Origin of Lherzolite Inclusions in the Malapai Hill Basalt, Joshua Tree National Monument, California

ROBERT J. STULL Department of Geology, California State University, Los Angeles, Los Angeles, California 90032 KENT McMILLAN Department of Geological Sciences, Stanford University, Stanford, California 94305

ABSTRACT dence that the nodules could be the end product of more than one partial melting. Alkali olivine basalt at Malapai Hill, Cali- fornia, occurs as a late Cenozoic stock that has INTRODUCTION intruded the Cretaceous White Tank Monzon- Basalts and ultramafic nodules from the ite. The basalt is chemically and mineralogi- Mojave Desert have been described in several cally similar to other alkaline basalts in the papers. Ross and others (1954) reported min- Mojave Desert, although it is devoid of zeolites. eral compositions of peridotite inclusions from The strontium isotopic composition of the Dish Hill and noted the world-wide similarity basalt (Sr87/Sr86 = 0.7030 ± 0.0006) suggests of nodules. Hess (1955) published one analysis that it is derived from a mantle that has of a nodule from Dish Hill (Fig. 1). Wise already experienced one period of partial (1966, 1969) described the characteristics of ba- melting. OUvine-rich lherzolite nodules in the salts in the Mojave Desert and provided a basalt are high in Mg and low in Si, Al, Ca, viable theory for the sequence of lava at Na, and K. The nodules are xenomorphic Pisgah Crater. Most petrologists agree that granular with a tectonite fabric and forsteritic basalt forms in the upper mantle (for example, olivine (F094-88). The Sr87/Sr86 ratio of the Green and Ringwood, 1967; Jackson and nodules is 0.7043 + 0.0008. Olivine xenocrysts Wright, 1970), and that nodules probably form and corroded xenolith margins suggest that as a result of a variety of upper mantle processes reaction between the nodules and basalt has (Wilshire and Binns, 1961; White, 1966). This occurred. paper examines the chemical character of the Similar Sr87/Sr86 ratios of lherzolite nodules Malapai Hill basalt and ultramafic nodules, and alkali olivine basalt hosts at Malapai Hill and the relation of the xenoliths and host rock. are consistent with a related origin for the two rocks. The tectonite fabric and olivine composition of the nodules rule out a cognate origin by fractional crystallization of the basalt. Instead, the nodules are mantle materials that have been depleted in the most easily fusible elements by one or more periods of partial melting. The nodules may represent refractory residue from the area of partial melting or depleted mantle material, unrelated to the basalt but accidentally incorporated into it. Interpretation of the nodules as refractory residue from the site of melting is favored due to the similarity of the nodules and host rocks in strontium isotopic composition, the extreme chemical and petrologic uniformity of the inclusions, and chemical evi- Pisgah, Dish Hill, and Amboy volcanoes.

Geological Society of America Bulletin, v. 84, p. 2343-2350, 1 fig., July 1973 2343

