American Mineralogist, Volume 67, pages 14J7, 1982
Mineralogy of mafic and Fe.Ti oxide-rich differentiatesof the Marcy anorthositemassif, Adirondacks, New york
LBwrs D. Asuwnl Lunar and Plnnetary Institute 3303 NASA Road l, Houston, Texas 77058
Abstract
Rocks enriched in mafic silicates, Fe-Ti oxides and apatite form a minor but ubiquitous facies of nearly all Proterozoic massif-typeanorthosite complexes.In the Marcy massif of the Adirondack highlands,New York, the mafic rocks have two modesof occurrence: l) as conformable segregationsinterpreted as cumulate layers in the border zones, and 2) as dikes throughout the massif, interpreted as having crystallized from residual liquids extracted at varying stagesduring differentiation. Primary mineral compositions in these rocks are commonly preserved,despite the effectsof subsolidusrecrystallization in the high pressure granulite facies. In the mafic rock suite, primary compositions of mafic silicates reveal an iron enrichment trend which is broadly similar to that of basic layered intrusions, but suggestive of somewhat higher crystallization temperatures. Textural relationships suggest the following crystallization sequence: plagioclase, pigeonite + augite, hemo-ilmenite * magnetite,apatite. Fe-rich olivine replacedpigeonite in the latest- stage residual liquids. The mineralogy and field relationships of these mafic rocks are consistent with their origin as diferentiates from the same melts which produced the anorthosites. This conclusion agrees with recent geochemical data that suggest an independentorigi-n for the spatially associatedmangerite-charnockite suite.
Introduction whose associationwith anorthositemassifs is well For the past several decades,the controversy known (Rose, 1969).Itis thesemafic rocks, and not over the origin of massif-type anorthosites has the mangerite-charnockites,which complementthe centered around the question of the consanguinity anorthosites,as demonstratedby REE geochemical of anorthositic rocks and spatially associatedsuites relationships(Ashwal and Seifert, 1980).The pur- of orthopyroxene-bearinggranitic rocks (charnock- pose of this paper is to describe the field relation- ite-mangerite series). Recent trace element geo- ships and mineralogical characteristics of mafic chemical studies focusing on, but not limited to, rocks associatedwith the Marcy anorthosite massif rare earth elements (REE) (Philpotts et al., 1966; in the Adirondack highlands of northern New York Greenet al., 1969,1972;Seifert et a|.,1977;Seifert, State, and to emphasize the importance of these 1978; Simmons and Hanson, 1978; Ashwal and rocks in understandingthe fractionation histories of Seifert, 1980)demonstrate that the acidic rocks do this and other massif-typeanorthosite complexes. not represent differentiates from the melts which producedthe anorthosites.This was recognizedas Field relations of mafic faciesof anorthosite early as 1939by A. F. Buddingtonon the basis of In the Marcy massif,the most felsic anorthosites field relationships (summarized by Buddington, are found in the central regions, and more mafic 1969). varieties occur near the margins. Becauseof the In addition to huge volumes of pure anorthosite, domical form of the massif, the mafic border facies the typical massif anorthosite suite contains minor overlies the anorthositic core zone (Buddington, facies with larger proportions of mafic silicates, Fe- 1939,1960,1969). In someplaces there is a system- Ti oxides and apatite. Extreme concentrations of atic increase in mafic silicates and oxide minerals these minerals give rise to minor ultramafic rocks, from coarse, core zone anorthosite (Marcy facies) as well as the ilmenite-magnetite ore deposits structurally upwards to finer-grained, border zone 0003-004)v82t0r02-0014$02.00 14 ASHWAL : OXIDE.RICH DIFFERENTIATES, MARCY ANORTHO SITE t5
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1'51 Ptedominontly leucogobbro ond ltons"rir"-rhornockire series .t ( Mofi< or ultromoli< rhythmically repeated several times on the scale of Conformable occurrences of mafic rocks individual outcrops. The attitudes of the layers are Modes of conformable mafic facies rocks from in most placesconsistent with the domical shapeof the Marcy massif are given in Table 1. There is the massifs(Fig. 1), althoughtheir lateral extent is generally a progressivedecrease in mafic and oxide difficult to estimatedue to the paucity of exposures. minerals with increasing stratigraphic height above There are also mafic rocks which occur as sharp- the basalcontact of a cumulate layer; the scale over walleddikes of variedcomposition, crosscutting the which this variation in modal mineralogy takes anorthositic foliation at high angles. These dikes place ranges from centimeters to meters. Cumulus may have crystallized from residual liquids extract- phasesinclude augite,inverted pigeonite,ilmenite, ed at various stages of differentiation of the anor- magnetite,and, lesscommonly, Fe-rich olivine and thosite suite (Ashwal, 1978a,b). In the Marcy apatite. The primary mineralogies and textures of massif, mafic dikes are not spatially restricted to the theserocks, however,have been affected to varying border facies, but may be found even in the central degreesby subsolidusrecrystallization, which has regions(Fie. 1). The dikes are generally less than resulted in the production of metamorphic garnet 7 m thick, although Buddington (1939,p. 50-51) and hornblende,and in the reconstitutionofcoarse- described a mafic gabbro dike some 60 m wide in ly exsolvedpyroxenes into smallerdiscrete grains the Carthage anorthosite massif in the western with different compositions. Zones of garnet Adirondacks. 1-5 mm thick commonly occur betweenthe basalcon- tacts of mafic layers and underlying leucogabbros Mineral constitution and petrography or leuconorites. Although metamorphic garnet, hornblende, and pyroxenes constitrrte nearly 20Vo Primary minerals of the Marcy anorthosite com- of some samples,other rocks appearto have com- plex includeplagioclase, high-Ca pyroxene, low-Ca pletely retained their primary mineralogiesand tex- pyroxene, olivine, ferrian ilmenite, titaniferous tures (Table 1, sample SA-3D). In general, it is magnetite, and apatite. Metamorphic minerals in- possible to see through the overprinting effects of clude garnet, hornblende, biotite and quartz, in subsolidusrecrystallization, as discussedbelow. addition to recrystallized equivalentsof the primary The color indices of the lower, most mafic parts phases,suggesting equilibration in the high pressure of the layers vary between approximately 60Voand granulitefacies (deWaard,1965). 