23 results on '"Li, Xianhua"'
Search Results
2. Long-Term Reproducibility of SIMS Zircon U-Pb Geochronology
- Author
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Zhao, Wenhao, Li, Qiuli, Liu, Yu, Tang, Guoqiang, Ling, Xiaoxiao, Li, Jiao, and Li, Xianhua
- Published
- 2022
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3. Tetrad Effect of Rare Earth Element Fractionation in Zircon from the Pegmatite of the Adui Massif, Middle Urals.
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Levashova, Ekaterina V., Skublov, Sergey G., Zamyatin, Dmitry A., Li, Qiuli, Levashov, Dmitry S., and Li, Xianhua
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RARE earth metals ,ZIRCON ,TRACE elements in water - Abstract
The zircon from the pegmatite of the Adui granitic massif displays the unique the rare earth element (REE) distribution spectrum with the tetrad effect in REE fractionation. The tetrad effect often occurs in granitoid rocks, but it is rarely encountered in minerals, e.g., zircon. Fluid saturated with volatiles, water and trace elements is a factor responsible for the tetrad effect in the zircon. The detailed isotopic-geochemical study of the zircon has revealed several zones differing in internal structure (in the back-scattered electron (BSE) image), composition and REE distribution. The zones indicate changes in the crystallization environment provoked by the evolution of the pegmatite-forming melt. They occur as the gradually growing changes in composition from the unaltered zones that are light-colored in BSE to the altered zones that are dark-colored in BSE. The unaltered zones are consistent in composition and geochemical features with magmatic zircons. The high content of trace (U, Th, REE) and volatile elements (F, Cl) in water suggests its crystallization from the fluid-saturated magmatic melt. The altered zircon zones occur as recrystallized zones with high content of non-formula elements (Y, Ca, Sr, Nb, P), a non-differentiated REE distribution spectrum and an absent Ce anomaly. These features are consistent with those of hydrothermal-metasomatic zircon. [ABSTRACT FROM AUTHOR]
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- 2024
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4. Progress in the principle and application of zircon trace element
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Jiang JiLian, Zou XinYu, Qin KeZhang, Yang Wei, Li XianHua, and Zhang YiGang
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Geochemistry and Petrology ,Trace element ,Geochemistry ,Geology ,Zircon - Published
- 2021
5. Qinghu zircon: A working reference for microbeam analysis of U-Pb age and Hf and O isotopes
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Li, XianHua, Tang, GuoQiang, Gong, Bing, Yang, YueHeng, Hou, KeJun, Hu, ZhaoChu, Li, QiuLi, Liu, Yu, and Li, WuXian
- Published
- 2013
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6. Role of mantle-derived magma in genesis of early Yanshanian granites in the Nanling Range, South China: in situ zircon Hf-O isotopic constraints
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Li, XianHua, Li, WuXian, Wang, XuanCe, Li, QiuLi, Liu, Yu, and Tang, GuoQiang
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- 2009
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7. SHRIMP U-Pb zircon dating of the uppermost cretaceous furao formation near the Heilong River: An age closest to the K/T boundary
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Li, Xianhua, Li, Wuxian, Chen, Peiji, Wan, Xiaoqiao, Li, Gang, Song, Biao, Jiang, Jianhong, Liu, Jicai, Yin, Deshun, and Yan, Wei
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- 2004
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8. SHRIMP U-Pb zircon age of the Jinchuan ultramafic intrusion and its geological significance
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Li, Xianhua, Su, Li, Song, Biao, and Liu, Dunyi
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- 2004
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9. SHRIMP U-Pb zircon age, geochemistry and Nd-Hf isotope of Neoproterozoic mafic dyke swarms in western Sichuan: Petrogenesis and tectonic significance
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Li Xianhua, Lin GuangChun, and Li WuXian
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Asthenosphere ,Rodinia ,Geochemistry ,General Earth and Planetary Sciences ,Island arc ,Crust ,Mafic ,Geology ,Mantle plume ,Petrogenesis ,Zircon - Abstract
Neoproterozoic magmatic rocks are widespread in the western margin of the Yangtze block, and their origin and genesis have significant implications for understanding the evolution of the Rodinia super-continent. However, there are currently two opposing interpretations for their petrogenesis and tectonic setting: mantle plume-related and island arc origin. To further verify these two competing models, SHRIMP U-Pb zircon age determinations and geochemical and Nd-Hf isotopic analyses are conducted on the mafic dykes in the Kangdian Rift, western Sichuan. U-Pb dating suggests that these mafic dykes were emplaced at 780–760 Ma, spatially and temporally coeval with the Kangding granitoid complex. The parental magmas of these dykes were derived from a depleted asthenosphere mantle source likely triggered by an anomalously-hot mantle plume. Despite some arc-geochemical features caused by variable degrees of contamination of young island arc crust during magma ascending and emplacement, they show general geochemical and Nd-Hf isotopic features similar to those of the intraplate basalts. Our results support the reconstruction model of Rodinia in which the South China block was located between Australia and Laurentia.
