The North China Craton (NCC) was originally formed by the amalgamation of the eastern and western blocks along an orogenic belt at ∼1.9 Ga. After cratonization, the NCC was essentially stable until ...the Mesozoic, when intense felsic magmatism and related mineralization, deformation, pull-apart basins, and exhumation of the deep crust widely occurred, indicative of destruction or decratonization. Accompanying this destruction was significant removal of the cratonic keel and lithospheric transformation, whereby the thick (∼200 km) and refractory Archean lithosphere mantle was replaced by a thin (<80 km) juvenile one. The decratonization of the NCC was driven by flat slab subduction, followed by a rollback of the paleo-Pacific plate during the late Mesozoic. A global synthesis indicates that cratons are mainly destroyed by oceanic subduction, although mantle plumes might also trigger lithospheric thinning through thermal erosion. Widespread crust-derived felsic magmatism and large-scale ductile deformation can be regarded as petrological and structural indicators of craton destruction.
A craton, a kind of ancient continental block on Earth, was formed mostly in the early Precambrian (>1.8 Ga).
A craton is characterized by a rigid lithospheric root, which provides longevity and stability during its evolutionary history.
Some cratons, such as the North China Craton, can be destroyed by losing their stability, manifested by magmatism, deformation, earthquake, etc.
Zircon and baddeleyite U–Pb geochronological dating is widely used in solid Earth sciences and the advent of rapid in-situ methods of analysis, such SIMS and ICP-MS, has re-emphasized the importance ...of having uniform standards. Recently, it has been shown that Hf isotopic data can provide important information on these minerals since they contain high concentrations of Hf, but have low Lu/Hf ratios, which results in negligible age correction. However, the complex internal structures that result from multiple thermal events, such as inherited cores and metamorphic overgrowths, require that the Hf isotopic data be measured with high spatial resolution. However, the isobaric interferences of
176Yb and
176Lu on
176Hf hamper the precise determination of the
176Hf/
177Hf ratio during in-situ laser ablation MC-ICPMS analysis. It is shown here that mass biases of Yb (
β
Yb) and Hf (
β
Hf) change with time during analyses and behave differently for solutions and solid material. Therefore, it is suggested that the mean
β
Yb value of the individual spot be used to obtain the precise isotopic composition for in-situ zircon and baddeleyite Hf isotopic analyses. For low Yb/Hf (
176Yb/
177Hf
<
0.001) zircon and baddeleyite, the different methods used to obtain the
β
Yb value have little effect on the accuracy of the Hf isotopic composition. However, the appropriate Yb isotopic abundance is necessary for high Yb/Hf (
176Yb/
177Hf
>
0.001) zircons and baddeleyites, since the interference of
176Yb on
176Hf is significant. Using the mean
β
Yb value of the individual spot and newly published Yb isotopic abundance data, six standard zircons and two standard baddeleyites, have been investigated using a Neptune MC-ICPMS, with 193 nm laser. For zircons, the obtained
176Hf/
177Hf ratios are 0.282307
±
31 (2SD) for 91500, 0.282680
±
31 (2SD) for TEMORA, 0.281729
±
21 (2SD) for CZ3, 282177
±
17 (2SD) for CN92-1, 0.282983
±
17 (2SD) for FM0411, and 281234
±
11 (2SD) for Phalaborwa. The baddeleyites from Phalaborwa and SK10-2 have
176Hf/
177Hf ratios of 0.281238
±
12 and 0.282738
±
13 (2SD). These results agree well with the values obtained by the solution method and indicate that these standards have different Hf isotopic compositions, in which the extremely low
176Lu/
177Hf and
176Yb/
177Hf values of CZ3 zircon and Phalaborwa baddeleyite make them excellent standards for machine calibration during in-situ zircon Hf isotopic measurement, with the other standards being more suitable for the development of the correction method.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The North China Craton (NCC) is the typical example of destruction of an ancient craton. However, the destruction mechanism and geodynamic controlling factors still remain enigmatic due to ...controversy on the timing of destruction, which is the key to understanding the destruction processes. Based on temporal and spatial distributions of the igneous rocks, and their sources and tectonic settings, it is recognized that six stages of tectono-magmatism occurred in the NCC during the Phanerozoic, i.e., Carboniferous to Early Permian, Late Permian to Middle Triassic, Late Triassic, Jurassic, Early Cretaceous and Cenozoic. Among them, Cenozoic magmatism mainly consists of alkali basalts and is found only occasionally in the eastern NCC. The first four stages of magmatism and tectonism, related to the southward subduction of the Paleo-Asian plate and the assembly of Sino-Korean and Yangtze cratons, are locally distributed in limited parts of the NCC, reflecting a multiple stage modification of the NCC from the Late Carboniferous to Jurassic. However, the intensive development of Early Cretaceous magmatism, extensional deformation and associated gold mineralization, with significant continental crustal growth, indicate that the eastern NCC was destroyed during this time period. This destruction was the result of Paleo-Pacific subduction beneath the eastern Asian continent, with lithospheric removal and/or replacement of an ancient cratonic lithosphere by a juvenile oceanic lithosphere.