100%(Table l). The layers generally lie on and are Table l. Point counted modes of conformable mafic rich rocks from the Marcv massif sA-3D SA-3A SA-5 SL-IIY SIJ-IIA SA-15A SA-I5B Mtr-568 MM-56A SL-2IA Sr,-21 Plagioclase L.2r 63.7 66. S 2.4 75.6* 42.6* 73.5* 20.9 74,O* 19,3* 51.5* 27.L* qq)1 Inverted pigeonite I 4.1 tr 7.L 3.2 L.7 cr Orthopyroxene 3.2 2.4 7.! 3.4 4.8 2.L t.u J-b 0.9 1.9 Clinopyroxene t ,:t 52.3 13.4 19.0 II.4 2A.9 II.2 48.6 t5.5 9.5 Ollvine _n IIrenite 25.6 I.1 0.9 t8.9 4.5 ]5.3 4 .2 4.3 1,, - 8.4 Magnetite 13.9** 0.6 0.I 4.2 0.3 I I nt I.O O.7 L6.2 f"' 3.3 Apatite - 0.2 0.5 - u.b q Garnet - 11 2 ? - 2.2 10.5 4.1 l. r L5.2 18.O Hornblende v.z 9.0 L4.7 0.5 Sulfides 0.5 - 0.I I.O O.2 Biotite tr o.2 0.4 0.5 ScatrpLite _ 0.3 Other secondaries**r -tr 0.5 0.5 100.0 100.0 100.0 r00.0 Ioo.0 100.0 100.0 100.0 r00.0 100.0 loo.0 100.0 Color index 94.8 36.3 91.2 24.4 57.4 25.5 79.1 26.0 80.7 48.0 72.9 oxide- leuco- Ieuco- oxide- Ieuco- oxide- leuco- oxide- leuco- oxide- oxide- oxide- rich norite norite rich norite rich ga-bbro rich gabbro rich rich rich pyrox- host host pyrox- host gabbro host mfic host @f ic aabbro mf lc enr!e enrte Iayer gabbro gabbro host troqto- layer Iayer Iayer layer lite Layer * rr includes nj.nor iltiperthite; includes trace arcut of pleonaste, *** includes sericite aal haatite alteration ASHWAL : OXIDE-RICH DIFFERENTIATES, MARCY ANORTHOSITE l7 gradational structurally upwards into host rocks of All of the conformable mafic layers contain major leucogabbroic or leuconoritic composition (color amounts(>10%) of ilmeniteand magnetite.In some index26Voto 36Vo),although in somecases the host cases,the oxide mineral content is sufficiently high rock has a color index as high as 46% (Table l, that the rock can be consideredore grade. Con- sampleSL-21). formable oxide mineral-rich layers within gabbro or In all layers, high-Ca pyroxene (augite) domi- leucogabbro are particularly abundant in the San- nates over low-Ca pyroxene (inverted pigeonite ford Lake area where they are mined for their and/or orthopyroxene). The large high-Ca/low-Ca ilmenite concentrations(Gross, 1968),but similar pyroxene ratio in the highly recrystallized rocks layers of much lesser extent have been reported (e.9., MM-56B) may be due to the increase in from elsewherein the Marcy massif (Buddington, discrete augite grains from the recrystallization of 1953, Table 1, sample no. 20). Ilmenite usually coarsely exsolved primary pyroxenes. The paucity predominates over magnetite in the conformable of low-Ca pyroxene in other specimens(e.9., SL- layers, although there are examples where the re- 21, SL-21A,5683d)is relatedto the onsetof Fe-rich verseis true (Table 1, sampleSL-2IA). olivine crystallization,which replacedlow-Ca py- roxene during the later stages of solidification. Mafic dikes Olivine-bearinglayers such as representedby speci- Modes of mafic dikes from the Marcy massif are men 5683d do, however, contain minor inverted given in Table 2. The dikes show wide rangesin pigeonite.The low-Ca pyroxene-deficientor oliv- color index (approximately 40-90%), and mineral ine-bearinglayers, or both, contain abundant apa- constitutions.It is important to determinewhich, if tite, which alsomust be a late-stagecumulus phase. any, ofthese dike rocks representliquids. They are In addition to their mineralogy, the location of these finer grained than the mafic cumulate rocks; howev- layers at the extreme margins of the massifs (Fig. er, primary texturesin the dike rocks are generally 1), and hence at the highest stratigraphiclevels, not well preserved. Many contain abundant garnet suggeststhat they may represent some of the very (Table 2). The profound effect ofgarnet production last accumulations from late stage mafic liquids on modal mineralogy (particularly color index) may which had been segregatedto the upper regions of be seenby comparingthe modes of samplesSR-9 the massifs. and MM-6 (Table 2), which despite their large Table 2. Point counted modes of mafic rich dikes from the Marcy massif MM-I A MM-13A sA-14A MM-44A Plagioclase 8.0 33.8r 45.6* 42.3 43-2 26.4 50.0* o _n Invertedl pigeonite 22.5 no orthopyioxene 63.4 1.9 10.8 6-4 ?l cLinopyroxene LZ.Z t7.7 14.3 24.7 L7.5 17.0 23.3 olivlnett 14-4 9.7 42.r Ilnenite 10.9 6. / I 11.r 10.r 6.8 13.r I 3.0 t7-2 Magnetite z.o 3.1 I J.v 5.8 9.2 (7 Apatite 5.4 4.7 2.3 0.5 4.3 6.O Garnet ql 8.4 23.9 4-L L9.7 4.4 Hornblende t:t 1.6 lo. 2 "-n Sulfiales o.4 ET Other secondariesr*i J.O 1.9 1.5 100.o loo.0 r00. 0 100.0 100.0 100.0 100,0 100.0 color index 92.O 66.2 54.4 54.r 56.8 7L.3 50.0 98.r nock tl4)e pyroxenLte oxitle- oxide- gabbro oxide- oxide- oxide- oxicle- rich rich rich rich rich rich nafic gabbro gabbro mafic gabbro wehrlite norite gabbro * includes flinor antiperthiter ** includes iddlingsite alteration; *** includes selicite andl hffitite alteration l8 ASHWAL : OXIDE-RIC H DIFFERENTIATES, MARCY ANORTHOSITE mineralogicaldifferences, have similar bulk compo- textureis that the anorthositesrepresent accumula- sitions. Thin layers of garnet are also found at the tions of pligioclase concentratedeither gravitation- contacts between some of the dikes and the sur- ally or by flowage(Emslie, 1975;Martignole,1974; rounding anorthositic rocks in a manner similar to Morse, 1969;Olmstead, 1969). that of the garnet zones at the basal contacts of the Primary textures suggestthat the pyroxenescrys- ultramafic cumulates. Because of these garnet tallized after plagioclase,and in turn were followed zones,it is impossibleto determinewhether these by the Fe-Ti oxide minerals. It is not possibleon dikes once had chilled margins. textural grounds to determine whether augite or Oxide-rich, olivine gabbro or mafic gabbro dikes pigeonite crystallized first, but it is likely that they which lack low-Ca pyroxene (samples SR-9 