Major Characteristics of the Lajishan Orogenic Belt of the South Qilian Mountains and Its Geotectonic Attribute

Yang, Wei; Qing-lu, Deng; Wu, Xiaoxia

doi:10.1111/j.1755-6724.2002.tb00076.x

Cited by 17 publications

(1 citation statement)

References 3 publications

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“…The Central Qilian Block is primarily composed of basement rocks from the Neoproterozoic Huangyuan Group and Huangzhong Group metamorphic rocks. The U–Pb age of zircons from the Huangyuan Group granite correspond to 910 ± 6.7 Ma and 917 ± 12 Ma (Guo et al, 2000; Yang et al, 2002). In contrast, the South Qilian Block is mainly composed of medium‐ to high‐grade metamorphic rocks of the Paleoproterozoic Hualong Group (Guo & Li, 1999; Yan et al, 2015).…”

Section: Geological Settingmentioning

confidence: 99%

The giant ShangzhuangREE‐rich apatite deposit, western China: Genesis by ultramafic magma differentiation

Wang¹,

Chen

Wan-wen³

et al. 2023

Geological Journal

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The origin of giant rare earth element (REE)‐rich phosphorus deposits related to ultramafic rocks is unclear. To characterize the genetic linkage between ultramafic rocks and P–REE mineralization, we investigated the whole‐rock geochemistry, geochronology and Hf isotopic compositions, along with previously published data of barren and ore‐bearing clinopyroxenites from the giant Shangzhuang REE‐rich apatite deposit (containing about 51.1 million tonnes of P2O5 and 157,400 tonnes of REEs) in the Lajishan suture, Western China. The P–REE ores and barren biotite clinopyroxenites are composed predominantly of clinopyroxene and biotite, with high levels of apatite, amphibole, allanite, sulfide and oxide minerals in the ore‐bearing samples. Zircon and allanite U–Pb ages for the barren and ore‐bearing clinopyroxenites indicate they were formed between 467 and 465 Ma. The barren and ore‐bearing samples are characterized by high CaO and low SiO2 contents, as well as similar Hf isotope ratios (εHf[t]: +3.4 to +7.7), indicating that they represent an ultramafic magma system and have been derived from a similar source. They are enriched in light REEs and depleted in Nb–Ta–Zr–Hf–Ti, similar to arc‐related lavas found worldwide. The weakly evolved barren samples have high Ba/La, Rb/Y and Dy/Yb values, and their ages are coeval with calc‐alkaline granitic plutons in the belt, which postdate the formation of the Lajishan ophiolite by ~30 myr. This suggests that the primary magma originated from garnet peridotite mantle modified by subducted Proto‐Tethys oceanic crust‐derived fluids in an arc setting. The presence of apatite intergrowth with cumulus clinopyroxene without alteration features indicates that the deposit has a magmatic origin. The ore‐bearing clinopyroxenite contains higher contents of P, REEs, and high‐field‐strength elements than the barren clinopyroxenite, which could be attributed to the in situ accumulation of apatite and allanite in the residual magma. Thus, the formation of the P‐dominated orebodies results from phosphate saturation due to the extensive fractionation crystallization of clinopyroxene and biotite during magmatic evolution. REEs were primarily enriched in the late‐stage melt, which was compatible with apatite and allanite. We propose that the formation of the Shangzhuang REE‐rich apatite deposit can be attributed to a simple differentiation of ultramafic melts in an evolved magmatic system.

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Section: Geological Settingmentioning

confidence: 99%

The giant ShangzhuangREE‐rich apatite deposit, western China: Genesis by ultramafic magma differentiation

Wang¹,

Chen

Wan-wen³

et al. 2023

Geological Journal

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The nature and history of the South Qilian orogenic belt: Constraints from compositions of rivers' sediments and their detrital zircon U–Pb geochronology, Lu‐Hf isotopic compositions

Kang

Chen

2019

Geological Journal

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Detrital zircon U-Pb dating, Hf isotopic data, and Nd isotopic compositions of river sediments are used to constrain crustal evolution processes of their provenance in the South Qilian orogenic belt. The detrital zircons from the Yuka, Tataleng, and Bayinguole rivers range in age from Neoarchean (2,772 Ma) to Permian (261 Ma), with age peaks at ca. 2.4 Ga, ca. 1.95 Ga, and ca. 0.45 Ga. Hf isotopic compositions of Paleoproterozoic, Pan-African, and Caledonian zircon age groups display a wide range of ε Hf (t) values, suggesting diverse sources of host magma of the zircon grains. The basement formation of the South Qilian orogenic belt from depleted mantle occurred at two stages; ca. 3.1-2.5 Ga and ca. 2.0-1.6 Ga. Meanwhile, the Nd model ages of silt-mud from the region are between 1.98 Ga and 2.27 Ga with an average value of 2.12 Ga. Our study indicates that the Qilian oceanic plate formed between the Qaidam and Alxa blocks from late Neoproterozoic to Silurian. The South Qilian orogenic belt is a product of the Qilian Ocean closure and subsequent collision between the Qaidam Block and central Qilian belt during Ordovician-Silurian times. Combining regional tectonothermal events with new results of river sediments suggests that rifting from a continent and opening of the Qilian Ocean occurred at ca. 780-520 Ma, subduction of the oceanic crust at ca. 520-440 Ma, ocean closure and continental subduction at ca. 440-420 Ma, exhumation of subducted crust at ca. 420-400 Ma, and orogenic collapse and extension at ca. 400-360 Ma. KEYWORDS detrital zircon, formation and evolution of crust, Nd isotope, Qilian oceanic plate, South Qilian orogenic belt, U-Pb-Hf isotopes

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Early Cambrian Muli arc–ophiolite complex: a relic of the Proto-Tethys oceanic lithosphere in the Qilian Orogen, NW China

Yan

Aitchison

et al. 2019

Int J Earth Sci (Geol Rundsch)

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Major Characteristics of the Lajishan Orogenic Belt of the South Qilian Mountains and Its Geotectonic Attribute

Cited by 17 publications

References 3 publications

The giant ShangzhuangREE‐rich apatite deposit, western China: Genesis by ultramafic magma differentiation

The giant ShangzhuangREE‐rich apatite deposit, western China: Genesis by ultramafic magma differentiation

The nature and history of the South Qilian orogenic belt: Constraints from compositions of rivers' sediments and their detrital zircon U–Pb geochronology, Lu‐Hf isotopic compositions

Early Cambrian Muli arc–ophiolite complex: a relic of the Proto-Tethys oceanic lithosphere in the Qilian Orogen, NW China

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