Petrogenesis, tectonic setting and formation age of the metaperidotites in the Lajishan ophiolite, Central Qilian Block, NW China

Zhao, Jing; Long, Xiaoping; Dong, Yunpeng; Li, Jie; Gao, Yilin; Zhao, Bingshuang

doi:10.1016/j.jseaes.2019.104076

Cited by 11 publications

(4 citation statements)

References 94 publications

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“…These oceanic basalts contain low Nb/Yb ratios (0.41–0.59), high Zr/Nb ratios (43.65–79.40), and high ε Nd (t) values greater than 0 (6.1–8.4), which are reliable evidence for a depleted mantle source (Basta, Maurice, Bakhit, Ali, & Manton, 2011; He et al, 2010; H. F. Zhang, Wu, & Lin, 2012). On the other hand, recent studies on mantle peridotites from the ophiolites in the Qilian Orogenic Belt demonstrated that the lithospheric mantle probably experienced at least once melt extraction before the onset of the Palaeozoic oceans (J. Zhao et al, 2019, 2021). In other words, the mantle source had already become depleted prior to the generation of these oceanic basalts.…”

Section: Discussionmentioning

confidence: 99%

“…On the other hand, recent studies on mantle peridotites from the ophiolites in the Qilian Orogenic Belt demonstrated that the lithospheric mantle probably experienced at least once melt extraction before the onset of the Palaeozoic oceans (J. Zhao et al, 2019Zhao et al, , 2021. In other words, the mantle source had already become depleted prior to the generation of Pearce & Norry, 1979).…”

Section: Refractory Nature Of the Mantle Sourcementioning

confidence: 99%

“…Previous studies have already demonstrated that ophiolites always provide significant constraints on crust–mantle interactions (Aldanmaz, Schmidt, Gourgaud, & Meisel, 2009), metamorphism (J. P. Zheng, Xiong, Zhao, & Li, 2019), mantle heterogeneity (Khedr, Arai, Python, & Tamura, 2014; Uysal, Ersoy, Dilek, Kapsiotis, & Sarıfakıoğlu, 2016), fluid/melt metasomatism (H. Liu & Zhang, 2019; J. Zhao et al, 2021), and magmatism (Perez et al, 2013; Safonova et al, 2012; Y. Q. Zhang et al, 2017). Most importantly, ophiolites can serve as the best candidates for further understanding of the tectonic evolution of ancient oceans and associated orogenic belts (e.g., Dong et al, 2008; Shervais, 2001; J. F. Xu, Zhang, & Han, 2008; J. Zhao et al, 2019). Dilek and Furnes (2014) recently summarized that “a completed ophiolitic sequence includes upper mantle peridotites, layered ultramafic‐mafic rocks, layered to isotopic gabbros, sheeted dikes, extrusive rocks, and a sedimentary cover from bottom to top.” A representative example would be the Noorabad‐Harsin ophiolite in Iran (Tahmasbi, Kiani, & Khalaji, 2016).…”

Section: Introductionmentioning

confidence: 99%

“…Dilek and Furnes (2014) recently summarized that “a completed ophiolitic sequence includes upper mantle peridotites, layered ultramafic‐mafic rocks, layered to isotopic gabbros, sheeted dikes, extrusive rocks, and a sedimentary cover from bottom to top.” A representative example would be the Noorabad‐Harsin ophiolite in Iran (Tahmasbi, Kiani, & Khalaji, 2016). In fact, with respect to ultramafic rocks, which are easily altered and dismembered owing to late‐stage tectonic movements (e.g., Tadesse & Allen, 2005; J. Zhao et al, 2019, 2021; R. G. Zheng, Wu, Zhang, Xu, & Meng, 2013), most of these oceanic crust rocks (e.g., basalt and gabbro) are well preserved in oceanic subduction zones and witness the opening‐subduction transition of the oceans.…”

