An alternative perspective of the origin of oxide gabbros from ocean ridge: The case of the ODP 735B core from the Southwest Indian Ridge

doi:10.13745/j.esf.sf.2020.6.32

Abstract

Abstract:

ODP 735B core from the Southwest Indian Ridge is highly abundant in Fe-Ti oxide-rich gabbros, which is particularly significant in lothologic Unit Ⅳ of this core. Meanwhile, the primary silicate minerals in Unit Ⅳ display unique trend of compositional variations. The formation and the unusual compositional variations of the oxide gabbros are commonly considered to have occurred through modifications by highly differentiated Fe-Ti-rich melts forming beneath or adjacent to Hole 735B, which migrated into the section along shear zones and reacted with an upwardly differentiated olivine gabbro protolith. Here, we report the detailed petrographic features and structure-controlled mineral profiles of the Unit Ⅳ oxide gabbros to provide a new perspective on the their formation. It can be seen that when some evolved silicate minerals formed due to the injection of exotic materials, Fe-Ti oxides should have remained unsaturated in the liquid. Additionally, the clinopyroxenes follow the crystallization sequence of augite → pigeonite → augite during crystallization, and near contacts with the later-formed minerals in the oxide gabbros (e.g., Fe-Ti oxides or orthopyroxene), the clinopyroxenes have significantly evolved compositions. Based on the detailed petrographic features and mineral compositional microprobe data, combining with discussion on Fe-Ti-rich melts by former researchers, we propose exotic mantle-derived hydrous fluids or liquid mixtures of hydrous fluids and basaltic melts, rather than just highly differentiated Fe-Ti-rich melts, as the suitable exotic materials involved within the formation of the oxide gabbros in Unit Ⅳ. Theoretically, these fluids might not originate from the same source region as the basaltic melt, which means that these fluids might migrate not only vertically, but also laterally over long distances. Therefore, it is reasonable to speculate that oxide gabbros in Unit Ⅳ should have unique isotopic features, which would be important clues in testing the mechanism of the formation of oxide gabbros in Unit Ⅳ, even in the whole 735B core.

Key words: exotic hydrous fluids, oxide gabbros, lithologic unit Ⅳ, ODP 735B core, Southwest Indian Ridge

CLC Number:

JIN Ye, FANG Nianqiao, YUAN Xiaobo, HU Ke. An alternative perspective of the origin of oxide gabbros from ocean ridge: The case of the ODP 735B core from the Southwest Indian Ridge[J]. Earth Science Frontiers, 2021, 28(1): 334-352.

