Citation:

dsdp.proc.54.124.1980

Name: (Table 1) Geochemistry of sector-zoned crystal at DSDP Hole 45-395A
Creator: James H Natland
Published: 1980
License: https://creativecommons.org/licenses/by/3.0/

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Abstract:

Variations in crystal morphologies in pillow basalts and probable sheet flows sampled from the region of the East Pacific Rise drilled during Leg 54 are related both to differences in composition and to an extreme range of cooling rate experienced upon extrusion. The basalts range in composition from olivine-rich tholeiites to tholeiitic ferrobasalts, and include some more alkaline basalts. The kinetics of crystal growth in some samples appears to have been influenced by the amount of initial superheating (or supercooling) of the magma, or possibly by differential retention of volatiles. Olivine in quartznormative ferrobasalts apparently formed metastably at high undercooling.

Despite these effects, reliable petrographic criteria are established to distinguish the principal rock types described regardless of the crystallinity and grain size. Microphenocrysts formed prior to pillow formation correspond closely to mineral assemblages inferred from normative plots and variation diagrams to control crystal fractionation at various stages. The details of spherulitic and dendritic growth also provide some clues about composition.

Petrographic evidence for magma mixing is scant. Only some Siqueiros fracture zone basalts contain zoned plagioclase phenocrysts with glass inclusions similar to those used to infer mixing among Mid-Atlantic Ridge basalts. All basalts from the summit and flanks of the East Pacific Rise are aphyric. One possible petrographic consequence of mixing between olivine tholeiites and ferrobasalts - formation of clinopyroxene phenocrysts - is not evident in any fracture zone or Rise crest basalt. Highly evolved ferrobasalts with liquidus low-Ca clinopyroxene have not been sampled, nor does textural evidence indicate that any basalts sampled are hybrid compositions between such magmas and less fractionated compositions. Evidently the sampled ferrobasalts are close to the most evolved compositions that occur in any abundance on this portion of the East Pacific Rise.

Project(s):

Deep Sea Drilling Project (DSDP)

Coverage:

Latitude: 22.755800 * Longitude: -46.081700

Date/Time Start: 1975-12-09T00:00:00 * Date/Time End: 1975-12-09T00:00:00

Minimum Elevation: -4484.0 m * Maximum Elevation: -4484.0 m

Event(s):

45-395A * Latitude: 22.755800 * Longitude: -46.081700 * Date/Time: 1975-12-09T00:00:00 * Elevation: -4484.0 m * Penetration: 664.1 m * Recovery: 112 m * Campaign: * Basis: Glomar Challenger * Method/Device: Drilling/drill rig (DRILL) * Comment: 68 cores; 624.1 m cored; 9.4 m drilled; 17.9 % recovery

Comment:

Analyses made on the Edinburgh University Mark V electron microprobe. Contribution by Colin H. Donaldson.

Parameter(s):

#	Name	Short Name	Unit	Principal Investigator	Method/Device	Comment
1	Sample code/label	Sample label		Natland, James H	DSDP/ODP/IODP sample designation
2	Comment	Comment		Natland, James H
3	Silicon dioxide	SiO2	%	Natland, James H	Electron microprobe (EMP)
4	Titanium dioxide	TiO2	%	Natland, James H	Electron microprobe (EMP)
5	Aluminium oxide	Al2O3	%	Natland, James H	Electron microprobe (EMP)
6	Chromium(III) oxide	Cr2O3	%	Natland, James H	Electron microprobe (EMP)
7	Iron oxide, FeO	FeO	%	Natland, James H	Electron microprobe (EMP)	Total iron
8	Manganese oxide	MnO	%	Natland, James H	Electron microprobe (EMP)
9	Magnesium oxide	MgO	%	Natland, James H	Electron microprobe (EMP)
10	Calcium oxide	CaO	%	Natland, James H	Electron microprobe (EMP)
11	Sodium oxide	Na2O	%	Natland, James H	Electron microprobe (EMP)
12	Total	Total	%	Natland, James H	Electron microprobe (EMP)
13	Silicon	Si	# of ions	Natland, James H	Calculated based on oxygen number
14	Aluminium (IV)	Al(IV)	# of ions	Natland, James H	Calculated based on oxygen number
15	Aluminium (VI)	Al(VI)	# of ions	Natland, James H	Calculated based on oxygen number
16	Titanium	Ti	# of ions	Natland, James H	Calculated based on oxygen number
17	Chromium	Cr	# of ions	Natland, James H	Calculated based on oxygen number
18	Iron 2+ and 3+	Fe	# of ions	Natland, James H	Calculated based on oxygen number
19	Manganese	Mn	# of ions	Natland, James H	Calculated based on oxygen number
20	Magnesium	Mg	# of ions	Natland, James H	Calculated based on oxygen number
21	Calcium	Ca	# of ions	Natland, James H	Calculated based on oxygen number
22	Sum	Sum	#	Natland, James H	Calculated based on oxygen number

License:

Creative Commons Attribution 3.0 Unported (CC-BY-3.0)

Size:

66 data points

Data

Download dataset as tab-delimited text — use the following character encoding:

1 Sample label	2 Comment	3 SiO2 [%]	4 TiO2 [%]	5 Al2O3 [%]	6 Cr2O3 [%]	7 FeO [%]	8 MnO [%]	9 MgO [%]	10 CaO [%]	11 Na2O [%]	12 Total [%]	13 Si [# of ions]	14 Al(IV) [# of ions]	15 Al(VI) [# of ions]	16 Ti [# of ions]	17 Cr [# of ions]	18 Fe [# of ions]	19 Mn [# of ions]	20 Mg [# of ions]	21 Ca [# of ions]	22 Sum [#]
45-395A-15-1,55-58	Core of Sector 100	52.73	0.67	2.33	0.66	5.81	0.13	17.31	20.26	<0.1	99.90	1.929	0.071	0.030	0.019	0.019	0.178	0.005	0.944	0.794	3.989
45-395A-15-1,55-58	Rim of Sector 100	51.24	0.91	3.31	0.54	6.46	0.25	16.50	20.31	<0.1	99.52	1.895	0.105	0.040	0.026	0.016	0.200	0.008	0.910	0.805	4.005
45-395A-15-1,55-58	Core of Sector 001	52.61	0.47	1.95	0.60	5.40	0.13	17.83	20.14	<0.1	99.13	1.937	0.063	0.021	0.013	0.018	0.166	0.004	0.977	0.793	3.992