Contribution of continental subduction to very light B isotope signatures in post-collisional magmas: Evidence from southern Tibetan ultrapotassic rocks

Hao, Lu‐Lu; Wang, Qiang; Kerr, Andrew C.; Wei, Gangjian; Huang, Fang; Zhang, Miaoyan; Qi, Yue; Ma, Lin; Chen, Xuefei; Yang, Ya‐Nan

doi:10.1016/j.epsl.2022.117508

Cited by 25 publications

(12 citation statements)

References 51 publications

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“…Our explanation has been further verified by the very light B isotope compositions and low B/Nb ratios of the Sailipu ultrapotassic rocks, which are markedly similar to those of the post‐collisional ultrapotassic rocks from the TYXR in the Lhasa block (Hao, Wang, Kerr, et al., 2022). The very low B/Nb ratios of these post‐collisional ultrapotassic rocks indicate a fluid‐starved source and their low δ 11 B values cannot be derived from oceanic sediments or a stalled dehydrated oceanic slab.…”

Section: Discussionsupporting

confidence: 70%

“…(2015); Hao, Wang, Kerr, et al. (2022) and references therein. (c) Chondrite‐normalized rare earth element diagram.…”

Section: Resultsmentioning

confidence: 99%

“…The very low B/Nb ratios of these post-collisional ultrapotassic rocks indicate a fluid-starved source and their low δ 11 B values cannot be derived from oceanic sediments or a stalled dehydrated oceanic slab. Combined with the light B isotope compositions of the schists and gneisses of the Tethyan Himalaya (Fan et al, 2023), Hao, Wang, Kerr, et al (2022 proposed that the very light B isotope compositions of these post-collisional ultrapotassic rocks in southern Tibet are most likely derived from the subducted Indian continental crust.…”

Section: Light Mo Isotopic Compositions Sourced From Subducted Indian...mentioning

confidence: 99%

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Light Mo Isotopes of Post‐Collisional Ultrapotassic Rocks in Southern Tibet Derived From Subducted Indian Continental Crust

Zhang,

Huang,

Hao

et al. 2023

Geochem Geophys Geosyst

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Recycling of molybdenum isotopes in continental subduction zones remains debated. In this contribution, we re‐visit the Mo isotope compositions of the Sailipu post‐collisional ultrapotassic rocks in the Himalaya‐southern Tibet orogen. These ultrapotassic rocks have very varying δ98/95Mo values of −0.66 to −0.07‰ and Mo/Ce ratios of 0.0008–0.005, which are lower than those of mid‐ocean ridge basalts (MORB; δ98/95Mo = −0.20 ± 0.06‰, and Mo/Ce = 0.03) and oceanic subduction‐related (i.e., mantle source involving fluids, residual slab, or oceanic sediments) magmatic rocks (e.g., modern arc lavas, Cenozoic OIB‐type basalts in eastern China and the central Mariana Trough basalts in the back‐arc basin, syn‐collisional andesitic rocks in southern Tibet). Combined with the light Mo isotopes of the Himalayan schists and gneisses, we suggest that the light Mo isotopic signature of the Sailipu ultrapotassic rocks is derived from subducted Indian continental crust. This is consistent with the extremely low δ11B (−17.4 to −9.7‰) and B/Nb (0.16–1) values and enriched Sr‐Nd‐Pb isotopes of the Sailipu ultrapotassic rocks. Thus, this study reveals the recycling of light Mo‐B isotopes during continental subduction and demonstrates that Mo‐B isotopes can effectively distinguish between continental and oceanic subduction.

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Section: Discussionsupporting

confidence: 70%

“…(2015); Hao, Wang, Kerr, et al. (2022) and references therein. (c) Chondrite‐normalized rare earth element diagram.…”

Section: Resultsmentioning

confidence: 99%

Section: Light Mo Isotopic Compositions Sourced From Subducted Indian...mentioning

confidence: 99%

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Light Mo Isotopes of Post‐Collisional Ultrapotassic Rocks in Southern Tibet Derived From Subducted Indian Continental Crust

Zhang,

Huang,

Hao

et al. 2023

Geochem Geophys Geosyst

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“…Lhasa terrane can be partially explained by the northward decrease of the mantle enrichment in the past, that is, at least since Miocene, and the percentage of mantle components in gas samples in Lhasa terrane are higher than previously computed results assuming this new enriched mantle endmember (Figure 5a). We suggest that the recycled crustal components from subducting Indian slab are responsible for the enrichment (Figure 9a), supported by systematic N-S trends of Pb-Nd-Sr isotopes and light δ 11 B measured in the ultrapotassic rocks (Figure S6 in Supporting Information S1; Guo et al, 2013;Hao et al, 2022).…”

