Karson, J.A., Cannat, M., Miller, D.J., and Elthon, D. (Eds.), 1997 Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 153 27. DATA REPORT: MINERALOGY AND Sr- AND Nd-ISOTOPIC COMPOSITION OF GABBROIC OCEANIC CRUST RECOVERED FROM HOLES 923A AND 921E IN THE MARK AREA 1 Norie Fujibayashi, 2 Hiroo Kagami, 3 and Yoshiyuki Oishi 3 ABSTRACT Gabbroic rocks recovered from Holes 923A and 92IE in the MARK area include troctolite, clinopyroxene-olivine gabbro, olivine-clinopyroxene gabbro, gabbro, gabbronorite, oxide gabbro, and quartz diorite. Clinopyroxene and Plagioclase occur in all rock types, whereas olivine is supplanted by orthopyroxene in the evolved rock types and in the intercumulus stage. Forster- ite (Fo) content of olivine, magnesium number (Mg#) of pyroxenes, and anorthite (An) content of Plagioclase systematically decrease with decreasing modal olivine content, and Plagioclase is most sodic in the quartz diorite. Sr- and Nd-isotopic compo- sitions are characteristic of N-type MORB. INTRODUCTION Gabbroic oceanic crust was drilled at the Mid-Atlantic Ridge near the Kane Fracture Zone (MARK, 23°N) during Leg 153. The rock types obtained span a wide range, including troctolite, olivine gab- bro, gabbro, gabbronorite, oxide gabbro, and quartz diorite. Petrogra- phy, mineralogy, and Sr- and Nd-isotopes are reported for a suite of 27 gabbroic rocks from Holes 923A (23°32.55'N, 45°01.90'W) and 921E (23°32.40'N, 45°01.85'W) on the western median valley wall of the Mid-Atlantic Ridge about 10 km south of the Kane Transform Fault (Table 1). PETROGRAPHY Troctolite Troctolites occur as thin (a few centimeters) layers or as dikes em- placed in gabbro, clinopyroxene-olivine gabbro, and olivine-clinopy- roxene gabbro. Sample 153-923A-8R-2, Piece 1, is a thin dike. Sam- ple 153-923A-12R-1, Piece 4B, is composed of layered troctolite and clinopyroxene-olivine gabbro; the troctolite part is labeled 153- 923A-12R-1, Piece 4B-Tr. These troctolites have large, tabular but anhedral, Plagioclase, and anhedral olivine with less than 5% intersti- tial clinopyroxene and rare orthopyroxene. Orthopyroxene occurs partly rimming olivine grains. Clinopyroxene-Olivine Gabbro Clinopyroxene-olivine gabbro is a subtype of olivine gabbro after the IUGS classification scheme (Streckeisen, 1976), as is olivine-cli- nopyroxene gabbro, which is distinguished by a modal olivine/cli- nopyroxene ratio less than 1. Clinopyroxene-olivine gabbro is composed of olivine, clinopy- roxene, Plagioclase, and occasional small amounts of ilmenite and Ni-Fe sulfide. Samples 153-923A-13R-1, Piece 6, and 153-923A- 7R-2, Piece 1, have large olivine and Plagioclase crystals (average length 2-4 mm, up to 6 mm) and fine interstitial clinopyroxene. 'Karson, J.A., Cannat, M., Miller, D.J., and Elthon, D. (Eds.), 1997. Proc. ODP, Sci. Results, 153: College Station, TX (Ocean Drilling Program). department of Geology, Faculty of Education, Niigata University, Niigata, 950-21, Japan, [email protected]'Institute for Study of the Earth's Interior, Okayama University, Tottori, 682-01, Japan. Some olivine grains include partly subhedral to anhedral Plagioclase laths. Samples 153-923A-7R-1, Piece 2B, 7R-2, Piece 8, 8R-2, Piece 6, and 9R-2, Piece 8A, contain oikocrystic olivine. In these rocks, large oikocrystic olivine (up to 6-10 mm across) encloses Plagioclase laths. Plagioclase and clinopyroxene crystals tend to be smaller (av- erage 1 mm) than olivine grains, and clinopyroxene usually occurs interstitially. Some Plagioclase grains are large, as much as 6 mm in length. Sample 153-923A-12R-1, Piece 4B-COGb, is characterized by poikilitic clinopyroxene that encloses rounded olivine and plagio- clase laths. The grain size of poikilitic clinopyroxene is as much as a few centimeters across. Olivine-Clinopyroxene Gabbro Most of the olivine-clinopyroxene gabbros are primarily equigranular, and are often modified into a Porphyroclastic texture. Samples 153-923A-5R-1, Piece 2A, 9R-1, Piece 3D, 9R-2, Piece 9A, 10R-3, Piece 1,153-921E-2R-1, Piece 6, and 4R-1, Piece 5, showpri- mary equigranular texture, and are composed of Plagioclase, clinopy- roxene, olivine, and ilmenite. Samples 153-923A-2R-1, Piece 3, 9R- 