University Mlcrohlm#, a JOQQH Company. Arm Arbor. Michigan

72-15,236

KURYVIAL, Robert Joseph, 19W» BEHAVIOR OF SOME MINOR EtfKENTS IN CŒXISTIHQ FLAGIOCLASE, ORTHOCLASE, AND BIOTITE FROM THREE INTRUSIVE BODIES IiOCATGD IH THE CENTRAL WASATCH RANGE.

The Ohio State University and Miami (Ohio) University, Ph.D., 1971 Mineralogy

University MlcroHlm#, A JOQQH Company. Arm Arbor. Michigan

THIS IHSSERTATIOM HAS BEEN MICROFILMED E X A C W AS RECEIVED BEHAVIOR OP SOME MINOR ELEMENTS IN COEXISTING FLAOIOCLASEi ORTHOCLASE» AND BIOTITE FROM THREE INTRUSIVE BODIES LOCATED IN THE CENTRAL WASATCH RANGE

DISSERTATION PrtBsnttd In Partial Fulfilloant of tha Rtquiraatnts for tha Dagraa Doctor of Philoaophy in tha Graduata Sohool of Tha Ohio Stata Univaraity

By Robert Joaaph Kuryvial» 3*3** M.S. *****

Tha Ohio Stata Univaraity 1971

Approved by

Laar Dapartaant/of Mineralogy PLEASE NOTE;

Sorrw pmgw h#v# indEftinct print Filmed w r#o##v#d.

Unlvenlty MkrofHmt A Xerox Educetlon Compeny AOXNOWLEDQMSNIS

Th« writer wiah*« to thmnk Profooeors R.T. Tottonhorst and E.G. Ehlera for their auggeetlona and oritlolan during the preparation of thia dlaeertation. Thank# are alao due the other nembera of my reading committee, Frofeaaora D*H« Seotford, Q« Paure, and H*E* Wenden# for their help ful commenta« Electron mioroprobe analyaea were performed by the Battelle Memorial Inatitute, Oolumbua laba.

ii VITA

Mfty 15f 1943 Bom-D*troitt Niohlgan 1961*1963...... Studied Eleotroniae Technology at Henry Ford Oomwmity College, Dearborn Michigan 1963-1963..,.#.#.# Co-operative Trainee in Slectrioal Engineering with Ford Motor Coapany and Ilea to m Michigan Univeraity 1967...... B«S*# Wayne State Univeraity, in Geology, Detroit, Michigan 1967-1970...... N.D.E.A, Title IV Felloirahip 196 9...... M.S., Miami Univeraity* in Geology, Oxford, Ohio 1966-1969...... Studied Mineralogy, Ohio State Univeraity, Oolumbua, Ohio 1969-1970...... Reaearch Aaaoeiate, Miami Univeraity* Oxford, Ohio 1970...... Aaaiatant Project Leader* Kenneoott Copper Corporation Reaearch Center, Salt Lake City, Utah 197 0...... Mineralogiat* Battelle Memorial Inatitute* Oolumbua, Ohio

FIELDS OF STUDY Major FieldI Mineralogy-Qeology studies in Petrology* Professor David M* Seotford Studies in Geoohemiatry* Frofeaaor Alan M, Stueber Studies in Mineralogy* Profeaaora Rodney T# Tettenhorat* Bmeat 0* Bhlera, and Henry B, tfSnden ill TABLE OP CONTENTS Pftgt ...... li VITA...... ill LIST OF TABLES...... vil LIST OF FIGURES...... Viii INTRODUCTION AND BACKGROUND 1 1# 0#n#rml ...... 1 2t Cryital Oh«aio«l Controls of Elomontml Bohsvlor During Nmgmmtlo Cryotollliation 2 3« OBoorvod Bohmvior of Bmrlum, Strontium# Rubidium# and Galeium*** ...... S m# Rubidium b. Barium o« Strontium d, Rolmtivo Bohmvior of Barium# Strontium# and Calcium a# Barium/Rubidium Ratio 4# Distribution of Traos Elamonts Batwaan Coaxisting Faldapars...... ,###.,#*####, #. 15 GEOLOGIC SETTING OP INTRUSIVE BODIES...... 19 1# ...... 19

