Eocene supra-subduction zone mafic magmatism in the Sibumasu Block of SW Yunnan: Implications for Neotethyan subduction and India–Asia collision

Yuejun Wang, Limin Zhang, Peter A. Cawood, Liyan Ma, Weiming Fan, Aimei Zhang, Yuzhi Zhang, Xianwu Bi

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Geochemical and isotopic data for metabasic rocks in NW Yunnan constrain the nature of the mantle source beneath the East Himalayan Syntaxis during the Neotethyan subduction and the timing of initial collision between India and Asia. Our results indicate that these mafic rocks crystallized at 50-55Ma and were metamorphosed at ~39Ma, contemporaneous with magmatic flare-ups and high-grade metamorphism in South Tibet. The mafic rocks in NW Yunnan are divisible into three groups. Group 1, from Nabang, shows geochemical affinity to a MORB-like source modified by the recycled component with εNd(t) of +5.1 to +9.5 and εHf(t) of +5.1 to +11.6, and resembles back-arc basin basalt. Group 2 is mainly from Jinzhouzhai and Tongbiguan to the east of Group 1, and is marked by high Al2O3, enrichment in LILEs and depletion in HFSEs, along with negative εNd(t) (-1.1 to -5.6) and εHf(t) (-4.6 to -0.9) values. Group 2 is interpreted to have originated from the lithospheric mantle modified by input from a slab-derived component in a continental arc setting. Group 3, from Nanjingli, is located a considerable distance east from Group 1, and exhibits negative εNd(t) (-6.7 to -7.6) and εHf(t) (-7.1 to -2.2), and is inferred to be derived from the Tengchong lithospheric mantle but with limited involvement of a slab-derived component. Overall Nd-Hf isotopic compositions show a sharp decrease from Group 1 to Group 2 and then a more subdued decrease to Group 3, with the three groups corresponding to an overall spatial distribution from west to east. Our results suggest that early Eocene magmatism in NW Yunnan represents the eastward continuation of the Gangdese magmatic belt and that the Neotethyan subduction continued until ~50Ma followed by the India-Asia collision. It is proposed that at least two eastward-dipping subduction zones are involved in the Neotethyan suprasubduction system prior to 55Ma. The sudden decrease in convergence rate in the early Eocene (55-50Ma), together with the inferred positive buoyancy of the Tengchong lithosphere, stimulated rollback of down-going slab and induced melting of heterogeneous mantle sources to result in a flare-up in magmatic activity.

Original languageEnglish
Pages (from-to)384-399
Number of pages16
JournalLithos
Volume206-207
Issue number1
DOIs
Publication statusPublished - 2014
Externally publishedYes

Keywords

  • Early Eocene mafic rocks
  • Gangdese belt
  • Geochronological and geochemical constrains
  • Mantle source
  • Neotethyan suprasubduction
  • NW Yunnan

Cite this

Wang, Yuejun ; Zhang, Limin ; Cawood, Peter A. ; Ma, Liyan ; Fan, Weiming ; Zhang, Aimei ; Zhang, Yuzhi ; Bi, Xianwu. / Eocene supra-subduction zone mafic magmatism in the Sibumasu Block of SW Yunnan : Implications for Neotethyan subduction and India–Asia collision. In: Lithos. 2014 ; Vol. 206-207, No. 1. pp. 384-399.
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title = "Eocene supra-subduction zone mafic magmatism in the Sibumasu Block of SW Yunnan: Implications for Neotethyan subduction and India–Asia collision",
abstract = "Geochemical and isotopic data for metabasic rocks in NW Yunnan constrain the nature of the mantle source beneath the East Himalayan Syntaxis during the Neotethyan subduction and the timing of initial collision between India and Asia. Our results indicate that these mafic rocks crystallized at 50-55Ma and were metamorphosed at ~39Ma, contemporaneous with magmatic flare-ups and high-grade metamorphism in South Tibet. The mafic rocks in NW Yunnan are divisible into three groups. Group 1, from Nabang, shows geochemical affinity to a MORB-like source modified by the recycled component with εNd(t) of +5.1 to +9.5 and εHf(t) of +5.1 to +11.6, and resembles back-arc basin basalt. Group 2 is mainly from Jinzhouzhai and Tongbiguan to the east of Group 1, and is marked by high Al2O3, enrichment in LILEs and depletion in HFSEs, along with negative εNd(t) (-1.1 to -5.6) and εHf(t) (-4.6 to -0.9) values. Group 2 is interpreted to have originated from the lithospheric mantle modified by input from a slab-derived component in a continental arc setting. Group 3, from Nanjingli, is located a considerable distance east from Group 1, and exhibits negative εNd(t) (-6.7 to -7.6) and εHf(t) (-7.1 to -2.2), and is inferred to be derived from the Tengchong lithospheric mantle but with limited involvement of a slab-derived component. Overall Nd-Hf isotopic compositions show a sharp decrease from Group 1 to Group 2 and then a more subdued decrease to Group 3, with the three groups corresponding to an overall spatial distribution from west to east. Our results suggest that early Eocene magmatism in NW Yunnan represents the eastward continuation of the Gangdese magmatic belt and that the Neotethyan subduction continued until ~50Ma followed by the India-Asia collision. It is proposed that at least two eastward-dipping subduction zones are involved in the Neotethyan suprasubduction system prior to 55Ma. The sudden decrease in convergence rate in the early Eocene (55-50Ma), together with the inferred positive buoyancy of the Tengchong lithosphere, stimulated rollback of down-going slab and induced melting of heterogeneous mantle sources to result in a flare-up in magmatic activity.",
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author = "Yuejun Wang and Limin Zhang and Cawood, {Peter A.} and Liyan Ma and Weiming Fan and Aimei Zhang and Yuzhi Zhang and Xianwu Bi",
year = "2014",
doi = "10.1016/j.lithos.2014.08.012",
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volume = "206-207",
pages = "384--399",
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Eocene supra-subduction zone mafic magmatism in the Sibumasu Block of SW Yunnan : Implications for Neotethyan subduction and India–Asia collision. / Wang, Yuejun; Zhang, Limin; Cawood, Peter A.; Ma, Liyan; Fan, Weiming; Zhang, Aimei; Zhang, Yuzhi; Bi, Xianwu.