► Destruction of the North China Craton (NCC) ► Carboniferous to Triassic modification by subduction of the Paleo-Asian Ocean ► Triassic modification by the assembly of North China and Yangtze cratons ► Jurassic modification by subduction of the Paleo-Pacific plate ► Early Cretaceous destruction of the NCC by subduction of Paleo-Pacific plate
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Apatite is an important common U- and Th-bearing accessory mineral in igneous, metamorphic and clastic sedimentary rocks. The advent of in situ U–Th–Pb apatite geochronology by the SIMS and ...LA-(MC)-ICP-MS methods has demonstrated the importance of having uniform and homogeneous reference materials. Recently, it has been shown that Sr and Nd isotopic data combined with U–Pb age and trace element concentration data can provide important constraints on apatite paragenesis because this phase usually exhibits high Sr and REE concentrations but has low Rb/Sr ratios which result in negligible corrections for the ingrowth of radiogenic Sr. However, as apatite can potentially have complex internal structures resulting from multiple thermal events, such as inherited cores and metamorphic overgrowths, requires that the Sr and Nd isotopic data should be measured with high spatial resolution. However isobaric interferences hamper the precise determination of Sr or Nd isotopic compositions in LA-MC-ICP-MS analysis. In this work we undertook in situ measurements of Sr and Nd isotopic compositions of eleven apatite reference materials (AP1, AP2, Durango, MAD, Otter Lake, NW-1, Slyudyanka, UWA-1, Mud Tank, McClure Mountain and SDG) commonly used in U–Th–Pb geochronology. Our obtained Sr and Sm–Nd isotopic compositions for these apatite samples are consistent with those values obtained by solution-based methods (isotope dilution and ion chromatography) using MC-ICP-MS or TIMS, which demonstrates the reliability and robustness of our analytical protocol.
Display omitted
•Sr and Nd isotopes by laser and solution analysis are reported for eleven apatites.•AP1, AP2, MAD, Otter Lake, NW-1 and SDG are potential reference materials.•Durango, UWA-1, Mud Tank and McClure are not promising reference materials.•Matrix effects during laser ablation are investigated for different materials.
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The North China Craton is one of the few places in the world where >3.8
Ga crustal material exists, since zircons of this age have been found in the Baijiafen and Dongshan gneisses from Anshan in ...northeastern China. However, it has been questioned whether any 3.8
Ga rock exists in the area, since various younger zircons exist within single rock samples, and zircons with age of ∼3.8
Ga are few and can be interpreted as inherited in origin. A study of zircons using combined cathodoluminescence imaging and SHRIMP U–Pb dating indicates that the Baijiafen and Dongshan gneisses record several stages of granitic magmatism. The oldest magmatic event is recorded by a zircon with an age of 3887
±
5
Ma, with a subsequent magmatic event at 3.8
Ga (3808
±
24, 3798
±
30, 3802
±
11 and 3799
±
6
Ma), confirming the existence of 3.8
Ga materials in the area. The next magmatic event took place at ∼3.6–3.7
Ga. However, all samples contain younger zircons with ages of 3.1–3.3
Ga, although they contain a few zircon grains with ages of ∼3.6–3.8
Ga. The 3.1–3.3
Ga zircons show typical igneous oscillatory zoning and do not show any evidence that were produced by metamorphism, indicating that these samples were emplaced at 3.3 and 3.1
Ga, respectively and the zircons with older ages are interpreted as inherited in origin. The exposure of 3.8
Ga rock is therefore much smaller than previously thought.