Z* Looation...... 20

3* Raglonal Structura...... 21 PREVIOUS WORK ON INTRUSIVES...... 2? PETROLOGY OF INTRUSIVES...... 32 1. Tha Clayton Paak Stock...... 32

iv TABLE OP CONTENTS (oont*) Pmge 2# Tht Altm Stock ...... »...... 34 3* The Little Cottonwood Stock , 38 EXPERIMENTAL DETERMINATION Of DISTRIBUTION COEFFICIENTS...... 42

ANALYTICAL METHODS...... 45 1* Smmpl# Proparation ...... 45 2. Ppoooduraa for Atomic Abaorption Analyala 46 3# Accuracy and Praciaion of A.A.S. Analyala 4? 4. Electron Mioroprobe Analyala...... 49 A.A.S. ANALYTICAL RESULTS...... 51

INTERPRETATION AND DISCUSSION OF ANALYTICAL RESULTS...... $6 1. Elemental Behavior In the Alkali feldapara.... 56 a. Potaaaium/Rubidlum Ratio b. Barium c. Barlum/Rubldlum Ratio d. Strontium e. Oalolum 2. Elemental Behavior In the Plagloclaaea 73 a. Strontium b# Barium 3* Partitioning of Barium and Strontium Between Coexlatlng Feldapara...... 76 a. Barium b* Strontium 4. Potaealua/Rubldlum Ratio of Blctlte ... 81 V TABIaE OP CONTENTS (oont. ) ^ Pag# 5* Visual Isad Ssqutnea of Events...... 64

BIBLIOGRAPHY...... 66

vi LIST OP TABLES TABLE Pag* 1* Bonding Energi##gio# of Hotal-Oxygtn __ Bonds Oml* eulatid for Six-Fold Coordination*»*...... 6 2. Atomic Paramotora for K* RB, Na« Oa, Sr* and Ba.» 9

3 Analysas of Spaoimans from Littla Cottonwood# Alta# and Clayton Paak Stocks ...... >• 29 4 Absoluts Aga Oataminatiens of Intrusivas In Millions of Tsars...... 31 5 Comparison of Values Obtained on U*8»Q*S» Rock Standards with Published Values,...... 48 Duplicata Analysis of Alkali Feldspar Separata to Détermina Rsproduoabllity *...... 30 7 A.A,8. Results for Alkali Feldspars...... 32 6 A,A,S, Results for Alkali Feldspar Phenoorysts**» 52 9 A.A.S. Results for Plagioclasa 53 10 A.A.S. Results for Biotites...... »...... 54 11 Whole Rook Analyses for Ba and ...... 55 12 l^Rb Ratios of Alkali Feldspar Separates 58 13 Ba/Rb Ratio of Alkali Feldspar Separates. ,,.».» 68 14 K/kb Ratio of Biotite Separates...... • • . . 8 3

Yii LIST OP FIGURES Figure Page 1* Generalised geologic setting of intrusive stocks...... ZZ Dlmgrmmmatio geologic map showing alignment of projection of Uinta Mountains and intrusive bodies...... 25 )# Fhotomiorograph showing typical texture of Clayton Peak stock...... 33 4. Photomicrograph showing a subhedral alkali feldspar crystal...... 33 5* Sample locations for the Alta and Clayton Peak stocks,.»...... *...... 35 6, Photomicrograph showing texture of nonpor» phyritic facies of Alta stock...... 37 7* Photomicrograph showing texture of porphyritic facies of Alta stock...... 37 8* Photomicrograph showing interstitial orthoclase in the Little Cottonwood quarts monsonite...... 40 9" Photomicrograph showing a portion of a twinned orthoclase phenooryat...... 40 10. Sample locations for the Little Cottonwood quarts monsonite...... 41 11. Plot of potassium versus rubidium for the alkali feldspars,,...... 57 12. Plot of weight percent barium versus mole per cent Or for the alkali feldspar,60 13. Plot showing the distribution of barium across an alkali feldspar phenociyst from sample LOW-45...... ;..63 14. Plot showing the distribution of barium across an alkali feldspar phenociyst from sample LCW-46...... 64 viii LIST OF FIGURES (oont.) Figure Fmg# 15* Plot ohowing the dietribution of b&rium ttoroee mn mlkmli feldepmr phenooryst from ••mplt LOW-5 0...... 65 16* Plot of rubidium versus barium for the mlkmli feldmpmrs...... «...... 67 1 7 . Plot of strontium versus mole percent Or for the mlkmli feldspmrs*...... 70 18, Plot of omloiun versus mole percent Or for the mlkmli feldspmrs»...... «...... 72 19* Plot of strontium versus mole percent An for the plmgioolmse feldspmrs...... 74 20. Plot of bmrium versus mole percent An for the plmgioolmse feldspmrs...... 75 21. Plot of bmrium in coexisting mlkmli end plmgioolmse feldspmr...... 78 22. Plot of strontium in coexisting mlkmli end plmgioolmse feldspmr...... 82