- Published
- 2007
10. GHR1 Zircon – A New Eocene Natural Reference Material for Microbeam U‐Pb Geochronology and Hf Isotopic Analysis of Zircon.
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Eddy, Michael P., Ibañez‐Mejia, Mauricio, Burgess, Seth D., Coble, Matthew A., Cordani, Umberto G., DesOrmeau, Joel, Gehrels, George E., Li, Xianhua, MacLennan, Scott, Pecha, Mark, Sato, Kei, Schoene, Blair, Valencia, Victor A., Vervoort, Jeffrey D., and Wang, Tiantian
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ZIRCON ,REFERENCE sources ,GEOLOGICAL time scales ,URANIUM-lead dating ,CENOZOIC Era - Abstract
We present multitechnique U‐Pb geochronology and Hf isotopic data from zircon separated from rapakivi biotite granite within the Eocene Golden Horn batholith in Washington, USA. A weighted mean of twenty‐five Th‐corrected 206Pb/238U zircon dates produced at two independent laboratories using chemical abrasion‐isotope dilution‐thermal ionisation mass spectrometry (CA‐ID‐TIMS) is 48.106 ± 0.023 Ma (2s analytical including tracer uncertainties, MSWD = 1.53) and is our recommended date for GHR1 zircon. Microbeam 206Pb/238U dates from laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) and secondary ion mass spectrometry (SIMS) laboratories are reproducible and in agreement with the CA‐ID‐TIMS date to within < 1.5%. Solution multi‐collector ICP‐MS (MC‐ICP‐MS) measurements of Hf isotopes from chemically purified aliquots of GHR1 yield a mean 176Hf/177Hf of 0.283050 ± 17 (2s, n = 10), corresponding to a εHf0 of +9.3. Hafnium isotopic measurements from two LA‐ICP‐MS laboratories are in agreement with the solution MC‐ICP‐MS value. The reproducibility of 206Pb/238U and 176Hf/177Hf ratios from GHR1 zircon across a variety of measurement techniques demonstrates their homogeneity in most grains. Additionally, the effectively limitless reserves of GHR1 material from an accessible exposure suggest that GHR1 can provide a useful reference material for U‐Pb geochronology of Cenozoic zircon and Hf isotopic measurements of zircon with radiogenic 176Hf/177Hf. Key Points: We suggest a new Eocene zircon reference material, GHR1.U‐Pb and Hf isotopic systematics in GHR1 zircon are homogeneous with a 206Pb/238U date of 48.106 +/‐ 0.023 Ma (2s) and a 176Hf/177Hf of 0.283050 +/‐ 17 (2s).GHR1 fulfills a need for abundant and easily available Cenozoic zircon reference materials. [ABSTRACT FROM AUTHOR]
- Published
- 2019
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11. Geochemistry of granitoid rocks from Zhejiang Province and crustal evolution—I. Phanerozoic granitoid rocks
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Bao Zhiwei, Wang Yixian, Zhao Zhenhua, and Li Xianhua
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Tectonics ,Geochemistry and Petrology ,Proterozoic ,Phanerozoic ,Geochemistry ,Partial melting ,Mesozoic ,Petrology ,Geology ,Mantle (geology) ,Petrogenesis ,Zircon - Abstract
The Phanerozoic granitoid rocks include the Caledonian, Indosinian and Yenshanian granitoid rocks. The existence of Caledonian and Indosinian granites was evidenced by zircon U-Pb ages. The study of the characteristics of major, trace and rare-earth elements, isotopic composition and petrogenesis for the granitoid rocks has been made. The Caledonian and Indosinian granites were derived from partial melting of the Proterozoic basement rocks and the two tectonic activities were weak. The Yenshanian granitoid rocks were derived from mixing of mantle and crustal materials. It implies that the crustal accretion took place in Mesozoic time.
