Episodic slab rollback and back-arc extension in the Yunnan-Burma region: Insights from cretaceous Nb-enriched and oceanic-island basalt-like mafic rocks

Huichuan Liu, Yuejun Wang, Peter A. Cawood, Xiaofei Guo

Research output: Contribution to journalArticleResearchpeer-review

Abstract

One highly debated topic related to the nature of the Cretaceous mantle and geodynamic processes in SE Asia is whether they were dominated by the Tethyan or Pacific Ocean subductions. The main reason for this puzzle is the lack of geochemical studies on mantle-derived mafic rocks in SE Asia. In this paper, we report Early Cretaceous Nbenriched diabases (ca. 139 Ma) and Late Cretaceous Nb-enriched (ca. 68 Ma) and oceanic-island basalt (OIB)-like (ca. 73 Ma) amphibolites from the Ailaoshan tectonic zone in the Yunnan-Burma region. The ca. 139 Ma diabases and ca. 68 Ma amphibolites display similar geochemical features with typical Nb-enriched basalts, e.g., high Na2O, TiO2, and Nb (>7 ppm) contents, and high (Nb/Th)PM, (Nb/La)PM, and Nb/U ratios. Unlike adakite-associated Nb-enriched basalts, our Nb-enriched diabases and ampibolites were derived through mixing between OIBlike and arc-like mantle source components in the spinel stability field (<70 km), and the Nb-enriched diabases involved an additional high degree (~18%) of partial melting of the mixed source. In comparison with the Nb-enriched mafic rocks, the ca. 73 Ma OIB-like amphibolites have lower Mg# values, higher TiO2 and Nb (20.0-26.0 ppm) contents, and OIB-like rare earth element patterns and trace-element spidergrams. The OIB-like rocks were generated by a low degree of partial melting of garnet-facies peridotite (>80 km). In combination with previous Cretaceous to early Eocene age data from granitoids, three significant magmatic flare-ups are identified at 140-115 Ma, 75-64 Ma, and 55-50 Ma, with two magmatic gaps at 115-75 Ma and 64-55 Ma. Given the distances of the studied area from the Pacific and Neotethyan trenches (2400-5000 km and 320 km, respectively), these Cretaceous igneous rocks more likely formed in a Neotethyan subduction-related tectonic setting, rather than a Pacific Ocean-related setting. We propose a tectonic model involving episodic flat slab subduction, slab rollback, and intracontinental back-arc extension for Neotethyan subduction in the Yunnan-Burma region.

Original languageEnglish
Pages (from-to)698-714
Number of pages17
JournalGeological Society of America Bulletin
Volume129
Issue number5-6
DOIs
Publication statusPublished - 1 May 2017
Externally publishedYes

Keywords

  • Porphyry
  • Porphyry copper
  • Zircon

Cite this

@article{a31e1a299906414c91cf379ccb9261d6,
title = "Episodic slab rollback and back-arc extension in the Yunnan-Burma region: Insights from cretaceous Nb-enriched and oceanic-island basalt-like mafic rocks",
abstract = "One highly debated topic related to the nature of the Cretaceous mantle and geodynamic processes in SE Asia is whether they were dominated by the Tethyan or Pacific Ocean subductions. The main reason for this puzzle is the lack of geochemical studies on mantle-derived mafic rocks in SE Asia. In this paper, we report Early Cretaceous Nbenriched diabases (ca. 139 Ma) and Late Cretaceous Nb-enriched (ca. 68 Ma) and oceanic-island basalt (OIB)-like (ca. 73 Ma) amphibolites from the Ailaoshan tectonic zone in the Yunnan-Burma region. The ca. 139 Ma diabases and ca. 68 Ma amphibolites display similar geochemical features with typical Nb-enriched basalts, e.g., high Na2O, TiO2, and Nb (>7 ppm) contents, and high (Nb/Th)PM, (Nb/La)PM, and Nb/U ratios. Unlike adakite-associated Nb-enriched basalts, our Nb-enriched diabases and ampibolites were derived through mixing between OIBlike and arc-like mantle source components in the spinel stability field (<70 km), and the Nb-enriched diabases involved an additional high degree (~18{\%}) of partial melting of the mixed source. In comparison with the Nb-enriched mafic rocks, the ca. 73 Ma OIB-like amphibolites have lower Mg# values, higher TiO2 and Nb (20.0-26.0 ppm) contents, and OIB-like rare earth element patterns and trace-element spidergrams. The OIB-like rocks were generated by a low degree of partial melting of garnet-facies peridotite (>80 km). In combination with previous Cretaceous to early Eocene age data from granitoids, three significant magmatic flare-ups are identified at 140-115 Ma, 75-64 Ma, and 55-50 Ma, with two magmatic gaps at 115-75 Ma and 64-55 Ma. Given the distances of the studied area from the Pacific and Neotethyan trenches (2400-5000 km and 320 km, respectively), these Cretaceous igneous rocks more likely formed in a Neotethyan subduction-related tectonic setting, rather than a Pacific Ocean-related setting. We propose a tectonic model involving episodic flat slab subduction, slab rollback, and intracontinental back-arc extension for Neotethyan subduction in the Yunnan-Burma region.",
keywords = "Porphyry, Porphyry copper, Zircon",
author = "Huichuan Liu and Yuejun Wang and Cawood, {Peter A.} and Xiaofei Guo",
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pages = "698--714",
journal = "Geological Society of America Bulletin",
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Episodic slab rollback and back-arc extension in the Yunnan-Burma region : Insights from cretaceous Nb-enriched and oceanic-island basalt-like mafic rocks. / Liu, Huichuan; Wang, Yuejun; Cawood, Peter A.; Guo, Xiaofei.