3, Piece 3B (sheared), 10R-2, Piece 2A, 11R-1, Piece 12, and 11R-2, Piece 3, are somewhat sheared and show Porphyroclastic textures. An olivine-clinopyroxene gabbro, Sample 153-921E-7R-1, Piece B, is characterized by poikilitic clinopyroxene. The poikilitic cli- nopyroxene is up to 2-3 cm across and encloses anhedral olivine and Plagioclase crystals. Orthopyroxene rarely rims olivine grains. Gabbro Gabbro is composed of clinopyroxene, Plagioclase, and minor amounts of olivine (<5%), orthopyroxene (<1%), and opaque miner- als (l%-2%). Opaque minerals are ilmenite and iron sulfide, and the total amount is high, up to a few percent. Some of these gabbros are called microgabbros because of their highly recrystallized, fine- grained texture. Samples 153-923A-5R-1, Piece 2A, and 5R-3, Piece 1, are typical coarse-grained gabbro without deformation texture. They are com- posed of equigranular, anhedral Plagioclase, olivine, clinopyroxene, and interstitial orthopyroxene and opaque minerals. Modal olivine is less than 5%. Sample 153-923A-3R-2, Piece IB, is highly sheared gabbro, hav- ing porphyroclasts of olivine, clinopyroxene, and Plagioclase. 471
Transcript
Karson, J.A., Cannat, M., Miller, D.J., and Elthon, D. (Eds.), 1997Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 153
27. DATA REPORT: MINERALOGY AND Sr- AND Nd-ISOTOPIC COMPOSITION OF GABBROICOCEANIC CRUST RECOVERED FROM HOLES 923A AND 921E IN THE MARK AREA1
Norie Fujibayashi,2 Hiroo Kagami,3 and Yoshiyuki Oishi3
ABSTRACT
Gabbroic rocks recovered from Holes 923A and 92IE in the MARK area include troctolite, clinopyroxene-olivine gabbro,olivine-clinopyroxene gabbro, gabbro, gabbronorite, oxide gabbro, and quartz diorite. Clinopyroxene and Plagioclase occur inall rock types, whereas olivine is supplanted by orthopyroxene in the evolved rock types and in the intercumulus stage. Forster-ite (Fo) content of olivine, magnesium number (Mg#) of pyroxenes, and anorthite (An) content of Plagioclase systematicallydecrease with decreasing modal olivine content, and Plagioclase is most sodic in the quartz diorite. Sr- and Nd-isotopic compo-sitions are characteristic of N-type MORB.
INTRODUCTION
Gabbroic oceanic crust was drilled at the Mid-Atlantic Ridge nearthe Kane Fracture Zone (MARK, 23°N) during Leg 153. The rocktypes obtained span a wide range, including troctolite, olivine gab-bro, gabbro, gabbronorite, oxide gabbro, and quartz diorite. Petrogra-phy, mineralogy, and Sr- and Nd-isotopes are reported for a suite of27 gabbroic rocks from Holes 923A (23°32.55'N, 45°01.90'W) and921E (23°32.40'N, 45°01.85'W) on the western median valley wallof the Mid-Atlantic Ridge about 10 km south of the Kane TransformFault (Table 1).
PETROGRAPHY
Troctolite
Troctolites occur as thin (a few centimeters) layers or as dikes em-placed in gabbro, clinopyroxene-olivine gabbro, and olivine-clinopy-roxene gabbro. Sample 153-923A-8R-2, Piece 1, is a thin dike. Sam-ple 153-923A-12R-1, Piece 4B, is composed of layered troctolite andclinopyroxene-olivine gabbro; the troctolite part is labeled 153-923A-12R-1, Piece 4B-Tr. These troctolites have large, tabular butanhedral, Plagioclase, and anhedral olivine with less than 5% intersti-tial clinopyroxene and rare orthopyroxene. Orthopyroxene occurspartly rimming olivine grains.
Clinopyroxene-Olivine Gabbro
Clinopyroxene-olivine gabbro is a subtype of olivine gabbro afterthe IUGS classification scheme (Streckeisen, 1976), as is olivine-cli-nopyroxene gabbro, which is distinguished by a modal olivine/cli-nopyroxene ratio less than 1.
Clinopyroxene-olivine gabbro is composed of olivine, clinopy-roxene, Plagioclase, and occasional small amounts of ilmenite andNi-Fe sulfide. Samples 153-923A-13R-1, Piece 6, and 153-923A-7R-2, Piece 1, have large olivine and Plagioclase crystals (averagelength 2-4 mm, up to 6 mm) and fine interstitial clinopyroxene.
'Karson, J.A., Cannat, M., Miller, D.J., and Elthon, D. (Eds.), 1997. Proc. ODP, Sci.Results, 153: College Station, TX (Ocean Drilling Program).
department of Geology, Faculty of Education, Niigata University, Niigata, 950-21,Japan, [email protected]
'Institute for Study of the Earth's Interior, Okayama University, Tottori, 682-01,Japan.