- Published
- 1998
12. SHRIMP ion microprobe zircon U-Pb Age and Sm-Nd isotopic characteristics of the NE Jiangxi ophiolite and its tectonic implications
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C. M. Fanning, Zhou Guoqing, Zhao Jianxin, W. Compston, and Li Xianhua
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Isochron ,Tectonics ,Microprobe ,Geochemistry and Petrology ,Geochemistry ,Metamorphism ,Ophiolite ,Geology ,Mantle (geology) ,Zircon ,Shrimp - Abstract
The new SHRIMP zircon U-Pb isotopic study suggests that the crystallization age of a highly fractionated magma in the NE Jiangxi ophiolite suite is 968±23 Ma. Re-calculated Sm-Nd isochron age of 955±44 Ma is within analytical errors. consistent with the zircon U-Pb age. With the exception of two anomalous Sm-Nd data, the remaining 15 analyses so far obtained for the ophiolite gaveeNd (T) values falling into a limited range from +4.3 to +6.7, indicating that the ophiolite was derived from a relatively strongly depleted mantle source. Sm-Nd isotopic systematics in some samples may have been strongly affected by post-magmatic events, such as alteration, deformation and metamorphism, resulting in anomalouseNd (T) values. Combined with published40Ar39Ar age data, it can be concluded that the collision between the Yangtze and South China Blocks occurred during 0.97-0.80 Ga.
- Published
- 1994
13. Accuracy of LA-ICPMS zircon U-Pb age determination: An inter-laboratory comparison.
- Author
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Li, XianHua, Liu, XiaoMing, Liu, YongSheng, Su, Li, Sun, WeiDong, Huang, HuiQing, and Yi, Keewook
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URANIUM-lead dating , *ZIRCON , *DIORITE , *LASER ablation inductively coupled plasma mass spectrometry , *EARTH sciences - Abstract
LA-ICPMS zircon U-Pb dating has been greatly advanced and widely applied in the past decade because it is a cheap and fast technique. The internal error of LA-ICPMS zircon U-Pb dating can be better than 1%, but reproducibility (accuracy) is relatively poor. In in order to quantitatively assess the accuracy of this technique, zircons from two dioritic rocks, a Mesozoic dioritic microgranular enclave (FS06) and a Neoproterozoic diorite (WC09-32), were dated independently in eight laboratories using SIMS and LA-ICPMS. Results of three SIMS analyses on FS06 and WC09-2 are indistinguishable within error and give a best estimate of the crystallization age of 132.2 and 760.5 Ma (reproducibility is ∼1%, 2RSD), respectively. Zircon U-Pb ages determined by LA-ICPMS in six laboratories vary from 128.3±1.0 to 135.0±0.9 Ma (2SE) for FS06 and from 742.9±3.1 to 777.8±4.7 Ma (2SE) for WC09-32, suggesting a reproducibility of ∼4% (2RSD). Uncertainty produced during LA-ICPMS zircon U-Pb analyses comes from multiple sources, including uncertainty in the isotopic ratio measurements, uncertainty in the fractionation factor calculation using an external standard, uncertainty in the age determination as a result of common lead correction, age uncertainty of the external standards and uncertainty in the data reduction. Result of our study suggests that the uncertainty of LA-ICPMS zircon U-Pb dating is approximately 4% (2RSD). The uncertainty in age determination must be considered in order to interpret LA-ICPMS zircon U-Pb data rationally. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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14. New SIMS U-Pb zircon age and its constraint on the beginning of the Nantuo glaciation.