and precipitated simultaneouslyduring most of the crys- MM-6, Table2) may have crystallized from the final tallization history. In the anorthosites,leucogab- liquid differentiates of the anorthosite suite, since bros, and leuconorites,coarsely exsolvedprimary their REE patterns (Ashwal and Seifert, 1980)are pyroxenesor their metamorphic equivalentspartial- characteized by high total abundancesand nega- ly surround earlier and larger plagioclasecrystals in tive Eu anomalies,and relativelight REE depletion. a subophitic relationship. More mafic rocks also These patterns are complementary to anorthosites have subophitictextures; however, the presenceof and leucogabbros,which exhibit low REE abun- large,discrete pyroxene crystals of probablecumu- dances,positive Eu anomalies,and relative light late origin suggestco-crystallization of plagioclase REE enrichment(Seifert et a|.,1977;Simmons and and pyroxene. In contrast to the tabular shape of Hanson,1978). Mineral compositionsof thesedikes plagioclase,cumulus mafic silicatesare equant in are consistentwith their origin as latest-stagediffer- shape, and the ultramafic cumulates (oxide-rich entiates,as discussedbelow. pyroxenites) have an equigranular texture. Although the mafic dikes probably in large part In a similar manner, ilmenite and magnetite par- represent liquid compositions, the possibility of tially or completely surround the pyroxenes, sug- mineral accumulation or loss in these liquids during gesting that the oxides crystallized later, and this or after their emplacementas dikes must be consid- texture is particularly well developed in the oxide- ered. Additionally, there are rare examplesof ultra- rich pyroxenite cumulate layers. The oxide miner- mafic dikes includinghypersthenite (sample MM-8) als may constitute up to 40Voof these rocks (Table and oxide-rich wehrlite (sample MM-44A) which 1), and since the layers grade structurally upwards may represent remobilized cumulates (deWaard, into less oxide-rich rocks, the textures may be 1970). These complications must be taken into interpreted to represent cumulus Fe-Ti oxides account before accurate liquid lines of descent can which have been extended interstitially by post- be determined. cumulus growth. Oxide rich pyroxenite layers with similar textures have been reported from other Petrographicdetermination of crystallization anorthositemassifs (Subramaniam,1956, Fig. 3) and are also present in zoned ultramafic complexes (Taylor and Noble, 1969,Fig. 10). Despite the effects of subsolidus recrystalliza- Apatite occurs as a cumulus phase only in the tion, primary igneous textures are preserved in very late-stagelow-Ca pyroxene-deficientor oliv- many cases,permitting the distinction of cumulus ine-bearingcumulates, or both. In these rocks it and post-cumulusphases and allowing the determi- occurs as intergrowths with the Fe-Ti oxides, al- nation of crystallizationsequences. Plagioclase in though aggregatesof very coarse apatite crystals the Marcy massif and in other anorthosite complex- (up to 1 mm across) are also found. Olivine occurs es was the first phaseto crystallize. Evidence for as largecumulus grains up to 5 mm acrosswhich, in this conclusionincludes large, euhedralor subhe- some cases,poikilitically enclosepyroxenes, apa- dral plagioclasecrystals with smaller, anhedral py- tite and plagioclase; it also occurs as smaller, roxenes in interstitial areas. A common feature of roundedgrains within cumulus augite crystals (sam- anorthositic rocks in the central parts of massifs is ple 5683d).Sparse grains of inverted pigeonite are the alignment of tabular plagioclase crystals with invariably present in this layer, which represents their longest dimensions subparallel,forming a pla- the only known coexistence of three primary mafic nar fabric in the rock. The implication of this silicatesin the Marcy massif. ASHW AL : OXI DE-RICH DIF F ERENTIATES. MARC Y AN ORTHO S ITE l9 Mineral compositions reflect higher initial crystallization temperatures than those of the Skaergaardintrusion (Fig. 3). Pyroxenes and olivines The coexisting mafic silicates from cumulate lay- All primary minerals in the anorthosite-mafic ers definea trend of increasingfe* with increasing gabbro suite with the exception of olivine and stratigraphicheight. For example, sample SA-3D, apatitecontain complex subsolidusexsolution fea- an oxide-rich pyroxenite layer, contains the most tures. Primary pyroxene compositions, however, magnesianaugite-inverted pigeonite pair yet found can be reasonably ascertainedby bulk analysis in the Marcy massif (fe* of low-Ca pyroxene : usingbroad-beam electron microprobetechniques. 0.36). Samples SA-3A and SA-5 are more feld- This has been done for pyroxenes of the Adiron- spathic leuconoriteswhich are conformablewith, dack Marcy massif using a combinationof energy and occur within a few meters stratigraphically dispersive(ED) and wavelength dispersive (WD) microprobetechniques.3 In the Marcy massif, many low-Ca pyroxenes contain broad exsolution lamellae of augite inclined to the (001)directions of the presentorthopyroxene hosts,and later fine augitelamellae parallel to (100) of their hosts (Fig. 2a). These textures suggest initial crystallizationof pigeonite,followed by exso- lution and inversion to orthopyroxenein response to slow cooling. Coexistingaugites commonly con- tain several generationsof pigeonite lamellae, as describedin detail by Jaffe et al. (1975). Primarycompositions of coexistingaugite-invert- ed pigeonite and augite-olivine pairs from mafic cumulatelayers and dikes are plotted in Figure 3a. RepresentativeED and WD microprobe analyses for one sampleare given in Table 3.aThe composi- tions showa wide rangein fe* [molar Fe/(Fe+Mg)], and define a fractionation trend which is broadly similar to that of basic layered intrusions. In the Marcy massif, however, the coexistingpyroxenes are consistentwith a narrower solvus, and may 3Primarycompositions of coarsely exsolved pyroxenes were determined using an ED microprobe technique, whereby the electronbeam was broadened,in somecases up to 100microns, in order to incorporate entire grains. This method is successful for major elements;ED analysesof host and lamella phasesare generally