Geochemistry of Eocene high-Mg# adakitic rocks in the northern Qiangtang terrane, central Tibet: Implications for early uplift of the plateau

Chen, Jianlin; Wu, Jianbin; Xu, Ji‐Feng; Dong, Yanhui; Wang, Baodi; Kang, Zhiqiang

doi:10.1130/b30755.1

Cited by 41 publications

(42 citation statements)

References 117 publications

(217 reference statements)

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“…The age of the Nariniya volcanic rocks hence provides important constraints for the timing of surface uplift in central Tibet. The tectonic reconstruction based on our geochemical observations implies that the uplift of central Tibet could have been initiated slightly before 38 Ma, which is possibly later than previously thought (Chen et al, 2013;Wang et al, 2008). This interpretation also supports a recent view that the Eocene paleo-elevation of central plateau was lower (~1,000 m; Deng et al, 2012;Sun et al, 2014;Botsyun et al, 2019) than previously estimated (Rowley & Currie, 2006).…”

Section: 1029/2019jb018197supporting

confidence: 88%

“…These values are close to the parental source of Tengchong potassic rocks from southeast Tibet but far from the granulite xenoliths in northern Qiangtang (Lai et al, 2011) and lower crust-derived potassic rocks from Lhasa terrane (Chen et al, 2010). In contrast, the Nariniya volcanic rocks exhibit higher initial 87 Sr/ 86 Sr (i) (0.707549-0.707575) and lower ɛ Nd (t) (−4.65 to −4.04) (Figure 4a), which are similar to the other adakitic rocks exposed in northern Qiangtang (e.g., Chen et al, 2013;Lai & Qin, 2013;Ou et al, 2017;Wang et al, 2008).…”

Section: Sr-nd-mg-li Isotopic Compositions Of Duocaima and Nariniya Vmentioning

confidence: 61%

“…The Qiangtang terrane has a large volume of Cenozoic volcanic rocks with ages from approximately 51 Ma to the recent (primarily 45-20 Ma) ( Figure 1). They have adakitic, potassic, and ultrapotassic compositions (e.g., Chen et al, 2013Chen et al, , 2017Ding et al, 2003Ding et al, , 2007Guo et al, 2006;Lai et al, 2007;Lai & Qin, 2013;Wang et al, 2008), and some of them host ultramafic, mafic, and felsic granulite xenoliths (Ding et al, 2007;Hacker et al, 2000;Lai et al, 2011). The petrogenesis of these volcanic rocks is still controversial.…”

Section: Geological Background and Samplesmentioning

confidence: 99%

“…Sun and McDonough (1989); and (d) adakite discrimination diagram of Sr/Y versus Y (modified from Castillo, 2012;Richards & Kerrich, 2007). Data sources: ultrapotassic rocks in northern Qiangtang terrane , potassic volcanic rocks from Tengchong, southeast Tibet (Tian et al, 2018), and adakitic rocks from northern Qiangtang terrane (Chen et al, 2013;Lai et al, 2003Lai et al, , 2007Lai & Qin, 2013;Li et al, 2004;Wang et al, 2008). The Changbaishan volcanic rocks with SiO 2 ranging from around 66.0 to 68.8 wt.% are plotted for comparison (Tian et al, 2019).…”

Section: Whole-rock Sr Nd Mg and LI Isotopic Analysesmentioning

confidence: 99%

“…The widely distributed Eocene postcollisional felsic volcanic and intrusive rocks in central Tibet, particularly the adakitic rocks (e.g., Chen et al, 2013Chen et al, , 2017Guo et al, 2006;Lai & Qin, 2013;Ou et al, 2017;Wang et al, 2008Wang et al, , 2010, provide a means for studying the early uplift history of Tibet and associated deep geodynamic processes. However, their origins are still debated with numerous models being proposed, including partial melting of thickened lower crust (Long et al, 2015;Ou et al, 2017), delaminated lower crust (Chen et al, 2013;Liu et al, 2008), subducted continental crust (Lai & Qin, 2013;Wang et al, 2008), and low-degree melting of a metasomatized lithospheric mantle . Magnesium and lithium isotopes can provide new constraints on the petrogenesis of the volcanic rocks based on the following reasons.…”

