Geology and Petrology of the Mcmurdo Volcanic Group at Rainbow Ridge, Brown Peninsula, Antarctica

Home , Benmoreite, McMurdo Volcanic Group

Geology and petrology of the McMurdo Volcanic Group at Rainbow Ridge, Brown Peninsula, Antarctica

PHILIP R. KYLE Institute of Polar Studies, Ohio State University, Columbus, Ohio 43210 JOHN ADAMS Department of Geology, Victoria University, Wellington, New Zealand PETER C. RANKIN Soil Bureau, Department of Scientific and Industrial Research, Lower Hütt, New Zealand

ABSTRACT

Strongly undersaturated rocks of the McMurdo Volcanic Group of late Cenozoic age at Brown Peninsula form three eruptive cycles of basaltic to salic lavas. Two cycles at Rainbow Ridge show a basanite to nepheline-hawaiite to nepheline-benmoreite and a basanite to nepheline-benmoreite eruptive sequence. Fractional crystallization processes for the sequence have been modeled using major-element least squares mass-balance models. Two models can explain the basanite to nepheline-hawaiite transition. Model 1 involves fractionation of olivine, clinopyroxene, plagioclase, opaque oxides, and apatite; model 2 is similar, but also includes kaersutite. The nepheline-hawaiite to nepheline-benmoreite transition involves fractionation of clinopyroxene, kaersutite, plagioclase, opaque oxides, and apatite. Trace-element (includ- ing rare-earth element) contents calculated using solutions from the mass-balance models are compatible with both models for the formation of nepheline-hawaiite. Excellent agreement is shown between calculated and observed trace-element data for the nepheline-benmoreite. Small pods of basanite, derived from a garnet peridotite mantle by a low degree of partial melting, have been intruded into the crust where subsequent fractional crystallization formed the intermediate and salic rocks. This process has apparently occurred re- peatedly at many eruptive centers in the McMurdo Sound area.

INTRODUCTION

Undersaturated alkalic volcanic rocks of late Cenozoic age in the McMurdo Sound area constitute the Erebus volcanic province of the McMurdo Volcanic Group (Kyle and Figure 1. Generalized geological map of Brown Peninsula, showing location of Rain- Cole, 1974). The lavas range in composi- bow Ridge (after Cole and Ewart, 1968). Inset shows location map of McMurdo Sound tion from basanite (basanitoid) to phono- area.

Geological Society of America Bulletin, Part I, v. 90, p. 676-688, 9 figs., 8 tables, July 1979, Doc. no. 90710.

676

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/7/676/3419086/i0016-7606-90-7-676.pdf by guest on 01 October 2021 McMURDO VOLCANIC GROUP, ANTARCTICA 677

lite. Trachyte has been reported at one lo- dertaken in January 1973 as part of tatively proposed were (youngest to oldest) cation (Smith, 1954; Goldich and others, Victoria University of Wellington Antarctic (1) Trachyte Hill Formation, (2) Nubian 1975) but is volumetrically insignificant. Expedition (VUWAE) 17. Although Rain- Basalt Formation, (3) Aurora Trachyte Two lava lineages have been recognized on bow Ridge was almost completely snow- Formation, and (4) Melania Basalt Forma- the basis of mineralogical and detailed free, geologic contacts were commonly tion. Black Island was the type area for the geochemical data (Kyle and Rankin 1976; obscured by loose debris. A geological map three older formations, Cape Bird the type Sun and Hanson, 1976). The Dry Valley (Fig. 2) has been compiled from field obser- area for the youngest. Cole and Ewart Drilling Project (DVDP) lineage of basanite, vations and petrological examination of 54 (1968, p. 802) qualified their tentative nepheline-hawaiite, nepheline-mugearite, samples. proposal by stating that it was "quite likely nepheline-benmoreite, mafic phonolite that each formation was erupted over a evolved by fractional crystallization of VOLCANIC STRATIGRAPHY period and eruptions in one area do not olivine, clinopyroxene, kaersutite, spinel, necessarily exactly correspond in time to feldspar, and apatite (Kyle, unpub.), Cole and Ewart (1968) mapped alternat- eruptions in another area." Cole and others whereas evolution of the Erebus lineage of ing basalt-trachyte-basalt-trachyte eruptive (1971) extended the use of these formation basanite(P) nepheline-hawaiite, nepheline- sequences at Black Island, Brown Peninsula, names to eruptive events at Hut Point benmoreite, anorthoclase phonolite (ke- and Cape Bird in the McMurdo Sound area. Peninsula, Cape Crozier, and White Island. nyte) involved fractionation of the minerals Because of the morphological similarity of They did comment (p. 534) that "prelimi- listed above, with the exception of kaersu- the eruptive sequences, a series of four for- nary K/Ar dates indicate that formations in tite. DVDP lineage lavas are best exposed at mations were proposed and correlated be- different areas within McMurdo Sound Hut Point Peninsula in surface exposures tween the three areas. The formations ten- were erupted at different times." and drill cores from DVDP holes 1, 2, and 3 (Kyle and Rankin, 1976; Kyle, 1976; Kyle and Treves, 1974a). m A petrogenetic model for the origin of 2.7± 0.09 m.y x \ Brown Peninsula lavas is developed here \ 24087 \ and shown to be similar to that for lavas in \ the Hut Point Peninsula area. A model in- Inclusionx | : volving the intrusion of small pods of ..: Flow-. -v mantle-derived basanite magma into an Vl-v.;? upper mantle and/or crustal magma chamber, followed by crystal fractionation, j|:-yx\24090Íy would account for the eruptive sequence at m Rainbow Ridge. The model is believed to be generally applicable to mafic phonolite ISpít- * - . • o f y lavas in the Erebus volcanic province but 'vIV'V-VV.'A;-» will not explain the eruptive history of the anorthoclase phonolite lavas from Mt. wà.f" Erebus. m Rainbow Ridge is situated at the north- western end of Brown Peninsula (Fig. 1). It is 300 m wide and trends north-northeast lOOm. for 1 km (Fig. 2); the highest point is about 380 m above sea level and 150 m above KEY nearby Lake Auger. (Topographic features Inferred stratigraphy at Rainbow Ridge have been given informal (youngest to oldest) names to aid discussion of the geology; 17;:;:] Ne- benmoreite these names, shown in Figure 2, have not ÎÏÏT1 Basanite been approved by the New Zealand Geo- K;-1 Ne-benmoreite graphic Board.) Cole and Ewart (1968) Ne- hawaiite mapped the geology of Rainbow Ridge and considered a flow on the north side to be H3 Basanite one of the youngest flows on Brown Penin- m Moraine sula. K-Ar age determinations (available in X Sample location 1972 and later published by Armstrong, Contact obscured 1978) indicated possible inconsistencies in the inferred eruptive events. A detailed B Grey Cone removed by ice- study of Rainbow Ridge was therefore un- Inclusion Flow Mound Figure 2. Geological map and cross section of Rainbow Ridge, Brown Peninsula.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/7/676/3419086/i0016-7606-90-7-676.pdf by guest on 01 October 2021 678 KYLE AND OTHERS