within 5 relative Vo of WD analyses, and calculated ratios of mineral moleculesshow excellent agreement(Table 3). However, the poor system resolution and low peak/background ratios make quantitative ED determination of minor element Fig.2.Photomicrographs illustrating progressive oxides essentiallyimpossible, as illustratedby comparisonof recrystallization of primary pyroxenes (crossed nicols). (A): valuesfor MnO by WD and ED techniques(Table 3). Becauseof Primary inverted pigeonite surrounded by primary augite. this, primary pyroxene compositions were determined by re- Coarse augite lamellae (white) are inclined to the (001)direction integratingfine-beam WD analysesof host and lamella phasesin of host orthopyroxene (at extinction). A later set of fine (100) the proportions given by the ED analysesin terms of Wo, En and augite lamellae (nearly vertical) is also present. Length of Fs (Table3). photograph: I mm. (B): Partially recrystallized inverted aA complete table of pyroxene and olivine microprobe analy- pigeonite illustrating the migration and coalesccenceof coarse sesmay be obtainedby ordering Document AM-82-183from the augite lamellae at grain boundaries. Length of photograph: 1.5 BusinessOffice, Mineralogical Society of America, 2000Florida mm. (C): Granular mosaic of augite and orthopyroxene Avenue,N.W., Washington,D.C. 20009.Please remit $1.00in illustrating final result of recrystallizatron. Length of advancefor the microfiche. photograph: 2mm. ASHWAL : OXIDE-RIC H DIFFERENTIATES, MARC Y ANORTHASITE Table 3. Representative.microprobeanalyses of pyroxene and olivine from sample 5683d Meta. Meta. Meta. Meta. Primary Pri$ary Olivinef + opx. I opx.5 cpx.' cpx.9 pig** cpx.f si02 5I. 03 50.6 50.92 51 .8 'I.UU 51 .18 32.53 Ti02 0.tr 0.34 na 0 .17 o -27 na Nzog 1.38 2-6 5.UO I .8r 2.AO 0. 00 ct2o3 0.05 0 .00 na 0.04 0.00 na Fe0* 30.59 29.6 r3 .79 LS-Z 26.27 L7.29 tz.fu Mn0 0.45 0.6 0.1 o.39 o.2a o.44 M9o 16.0 11.0t 11.3 L5.26 1I.98 14.96 0.55 0.6 19.84 19.4 5.51 L6.L2 0.01 Na2O 0.00 na o-77 na o.20 na Total 100.89 100.0 99.94 100.0 100.65 100 .69 ro0 .44 structural Formula based on 6 oxygens (pyroxene) or 4 oxygens (olivine) si 1.960 L.952 1.935 r.946 1.953 r.940 0.988 Alrv o.o4o o.o4g 0.065 0.054 o.o4? 0.060 0.o00 2.000 2.000 2.000 2.000 2.000 2 .000 0. 988 -,vl o.o22 o.o72 o.o72 0.134 0.035 0. 065 Ti 0.003 0 .010 . 0.005 0 .008 0.002 0.000 - 0.001 o.000 Fe* 0.983 0.950 0,438 o,4r4 0.841 0. 548 I .334 Mn 0. oI5 0.021 0.007 0.002 0.013 0.o09 0.0I1 t{s 0. 958 0. 9I9 o -624 0.633 0.871 o.677 o. 678 Ca o.023 o.026 0.808 o.77A 0.226 0.65s 0. 000 Na 0.000 o. 057 0 .057 2.006 r.988 2 .015 I.961 2.OO7 2.019 2.O23 Wo L.2 L.4 43.2 42.6 11.7 34.8 En(Fo) 48.8 48. 5 33.4 34.7 45.0 36.O (33.7) Fs (Fa) 50.0 50.0 23-4 22.7 43.3 29.2 (66.3) na not aalyzed forr * total Fe as FeOt ** cornposition of prinary inverted pigeonite calculated by conrbining wDA analyses of host and lmella in proportions given by broad beil EDA analysest T wavelength dispersive analysis (wDA), 5 energy dispersive analysis notmalized to 1O0t for cooparison with tlD analysls above, this ultrarnafic cumulate layer, and contain With increasingdegrees of metamorphicrecrys- progressivelymore Fe-rich pyroxene compositions tallization,the pyroxenetextures and compositions with increasing distance above the basal contact change in a regular fashion. Augites become pro- (Fig. 3a). On a larger scale, sample5683d, a mafic gressively more calcic as they are transformed, by cumulate layer from near the outer margin of the meansof exsolution of low-Ca pyroxene and ac- massif(Fig. 1), containsFe-rich olivine in addition companyingrecrystallization, from coarse,primary to augite and inverted pigeonite. The compositions crystals into finer grained aggregateswith mosaic of thesephases are consistentwith the idea previ- texture (Fig. 2). For the low-Ca pyroxenes, the ously discussedthat this samplemay representan coarse augite lamellae, originally exsolved parallel accumulationof mafic crystals from very late-stage to the (001)directions of host pigeonites(Fig. 2a), liquid. The mineral assemblagein this rock repre- have gradually migrated to the borders of the sentsthe last appearanceof low-Ca pyroxene (in- grains, where they have coalescedinto polygonal verted pigeonite), which had apparently reacted aggregates(Fie. 2b). The final result ofthis process with the liquid to form Fe-rich olivine. is a fine-grained,granular mosaic of hypersthene Coexisting augites and olivines from mafic dikes andaugite (Fig. 2c) whosecompositions correspond SR-9 and MM-6 are among the most Fe-rich mafic to thoseof the host and lamellarphases, respective- silicatesof anorthositesuite rocks. Their composi- ly, of the original primary grains. Tie-linesjoining tions are consistent with the hypothesis that these these metamorphic augites and orthopyroxenes dikes crystallizedfrom the latest-stageresidual liq- have a shallower slope than those joining the uids of the anorthosite suite. primary augite-pigeonite pairs (Fig. 3b), con- ASHWAL : OXIDE-RICH DIFFERENTIATES. MARCY AN ORTHOSITE 2l A oLrvlNEs Fs Fig. 3 (A) Primary pyroxene compositionsas determinedusing broad beamenergy dispersive techniques, and olivine compositions as determinedusing wavelengthdispersive analyses. Solid tie lines: mafic cumulatelayers. Dashedtie lines: mafic dikes. Skaergaard trend after Wager and Brown (1968).(B) Compositionsofprimary igneouSpyroxene and pyroxene-olivine pairs (short dashedlines) and reconstitutedmetamorphic pairs (solid lines) plotted with respectto the augite-pigeonitesolvus (dashedcontours) and the augite orthopyroxenesolvus (solid contours) of Ross and Huebner (1975). : sistent with the higher K, (Fe/Mg)ro*-c. o",o*"."