In situ zircon Hf isotopic analyses indicate that these granitic rocks were derived from juvenile crust with age peaks of crustal growth at ∼3.4, 3.6 and 3.9
Ga, there is no evidence for existence of crustal material older than 4.0
Ga.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A new natural zircon reference material SA01 is introduced for U‐Pb geochronology as well as O and Hf isotope geochemistry by microbeam techniques. The zircon megacryst is homogeneous with respect to ...U‐Pb, O and Hf isotopes based on a large number of measurements by laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) and secondary ion mass spectrometry (SIMS). Chemical abrasion isotope dilution thermal ionisation mass spectrometry (CA‐ID‐TIMS) U‐Pb isotopic analyses produced a mean 206Pb/238U age of 535.08 ± 0.32 Ma (2s, n = 10). Results of SIMS and LA‐ICP‐MS analyses on individual shards are consistent with the TIMS ages within uncertainty. The δ18O value determined by laser fluorination is 6.16 ± 0.26‰ (2s, n = 14), and the mean 176Hf/177Hf ratio determined by solution MC‐ICP‐MS is 0.282293 ± 0.000007 (2s, n = 30), which are in good agreement with the statistical mean of microbeam analyses. The megacryst is characterised by significant localised variations in Th/U ratio (0.328–4.269) and Li isotopic ratio (−5.5 to +7.9‰); the latter makes it unsuitable as a lithium isotope reference material.
Keypoints
The homogeneity of the SA01 zircon megacryst was assessed by microbeam techniques for U‐Pb geochronology, and Li, O and Hf isotope geochemistry.
SA01 is homogeneous in terms of U‐Pb, O and Hf isotopes.
SA01 is unsuitable as a lithium isotope reference material.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
In situ zircon U-Pb and Hf-isotopic data have been determined for mafic microgranular enclaves and host granitoids from the Early Cretaceous Gudaoling batholith in the Liaodong Peninsula, NE China, ...in order to constrain the sources and petrogenesis of granites. The zircon U-Pb age of the enclaves (120 +/- 1 Ma) is identical to that of the host monzogranite (120 +/- 1 Ma), establishing that the mafic and felsic magmas were coeval. The Hf isotopic composition of the enclaves epsilon Hf(t) = +4.5 to -6.2 is distinct from the host monzogranite epsilon Hf(t) = -15.1 to -25.4, indicating that both depleted mantle and crustal sources contributed to their origin. The depleted mantle component was not previously revealed by geochemical and Nd and Sr isotopic studies, showing that zircon Hf isotopic data can be a powerful geochemical tracer with the potential to provide unique petrogenetic information. Some wall-rock contamination is indicated by inherited zircons with considerably older U-Pb ages and low initial Hf isotopic compositions. Hafnium isotopic variations in Early Cretaceous zircons rule-out simple crystal-liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks. Instead, mixing of mantle-derived mafic magmas with crustal-derived felsic magmas, coupled with assimilation of wall rocks, is compatible with the data. PUBLICATION ABSTRACT
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Highly precise and accurate measurements of Fe isotope ratios for fourteen reference materials from the USGS, MPI-DING and CGSG were successfully carried out using a developed analytical technique by ...fs LA-MC-ICP-MS. A synthetic standard, i.e. , Cr-979S, was produced as a calibration standard for instrumental mass bias and isobaric interference corrections. The results for samples with low Cr concentration ( 54 Cr/ 54 Fe < 0.0001), e.g. , δ 56 Fe values of BCR-2G ( δ 56 Fe = 0.12 ± 0.10‰, 2SD, n = 15), were in excellent agreement with data from solution MC-ICP-MS within the measurement precision without the use of the Cr-979S standard. For the samples with high Cr concentration ( 54 Cr/ 54 Fe > 0.0001), e.g. , BHVO-2G, δ 56 Fe values deviated from reference values when using the standard-sample bracketing method alone. Combining the standard-sample bracketing method with Cr-979S standard corrections and standard sample cone + H skimmer cone, the measured Fe isotopic compositions of GOR128-G and GOR132-G with extremely high Cr concentrations ( 54 Cr/ 54 Fe > 0.01) were identical to reference values within errors ( δ 56 Fe = −0.01 ± 0.13‰, 2SD, n = 18; δ 56 Fe = 0.00 ± 0.13‰, 2SD, n = 13; respectively). A series of reference materials with varying Cr concentrations, including the USGS reference glasses (BCR-2G, BHVO-2G, BIR-1G, TB-1G, NKT-1G, GSD-1G and GSE-1G), MPI-DING reference glasses (KL2-G, ML3B-G, GOR128-G and GOR132-G) and CGSG reference materials (CGSG-1 and CGSG-4), were used to test our developed method of in situ Fe isotopic measurements using the combined standard-sample bracketing method and Cr-979S standard corrections by fs LA-MC-ICP-MS. All the reference materials yield relatively homogeneous Fe isotopic compositions with δ 56 Fe values ranging from −0.03‰ to 0.13‰ and δ 56 Fe reproducibility is below 0.15‰ (2SD), suggesting that the proposed isobaric interference correction and mass bias correction method is a useful tool for providing high-quality in situ Fe isotopic data of geological samples with both low and high Cr concentrations.