It is apparent from the extensive K/Ar Figure 3 gives suggested stratigraphie Antarctica. Its present status (Fig. 3) is re- dating by Armstrong (1978) that there is nomenclature for the McMurdo Volcanic tained, however, but with caution. little age overlap in volcanic activity among Group, which has been subdivided into four K-Ar ages (Armstrong, 1978) indicate the many eruptive centers in McMurdo informal volcanic provinces (Kyle and Cole, that the timing of an eruptive sequence at Sound. The volcanic centers probably acted 1974; Hamilton, 1972). Inclusion of the any major eruptive center is largely inde- individually, so correlation of these eruptive Balleny volcanic province within the pendent of eruptive sequences at other cen- events is erroneous and misleading. There- McMurdo Volcanic Group can be ques- ters. Therefore, formal or informal strati- fore, it is proposed to discontinue the use of tioned, particularly as it occurs in an graphic names can be applied only locally. formation names in areas other than their oceanic environment and appears to be un- Unfortunately, this will lead to a prolifera- type locality (Kyle, unpub.). related to volcanism within continental tion of names, but this apparently is un-

McMurdo Volcanic Group (1,2)

Balleny volcanic province (3) Erebus ^volcanic province (4)

Hut Point Peninsula Black Island volcanic Bird volcanic volcanic center (6) center (6) center (6) I I I Roberts Cliff Tuffite Twin Crater Nubian Basalt Trachyte Hill (Formation) (7) sequence (8) Formation (9) Formation (9) Herschel Tuffaceous Moraine Half Moon Crater Aurora Trachyte (Formation) (7) sequence (8) Formation (9) Castle Rock Melania Basalt sequence (8) Formation (9) Observation Hill sequence(8) Crater Hill sequence (8) References (1) Harrington (1958) (6) This paper (2) Nathan and Schulte (1968) (7) Harrington and others (1964, 1967) Figure 3. Suggested stratigraphie (3) Hamilton (1972) (8) Kyle and Treves (1974 b) hierarchy for McMurdo Volcanic (4) Kyle and Cole (1974) (9) Cole and Ewart (1968) (5) Kyle (1976); Kyle and Rankin (1976) Group rocks.

TABLE 1. WHOLE-ROCK K-Ar AGE DETERMINATIONS OF McMURDO VOLCANIC GROUP ROCKS FROM BROWN PENINSULA, ANTARCTICA

Sample Location1 Rock type+ and occurrence Former formation name* Age no. (Cole and Ewart, 1968) (m.y.)

21068 3 km west-northwest Kaersutite basanite flow Melania Basalt Formation 2.1 ± 0.4 of Mt. Wise (hornblende basalt) 21094 1.5 km southeast of Olivine-augite basanite flow Nubian Basalt Formation 2.2 ± 0.09 Mt. Wise (olivine-augite basalt) 21047 2 km northeast of Kaersutite flow Aurora Trachyte Formation 2.25 ± 0.05 Mt. Wise (hornblende trachyte) 21001 Rainbow Ridge Kaersutite benmoreite flow Trachyte Hill Formation 2.7 ± 0.09 (hornblende trachyte)

Note: Data from Armstrong (1978). Victoria University of Wellington sample numbers. * See Figure 1. Rock types have been classified to accord with the nomenclature used in this paper. The terminology of Cole and Ewart (1968) is given in parentheses. * The use of these formation names at Brown Peninsula is no longer recommended (Kyle, unpub.), but they are given here to allow comparison to the earlier work of Cole and Ewart (1968).

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/7/676/3419086/i0016-7606-90-7-676.pdf by guest on 01 October 2021 McMURDO VOLCANIC GROUP, ANTARCTICA 679

avoidable. The formal term "formation" is of the basanite was followed by the forma- Coombs and Wilkinson (1969). Several retained as the fundamental rock-strati- tion of a steep-sided nepheline-hawaiite points should be noted, however: (1) The graphic unit, and the informal equivalent scoria cone and then by eruption of viscous terms "basanite" (modal nepheline present) "sequence" has been introduced by Kyle sheets of nepheline-benmoreite from the and "basanitoid" (no modal nepheline) are and Treves (1974b). "Sequence" can be same vent. used here synonymously, for although defined as an informal, mappable rock- Grey Cone was extensively modified by nepheline is not usually observed in routine stratigraphic unit, characterized by ice, and at least 40 m of the center of the thin-section examinations, it is often found lithologic homogeneity or distinctive fea- cone was removed. The nepheline-ben- in the groundmass by staining, X-ray dif- tures that are volcanic in origin. A major moreite was more resistant to ice erosion fraction, or electron microprobe tech- eruptive vent or collection of smaller vents, than the scoriaceous nepheline-hawaiite, so niques. (2) The intermediate lavas have the products of which may or may not con- a central depression was formed, with the >10% normative nepheline (ne). Coombs sist of a collection of formations or se- more resistant plug remaining as a low rise and Wilkinson (1969) recommended in quences, is informally termed a "volcanic in the center. such cases to prefix the term "nepheline" to center" (Fig. 3). Eruption of the younger basanite from a the rock names. (3) The nepheline-hawaiite more southerly vent to form Red Mound and nepheline-mugearite are defined on the GEOLOGY OF BROWN PENINSULA was followed by the extrusion of two basis of their chemistry. The modal min- younger nepheline-benmoreite flows as the eralogy of the samples does not conform to Brown Peninsula consists of a series of final phase. The northern younger neph- the original concepts and definitions of north-south—aligned basaltic and salic eline-benmoreite, dated at 2.7 ± 0.09 m.y. hawaiite and mugearite, in which olivine is eruptive centers (Fig. 1). Vents from Tuff (Table 1) has not been modified by glacial an essential groundmass phase. Bluff to Frame Ridge and at Rainbow Ridge erosion. appear to be the oldest and have been con- Descriptions siderably modified by glacial erosion (Cole PETROGRAPHY and Ewart, 1968). The youngest vents, cen- Modal analyses of analyzed samples are tered about Mt. Wise, do not show any Nomenclature given in Table 3, and photomicrographs of marked glacial erosion. representative thin sections are shown in Four K-Ar age determinations (Table 1) Nomenclature of McMurdo Volcanic Figure 4. give some indication of the eruptive se- Group rocks is confused because of ill- The basanites are porphyritic with seriate quence at Brown Peninsula. A single age de- defined and infrequently used names (com- phenocrysts (as much as 3 mm long) of col-