Figures/Tables 13

References 68

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测试点			矿物类型			w_B/%
测试点			矿物类型			SiO₂		TiO₂		Al₂O₃		Cr₂O₃		FeO		MnO		MgO		CaO		Na₂O	K₂O		P₂O₅		NiO		V₂O₅		CoO		CuO		ZnO		SO₃		F		Cl	总量
剖面A-B	1	斜长石		59.599	0.066		24.747		0.019		0.170		0.039		0.009		7.350		6.995		0.179			0.047		0.003		—		0.012		0.024		—		0.005		—		0.032		99.296
	2	斜长石		60.449	0.116		24.799		0.011		0.169		0.003		0.005		7.203		7.091		0.160			—		—		0.010		0.023		0.005		0.028		—		—		—		100.072
	3	斜长石		60.034	0.030		24.727		—		0.189		—		0.036		7.474		7.050		0.117			0.054		—		0.048		0.016		—		0.055		0.021		—		0.015		99.866
	4	钛铁氧化物^a		0.082	5.952		4.115		0.003		79.755		0.256		0.289		—		0.058		0.008			—		0.020		1.938		0.147		—		0.063		—		—		0.013		92.699
	5	钛铁氧化物^b		0.025	53.629		0.001		0.026		44.675		0.840		0.733		—		0.008		0.011			—		0.030		0.576		0.067		—		0.056		—		—		—		100.677
	6	钛铁氧化物^a		0.102	6.577		4.361		0.072		78.576		0.267		0.442		—		0.045		—			—		0.022		1.934		0.183		—		0.150		—		—		0.016		92.747
	7	单斜辉石		51.355	0.686		1.879		—		11.866		0.363		12.507		20.026		0.483		0.017			—		0.045		0.071		0.021		—		0.066		—		—		0.017		99.402
	8	单斜辉石		51.214	0.900		2.118		—		12.408		0.383		12.585		18.778		0.501		—			0.064		—		0.098		0.032		—		0.131		0.023		—		—		99.235
	9	单斜辉石		49.996	0.748		2.078		—		14.393		0.379		13.602		17.466		0.430		—			0.058		0.021		0.123		0.054		0.066		0.032		—		—		—		99.446
	10	单斜辉石		50.532	0.739		2.203		—		12.211		0.359		12.811		21.092		0.518		0.005			0.025		0.021		0.095		0.035		—		0.064		—		—		—		100.710
	11	单斜辉石		51.826	0.489		1.916		—		10.898		0.275		13.207		19.962		0.359		0.002			0.013		0.007		0.101		0.030		0.012		—		0.015		—		—		99.112
	12	钛铁氧化物^b		0.044	52.552		0.093		—		45.459		1.143		0.420		—		—		0.021			—		—		0.599		0.099		—		—		—		0.043		0.013		100.486
	13	单斜辉石		51.164	0.690		2.033		0.019		11.976		0.370		13.000		20.939		0.495		—			—		0.020		0.037		0.001		0.020		—		0.015		0.074		—		100.853
	14	单斜辉石		50.964	0.813		2.219		0.023		12.022		0.420		12.408		19.749		0.508		—			0.019		0.005		0.116		0.077		0.056		—		—		0.029		0.003		99.431
	15	单斜辉石		51.485	0.381		0.991		—		23.347		0.642		17.391		4.918		0.099		—			—		—		0.040		0.051		0.026		0.099		0.021		0.051		0.001		99.543
