Survival of the Lhasa Terrane during its collision with Asia due to crust-mantle coupling revealed by ca. 114 Ma intrusive rocks in western Tibet

Qing Wang, Di Cheng Zhu, An Lin Liu, Peter A. Cawood, Sheng Ao Liu, Ying Xia, Yue Chen, Hao Wang, Liang Liang Zhang, Zhi Dan Zhao

Research output: Contribution to journalArticleResearchpeer-review

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Abstract

Survival of the Lhasa Terrane during its drift across the Tethyan Ocean and subsequent collision with Asia was likely maintained by mechanical coupling between its ancient lithospheric mantle and the overlying crust. Evidence for this coupling is provided by geochronological and geochemical data from high-Mg dioritic porphyrite dikes that intruded into granodiorites with dioritic enclaves within the Nixiong Batholith in the western segment of the central Lhasa subterrane, southern Tibet. Zircon LA-ICP-MS U-Pb dating indicates synchronous emplacement of dioritic porphyrite dikes (113.9 ± 2 Ma), dioritic enclaves (113.9 ± 1 Ma), and host granodiorites (113.1 ± 2 Ma). The hornblende-bearing granodiorites are metaluminous to weakly peraluminous (A/CNK = 0.95–1.05) and belong to high-K calc-alkaline I-type granite. These rocks are characterized by low Mg# (37–43), negative zircon εHf(t) values (−6.8 to −1.2), and negative whole-rock εNd(t) values (−8.1 to −5.4), suggestive of derivation through anatexis of ancient lower crust. The two least-mixed or contaminated dioritic porphyrite dike samples have high MgO (8.46−8.74 wt%), high Mg# (69−70), and high abundances of compatible elements (e.g., Cr = 673−646 ppm, Ni = 177−189 ppm), which are close to those of primitive magma. They are high-K calc-alkaline and show negative whole-rock εNd(t) values (−1.9 to −1.2), indicating that these samples are most likely derived from the partial melting of ancient lithospheric mantle that was metasomatized by slab-derived fluids. The dioritic enclave samples are metaluminous high-K calc-alkaline and have varying negative whole-rock εNd(t) values (−7.8 to −3.7), which are interpreted as the result of magma mixing between the ancient lower crust-derived melts and asthenospheric mantle- (rather than lithospheric mantle-) derived melts. The Nd isotope mantle model ages of the least-mixed or contaminated high-Mg dioritic porphyrite dike samples (1.1−1.4 Ga) are close to the Nd isotope two-stage model ages (1.3−1.6 Ga) and the zircon Hf isotope crustal model ages (1.1−1.5 Ga) of the ancient lower crust-derived granodiorites, indicating that the lithospheric mantle of the western segment of the central Lhasa subterrane is mechanically coupled to the overlying crust at ~114 Ma. In combination with the Proterozoic crustal rocks documented in the central and eastern segments of the central Lhasa subterrane, we propose that this coupling enabled it to resist subduction during accretion to Asia.

Original languageEnglish
Pages (from-to)200-210
Number of pages11
JournalLithos
Volume304-307
DOIs
Publication statusPublished - 1 Apr 2018

Keywords

  • Ancient lower crust-derived melts
  • Crust-mantle coupling
  • Early Cretaceous
  • High-Mg dioritic porphyrite dike
  • Lhasa Terrane
  • Lithospheric mantle-derived melts