termination of 2.7 ± 0.09 m.y. (Table 1) on pare Smith, 1954; Treves, 1967; Cole and orless olivine (Fa10-2o) and clinopyroxene the youngest flow at Rainbow Ridge post- Ewart, 1978; Goldich and others, 1975; (Fig. 4, A). The clinopyroxene is weakly dated glacial erosion. In the Mt. Wise area Kyle and Rankin, 1976). In the field it is pleochroic pale brown or purplish and three K-Ar age determinations have ana- possible only to distinguish dark-colored shows strong regular and sector zoning; lytical uncertainties that overlap. The dates basic from light-colored salic rocks. The green sodic ferrosalite cores also occur. In indicate that the eruptive events at Mt. Wise field problem led to the use of simple rock the groundmass, plagioclase (An 74—40) oc- were only short-lived and occurred about names — basalt and trachyte — prefixed by curs as small prismatic crystals (less than 2.2 m.y. ago. phenocryst names. 0.2 mm in length), and equant grains of The eruptive sequence at Brown Penin- The nomenclature used here (Table 2) is opaque oxides (less than 0.1 mm) are abun- sula consists of at least three basaltic based on the chemical composition and the dant; they are set in a matrix of brownish (basanite, hawaiite, mugearite) to salic CIPW percent by weight normative min- isotropic glass. (benmoreite, phonolite) eruptive cycles. The eralogy. It follows closely that used by The nepheline-hawaiites are vesicular, oldest dated cycles occur at Rainbow Ridge, with phenocrysts of brown pleochroic kaer- where two basaltic to salic eruptive se- TABLE 2. NOMENCLATURE USED TO DESCRIBE McMURDO sutite (1 mm long) and rare pale greenish quences are found. These are followed by a VOLCANIC GROUP ROCKS FROM euhedral clinopyroxene (Fig. 4, B). Rare younger basaltic-salic-basaltic eruptive se- McMURDO SOUND AREA xenocrysts of olivine are surrounded by a quence at Mt. Wise. Further radiometric narrow reaction rim of clinopyroxene or Name Classification criteria dating of lavas in the Frame Ridge area will kaersutite. The groundmass contains fresh probably indicate more cycles. Basanite An > 50 Ne > 5% kaersutite, brownish clinopyroxene, equant Nepheline- grains of opaque oxides, and laths of hawaiite An = 31--50 Ne > 10% FIELD RELATIONSHIPS AT plagioclase (An6o_33), all set in brown iso- Nepheline- RAINBOW RIDGE tropic glass. mugearite An = 10--30 Ne > 10% Nepheline- The nepheline-benmoreites are porphyri- A detailed discussion of the field geology benmoreite DI = 65--75 Ne > 10% tic, with seriate phenocrysts of subhedral and stratigraphy was given by Adams Phonolite DI > 75 Ne > 10% kaersutite (as much as 2 mm long), minor (1973) and is summarized in Figure 2. A euhedral clinopyroxene, and rare un- Note: An = normative 100 An/(An + Ab), series of basanite pyroclastic eruptions with Ne = normative nepheline. DI = differentiation twinned oligoclase (Fig. 4, C). Opaque minor lava flows formed most of the ridge. index (normative Q + Ab + Or + Ne + Lc) of oxides rim the kaersutite phenocrysts, Palagonitic tuffs that occur to the north and Thornton and Turtle (1960). CIPW norms, in whereas the microphenocrysts are usually east may be related to this phase. Eruption percent by weight, used throughout. completely oxidized. Rare olivine xeno-

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/7/676/3419086/i0016-7606-90-7-676.pdf by guest on 01 October 2021 TABLE 3. ANALYSES OF VOLCANIC ROCKS FROM BROWN PENINSULA

1 2 3 4 5 6 7 8 9 10 11 24085 24087 24086 24088A 24088B 24091 24089 24090

Si02 41.3 41.88 42.03 42.52 43.8 48.46 48.55 52.14 52.60 52.87 58.64 Ti02 4.08 3.72 3.82 3.80 3.47 2.56 2.56 1.40 1.38 1.26 0.28 AI2O3 12.9 13.37 14.19 14.50 14.5 18.17 18.07 19.72 20.02 20.04 22.55 Fe203 4.87 13.11 13.86 13.09 4.56 9.53 9.56 6.43 6.44 6.09 0.97 FeO 7.39 7.85 0.99 MnO 0.20 0.20 0.22 0.21 0.23 0.20 0.19 0.19 0.19 0.20 Tr. MgO 10.2 9.88 8.16 7.98 7.75 3.91 3.95 1.97 2.10 1.79 0.16 CaO 11.0 11.70 10.63 11.54 10.3 7.24 7.29 4.68 4.46 4.41 1.43 Na20 3.59 3.46 3.99 3.74 4.11 6.37 6.38 8.01 7.77 8.05 9.87 K2O 0.63 1.33 1.77 1.69 1.78 3.04 3.02 3.90 4.04 3.97 4.98 P2O5 0.82 0.85 1.07 0.91 0.98 0.74 0.74 0.45 0.44 0.41 Tr. + H2O 1.19 0.60* 0.67* 0.36 0.07* 0.07* 0.78* 0.56* 0.67* 0.35 H2O~ 0.72 0.07 0.08 co2 0.82 0.03 Total 99.71 100.10 100.41 99.98 99.79 100.29 100.38 99.67 100.00 99.76 100.30 Rb 24 30 37 32 49 77 76 105 110 101 Ba 290 287 338 287 580 493 498 652 638 645 Sr 880 930 1250 1062 1200 1063 1063 912 896 892 Y 31 40 Zr 330 370 Zn 110 100 107 102 113 112 111 102 107 107 Cu 41 58 42 58 32 28 27 15 16 14 Ni 200 184 119 131 140 34 34 13 18 15 V 280 272 241 265 260 143 141 56 59 55 Cr 460 356 233 292 350 70 71 31 53 27 K% 0.52 1.10 1.47 1.40 1.48 2.52 2.51 3.24 3.35 3.30 K/Rb 218 367 397 438 302 327 330 308 304 327 Mg no. 65.4 64.7 58.8 59.7 58.6 49.9 50.1 CIPW norms (% by weight)* Or 3.72 7.86 10.46 9.99 10.52 17.96 17.85 23.05 23.87 23.46 29.43 Ab 16.32 3.02 4.78 4.05 12.86 19.42 19.54 27.06 28.05 28.99 39.01 An 17.22 17.02 15.58 17.78 15.86 12.01 11.75 6.33 7.82 6.82 2.52 Ne 7.62 14.22 15.70 14.95 11.87 18.68 18.66 22.06 20.42 21.19 24.11 Di-wo 11.19 14.81 12.60 14.00 11.96 7.96 8.18 5.82 4.78 5.17 0.95 Di-fs 1.11 4.25 4.45 4.65 2.36 2.79 2.85 1.83 1.45 1.58 0.55 Di-en 8.83 9.56 7.50 8.56 8.54 4.76 4.90 3.64 3.02 3.26 0.40 Wo 0.96 Fo 11.61 10.54 8.98 7.93 7.54 3.49 3.46 0.89 1.55 0.84 Fa 1.60 5.16 5.87 4.74 2.30 2.25 2.22 0.49 0.82 0.45 Mt 7.06 2.90 2.90 2.90 6.61 3.63 3.62 3.62 3.62 3.62 1.41 11 7.75 7.06 7.26 7.22 6.59 4.86 4.86 2.66 2.62 2.39 0.53 Ap 1.90 1.97 2.48 2.11 2.27 1.72 1.72 1.04 1.02 0.95 Others 3.77" 0.60 0.67 0.50 0.07 0.07 0.78 0.56 0.67 0.43 Total 99.71 98.99 99.22 98.87 99.79 99.59 99.68 99.28 99.61 99.40 100.30

DI 27.7 25.1 30.9 29.0 35.2 56.1 56.0 72.2 72.3 73.6 92.6 An/(An + Ab) 51.4 84.9 76.5 81.5 55.2 38.2 37.5 19.0 21.8 19.0 6.1

Modal analyses Phenocrysts Olivine 6.6 4.7 5.8 Clinopyroxene 11.7 8.7** 11.6 1.5 Kaersutite 6.7+++ 10.1''' 14.6+" Plagioclase 0.2 0.5 1.9 Groundmass 81.7 85.4 82.6 91.6 89.4 83.4 Olivine 0.5 0.3 Clinopyroxene 4.7 29.5 8.5 3.0 15.9 3.3 Kaersutite 4.9 Plagioclase 2.4 10.5 2.4 14.3 44.6 21.7 Alkali feldspar n.di. WI n.d.*** Opaque oxides 0.8 4.7 0.3 0.4 13.0 3.6