	16	钛铁氧化物^b		0.014	53.222		0.013		0.011		44.909		0.704		1.144		—		0.002		—			0.138		—		0.575		0.058		—		0.036		0.011		—		0.007		100.844
	17	钛铁氧化物^b		0.011	52.626		0.030		—		44.604		0.619		1.648		—		—		0.001			0.133		—		0.672		0.064		—		—		—		—		0.010		100.418
	18	钛铁氧化物^a		0.048	4.412		2.147		0.069		82.596		0.136		0.281		—		—		—			—		—		2.018		0.136		0.002		0.104		—		—		0.001		91.950
	19	单斜辉石		50.850	0.811		2.111		—		12.111		0.320		12.631		21.104		0.490		—			0.045		0.037		0.130		0.006		—		0.030		—		—		—		100.676
	20	单斜辉石		51.265	0.366		0.972		0.008		24.307		0.562		17.483		5.576		0.132		0.003			—		0.014		0.053		0.072		—		0.134		—		—		0.001		100.948
	21	单斜辉石		51.325	0.509		1.646		0.022		17.170		0.529		14.788		12.872		0.312		—			0.026		0.024		0.091		0.054		0.014		0.075		—		0.014		0.002		99.473
剖面C-D	1	单斜辉石		51.232	0.581		1.837		0.009		12.727		0.311		12.935		20.275		0.482		—			0.038		—		0.096		—		0.032		0.029		—		0.015		—		100.599
	2	斜长石		60.162	0.063		24.729		0.026		0.198		—		0.027		7.028		7.095		0.209			0.040		—		0.014		0.020		0.049		—		0.035		—		—		99.695
	3	单斜辉石		51.005	0.474		1.378		0.029		11.487		0.358		13.076		21.513		0.461		0.008			0.019		—		0.012		0.010		—		0.026		—		—		—		99.856
	4	硫化物		2.284	—		0.155		0.121		55.907		0.032		0.238		0.312		0.424		0.146			0.044		0.21		0.009		0.463		0.161		0.091		59.743		—		0.057		120.397
	5	斜方辉石		51.957	0.206		0.753		0.006		25.527		0.580		18.909		1.589		0.035		—			—		—		0.038		0.074		0.019		0.057		0.003		0.074		0.003		99.830
	6	单斜辉石		51.306	0.421		1.299		0.003		21.559		0.603		16.274		7.912		0.201		0.026			—		—		0.053		0.058		—		—		—		—		0.012		99.727
剖面E-F	1	单斜辉石		51.074	0.479		1.499		0.045		13.729		0.400		13.656		18.479		0.402		—			0.038		—		0.118		0.002		—		0.019		—		—		0.012		99.952
	2	斜方辉石		52.026	0.261		0.655		0.003		27.064		0.659		18.904		0.933		0.001		—			0.046		0.018		0.013		0.061		—		—		0.005		0.049		—		100.698
	3	硫化物		0.910	—		0.023		0.075		59.602		0.026		0.066		0.033		0.499		0.150			0.038		0.125		—		0.360		—		0.072		61.813		—		0.043		123.835
	4	单斜辉石		50.654	0.602		1.984		0.024		12.937		0.342		12.983		19.749		0.523		0.021			0.019		0.021		0.085		—		0.049		—		—		—		0.007		100.000