ix INTRODUCTION AND BACKGROUND

Q m m l Statement It h M long boon known that tho growth of a wlnoral phoflo in nmturo io oooonpaniod by tho Ineorporation of rolatlYoly minor olomonto# gonorally ignorod in tho ehomioal formula of tho phaoo* prooont in tho onvlronmont of oryotal- liiation of tho minorai phaao, Suoh minor and traoo olomont ooneontrationo tond to bo particularly oonoitlvo indioatoro of prooooooo of difforontiatlon and onviron- montal paramotora» much moro oo than tho major oompononta (Kolntirot 196))» In tho prooont work» an attompt haa boon mado to atudy and mako uoo of minor olomont ooneontrationo of Ba» 8r# Rb» and Ca» principally in alkali and plagioolaao feldapara# to dotomino tho potrogonoaia of throo ignooua intruaivo bodiOB boliovod to havo boon dorivod from a common aouroo* Thoao arc tho Clayton Poak# Alta# and Littla cottonwood atooka of northom Utah# Alkali and plagioolaao foldapara aro of primary intoroat bocauao of tholr groat abundanoo and ubiquitoua ooourronoo» It ia hopod that now data pro- aontod horo will bo of oomo further uao in tho atudy of othor ignooua intruaivoa# To roach a full undoratandlng of minor olomont bohavior during nagmatio cryotallisation 2 it is nAmssary to aeeunulat* data from many différant bodiaa# last intanaiva atudlaa of a fa# ignaoua bodiao un duly prajudioa thinking* Othor avidanea auggaating a com* mon origin for tha bodlaa* aa ralativa agaa of intrusion, ralatlon to tootonic avanta in tha araa, apatial relation* ahip along a major structural faatura, major clamant con centrât ions, and ralativa grain alia will alao ba praaantad* In order to provide an adequate parapactiva for tha following atudy, it ia banafioial to review tha oryatal- ehamioal controls imposed on tha aubatitution of trace and minor alamanta for major alamanta during tha ciyatallisation of a mineral phase.