Some olivine grains include partly subhedral to anhedral Plagioclaselaths.
Samples 153-923A-7R-1, Piece 2B, 7R-2, Piece 8, 8R-2, Piece 6,and 9R-2, Piece 8A, contain oikocrystic olivine. In these rocks, largeoikocrystic olivine (up to 6-10 mm across) encloses Plagioclaselaths. Plagioclase and clinopyroxene crystals tend to be smaller (av-erage 1 mm) than olivine grains, and clinopyroxene usually occursinterstitially. Some Plagioclase grains are large, as much as 6 mm inlength.
Sample 153-923A-12R-1, Piece 4B-COGb, is characterized bypoikilitic clinopyroxene that encloses rounded olivine and plagio-clase laths. The grain size of poikilitic clinopyroxene is as much as afew centimeters across.
Olivine-Clinopyroxene Gabbro
Most of the olivine-clinopyroxene gabbros are primarilyequigranular, and are often modified into a Porphyroclastic texture.Samples 153-923A-5R-1, Piece 2A, 9R-1, Piece 3D, 9R-2, Piece 9A,10R-3, Piece 1,153-921E-2R-1, Piece 6, and 4R-1, Piece 5, show pri-mary equigranular texture, and are composed of Plagioclase, clinopy-roxene, olivine, and ilmenite. Samples 153-923A-2R-1, Piece 3, 9R-3, Piece 3B (sheared), 10R-2, Piece 2A, 11R-1, Piece 12, and 11R-2,Piece 3, are somewhat sheared and show Porphyroclastic textures.
An olivine-clinopyroxene gabbro, Sample 153-921E-7R-1, PieceB, is characterized by poikilitic clinopyroxene. The poikilitic cli-nopyroxene is up to 2-3 cm across and encloses anhedral olivine andPlagioclase crystals. Orthopyroxene rarely rims olivine grains.
Gabbro
Gabbro is composed of clinopyroxene, Plagioclase, and minoramounts of olivine (<5%), orthopyroxene (<1%), and opaque miner-als (l%-2%). Opaque minerals are ilmenite and iron sulfide, and thetotal amount is high, up to a few percent. Some of these gabbros arecalled microgabbros because of their highly recrystallized, fine-grained texture.
Samples 153-923A-5R-1, Piece 2A, and 5R-3, Piece 1, are typicalcoarse-grained gabbro without deformation texture. They are com-posed of equigranular, anhedral Plagioclase, olivine, clinopyroxene,and interstitial orthopyroxene and opaque minerals. Modal olivine isless than 5%.
Sample 153-923A-3R-2, Piece IB, is highly sheared gabbro, hav-ing porphyroclasts of olivine, clinopyroxene, and Plagioclase.
471
DATA REPORT
Table 1. List of gabbroic rocks studied, Holes 921E and 923A.
Variably deformed gabbro and olivine gabbroVariably deformed gabbro and olivine gabbroVariably deformed gabbro and olivine gabbroVariably deformed gabbro and olivine gabbroVariably deformed gabbro and olivine gabbroInterlayered troctolite and olivine gabbroInterlayered troctolite and olivine gabbroInterlayered troctolite and olivine gabbroInterlayered troctolite and olivine gabbroInterlayered troctolite and olivine gabbroInterlayered troctolite and olivine gabbroInterlayered troctolite and olivine gabbroInterlayered troctolite and olivine gabbroInterlayered troctolite and olivine gabbroInterlayered troctolite and olivine gabbroInterlayered troctolite and olivine gabbroInterlayered troctolite and olivine gabbroPoikilitic olivine gabbro and troctolitePoikilitic olivine gabbro and troctoliteTroctolite and poikilitic olivine gabbro
Microgabbro consists of a foliated fine-grained equigranular ag-gregate of clinopyroxene, plagoiclase, and brown hornblende, some-times associated with olivine. Sample 153-923A-2R-1, Piece 3, is atypical microgabbro. Olivine and clinopyroxene occur rarely as por-phyroclasts (1-2 mm across). Brown hornblende substitutes at themargins of clinopyroxene grains.
Gabbronorite
Gabbronorite generally occurs as a Porphyroclastic dike intrudedinto the olivine gabbro. Gabbronorite (Sample 153-921E-8R-1, Piece7B) was collected from such a dike, whose thickness is around 1 or 2m. The sample is composed of Plagioclase, clinopyroxene, orthopy-roxene, and opaque oxides. Pyroxenes show exsolution texture, andare elongated by shear stress.
Oxide Gabbro
Oxide gabbro usually forms thin veins in olivine gabbro. Sample153-921E-3R-1, Piece 5, is a small vein (a few cm thick) intrudedinto the shear zone formed at the boundary between Units 1 (pegma-titic gabbro) and 2 (olivine gabbro). The anhedral Plagioclase, cli-nopyroxene, and orthopyroxene grains are primarily cemented by il-menite and titanomagnetite, and are deformed into a Porphyroclastictexture.