/ Plagioclase (Fe/Mg)6g6-capyroxene values of metamorphicallyre- equilibratedpyroxenes (Kretz, 1963).When applied Plagioclasein anorthositic rocks from most mas- to the pyroxenesolvus of Rossand Huebner(1975), sif-type complexesgenerally rangesin composition the igneous pyroxene pairs yield temperatures in from Ana6 to An65 (mole Vo) (Anderson, 1969). excessof 1100"C, whereasthe metamorphicpairs Becauseof the extremely large grain size and the yield temperaturesbetween 600' C and 900" C (Fig. rather irregular distribution of exsolved antiperthit- 3b). Both igneousand metamorphictemperatures ic lamellae,the primary compositionsof anorthosit- must, however, be consideredas minimum values ic plagioclasesare difficult to determine, particular- becauseof the uncertaineffects of increasedpres- ly by microprobeanalysis. For the Marcy massif, sure on the pyroxene solvus. Similar relationships however, Isachsenand Moxham (1969)have ana- for pyroxenes from the Marcy massif have been lyzed bulk megacrystcompositions from two exten- reportedby Bohlen and Essene(1978). sive vertical sections using spectrographicmeth- 22 ASHWAL : OXIDE-RICH DIFFERENTIATES, MARCY ANORTHOSITE ods. Their measuredcompositional range among 45 example, microprobe analyses of plagioclase in specimensanalyzed was Ana2.6to An55.2and Or1.7 oxide-richmafic gabbro dike MM-6 yield composi- to Or1s.6,with averagevalues of Anae.7and Or5.2. tions adjacent to lamellar or corona garnet which (These values, given in mole 70 were converted are 11to 15mole Volowerin An and approximately from the weight percentagesreported by Isachsen I mole %higher in Or comparedto compositionsfar andMoxham,1969.) The high K contentof anortho- removed from garnet (Fig. a). Representativemi- sitic plagioclaseis in accordancewith relatively croprobe analysesof plagioclasein mafic rocks are high temperaturesof crystallization(Sen, 1959),but givenin Table4. The analysesin the centralregions precipitation of high-K plagioclasefrom melts rich- of grains have the best chance of representing the er in K than typical unfractionatedbasalts must also primary igneouscompositions, and are in general be consideredas a possibility (Morse, 1981;Ran- somewhat more sodic than anorthositic plagio- son,1981). clases,as would be expectedfor later differentiates. In addition to antiperthiticlamellae, anorthositic However, the effects of the garnet-producingreac- plagioclasescommonly contain minute rodlets and tions on plagioclasecompositions in these rocks particlesof Fe-Ti oxide minerals, also thought to makes determination of plagioclase fractionation have originatedby meansof exsolution(Anderson, trends by direct measurementrather difficult. 1966).Minor element analysesof plagioclasecon- centratescontaining these oxide inclusions(Isach- Fe-Ti oxides senand Moxham, 1969)reveal substantialamounts Fe-Ti oxide minerals are a ubiquitous constituent of Fe and Ti (wt.% FeO : 0.27-1.48,avg. : 0.51' of anorthositesuite rocks, and are presentin major wt.VoTiO2 : 0.04-0.85,zy5. : 0.28),consistent proportions in the mafic rocks and associatedore either with high crystallization temperatures deposits. Like the pyroxenes, the oxides exhibit (Smith, 1975),or with high contentsof Fe and Ti in complex subsolidusexsolution features. However, the parental magma. in addition to exsolutionin the strict sense(hema- In the mafic rocks, the determination of primary tite lamellaein ilmenite, pleonastelamellae in mag- plagioclasecomposition is further complicatedby netite), textural and compositional relations among the presenceof abundant garnet, which formed by the Fe-Ti oxides may be further complicated to means of a subsolidus reaction involving a net varying degreesby subsolidusoxidation-reduction consumptionof anorthite component (Mclelland reactions.This hasproduced, for example,ilmenite and Whitney, 1977).In many casesthis resultedin oxy-exsolutionlamellae in magnetite.Both ED and strongly zoned plagioclase,enriched in albite and WD microprobe techniques were used in analyzing orthoclase components towards the garnet. For the compositionsof these Fe-Ti oxide minerals. For the ED analyses,a defocussedbeam ofup to 20 microns in diameter was used in an attempt to incorporate hematite lamellae in ilmenite and pleo- naste lamellae in magnetite. No attempt was made to integrateoxy-exsolution lamellae, but in some casesthese could not be avoided.Textural relations and ED compositionsof Fe-Ti oxides are summa- rized in Table 5. Average ED compositionsare plotted on a TiO2-FeO-Fe2O3diagram in Figure 5. Primary igneous compositions of Fe-Ti oxides are rarely preservedin plutonic rocks becauseof the extensivedegree to which coexistingtitanomag- 1 2 3 4 5 6 7 8 9 l0 netite and ferrian ilmenite react upon cooling ac- cording to the equation Ab 76,8 72.9 70,4 63,7 70,2 64,0 6l,5 61.5 6t.9 72.1 An 20.7 25,0 27,8 34,6 27.4 34,2 36.6 36,7 36,3 25,2 Hem"" + IJsp"" : M&9., * Ilm".. (1) 'l 'l 0r 2,5 2,1 |.8 ,7 2.4 I,8 .9 I,8 L8 2,7 This results in oxidation of the ulvospinel compo- Fig. 4 Photomicrograph illustrating variability of plagioclase (white) composition (mole Vo) inrelation to lamellar or coronitic nent in titanomagnetiteand correspondingreduc- garnet (dark, high reliefl. Sample MM-6. Length of photograph is tion of the hematite component in ferrian ilmenite, approximately 6 mm. formingilmenite and magnetite,respectively, either AS HWAL : OXIDE.RICH DIFFERENTIATES. MARCY ANORTHO SITE 23 Table 4. Representativewavelength dispersivemicroprobe analysesof plagioclases sR-9 ru ran core rim si02 56.05 60.17 55-72 56.89 5A.77 60.77 5A.92 6r.88 59,.?0 62.20 TlO2 o. 00 o. 00 0 .04 0. 0I o.o0 0.00 0.00 0.o4 0.00 0.02 Nzog 27.79 25.59 27.77 26.8A 26.27 24.63 26.29 24-24 25.01 24.2r Fe0* 0.39 o-24 0. l1 U.IO 0.06 0.14 o.r2 0.13 o.0I 0.15 !4gO 0. 06 0.00 0.00 0.00 o.00 0.00 o.00 0.00 0.00 . 0.oo ca0 b- 5v 9.60 8. 33 7.76 5.88 7.55 5.29 6.38 5.O9 Na20 6.00 7.60 5. 69 6.t5 t.Lt d-zo 7.01 4.37 7.64 8.61 *zo 0. 57 0. 59 0. 55 o.62 0.38 0.29 0.33 0.47 0.34 0.42 Tota1 99.63 l-00.78 99.49 99.O4 1o0.41 99.99 LOO.22 100.46 99.08 100.70 Structural Formula based on 8 oxygens si 2.530 2.665 2.52L z-tI) 2.6LA 2.705 z.oz) 2.736 2.6A2 2.742 A1 L.479 1.336 1.481 r.434 r.380 L.293 I.38I L.2t6 L.324 1.258 4. 009 4. OOl 4 l,O2 4. O09 3.998 3.998 4. O05 4.OO2 4.006 4.000 Ti. - 0.001 o.001 - 0.001 Fer 0.015 0.009 0.004 0.006 0.002 0.005 0. 005 0. 005 - 0.006 M9 0.004 Ca o.424 U.JIJ U.4bf, o-404 0.370 0.280 0.360 0.250 0.307 0.24L NA 0. s25 0.653 0.499 0. 540 o.619 0.715 0.606 0.718 0.665 0.736 K o. o33 0.033 0.032 0.036 0.021 0.0r7 o.0r9 0.027 0.019 0.o24 1.001 I.008 1.001 0.986 r.012 r.0r7 0.990 r.001 0.991 l-.008 Ab 53.5 65.4 50.1 55.r 6r.3 70.6 61. 