Note: 1: Basanite; younger flow contains minor carbonate and altered olivine. Goldich and others, (1975). 2, 3, 4: Basanite; Rainbow Ridge. 5: Basanite; core of pillow, older flow on Brown Peninsula (Goldrich and others, 1975). 6: Nepheline-hawaiite; Rainbow Ridge. 7: Duplicate specimen of sample 24088. 8, 9, 10: Nepheline-benmoreite; Rainbow Ridge. 11: Phonolite (phonolitic trachyte; Prior, 1907). * Loss on ignition at 1000 °C. 2+ ' Mg no. = 100 Mg/(Mg + Fe ) atomic ratio with Fe203/Fe0 standardized at 0.25 (Kesson, 1973). *For samples without FeO determinations standardized values were used (Thompson and others, 1972). " Includes Cc = 1.86%. Based on 700 points. No clear distinction into phenocryst/groundmass. "1* t Not recognized. Includes magnetite rims. *** Present but not determined.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/7/676/3419086/i0016-7606-90-7-676.pdf by guest on 01 October 2021 McMURDO VOLCANIC GROUP, ANTARCTICA 681

crysts have either a reaction rim of granular ble 3, analyses 6 and 7). Three representa- sult in any marked change in the normative clinopyroxene or opaque oxides or kaersu- tive samples were analyzed for rare-earth silica undersaturation of the lavas. tite overgrowths. Occasional cognate elements (REE), Cs, Hf, Pb, Th, and U by xenoliths consist of granular aggregates of spark-source mass spectrometry; the ana- Major Elements oligoclase, clinopyroxene, kaersutite, and lytical technique has been described by Kyle minor olivine. The pilotaxitic groundmass and Rankin (1976). Oxide variation diagrams (Figs. 5, 6) consists of laths of oligoclase (An20) zoned show well-defined trend lines consistent to albite, with alkali feldspar rims, colorless Results with a fractional crystallization origin for

clinopyroxene, and opaque oxides. the lava series. In detail, CaO, Ti02, and Seven samples were analyzed (one in du- 2FeO decrease linearly from basanite to

PETROCHEMISTRY plicate). Analyses are listed according to in- phonolite when plotted against Si02. creasing Si02 content in Table 3; three pre- Although MgO also decreases with increas- Analytical Methods viously published analyses of Brown Penin- ing Si02 content, it is nonlinear; there is a sula samples are also included for compari- rapid decrease from basanite to nepheline-

Major-element (except Na20) and trace- son. The data are presented graphically in hawaiite, followed by a flattening in the element analyses were made by X-ray oxide variation diagrams (Figs. 5, 6, 7). trend with further fractionation. P205 may fluorescence spectroscopy using the tech- The analyzed samples are strongly silica show a slight increase up to 44% Si02 but niques of Norrish and Chappell (1967) and undersaturated; all have greater than 5% then decreases nonlinerarly throughout the Norrish and Hutton (1969). Sodium was normative nepheline (Table 3). Calculation remainder of the series. A1203, K20, and determined using atomic absorption spec- of the ne content and hence the degree of Na20 increase linearly with increasing troscopy. The analytical precision can be undersaturation is, however, dependent on Si02.

assessed from the determinations on two the partition of Fe between Fe203 and FeO. A plot of total alkalis versus silica (Fig. 6) 1 separate specimens of sample 24088 (Ta- Only total Fe as Fe203 was determined for illustrates the strong alkalic nature of the samples analyzed in this study. Stan- Brown Peninsula lavas and shows a well- dardized values of FeO were used in cal- defined very slightly curvilinear trend of in- 1 Sample numbers refer to the petrological collection of the Department of Geology, Victoria culating the CIPW norms. A decrease in the creasing alkalis with increasing silica. University of Wellington. assumed FeO content will not, however, re- The alkalis have a near constant K20:

Figure 4. Photomicrographs of volcanic rocks from Rainbow Ridge. Field of view is 4.5 mm in all photos. A: Basanite (sample 24087). Phenocrysts of olivine (upper left quadrant) and clinopyroxene set in groundmass of clinopyroxene, opaque oxides, olivine, and plagioclase. Clinopyroxene phenocryst on right has green sodic core; core of phenocryst on lower left is completely oxidized. B: Nepheline-hawaiite (sample 24088). Phenocrysts of kaersutite and clinopyroxene in groundmass of plagioclase, kaersutite, clinopyroxene, opaque oxides, and glass. C: Nepheline-benmoreite (sample 24090). Phenocrysts and microphenocrysts of kaersutite and clinopyroxene in pilotaxitic groundmass. Note opaque oxide rims on kaersutite phenocrysts and completely oxidized microphenocrysts. Partially crossed nicols.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/7/676/3419086/i0016-7606-90-7-676.pdf by guest on 01 October 2021 682 KYLE AND OTHERS

Na20 ratio of 1:2 and therefore place the and Rankin (1976). Basanites at Brown varying proportions (Kesson and Price, Brown Peninsula lavas in the sodic series of Peninsula (Table 3) have Mg numbers [100 1972); therefore, it is difficult to demon- 2+ the alkali lavas. Coombs and Wilkinson Mg/(Mg + Fe ), Fe203/Fe0 standardized strate the effect of kaersutite during frac-

(1969) examined the K20:Na20 ratio of at 0.25J (Kesson, 1973), ranging from 59 to tional crystallization from the trace-element alkalic lavas from the East Otago Volcanic 65. Primary basanite in equilibrium with data. The REE chemistry may be charac- Province, New Zealand, and several other mantle olivine (Fo88 to Fo92) should have teristic (Kyle and Rankin, 1976); fractiona- volcanic centers from around the world. Mg numbers of 68 to 77 (Green, 1971, tion of kaersutite will normally result in a They suggested that classification of lava 1973). This implies that the Brown Penin- marked depletion of the middle REE. series and hence lava nomenclature on the sula basanites have fractionated during To quantitatively evaluate the crystal basis of K20:Na20 ratios as proposed by their ascent to the surface. However, allow- fractionation hypotheses for evolution of Macdonald (1960) and Macdonald and ing for this, the REE (Fig. 8), favor an origin the Rainbow Ridge lava lineage, a large Katsura (1964) was limited due to the ten- for the primary basanites by a low degree of number of least squares mass-balance dency in lava lineages toward increase of partial melting of garnet peridotite mantle models were calculated. Two steps were K20:Na20 with differentiation. This limi- at about 30 kb pressure (Kay and Gast, considered; basanite to nepheline-hawaiite tation is not apparent in the Brown Penin- 1973). and nepheline-hawaiite to nepheline- sula lava lineage. The major-element and trace-element benmoreite. analyses considered in conjunction with the The following models were calculated Trace Elements known phenocryst phases help elucidate the using the computer program of Bryan and fractional crystallization model for the ori- others (1970); procedures were similar to Plots of trace-element concentrations gin of the Brown Peninsula lavas. The sharp those suggested by Wright (1974). All against silica (Fig. 7) also define trends decrease in MgO, Ni, and Cr indicates ini- analyses used in the models were nor- consistent with a fractionation crystalliza- tial fractionation of mafic phases — malized to 100%, water-free, and with total tion origin for the lava series. Cr and Ni are namely, olivine, clinopyroxene, and spinel. Fe as FeO. Mineral analyses are of typical similar to MgO and show an initial sharp Fractionation of olivine would deplete the phenocryst phases found in McMurdo Vol- decrease in concentration, followed by a residual liquid of Ni, while pyroxene and canic Group rocks from the McMurdo flattening of the trend from nepheline- spinel would deplete Cr and possibly V. Sound area (Kyle, 1974). Feldspar analyses hawaiite to nepheline-benmoreite. Rb and Kaersutite and clinopyroxene are the main are of ideal compositions with the addition