Quartz Diorite
Only two discrete samples of quartz diorite were recovered duringLeg 153, both from Hole 921E: Samples 153-921E-7R-1, Piece 4,and 8R-1, Piece 1. These specimens are composed of Plagioclase, cli-nopyroxene, orthopyroxene, ilmenite, titanomagnetite, and quartz.Plagioclase grains are large and euhedral to subhedral in shape. Cli-nopyroxene, orthopyroxene, ilmenite, titanomagnetite, and quartz arethe intergranular minerals. Pyroxenes are relict minerals and occur inthe center part of the hornblendes and clay minerals. Clinopyroxeneis surrounded by brown hornblende. Orthopyroxene is replaced bymuscovite, chlorite, green hornblende, and so forth, at the margins.
MINERALOGY
Mineral compositions of Plagioclase, olivine, and pyroxenes ingabbroic rocks from Holes 923A and 92IE were determined usingthe JEOL JXA-8600 Electron Microprobe at Niigata University.Standard silicate analyses were performed at an accelerating poten-tial of 15 kV, a beam current of 1.3 × I0"8 A, and a spot size of 10 µm.The standards used for calibration were diopside (Si, Ca), syntheticTiO2, A12O3, Cr2O3, Fe2O3, NiO, periclase (Mg), jadeite (Na), and ad-ularia (K). Consistency of the data was checked by daily analyses ofa kaersutite standard. Representative analyses are listed in Tables 2,3, 4, and 5.
Plagioclase
Plagioclases in troctolite and clinopyroxene-olivine gabbro havehigh maximum anorthite (An) contents, typically >72 (Fig. 1, Table2). Plagioclases in olivine-clinopyroxene gabbro are less calcic, butstill have maximum An contents >60. The maximum An contents ofplagioclases in gabbro are less than 60. Porphyroclastic grains in gab-bronorite have homogeneous An ranges between 45 and 47. In oxidegabbro, some grains have calcic cores with An of 69-71, and the oth-ers have sodic cores with An of 45. Plagioclase grains in quartz dior-ite are sodic, having homogeneous cores characterized by An of 26-27, rimmed by a more sodic solution, whose An equals 7.
Olivine
Olivine grains in troctolite and clinopyroxene-olivine gabbrohave magnesian compositions with a forsterite (Fo) content >76, upto 86 (Fig. 2, Table 3). Olivines in Samples 153-923A- 12R-1, Piece4B-Tr, 12R-1, Piece 4B-COGb, 13R-1, Piece 6, and 7R-2, Piece 1,are magnesian, and have NiO contents greater than 0.24 wt% (Figs.2, 3). Maximum Fo contents of olivine in olivine-clinopyroxene gab-bro generally range from 72 to 74, except in Samples 153-921E-4R-1, Piece 5, and 153-921E-7R-1, Piece 9B, which equal 75 and 78, re-spectively. Olivines in gabbro samples (Samples 153-923A-2R-1,Piece 3, and 5R-1, Piece 2A) have maximum Fo values of 73 and 74,
472
Table 2. Representative microprobe analyses of Plagioclase for gabbroic rocks from Holes 921E and 923A.
DATA REPORT
Hole:
Core, section:
Piece no.:
Rock name:
SiO2
TiO2A12O3FeOMnOMgOCaONa2OK2OTotalAtomic no.
SiTiAlFeMnMgCaNaKTotal
AnAbOr
923A
2R-3
1
Gb
54.210.00
28.380.100.000.02
11.095.040.00
98.83(O = 32)
9.8860.0006.1000.0140.0000.0052.1671.7810.000
19.954
54.945.1
0.0
923A
3R-2
1
Gb
53.600.05
29.120.360.100.02
11.634.720.07
99.68
9.7310.0076.2310.0540.0160.0052.2631.6630.016
19.986
57.442.2
0.4
923A
3R-2
1
Gb
55.230.04
28.330.200.030.02
10.355.750.10
100.04
9.9540.0056.0170.0290.0050.0062.0012.0090.022
20.048
49.649.8
0.5
923A
3R-2
1
Gb
56.950.01
27.150.220.110.009.216.280.11
100.03
10.2260.0025.7460.0330.0160.0011.7722.1860.024
20.005
44.554.90.6
923A
5R-1
2A
Gb
53.310.04
29.700.210.050.03
11.894.690.05
99.97
9.6510.0066.3370.0310.0070.0082.3081.6470.011
20.004
58.241.5
0.3
923A
5R-1
2A
Gb
54.470.04
28.900.310.000.04
10.955.000.06
99.76
9.8460.0056.1560.0470.0010.0102.1221.7530.014
19.954
54.645.1
0.4
923A
5R-3
1
Gb
53.530.07
29.060.320.000.02
11.544.710.06
99.31
9.74250.0106.2340.0490.0000.0052.2521.6610.015
19.968
57.342.3
0.4
923A
5R-3
1
Gb
55.710.13
27.770.310.000.01
10.045.680.09
99.74
10.0550.0175.9070.0470.0000.0031.9421.9890.020
19.979
49.250.30.5
923A
7R-1
2B
COGb
49.180.07
31.690.310.020.04
14.932.880.02
99.12
9.0640.0096.8850.0470.0020.0102.9491.0290.005
