The three-dimensional UPb method: Generalized models and implications for UPb two-stage systematics

Zheng, Yong‐Fei

doi:10.1016/0009-2541(92)90099-q

Cited by 25 publications

(13 citation statements)

References 38 publications

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“…, 2006). As a result, these U–Pb isotope data were statistically processed as an isochron age by means of the isoplot program of Ludwig (2003) following physical interpretations of U–Pb isotopic systematics in concordia spaces (Zheng, 1990, 1992; Ludwig, 1998; Zheng et al. , 2007b).…”

Section: Resultsmentioning

confidence: 99%

“…This scatter is probably caused by varying amounts of common Pb present in the zircon . As a result, these U-Pb isotope data were statistically processed as an isochron age by means of the ISOPLOT ISOPLOT program of Ludwig (2003) following physical interpretations of U-Pb isotopic systematics in concordia spaces (Zheng, 1990(Zheng, , 1992Ludwig, 1998;Zheng et al, 2007b). The result yields an isochron age of 221 ± 2 Ma with an MSWD ¼ 2.8 (Fig.…”

Section: Zircon U-pb Agesmentioning

confidence: 99%

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Zircon U–Pb age and Hf isotope evidence for contrasting origin of bimodal protoliths for ultrahigh‐pressure metamorphic rocks from the Chinese Continental Scientific Drilling project

Chen

Zheng

Zhao³

et al. 2007

Journal Metamorphic Geology

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A combined study of zircon morphology, U-Pb ages and Hf isotopes as well as whole-rock major and trace elements was carried out for ultrahigh-pressure (UHP) eclogite and felsic gneiss from the main hole (MH) of the Chinese Continental Scientific Drilling (CCSD) project in the Sulu orogen. The results show contrasting Hf isotope compositions for bimodal UHP metaigneous rocks, pointing to contrasting origins for their protoliths (thus dual-bimodal compositions). The samples of interest were from two continuous core segments from CCSD MH at depths of 734.21-737.16 m (I) and 929.67-932.86 m (II) respectively. Zircon U-Pb dating for four samples from the two core segments yields two groups of ages at 784 ± 17 and 222 ± 3 Ma, respectively, corresponding to protolith formation during supercontinental rifting and metamorphic growth during continental collision. Although the Triassic UHP metamorphism significantly reset the zircon U-Pb system of UHP rocks, the Hf isotope compositions of igneous zircon can be used to trace their protolith origin. Contrasting types of initial Hf isotope ratios are, respectively, correlated with segments I and II, regardless of their lithochemistry. The first type shows positive e Hf (t) values of 7.8 ± 3.1 to 6.0 ± 3.0, with young Hf model age of 1.03 and 1.11 Ga. The second type exhibits negative e Hf (t) values of )6.9 ± 1.6 to )9.1 ± 1.1, with old Hf model ages of 2.11 and 2.25 Ga. It appears that the UHP rocks from the two segments have protoliths of contrasting origin. Consistent results are also obtained from their trace element compositions suggesting that midNeoproterozoic protoliths of bimodal UHP metaigneous rocks formed during supercontinental rifting at the northern margin of the South China Block. Thus, the first type of bimodal magmatism formed by rapid reworking of juvenile crust, whereas the second type of bimodal magmatism was principally generated by rift anatexis of Paleoproterozoic crust. Melting of orogenic lithosphere has potential to bring about bimodal magmatism with contrasting origins. Because arc-continent collision zones are the best place to accumulate both juvenile and ancient crusts, the contrasting types of bimodal magmatism are proposed to occur in an arc-continent collision orogen during the supercontinental rifting, in response to the attempted breakup of the supercontinent Rodinia at c. 780 Ma.

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Section: Resultsmentioning

confidence: 99%

Section: Zircon U-pb Agesmentioning

confidence: 99%

Zircon U–Pb age and Hf isotope evidence for contrasting origin of bimodal protoliths for ultrahigh‐pressure metamorphic rocks from the Chinese Continental Scientific Drilling project

Chen

Zheng

Zhao³

et al. 2007

Journal Metamorphic Geology

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show abstract

“…6). In contrast, a preferential loss of U relative to Pb (or gain of Pb relative to U) is suggested if the U-Pb data points are distributed above the concordia curve (Zheng, 1992). On the other hand, a prominent phenomenon from our SIMS dating is the continuous distribution of U-Pb data points along the concordia curve in the age range from ϳ780 to 560 Ma at Yangkou (Fig.…”

mentioning

confidence: 85%

“…Conventional U-Pb discordia dating of low ␦ 18 O zircons from granitic gneiss from the Dabie-Sulu orogenic belt, indicated as solid triangles in Figure 1. For principles of constructing the concordia and discordia in 206 Pb/ 207 Pb vs. 235 U/ 207 Pb space refer to Zheng (1990Zheng ( , 1992.…”

Section: Timing Of 18 O Depletion In Metaigneous Rocksmentioning

confidence: 99%

“…All the analysed results are listed in Table 3. ISOPLOT (Ludwig, 1996) was used to calculate U-Pb discordia ages in 206 Pb/ 207 Pb vs. 235 U/ 207 Pb space (Zheng, 1990(Zheng, ,1992. The advantage of this type of U-Pb discordia diagram is that the concordia curve is expanded relative to the Wetherill-type concordia curve for young ages (Ͻ1000 Ma), and thus a stronger curvature of the concordia curve is obtained to graphically show the intersection relationship between discordia line and concordia curve for the samples having Neoproterozoic and Phanerozoic ages.…”

Section: Isotopic Analysesmentioning

confidence: 99%

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