5 72.t 67.L 73.6 An 43.2 31.3 46.7 4L.2 Jb.b zt.t 36.6 25.2 31.0 24.O Or 3'.3 3.3 3.2 3.7 1.9 z.l r.v 4.1 * Total Fe as Feor r* See Fig. 4 as discrete grains (external granule "exsolution") Despite the effects of subsolidus recrystalliza- or as thin lamellae in the host grains (Buddington tion, there is a perceptible compositional trend and Lindsley, 1964). The overall result is an in- among the Fe-Ti oxide minerals. In the anortho- creasein the ilmenite and magnetitecomponents of sitesand other early cumulates,ilmenites tend to be the rhombohedraland spinel seriesphases, respec- richer in hematite component, and coexisting spin- tively, causing a counterclockwise rotation of their els richer in magnetitecomponent, comparedto the tielines on the TiO2-FeO-Fe2O3diagram. oxides in later cumulates and mafic gabbro dikes. While hematite lamellae in ilmenite and pleonaste Similar relationships in other anorthosite massifs lamellae in -magnetite were incorporated in the (Hargraves,1962; Anderson, 1966;Duchesne, 1972) defocussedbeam ED microprobe analyses, oxy- have been interpreted as an indication of progres- exsolution lamellae in magnetite and magnetite re- sive reduction of the melts during differentiation. duction-exsolutionlamellae in ilmenite were avoid- However. becauseof the effectsof counter-clock- ed, and as a result, many of the compositionsof wise rotation of Fe-Ti oxide tie lines in responseto coexisting Fe-Ti oxides shown in Figure 5 repre- reaction(1) duringcooling, as previouslydiscussed, sentthose which resultedafter subsolidusreconsti- rockswhose bulk oxide assemblageis dominatedby tution. Attempts to re-integrate the oxidation or ilmenite [ilm/(ilm + mag) = 0.9] will tend to retain reduction lamellae to obtain primary compositions near-primary ilmenite compositions, but magnetite would not be possible because of the unknown compositions will be widely different (much more extent of previous external granule "exsolution" Ti-poor) than primary values. Conversely, magne- (Buddington and Lindsley, 1964). tite-rich rocks [ilm/(ilm + mag) < 0.75] will contain ASHWAL : OXIDE.RICH DIFFERENTIATES, MARCY ANORTHO SITE threefold increase in V2O3 among magnetites, to a maximum of 3.0 wt.Voin sample SA-5 (Table 6). Discussion The mafic cumulates and dikes of the Marcy massif are interpreted as late-stage differentiates from a magma that had undergone extensive frac- tionation of plagioclase, followed sequentially by crystallization and accumulation of pyroxenes, Fe- Ti oxides, apatite, and Fe-rich olivine. Crosby (1968)and Buddington (1969)have proposed flow . differentiation models by which plagioclasecrystals migrated to the central regions of ascending mag- mas,to form a core zone of relatively pure, coarse- grained anorthosite. The liquid in the outer regions became progressively enriched in mafic constitu- tents, and subsequentlycrystallized as a somewhat finer-grained sheath of more mafic material. Local incorporation of earlier-formedplagioclase accumu- lations by this mafic-enrichedliquid could account for the block structures common in most anortho- site massifs (Isachsen, 1969).Although flow differ- Mog entiation appearsto be a satisfactory mechanismto Fig. 5 Average ED microprobe compositions of Fe-Ti oxide account for the formation of the pure anorthosites minerals from the Marcy massif plotted in terms of TiOrFeO- Fe2O3.Dots represent bulk compositions of oxide assemblages and their restriction to the central regions of the givenfrom modes.Enlarged area represents shaded area in inset. massifs.the nature of the conformable mafic-ultra- mafic layers describedhere suggeststhat they were formed by gravitational accumulation. It is suggest- magnetiteswith compositions closer to primary ed here that differentiation by gravitational means valuesthan coexistingilmenites. This relationship became the dominant mechanism subsequentto is supportedby the distinct correlationbetween Fe- emplacementof the partially solidified melts. In the Ti oxide compositionsand the modalproportions of case of the Marcy massif, final emplacement is ilmeniteand magnetite(Table 5, Fig. 5). The geoth- inferred to have taken place at a stage in the ermometer-oxygen barometer of Buddington and crystallization history at least as early as the time Lindsley (1964) thus cannot be used to obtain when the pyroxenes first precipitated, allowing the estimatesof primary temperature andfOz. formation of the early, Mg-rich ultramafic cumu- WD microprobe analyses of coexisting Fe-Ti lates in a relatively static environment. The occur- oxidesfrom a layered cumulatesequence which is rence of the mafic facies in the border zones of the gradationalupwards from a basal oxide-rich pyrox- massif, and hence structurally above the earlier- enite to leuconorite are given in Table 6. There is a formed anorthosites of the core zone. could be slight but progressive increase in hematite compo- interpreted as evidence that plagioclase sank, at nent in ilmenite and a decreasein ulvospinelcom- least in the early stagesof crystallization. ponent in magnetite stratigraphically upward in this The relatively minor volume of mafic rocks com- sequence,but these may not reflect primary varia- pared to the associatedanorthosites is consistent tions, as discussedabove. However, minor ele- with a rather feldspathic parental magma composi- ments may be used as reliable indicators of primary tion, possiblyin the gabbroicanorthosite (77.5-90% fractionationtrends (Himmelbergand Ford, 1977). normative plagioclase) range. The exact composi- Both magnetitesand ilmenites from this sequence tion of the parental magma is difficult to determine show a progressivedecrease in Al2O3,MnO, and becausean accurate field estimation of the volume MgO, and a progressiveincrease in Cr2O3and V2O3 of mafic rich rock is not possible. Although highly with stratigraphic height. Noteworthy is the nearly aluminous magmas such as gabbroic anorthosite ASHWAL : OXIDE.NCH DIFFERENTIATES, MARCY AN ORTHOSITE 25 Table 5. Microtextures and compositions (EDA) of coexisting Fe-Ti oxides ModalCompositions Sample Cornpositional Average No. of No. RockType I I flrrMag Ilm/ ( Ilm+Mag) Microtextures Range Comp. Analyses CUMULATES: t.a H"tr 7 5654'A Anorthosite 0.90 I'lm: coarse hem. lanellae H*ro.q - r5.6 3.3 Mag: homogeneous UtPo. 6 o H"tr 4 SL-l'lY Oxiderich ?3.1 0.82 Ilm: coarse hem. lamellae, H"tIr.l - r7.0 4.5 pyroxenite depleted near mag. utPo.o UtPo.2 8 Mag: honogeneous - 0.5 SL-'llA Leuconorite 4.5 0.90 Iln: coarse hem lamellae, Hemg.g Hem,^. 