Middle Jurassic MORB-type gabbro, high-Mg diorite, calc-alkaline diorite and granodiorite in the Ando area, central Tibet: Evidence for a slab roll-back of the Bangong-Nujiang Ocean

Yan, Haoyu; Long, Xiaoping; Wang, Xuan‐Ce; Li, Jie; Wang, Qiang; Yuan, Chao; Sun, Min

doi:10.1016/j.lithos.2016.09.002

Cited by 30 publications

(34 citation statements)

References 102 publications

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“…We therefore infer that they formed either through partial melting of pre-existing crustal materials or via assimilation, fractionation, and contamination (AFC) processes from mafic magma and will evaluate the two mechanisms based on their geochemical composition and regional geology as below. and were likely generated by partial melting of ancient lower crust, followed by variable degrees of mixing with mantle-derived magma (M. Liu et al, 2010;Yan et al, 2016). Although the Amdo volcanic rocks in this study are contemporaneous with these intrusive rocks, they have different source regions because of their distinct major-and trace-element and Sr-Nd-Hf isotopic compositions.…”

Section: Petrogenesis Of the Amdo Volcanic Rocksmentioning

confidence: 85%

“…Mantle-derived magmas that underplated the base of continental crust in an active continental margin will generally undergo melt, assimilation, storage, and homogenization (MASH) processes (e.g., Annen, Blundy, & Sparks, 2006;Hildreth & Moorbath, 1988). However, the Amdo volcanic rocks have similar (or more depleted) Sr-Nd isotopic compositions to the Jurassic gabbros exposed in the Amdo region (Yan et al, 2016; Figure 7a). As shown in Figures 7a and 8, only a small volume of Amdo basement material incorporating into such gabbro will increase the initial 87 Sr/ 86 Sr and decrease ε Nd isotopic composition considerably that is inconsistent with the feature of the Amdo volcanic rocks.…”

Section: Petrogenesis Of the Amdo Volcanic Rocksmentioning

confidence: 99%

“…First, in the Amdo region, subduction of the BNO crust was directed northward (e.g., Guynn et al, 2006;M. Liu et al, 2010;Yan et al, 2016). Therefore, if the Amdo volcanic rocks formed due to heat transfer from a back-arc basin (Hanyu et al, 2006), they should be located close to the southern branch of the Amdo ophiolite.…”

Section: Figurementioning

confidence: 99%

“…Magmatic rocks in the Amdo region mainly comprise Early-Middle Jurassic granites with minor Neoproterozoic, Cambrian, and Cretaceous granite genesis (Bai et al, 2005;Kapp et al, 2005;M. Liu et al, 2010;Yan et al, 2016;K. J. Zhang, Zhang, et al, 2012;Zhu et al, 2011).…”

mentioning

confidence: 99%

“…(b) Also shown are the suggested fields in which silicic magmas generated by partial melting of MOR gabbro and fractional crystallization of MOR basalt magma should plot(Koepke, Berndt, Feig, & Holtz, 2007). Previously acquired data for the Amdo volcanic rocks are fromLi et al (2017); Amdo granodiorite data are fromYan et al (2016); Amdo diorite-granite data are from M Liu et al (2010)Lai and Liu (2003) and X.…”

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confidence: 99%

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Petrogenesis of Early Jurassic (ca. 181 Ma) dacitic–rhyolitic volcanic rocks in the Amdo ophiolite mélange, central Tibetan Plateau: Low‐pressure partial melts of Bangong–Nujiang Tethys oceanic crust?

Zeng

et al. 2019

Geological Journal

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The identification of oceanic-crust-derived melts is critical to improving our understanding of oceanic lithosphere subduction in various geodynamic settings. However, low-pressure melts derived from the oceanic crust can be misidentified because their compositions are often indistinguishable from those of typical arc-related rocks. In this study, we report geochronological and geochemical data for the Amdo volcanic rocks in the central Tibetan Plateau. Zircon U-Pb dating indicates that they were generated in the Early Jurassic (ca. 181 Ma), simultaneous with spatially associated MORB-like rocks of the Amdo ophiolite. The Amdo volcanic rocks are characterized by high SiO 2 and Na 2 O concentrations, low MgO, K 2 O, and Fe 2 O 3 T concentrations, and low Mg# values. They are enriched in light rare earth and large-ion lithophile elements, display negative Eu, Nb, and Ta anomalies, and yield low Sr (<360 ppm) and high Y (up to 57.6 ppm) concentrations with low Sr/Y ratios (<15.4). Whole-rock Sr-Nd and zircon Hf isotopic compositions (( 87 Sr/ 86 Sr) i = 0.7040-0.7058, ε Nd (t) = +3.9to +6.8, and zircon ε Hf (t) = +13.9 to +17.9) are different from those of regional continental-crust-derived granitoids but similar to those of contemporary MORBlike rocks that occur in regional ophiolites. Furthermore, zircon from the Amdo volcanic rocks yields U/Yb ratios similar to those of oceanic zircon. These characteristics, combined with regional geological observations, indicate that the Amdo volcanic rocks are a component of the Amdo ophiolite mélange and represent low-pressure partial melts of oceanic crust, generated during incipient northward subduction of the Bangong-Nujiang oceanic lithosphere beneath the Qiangtang terrane. Our study helps to constrain the history of the Bangong-Nujiang Ocean and provides a case study on the low-pressure melting of oceanic crust.

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Section: Petrogenesis Of the Amdo Volcanic Rocksmentioning

confidence: 85%

Section: Petrogenesis Of the Amdo Volcanic Rocksmentioning

confidence: 99%

Section: Figurementioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Petrogenesis of Early Jurassic (ca. 181 Ma) dacitic–rhyolitic volcanic rocks in the Amdo ophiolite mélange, central Tibetan Plateau: Low‐pressure partial melts of Bangong–Nujiang Tethys oceanic crust?