Ba both act as residual elements and are mafic phenocryst phases in the intermediate of appropriate quantities of K20. concentrated with fractionation. Rb shows lavas and are considered to be removed dur- Models for the basanite to nepheline- more than a threefold increase, whereas Ba ing differentiation of nepheline-hawaiite to hawaiite step gave two acceptable solutions slightly more than doubles from basanite to form nepheline-benmoreite. Kaersutite may in terms of the major-element chemistry nepheline-benmoreite. V and Cu decrease in contain a large number of trace elements in (Tables 5, 6). a linear manner, whereas Zn remains nearly constant in all analyzed samples. Sr is vari- able in the basanites but clearly shows a trend of decreasing concentration from nepheline-hawaiite to nepheline-benmoreite. Rare-earth element (REE) concentrations (Table 4) are plotted on a chondrite- normalized diagram (Fig. 8). Notable is the increase in light (La, Ce, Pr) and heavy (Er, Yb) REE from basanite to nepheline- benmoreite. The middle REE (Nd-Ho) generally show little enrichment and are very similar in all three samples. The samples all have a small positive Eu anomaly (Eu/Eu"'). Basanites and other strongly undersaturated lavas typically have small positive Eu anomalies, which are believed to be a natural consequence of partial melting in the mantle (Sun and Hanson, 1975). The Eu anomalies in the nepheline-hawaiite and nepheline-benmoreite are undoubtedly in- herited from the basanite.

PETROGENESIS

Petrogenesis of the basanite lavas in the Figure 5. Variation of major-element oxides plotted against silica (in percent by weight) Erebus volcanic province has been dis- for volcanic rocks from Brown Peninsula. Dots = new analyses (this paper); triangles = cussed by Sun and Hanson (1975) and Kyle analyses by Prior (1907) and Goldich and others (1975). Trend line is a visual best fit.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/7/676/3419086/i0016-7606-90-7-676.pdf by guest on 01 October 2021 0 I I I I I I I I I I I I I I I I I I I 40 42 44 46 48 50 52 54 56 58 60

Si02 Figure 6. Plot of total alkalis versus silica for all analyzed volcanic rocks from Erebus volcanic province. Dots = Brown Peninsula (this study); triangles = Brown Peninsula

(Prior, 1907; Goldich and others, 1975); crosses = DVDP 1 and 2 and Hut Point Peninsula 40 44 48 52 56 (Kyle and Rankin, 1976); squares = trachyte, Mt. Cis (Smith, 1954; Goldich and others, SiÛ2 1975); circles = other Erebus volcanic province (Smith, 1954; Cole and Ewart, 1968; Goldich and others, 1975; Kyle and Rankin, 1976). Figure 7. Variation of trace elements (in parts per million) plotted against silica (in percent by weight) in volcanic rocks from Brown Peninsula. Symbols as in Figure 5. Trend line is a visual best fit.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/7/676/3419086/i0016-7606-90-7-676.pdf by guest on 01 October 2021 TABLE 4. ANALYSES OF RARE-EARTH 500 AND OTHER TRACE ELEMENTS IN SELECTED BROWN PENINSULA SAMPLES Basanite ^/e-hawaiite 24085 24088A 24089 ^e-benmoreite Cs 0.52 1.2 1.8 La 52 86 125 Ce 120 195 235 Pr 14 18 21 Nd 54 65 66 Sm 10 10.5 10.5 Eu 3.4 3.4 3.6 Gd 8.8 8.7 9.0 Tb 1.1 1.2 1.2 Dy 5.9 6.1 6.4 Ho 1.1 1.2 1.2 Er 2.9 2.9 3.6 Yb 2.9 3.2 4.2 Hf 6.6 8.5 10 Pb 11 17 20 < i Th 6.8 16 23 U 2.6 4.4 7.3

Eu/Eu* 1.16 1.16 1.22 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Yb La/Yb 17.9 26.9 29.8 Figure 8. Chondrite-normalized rare-earth element abundances in volcanic rocks from 402 487 2 REE 276 Brown Peninsula. Dots = basanite, circles = nepheline-hawaiite, and crosses = Note: Values are parts per million. nepheline-benmoreite. Normalized to average abundance in chondrite given by Price and Taylor (1973).

TABLE 5. CRYSTAL FRACTIONATION MODELS FOR TRANSITION BASANITE TO NEPHELINE-HAWAIITE

Model 1 Nepheline- Olivine Cpx Timt 11 Plag Ap Basanite Residual hawaiite + 10% An«, Est. Obs. (mean of 2) chrome (24085) spinel

Si02 48.84 35.91 45.1 53.3 42.69 42.65 0.038 TiOz 2.58 0.35 3.29 17.0 52.0 3.79 3.79 -0.003 AI2O3 18.24 2.32 9.27 8.0 29.7 13.59 13.62 -0.030 FeO* 8.65 13.6 8.34 68.1 42.3 12.03 12.02 0.007 MnO 0.20 0.17 0.14 0.7 0.7 0.19 0.20 -0.006 MgO 3.96 44.3 10.7 6.2 5.0 10.03 10.06 -0.031 CaO 7.32 0.23 22.3 12.1 54.7 11.87 11.92 -0.046 Na20 6.42 1.04 4.7 3.39 3.52 -0.126 K2O 3.05 0.2 1.30 1.35 -0.051 P2O5 0.74 45.3 0.93 0.87 0.056

Proportion 42.09 10.26 31.83 5.56 1.29 7.67 1.36 0.027F as %

Model 2 Nepheline- Olivine Cpx Kaer Timt Plag Ap Basanite Residual hawaiite +5% An«) Est. Obs. (mean of 2) chrome (24085) spinel

Si02 48.84 37.91 45.1 38.1 53.3 42.65 42.65 0.001 Ti02 2.58 0.17 3.29 6.23 17.0 3.77 3.79 -0.024 AI2O3 18.24 1.16 9.27 14.0 8.00 29.7 13.63 13.62 0.010 FeO* 8.65 12.76 8.34 11.4 68.1 12.03 12.02 0.005 MnO 0.20 0.17 0.14 0.13 0.70 0.19 0.20 -0.011 MgO 3.96 46.06 10.7 11.6 6.20 10.06 10.06 -0.003 CaO 7.32 0.24 22.3 11.9 12.1 54.7 11.92 11.92 -0.000 Na20 6.42 1.04 2.41 4.7 3.44 3.52 -0.080 K2O 3.05 1.30 0.2 1.45 1.35 0.100 P2O5 0.74 45.3 0.87 0.87 0.000

Proportion 41.06 7.63 27.06 14.62 5.25 3.63 1.25 0.017T as %

Note: Cpx = clinopyroxene, Kaer = kaersutite, Timt = titanomagnetite, Plag = plagioclase, Ap = apatite. * Total Fe as FeO. 2 (residual)2.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/7/676/3419086/i0016-7606-90-7-676.pdf by guest on 01 October 2021 McMURDO VOLCANIC GROUP, ANTARCTICA 685