20.001
74.025.80.1
923A
7R-1
2B
COGb
53.300.06
29.140.180.050.03
11.544.740.04
99.08
9.7220.0086.2650.0270.0080.0082.2571.6750.008
19.979
57.342.5
0.2
923A
7R-1
2B
COGb
52.930.05
29.600.250.050.03
12.234.410.03
99.59
9.6250.0076.3430.0380.0080.0092.3841.5550.008
19.978
60.439.40.2
923A
7R-2
1
COGb
49.750.02
31.240.220.100.04
14.633.130.03
99.15
9.1600.0036.7780.0340.0150.0102.8871.1170.008
20.011
72.027.80.2
923A
7R-2
1
COGb
52.660.02
29.900.290.090.03
12.764.270.05
100.06
9.5520.0036.3910.0440.0140.0092.4811.5000.012
20.005
62.137.60.3
Notes: Tr = troctolite, COGb = clinopyroxene-olivine gabbro, OCGb = olivine-clinopyroxene gabbro, Gb = gabbro, GbN = gabbronorite, OxGb = oxide gabbro, QzDi = quartz diorite.Oxide and elemental analyses are reported in weight percent; An, Ab, and Or are reported in mole percent.
respectively, and those in Samples 153-923A-5R-3, Piece 1, and 3R-2, Piece 1, have maximum Fo contents of 71 and 66, respectively.
Clinopyroxene
Clinopyroxenes in troctolite, clinopyroxene-olivine gabbro, oliv-ine-clinopyroxene gabbro, and gabbro have a significant range in di-opside, endiopside, and augite contents (Fig. 4). Clinopyroxenes inprimitive samples, such as troctolite (Samples 153-923A-12R-1,Piece 4B-Tr), and clinopyroxene-olivine gabbros (Samples 153-923A-7R-2, Piece 1, 12R-1, Piece 4B-COGb, and 13R-1, Piece 6),plot entirely in the diopside and endiopside fields. The maximum
magnesium numbers (Mg#) of clinopyroxenes in these four samplesare high (88 and 89) (Table 4). Clinopyroxenes in clinopyroxene-oli-vine gabbro (Samples 153-923A-7R-2, Piece 1, and 153-923A-12R-1, Piece 4B-COGb) also have high Cr2O3 contents, up to 1.3 (wt%)(Fig. 5). Clinopyroxenes in gabbronorite, oxide gabbro, and quartzdiorite have low maximum Mg# values, ranging from 64 to 74, andplot along the boundary between the salite and augite fields (Fig. 4).
Orthopyroxene
Orthopyroxenes in troctolite, clinopyroxene-olivine gabbro, andolivine-clinopyroxene gabbro are classified as bronzite (Fig. 4).
Among those, crystals in Samples 153-923A-12R-1, Piece 4B-COGband -Tr, have the highest Mg# (76-77). Orthopyroxenes in most gab-bro samples also plot in the bronzite field, whereas those in gab-bronorite plot near the boundary between bronzite and hypersthene.Orthopyroxenes in oxide gabbro and quartz diorite are classified ashypersthene. Neither pigeonite nor inverted pigeonite occur in the ex-amined samples.
Sr- AND Nd-ISOTOPIC COMPOSITION
Six samples of various rock types were selected for isotopic anal-yses. Samples were crushed in a tungsten carbide mill to a few milli-
meters in size, and then warmed on a hot plate and washed ultrason-ically in distilled water until no AgCl was produced by reaction with2% AgNO3. The sample for bulk analysis was segregated at this stageand ground in a tungsten carbide mill. The washed chips were againcrushed for mineral separates to the 60 mesh size, and then warmedin 6-N HC1 for 30 min to obtain fresh mineral separates by dissolvingclay minerals. Samples then were cleaned ultrasonically and rinsed indistilled water. Plagioclase and pyroxene were separated using isody-namic magnetic separators.
Sr- and Nd-isotope analyses were performed using a FinniganMAT 261 multicollector mass spectrometer at the Institute of Studyfor Earth's Interior, Okayama University. The Sr and Nd extractionsfollowed the procedures described by Kagami et al. (1987, 1989).
The extracted elements were loaded on Ta-filament in a double fila-ment mode. Blanks for both Sr and Nd were less than 1 ng. The av-erage 87Sr/86Sr ratio for the NBS987 standard was 0.710258 ± 14 (±represents an analytical reproducibility in terms of 2σ) and the aver-age 143Nd/144Nd for the BCR-1 was 0.512612 ± 11.87Sr/86Sr was nor-malized to 86Sr/88Sr = 0.1194; 143Nd/144Nd was normalized to a valueof 146Nd/144Nd = 0.7219. The results are listed in Table 6. The 143Nd/144Nd ratios are reported relative to 143Nd/144Nd = 0.512640 for BCR-1 (Wasserburg et al., 1981).
