Geochronology and geochemistry of 830 Ma gabbro in the western segment of the Jiangnan Orogen and constraint on its petrogenesis

doi:10.13745/j.esf.sf.2021.7.11

Abstract

Abstract:

We report gabbro discovered in the western segment of the Jiangnan Orogen Belt, Sibao area, northern Guangxi Province. The gabbro contains mostly plagioclase and clinopyroxene and a small amount of olivine and Fe-Ti oxide minerals, indicating likely fractionation of plagioclase, clinopyroxene and some olivine within the magma chamber. The gabbro specimen has a zircon SIMS U-Pb age of (830±7) Ma, suggesting gabbro emplacement at ~830 Ma. The bulk-rock is characterized by relatively low SiO₂ (48.46%-53.99%) and high MgO (9.27%-25.22%) contents with Mg^# of 62-79. It belongs to typical calc-alkalic arc rock, characterized by enrichments of light rare earth elements and large-ion lithophile elements relative to heavy rare earth elements ((La/Yb)_N=2.2-3.7, (La/Sm)_N=2.5-2.9), significantly negative Nb, Ta and Ti anomalies, and relatively high Th/Nb (0.7-0.8) and low Nb/La (0.4-0.6) ratios. The gabbro specimen has negative ε_Nd(t) (-6.3--3.0) and positive ε_Hf(t) (8.0-12.1), indicating it is sourced from depleted mantle with the addition of enriched components. In combination with the regional geology, we infer the gabbro is derived from depleted mantle wedge metasomatized by sediment-derived fluids and formed in the active continental margin in a subduction setting.

Key words: western Jiangnan Orogen, Neoproterozoic mafic intrusion, Zircon SIMS U-Pb dating, petrogenesis, tectonic setting

CLC Number:

KOU Caihua, LIU Yanxue, LI Jiang, LI Tingdong, DING Xiaozhong, LIU Yong, JIN Shengkai. Geochronology and geochemistry of 830 Ma gabbro in the western segment of the Jiangnan Orogen and constraint on its petrogenesis[J]. Earth Science Frontiers, 2022, 29(2): 218-233.

Figures/Tables 15

References 52

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样号	w_B/%																																						Mg^#
样号	SiO₂			Al₂O₃			FeO^T			MgO			CaO				Na₂O			K₂O				MnO			TiO₂			P₂O₅				LOI		Total			Mg^#
1211-6	51.45			12.56			12.31			11.54			7.31				2.10			1.76				0.22			0.69			0.07				5.15		94.85			67
1211-7	48.82			17.07			13.42			10.24			6.64				1.43			1.48				0.22			0.61			0.06				4.00		96.00			62
1211-8	52.28			12.49			11.97			11.36			7.38				2.22			1.31				0.24			0.67			0.07				4.91		95.09			67
1211-9	53.99			14.53			10.04			9.27			7.88				2.32			1.10				0.25			0.56			0.06				2.44		97.56			66
1211-10	48.82			9.15			12.93			21.23			6.82				0.26			0.07				0.19			0.48			0.06				5.33		94.67			78
1211-11	49.19			8.44			13.31			21.97			6.05				0.28			0.06				0.22			0.42			0.07				5.41		94.59			78
1211-12	48.59			9.64			13.15			21.50			6.23				0.29			0.06				0.18			0.48			0.05				5.36		94.64			78
1211-13	48.46			7.50			14.05			25.22			4.06				0.08			0.03				0.18			0.39			0.05				6.99		93.01			79
1211-14	48.50			8.56			13.65			23.09			5.31				0.20			0.05				0.18			0.42			0.04				5.93		94.07			78
样号	w_B/10^-6
样号	Rb		Ba			Th			U			Nb			Ta			La			Ce		Pr			Sr			Nd			Sm			Zr		Hf			Eu
1211-6	114		473			5.01			0.876			6.06			0.568			10.70			20.2		2.67			149			10.90			2.61			46.9		1.81			0.738
1211-7	103		90.2			3.38			0.507			4.01			0.427			6.67			12.9		1.70			162			7.03			1.74			24.6		1.00			0.453
1211-8	59.9		550			4.28			0.918			5.87			0.485			11.40			21.7		2.83			149			11.50			2.69			60.5		1.93			0.776
1211-9	74.2		128			3.15			0.574			4.32			0.404			8.99			17.7		2.34			138			9.56			2.29			32.3		1.20			0.600
1211-10	8.81		84.0			2.83			0.817			3.89			0.390			7.00			14.6		1.90			21.6			7.88			1.82			59.2		1.70			0.424
1211-11	2.96		3.94			2.52			0.659			3.37			0.338			7.84			15.2		1.93			12.7			7.95			1.79			47.0		1.38			0.505
1211-12	1.42		3.81			2.74			0.586			3.48			0.381			6.77			13.4		1.75			13.9			7.23			1.67			49.7		1.57			0.486
1211-13	1.09		4.00			2.36			0.441			3.04			0.321			5.55			11.1		1.42			18.3			5.93			1.37			27.9		0.889			0.219
1211-14	0.925		3.28			2.65			0.495			3.28			0.337			7.02			11.4		1.28			9.81			6.90			1.54			41.5		1.29			0.274
样号	w_B/10^-6																																(La/Sm)_N					(La/Yb)_N			δEu
样号	Ti	Gd			Tb			Dy			Ho			Y		Er			Tm			Yb			Lu			Cr			Ni		(La/Sm)_N					(La/Yb)_N			δEu
1211-6	4 109	2.55			0.562			3.47			0.756			18.3		2.15			0.405			2.46			0.359			846			499		2.65					3.12			0.86
1211-7	3 659	1.81			0.428			2.68			0.624			15.3		1.81			0.359			2.18			0.326			536			125		2.47					2.19			0.77
1211-8	4 036	2.69			0.573			3.48			0.795			18.7		2.13			0.401			2.48			0.353			881			604		2.74					3.30			0.87
1211-9	3 371	2.32			0.512			3.18			0.722			17.4		1.99			0.377			2.26			0.310			555			109		2.53					2.85			0.79
1211-10	2 876	1.87			0.400			2.48			0.533			13.1		1.50			0.281			1.78			0.258			2 434			498		2.48					2.82			0.70
1211-11	2 543	1.76			0.373			2.20			0.486			12.0		1.40			0.257			1.59			0.223			2 598			575		2.83					3.54			0.86
1211-12	2 891	1.70			0.374			2.22			0.512			12.0		1.41			0.269			1.58			0.232			2 765			587		2.62					3.07			0.87
1211-13	2 309	1.33			0.272			1.64			0.359			8.35		0.994			0.186			1.1			0.170			2 548			615		2.62					3.62			0.49
1211-14	2 524	1.53			0.324			1.97			0.447			10.5		1.23			0.232			1.37			0.201			2 957			618		2.94					3.68			0.54