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ANALYTICAL PROCEDURES TABLE 1. MODES AND PETROGRAPHIC SUMMARY OF MALAPAI HILL BASALT AND ULTRAMAFIC NODULES Basalt number 1 (Table 3) and ultramafic nodule number 1 (Table 4) were analyzed with Modal Mode wet chemical techniques by Dr. Ken-Ichiro minerals (%) Pétrographie summary Aoki. These samples served as standards when determining Si by x-ray fluorescence methods Basali' and the remaining elements by atomic absorp- Olivine 10 Anhedral phenocrysts and tion spectrophotometry. groundmass; 0.1 to 4 mm diameter; 2V = -80° to -85° The strontium isotopic compositions were phenocrysts have uniform or determined with a 9-in.-60° mass spectrometer undulatory extinction and with a single rhenium filament. Data were re- kink bands Tan, euhedral to subhedral corded digitally and reduced with a computer Augite 25 86 88 crystals; 0.1 to 0.2 mm long; and normalized to a Sr /Sr ratio of 0.1194. replaces bronzite and quartz The Sr87/Sr86 ratio of the Eimer and Amend xenocrysts standard SrCC>3 was determined to be 0.7080, Plagioclase 48 Euhedral; 0.1 to 0.2 mm long; consequently no normalization of the data normal zoning An56_3o Alkali feldspar Anhedral; interstitial to was necessary, Ultramafic sample number 1 plagiochse laths was exactly repeated as a test of analytical Oxides and 16 Magnetite calcite, chlorite, precision. secondary biotite, ¡ipatite Olivine compositions were determined by minerals x-ray diffraction. The position of the (130) Lherzolitet and (241) olivine peaks were accurately mea- Olivine 75 Equigranular, anhedral, 1 to 4 sured with the aid of a Cominco ultrapure mm diameter; 2V = 90°, undulatory extinction and silver standard. deformation lamellae sub- Optic axial angles were measured with a parallel :o (100) 4-axis universal stage. Bronzite 13 Nonpleochroic, subhedral, 1 to 4 mm long; bent clinopyroxene LOCATION, GEOLOGY, exsoluticin lamellae; 2V = AND PETROGRAPHY -85° Diopside Anhedral, 1 to 2 mm long; bent Malapai Hill is a small basalt stock in Joshua orthopy::oxene exsolution Tree National Monument, California (Fig. 1). lamellae ;2V = +77° Rogers (1954) mapped the stock and observed Serpentine 6 Along fractures Spinel 1 Brown; anhedral no associated lava flows. The stock intruded Oxides and tr. the late Mesozoic White Tank Monzonite and secondary is probably late Cenozoic in age. minerals The lherzolite nodules are moderately abun- dant and strikingly uniform throughout the 'Basalt texture: Holocrystalline, aphanitic; porphy- ritic with olivine phenocrysts. stock. They are rounded, 1 to 5 cm in diameter, t Nodule texture: Tectonite fabric; medium-grained, medium-grained, equigranular, allotriomor- xenomorphic granular. phic, and not layered. The mineral composition of the inclusions (Table 1) and the forsterite composition of the olivine (Table 2) are similar groundmass and commonly replaces olivine, to lherzolite in alkaline basalt from many parts bronzite, or rarely, quartz xenocrysts. Simi- of the world (Ross and others, 1954; White, larly, subhedral augite crystals occur in reaction 1966). A tectonite fabric is expressed as bent rims where bronzite is at the exterior of a pyroxene exsolution lamellae, undulatory ex- lherzolite nodule. tinction, and kink bands. Xenoliths of White Tank. Monzonite, up to The basalt is aphanitic alkali olivine basalt 20 cm in diameter, are rare and are corroded, with phenocrysts of olivine and a groundmass suggesting partial assimilation into the basalt. of olivine, augite, plagioclase, alkali feldspar, Sodic andesine xenocrysts are invariably par- and magnetite. Olivine phenocrysts with kink tially resorbed. bands and undulatory extinction are xenocrysts derived from the nodules. Optic axial angles CHEMISTRY OF THE BASALT indicate that olivine xenocrysts are more The Malapai Hill basalt is typical alkali magnesian (Fogo) than the cognate olivine olivine basalt approaching basanite in composi- phenocrysts (F075). Augite is ubiquitous in the tion (Table 3). Although the normative nephe-

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TABLE 2. FORSTERITE CONTENTS OF OLIVINE IN raised the SiC>2 content of the basalt and this LHERZOLITE NODULES FROM MALAPAI HILL AS is not apparent. DETERMINED FROM 20ISO AND 20JU The strontium isotopic composition of the Malapai Hill basalt is within the range of Sample no. 2 0Î41 20130 oceanic island basalt reported by Peterman

1 90 90.6 and Hedge (1971), and at the lower extreme 2 91 94 of Basin and Range basalt analyzed by Leeman 3 92 90 (1970) and Peterman and others (1970). The 4 88 90 Malapai Hill basalt was derived from a source 5 92 91 region beneath the Mojave Desert which is 6 93.5 91 isotopically similar to oceanic mantle with respect to strontium. lene is less than 5 percent, these rocks are Wise (1969) found that the Pisgah lava field chemically similar to basanite of the Pisgah represents a sequence of eruptions that ranged lava field described by Wise (1969). The from basanite through alkali olivine basalt to Malapai Hill basalt is higher in Rb and Sr and subalkaline, low-alumina basalt. The sequence lower in CaO than the basalts from both Dish was interpreted as an upward-migrating zone Hill and Pisgah Crater (Wise, 1966, 1969). of melting that was successively affected by Over-all, the chemical differences are minor. lower pressures. The sequence from basanite to The chemical data indicate no reaction be- subalkaline basalt was marked by progressive tween the basalt and the White Tank Monzo- decreases of alkalis and increases of alumina nite unless it is reflected in the slightly raised and silica. The chemical similarity of the Rb values. The low Sr87/Sr86 ratios (Table 3) Malapai Hill basalt to the early members of are not indicative of significant reaction be- this sequence suggests a deep level origin fol- tween the basalt and the more radiogenic lowed by rapid intrusion into the upper crust quartz monzonite. Contamination should have with a minimum of sialic contamination.