In: Geological Society of America Bulletin, Vol. 129, No. 5-6, 01.05.2017, p. 698-714.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Episodic slab rollback and back-arc extension in the Yunnan-Burma region

T2 - Insights from cretaceous Nb-enriched and oceanic-island basalt-like mafic rocks

AU - Liu, Huichuan

AU - Wang, Yuejun

AU - Cawood, Peter A.

AU - Guo, Xiaofei

PY - 2017/5/1

Y1 - 2017/5/1

N2 - One highly debated topic related to the nature of the Cretaceous mantle and geodynamic processes in SE Asia is whether they were dominated by the Tethyan or Pacific Ocean subductions. The main reason for this puzzle is the lack of geochemical studies on mantle-derived mafic rocks in SE Asia. In this paper, we report Early Cretaceous Nbenriched diabases (ca. 139 Ma) and Late Cretaceous Nb-enriched (ca. 68 Ma) and oceanic-island basalt (OIB)-like (ca. 73 Ma) amphibolites from the Ailaoshan tectonic zone in the Yunnan-Burma region. The ca. 139 Ma diabases and ca. 68 Ma amphibolites display similar geochemical features with typical Nb-enriched basalts, e.g., high Na2O, TiO2, and Nb (>7 ppm) contents, and high (Nb/Th)PM, (Nb/La)PM, and Nb/U ratios. Unlike adakite-associated Nb-enriched basalts, our Nb-enriched diabases and ampibolites were derived through mixing between OIBlike and arc-like mantle source components in the spinel stability field (<70 km), and the Nb-enriched diabases involved an additional high degree (~18%) of partial melting of the mixed source. In comparison with the Nb-enriched mafic rocks, the ca. 73 Ma OIB-like amphibolites have lower Mg# values, higher TiO2 and Nb (20.0-26.0 ppm) contents, and OIB-like rare earth element patterns and trace-element spidergrams. The OIB-like rocks were generated by a low degree of partial melting of garnet-facies peridotite (>80 km). In combination with previous Cretaceous to early Eocene age data from granitoids, three significant magmatic flare-ups are identified at 140-115 Ma, 75-64 Ma, and 55-50 Ma, with two magmatic gaps at 115-75 Ma and 64-55 Ma. Given the distances of the studied area from the Pacific and Neotethyan trenches (2400-5000 km and 320 km, respectively), these Cretaceous igneous rocks more likely formed in a Neotethyan subduction-related tectonic setting, rather than a Pacific Ocean-related setting. We propose a tectonic model involving episodic flat slab subduction, slab rollback, and intracontinental back-arc extension for Neotethyan subduction in the Yunnan-Burma region.

AB - One highly debated topic related to the nature of the Cretaceous mantle and geodynamic processes in SE Asia is whether they were dominated by the Tethyan or Pacific Ocean subductions. The main reason for this puzzle is the lack of geochemical studies on mantle-derived mafic rocks in SE Asia. In this paper, we report Early Cretaceous Nbenriched diabases (ca. 139 Ma) and Late Cretaceous Nb-enriched (ca. 68 Ma) and oceanic-island basalt (OIB)-like (ca. 73 Ma) amphibolites from the Ailaoshan tectonic zone in the Yunnan-Burma region. The ca. 139 Ma diabases and ca. 68 Ma amphibolites display similar geochemical features with typical Nb-enriched basalts, e.g., high Na2O, TiO2, and Nb (>7 ppm) contents, and high (Nb/Th)PM, (Nb/La)PM, and Nb/U ratios. Unlike adakite-associated Nb-enriched basalts, our Nb-enriched diabases and ampibolites were derived through mixing between OIBlike and arc-like mantle source components in the spinel stability field (<70 km), and the Nb-enriched diabases involved an additional high degree (~18%) of partial melting of the mixed source. In comparison with the Nb-enriched mafic rocks, the ca. 73 Ma OIB-like amphibolites have lower Mg# values, higher TiO2 and Nb (20.0-26.0 ppm) contents, and OIB-like rare earth element patterns and trace-element spidergrams. The OIB-like rocks were generated by a low degree of partial melting of garnet-facies peridotite (>80 km). In combination with previous Cretaceous to early Eocene age data from granitoids, three significant magmatic flare-ups are identified at 140-115 Ma, 75-64 Ma, and 55-50 Ma, with two magmatic gaps at 115-75 Ma and 64-55 Ma. Given the distances of the studied area from the Pacific and Neotethyan trenches (2400-5000 km and 320 km, respectively), these Cretaceous igneous rocks more likely formed in a Neotethyan subduction-related tectonic setting, rather than a Pacific Ocean-related setting. We propose a tectonic model involving episodic flat slab subduction, slab rollback, and intracontinental back-arc extension for Neotethyan subduction in the Yunnan-Burma region.

KW - Porphyry

KW - Porphyry copper

KW - Zircon

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