6 - r6.2 tz.a depleted near mag. b Mag: homogeneous u'Po.o- 0.3 uspO..l SA-3D Oxiderich 0.65 Ilm: homogeneous H"tz.9-4.0 Hem- . J pyroxenite pleonaste Mag: 3 sets of utPra.S u'Pr lamellae, discrete - r4.g 4.5 p l eonaste SA-3A Leuconorite 0.65 Ilm: nomo9ene0us Hem^ Hem^ ^ 6 z.t, - +.t pleonaste Mag: few lamel lae, utPo.6 uspl few i lm ox'id, lamel lae - q.o .9 H"tr 9 SA-5 Leuconorite 1.0 0.90 I tm: fine hem. lamellae, H"t8.3 - r2.4 0.9 depleted near mag. Uspo.8 9 Mag: homogeneous "'Po.o - 3.0 'r5. !f'1-568 H"r.l 6 oxide rich 3 0.94 I lm: coarse hem. lamellae, H"t]g.2 - r8.2 5. 5 mafic aabbro depleted near mag. pleonaste utPo.3 utPt .l 6 Mag: few tiny - r.5 . I amelI ae 'r3.6 SA-l5A Oxiderich neml7.9 Hen,^ . 0.90 Ilm: coarsehem lamellae, - 20.9 tv.o gabbro depletednear mag. pleonaste utp0. .l I Mag: fine lamellae utPo.o- 0.8 Hem,, 3 5683d 0xide rich ll.7 0.72 Ilm: homogeneous Heml r - pleonaste t.r 5-z mafic troctol ite Mag: 2'lamellae, sets of tiny utPr l4 abundantilm utPro.o- 2r.5 5.7 oxid. IamelIae DIKES: Htts.B H"t7. 9 Ml"l-l4A 0xide rich 13.5 0.8t Ilm: homogeneous - 9.r 5 mafic norite pleonaste 'l.5 UtPo. lz Mag: fine u"Po.2- B I amelI ae 2 I't'l-6 0xide rich 0.72 I lm: homogeneous H"tr.o - 2.6 H"rl.8 mafic Aabbro Mag: few pleonaste utp22. 3 IamelIae,few ilm "'P21.4- 22.3 o oxid. Iamel'lae 4 SR-g 0xide rich 0. s4 Ilm: homogeneous H"to.8- 2.4 H"tl.8 gabbro urp27. 3 Mag: feli p]eonaste utPz6.g - 27.7 I lamellae have been suggestedas much as forty years ago produced by high-pressurefractionation of olivine (Buddington,1939),their existencehas been ques- and orthopyroxene from mantle-derived olivine tionedand their possiblemodes of origin havebeen tholeiite magmaswhich accumulatednear the base debated.The recent discovery of sills and dikes of of the continental crust. The aluminous melts were gabbroic anorthosite composition provides the first then emplacedinto higher levels in the crust, where direct evidence for the existence of these magmas they precipitatedonly plagioclaseat the liquidus. (Crosby,1969; Husch et a|.,1975;Isachsen et al., This model accounts for the relatively high fe* of 1975;Simmons, et a|.,1980;Wiebe ,1979), although the anorthositicrocks (Emslie, 1973;Simmons and their origin remains somewhatof a problem. Emslie Hanson, 1978),and is consistentwith recent Sm- (1978)has proposed that the aluminous magmas Nd isotopestudies of the AdirondackMarcy massif which gave rise to massif-typeanorthosites were which indicate an ultramafic source area for the 26 AS HWAL : OXIDE-RIC H DIFFERENTIATES. MARC Y ANORTHO SITE Table 6. Representative WD microprobe analyses of Fe-Ti References oxides Anderson, A. T., Jr. (1966)Mineralogy of the Labrieville anor- thosite, Quebec. American Mineralogist 51, 167l-l7 ll. lilagneti tes I I menites Anderson, A. T., Jr. (1969)Massif type anorthosite:a wide- 5A-3D SA-3A sA-5 SA-3A SA-5 spread Precambrian igneous rock. In Origin of Anorthosite and RelatedRocks, Y. W. Isachsen,ed., New York State si0. 0.03 0.07 0.05 o.o2 0.01 0.01 Museumand ScienceService Memoir 18,47-55, N. Y. Ti0^ 3.34 0.67 0.05 52.61 50.92 47.86 Ashwal, L. D. (1978a) Crystallization history of massif-type Al^0^ l.5t 0.67 0.54 0.06 0.04 0.03 anorthosite (abstract). EOS: Transactions of the American cr^0^ 0.37 t.t6 3.84 0.01 0.03 0.15 GeophysicalUnion 59, 393. 8.34 Fe^0. 58 t5 61.83 6l.12 2.22 3.03 Ashwal, L. D. (1978b)Petrogenesis of massif-typeanorthosites: 42.77 4?.23 4l.ll Fe0 33.65 30.BB 3t .31 crystallizationhistory and liquid line of descentof the Adiron- 0.07 0.02 0.01 0.46 0.27 0.26 i4n0 dack and Morin complexes.Ph.D. thesis, Princeton Universi- ltlS0 0.18 0.07 0.01 2.30 I .85 0.94 ty, 136pp. v^0.* t.r8 2.10 3.00 0.13 0.22 0.59 Ashwal, L. D. and Seifert, K. E. (1980) Rare earth element 98.60 99.29 Total 98.48 97.47 99.93 I 00.58 geochemistryof anorthosite and related rocks from the Adi- rondacks,New York, and other massif-typecomplexes. Bulle- Structural formulabased on 3 cations (maqnetite)or 2 cations (ilmenite) tin of the GeologicalSociety of America 91, 105-107,659-684. Si 0.001 0.003 0.002 0.000 0.000 0.000 Ashwal,L. D., Wooden,J. L. and Shih,C. -Y. (1980)Nd and Sr Ti 0.097 0.020 0.001 0.977 0.968 0.91? isotope geochronologyof the Marcy anorthosite massif, Adi- 0.002 0.001 0.001 AI 0 069 0.031 0.024 rondacks, New York (abstract).Geological Society of Ameri- Cr 0.0]t 0.036 0.116 0.000 0.001 0.003 't.689 ca Abstractswith Programs,12, 380. Fe"' 1.325 1.761 0.041 0.058 0.159 ,l.003 E. (1978)Igneous pyroxenes from Fe- r.085 1.014 0.882 0.892 0.871 Bohlen,S. R. and Essene, J. Mn 0 002 0.00] 0.000 0.010 0.006 0.006 metamorphosedanorthosite massifs. Contributions to Miner- !19 0 010 0.004 0.001 0.085 0.070 0.036 alogy and Petrology 65,433-442. 0.036 0.066 0.092 0.003 0.004 0.012 Buddington, A. F. (1939) Adirondack igneous rocks and their metamorphism. Geological Society of America Memoir 18, 3.000 3 000 3.000 2.000 2.000 2.000 pp. l4as( Iln) 89.70 97.BB 99 84 (e7.71) (e6.87) (et.63) 343 usp (Hem)10.30 2.12 0 t6 (2.2s) (3.r3) (8.37) Buddington, A. F. (1953)Geology of the SaranacQuadrangle, New York. New York State Museum Bulletin 346, 100pp. *V203 an abundanceswere corrected for TiKBoverlap by subtracting Buddington, A. F. (1960)The origin ofanorthosite reevaluated. of TiKo countsfrom vKocounts prior to further empirically determinedl% RecordsGeological Survey of India 86, Paft 3, 421-432. natrix corrections. Buddington, A. F. (1969) Adirondack anorthosite series. In Y. W. Isachsen, ed., Origin of Anorthosite and Related Rocks,New York StateMuseum and ScienceService, Mem- melts parental to the anorthosites and related mafic oir 18,215-231. (1964) titanium differentiates (Ashwal et al., 1980). Buddington,A. F. and Lindsley, D. L. Iron oxide mineralsand synthetic equivalents.Journal ofPetrology 5,310-357. Crosby, P. (1968) Igneous differentiation of the Adirondack Acknowledgments anorthositeseries. XXXIII International GeologicalCongress 2, tt-48. This studywas done in partialfulfillment