- Author
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Liu, Pengju, Li, Xianhua, Chen, Shouming, Lan, Zhongwu, Yang, Ben, Shang, Xiaodong, and Yin, Chongyu
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ZIRCON , *GLACIATION , *URANIUM-lead dating , *VOLCANOLOGY - Abstract
A new SIMS U-Pb zircon age of 654.2 ± 2.7 Ma was reported from the middle Datangpo Formation in Changyang County of Hubei Province, China. The age is identical with that of 654 ± 3.8 Ma from the top Datangpo Formation in western Hunan Province, revealing that the volcanic activities (~654 Ma) may have occurred widely in South China. The occurrence of the tuff beds (~654 Ma) at different intervals of the Datangpo Formation indicates that the erosion process after the Datangpo deposition varied significantly in different areas. It is thus consequently suggested that the rift in South China was active until the Nantuo glaciation. In addition, the new age confirms that the Nantuo glaciation started much later than 654 Ma. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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15. Petrogenesis of early Yanshanian highly evolved granites in the Longyuanba area, southern Jiangxi Province: Evidence from zircon U-Pb dating, Hf-O isotope and whole-rock geochemistry.
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Tao, JiHua, Li, WuXian, Li, XianHua, and Cen, Tao
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PETROGENESIS ,GRANITE ,ZIRCON ,HAFNIUM isotopes ,GEOCHEMISTRY - Abstract
Early Yanshanian (Jurassic) granitoids are widespread in the Nanling Range, South China. Whereas large granitic batholiths commonly crop out in the center of the Nanling Range (corresponding geographically to the central and northern parts of Guangdong Province), many small stocks occur in the southern part of Jiangxi Province. Most of the small stocks are associated closely with economically significant rare-metal deposits (W, Sn, Nb, Ta). Here we report the results for biotite granites and two-mica granites from three Yanshanian stocks of the Longyuanba complex. LA-ICPMS U-Pb dating of zircon yields an age of 156.1±2.1 Ma for Xiaomubei biotite granite, and U-Pb zircon dating using SIMS yields an age of 156.7±1.2 Ma for Longyuanba-Chengjiang biotite granite and 156.4±1.3 Ma for Jiangtoudong two-mica granite. Biotite granites are silica-rich (SiO=70%-79%), potassic (KO/NaO>1.9), and peraluminous (ASI=1.05-1.33). Associated samples are invariably enriched in Rb, Th, Pb and LREE, yet depleted in Ba, Nb, Sr, P and Ti, and their REE pattern shows a large fractionation between LREE and HREE ((La/Yb)=10.7-13.5) and a pronounced Eu negative anomaly ( δEu=0.28-0.41). Two-mica granite samples are also silica-rich (SiO=75%-79%), potassic (KO/NaO>1.2), and peraluminous (ASI=1.09-1.17). However, in contrast to the biotite granites, they are more enriched in Rb, Th, Pb and extremely depleted in Ba, Nb, Sr, P and Ti, and exhibit nearly flat ((La/Yb)=0.75-1.08) chondrite-normalized REE patterns characterized by strong Eu depletion ( δEu=0.02-0.04) and clear tetrad effect (TE=1.10-1.14). Biotite granites and two-mica granties have comparable Nd isotopic signatures, and their ɛNd( t) are concentrated in the −13.0 to −9.6 and −11.5 to −7.7 respectively. Their zircon Hf-O isotopes of both also show similarity (biotite granites: ɛHf( t)=−10.8-−7.9, δO=7.98‰-8.89‰ and ɛHf( t)= −13.8 to −9.1, δO=8.31‰-10.08‰; two-mica granites: ɛHf( t)=−11.3 to −8.0, δO=7.91‰-9.77‰). The results show that both biotite and two-mica granites were derived mainly from sedimentary source rocks with a minor contribution from mantle-derived materials. In spite of some S-type characteristics, the biotite granites were formed by fractional crystallization of I-type magma and assimilation of peraluminous sedimentary rocks during their ascent to the surface. Therefore, they belong to highly fractionated I-type granites. Two-mica granites exhibit a tetrad effect in their REE patterns, but share the same isotopic features with the biotite granites, suggesting that they are highly fractionated I-type granites as well. Their Lanthanide tetrad effects may be attributed to the hydrothermal alteration by magmatic fluids that have suffered degassing at late stages. Granitic magmas undergoing fractional crystallization and wall-rock assilimation can generate highly evolved granites with no REE tetrad effect in the uni-phase system. However, in the late-stage of magmatic evolution in the multi-phase system (i.e., magmatic-hydrothermal system), these magmas also can lead to the highly evolved granites exhibiting mew-shaped REE pattern characterized by tetrad effect as the consequence of melt-fluid and fluid-vapor fractionation, and the resultant autometasomatism. We thus suggest that the REE pattern exhibiting tetrad effect feature is an important indicator of rare metal mineralization in the early Yanshanian time in southern China, implying the metamorphism of the ore fluid. [ABSTRACT FROM AUTHOR]
- Published
- 2013
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16. Age constraint on Burmese amber based on U–Pb dating of zircons.