TABLE 3. CHEMICAL ANALYSES OF MALAPAI HILL BASALT

Sample number 1 2 3 4 5 6 7

Oxides Si02 45.31 45.20 46.10 45.90 45.20 45.00 45.00 Ti02 2.77 2.50 2.74 2.73 2.70 2.79 2.83 AI2O3 14.76 14.94 14.81 14.95 14.70 14.81 14.72 Fe2Oa 4.03 FeO 8.63 12.73 12.32 12.21 12.40 12.37 12.79 MnO 0.19 0.21 0.22 0.21 0.21 0.21 0.21 MgO 7.70 8.28 7.85 8.02 7.90 7.69 7.46 CaO 7.85 7.97 8.45 8.34 8.26 8.34 8.25 Na20 3.64 3.33 3.58 3.11 3.19 4.01 3.86 K2O 1.70 1.77 1.91 1.71 1.75 1.20 1.26 H2O+ 1.49 H2O- 0.87 2.50 2.09 2.56 2.97 2.34 2.85 P2O6 0.58 Total 99.52 99.43 100.07 99.74 99.28 98.66 99.23 Elements Co 74 85 81 95 67 81 Cr 200 170 125 195 95 130 Ni 197 226 219 210 201 201 Cu 42 40 42 41 44 45 Rb 37 41 29 30 29 41 Sr 830 834 798 921 760 750 K/Rb 396 382 490 477 345 255 Rb/Sr 0.044 0.050 0.036 0.033 0.038 0.055 87 88 Sr /Sr 0.7036 0.7028 0.7028 2 a 0.0006 0.0006 0.0006

Trace elements are in ppm. Total Fe is reported as FeO for samples 2 through 7.

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CHEMISTRY OF THE NODULES of the Malapai Hill inclusions. The Sr87/Sr86 The lherzolite xenoliths from Malapai Hill ratios of the Malapai Hill nodules (Table 4) (Table 4) are uniform in composition and are are distinctly lower than most ratios reported exceedingly low in Ti, Al, Ca, Na, and K, and for peridotite nodules by other workers (Leggo slightly high in Mg. The Ti, Al, and Ca con- and Hutchison, 1968; Peterman and others, tents are less than half that of many lherzolites 1970). This suggests that the nodules are de- and much of the K present may have been rived from a mantle which was depleted in introduced from the basalt as has been shown the easily fusible elements during the early for a variety of upper mantle materials by part of earth history. Furthermore, the 0.7043 electron microprobe analysis (Erlank, 1970). ratio is nearly identical to the average Mojave Harris and others (1967, 1972) compared the Desert basalt reported by Leeman (1970) and compositions of xenoliths from different world- Peterman and others (1970). wide localities and separated them according DISCUSSION to their Ti02, CaO, A1203, Na20, and K20 contents. Those least depleted in these ele- Several interpretations have been suggested ments are spinel lherzolites from Monistrol for the origin of ultramalic nodules (Wilshire d'Allier and are believed to represent a nearly and Binns, 1961; White, 1966). Lherzolite undepleted upper mantle composition similar nodules may be cognate material formed by to Ringwood's pyrolite (1966a, 1966b). Xeno- fractional crystallization cf the basalt as pro- liths depleted in these easily fusible elements posed by Wise (1966) for the Dish Hill nod- were assumed to represent mantle material ules. Alternatively, ultrar.iafic xenoliths may from which basaltic liquid has been extracted. be primary or depleted mantle from either the The nodules from Malapai Hill are most similar site of partial melting or shallower levels to extremely depleted mantle. traversed by the ascending magma. The two nodules selected for strontium The allotriomorphic-gninular texture and isotopic analysis were fresh and representative tectonite fabric of the Malapai Hill nodules