In: Lithos, Vol. 206-207, No. 1, 2014, p. 384-399.

Research output: Contribution to journalArticleResearchpeer-review

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T1 - Eocene supra-subduction zone mafic magmatism in the Sibumasu Block of SW Yunnan

T2 - Implications for Neotethyan subduction and India–Asia collision

AU - Wang, Yuejun

AU - Zhang, Limin

AU - Cawood, Peter A.

AU - Ma, Liyan

AU - Fan, Weiming

AU - Zhang, Aimei

AU - Zhang, Yuzhi

AU - Bi, Xianwu

PY - 2014

Y1 - 2014

N2 - Geochemical and isotopic data for metabasic rocks in NW Yunnan constrain the nature of the mantle source beneath the East Himalayan Syntaxis during the Neotethyan subduction and the timing of initial collision between India and Asia. Our results indicate that these mafic rocks crystallized at 50-55Ma and were metamorphosed at ~39Ma, contemporaneous with magmatic flare-ups and high-grade metamorphism in South Tibet. The mafic rocks in NW Yunnan are divisible into three groups. Group 1, from Nabang, shows geochemical affinity to a MORB-like source modified by the recycled component with εNd(t) of +5.1 to +9.5 and εHf(t) of +5.1 to +11.6, and resembles back-arc basin basalt. Group 2 is mainly from Jinzhouzhai and Tongbiguan to the east of Group 1, and is marked by high Al2O3, enrichment in LILEs and depletion in HFSEs, along with negative εNd(t) (-1.1 to -5.6) and εHf(t) (-4.6 to -0.9) values. Group 2 is interpreted to have originated from the lithospheric mantle modified by input from a slab-derived component in a continental arc setting. Group 3, from Nanjingli, is located a considerable distance east from Group 1, and exhibits negative εNd(t) (-6.7 to -7.6) and εHf(t) (-7.1 to -2.2), and is inferred to be derived from the Tengchong lithospheric mantle but with limited involvement of a slab-derived component. Overall Nd-Hf isotopic compositions show a sharp decrease from Group 1 to Group 2 and then a more subdued decrease to Group 3, with the three groups corresponding to an overall spatial distribution from west to east. Our results suggest that early Eocene magmatism in NW Yunnan represents the eastward continuation of the Gangdese magmatic belt and that the Neotethyan subduction continued until ~50Ma followed by the India-Asia collision. It is proposed that at least two eastward-dipping subduction zones are involved in the Neotethyan suprasubduction system prior to 55Ma. The sudden decrease in convergence rate in the early Eocene (55-50Ma), together with the inferred positive buoyancy of the Tengchong lithosphere, stimulated rollback of down-going slab and induced melting of heterogeneous mantle sources to result in a flare-up in magmatic activity.

AB - Geochemical and isotopic data for metabasic rocks in NW Yunnan constrain the nature of the mantle source beneath the East Himalayan Syntaxis during the Neotethyan subduction and the timing of initial collision between India and Asia. Our results indicate that these mafic rocks crystallized at 50-55Ma and were metamorphosed at ~39Ma, contemporaneous with magmatic flare-ups and high-grade metamorphism in South Tibet. The mafic rocks in NW Yunnan are divisible into three groups. Group 1, from Nabang, shows geochemical affinity to a MORB-like source modified by the recycled component with εNd(t) of +5.1 to +9.5 and εHf(t) of +5.1 to +11.6, and resembles back-arc basin basalt. Group 2 is mainly from Jinzhouzhai and Tongbiguan to the east of Group 1, and is marked by high Al2O3, enrichment in LILEs and depletion in HFSEs, along with negative εNd(t) (-1.1 to -5.6) and εHf(t) (-4.6 to -0.9) values. Group 2 is interpreted to have originated from the lithospheric mantle modified by input from a slab-derived component in a continental arc setting. Group 3, from Nanjingli, is located a considerable distance east from Group 1, and exhibits negative εNd(t) (-6.7 to -7.6) and εHf(t) (-7.1 to -2.2), and is inferred to be derived from the Tengchong lithospheric mantle but with limited involvement of a slab-derived component. Overall Nd-Hf isotopic compositions show a sharp decrease from Group 1 to Group 2 and then a more subdued decrease to Group 3, with the three groups corresponding to an overall spatial distribution from west to east. Our results suggest that early Eocene magmatism in NW Yunnan represents the eastward continuation of the Gangdese magmatic belt and that the Neotethyan subduction continued until ~50Ma followed by the India-Asia collision. It is proposed that at least two eastward-dipping subduction zones are involved in the Neotethyan suprasubduction system prior to 55Ma. The sudden decrease in convergence rate in the early Eocene (55-50Ma), together with the inferred positive buoyancy of the Tengchong lithosphere, stimulated rollback of down-going slab and induced melting of heterogeneous mantle sources to result in a flare-up in magmatic activity.

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KW - Mantle source

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