The 87Sr/86Sr ratio ranges from 0.70232 to 0.70260, and 143Nd/144Nd ranges from 0.513243 to 0.513252. All the 87Sr/86Sr of analyzedsamples are less than 0.7030 and in the range of N-type MORB (Wil-son, 1989).
ACKNOWLEDGMENTS
REFERENCES
Kagami, H., Iwata, M., Sano, S., and Honma, H., 1987. Sr and Nd isotopic
compositions and Rb, Sr, Sm and Nd concentrations of standard samples.
Tech. Repts. ISEI, Okayama Univ., Sen B, 4:1-16.
Kagami, H., Yokose, H., and Honma, H., 1989. 87Sr/86Sr and 143Nd/144Nd
ratios of GSJ rock reference samples: JB-la, JA-1 and JG-la. Geochem.
J., 23: 209-214.
Streckeisen, A., 1976. To each plutonic rock its proper name. Earth Sci. Rev.,
12:1-33.
Wasserburg, G.J., Jacobsen, S.B., De Paolo, D.J., McCulloch, M.T., and
Wen, T., 1981. Precise determination of Sm/Nd ratios, Sm and Nd isoto-
pic abundances in standard solutions. Geochim. Cosmochim. Acta,
45:2311-2323.
Wilson, M., 1989. Igneous Petrogenesis: A Global Tectonic Approach: Lon-
don (Unwin Hyman).
We sincerely thank the scientists, Ocean Drilling Program staff,and crew of the JOIDES Resolution for their support during and afterLeg 153. We also thank Dr. S. Miyashita, Dr. T. Shimura, and Mr. U.Sakai of Niigata University for their assistance with EPMA analyses.
Date of initial receipt: 6 September 1995
Date of acceptance: 1 February 1996
Ms 153SR-028
475
DATA REPORT
Table 3. Representative microprobe analyses of olivine for gabbroic rocks from Holes 921E and 923A.
Hole:
Core, section:
Piece no.:
Rock name:
SiO2
A12O3TiO2FeOMnONiOMgOCaOTotalAtomic no.
SiAlTiFeMnMgCaTotal
Fo
923A
2R-1
3Gb
37.940.000.00
24.990.450.10
36.330.09
99.88(O = 4)
1.0030.0000.0000.5520.0101.4300.0022.997
72.1
923A
2R-1
3Gb
37.650.000.00
26.170.360.11
35.510.06
99.85
1.0010.0000.0000.5820.0081.4060.0022.999
70.7
923A
3R-2
1
Gb
37.050.020.00
30.100.540.05
32.070.04
99.87
1.0040.0010.0000.6820.0121.2950.0012.996
65.5
923A
3R-2
1
Gb
36.680.030.01
31.720.540.11
31.850.05
100.99
0.9920.0010.0000.7170.0121.2830.0023.007
64.1
923A
5R-1
2A
Gb
38.440.000.01
24.880.380.06
37.830.02
101.61
0.9960.0000.0000.5390.0081.4600.0013.004
73.0
923A
5R-3
1
Gb
37.700.010.01
26.560.440.15
35.270.07
100.21
1.0010.0000.0000.5900.0101.3960.0022.999
70.3
923A
5R-3
1
Gb
37.680.000.02
27.850.440.09
34.700.05
100.82
1.0000.0000.0000.6180.0101.3710.0013.000
68.9
923A
7R-1
2B
COGb
38.630.000.00
20.730.310.12
40.070.08
99.94
0.9990.0000.0000.4480.0071.5440.0023.001
77.5
923A
7R-1
2B
COGb
38.130.000.04
22.490.410.14
38.260.04
99.51
1.0000.0000.0010.4930.0091.4950.0012.999
75.2
923A
7R-1
2B
COGb
37.230.000.04
24.290.330.15
38.390.05
100.48
0.9770.0000.0010.5330.0071.5020.0013.022
73.8
923A
7R-2
1
COGb
39.730.010.01
15.790.250.24
43.710.05
99.78
1.0050.0000.0000.3340.0051.6480.0012.994
83.1
923A
7R-2
1
COGb
39.790.000.01
17.410.310.17
43.240.03
100.95
1.0020.0000.0000.3660.0071.6220.0012.998
81.6
923A
7R-2
8
COGb
38.400.000.02
22.380.460.23
39.130.04
100.64
0.9960.0000.0000.4850.0101.5120.0013.004
75.7
Notes: Tr = troctolite, COGb = clinopyroxene-olivine gabbro, OCGb = olivine-clinopyroxene gabbro, and Gb = gabbro. Analyses are reported in weight percent.
Table 3 (continued).
Hole:
Core, section:
Piece no.:
Rock name:
SiO2A12O3TiO2FeOMnONiOMgOCaOTotalAtomic no.