Model 1 (Table 5) indicates that the mineral partition coefficients were selected Because clinopyroxene and kaersutite are nepheline-hawaiite formed as a 42.1% re- from the literature (Table 7). Calculated the main phases removed in the models, any sidual after separating 10.3% olivine plus REE are given in Table 8 and are compared irregularities in the partition coefficients are spinel, 31.8% clinopyroxene, 7.7% graphically with the observed values in Fig- likely to occur in these two phases. Higher

plagioclase (An60), 5.6% titanomagnetite, ure 9. partition coefficients for clinopyroxene will 1.3% ilmenite, and 1.4% apatite from Calculated REE values in nepheline- result in both models showing closer basanite sample 24085. Model 2 (Table 5) hawaiite using models 1 and 2 are remark- agreement with the observed, while higher is similar to model 1 except that it contains ably similar. Model 2 has slightly lower coefficients for kaersutite will improve only no ilmenite but includes kaersutite. In this concentration than model 1 (Table 8; Fig. model 2. No strong bias is shown toward model nepheline-hawaiite is a 41.1% re- 9) and also shows the closest agreement either model; however, model 2 is favored sidual after removing 7.6% olivine plus with the observed REE in the nepheline- because the calculated trace elements show spinel, 27.1% clinopyroxene, 14.6% kaer- hawaiite. Both models predict higher con- the closest agreement with the observed. sutite, 5.2% titanomagnetite, 3.6% plagio- centrations for most REE and a small en- Model 2 is also very similar to that calcu-

clase (An60), and 1.25% apatite. The richment of Eu compared to the observed lated from chemically and mineralogically models gave extremely good solutions with abundances. The Eu anomaly would not similar lavas from Hut Point Peninsula low residuals, and both are considered ac- occur if the partition coefficients for clino- (Kyle and Rankin, 1976; Sun and Hanson, ceptable. pyroxene and apatite did not have small 1976). Removal of 9.3% clinopyroxene, 10.3% negative Eu anomalies. Calculated REE in the nepheline-ben- kaersutite, 3.5% titanomagnetite, 2.3% plagioclase (Aruo), and 0.8% apatite from TABLE 6. CRYSTAL FRACTIONATION MODEL FOR nepheline-hawaiite leaves a residual of TRANSITION NEPHELINE-HAWAIITE TO NEPHELINE-BENMOREITE 73.8% nepheline-benmoreite (Table 6). Nepheline- Cpx Kaer Timt Plag Ap Nepheline-hawaiite Residual This model is very similar to that for crystal benmoreite ArLjo Est. Obs. fractionation of nepheline-hawaiite to give (mean of 3) (mean of 2) nepheline-benmoreite for the DVDP drill core (Kyle and Rankin, 1976; Kyle, un- Si02 53.33 43.8 39.2 58.3 48.82 48.84 -0.022 TiO 1.37 3.7 6.4 17.0 2.62 2.58 0.036 pub.). z AI2O3 20.23 10.1 14.4 8.0 27.1 18.27 18.24 0.025 The major-element mass-balance models FeO'/a 5.78 8.0 11.8 68.1 8.64 8.65 -0.010 were used to evaluate the trace-element MnO 0.19 0.13 0.15 0.7 0.19 0.20 -0.008 concentrations. The concentration of a MgO 1.98 11.0 12.0 6.2 3.94 3.96 -0.023 trace element in a liquid can be described by CaO 4.59 22.3 12.3 8.0 54.7 7.36 7.32 0.038 Na20 8.0 6 0.90 2.5 7.1 6.45 6.42 0.034 the equation (Arth, 1976) K2O 4.03 1.3 0.4 3.12 3.05 0.066 P2O5 0.44 45.3 0.69 0.74 -0.047

Propor- 73.78 9.31 10.27 3.55 2.35 0.81 0.012+ CltC° = F + D (1 -F) ' (1) tion as %

» Total Fe as FeO. S (residual)2. where C0 is the concentration in the initial

system, CL is the concentration in the residual liquid, F is the fraction of residual TABLE 7. MINERAL/MELT PARTITION COEFFICIENTS liquid, and D is the bulk distribution coefficient. Olivine Clinopyroxene Kaersutite Plagioclase Apatite Rb acts as a residual element and shows a An65 ~An,o threefold increase from basanite to neph- La (0.009) (0.30) 0.31 1.44 (0.023) 0.280 (15.2) eline-benmoreite. The calculated Rb con- Ce 0.009 0.359 0.49 1.98 0.023 0.215 16.6 tent of the nepheline-hawaiite, assuming a Pr (0.010) (0.52) (0.67) (2.60) (0.023) (0.193) (18.0) bulk distribution coefficient of zero, using Nd 0.010 0.69 0.85 3.21 0.023 0.170 21.0 Sm the two mass-balance models show good 0.011 0.98 1.07 3.85 0.024 0.135 20.7 Eu 0.010 0.85 1.09 2.70 0.232 1.10 14.5 agreement (Table 8) with the observed Gd 0.012 (1.08) 1.16 3.83 (0.017) 0.127 21.7 value. Model 2, which contains kaersutite, Tb (0.013) (1.13) (1.12) (3.44) (0.018) (0.111) (19.8) gives the closest estimate; however, both Dy 0.014 1.18 1.08 3.05 0.018 0.094 16.9 models show agreement within the ana- Ho (0.016) (1.18) (1.02) (2.50) (0.019) (0.086) (15.5) Er 0.017 1.17 0.96 2.34 0.020 0.078 14.1 lytical uncertainty. Because of the uncer- Yb 0.023 1.05 0.78 2.02 0.030 0.062 9.4 tainty in the nepheline-hawaiite models, the measured trace-element values, rather than Sr 0.009 0.119 0.58 0.58 1.36 4.62 0.83 the calculated concentrations, were used in Ba 0.009 0.031 0.62 0.62 0.15 1.47 0.014 calculating the model for nepheline-ben- Reference* : 1,2 3 3, 4 3,4 1,2 4 5, 6 moreite. The calculated Rb content of the nepheline-benmoreite is in excellent agree- Note: Values in parentheses determined by interpolation and extrapolation. ment with that observed (Table 8). * 1: Schnetzler and Philpotts (1970); 2: Philpotts and Schnetzler (1970); 3: Nagasawa (1973); For the REE, Sr, and Ba, appropriate 4: Sun and Hanson (1976); 5: Nagasawa and Schnetzler (1971); 6: Mason (1972).

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/7/676/3419086/i0016-7606-90-7-676.pdf by guest on 01 October 2021 686 KYLE AND OTHERS

