerable amounts of U and light rare earth elements in its structure, making it a versatile mineral for in situ U‐Pb dating ...and Sm‐Nd isotopic measurement. Here, we present in situ U‐Pb ages and Sm‐Nd isotope measurement results for four well‐known titanite reference materials (Khan, BLR‐1, OLT1 and MKED1) and eight titanite crystals that could be considered potential reference material candidates (Ontario, YQ‐82, T3, T4, TLS‐36, NW‐IOA, Pakistan and C253), with ages ranging from ~ 20 Ma to ~ 1840 Ma. Results indicate that BLR‐1, OLT1, Ontario, MKED1 and T3 titanite have relatively homogeneous Sm‐Nd isotopes and low common Pb and thus can serve as primary reference materials for U‐Pb and Sm‐Nd microanalysis. YQ‐82 and T4 titanite can be used as secondary reference materials for in situ U‐Pb analysis because of their low common Pb. However, internal structures and mineral inclusions in YQ‐82 will require careful selection of suitable target domains. Pakistan titanite is almost concordant with an age of 21 Ma and can be used as a reference material when dating Cenozoic titanite samples.
Key Points
In situ measurement results for trace element mass fractions and U‐Pb and Sm‐Nd isotope ratios from natural titanite crystals are presented.
Sm‐Nd isotope ratios of natural titanites are precisely determined by ID‐MC‐ICP‐MS.
BLR‐1, OLT1, Ontario, MKED1 and T3 can serve as ideal primary reference materials.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Bastnäsite is the end member of a large group of carbonate–fluoride minerals with the common formula (REE) CO3F·CaCO3. This group is generally widespread and, despite never occurring in large ...quantities, represents the major economic light rare earth element (LREE) mineral in deposits related to carbonatite and alkaline intrusions. Since bastnäsite is easily altered and commonly contains inclusions of earlier‐crystallised minerals, in situ analysis is considered the most suitable method to measure its U‐Th‐Pb and Sr‐Nd isotopic compositions. Electron probe microanalysis and laser ablation (multi‐collector) inductively coupled plasma‐mass spectrometry of forty‐six bastnäsite samples from LREE deposits in China, Pakistan, Sweden, Mongolia, USA, Malawi and Madagascar indicate that this mineral typically has high Th and LREE and moderate U and Sr contents. Analysis of an in‐house bastnäsite reference material (K‐9) demonstrated that precise and accurate U‐Th‐Pb ages could be obtained after common Pb correction. Moreover, the Th‐Pb age with its high precision is preferable to the U‐Pb age because most bastnäsites have relatively high Th rather than U contents. These results will have significant implications for understanding the genesis of endogenous ore deposits and formation processes related to metallogenic geochronology research.
Key Points
Bastnäsite from China, Pakistan, Sweden, Mongolia, USA, Malawi and Madagascar are investigated.
Bastnäsite can be considered a promising dating and tracing tool for carbonatites, alkaline rocks and related LREE deposits.
The capability and applicability of bastnäsite for U‐Th‐Pb age and Sr‐Nd isotope obtained by LA‐(MC)‐ICP‐MS is demonstrated.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
Major and trace element, whole rock Sr and Nd isotope and zircon Hf isotope data are reported for a suite of A-type granites and mafic microgranular enclaves from the Early Cretaceous (126
±
2 Ma) ...Qianshan pluton, Liaodong Peninsula, northeast China, with the aim of investigating the sources and petrogenesis of A-type granites. The Qianshan pluton includes hornblende alkali-feldspar granite, graphic biotite granite and mafic microgranular enclaves. The hornblende alkali-feldspar granites have high SiO
2, Fe
2O
3T
/
MgO, K
2O
+
Na
2O, Rb, Zr and LREE contents and low Ba and Sr concentrations with strongly negative Eu anomalies. Their high Rb
/
Sr (
87Rb
/
86Sr
=
16.76–24.15) and initial
87Sr
/
86Sr ratios (0.7215 to 0.7283), negative
ε
Nd(
t) values (−
14.1 to −
16.5) and zircon
ε
Hf(
t) values (−
18.9 to −
11.5) indicate they were mainly derived from a crustal source, but with involvement of high
ε
Nd(
t) and
ε
Hf(
t) materials. Graphic biotite granites have similar geochemical features and Sr–Nd–Hf isotopic compositions to enclaves, indicating they were the result of crystal fractionation of evolved mafic magmas, but with involvement of low
ε
Nd(
t) and
ε
Hf(
t) materials. The mafic enclaves have an igneous texture and contain acicular apatite, suggesting quenching of mafic magmas that have co-mingled with the host granites. They have low initial
87Sr
/
86Sr ratios (0.7097–0.7148), negative
ε
Nd(
t) (−
14.5 to −
11.9) and zircon
ε
Hf(
t) (−
17.1 to −
6.9) values, and are enriched in LILEs and LREEs and depleted in HFSEs. When coupled with the high MgO (Mg# up to 54), this indicates derivation from an enriched lithospheric mantle source, but contaminated by crustal materials.