SiAlTiFeMnMgCaTotal
Fo
923A
7R-2
8
COGb
37.650.000.02
23.480.390.22
38.140.03
99.94
0.9900.0000.0000.5160.0091.4940.0013.010
74.3
923A
8R-2
1
Tr
39.330.010.00
19.900.270.09
41.310.04
100.94
1.0010.0000.0000.4240.0061.5670.0012.999
78.72
923A
8R-2
1
Tr
39.500.010.01
21.200.340.10
40.240.04
101.44
1.0060.0000.0000.4520.0071.5270.0012.994
77.18
923A
8R-2
6
COGb
38.300.000.00
20.540.450.06
39.660.06
99.07
0.9990.0000.0000.4480.0101.5420.0023.001
77.5
923A
8R-2
6
COGb
38.030.000.00
21.650.360.07
39.520.07
99.68
0.9910.0000.0000.4720.0081.5350.0023.009
76.5
923A
9R-1
3
OCGb
38.190.030.00
21.910.310.01
39.390.04
99.88( 0 = 4)
0.9940.0010.0000.4770.0071.5270.0013.006
76.2
923A
9R-1
3OCGb
37.890.020.00
22.600.330.03
38.970.01
99.86
0.9900.0010.0000.4940.0071.5170.0003.010
75.4
923A
9R-2
8
COGb
39.780.030.11
20.720.290.05
40.800.01
101.79
1.0060.0010.0020.4380.0061.5380.0002.992
77.82
923A
9R-2
8
COGb
38.510.000.00
21.320.300.12
39.870.05
100.18
0.9970.0000.0000.4610.0071.5370.0013.003
76.92
923A
9R-2
9
OCGb
38.090.000.08
24.060.310.10
37.630.01
100.28
0.9970.0000.0020.5270.0071.4680.0003.001
73.6
923A
9R-2
9
OCGb
38.110.000.02
24.970.380.08
36.910.03
100.50
1.0000.0000.0000.5480.0081.4430.0013.000
72.5
923A
9R-3
3
OCGb
37.990.000.00
24.560.400.11
37.270.04
100.36
0.9970.0000.0000.5390.0091.4570.0013.003
73.0
923A
9R-3
3B
OCGb
37.590.000.00
25.920.350.12
36.130.05
100.17
0.9950.0000.0000.5740.0081.4260.0013.005
71.3
Table 3 (continued).
Hole:
Core, section:
Piece no.:
Rock name:
SiO2A12O3
TiO2FeOMnONiOMgOCaOTotalAtomic no.
SiAlTiFeMnMgCaTotal
Fo
923A
10R-2
2
OCGb
38.590.010.01
24.670.290.12
37.830.05
101.57
0.9990.0000.0000.5340.0061.4590.0013.000
73.2
923A
10R-3
1
OCGb
37.620.000.01
25.350.470.10
36.580.03
100.15
0.9940.0000.0000.5600.0101.4400.0013.006
72.0
923A
10R-3
1
OCGb
37.150.020.01
30.760.490.07
32.400.02
100.93
0.9990.0010.0000.6920.0111.2980.0013.001
65.2
923A
11R-1
12
OCGb
37.250.030.01
23.860.320.07
37.360.06
98.96
0.9900.0010.0000.5300.0071.4790.0023.010
73.6
923A
11R-2
3
OCGb
38.100.020.04
23.830.450.01
37.500.04
99.99
0.9990.0010.0010.5230.0101.4650.0013.000
73.7
923A
11R-2
3
OCGb
37.700.000.00
26.670.430.00
35.480.05
100.32
0.9990.0000.0000.5910.0101.4000.0013.001
70.3
923A
12R-1
4B
Tr
39.670.000.07
14.830.290.28
44.320.06
99.52
1.0030.0000.0010.3140.0061.6700.0022.996
84.19
923A
12R-1
4B
Tr
39.860.020.05
15.390.220.11
44.710.05
100.41
0.9990.0010.0010.3230.0051.6700.0013.000
83.81
923A
12R-1
4B
COGb
39.760.000.07
14.030.190.24
45.340.07
99.70
0.9990.0000.0010.2950.0041.6980.0022.999
85.20
923A
12R-1
4B
COGb
39.680.010.06
14.240.280.17
45.190.04
99.66
0.9980.0000.0010.3000.0061.6940.0013.000
84.97
923A
13R-1
6
COGb
39.430.010.02
17.760.290.22
42.540.06
100.33(0 = 4)
1.0020.0000.0000.3770.0061.6100.0022.998
81.0
921E
2R-1
6
OCGb
38.140.000.03
25.200.410.07
36.780.05
100.67
1.0000.0000.0010.5520.0091.4370.0013.000
72.2
921E
2R-1
6
OCGb
37.700.000.02
26.110.310.05
36.050.07
100.30
0.9970.0000.0000.5770.0071.4200.0023.003
71.1
476
DATA REPORT
Table 3 (continued).
Hole:
Core, section:
Piece no.:
Rock name:
SiO2A12O3TiO2FeOMnONiOMgOCaOTotalAtomic no.