moreite (Table 8) show excellent agreement different phases, at least over part of the Mass-balance models are valuable, how- with those measured (Fig. 9). trend, it is premature to separate them into ever, because they allow quantitative esti- Calculated Ba contents show good two lava lineages, because their whole-rock mations of possible fractionated phases. agreement with the observed values in all chemistries are so similar. Lava lineages Further studies of Erebus volcanic prov- models; however, Sr shows poor agree- thus should still be recognized on the basis ince lavas will inevitably result in recogni- ment. The discrepancy in Sr may be due to a of chemistry and not on fractionated phases tion of other fractionation trends. Until number of factors, the most obvious being as determined from mass-balance models. such times, the preliminary names, of the partition coefficients. Stuckless and Ericksen (1976) reported 1,000 ppm Sr in a TABLE 8. CALCULATED AND OBSERVED REE, Sr, Ba, AND kaersutite megacryst from a Hut Point Rb ABUNDANCES IN BROWN PENINSULA ROCKS Peninsula basanite host. This suggests that the Sr partition coefficient for kaersutite Nepheline-hawaiite Nepheline-benmoreite may well exceed one. Kaersutite partition Model 1 Model 2 Calc. Calc. Obs. coefficients may also be strongly dependent Calc. Obs. on temperature and/or composition (Sun La 87 87 86 105 125 and Hanson, 1976). If discrepancies in Ce 194 189 195 233 235 kaersutite partition coefficients occurred, Pr 21 20 18 21 21 Nd 76 72 65 73 66 this would add further support to model 2 Sm 13 12 10.5 11.5 10.5 for evolution of the nepheline-hawaiite. Eu 4.8 4.5 3.4 3.9 3.6 Gd 11.1 10.4 8.7 9.5 9.0 COMPARISON WITH OTHER Tb 1.4 1.3 1.2 1.3 1.2 Dy 7.6 7.2 6.1 6.9 6.4 EREBUS VOLCANIC Ho 1.4 1.4 1.2 1.4 1.2 PROVINCE LAVAS Er 3.9 3.7 2.9 3.4 3.6 Yb 4.2 4.0 3.2 3.8 4.2 All published analyses of Erebus volcanic province rocks are plotted on an alkali ver- Sr 1,822 1,805 1,063 1,351 900 Ba 661 607 496 649 645 sus silica diagram (Fig. 6). The trend of Rb 71 73 76 103 105 Brown Peninsula analyses is similar to that defined by analyses of representative core Note: Values are parts per million. samples (Kyle and Rankin, 1976) from DVDP holes 1, 2, and 3 (Kyle and Treves, 2 Or 1974a) and surface samples from Hut Point Peninsula. The agreement is enhanced if 1-8 • /Ve-hawaiite analyses of DVDP and Hut Point Peninsula lavas (Kyle, unpub.) are also plotted. The 1-6 • same applies to the other major-element o and trace-element data. The Brown Penin- sula lavas plot within the field of Erebus 1-4 - volcanic province lavas (Fig. 6) but have o higher alkalis than most of the previously 1-2 analyzed samples. observed Although sampling on a regional basis 10 • may indicate a broad basanite-phonolite lava association for the Erebus volcanic 0-8 • J L J L J L province (Smith, 1954; Goldich and others, 1975), evaluation of fractionation trends must be made on a local basis. Ideally, to establish such trends a sequence of lavas from a single or several closely related vents should be examined. Thus far, fractionation trends of two lava lineages have been recognized in the Erebus volcanic province (Kyle and Rankin, 1976; Sun and Hanson, 1976). The general similarity of the Brown 0-8 Peninsula and Hut Point Peninsula lavas La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Yb suggests that they should both be consid- Figure 9. Comparison of observed and calculated REE abundances in nepheline- ered variants of a single fractionation trend. hawaiite and nepheline-benmoreite. For nepheline-hawaiite, Co = concentration in basa-

Even though the mass balance models for nite sample 24085; for nepheline-benmoreite, C0 = measured concentration in nepheline- Brown Peninsula suggest fractionation of hawaiite.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/7/676/3419086/i0016-7606-90-7-676.pdf by guest on 01 October 2021 McMURDO VOLCANIC GROUP, ANTARCTICA 687

DVDP lineage (Kyle, unpub.) for the DVDP similarity of the Rainbow Ridge eruptive Green, D. H., 1971, Composition of basaltic lavas and of Erebus lineage (Kyle and Ran- sequence to those at Hut Point Peninsula magmas as indicators of conditions of ori- kin, 1976) for the Mt. Erebus lavas, will be (DVDP), Cape Bird, Cape Crozier, and gin: Application to oceanic volcanism: Royal Society of London Philosophical retained. The eruptive sequence at Rainbow Black Island (Fig. 1), suggests that the Transactions, v. 268A, p. 707-725. Ridge is therefore another example of the model developed here is generally applica- 1973, Conditions of melting of basanite DVDP lineage. ble to most centers in the Erebus volcanic magma from garnet peridotite: Earth and province. Planetary Science Letters, v. 17, p. 456- 465. CONCLUSIONS Hamilton, W., 1972, The Hallett Volcanic prov- ACKNOWLEDGMENTS ince: U.S. Geological Survey Professional This study has successfully used least Paper 456-B, 62 p. squares mass-balance calculations to quan- Field work by Adams was supported by Harrington, H. J., 1958, Nomenclature of rock tify the fractional crystallization of the un- the New Zealand University Grants Com- units in the Ross Sea region, Antarctica: Nature, v. 182, p. 290. dersaturated magma erupted at Rainbow mittee and Antarctic Division, Department Harrington, H. J., and others, 1964, The geology Ridge. It is evident from this study, how- of Scientific and Industrial Research, of Cape Hallett-Tucker Glacier district, in ever, that the calculations are only models, Christchurch, New Zealand. Adams thanks Adie, R. J., ed., Antarctic geology: Amster- and more than one acceptable solution may the Analytical Facility, Victoria University, dam, North Holland Pub. Co., p. 220-228. be possible. When mass-balance calcula- for assistance with major-element analyses. 1967, Topography and geology of the Cape Hallett district, Victoria Land, Antarctica: tions are attempted, other possible models We thank J. W. Cole and D. H. Elliot for New Zealand Geological Survey Bulletin, should be sought even after a satisfactory critically reviewing the manuscript. Kyle v. 80, 100 p. solution has been obtained. It is not always acknowledges support from National Sci- Kay, R. W., and Gast, P. W., 1973, The rare easy to establish which mineral phases are ence Foundation Grant DPP 76-23440. earth content and origin of alkali-rich involved during fractional crystallization at basalts: Journal of Geology, v. 81, p. 653-682. depth. Obviously, the observed phenocryst Kesson, S. E., 1973, The primary geochemistry of or possible megacryst phases, if they exist, REFERENCES CITED the Monaro alkaline volcanics, southeast- are good indicators of possible fractionated ern Australia — Evidence for upper mantle phases. However, in some cases it may be Adams, J., 1973, Petrology and petrochemistry heterogeneity: Contributions to Mineralogy and Petrology, v. 42, p. 93-108. necessary to postulate the presence of other of an alkaline cone, McMurdo Sound [B.Sc. honors thesis]: Wellington, N.Z., Victoria Kesson, S. E., and Price, R. C., 1972, The major phases during differentiation. The con- University, 36 p. and trace element chemistry of kaersutite straints are obviously the agreement of the Armstrong, R. L., 1978, K-Ar dating: McMurdo and its bearing on the petrogenesis of mass-balance model with the observed Volcanics and Dry Valley glacial history, alkaline rocks: Contributions to Mineral- major-element chemistry and whether the Victoria Land, Antarctica: New Zealand ogy and Petrology, v. 35, p. 119—124. Journal of Geology and Geophysics, v. 21 trace-element data (especially the REE) are Kyle, P. R., 1974, Electron microprobe analyses (in press). of minerals in core samples from Dry Valley also satisfied by the model. Even with the Arth, J. G., 1976, Behavior of trace elements dur- Drilling Project (DVDP) holes 1 and 2, Ross difficulties discussed above, least squares ing magmatic processes — A summary of Island, Antarctica: Department of Geology, mass-balance models offer the petrologist a theoretical models and their applications: Victoria University of Wellington, Antarc- method of demonstrating in a quantitative U.S. Geological Survey Journal of Research, tica Data Series 4, 27 p. v. 4, p. 41-47. 1976, Geology, mineralogy and geochemis- manner what processes are possible at Bryan, W. B., Finger, L. W., and Chayes, F., try of the Late Cenozoic McMurdo Vol- depth. 1970, Estimating proportions in petro- canic Group, Victoria Land, Antarctica Fractional crystallization is the dominant graphic mixing equations by least squares [Ph.D. thesis]: Wellington, N.Z., Victoria approximation: Science, v. 163, p. 672- University, 444 p. process controlling the evolution of the 679. Kyle, P. R., and Cole, J. W., 1974, Structural lavas at Rainbow Ridge. At Brown Penin- Cole, J. W., and Ewart, A., 1968, Contributions control of volcanism in the McMurdo Vol- sula and many other areas in the Erebus to the volcanic geology of the Black Island, canic Group, Antarctica: Bulletin Vol- volcanic province, small cones and flows of Brown Peninsula and Cape Bird areas, canologique, v. 38, p. 16—25. kaersutite-bearing and/or clinopyroxene- McMurdo Sound, Antarctica: New Zea- Kyle, P. R., and Rankin, P. C., 1976, Rare earth land Journal of Geology and Geophysics, element geochemistry of Late Cenozoic bearing salic lavas (nepheline-benmoreite v. 11, p. 793-828. alkaline lavas of the McMurdo Volcanic and phonolite) are common. The cones are Cole, J. W., Kyle, P. R., and Neall, V. E., 1971, Group, Antarctica: Geochimica et Cos- small, and most involved the eruption of Contributions to the Quaternary geology of mochimica Acta, v. 40, p. 1497-1507. less than 0.5 km3 of material. It is envisaged Cape Crozier, White Island and Hut Point Kyle, P. R., and Treves, S. B., 1974a, Geology of Peninsula, McMurdo Sound region, Ant- that small pods of basanite magma were in- DVDP 3, Hut Point Peninsula, Ross Island, arctica: New Zealand Journal of Geology Antarctica: DeKalb, Northern Illinois Uni- truded into upper mantle and/or crustal and Geophysics, v. 14, p. 528-546. versity, Dry Valley Drilling Project Bulletin, magma chambers where the magma differ- Coombs, D. S., and Wilkinson, J.F.G., 1969, v. 3, p. 13-18. entiated to give the intermediate and salic Lineages and fractionation trends in under- 1974b, Geology of Hut Point Peninsula, lavas. This process has occurred at least saturated volcanic rocks from the East Ross Island: Antarctic Journal of the U.S., Otago Volcanic Province (New Zealand) v. 9, p. 232-234. three times at Brown Peninsula. At Mt. and related rocks: Journal of Petrology, Macdonald, G. A., 1960, Dissimilarity of conti- Erebus, in contrast, anorthoclase phonolite v. 10, p. 440-501. nental and oceanic rock types: Journal of lavas have been erupted in volumes consid- Goldich, S. S., Treves, S. B., Suhr, N. H., and Petrology, v. 1, p. 172-177. erably greater than the mafic phonolites, Stuckless, J. S., 1975, Geochemistry of the Macdonald, G. A., and Katsura, T., 1964, Chem- and there is also no evidence of alternating Cenozoic volcanic rocks of Ross Island and ical composition of Hawaiian lavas: Jour- vicinity, Antarctica: Journal of Geology, nal of Petrology, v. 5, p. 82-133. eruptions of basaltic and salic lavas. The v. 83, p. 415-435. Mason, B., 1972, Minor and trace element dis-