Section: Introductionmentioning

confidence: 99%

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Compositional and Sr‐Nd isotopic features of the Xiejiayao ophiolite in the North Qilian Orogenic Belt, NW China: Implications for the petrogenesis and tectonic setting

Zhao

et al. 2022

Geological Journal

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The ophiolites along the North Qilian Orogenic Belt are considered to be fragments of ancient oceanic crusts and lithospheric mantle of the Palaeozoic North Qilian Ocean (a branch of the Proto‐Tethys). Compared with other ophiolites in this belt, the genesis of the Xiejiayao ophiolite has been poorly studied so far, making it difficult to understand the tectonic evolution of the ocean. In this study, we present new compositional and Sr‐Nd isotopic analyses of basaltic rocks from the Xiejiayao ophiolite to shed light on its petrogenesis and geodynamic background. These oceanic basalts are characterized by flat REE patterns, low elemental ratios of high‐field‐strength elements (e.g., La/Sm, Sm/Yb, La/Yb, Gd/Yb, [Th/Yb]PM) and abundant spinels, implying that they were generated via partial melting in the spinel stability field of the mantle. Their positive εNd(t) values (6.1–8.4), high Zr/Nb (43.65–79.40) as well as low Nb/Ta (10.91–15.09), Zr/Hf (34.64–39.28), and Nb/Yb (0.41–0.59) ratios further reflect that the ancient mantle had already become depleted to some extent before the onset of the Palaeozoic ocean. Additionally, basalts share many geochemical similarities (e.g., Zr, Y, Ti, and V) with both mid‐ocean ridge and island arc basalts. This supports the strong likelihood of origin in a back‐arc basin close to the suprasubduction zone for the ophiolite. Therefore, accompanied by the northward subduction of the oceanic lithosphere during the early Palaeozoic, a large‐scale back‐arc basin developed progressively in response to the back‐arc expansion. The Xiejiayao basaltic magmas were generated in the back‐arc basin via partial melting of the depleted mantle and their source was probably mixed with subducted melts/fluids from the dehydration and melting of oceanic slabs and sediments.

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Section: Discussionmentioning

confidence: 99%

Section: Refractory Nature Of the Mantle Sourcementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Compositional and Sr‐Nd isotopic features of the Xiejiayao ophiolite in the North Qilian Orogenic Belt, NW China: Implications for the petrogenesis and tectonic setting

Zhao

et al. 2022

Geological Journal

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Emplacement ages and petrogenesis of intermediate‐acid intrusive rocks in the Lajishan region of the Central Qilian Belt, China: Constraints from zircon U–Pb ages, Hf isotopes, and whole‐rock geochemistry

Wang

Jing

et al. 2021

Geological Journal

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As a major tectonic unit along the southwestern rim of the Central Qilian Belt, the Lajishan region plays an important role in the amalgamation of continental plates in the Qilian Orogenic Belt. In this study, zircon laser ablation inductively coupled plasma mass spectrometry for U–Pb dating and Hf isotope analysis, as well as geochemical analysis of intermediate‐acid intrusive rocks from the Lajishan area were conducted. Results show that formation ages of the intermediate‐acid intrusive rocks are 438–452 Ma. Whole‐rock geochemistry results show that the diorite and monzodiorite are metaluminous, low‐ to medium‐K series, and characterized by obvious Nb, Ta, and Ti depletions as well as large‐ion lithophile element and light rare earth element enrichments. The εHf(t) values of zircons from monodiorite range from +2.71 to +10.59 and the two‐stage model ages range from 751 to 1,253 Ma. A large transversal span of εHf(t) values suggests that the source of depleted mantle was mixed with a small amount of older crustal material. The diorite and monzodiorite show a covariant relationship between εHf(t) values and Th/U ratios, which imply the existence of source heterogeneity. The diorites and monzodiorites were most likely produced in an arc setting. The granites are low K in composition and metaluminous to weakly peraluminous. In view of obvious Nb, Ta, and Ti depletions as well as large‐ion lithophile element and light rare earth element enrichments, parent magmas of the granites are suggested to have formed with the participation of crustal source materials. The εHf(t) values of zircons from granite range from +5.82 to +8.90, and the two‐stage model ages range from 861 to 1,057 Ma, indicating that magmas of the granites were mainly derived from partial melting of depleted mantle or juvenile thickened lower crust. The granites were most likely produced in an arc setting and share a similar source with the diorite and monzodiorite. Correlation between major oxides and SiO2 show that during the formation of the three kinds of rocks, crystallization and differentiation both played important roles. Combined with published data from the Central Qilian Belt and its vicinity, our results conclude that the northward subduction of oceanic crust contributed to the formation of an Early Palaeozoic subduction–accretion system in the Lajishan region. This model reveals a tectonic–magmatic thermal event and provides important insights into the tectonic evolution process in the Qilian region, as well as the Central Orogenic Belt during the Early Palaeozoic.

