Late-Paleoanthics diabase from the eastern part of the Bangong Lake-Nujiang subduction belt: U-Pb geochronology, Hf isotopic composition and geological characteristics

doi:10.13745/j.esf.sf.2021.7.27

Abstract

Abstract:

The Jiayuqiao-Tongka mélanges are located within the eastern part of the Bangong Lake-Nujiang subduction-accretion complex belt from Jiayuqiao to Bangda area whose spatial distribution, material composition, tectonic setting and genesis have been discussed to some extent by previous researchers but have not been studied in detail. For example, the formation era of the subduction-accretion complex has been determined to be the Late Paleozoic by geological survey (1: 250000) but lacked precise geochronological and geochemical constraints. In this contribution, the diabase of the Bangda Formation is investigated through detailed petrographic, geochemical and chronologic analyses to shed light on the development time and tectonic setting of the Bangong Lake-Nujiang structural zone. The diabase was found to be enriched in LILEs (Rb, Ba) and depleted in high HFSEs (Nb, Zr) and exhibited the geochemical characteristics of N-MORB. Its LREE pattern indicated a depleted N-MORB mantle source, while geochemical analysis further suggested the diabase is sourced from 30% partial melting of spinel lherzolite formed in a back-arc rift basin. The LA-ICP-MS U-Pb dating of zircon from the diabase yielded an average zircon age of (330.9 ± 1.6) Ma, which represents the crystallization age of diabase, indicating the Bangda diabase is formed in the Early Carboniferous epoch, and supporting the notion that the Bangong Lake-Nujiang structural zone retains geological information of the residual Paleo-Tethys. The results of this study on the Early Carboniferous N-MORB diabase provided an important reference for the reconstruction of the regional tectonic setting as well as for future studies on the spatio-temporal evolution of the Paleo-Tethys in the Bangong Lake-Nujiang region.

Key words: Bangong Lake-Nujiang subduction-accretion complex belt, Jiayuqiao-Tongka mélange belt, U-Pb age, N-MORB, geotectonics

CLC Number:

REN Fei, YIN Fuguang, PENG Zhimin, PAN Guitang, WEI Dong. Late-Paleoanthics diabase from the eastern part of the Bangong Lake-Nujiang subduction belt: U-Pb geochronology, Hf isotopic composition and geological characteristics[J]. Earth Science Frontiers, 2022, 29(2): 164-179.

Figures/Tables 16

References 55

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点位	Age/Ma	¹⁷⁶Hf/¹⁷⁷Hf	1σ	¹⁷⁶Lu/¹⁷⁷Hf	1σ	¹⁷⁶Yb/¹⁷⁷Hf	1σ	ε_Hf(0)	ε_Hf(t)	t_DM1	t_DM2	f_Lu/Hf
NJ-7-01	328	0.282 72	0.000 011	0.001 627	0.000 052	0.045 599	0.001 391	-1.84	5.09	766	928	-0.95
NJ-7-02	329	0.282 724	0.000 009	0.001 321	0.000 026	0.036 33	0.000 724	-1.69	5.30	754	916	-0.96
NJ-7-03	326	0.282 710	0.000 009	0.000 592	0.000 021	0.016 125	0.000 558	-2.2	4.95	760	936	-0.98
NJ-7-04	329	0.282 721	0.000 012	0.001 191	0.000 03	0.033 257	0.000 96	-1.8	5.22	756	921	-0.96
NJ-7-05	331	0.282 709	0.000 011	0.001 528	0.000 016	0.043 11	0.000 492	-2.23	4.72	780	949	-0.95
NJ-7-06	331	0.282 728	0.000 011	0.002 725	0.000 097	0.079 218	0.002 953	-1.56	5.13	778	926	-0.92
NJ-7-07	332	0.282 741	0.000 012	0.002 052	0.000 099	0.055 263	0.002 582	-1.1	5.74	745	892	-0.94
NJ-7-08	335	0.282 726	0.000 012	0.003 022	0.000 021	0.082 842	0.000 598	-1.63	4.99	788	933	-0.91
NJ-7-09	334	0.282 737	0.000 011	0.001 064	0.000 023	0.029 42	0.000 608	-1.25	5.80	732	889	-0.97
NJ-7-10	329	0.282 733	0.000 012	0.002 1	0.000 044	0.057 157	0.001 173	-1.37	5.45	757	908	-0.94
NJ-7-11	330	0.282 683	0.000 01	0.001 049	0.000 011	0.030 204	0.000 342	-3.16	3.89	807	995	-0.97
NJ-7-12	333	0.282 731	0.000 01	0.000 807	0.000 06	0.021 568	0.001 555	-1.44	5.66	734	896	-0.98
NJ-7-13	327	0.282 721	0.000 011	0.000 998	0.000 011	0.027 777	0.000 418	-1.82	5.24	753	920	-0.97
NJ-7-14	327	0.282 729	0.000 011	0.001 481	0.000 061	0.039 949	0.001 847	-1.5	5.45	750	908	-0.96
NJ-7-15	332	0.282 733	0.000 01	0.000 93	0.000 013	0.025 509	0.000 357	-1.37	5.71	734	894	-0.97