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Shi, Guanghai, Grimaldi, David A., Harlow, George E., Wang, Jing, Wang, Jun, Yang, Mengchu, Lei, Weiyan, Li, Qiuli, and Li, Xianhua
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RADIOACTIVE dating ,ZIRCON ,AMBER ,RESOURCE exploitation ,PALEOBIOLOGY - Abstract
Abstract: Amber from northern Myanmar has been commercially exploited for millennia, and it also preserves the most diverse palaeobiota among the worlds'' seven major deposits of Cretaceous amber. Recent estimated ages vary from Albian to Cenomanian, based on palynology, an ammonoid, and Mesozoic insect taxa preserved within the amber. The burmite-bearing rock is sedimentary and consists mainly of rounded lithic clasts (0.03∼0.15mm in diameter), with minor fragments of quartz and feldspar. Among the lithic clasts are mostly volcanic rocks. Zircons separated from the amber matrix form two groups: Group-I zircons are overgrown and have variable CL patterns, experienced slight geological disturbances after they formed, and their Ion microprobe
206 Pb/238 U ages fall into a very narrow range of ∼102Ma–∼108Ma; Group-II zircons are typical magmatic ones with rhythmically flat zones, inferred to be derived from volcanic rock clasts, and yielded a concordia206 Pb/238 U age of 98.79±0.62Ma. The dating on Group-I zircons is only for their interiors, thus hiding what age excursion might come from the overgrowth. Considering the nearshore marine environment and 1-m thickness of the burmite-bearing sediments, and the syn- and post-eruption deposition of volcanic clasts, the age of 98.79±0.62Ma therefore can be used as a maximum limit for the burmite (either at or after), establishing an earliest Cenomanian age for the fossilized inclusions. The age also indicates that volcanic eruption occurred at 98.79±0.62Ma in the vicinity of the Hukawng Valley. [Copyright &y& Elsevier]- Published
- 2012
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17. In situ U-Pb dating of titanite by LA-ICPMS.
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Sun, JinFeng, Yang, JinHui, Wu, FuYuan, Xie, LieWen, Yang, YueHeng, Liu, ZhiChao, and Li, XianHua
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SPHENE ,URANIUM-lead dating ,MATRIX effect ,INDUCTIVELY coupled plasma mass spectrometry ,LASER ablation ,ZIRCON ,CRETACEOUS Period - Abstract
Titanite is an ideal mineral for U-Pb isotopic dating because of its relatively high U, Th and Pb contents. Here, we developed a technique for U-Pb dating of titanite using the 193 nm ArF laser-ablation system and Agilent 7500a Q-ICP-MS. Standards of titanite (BLR-1 and OLT-1) and zircon (91500 and GJ-1) were dated using single spot and line raster scan analytical methods. To check the matrix effect, titanite (BLR-1) and zircon (91500) standards were analyzed as the external standards. The weighted mean Pb/U ages of OLT-1 titanite are 1015±5 Ma (2 σ, n=24) and 1017±6 Ma (2 σ, n=24) by single spot and line raster scan analyses, respectively, using BLR-1 titanite as the external standard. These ages are consistent with its reference age of about 1014 Ma. However, using 91500 zircon as the external standard, the weighted mean Pb/U ages are 917±4 Ma (2 σ, n=24) and 927±5 Ma (2 σ, n=24) for BLR-1 titanite, and 891±4 Ma (2 σ, n=24) and 901±5 Ma (2 σ, n=24) for OLT-1 titanite by single spot and line raster scan analyses, respectively. It is evident that these ages are ∼12% younger than their reference values. Our results reveal that significant matrix effect does exist between different kinds of minerals during LA-ICPMS U-Pb age determination, whereas it is insignificant between same minerals. Therefore, same mineral must be used as the external standard for fractionation corrections during in situ LA-ICPMS U-Pb age analysis. In addition, we determined U-Pb ages for titanites from the Early Cretaceous Fangshan pluton, which indicates a rapid cooling history of this pluton. [ABSTRACT FROM AUTHOR]
- Published
- 2012
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18. Zircon SHRIMP U-Pb dating for the Cangshuipu volcanic rocks and its implications for the lower boundary age of the Nanhua strata in South China.