Orvtml Qh#mioml Control! of Behmvior During «a— atlo Crvfllliatlon Present views regarding tha ralativa behavior of alamanta during magaatic crystallisation are largely due to tha rules governing tha substitution of ions in a crystal structure put forth by Ooldaohmidt (1937)# Ooldsohmidt*a rules emphasise tha importance of Ionic radii and charge of tha alamanta* Stated generally, tha rules given by Ooldaohmidt are# 1) Por two ions to ba able to replace each other, the Sima of the ions should ba similar within 13## 2) Por two ions having tha same charge and different 3 lonio radii oonpatlng for tha « m a aita, tha ion with tha anallar radii will ba prafarantially inoorporatad into tha aita* 3) Por two iona having aiailar ionic radii but diffarant ehargaa oenpating for tha aana aita# tha ion with tha highar oharga will ba prafarantially in oorporatad into tha aita, Baoauaa pradiotlona of alamantal bahavior baaad on thaaa rulaa ara in ganaral aeoord with obaarvad gaologie fraction ation prooaaaaa, thay have baan widaly uaad aa a ganaral baaia for diaouaaion of tha diatribution of traoa alamanta• Howavar# it haa baan fait by many that thaaa rulaa ara ovar-aimplifioationa with many axoaptiona ooourrlng, Shaw (1953) criticiaad tha notion that ionic aiaa waa tha con trolling influença in diadcehy, Ha gava a number of inatanoaa where tha law# ara not obeyed and further pointed cut that ionic radii could not alone account for fraction ation bahaviOr of alamanta in a ayatam having oontinuoua aolid aclution with a minumum or maximum molting point# In an effort to aupplamant tha Ooldaohmidt rulaa by taking into account tha nature of tha chemical bonding batwaan the aub- atitttting iona and tha iona in tha atructura# Ahrana (1953)» Aingwood (1953)» and Pyfa (1951) amphaaiaad tha added in fluence of ioniiaticn potential and alactronagativity on diadoohy# Tha raaulting modified rulaa have had a good deal of auccaaa in pradieting gaochamioal bahavior of tha alamanta# but tha tack of obtaining a quantitative maaaure of bond typo otlll proonoti m problem# with olootro* nogmtlvltioe being ineufflelent to explain certain elemental aubetitutiona obaerved* Suoh exoeptiona are noted and diaeuaaed by Tauaon (196^), Nookolda (1966) attempted to eatimmte the bonding anergiea for dimtomio metal to oxygen bonda in a unified approach and to uae the value# obtained to predict the behavior of element# during fractional oryatalliamtion of a magma. Hi# oalculationa of approximate total bond energy were oompoaed of three parta» the covalent contribution, the lonio con* trlbution, and the oryatal field atabiliaation energy. After allowing for multiple bonda in a aix fold aite, hie oalculationa were deaigned to provide a quantitative aub- atitute for Ooldaohmidt*# rule#, by incorporating the bonding conaiderationa atreaaad by Ringwood and Pyfe. Ncokolda gave two aimpie rule# for the behavior of metala during fractional oryatalliamtion, in li^ht of relative total bonding energieai 1)**When two oationa of the aame valency are capable of aubatitution in a oryatal lattice, tha one having the greater relative total bonding energy will be incorporated preferentially, 2) When two oationa of different valency, involving coupled aubatitution, are capable of aubatitution in a oryatal lattice, that aubatitution will take place preferentially whoa# aum of relative total bonding energy ia the greater. **

Damon (1966) made a modification of hookolda* (1966) equation for the calculation of total bond energy in order to make it dimenaionally valid and give a better approx* iwation of lonio rooonuioo onorgy, Dmmon liotod tabloo of^ motal-oaygon bond onorgloo In KOal/nolo for six fold co ordination, and gavo oxamploo of thoir uao. The data in Table 1 is taken direotly fro* Damon (I9 6 8). From thia table the predicted order of preferred aubatitution for in alkali feldapar, whioh for divalent iona involvea aimultaneoua aubatitution of Al+^ for Si^, would be according to Nookolda' ruleai Ca+*Al+3 Sr+^Al***^ Ba+^Al+3 Na+^Sl**^ K+^8i+^ Rb+^8i^ 572 559 545 505 493 467 Kdal/«ole