Mesozoic volcanic rocks and granitoids are widespread in the Great Xing'an Range, which is part of a large igneous province in the eastern China. However, the ages of the volcanic rocks, especially ...those in the southern segment of the range, are poorly constrained. Here we present zircon U–Pb and whole rock Ar–Ar ages of 43 volcanic rocks from the four recognized formations (Manketouebo, Manitu, Baiyingaolao and Meiletu) in the southern Great Xing'an Range. The volcanic rocks of the Manketouebo Formation have a large span of ages ranging from 174 to 122
Ma, while those of the Manitu Formation exhibit a smaller age range from 156 to 125
Ma. The Baiyingaolao and Meiletu volcanic rocks both have Early Cretaceous ages between 139 and 124
Ma. These data indicate that the mapped units are not strictly ‘formations’ and further studies are required to resolve this issue. However, when taken together, these new data define two episodes of magmatism (Late Jurassic and Early Cretaceous) with the Early Cretaceous volcanic rocks being dominant. Combined with previously published data from the northern Great Xing'an Range, and available age data from other parts of northeastern China and surrounding regions, two stages of magmatism, i.e., Jurassic and Early Cretaceous, can be identified throughout this part of Asia. The Jurassic rocks mainly comprise granites, while volcanic rocks are dominant in the Early Cretaceous. These two stages of magmatism form opposite spatial trends, that is, the Jurassic rocks become younger to the west, whereas the Cretaceous rocks become younger to the east. Between the two stages of magmatism, the ‘magma gap’ increases eastward in duration from less than 10
Ma in the Great Xing'an Range to more than 40
Ma in Japan. These trends can be explained by westward subduction of the Paleo-Pacific oceanic Plate and its control on subsequent geodynamic processes. Jurassic subduction of the oceanic slab caused crustal shortening and thickening, and formed the westward decrease in age of the granites with characteristics of an active continental margin, while volcanism was rare. By the end of the Jurassic, westward flat-slab subduction of the Paleo-Pacific Oceanic plate changed its direction to the north or northwest. This subsequently caused a transformation in tectonic regime from compression to extension in the Cretaceous and induced large-scale delamination of the thickened lower crust and lithospheric mantle. Delamination was initiated at the western margin of the subducting slab, and migrated eastward. Delamination and consequent upwelling of the asthenosphere triggered extensive volcanic eruption, with only minor granite emplacement. Similar age trends are also observed for other parts of eastern China, suggesting this model can also be applied to explain the geodynamic setting of the Mesozoic large igneous events in China and adjacent regions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Water is essential for the formation of granites, but its origin and role in granite generation (i.e., dehydration vs. water‐fluxed melting) remain uncertain. These issues are addressed by combining ...water abundances and other geochemical indices in zircons from Late Mesozoic granites generated during the destruction of the North China Craton (NCC). The water contents in zircons from the NCC Early Cretaceous granites (763 ppm, median) are much higher than those of the NCC Jurassic granites (424–513 ppm), upper mantle and continental arc magmas (92–477 ppm). More importantly, the higher water contents in the voluminous Early Cretaceous granites also have higher zircon saturation temperatures, εHf(t), and lower δ18O values. These observations suggest a predominantly mantle origin for the water, and water‐fluxed crustal melting, in which larger water ingression produced more voluminous melts. The high‐water flux was likely related to the subduction of the Paleo‐Pacific Plate, which ultimately destabilized the NCC.
Plain Language Summary
The fact that water is essential in generating granites has been known for a long time. However, its detailed role is poorly understood due to heterogeneous source and complex melting reactions involved in the generation of granites. As a fundamental issue of granite genesis, it remains a long‐standing problem to distinguish the two major mechanisms, that is, hydrous‐mineral‐dehydration melting versus external‐water‐added melting. In this study, the water content of zircon combined with other lines of clues of I‐type granites that generated during the destruction of North China Craton (NCC) in Late Mesozoic collectively points to water‐added crustal melting rather than dehydration melting. The isotope composition of zircon suggests a mantle provenance of water. The highest water contents occurred in the Early Cretaceous granites, corresponding to the climax of the NCC destruction. Higher zircon water contents in Early Cretaceous granites indicate higher water‐flux into thelithospheric mantle and overlying crust by the subduction of the paleo‐Pacific plate. Accordingly, water played a significant role in cratonic destruction.
Key Points
Water contents of zircons from North China Craton Jurassic granites are comparable with continental arc magmas
Higher zircon water contents are found in voluminous Early Cretaceous granites generated during the climax of cratonic destruction
Early Cretaceous granites were generated by water‐fluxed crustal melting, the water in which has a predominant mantle origin
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