Section: Introductionmentioning

confidence: 99%

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Magnesium and Lithium Isotopic Evidence for a Remnant Oceanic Slab Beneath Central Tibet

Tian,

Teng,

Hou

et al. 2020

JGR Solid Earth

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The voluminous Eocene postcollisional potassium-rich magmatism in central Tibet is crucial in understanding the deep geodynamic process and related uplift history of the Tibetan Plateau. Here, we present an integrated study of whole-rock Sr-Nd-Mg-Li isotopes and zircon U-Pb ages on two suites of lavas from Duocaima and Nariniya in the northern Qiangtang block. The Duocaima high-K calc-alkaline trachyandesites were formed at~35 Ma and are enriched in light rare earth elements and large ion lithophile elements. They have slightly lower δ 26 Mg (−0.41‰ to −0.33‰) and δ 7 Li (+1.0‰ to +2.6‰) relative to the mantle. Together with their high 87 Sr/ 86 Sr (i) (0.7066-0.7067) and low ɛ Nd (t) (−1.96 to −1.61) values, they most likely originated from the lithospheric mantle previously metasomatized by melts from subducted carbonate-bearing sediments. Model calculation suggests that~7-11% sediments were added into the mantle via melting. By contrast, the contemporaneous Nariniya adakitic trachytes have higher δ 26 Mg (−0.13‰ to −0.02‰) and δ 7 Li (+3.3‰ to +5.4‰) values, as well as higher Pb/Ce and Ba/La ratios, which most likely resulted from the thickened lower crust that was metasomatized by fluids released from downgoing Songpan-Ganzi oceanic slab. Our combined isotopic study suggests the existence of a remnant oceanic slab beneath central Tibetan Plateau during the late Eocene and implies that the initial uplift of central Tibet was before~38 Ma.

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Section: 1029/2019jb018197supporting

confidence: 88%

Section: Sr-nd-mg-li Isotopic Compositions Of Duocaima and Nariniya Vmentioning

confidence: 61%

Section: Geological Background and Samplesmentioning

confidence: 99%

Section: Whole-rock Sr Nd Mg and LI Isotopic Analysesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Magnesium and Lithium Isotopic Evidence for a Remnant Oceanic Slab Beneath Central Tibet

Tian,

Teng,

Hou

et al. 2020

JGR Solid Earth

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Crustal thickening prior to 43 Ma in the Himalaya: Evidence from lower crust‐derived adakitic magmatism in Dala, eastern Tethyan Himalaya, Tibet