Zeng

et al. 2019

Geological Journal

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Geochronology, geochemistry, origin, and tectonic implications of high‐pressure mafic granulites of the Amdo region, Central Tibet

et al. 2020

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The Amdo Terrane, Central Tibet, was previously located in the middle of the Bangong-Nujiang Ocean (BNO), and is key to understanding the subduction history of the BNO. However, the high-pressure (HP) mafic granulites of the Amdo Terrane remain poorly studied. Here, we report the petrology, geochemistry, and zircon U-Pb geochronology of the Amdo HP mafic granulites. The granulites occur mainly as enclaves or deformed dikes in granitic gneisses of the Amdo Terrane. Zircons from the granulites yield two clusters of ages, at 193-192 and 180 Ma. The former represents the best estimate of the age of peak metamorphism, and the latter represents the age of retrograde amphibolite-facies metamorphism. Although the contents of mobile elements in the granulites, including the large-ion lithophile elements (Rb, Sr, Cs, Pb, K), were significantly altered during metamorphism, the contents of the highfield-strength elements (HFSEs; Th, Nb, Zr, Ti) and rare earth elements (REEs) remained largely unchanged. The granulites belong to the tholeiitic basalt series, with SiO 2 contents of 47.05-51.03% and Mg# of 35-50. The REE contents of the granulites are characterised by flat chondrite-normalised patterns (La N /Yb N = 0.96-1.92; La N /Sm N = 1.0-1.59) and weak Eu anomalies (Eu/Eu* = 0.84-0.99). Most of the granulite samples have high TiO 2 contents, clear negative Nb and Ta anomalies, and high Pb enrichment, with positive zircon ε Hf (t) values (+8.14 to +16.02). The granulites exhibit both normal mid-ocean ridge basalt (N-MORB) and island-arc basalt (IAB) characteristics. Using the data presented here and previous data, we suggest that the protolith of the granulites were back-arc basin basalts derived from high-degree partial melting of depleted mantle in the spinel stability field, which records the early evolution of the BNO. Northward subduction of the BNO oceanic plate led to backarc spreading and the formation of back-arc basin basalts on the northern margin of the Amdo Terrane. The back-arc basin extended further to form an ocean basin, which separated the Amdo Terrane and the Southern Qiangtang-Baoshan (SQB) Terrane, resulting in the Amdo Terrane becoming an isolated microcontinent in the BNO.

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Geochemistry and geochronology of Pengco subduction‐related ophiolites, Tibet: Implications for Dongkaco microcontinent in the Bangong–Nujiang suture zone

Shao

Song

et al. 2021

Geological Journal

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The identification of a microcontinent in Bangong-Nujiang suture zone (BNSZ) is important to understanding the tectonic evolution of Bangong-Nujiang Tethys Ocean (BNTO). Subduction-related ophiolite is one of the keys to discriminate a microcontinent in suture zones, which can be generated during the oceanic subduction beneath the microcontinent. Generally, ophiolites in the adjacent area of a microcontinent would show characteristics of a volcanic arc, while ophiolites in adjacent area of an ocean show characteristics of a fore-arc. North Pengco ophiolites (NPOs) and South Pengco ophiolites (SPOs) were collected in the central section of BNSZ, and dated at 115.0-111.5 Ma by SHRIMP II. According to their trace element characteristics, NPOs were determined to have formed at a setting of subduction-related volcanic arc and affected by slab-derived fluids or melts. The diagram based on the Ce versus Ce/Y shows that NPOs originated from the partial melting of spinel peridotites. On the other hand, SPOs were generated from the partial melting of ultra-depleted mantle at a setting of subduction-related fore-arc on the basis of extraordinarily low REEs summation and HFSEs (e.g., Zr, Ti, Nb and Ta), relatively high concentrations of compatible elements (e.g., Cr, Ni), large ratios of CaO/TiO 2 (37.67-437.50) and Al 2 O 3 /TiO 2 (20.78-424.50), which were also affected by slab-derived fluids. Based on the relative location of NPOs and SPOs, it reasonably proposed that a northward subduction of a minor oceanic basin had occurred at the Early Cretaceous, trigged by the Dongkaco microcontinent (DMC). In reverse, these ophiolites provide evidence for the existence of DMC in BNTO. Combining with other subduction-related ophiolites developed in BNSZ, BNTO might have comprised of several minor oceanic basins separated by some blocks like DMC in the central and west sections, rather than a unified ocean basin.

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Middle Jurassic MORB-type gabbro, high-Mg diorite, calc-alkaline diorite and granodiorite in the Ando area, central Tibet: Evidence for a slab roll-back of the Bangong-Nujiang Ocean

Cited by 30 publications

References 102 publications

Petrogenesis of Early Jurassic (ca. 181 Ma) dacitic–rhyolitic volcanic rocks in the Amdo ophiolite mélange, central Tibetan Plateau: Low‐pressure partial melts of Bangong–Nujiang Tethys oceanic crust?

Petrogenesis of Early Jurassic (ca. 181 Ma) dacitic–rhyolitic volcanic rocks in the Amdo ophiolite mélange, central Tibetan Plateau: Low‐pressure partial melts of Bangong–Nujiang Tethys oceanic crust?

Geochronology, geochemistry, origin, and tectonic implications of high‐pressure mafic granulites of the Amdo region, Central Tibet

Geochemistry and geochronology of Pengco subduction‐related ophiolites, Tibet: Implications for Dongkaco microcontinent in the Bangong–Nujiang suture zone

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