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Mineral chemistry and geochemistry of serpentinites from the Bianmagou ophiolite in the North Qilian Belt, NW China: Implications for protoliths, melt extractions, and melt/fluid metasomatism

et al. 2021

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The North Qilian Belt in northwestern China contains a large number of ophiolites. Most ultramafic rocks from the ophiolites have been entirely transformed into serpentinites because of extensive serpentinization, making it difficult to determine their origin and tectonic significance and further hindering advancements in the understanding of the evolutionary history of the Palaeozoic North Qilian Ocean. In this study, we present new mineral chemistry and whole‐rock geochemistry analyses (including rare earth elements, [REE]) for the serpentinites from the Bianmagou ophiolite to discuss their protoliths, geodynamic environment, melt extractions, and melt/fluid interactions. The mineral chemistry of the relic minerals (e.g., olivine, orthopyroxene, and spinel) and the whole‐rock geochemical compositions (e.g., Mg#, Ni, etc.) strongly demonstrate that the protoliths of the serpentinites were refractory mantle residues after melt extractions and probably emplaced into a tectonic regime of mid‐ocean ridge akin to abyssal peridotites. They experienced high degrees of partial melting (15–20%) recorded by spinel Cr# values and bulk incompatible elements (e.g., Ti, heavy rare‐earth element), resulting from multiple episodes of melt depletion in the lithospheric mantle. Moreover, the serpentinites commonly have U‐shaped chondrite‐normalized REE patterns. The significantly elevated LREEs probably reflect the early partial‐melting processes overprinted by later melt‐dominated metasomatism. The medium to strong enrichment of certain fluid‐mobile elements (e.g., U, Pb, Ba, Sr, As, etc.) in the studied serpentinites was a consequence of the fluid/rock interactions during serpentinization. Overall, despite the variable serpentinization they experienced, this study indicates that the mineral chemical and geochemical proxies of serpentinites provide reliable constraints on the petrogenesis and mantle metasomatism of ancient ophiolites.

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Petrogenesis, tectonic setting and formation age of the metaperidotites in the Lajishan ophiolite, Central Qilian Block, NW China

Cited by 11 publications

References 94 publications

Compositional and Sr‐Nd isotopic features of the Xiejiayao ophiolite in the North Qilian Orogenic Belt, NW China: Implications for the petrogenesis and tectonic setting

Compositional and Sr‐Nd isotopic features of the Xiejiayao ophiolite in the North Qilian Orogenic Belt, NW China: Implications for the petrogenesis and tectonic setting

Emplacement ages and petrogenesis of intermediate‐acid intrusive rocks in the Lajishan region of the Central Qilian Belt, China: Constraints from zircon U–Pb ages, Hf isotopes, and whole‐rock geochemistry

Mineral chemistry and geochemistry of serpentinites from the Bianmagou ophiolite in the North Qilian Belt, NW China: Implications for protoliths, melt extractions, and melt/fluid metasomatism

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