SiAlTiFeMnMgCaTotal
Fo
921E
4R-1
5
OCGb
38.470.000.03
23.920.260.06
37.870.04
100.64
1.0010.0000.0010.5210.0061.4690.0012.998
73.8
921E
7R-1
9B
OCGb
38.630.000.03
21.130.290.16
40.080.03
100.36
0.9970.0000.0010.4560.0061.5410.0013.002
77.2
921E
7R-1
9B
OCGb
38.500.010.06
24.010.410.11
37.470.04
100.59
1.0040.0000.0010.5240.0091.4560.0012.995
73.5
Table 4. Representative microprobe analyses of primary clinopyroxene for gabbroic rocks from Holes 921E and 923A.
Figure 2. Fo (mol%) in olivine in troctolite, clinopyroxene-olivine gabbro, olivine-clinopyroxene gabbro, and gabbro from Holes 921E and 923A. Symbols arethe same as in Figure 1.
481
DATA REPORT
153-923A-2R-1,Piecθ3
60 70 80 90
153-923A-7R-1, Piece 2B
0.3
153-923A-8R-2, Piece 6
60 70 80 90Fo (mol%)
60 70 80 90
Fo (mol%)
153-923A:9R-3, PJθCθ 3B
0.3
0.2
60 70 80 90
Fo (mol%)
153-923A-3R-2, Piece 1B 153-923A-7R-2, Piece 1 153-923A-9R-1, Piece 3D
60 70 80 90
Fo (mol%)
60 70 80 90
Fo (mol%)
0.3
0.2
0.1
0 0
•
60 70 80 90
Fo (mol%)
153-923A-10R-2, Piece 2A
0.3
60 70 80 90
Fo (mol%)
153-923A-5R-1, Piece 2A 153-923A-7R-2, Piece8
60 70 80 90
Fo (mol%)
153-923A-9R-2, Piece 8A
60 70 80 90
Fo (mol%)
153-923A-10R-3, Piece 1
60 70 80 90
Fo (mol%)
0.060 70 80 90
Fo (mol%)
153-923A-5R-3. Piece 1 53-923A-8R-2. Piece 1
60 70 80 90
Fo (mol%)
153-923A-9R-2. Piece 9A 153-923A-11R-1. Piece 12
60 70 80 90
Fo (mol%)
60 70 80 90
Fo (mol%)60 70 80 90
Fo (mol%)
Figure 3. NiO (wt%) in olivine in troctolite, clinopyroxene-olivine gabbro, olivine-clinopyroxene gabbro, and gabbro from Holes 92IE and 923A. Symbols arethe same as in Figure 1.
482
DATA REPORT
153-923A-11R-2,Piθce3 153-921E-2R-1, Piece 6
60 70 80 90
153-923A-12R-1, Piece4b-Tr
0.3
60 70 80 90
Fo (mol%)
153-921E-4R-1,Piθce5
60 70 80 90
Fo (mol%)
153-923A-12R-1, Piece4b-COGB
0.3
60 70 80 90
Fo (mol%)
153-921E-7R-1, Piece 9B
60 70 80 90
Fo (mol%)
153-923A-13R-1,PiθCθ6
60 70 80 90
Fo (mol%)
60 70 80 90
Fo (mol%)
Figure 3 (continued).
483
DATA REPORT
153-923A-2R-1,Piβcθ3
Ca 0.5, Mg 0.5
/ /
/ /
/ /
/ / /
wΛΛ
\ \ \
153-923A-7R-1, Piece 2BCa 0.5, Mg 0.5
Mg Fe Mg
rr/ / \\\Λ \\ \\ \Fe
153-923A-3R-2, Piece 1B
Ca 0.5, Mg 0.5
/ /
/ /
\ \
\ \
Λ Λ/ / / \ \ \\ \ \
Mg
153-923A-5R-1, Piece 2A
Ca 0.5, Mg 0.5
\ \
/ / \ \/ / CM / I \ \ \
Mg Fβ
153-923A-7R-2,Ca 0.5, Mg 0.5
/ W^
/ /
/ /
/ / // / 1
Piece
\
\
\\
1
Λ
\ \
Λ \FΘ
M 9
153-923A-7R-2,Piece8
Ca 0.5, Mg 0.5
Fe
/ /
\ \
\ \
\ \
/ / // / / \ \ \
Mg Fe
153-923A-5R-3, Piece 1Ca 0.5, Mg 0.5
Mg
/ L
/ /
\ \
\ \Λ Λ
/ / / \ \ \Fe
153-923A-8R-2, Piece 1
Ca 0.5, Mg 0.5
Mg
/ /
/ /
/ / /
/ / X× /
\ \w\ \\ \ \\ \ \Fθ
Figure 4. Ca-Mg-Fe (atomic ratio) plot of pyroxenes in gabbroic rocks from Holes 92IE and 923A. Symbols are the same as in Figure 1. Open symbols are for