Geochemical and Sr-, Nd- and zircon Hf-isotopic compositions rule out simple crystal–liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks. Instead, magma mixing of mantle-derived mafic and crustal-derived magmas, coupled with crystal fractionation, is compatible with the data. This example shows that at least some A-type granites formed through a complex process involving mantle- and crustal-derived magma mixing, crystal fractionation and infracrustal melting.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Here we report the first set of thallium (Tl) isotope data in alkaline rocks from the North China Craton to constrain the nature of recycled materials in the metasomatized subcontinental lithospheric ...mantle. Samples from the Hekanzi and Saima alkaline complexes display Tl isotope compositions (ε205Tl) identical to the present‐day upper mantle and continental crust, suggesting that neither the recycled low‐temperature altered oceanic crust nor the pelagic sediments were involved in their sources. The volcanic rocks from the Liaodong‐Jinan region, whose source was previously proposed to contain recycled low‐temperature altered oceanic crust, also display modern mantle‐like Tl isotope composition, suggesting a significant Tl‐loss in the recycled oceanic crust during the subduction due to the dehydration process. Our Tl isotope data provide complementary constraints to the Sr‐Nd‐Hf‐O isotopes on the nature of metasomatic agent in the subcontinental lithospheric mantle.
Plain Language Summary
Recycling of crustal materials into Earth's mantle by subduction causes mantle heterogeneities. The sources of some alkaline rocks contain recycled crustal materials. Pelagic sediments, low‐temperature altered oceanic crust, and continental crust have sharp differences in thallium isotope compositions. Combined with Sr‐Nd‐Hf‐O isotopes, whole‐rock Tl isotopes place a better constraint on the metasomatic sources.
Key Points
Thallium isotope compositions of the alkaline rocks were analyzed to track crustal recycling in the subcontinental lithospheric mantle
Thallium isotope suggested that low‐temperature altered oceanic crust and pelagic sediments were not involved in the investigated sources
The O‐Nd‐Hf‐Tl isotope data for the Liaodong‐Jinan volcanics reveal a significant Tl‐loss in the subducted slab during dehydration process
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The occurrence of high‐pressure (HP) garnet‐bearing metamorphic rocks in the southern Barberton granitoid–greenstone terrane (BGGT), South Africa, has been proposed as a key indicator of the onset of ...modern plate tectonics at ca. 3.2 Ga. Here, we report new zircon/titanite U–Pb ages of garnet‐bearing HP metamorphic rocks and associated granitoids in the BGGT that argue against such an interpretation. The results show that HP metamorphism occurred synchronously with granitoid magmatism in the Stolzburg domain, the supposed subducted plate, during two episodes at 3.4 and 3.2 Ga, and that these two episodes of magmatism occurred on both sides of the assumed suture zone, a feature that cannot easily be explained by the subduction model. In contrast, the coupled magmatism and metamorphism probably resulted from partial convective overturn (PCO), another viable mechanism for production and differentiation of continental crust during early Archean.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Major and trace element, whole rock Sr‐, Nd‐and Hf‐isotopes and zircon U–Pb age and Hf–O isotope data have been determined for mafic to felsic intrusive rocks from the Late Triassic Mayihe (MYH), ...Longtou–Chaxinzi–Xiaoweishahe (LCX) and Nankouqian–Xidadingzi (NX) intrusions in the northern Liaodong Peninsula, NE China, in order to investigate their sources and petrogenesis related to decrationization of the North China Craton. The rocks include clinopyroxene diorite, monzodiorite, quartz diorite, granodiorite, monzogranite and mafic microgranular enclaves. Laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS) and secondary ion mass spectrometer (SIMS) U–Pb analyses of zircon from MYH, LXC to NX intrusions yield