- Author
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Wang Jian, Li Xianhua, Duan Taizhong, M., Liu Dunyi, Song Biao, Li Zhongxiong, M., and Gao Yonghua, M.
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ARCHAEOLOGICAL dating , *ZIRCON , *VOLCANIC ash, tuff, etc. , *GEOCHRONOMETRY - Abstract
Discusses the Zircon SHRIMP uranium-lead dating for the Cangshuipu volcanic rocks and its implications for the lower boundary age of the Nanhua strata in South China. Occurrence of the continental volcanic rocks and volcaniclastic sedimentary conglomerates of the Cangshuipu Formulation in Yiyang of Hunan Province; Configuration of the strata in the Yiyang region; Representation of the lower boundary with a younger age than previously reported.
- Published
- 2003
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19. Age and origin of the Tanghu Granite, southeast China: Results from U-Pb single zircon and Nd isotopes
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Li Xianhua, Wayne R. Premo, Gui Xun-Tang, and M. Tatsumoto
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Igneous rock ,Proterozoic ,Batholith ,Archean ,Pluton ,Geochemistry ,Geology ,Radiometric dating ,Mantle (geology) ,Zircon - Abstract
U-Pb single-zircon and Sm-Nd whole-rock isotopic data for the Tanghu Granite of the Zhuguangshan batholith suggest that a basement either composed of or derived from Middle Proterozoic to Late Archean rocks underlies southeast China The granite contains two kinds of inherited zircon components, whole anhedral zircons and small cores within younger magmatic zircons. The U-Pb data for a single analysis of four magmatic zircons yielded a concordant age of 433 ±2 Ma, whereas single zircons yielded two linear arrays with lower intercepts of 435 ±1 and 434 ±14 Ma and upper intercepts of 1415 ±3 and 2516 ±6 Ma, respectively. Xenocrystic zircons of Archean age had not previously been recognized in any rocks from southeast China Two whole-rock samples from the granite yielded ϵNd values of -7.1 and -8.3 at 434 Ma and Nd model ages of ∼1750 Ma relative to a depleted mantle. We conclude from this isotope data that the Tanghu Granite crystallized at 434 ±1.6 Ma (weighted average) and was derived from a source of unknown age, but had an average crustal-residence age of ∼1750 Ma, and was partially composed of a mixture of continental crustal material of at least two ages (∼1400 and ∼2500 Ma).