测试点			矿物类型			w_B/%
测试点			矿物类型			SiO₂		TiO₂		Al₂O₃		Cr₂O₃		FeO		MnO		MgO		CaO		Na₂O	K₂O		P₂O₅		NiO		V₂O₅		CoO		CuO		ZnO		SO₃		F		Cl	总量
剖面A-B	1	斜长石		59.599	0.066		24.747		0.019		0.170		0.039		0.009		7.350		6.995		0.179			0.047		0.003		—		0.012		0.024		—		0.005		—		0.032		99.296
	2	斜长石		60.449	0.116		24.799		0.011		0.169		0.003		0.005		7.203		7.091		0.160			—		—		0.010		0.023		0.005		0.028		—		—		—		100.072
	3	斜长石		60.034	0.030		24.727		—		0.189		—		0.036		7.474		7.050		0.117			0.054		—		0.048		0.016		—		0.055		0.021		—		0.015		99.866
	4	钛铁氧化物^a		0.082	5.952		4.115		0.003		79.755		0.256		0.289		—		0.058		0.008			—		0.020		1.938		0.147		—		0.063		—		—		0.013		92.699
	5	钛铁氧化物^b		0.025	53.629		0.001		0.026		44.675		0.840		0.733		—		0.008		0.011			—		0.030		0.576		0.067		—		0.056		—		—		—		100.677
	6	钛铁氧化物^a		0.102	6.577		4.361		0.072		78.576		0.267		0.442		—		0.045		—			—		0.022		1.934		0.183		—		0.150		—		—		0.016		92.747
	7	单斜辉石		51.355	0.686		1.879		—		11.866		0.363		12.507		20.026		0.483		0.017			—		0.045		0.071		0.021		—		0.066		—		—		0.017		99.402
	8	单斜辉石		51.214	0.900		2.118		—		12.408		0.383		12.585		18.778		0.501		—			0.064		—		0.098		0.032		—		0.131		0.023		—		—		99.235
	9	单斜辉石		49.996	0.748		2.078		—		14.393		0.379		13.602		17.466		0.430		—			0.058		0.021		0.123		0.054		0.066		0.032		—		—		—		99.446
	10	单斜辉石		50.532	0.739		2.203		—		12.211		0.359		12.811		21.092		0.518		0.005			0.025		0.021		0.095		0.035		—		0.064		—		—		—		100.710
	11	单斜辉石		51.826	0.489		1.916		—		10.898		0.275		13.207		19.962		0.359		0.002			0.013		0.007		0.101		0.030		0.012		—		0.015		—		—		99.112
	12	钛铁氧化物^b		0.044	52.552		0.093		—		45.459		1.143		0.420		—		—		0.021			—		—		0.599		0.099		—		—		—		0.043		0.013		100.486
	13	单斜辉石		51.164	0.690		2.033		0.019		11.976		0.370		13.000		20.939		0.495		—			—		0.020		0.037		0.001		0.020		—		0.015		0.074		—		100.853
	14	单斜辉石		50.964	0.813		2.219		0.023		12.022		0.420		12.408		19.749		0.508		—			0.019		0.005		0.116		0.077		0.056		—		—		0.029		0.003		99.431
	15	单斜辉石		51.485	0.381		0.991		—		23.347		0.642		17.391		4.918		0.099		—			—		—		0.040		0.051		0.026		0.099		0.021		0.051		0.001		99.543
	16	钛铁氧化物^b		0.014	53.222		0.013		0.011		44.909		0.704		1.144		—		0.002		—			0.138		—		0.575		0.058		—		0.036		0.011		—		0.007		100.844
	17	钛铁氧化物^b		0.011	52.626		0.030		—		44.604		0.619		1.648		—		—		0.001			0.133		—		0.672		0.064		—		—		—		—		0.010		100.418
	18	钛铁氧化物^a		0.048	4.412		2.147		0.069		82.596		0.136		0.281		—		—		—			—		—		2.018		0.136		0.002		0.104		—		—		0.001		91.950
	19	单斜辉石		50.850	0.811		2.111		—		12.111		0.320		12.631		21.104		0.490		—			0.045		0.037		0.130		0.006		—		0.030		—		—		—		100.676
	20	单斜辉石		51.265	0.366		0.972		0.008		24.307		0.562		17.483		5.576		0.132		0.003			—		0.014		0.053		0.072		—		0.134		—		—		0.001		100.948
	21	单斜辉石		51.325	0.509		1.646		0.022		17.170		0.529		14.788		12.872		0.312		—			0.026		0.024		0.091		0.054		0.014		0.075		—		0.014		0.002		99.473
剖面C-D	1	单斜辉石		51.232	0.581		1.837		0.009		12.727		0.311		12.935		20.275		0.482		—			0.038		—		0.096		—		0.032		0.029		—		0.015		—		100.599
	2	斜长石		60.162	0.063		24.729		0.026		0.198		—		0.027		7.028		7.095		0.209			0.040		—		0.014		0.020		0.049		—		0.035		—		—		99.695
	3	单斜辉石		51.005	0.474		1.378		0.029		11.487		0.358		13.076		21.513		0.461		0.008			0.019		—		0.012		0.010		—		0.026		—		—		—		99.856
	4	硫化物		2.284	—		0.155		0.121		55.907		0.032		0.238		0.312		0.424		0.146			0.044		0.21		0.009		0.463		0.161		0.091		59.743		—		0.057		120.397
	5	斜方辉石		51.957	0.206		0.753		0.006		25.527		0.580		18.909		1.589		0.035		—			—		—		0.038		0.074		0.019		0.057		0.003		0.074		0.003		99.830
	6	单斜辉石		51.306	0.421		1.299		0.003		21.559		0.603		16.274		7.912		0.201		0.026			—		—		0.053		0.058		—		—		—		—		0.012		99.727
剖面E-F	1	单斜辉石		51.074	0.479		1.499		0.045		13.729		0.400		13.656		18.479		0.402		—			0.038		—		0.118		0.002		—		0.019		—		—		0.012		99.952
	2	斜方辉石		52.026	0.261		0.655		0.003		27.064		0.659		18.904		0.933		0.001		—			0.046		0.018		0.013		0.061		—		—		0.005		0.049		—		100.698
	3	硫化物		0.910	—		0.023		0.075		59.602		0.026		0.066		0.033		0.499		0.150			0.038		0.125		—		0.360		—		0.072		61.813		—		0.043		123.835
	4	单斜辉石		50.654	0.602		1.984		0.024		12.937		0.342		12.983		19.749		0.523		0.021			0.019		0.021		0.085		—		0.049		—		—		—		0.007		100.000