点位	Age/Ma	¹⁷⁶Hf/¹⁷⁷Hf	1σ	¹⁷⁶Lu/¹⁷⁷Hf	1σ	¹⁷⁶Yb/¹⁷⁷Hf	1σ	ε_Hf(0)	ε_Hf(t)	t_DM1	t_DM2	f_Lu/Hf
NJ-7-01	328	0.282 72	0.000 011	0.001 627	0.000 052	0.045 599	0.001 391	-1.84	5.09	766	928	-0.95
NJ-7-02	329	0.282 724	0.000 009	0.001 321	0.000 026	0.036 33	0.000 724	-1.69	5.30	754	916	-0.96
NJ-7-03	326	0.282 710	0.000 009	0.000 592	0.000 021	0.016 125	0.000 558	-2.2	4.95	760	936	-0.98
NJ-7-04	329	0.282 721	0.000 012	0.001 191	0.000 03	0.033 257	0.000 96	-1.8	5.22	756	921	-0.96
NJ-7-05	331	0.282 709	0.000 011	0.001 528	0.000 016	0.043 11	0.000 492	-2.23	4.72	780	949	-0.95
NJ-7-06	331	0.282 728	0.000 011	0.002 725	0.000 097	0.079 218	0.002 953	-1.56	5.13	778	926	-0.92
NJ-7-07	332	0.282 741	0.000 012	0.002 052	0.000 099	0.055 263	0.002 582	-1.1	5.74	745	892	-0.94
NJ-7-08	335	0.282 726	0.000 012	0.003 022	0.000 021	0.082 842	0.000 598	-1.63	4.99	788	933	-0.91
NJ-7-09	334	0.282 737	0.000 011	0.001 064	0.000 023	0.029 42	0.000 608	-1.25	5.80	732	889	-0.97
NJ-7-10	329	0.282 733	0.000 012	0.002 1	0.000 044	0.057 157	0.001 173	-1.37	5.45	757	908	-0.94
NJ-7-11	330	0.282 683	0.000 01	0.001 049	0.000 011	0.030 204	0.000 342	-3.16	3.89	807	995	-0.97
NJ-7-12	333	0.282 731	0.000 01	0.000 807	0.000 06	0.021 568	0.001 555	-1.44	5.66	734	896	-0.98
NJ-7-13	327	0.282 721	0.000 011	0.000 998	0.000 011	0.027 777	0.000 418	-1.82	5.24	753	920	-0.97
NJ-7-14	327	0.282 729	0.000 011	0.001 481	0.000 061	0.039 949	0.001 847	-1.5	5.45	750	908	-0.96
NJ-7-15	332	0.282 733	0.000 01	0.000 93	0.000 013	0.025 509	0.000 357	-1.37	5.71	734	894	-0.97