- Published
- 1989
20. Zircons underestimate mantle depletion of early Earth.
- Author
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Liou, Peng, Guo, Jinghui, Mitchell, Ross N., Spencer, Christopher J., Li, Xianhua, Zhai, Mingguo, Evans, Noreen J., Li, Yanguang, McDonald, Bradley J., and Jin, Mengqi
- Subjects
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ZIRCON , *PLATE tectonics , *ZIRCON analysis , *ISOTOPIC analysis , *PETROGENESIS - Abstract
The mechanism and timing of crustal growth and differentiation on early Earth are debated. Evidence of crustal differentiation is detectable as deviations from Earth's assumed chondritic uniform reservoir (CHUR) as crust is extracted from the mantle leading to a melt-depleted reservoir. For the long-lived zircon Lu-Hf system, no incontrovertible evidence of significant mantle depletion >3.8 Ga exists. We conduct combined U-Pb and Lu-Hf isotopic analyses for the detrital zircon from the Caozhuang supracrustal sequence in North China. The zircon Hf isotopic compositions are broadly scattered along the CHUR evolution line. However, given the possibility of potential systematic biases in zircon petrogenesis and the unique tectonic setting of early Earth, we posit that magmatism controlled by the nascent forms of plate tectonics during the Eoarchean could have likely hidden the degree of ancient crust-mantle differentiation. The non-depleted zircon Hf isotopes observed in North China and globally during early Earth may in verity imply the existence of ubiquitous depleted mantle domains at that time. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
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21. Oxygen isotopic alteration rate of continental crust recorded by detrital zircon and its implication for deep-time weathering.
- Author
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Li, Gaojun, Yang, Ruiyu, Xu, Zhewen, Hartmann, Jens, Hedding, David W., Li, Xianhua, Ernst, Richard E., Li, Zhong-Hai, Zou, Hao, Li, Zhongquan, and Chen, Jun
- Subjects
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CHEMICAL weathering , *ZIRCON , *SUPERCONTINENT cycles , *WEATHER control , *OXYGEN isotopes , *LONG-Term Evolution (Telecommunications) , *CONTINENTAL crust - Abstract
• Oxygen isotope alteration rate of continental crust retrieved from zircon record. • Oxygen isotope alteration rate of continental crust is controlled by weathering. • Weathering history is linked to major evolution events of the Earth system. Weathering plays a significant role in the Earth system through the exchange of material among the lithosphere, atmosphere, hydrosphere, and biosphere. Variation of continental weathering in deep-time, however, remains elusive. This work investigates continental weathering recorded by detrital zircon. Zircon can record the oxygen isotopic composition (δ 18 O) of its parent crust at the time of crystallization, the value of which principally reflects the time-integrated effect of crustal alteration. The Hf isotopes and U-Pb isotopes of zircon also help to constrain the alteration history between crust generation and zircon crystallization. A new algorithm is introduced to reconstruct the average δ 18 O alteration rate of continental crust (R δ 18O-CC) through time by solving a set of linear equations based on a large population of detrital zircons with varying temporal coverage across the history of crustal alteration. A nearly three-billion-year history of R δ 18O-CC from 3.2 Ga to 0.3 Ga can be reconstructed using more than 5,000 globally distributed detrital zircons with coupled U-Pb-Hf-O isotopic records. The reconstructed R δ 18O-CC shows an overall bell-shape long-term evolution centered at ∼2 Ga superposed with variations that are coupled with supercontinental assembly cycles. The long-term evolution of the reconstructed R δ 18O-CC seems to be correlated with solid-earth CO 2 degassing expected from the age distribution of deleted mantle and the supercontinental cycles. Thus, the R δ 18O-CC is interpreted to reflect weathering considering the control of solid-earth CO 2 degassing on the total weathering flux of continental crust. However, independent evidence on the solid-earth CO 2 degassing is unavailable, interpreting R δ 18O-CC as a weathering record requires further testing. Nevertheless, this work provides an example of how the time-integrated signal, with large noise-to-signal ratio, preserved in geological archives can be deconvolved using a large dataset. The result also demonstrates the great potential that weathering history may have in reconstructing the operation of the Earth system across deep-time. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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22. Timing of eclogite facies metamorphism in the North Qinling by U–Pb and Lu–Hf geochronology
- Author
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Cheng, Hao, Zhang, Chao, Vervoort, Jeffrey D., Li, Xianhua, Li, Qiuli, Wu, Yuanbao, and Zheng, Shu