测试点		8个氧为基础计算阳离子数										端员组分指标
测试点		Si	Ti	Al	Fe	Mn	Mg	Ca	Na	K	Total	An	Ab	Or
剖面A-B	1	2.677	0.002	1.308	0.006	0.001	0.001	0.354	0.608	0.010	4.973	36.39	62.56	1.05
	2	2.691	0.004	1.299	0.006	-	-	0.343	0.611	0.009	4.966	35.65	63.40	0.95
	3	2.681	0.001	1.299	0.007	-	0.002	0.358	0.609	0.007	4.971	36.73	62.59	0.68
剖面C-D	2	2.688	0.002	1.300	0.007	-	0.002	0.336	0.614	0.012	4.967	34.98	63.78	1.24

测试点		8个氧为基础计算阳离子数										端员组分指标
测试点		Si	Ti	Al	Fe	Mn	Mg	Ca	Na	K	Total	An	Ab	Or
剖面A-B	1	2.677	0.002	1.308	0.006	0.001	0.001	0.354	0.608	0.010	4.973	36.39	62.56	1.05
	2	2.691	0.004	1.299	0.006	-	-	0.343	0.611	0.009	4.966	35.65	63.40	0.95
	3	2.681	0.001	1.299	0.007	-	0.002	0.358	0.609	0.007	4.971	36.73	62.59	0.68
剖面C-D	2	2.688	0.002	1.300	0.007	-	0.002	0.336	0.614	0.012	4.967	34.98	63.78	1.24

测试点			矿物类型		6个氧为基础计算阳离子数																							Mg^#		端员组分指标
测试点			矿物类型		Si		Ti		Al		Cr		Fe		Mn		Mg		Ca		Na			K		总量		Mg^#		Wo	En		Fs
剖面 A-B	7	单斜辉石		1.948		0.020		0.084		-		0.375		0.012		0.712		0.814		0.035		0.001	4.006		0.655		42.82		37.44			19.74
	8	单斜辉石		1.943		0.026		0.095		-		0.392		0.012		0.716		0.763		0.037		-	3.994		0.646		40.78		38.26			20.96
	9	单斜辉石		1.910		0.021		0.093		-		0.458		0.012		0.779		0.715		0.032		-	4.031		0.630		36.61		39.92			23.47
	10	单斜辉石		1.905		0.021		0.098		-		0.384		0.011		0.724		0.852		0.038		-	4.04		0.654		43.47		36.96			19.57
	11	单斜辉石		1.957		0.014		0.085		-		0.343		0.009		0.748		0.808		0.026		-	3.995		0.686		42.54		39.40			18.06
	13	单斜辉石		1.921		0.019		0.090		0.001		0.375		0.012		0.732		0.842		0.036		-	4.034		0.661		43.21		37.56			19.22
	14	单斜辉石		1.935		0.023		0.099		0.001		0.380		0.013		0.706		0.803		0.037		-	4.007		0.650		42.50		37.38			20.12
	15	单斜辉石		1.968		0.011		0.045		-		0.744		0.021		0.997		0.201		0.007		-	4.003		0.573		10.37		51.34			38.29
	19	单斜辉石		1.914		0.023		0.093		-		0.380		0.010		0.713		0.851		0.036		-	4.027		0.652		43.78		36.68			19.54
	20	单斜辉石		1.945		0.010		0.043		-		0.769		0.018		0.995		0.227		0.010		-	4.025		0.564		11.39		49.99			38.62
	21	单斜辉石		1.953		0.015		0.074		0.001		0.544		0.017		0.844		0.525		0.023		-	4.003		0.608		27.43		44.12			28.46
剖面 C-D	1	单斜辉石		1.929		0.016		0.081		-		0.399		0.010		0.731		0.818		0.035		-	4.026		0.647		41.99		37.51			20.50
	3	单斜辉石		1.934		0.013		0.061		0.001		0.363		0.011		0.744		0.874		0.034		-	4.037		0.672		44.13		37.55			18.33
	5	斜方辉石		1.978		0.006		0.034		-		0.810		0.019		1.080		0.065		0.003		-	4.003		0.571		3.32		55.25			41.44
	6	单斜辉石		1.958		0.012		0.058		-		0.686		0.019		0.931		0.323		0.015		0.001	4.007 5		0.576		16.67		48.00			35.33
剖面 E-F	1	单斜辉石		1.936		0.014		0.067		0.001		0.434		0.013		0.776		0.750		0.029		-	4.025		0.642		38.28		39.60			22.12
	2	斜方辉石		1.972		0.007		0.029		-		0.855		0.021		1.075		0.038		-		-	4.005		0.557		1.93		54.63			43.45
	4	单斜辉石		1.921		0.017		0.089		0.001		0.409		0.011		0.739		0.803		0.038		0.001	4.033		0.644		41.15		37.88			20.97