Section: Table 2 Summary Of Input Parameters and Output Results For M...mentioning

confidence: 60%

Subducting Indian Lithosphere Controls the Deep Carbon Emission in Lhasa Terrane, Southern Tibet

et al. 2022

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The India‐Asia orogenic zone is considered to participate significantly in the Earth's geological carbon budget. However, the carbon cycling process at orogenic belts with ongoing continental subduction is poorly constrained. Here, new He‐C‐N systematics of hydrothermal gases in Lhasa terrane are reported to explore carbon cycling and the role of the subducting Indian slab. Except for samples where the CO2 content and C isotopic signature were modified by calcite precipitation, gas samples in Lhasa terrane display low 3He/4He ratios of 0.015–0.895 RA but with increasing mantle‐helium input from south to north. Our modeling results show that the continuous subduction of the Indian continental slab has caused high Th‐U contents and time‐integrated 4He production rates in the present mantle wedge beneath the Lhasa terrane. The N‐S helium isotopic trend can be interpreted as a northward‐decreasing mantle enrichment. Compared to volatiles showing crustal helium but mantle‐like δ13C ratios, mantle‐helium‐richer fluids display heavier δ13C ratios, higher CO2/3He and molar C/N values, indicating a substantial carbonate input. We propose that the heavier carbon isotopes are inherited from the carbonated‐enriched mantle (CEM) rather than the carbonate assimilation of the overlying continental crust. Combined with an eastward increase in dip angle of the Indian lithosphere, we suggest that the slab rollback has caused asthenosphere heat flow and consequent decarbonation in CEM beneath northern and eastern Lhasa terrane, leading to enhanced isotopically heavier carbon release. Our study highlights the controlling role of subducting Indian lithosphere on the regional distribution of volatiles in the Lhasa terrane.

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“…This has for a long time been a puzzling issue, especially for the mantle-derived lamproites (Si-saturated), and leucitites and kamafugites (Si-undersaturated), which have the most extreme compositions: K 2 O up to 12 wt.%, 87 Sr/ 86 Sr up to 0.723, εNd down to -13 as well as highly forsteritic olivine (Fo up to 93 %) with δ 18 O V-SMOW values up to +11.5 ‰ 2,3 . These data establish a connection between the volcanism and the massive crustal recycling that must have played a crucial role in the mantle source preconditioning of AHOB 10 , and represent a global feature [11][12][13] . Some of the best-documented case studies come from AHOB, including the Upper Cretaceous Pontide and South Aegean arcs, but also Indonesian Batu Tara, Trans Mexican Volcanic Belt, Central and Southern Vosges Mts.…”

Section: Fore-arc Mantle As a Metasome Stowagementioning

confidence: 63%

Sediment recycling at the slab-mantle interface andfore-arc metasomatism: experimental production ofK-rich metasomes

Gülmez

Prelević

Förster

et al. 2023

Preprint

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Sediment contribution to the mantle is the key step for the generation of orogenic magmatism to produce its isotopic and geochemical inventory. Even though they are exceptional for the subduction settings, there are worldwide samples of arc-related ultrapotassic mafic magmas which require complex multi-stage processes along with sediment melting. To understand the metasomatism leading the mantle to produce ultrapotassic mafic melts we simulated the reactions of depleted (harzburgite)and fertile (lherzolite) mantle with subducted carbonate-rich sediment at relatively cold (800-850 oC) and shallow (2 GPa, 60-80 km) slab-mantle interfaces. The progressive devolatilization of the sediments can trigger the formation of immiscible and conjugate carbonatitic and silicic melts which flux the mantle to develop exotic minerals and dolomitic melts. The metasomatic growth product is a wehrlite composed of clinopyroxene, phlogopite, carbonate minerals, and amphibole

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Contribution of continental subduction to very light B isotope signatures in post-collisional magmas: Evidence from southern Tibetan ultrapotassic rocks

Cited by 25 publications

References 51 publications

Light Mo Isotopes of Post‐Collisional Ultrapotassic Rocks in Southern Tibet Derived From Subducted Indian Continental Crust

Light Mo Isotopes of Post‐Collisional Ultrapotassic Rocks in Southern Tibet Derived From Subducted Indian Continental Crust

Subducting Indian Lithosphere Controls the Deep Carbon Emission in Lhasa Terrane, Southern Tibet

Sediment recycling at the slab-mantle interface andfore-arc metasomatism: experimental production ofK-rich metasomes

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