样号	w_B/%																																						Mg^#
样号	SiO₂			Al₂O₃			FeO^T			MgO			CaO				Na₂O			K₂O				MnO			TiO₂			P₂O₅				LOI		Total			Mg^#
1211-6	51.45			12.56			12.31			11.54			7.31				2.10			1.76				0.22			0.69			0.07				5.15		94.85			67
1211-7	48.82			17.07			13.42			10.24			6.64				1.43			1.48				0.22			0.61			0.06				4.00		96.00			62
1211-8	52.28			12.49			11.97			11.36			7.38				2.22			1.31				0.24			0.67			0.07				4.91		95.09			67
1211-9	53.99			14.53			10.04			9.27			7.88				2.32			1.10				0.25			0.56			0.06				2.44		97.56			66
1211-10	48.82			9.15			12.93			21.23			6.82				0.26			0.07				0.19			0.48			0.06				5.33		94.67			78
1211-11	49.19			8.44			13.31			21.97			6.05				0.28			0.06				0.22			0.42			0.07				5.41		94.59			78
1211-12	48.59			9.64			13.15			21.50			6.23				0.29			0.06				0.18			0.48			0.05				5.36		94.64			78
1211-13	48.46			7.50			14.05			25.22			4.06				0.08			0.03				0.18			0.39			0.05				6.99		93.01			79
1211-14	48.50			8.56			13.65			23.09			5.31				0.20			0.05				0.18			0.42			0.04				5.93		94.07			78
样号	w_B/10^-6
样号	Rb		Ba			Th			U			Nb			Ta			La			Ce		Pr			Sr			Nd			Sm			Zr		Hf			Eu
1211-6	114		473			5.01			0.876			6.06			0.568			10.70			20.2		2.67			149			10.90			2.61			46.9		1.81			0.738
1211-7	103		90.2			3.38			0.507			4.01			0.427			6.67			12.9		1.70			162			7.03			1.74			24.6		1.00			0.453
1211-8	59.9		550			4.28			0.918			5.87			0.485			11.40			21.7		2.83			149			11.50			2.69			60.5		1.93			0.776
1211-9	74.2		128			3.15			0.574			4.32			0.404			8.99			17.7		2.34			138			9.56			2.29			32.3		1.20			0.600
1211-10	8.81		84.0			2.83			0.817			3.89			0.390			7.00			14.6		1.90			21.6			7.88			1.82			59.2		1.70			0.424
1211-11	2.96		3.94			2.52			0.659			3.37			0.338			7.84			15.2		1.93			12.7			7.95			1.79			47.0		1.38			0.505
1211-12	1.42		3.81			2.74			0.586			3.48			0.381			6.77			13.4		1.75			13.9			7.23			1.67			49.7		1.57			0.486
1211-13	1.09		4.00			2.36			0.441			3.04			0.321			5.55			11.1		1.42			18.3			5.93			1.37			27.9		0.889			0.219
1211-14	0.925		3.28			2.65			0.495			3.28			0.337			7.02			11.4		1.28			9.81			6.90			1.54			41.5		1.29			0.274
样号	w_B/10^-6																																(La/Sm)_N					(La/Yb)_N			δEu
样号	Ti	Gd			Tb			Dy			Ho			Y		Er			Tm			Yb			Lu			Cr			Ni		(La/Sm)_N					(La/Yb)_N			δEu
1211-6	4 109	2.55			0.562			3.47			0.756			18.3		2.15			0.405			2.46			0.359			846			499		2.65					3.12			0.86
1211-7	3 659	1.81			0.428			2.68			0.624			15.3		1.81			0.359			2.18			0.326			536			125		2.47					2.19			0.77
1211-8	4 036	2.69			0.573			3.48			0.795			18.7		2.13			0.401			2.48			0.353			881			604		2.74					3.30			0.87
1211-9	3 371	2.32			0.512			3.18			0.722			17.4		1.99			0.377			2.26			0.310			555			109		2.53					2.85			0.79
1211-10	2 876	1.87			0.400			2.48			0.533			13.1		1.50			0.281			1.78			0.258			2 434			498		2.48					2.82			0.70
1211-11	2 543	1.76			0.373			2.20			0.486			12.0		1.40			0.257			1.59			0.223			2 598			575		2.83					3.54			0.86
1211-12	2 891	1.70			0.374			2.22			0.512			12.0		1.41			0.269			1.58			0.232			2 765			587		2.62					3.07			0.87
1211-13	2 309	1.33			0.272			1.64			0.359			8.35		0.994			0.186			1.1			0.170			2 548			615		2.62					3.62			0.49
1211-14	2 524	1.53			0.324			1.97			0.447			10.5		1.23			0.232			1.37			0.201			2 957			618		2.94					3.68			0.54