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ECLOGITE , *METAMORPHISM (Geology) , *ZIRCON , *GEOLOGICAL time scales , *PETROLOGY , *SUBDUCTION - Abstract
Abstract: Although petrologic data from the North Qinling orogen in central China have provided essential information on the geodynamic history of the orogenic cycle, the timing of the continental collision between the North China block and the South China block in the North Qinling orogen remains essentially unconstrained. To refine existing geodynamic models, two eclogites from the North Qinling were dated by U–Pb and Lu–Hf geochronology. The upper limit of the pressure during the eclogite facies metamorphism was restricted within the quartz stability field at 2.6–2.8GPa within a temperature range of 660–710°C by combining conventional thermobarometry and pseudosection estimates. Mineral–whole rock dating for multi-garnet-(omphacite) fractions from two localities yielded ages of 516.4±5.8Ma (2σ) and 494.3±2.7Ma (2σ) with corresponding weighted mean zircon 206Pb/238U ages of 507.0±8.7Ma (2σ) and 490.0±4.1 (2σ) Ma, respectively. Garnet porphyroblasts from the two samples bore evidence of prograde elemental zonation, but the major portion of the garnet grains grew exclusively under eclogite facies conditions as indicated by the occurrence of omphacite inclusions from core to rim. Therefore, these Lu–Hf ages were interpreted to reflect high-pressure eclogite facies metamorphism. The difference between the two Lu–Hf ages likely represents the minimum duration of garnet growth and thus brackets the onset and the closure of the subduction. These results allow for more detailed insight into the subduction history of the North Qinling orogen. These new U–Pb and Lu–Hf ages mark the timing of the onset of the continental collision between the North China block and the South China block in the Qinling belt, suggesting that the entry of the leading edge of the South China block continent into the North China block trench occurred from ca. 516Ma to 490Ma in the North Qinling orogen. [Copyright &y& Elsevier]
- Published
- 2012
- Full Text
- View/download PDF
23. Contrasting zircon Hf and O isotopes in the two episodes of Neoproterozoic granitoids in South China: Implications for growth and reworking of continental crust
- Author
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Zheng, Yong-Fei, Zhang, Shao-Bing, Zhao, Zi-Fu, Wu, Yuan-Bao, Li, Xianhua, Li, Zhengxiang, and Wu, Fu-Yuan
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ZIRCON , *CRYSTAL growth , *HEAT transfer , *MASS transfer - Abstract
Abstract: The genetic links among rift magmatism, crustal growth and water–rock interaction are an important issue about mass and heat transfer between mantle and crust during supercontinent breakup. A combined study of Hf and O isotopes in zircons from Neoproterozoic granitoids in South China provides evidence for growth and reworking of juvenile and ancient crusts with different styles of water–rock interactions along rift tectonic zones. Two generations of the granitoids show contrasting features in both zircon Hf and O isotope compositions, indicating their distinct petrogenesis. The ∼825 Ma granitoids exhibit negative ε Hf(t) values of −3.4±0.8 to −1.6±0.8 with old model Hf ages of 1.81±0.07 to 1.92±0.10 Ga, and high δ 18O values of 8.7 to 10.4‰. These indicate that the source material of granitoid magmas was derived from melting of Paleoproterozoic basement that has the Hf isotope signature similar to the enriched mantle but experienced chemical weathering process before anatexis. Reworking of ancient crust is demonstrated to occur at ∼825 Ma in the orogenic collapse zone, with overprinting of subsolidus hydrothermal alteration during magma emplacement. In contrast, the 760–750 Ma bimodal intrusives are characterized by positive ε Hf(t) values of 3.5±0.8 to 9.9±0.8 with young model Hf ages of 0.94±0.06 to 1.18±0.06 Ga, and both low and high δ 18O values of 4.2 to 6.2‰ relative to 5.3±0.3‰ for the normal mantle zircon. Prompt reworking of juvenile crust is suggested to occur at ∼750 Ma in the rifted tectonic zone, with occurrence of supersolidus hydrothermal alteration and local low-18O magmatism during supercontinent breakup. Contributions of the depleted mantle to their magma sources are contrasting in the two episodes of magmatism in association with breakup of the supercontinent Rodinia. While the change in melt source from the crust to the mantle keeps pace with the advance from continental rifting to supercontinent breakup, significant transport of both heat and material from the depleted mantle to the continental crust only occurred along the active rifting zone. In either case, the growth and reworking of continental crust are episodically associated with rift magmatism. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
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