Dai

Dong

et al. 2019

Geological Journal

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The Himalayan-Tibetan orogen is the world's largest active orogen with the thickest continental crust on Earth. However, the timing of crustal thickening of this orogen remains controversial. In recent years, magmatic rocks with adakitic affinities have been widely used to constrain the crustal thickness. Here, we present zircon U-Pb ages, geochemical and Sr-Nd-Pb-Hf isotopic data for the Dala two-mica granites (eastern Tethyan Himalaya) that may shed light on this issue. Zircon U-Pb dating shows that the Dala two-mica granites were emplaced at ca. 43 Ma. The granites display adakitic signatures, including high SiO 2 , Al 2 O 3 and Sr contents, low Y and Yb contents with high Sr/Y (27−67) and La/Yb (35−99) ratios. High K 2 O and Th contents, low Nb/U, Ce/Pb, Ti/Eu and Nd/Sm ratios and low MgO, Mg#, Cr and Ni contents suggest that the Dala two-mica granites were derived from partial melting of a thickened lower crust. Low negative zircon ε Hf (t) values (−10.4 to −0.5) with old two-stage Hf model ages (1.1-1.8 Ga), high ( 87 Sr/ 86 Sr) i (0.715861-0.717665) with low ε Nd (t) (−12.5 to −11.3) and high Pb isotopes [( 206 Pb/ 204 Pb) i =18.783-18.861, ( 207 Pb/ 204 Pb) i =18.783-18.861 and ( 208 Pb/ 204 Pb) i =39.052-39.285], together with previous literature data, indicate that the magma source for the Eocene granites in the Yardoi area was composed of ancient lower crust consisting mainly of garnetamphibolite and probably subordinate metapelites of the High Himalayan Crystalline Sequence. The residual mineral assemblage of garnet + rutile + plagioclase ± amphibole in the source region demonstrates that the crust beneath the Himalaya could have been thickened to 50 km in the Eocene. Combining with previous studies, we propose that the Eocene magmatic rocks in the Tethyan Himalaya (e.g. ca. 43 Ma old Dala two-mica granites) can be best interpreted as the consequence of breakoff of the Neo-Tethyan oceanic slab.

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Formation of Late Cretaceoushigh‐Mggranitoid porphyry in central Lhasa, Tibet: Implications for crustal thickening prior to India–Asia collision

Dai

Huang

et al. 2020

Geological Journal

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The Tibetan Plateau is characterized by the largest crustal thickness on Earth, although the timing of formation of the plateau remains debated. In this study, we present in situ laser ablation-inductively coupled plasma-mass spectrometry zircon U-Pb ages and Hf isotopes, and whole-rock geochemical data on porphyritic granitoids of Sebuta in the central Lhasa block. Our zircon U-Pb data indicate that these rocks emplaced at ca. 89 Ma, in the early Late Cretaceous. Geochemically, the Sebuta biotite granite porphyry can be broadly divided into two subtypes, namely metaluminous porphyry and peraluminous porphyry. The metaluminous porphyry has high SiO 2 , Al 2 O 3 , Sr, low Y and Yb contents, and high Sr/Y and La N /Yb N ratios, showing adakitic features. These rocks have high K 2 O and Th contents, low Ti/Eu and Nd/Sm ratios, indicative of a continental crust affinity. Positive zircon ε Hf (t) values, along with high Mg # , Cr and Ni, imply that the Sebuta adakitic porphyry was most likely derived from partial melting of a delaminated thickened juvenile lower crust, and that the initial melts interacted with mantle peridotite during ascent. The field features, petrographic characteristics, formation age, ore-bearing potential, and Hf isotope of the peraluminous porphyry are similar to those of the Sebuta adakitic porphyry, indicating that the peraluminous porphyry was likely formed by contamination with ancient crustal material and fractional crystallization from the same primary adakitic magmas which generated the Sebuta adakitic porphyry. Residual phases of amphibole + plagioclase + garnet + rutile in the source region, together with previous studies, suggest that the crust beneath the centralnorthern Lhasa block experienced thickening during the early Late Cretaceous, and had already been thickened to more than 50 km by the Late Cretaceous (ca. 89 Ma).

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Geochemistry of Eocene high-Mg# adakitic rocks in the northern Qiangtang terrane, central Tibet: Implications for early uplift of the plateau

Abstract: It is generally believed that the Tibetan

Cited by 41 publications

References 117 publications

Magnesium and Lithium Isotopic Evidence for a Remnant Oceanic Slab Beneath Central Tibet

Magnesium and Lithium Isotopic Evidence for a Remnant Oceanic Slab Beneath Central Tibet

Crustal thickening prior to 43 Ma in the Himalaya: Evidence from lower crust‐derived adakitic magmatism in Dala, eastern Tethyan Himalaya, Tibet

Formation of Late Cretaceoushigh‐Mggranitoid porphyry in central Lhasa, Tibet: Implications for crustal thickening prior to India–Asia collision

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