样号	w_B/10^-6		¹⁴⁷Sm/¹⁴⁴Nd	¹⁴³Nd/¹⁴⁴Nd	Nd标准误差	(¹⁴³Nd/¹⁴⁴Nd)_i	εNd(t)
样号	Sm	Nd	¹⁴⁷Sm/¹⁴⁴Nd	¹⁴³Nd/¹⁴⁴Nd	Nd标准误差	(¹⁴³Nd/¹⁴⁴Nd)_i	εNd(t)
1211-6	2.42	10.10	0.144 2	0.512 085	0.000 004	0.511 291	-5.2
1211-7	1.56	6.21	0.151 8	0.512 184	0.000 006	0.511 348	-4
1211-8	2.44	10.30	0.143 6	0.512 086	0.000 006	0.511 295	-5.1
1211-9	2.09	8.50	0.148 5	0.512 219	0.000 006	0.511 401	-3
1211-10	1.70	7.19	0.143 0	0.512 056	0.000 007	0.511 268	-5.6
1211-11	1.69	7.40	0.138 3	0.512 009	0.000 018	0.511 247	-6
1211-12	1.58	6.76	0.141 3	0.512 055	0.000 008	0.511 277	-5.4
1211-13	1.19	4.98	0.144 7	0.512 041	0.000 006	0.511 244	-6.1
1211-14	1.34	5.50	0.146 9	0.512 042	0.000 009	0.511 330	-6.3

样号	w_B/10^-6		¹⁴⁷Sm/¹⁴⁴Nd	¹⁴³Nd/¹⁴⁴Nd	Nd标准误差	(¹⁴³Nd/¹⁴⁴Nd)_i	εNd(t)
样号	Sm	Nd	¹⁴⁷Sm/¹⁴⁴Nd	¹⁴³Nd/¹⁴⁴Nd	Nd标准误差	(¹⁴³Nd/¹⁴⁴Nd)_i	εNd(t)
1211-6	2.42	10.10	0.144 2	0.512 085	0.000 004	0.511 291	-5.2
1211-7	1.56	6.21	0.151 8	0.512 184	0.000 006	0.511 348	-4
1211-8	2.44	10.30	0.143 6	0.512 086	0.000 006	0.511 295	-5.1
1211-9	2.09	8.50	0.148 5	0.512 219	0.000 006	0.511 401	-3
1211-10	1.70	7.19	0.143 0	0.512 056	0.000 007	0.511 268	-5.6
1211-11	1.69	7.40	0.138 3	0.512 009	0.000 018	0.511 247	-6
1211-12	1.58	6.76	0.141 3	0.512 055	0.000 008	0.511 277	-5.4
1211-13	1.19	4.98	0.144 7	0.512 041	0.000 006	0.511 244	-6.1
1211-14	1.34	5.50	0.146 9	0.512 042	0.000 009	0.511 330	-6.3