Os–Nd–Sr isotopes in Miocene ultrapotassic rocks of southern Tibet: Partial melting of a pyroxenite-bearing lithospheric mantle?

Huang, Feng; Chen, Jianlin; Xu, Ji‐Feng; Wang, Baodi; Li, Jie

doi:10.1016/j.gca.2015.04.053

Cited by 56 publications

(27 citation statements)

References 108 publications

(240 reference statements)

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“…Therefore, their SiO 2 contents (59.03–63.62 wt %) are higher than those of typical melts (<55 wt %) from a peridotite source irrespective of the volume of H 2 O [Mitchell and Grove, , and reference therein]. Although melting of pyroxenite‐bearing lithospheric mantle, formed by the interaction of mantle peridotite and a Si‐oversaturated melt derived from sediments, could potentially generate such high SiO 2 and enriched isotopic compositions [ Sobolev et al ., ; Straub et al ., ], the Fe/Mn (<50) and Ni/MgO (<11) ratios of the DVRs are much lower than those of such pyroxenite‐derived HMAs (>80 and >30, respectively) [e.g., Huang et al ., ; Liu et al ., b]. The zircons from the DVRs show negative Eu anomalies and have higher Th and U contents than those from hydrated peridotite, which also precludes an origin direct from the mantle (Figures c and d).…”

Section: Discussionsupporting

confidence: 62%

Sediment melting during subduction initiation: Geochronological and geochemical evidence from the Darutso high‐Mg andesites within ophiolite melange, central Tibet

Zeng

Chen

et al. 2016

Geochem Geophys Geosyst

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110

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In addition to fluids, the concept of sediment‐derived melts infiltrating the fore‐arc mantle during subduction initiation has been proposed based on studies of modern subduction zones and ophiolite mélange. However, outcrops that contain the products of such melts are rare, especially in conjunction with boninite. New U‐Pb zircon dating reveals that the Darutso volcanic rocks (DVRs) within ophiolitic mélange in the Beila area, central Tibet, crystallized at ∼164–162 Ma. This is the first recognition of Jurassic volcanic rocks in the middle section of the Bangong‐Nujiang Suture Zone. Geochemically, the DVRs are high‐Mg andesites with moderate SiO2 (59.03–63.62 wt %) and high MgO (3.74–6.53 wt %), Cr (up to 395 ppm), and Mg# (50.3–67.9). They also have high Th contents, (La/Sm)N ratios, and (87Sr/86Sr)i values (0.7085–0.7147); low Ba/Th, U/Th, and Sr/Y ratios; and negative values of εNd(t) (−8.7 to −9.8) and zircon εHf(t) (−7.4 to −9.9). The εNd(t) values of the DVRs overlap those of regional sediments. Detailed analyses of these geochemical characteristics indicate that the DVRs were derived from partial melting of subducted sediments and subsequent interaction with overlying mantle peridotite in a shallow and hot setting. In combination with the regional geology, in particular adjacent ophiolites that contain MORB‐like and boninite mafic lavas, these rocks collectively recorded the evolution of a fore‐arc setting during the initiation of the northward subduction of the south branch of the Bangong‐Nujiang Ocean. Therefore, the results provide direct evidence for sediment melting during subduction initiation and constrain the Jurassic tectonic evolution of the Lhasa terrane.

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Section: Discussionsupporting

confidence: 62%

Sediment melting during subduction initiation: Geochronological and geochemical evidence from the Darutso high‐Mg andesites within ophiolite melange, central Tibet

Zeng

Chen

et al. 2016

Geochem Geophys Geosyst

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110

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“…Widespread magmatism initiated with adakitic rocks by ~26 Ma, followed by potassic-ultrapotassic rocks by ~24 Ma55. The chemistry of these magmas has been attributed to break-off the Indian continental lithosphere that had subducted beneath the Lhasa terrane and/or convective removal of the Tibetan lithospheric mantle5556. Ninety-six apatite fission track ages collected from the Lhasa terrane indicate three cooling age peaks at 22–15, 10–7, and 5–0 Ma, whereas the Palaeogene ages are more scattered57 (Fig.…”

Section: Discussionmentioning

confidence: 99%

Low palaeoelevation of the northern Lhasa terrane during late Eocene: Fossil foraminifera and stable isotope evidence from the Gerze Basin

Wei

Zhang

Garzione

et al. 2016

Sci Rep

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The Lhasa terrane is a key region for understanding the paleoelevation of the southern Tibetan Plateau after India-Asia collision. The Gerze Basin, located in the northern part of the Lhasa terrane, is a shortening-related basin. We discovered Lagena laevis (Bandy) fossils in upper Eocene strata of the Gerze Basin. This type of foraminifera is associated with lagoon and estuarine environments, indicating that the northern part of the Lhasa terrane was near sea level during the late Eocene. We speculate that these foraminifera were transported inland by storm surges to low elevation freshwater lakes during times of marine transgressions. This inference is consistent with the relatively positive δ18O values in carbonate from the same deposits that indicate low palaeoelevations close to sea level. Considering the palaeoelevation results from the nearby Oligocene basins at a similar latitude and the volcanic history of the Lhasa terrane, we infer that large-magnitude surface uplift of the northern Lhasa terrane occurred between late Eocene and late Oligocene time.

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“…The uncertainties in the analyses of internal standards and trace elements are ±5% for REEs and ±5%-10% for trace elements. The analytical procedures followed those described by Chen et al (2011) and Huang et al (2015b).…”

Section: Methodsmentioning

confidence: 99%

“…After the collision between India and Asia, three types of postcollisional magmatites were widely emplaced in the Lhasa Terrane: adakitic intrusive rocks, potassic-ultrapotassic volcanic rocks, and peraluminous granites were emplaced between 25 and 10 Ma (Chung et al, 2005Hou et al, 2004;Huang et al, 2015b;Liao et al, 2007;Mo et al, 2007;Zeng et al, 2015). The ultrapotassic volcanic rocks were derived from low-degree partial melting of metasomatized lithospheric mantle and are only found west of 87°E (Chung et al, 2005;Huang et al, 2015b;Williams et al, 2001;Zhao et al, 2009).…”

Section: Geological Backgroundmentioning

confidence: 99%

“…The ultrapotassic volcanic rocks were derived from low-degree partial melting of metasomatized lithospheric mantle and are only found west of 87°E (Chung et al, 2005;Huang et al, 2015b;Williams et al, 2001;Zhao et al, 2009). Other post-collisional magmatic rocks occur widely throughout the Lhasa Terrane, although their distributions are locally controlled by N- S striking normal fault systems that developed due to E-W extension in southern Tibet.…”

Section: Geological Backgroundmentioning

confidence: 99%

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Two Cenozoic tectonic events of N–S and E–W extension in the Lhasa Terrane: Evidence from geology and geochronology

Huang

Chen

et al. 2016

Lithos

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Os–Nd–Sr isotopes in Miocene ultrapotassic rocks of southern Tibet: Partial melting of a pyroxenite-bearing lithospheric mantle?

Cited by 56 publications

References 108 publications

Sediment melting during subduction initiation: Geochronological and geochemical evidence from the Darutso high‐Mg andesites within ophiolite melange, central Tibet

Sediment melting during subduction initiation: Geochronological and geochemical evidence from the Darutso high‐Mg andesites within ophiolite melange, central Tibet

Low palaeoelevation of the northern Lhasa terrane during late Eocene: Fossil foraminifera and stable isotope evidence from the Gerze Basin

Two Cenozoic tectonic events of N–S and E–W extension in the Lhasa Terrane: Evidence from geology and geochronology

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