TABLE 4. CHEMICAL ANALYSES OF ULTRAMAFIC: NODULES FROM MALAPAI HILL AND DISH HILL

Sample number 1 2 3 4 5 6 7 8 Oxides

Si02 43.58 44.50 42.40 43.50 43.00 44.20 43.50 44.35 TiOj 0.12 0.03 0.04 0.03 0.04 0.07 0.06 0.14 A12Oj 1.65 1.56 1.57 1.37 1.77 1.85 1.69 2.97 Cr2Os 0.46 0.45 0.44 0.41 0.70 0.48 0.34 0.41 FesOj 2.27 0.67 FeO 6.48 7.93 9.97 8.28 8.31 8.60 8.67 7.59 MnO 0.13 0.13 0.16 0.14 0.15 0.15 0.15 0.13 MgO 42.22 42.05 43.58 43.54 42.79 42.05 42.42 40.80 NiO 0.29 0.30 0.33 0.32 0.30 0.27 0.30 0.31 CaO 0.81 0.99 0.47 0.86 1.04 1.04 1.10 2.55 Na20 0.40 0.12 0.17 0.16 0.10 0.20 0.22 0.20 KJO 0.07 0.03 0.04 0.03 0.04 0.12 0.12 0.01 + H2O 0.89 0.06 H2O- 0.45 1.38 1.23 1.32 2.06 0.87 0.85 0.03 PIOE tr 0.02 Total 99.82 99.47 100.40 99.96 100.30 99.90 99.42 100.24 Elements Co 182 159 141 141 136 154 Cr 3140 3100 2970 2770 4780 3260 2260 Ni 2280 2390 2560 2520 2390 2070 2430 Cu 26 19 28 17 14 7 Rb tr tr ti tr tr tr Sr 4 6 3 15 22 22 Sr^/Sr8' 0.7043 0.7043 2a 0.0008 0.0008

Trace elements are listed in ppm. Numbers 1 through 7: Malapai Hill lherzolites. Total Fe is reported as FeO for samples 2 through 7. Number 8: Peridotite from Dish Hill reported by Hess (1955).

argue against a cognate origin. The nodules lulu Volcanic Series are largely accidental. are not layered, nor do they have a plagioclase Copious eruption of tholeiite produced a heter- interprecipitate. The presence of pyroxene ex- ogeneous mantle beneath Oahu; the Honolulu solution lamellae is not typical of cumulate Volcanic Series, generated at greater depths rocks nor does orthopyroxene crystallize from and at a later time, accidentally incorporated alkali olivine basalts. Bent pyroxene exsolution fragments of the heterogeneous mantle as they lamellae and olivine kink bands point to a moved toward the surface. Rare earth element metamorphic history for the nodules preceding studies on Hawaiian lavas (Nagasawa and their incorporation into the basalt. others, 1969) confirm this interpretation. In Furthermore, the olivine (Table 2) is more contrast to the Honolulu Volcanic Series, the forsterite-rich than that from the lowest levels nodules at Malapai Hill are uniform in character of layered ultramafic bodies. The forsterite and, although the basalt was probably gener- content of olivine from ultramafic nodules and ated at considerable depth, the lack of variety alpine peridotites falls in the range Fogg to does not typify what would be expected if the F093 (Green, 1964). The lowest cumulate inclusions were collected from a large section olivine in layered ultramafic sequences is often of heterogeneous upper mantle. Fogg (Green, 1964); it commonly has an ex- The strontium isotopic composition of the tended compositional range reaching below Malapai Hill basalt and other Mojave Desert F080 (Challis, 1965) due to iron enrichment in basalts previously reported (Peterman and the crystallizing magma. The olivine in the others, 1970; Leeman, 1970) indicates a de- Malapai Hill nodules is not cumulate material pleted mantle beneath the Mojave Desert. derived from the basalt. The 0.7028 to 0.7036 Sr87/Sr86 ratios of the Chemically, the Malapai Hill nodules are Malapai Hill basalt are similar to sea-floor not similar to rocks that have been interpreted tholeiites which Gast (1968) believes have as primary mantle and would not yield much formed from zones of the mantle that were alkaline basalt upon partial melting. The com- already depleted by a previous period of position of primary mantle puts limits on the magma generation. The low strontium isotopic amount of basalt that can be extracted from a ratios of the Mojave Desert basalts suggest given volume. Ringwood's (1966a, 1966b) that they were generated from a mantle which hypothetical pyrolite is three parts peridotite was depleted during a Precambrian episode of and one part basalt. Jackson and Wright (1970) crustal formation. This event reduced the chose garnet lherzolite as the parent that, upon Rb/Sr ratio of the mantle, thus causing the 87 86 50 percent melting, yielded the Hawaiian Sr /Sr ratio to grow very slowly. Conse- tholeiites; the alkaline Honolulu Volcanic quently, cognate lherzolite nodules and basalts Series was interpreted as having been derived formed in this depleted zone should have low from deeper level garnet pyroxenite and and similar Sr ratios. Nodules accidentally lherzolite. Reay (1965) found that garnet incorporated from shallower and perhaps less lherzolite from kimberlites is higher in SiC>2, depleted levels should be more radiogenic. Ti02, AI2O3, CaO, Na20, and K20 than nod- The similar strontium isotopic compositions ules from basalts and may represent primary of the nodules and host rocks permit, but do mantle. Harris and others (1972) concluded not prove, a cogenetic interpretation. Stueber that only 7 percent basalt can be extracted and Murthy (1966) reported two peridotite- from garnet lherzolite or spinel lherzolite. The basalt host pairs with similar strontium compo- lherzolite nodules from Malapai Hill, being sitions but concluded that isotopic data cannot exceptionally depleted in the fusible elements, distinguish between parent primary mantle, would yield very little basalt upon partial cognate refractory residue, and cumulate ma- melting. Partial melting would have had to terial. A cumulate origin for the Malapai Hill occur in an enormous volume if the Malapai nodules has been ruled out. The ultramafic Hill nodules represent the primary mantle nodules may represent depleted mantle ma- material from which the basalt formed. terial that formed during the Precambrian The Malapai Hill lherzolites may be either episode of crustal formation or depleted mantle infusible residue from the site of melting or that has undergone a second partial melting depleted mantle accidentally incorporated into to generate the late Cenozoic age Mojave the basalt. Jackson and Wright (1970) believe Desert basalts. Comparison of the Malapai that the dunite, lherzolite, garnet lherzolite, Hill nodules on Table 4 with one reported and garnet pyroxenite xenoliths in the Hono- from Dish Hill (Hess, 1955) indicates that the