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/7/676/3419086/i0016-7606-90-7-676.pdf by guest on 01 October 2021 688 KYLE AND OTHERS

tribution in minerals of the Muzzle River Price, R. C., and Taylor, S. R., 1973, The 1976, Rare-earth element evidence for dif- gabbro: New Zealand Journal of Geology geochemistry of Dunedin Volcano, East ferentiation of V'cMurdo Volcanics, Ross and Geophysics, v. 15, p. 464-475. Otago, New Zealand: Rare earth elements: Island, Antarctica: Contributions to Nagasawa, H., 1973, Rare-earth distribution in Contributions to Mineralogy and Petrol- Mineralogy and Petrology, v. 54, p. 139- alkali rocks from Oki Dogo Island, Japan: ogy, v. 40, p. 195-205. 155. Contributions to Mineralogy and Petrol- Prior, G. T., 1907, Report on the rock specimens Thompson, R. N., Esson, J., and Dunham, A. C., ogy, v. 39, p. 301-308. collected during the Discovery Antarctic 1972, Major element chemical variation in Nagasawa, H., and Schnetzler, C. C., 1971, Par- Expedition, 1901-4: National Antarctic the Eocene lavas of the Isle of Skye, Scot- titioning of rare-earth, alkali and alkaline Expedition 1901-4, Natural History, v. 1, land: Journal of Petrology, v. 13, p. 219- earth elements between phenocrysts and p. 101-160. 253. acidic igneous magma: Geochimica et Cos- Schnetzler, C. C., and Philpotts, J. A., 1970, Par- Thornton, C. P., and Tuttle, O. F., 1960, mochimica Acta, v. 35, p. 953—968. tition coefficients of rare-earth elements be- Chemistry of igneous rocks I. Differentia- Nathan, S., and Schulte, F. J., 1968, The geology tween igneous matrix material and rock- tion index: American Journal of Science, and petrology of the area between the forming mineral phenocrysts — II: Geo- v. 258, p. 664-684. Campbell and Aviator Glaciers: New Zea- chimica et Cosmochimica Acta, v. 34, p. Treves, S. B., 1967, Volcanic rocks from the Ross land Journal of Geology and Geophysics, 331-340. Island, Marguerite Bay, and Mt. Weaver v. 11, p. 940-975. Smith, W. C., 1954, The volcanic rocks of the areas, Antarctica, in Nagata, T., ed., Pro- Norrish, K., and Chappell, B. W., 1967, X-ray Ross Archipelago: British Antarctic ("Terra ceedings of the symposium on Pacific- fluorescence spectrography, in Zussman, J., Nova") Expedition 1910, Natural History Antarctic Sciences: Japanese Antarctic Re- ed., Physical methods in determinative Report, Geology, v. 2, p. 1-107. search Expedition Scientific Report, Special mineralogy: London and New York, Stuckless, J. S., and Ericksen, R. L., 1976, Stron- Issue, no. 1, p. 136-149. Academic Press, p. 161—214. tium isotopic geochemistry of the volcanic Wright, T. L., 1974, Presentation and interpreta- Norrish, K., and Hutton, J. T., 1969, An accu- rocks and associated megacrysts and inclu- tion of chemical data for igneous rocks: rate X-ray spectrographic method for the sions from Ross Island and vicinity, Ant- Contributions to Mineralogy and Petrol- analysis of a wide range of geological sam- arctica: Contributions to Mineralogy and ogy, v. 48, p. 233-248. ples: Geochimica et Cosmochimica Acta, v. Petrology, v. 58, p. 111-126. 33, p. 431-453. Sun, S. S., and Hanson, G. N., 1975, Origin of Philpotts, J. A., and Schnetzler, C. C., 1970, Ross Island basanitoids and limitations MANUSCRIPT RECEIVED BY THE SOCIETY AUGUST Phenocryst-matrix partition coefficients for upon the heterogeneity of mantle sources 3, 1977 K, Rb, Sr and Ba, with applications to anor- for alkali basalts and nephelinites: Con- REVISED MANUSCRIPT RECEIVED MARCH 13, thosite and basalt genesis: Geochimica et tributions to Mineralogy and Petrology, 1978 Cosmochimica Acta, v. 34, p. 307-322. v. 52, p. 77-106. MANUSCRIPT ACCEPTED MAY 22, 1978

Printed in U.S.A.

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/90/7/676/3419086/i0016-7606-90-7-676.pdf by guest on 01 October 2021