Late Triassic ages of 224–218Ma, establishing that the mafic and felsic magmas were coeval. The clinopyroxene diorites from the MYH pluton have high MgO concentrations at low silica contents, with positive whole rock εNd(t) (up to +3.8) and εHf(t) (up to +6.2) and zircon εHf(t) values and some mantle-like δ18O values. They are enriched in large ion lithophile (LILEs) and light rare earth elements (LREEs) and depleted in high field strength elements (HFSEs), which can be explained as melts derived from a depleted mantle, with some subsequent crustal contamination. However, the diorites from the LXC and NX intrusions are high‐K rocks and have high MgO concentrations and mantle-like δ18O values, but with negative whole rock εNd(t) (−12.9 to −7.6) and εHf(t) (−14.0 to −5.6) and zircon εHf(t) values, distinct from those of MYH pyroxene diorites, indicating that their parental magmas were derived from partial melting of an ancient lithospheric mantle. The granitoids from three plutons have high SiO2 contents and low MgO concentrations, suggesting they were mainly derived from crustal sources. However, the MYH monzogranite and granodiorite have positive whole rock εNd(t) and εHf(t) (up to +3.0) and zircon εHf(t) values, indicating a juvenile crustal source, whereas, the LXC and NX granitoids have strong negative and variable whole rock εNd(t) and εHf(t) and zircon εHf(t) values, indicating that they were derived from partial melting of ancient lower crustal materials with involvement of mantle components. Field observations, geochronology, geochemistry, Sr–Nd–Hf isotopic and zircon Hf–O isotopic compositions point to a complex petrogenesis, where mantle- and crust-derived magma mixing was coupled with crystal fractionation, thus explaining the genetic link between mafic and felsic rocks. Identification of four components, i.e., depleted and enriched mantle and juvenile and ancient crust in the Late Triassic magmatism in the northern Liaodong Peninsula suggests a strong mantle–crust interaction process related to decratonization of the North China Craton.
► Magmatism related to decratonization of the North China Craton (NCC). ► Zircon Hf–O isotopes show multiple sources in the origin of Late Triassic magmatism. ► Magma mixing and AFC processes in the genesis of granitoids. ► Lithospheric architecture related to decratonization.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Mesozoic igneous rocks are widespread throughout eastern China, but precise geochronological and petrogenetic constraints were previously lacking. Ten samples from the Liaodong Peninsula in ...northeastern China were chosen for zircon U–Pb SHRIMP and laser ablation ICP-MS dating. The magmatic ages range from 179
±
3 to 156
±
3 Ma. Data compilation indicates that contemporaneous granitic magmatism is widespread throughout eastern China, establishing the Jurassic as an important period of igneous activity in eastern China. Petrographically, these granites can be divided into three groups that underwent a complex history of crystal fractionation. Two end-members of granodioritic and monzogranitic magma are identified. The granodioritic rocks, having lower (
87Sr
/
86Sr)
i
and higher
ɛ
Nd(
t) values than those of the monzogranitic rocks, came from the partial melting of juvenile crust, whereas the monzogranitic rocks came from partial melting of the Precambrian basement. It is proposed that Pacific plate subduction resulted in crustal thickening and subsequent lithospheric delamination which resulted in the upwelling of asthenospheric mantle and formation of juvenile crust by underplating of mantle-derived magma in the lower crust. A subsequent underplating and heating event from the asthenosphere partially melted the overlying pre-existing underplated mafic rocks and ancient crust, leading to the formation of granodioritic and monzogranitic magmas. This thickening by subduction could have been a necessary precursor for limited delamination in the Jurassic and more extensive delamination in the Early Cretaceous.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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