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Malapai Hill nodules have much lower Ca and Erlank, A. J., 1970, Distribution of potassium in A1 contents and probably represent a more mafic and ultramafic nodules: Carnegie Inst. depleted mantle. This suggests that the Malapai Washington Year Book 68, p. 433-438. Hill nodules are the refractory residue of Gast, P. W., 1968, Trace element fractionation and mantle that had already experienced an episode the origin of tholeiitic and alkaline magma types: Geochim. et Cosmochim. Acta, v. 32, of depletion in Precambrian time. Partial melt- p. 1057-1086. ing of a large volume of already depleted Green, D. H., 1964, The petrogenesis of the high- mantle material would improve the chances of temperature peridotite intrusion in the Lizard refractory residue being included in the melt. area, Cornwall: Jour. Petrology, v. 5, p. Similarly, Reid and Frey (1971) concluded 134-188. from rare earth element data that spinel Green, D. H., and Ringwood, A., 1967, The genesis lherzolites at Salt Lake Crater, Hawaii, are of basaltic magmas: Contr. Mineralogy and cognate refractory residue formed when the Petrology, v. 15, p. 103-190. basaltic components were removed from the Harris, P. G., Reay, A., and White, I. G., 1967, Chemical composition of the upper mantle: original garnet pyroxenite mantle. This inter- Jour. Geophys. Research, v. 72, p. 6359-6369. pretation for the Malapai Hill nodules is based Harris, P. G„ Hutchison, R., and Paul, D. K., on the similarity of the nodule and host-rock 1972, Plutonic xenolith;; and their relation strontium isotopic compositions, the striking to the upper mantle: Royal Soc. London uniformity of the nodule types in the intrusion, Philos. Trans., v. 271, p. 313-323. and the extremely depleted chemical character Hedge, C. E„ and Noble, D. C„ 1971, Upper 8 s6 of the nodules. Cenozoic basalts with high Sr '/Sr and Sr/Rb Peterman and others (1970) reported thé ratios, southern Great Basin, western United strontium isotopic composition of minerals in States: Geol. Soc. America Bull., v. 82, p. 3503-3510. a Iherzolite inclusion from Dish Hill and con- Hess, H. H., 1955, The oceanic crust: Jour. Marine cluded that the inclusion is more radiogenic Research, v. 14, p. 423-439. than its enclosing lava and is accidental in Jackson, E. D„ and Wright, T. L„ 1970, Xenoliths origin. The more radiogenic character and the of the Honolulu Volcanic Series, Hawaii: different chemical composition of the Dish Jour. Petrology, v. 11, p. 405-430. Hill nodules indicate that the mantle beneath Leeman, W. F., 1970, The isotopic composition of the Mojave Desert is heterogeneous and pos- strontium in late Cenozoic basalts from the sibly vertically zoned as suggested by Hedge Basin-Range province, western United States: and Noble (1971). The nodules from Malapai Geochim. et Cosmochim. Acta, v. 34, p. 857-872. Hill may represent refractory residue from the Leggo, P. J., and Hutchison, R., 1968, A Rb-Sr depleted mantle source area of the Mojave isotope study of ultrabasic xenoliths and their Desert basalts. More radiogenic nodules at basaltic host rocks from the Massif Central, Dish Hill may represent a shallower, less de- France: Earth and Planetary Sci. Letters, pleted zone of the mantle. v. 5, p. 71-75. Nagasawa, H., Wakita, H., Higuchi, H., and ACKNOWLEDGMENTS Onuma, N., 1969, Rare earths in peridotite We are indebted to Terry Davis (California nodules: An explanation of the genetic rela- State University, Los Angeles) for his assistance tionship between basalt and peridotite nod- with the isotopic analyses and critical review ules: Earth and Planetary Sci. Letters, v. 5, p. 377-381. of the manuscript. George Tilton (University Peterman, Z. E., and Hedge, C. E„ 1971, Related of California, Santa Barbara) provided easy strontium isotopic and chemical variations in access to the mass spectrometer. Gary Novak oceanic basalts: Geol. Soc. America Bull., (California State University, Los Angeles) v. 82, p. 493-500. assisted with the olivine determinations. Ken- Peterman, Z. E., Carmichael, I.S.E., and Smith, Ichiro Aoki (Tohoku University) analyzed two A. L., 1970, Strontium isotopes in Quaternary samples for use as standards. basalts of southeastern California: Earth and Planetary Sci. Letters, v. 7, p. 381-384. Reay, A., 1965, Mantle composition and partial REFERENCES CITED fusion of mantle material [Ph.D. thesis]: Leeds, England, Univ. Leeds. Challis, G. A., 1965, The origin of New Zealand Reid, J. B„ ar.d Frey, F. A., 1971, Rare earth ultramafic intrusions: Jour. Petrology, v. 6, distributions in Iherzolite z.nd garnet pyroxe- p. 322-364. nite xenoliths and the constitution of the