Cite this

Wang, Qing ; Zhu, Di Cheng ; Liu, An Lin ; Cawood, Peter A. ; Liu, Sheng Ao ; Xia, Ying ; Chen, Yue ; Wang, Hao ; Zhang, Liang Liang ; Zhao, Zhi Dan. / Survival of the Lhasa Terrane during its collision with Asia due to crust-mantle coupling revealed by ca. 114 Ma intrusive rocks in western Tibet. In: Lithos. 2018 ; Vol. 304-307. pp. 200-210.
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abstract = "Survival of the Lhasa Terrane during its drift across the Tethyan Ocean and subsequent collision with Asia was likely maintained by mechanical coupling between its ancient lithospheric mantle and the overlying crust. Evidence for this coupling is provided by geochronological and geochemical data from high-Mg dioritic porphyrite dikes that intruded into granodiorites with dioritic enclaves within the Nixiong Batholith in the western segment of the central Lhasa subterrane, southern Tibet. Zircon LA-ICP-MS U-Pb dating indicates synchronous emplacement of dioritic porphyrite dikes (113.9 ± 2 Ma), dioritic enclaves (113.9 ± 1 Ma), and host granodiorites (113.1 ± 2 Ma). The hornblende-bearing granodiorites are metaluminous to weakly peraluminous (A/CNK = 0.95–1.05) and belong to high-K calc-alkaline I-type granite. These rocks are characterized by low Mg# (37–43), negative zircon εHf(t) values (−6.8 to −1.2), and negative whole-rock εNd(t) values (−8.1 to −5.4), suggestive of derivation through anatexis of ancient lower crust. The two least-mixed or contaminated dioritic porphyrite dike samples have high MgO (8.46−8.74 wt{\%}), high Mg# (69−70), and high abundances of compatible elements (e.g., Cr = 673−646 ppm, Ni = 177−189 ppm), which are close to those of primitive magma. They are high-K calc-alkaline and show negative whole-rock εNd(t) values (−1.9 to −1.2), indicating that these samples are most likely derived from the partial melting of ancient lithospheric mantle that was metasomatized by slab-derived fluids. The dioritic enclave samples are metaluminous high-K calc-alkaline and have varying negative whole-rock εNd(t) values (−7.8 to −3.7), which are interpreted as the result of magma mixing between the ancient lower crust-derived melts and asthenospheric mantle- (rather than lithospheric mantle-) derived melts. The Nd isotope mantle model ages of the least-mixed or contaminated high-Mg dioritic porphyrite dike samples (1.1−1.4 Ga) are close to the Nd isotope two-stage model ages (1.3−1.6 Ga) and the zircon Hf isotope crustal model ages (1.1−1.5 Ga) of the ancient lower crust-derived granodiorites, indicating that the lithospheric mantle of the western segment of the central Lhasa subterrane is mechanically coupled to the overlying crust at ~114 Ma. In combination with the Proterozoic crustal rocks documented in the central and eastern segments of the central Lhasa subterrane, we propose that this coupling enabled it to resist subduction during accretion to Asia.",
keywords = "Ancient lower crust-derived melts, Crust-mantle coupling, Early Cretaceous, High-Mg dioritic porphyrite dike, Lhasa Terrane, Lithospheric mantle-derived melts",
author = "Qing Wang and Zhu, {Di Cheng} and Liu, {An Lin} and Cawood, {Peter A.} and Liu, {Sheng Ao} and Ying Xia and Yue Chen and Hao Wang and Zhang, {Liang Liang} and Zhao, {Zhi Dan}",
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language = "English",
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Survival of the Lhasa Terrane during its collision with Asia due to crust-mantle coupling revealed by ca. 114 Ma intrusive rocks in western Tibet. / Wang, Qing; Zhu, Di Cheng; Liu, An Lin; Cawood, Peter A.; Liu, Sheng Ao; Xia, Ying; Chen, Yue; Wang, Hao; Zhang, Liang Liang; Zhao, Zhi Dan.

In: Lithos, Vol. 304-307, 01.04.2018, p. 200-210.

Research output: Contribution to journalArticleResearchpeer-review

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T1 - Survival of the Lhasa Terrane during its collision with Asia due to crust-mantle coupling revealed by ca. 114 Ma intrusive rocks in western Tibet

AU - Wang, Qing

AU - Zhu, Di Cheng

AU - Liu, An Lin

AU - Cawood, Peter A.

AU - Liu, Sheng Ao

AU - Xia, Ying

AU - Chen, Yue

AU - Wang, Hao

AU - Zhang, Liang Liang

AU - Zhao, Zhi Dan

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N2 - Survival of the Lhasa Terrane during its drift across the Tethyan Ocean and subsequent collision with Asia was likely maintained by mechanical coupling between its ancient lithospheric mantle and the overlying crust. Evidence for this coupling is provided by geochronological and geochemical data from high-Mg dioritic porphyrite dikes that intruded into granodiorites with dioritic enclaves within the Nixiong Batholith in the western segment of the central Lhasa subterrane, southern Tibet. Zircon LA-ICP-MS U-Pb dating indicates synchronous emplacement of dioritic porphyrite dikes (113.9 ± 2 Ma), dioritic enclaves (113.9 ± 1 Ma), and host granodiorites (113.1 ± 2 Ma). The hornblende-bearing granodiorites are metaluminous to weakly peraluminous (A/CNK = 0.95–1.05) and belong to high-K calc-alkaline I-type granite. These rocks are characterized by low Mg# (37–43), negative zircon εHf(t) values (−6.8 to −1.2), and negative whole-rock εNd(t) values (−8.1 to −5.4), suggestive of derivation through anatexis of ancient lower crust. The two least-mixed or contaminated dioritic porphyrite dike samples have high MgO (8.46−8.74 wt%), high Mg# (69−70), and high abundances of compatible elements (e.g., Cr = 673−646 ppm, Ni = 177−189 ppm), which are close to those of primitive magma. They are high-K calc-alkaline and show negative whole-rock εNd(t) values (−1.9 to −1.2), indicating that these samples are most likely derived from the partial melting of ancient lithospheric mantle that was metasomatized by slab-derived fluids. The dioritic enclave samples are metaluminous high-K calc-alkaline and have varying negative whole-rock εNd(t) values (−7.8 to −3.7), which are interpreted as the result of magma mixing between the ancient lower crust-derived melts and asthenospheric mantle- (rather than lithospheric mantle-) derived melts. The Nd isotope mantle model ages of the least-mixed or contaminated high-Mg dioritic porphyrite dike samples (1.1−1.4 Ga) are close to the Nd isotope two-stage model ages (1.3−1.6 Ga) and the zircon Hf isotope crustal model ages (1.1−1.5 Ga) of the ancient lower crust-derived granodiorites, indicating that the lithospheric mantle of the western segment of the central Lhasa subterrane is mechanically coupled to the overlying crust at ~114 Ma. In combination with the Proterozoic crustal rocks documented in the central and eastern segments of the central Lhasa subterrane, we propose that this coupling enabled it to resist subduction during accretion to Asia.

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KW - Crust-mantle coupling

KW - Early Cretaceous

KW - High-Mg dioritic porphyrite dike

KW - Lhasa Terrane

KW - Lithospheric mantle-derived melts

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