of the requirements Crosby, P. (1969) Petrogenetic and statistical implications of for the degreeof Doctorof Philosophyat PrincetonUniversity. modal studiesin Adirondack anorthosite. In Y. W. Isachsen, Financialsupport came from Nesa Grant NGL-31-001-283, Lin- ed., Origin of Anorthosite and RelatedRocks, New York State coln S. Hollister,principal investigator, and from the Depart- Museumand ScienceService Memoir 18, 289-303. mentofGeological and Geophysical Sciences, Princeton Univer- Davis, B. T. C. (1971)Bedrock geology of the St. RegisQuad- sity. Some of the data were collected while the author held a rangle, New York. New York State Museum and Science National ResearchCouncil Resident ResearchAssociateship at Service, Map and Chart SeriesNumber 16, 34 pp. r.rasA,/JohnsonSpace Center. A portion of the researchreported deWaard, D. (1965) A proposed subdivision of the granulite in this paper was done while the author was a ResidentResearch facies. American Journal of Science 263,455-461. Scientistat the Lunar and Planetary Institute, which is operated deWaard,D. (1970)The anorthosite-charnockitesuite ofrocks of by the Universities SpaceResearch Association under Contract Roaring Brook valley in the Eastern Adirondacks (Marcy No. N,c.sw-3389with the National Aeronautics and Space Ad- Massi0. American Mineralogist 55, 2063-2075. ministration. The manuscript was critically reviewed by R. B. Duchesne, I.-C. (1972) Iron-titanium oxide minerals in the Hargraves,E. Dowty, G. Ryder, J. L. Warner, R. F. Emslie, Bjerkrem-Sogndalmassif, southwestern Norway. Journal of and S. R. Bohlen.Assistance in the field was providedby F. B. Petrology13,57-81. Nimick, R. Warren, and M. A. Arthur. Maps were provided by Emslie, R. F. (1973)Some chemical characteristicsof anortho- Y. W. Isachsenand P. R. Whitney of the New York State site suites and their significance.Canadian Journal of Earth Museumand ScienceService. C. G. Kulick, R. W. Brown and Sciences10,54J1. D. W. Phelpsl provided assistance with the electron micro- Emslie, R. F. (1975) Nature and origin of anorthositic suites. probes.This is L.P.I. ContributionNo. 447. GeoscienceCanada 2, 99-104. ASHWAL : OXIDE.RICH DIFFERENTIATES. MARC Y ANORTHO SITE 27 Emslie, R. F. (1978)Anorthosite massifs,rapakivi granites, and Morse, S. A. (1981)Kiglapait geochemistry III: potassium and late Proterozoic rifting of North America. precambrian Re- rubidium. Geochimica et CosmochimicaActa 45. 163-180. search7,6l-98. Ohnstead,J. F. (1%9) Petrology of the Mineral Lake intrusion, Green,T. H., Brunfelt, A. O. and Heier, K. S. (1969)Rare earth northwestemWisconsin. In, Y. W. Isachsen,ed., Origin of element distribution in anorthosite and associatedhigh grade Anorthosite and RelatedRocks, New York State Museum and metamorphicrocks, Lofoten-Vesteraalen,Norway. Earth and ScienceService Memoir 18, 149-161. Planetary ScienceLetters 7, 93-98. Philpotts,J. A., Schnetzler,C. C. and Thomas, H. H. (1966) Green,T. H., Brunfelt,A. O. and Heier, K. S. (1972)Rare earth Rare earth abundancesin an anorthosite and a mangerite. elementdistribution and K/Rb ratios in granulites,mangerites, Nature 212, 805-806. and anorthosites,Lofoten-Vesteraalen, Norway. Geochimica Ranson, W. A. (1981)Anorthosites of diverse magma types in et CosmochimicaActa 36,241-257. the PuttuaalukLake area, Nain complex, Labrador. Canadian Gross, S. O. (1968) Titaniferous ores of the Lake Sanford Journal of Earth Sciences18, 26-41. district, New York. In J. D. Ridge, ed., Ore Deposits of the Rose, E. R. (1969)Geology of titanium and titaniferous deposits United States, American Institute of Mining, Metallurgical, of Canada. Geological Survey of Canada Economic Geology and PetroleumEngineers, N. Y., 140-154. ReportNo. 25,177 pp. Hargraves,R. B. (1962)Petrology of the Allard Lake anorthosite Ross, M. R. and Huebner, J. S. (1975) A pyroxene geother- suite, Quebec. 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(1977)Rare earths in the Marcy and Morin anorthosite Anorthosite contact relationshipsin the Adirondacks and their complexes. Canadian Journal of Earth Sciences 14, 1033- implicationsfor geologichistory. GeologicalSociety of Ameri- 1045. ca Abstracts with Programs7, 78. Sen, S. K. (1959)Potassium content of natural plagioclaseand Isachsen,Y. W. and Fisher,D. W. (1970)Geologic map of New the origin of antiperthites. Journal of Geology 67, 479495. York, Adirondack Sheet. University of the State of New Simmons,E. C. and Hanson, G. N. (1978)Geochemistry and York, The State Education Department, Albany, N. Y. origin of massif-type anorthosites. Contributions of Mineral- Isachsen,Y. (1969)Origin of anorthosite and related rocks-a ogy and Petrology66, l19-135. summarization.In, Y. W. Isachsen,ed., Origin of Anorthosite Simmons,E. C., Hanson, G. N. and Lumbers, S. B. 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(1956)Petrology of the anorthosite-gabbro tion with composition and calculated optimal phase bound- massat Kavadur, Madras, India. GeologicalMagazine 93, No. aries. American Mineralogist 60, 9-28. 4,287-300. Kretz, R. (1963) Distribution of magnesiumand iron between Taylor, H. P., Jr., and Noble, J. A. (1969)Origin of magnetitein otthopyroxene and calcic pyroxene in natural mineral assem- the zoned ultramafic complexes of southeasternAlaska. In, blages.Journal of Geology 71, 773-:785. H. D. B. Wilson, ed., MagmaticOre Deposits,Monograph 4, Martignole, J. (1974)MeOhanism of differentiation in the Morin Economic Geology Publishing Co., 209-230. anorthositecomplex. Contributions to Mineralogy and Petrol- Wager, R. L. and Brown, G. M. (1968)Layered Igneous Rocks, ogy 44,99-107. Oliver and Boyd, Ltd., Edinburgh, 588 pp. Mclelland, J. M. and Whitney, P. R. (1977)The origin of garnet Wiebe, R. A. (1979)Anorthositic dikes, southernNain complex, in the anorthosite-charnockitesuite ofthe Adirondacks. Con- Labrador. American Journal of Science279,394-410. tributions of Mineralogy and Petrology 60, 16l-181. Morse, S. A. (1969)Layered intrusions and anorthositegenesis. In, Y. W. Isachsen,ed., Origin of Anorthosite and Related Rocks, New York State Museum and ScienceService. Mem- Manuscript received, January 9, l98l; oir 18.175-187. acceptedfor publication,August 3I, 1981.