upper mantle: Jour. Geophys. Research, v. 76, in ultramafic rocks: Geochim. et Cosmochim. p. 1184-1196. Acta, v. 30, p. 1243-1259. Ringwood, A. E., 1966a, The chemical composition White, Richard W., 1966, Ultramafic inclusions in and origin of the earth, in Hurley, P. M., ed., basaltic rocks from Hawaii: Contr. Mineralogy Advances in earth science: Massachusetts and Petrology, v. 12, p. 245-314. Inst. Technology Press, Cambridge, p. 287- Wilshire, H. G., and Binns, R. A., 1961, Basic and 356. ultrabasic xenoliths from volcanic rocks of 1966b, Chemical evolution of the terrestrial New South Wales: Jour. Petrology, v. 2, p. planets: Geochim. et Cosmochim. Acta, v. 30, 185-208. p. 41-104. Wise, W. S., 1966, Zeolitic basanite from south- Rogers, J.J.W., 1954, Igneous and metamorphic eastern California: Bull. Volcanol., v. 29, p. rocks of the western portion of Joshua Tree 235-252. National Monument: California Div. Mines —— 1969, Origin of basaltic magmas in the Mojave and Geology Spec. Rept. 68, 26 p. Desert area, California: Contr. Mineralogy Ross, C. S., Foster, M. D., and Myers, A. T„ 1954, and Petrology, v. 23, p. 53-64. Origin of dunites and of olivine-rich inclusions in basaltic rocks: Am. Mineralogist, v. 39, MANUSCRIPT RECEIVED BY THE SOCIETY OCTOBER p. 693-737. 16, 1972 Stueber, A. M., and Murthy, V. R., 1966, Stron- REVISED MANUSCRIPT RECEIVED JANUARY 17, tium isotope and alkali element abundances 1973

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