In the preaent and other atudiea, the behavior of Oa, Sr, and Ba in alkali feldapara haa been ahown to be the revere* of the above prediction, with the preferred order of aub atitution for potaaaium being Ba, Sr, and da. In the aub atitution for calcium in plagioolaao, however, the above order appeara reaaonable, at leaat for An rich plagioolaee, Aa the plagioolaee beoomea richer in aodium, Sr ia pre ferred over da (Korringa and Noble, 1971)■ D u m a and Fyfe (1966) point cut on a theimodynamioal baaia that when oonaidering the fractionation of a given element between liquid and aolid phaaea, one muat take into account the bonding foroea exlating within the liquid aa well aa the aolid. Whether an element ooncentratea in tha liquid or aolid phaae upon magmatlo fractionation may well depend on the nature of Ita incorporation in the liquid. If a trendy held in the liquid, there may be little thermo dynamic motivation to enter the aolid. Whittaker (196?) TABLE X BONDING ENERGIES OP METAL-OXYOBN BONDS CALCULATED POR 9IX-P0LD COORDINATION (from Dmmon# I968) x-0 Bona Totmi Bonoing Energy (Keml/mQl#X Om+2-o 236 Mm+^-O 11? 388 A1^3-0 336 -0 105 Rb^^-0 99 Sr+*-0 223 Bm+^-0 209 pr#0#nt#d m liquid mod*I whioh h# f*lt m#y b# m woeful opproximotion for oome liquid oiliomt#*. Prom the preceding and from geologic oboervation# it appears that there are at least four factors controlling the distribution of elements during nagmatio orystalisationi 1} Propsrtieo of the individual elements (ionic radii, charge, bonding properties with a given anion, etc.) 2) Properties of the solid (ohenioal composition, structural modifications, or any other factor con trolling the nature of the site to be occupied} 3) Properties of the liquid (basically, the manner in whioh a given element is incorporated in the liquid) 4) The environment of crystallisation (pressure, temperature, degree of equilibrium, concentration, etc*) Not much reflection on these many factors is needed to soon realise that an aoourate theoretical prediction of the be havior of a given element is an extremely difficult task# As useful as approaches suoh as Nookolda (196?) may be, before much credenoe can be given them, they must first be able to explain with some degree of aoeuraoy the observed elemental distribution in completed igneous processes. e O b » T v a B#hmvlùr of Bmrium. Strontium. Rubidium, m a Cmlolim Whll# th# g«oohfmio«l behmvlor of amtiy minor olomonto during nogmmtio frmotionotion io not complotoly under* otood* onough dot» hovo oppoorod in tho litoroturo to glvo ot looflt o quolitotlvo pioturo oo to whioh olomonto oro tokon up by oolido oorly in oryotolliiotlon and whioh oro onriohod in tho rooiduol motfu* Tho ooourronoo of ftb« Bo, 8r, tnd Oo in olfcoli foldopor and plogioolooo aro of major oonoom in tho prooont atudy and will bo tho only olomonto dioeuaaod in thia aootion. A oemprohonaiwo roviow of trooo olomont bohavior during mofaatio cryatallioatlon woo givon by Taylor (1965), Tho following dioouooion io in largo port oummorimod from hio roviow and, whoro appropriato, io oupplomontod by finding» givon in moro rocont publioationo, Taylor govo oxplanationo for olomontol bohavior in toxmo of lonio radii, olootro* nogativity, ionic potontiala, and ionitotion potontiol, oooontially tho approach of Ringwood (1955)* Sinco thia approach givoo oo good on account of olomontal bohavior aa tho unifiod total bond onorgy approach of Nookolda (1966) and Damon (1968), it will bo foUowod horo. Table 2 givoo thoao paramotora for tho pertinent olomonto to bo dioeuaaod. For typical oonoontrationa of Kb, Ba, Sr, and Oa in foldapara tho roador ia roforrod to Hoior (1962).

Rubidium Probably moro ia known about tho abundance and dim- T A B U 2 ATOMIO PARAMETERS FOR K* Rb# Nm# 0«# Sr, and Ba

K a n t n T lonie Pauling loniaation lonie Radii Sltotnmag. Potantial Potantial (Ai ï#v) K 1 0 3 0*60 4.34 0.75 Rb 1.47 0,6 4.18 0,68 Na 0,97 0.9 5.14 1,03 Oa 0,99 1,0 6.11, 11.67 2.02 Sr 1,16 1,0 5,69, 11.03 1,69 Ba 1 , ^ 0,9 5.21, 10,00 1.49 10 trlbution of rubidium than any other traoa a lament, Tha raaaon for tha extraordinary Intaraat in rubidium ia due to ita cloaa gaoohamioal coharanca with potaaaium, Tha two alamanta ara ainilar in ionic charge* ionic aiaa, and bonding oharactariatioa. Baoauaa of thaaa aimilaritiaa, rubidium ia ganarally found in nature aubatituting for potaaaium in potaah rich mineral phaaaa* uaually in aoma definite ratio of K to Rb for aaoh phaaa, Tha ganarally accepted value for tha R/Rb ratio of tha aarth*a oruat ia 2)0. Since Ahrana at al (1952) firat pointed out tha atrong coharanca of potaaaium and rubidium in tarraatrial rocka and mataoritaa, much diaouaaion and many publicationa have followed oonoaming tha uaa of tha I^Rb ratio in tha atudy of patroganaaia, A large part of tha diaouaaion haa focuaad

on uhathar tha K/Hh ratio ramaina oonatant during ignaoua differentiation or deoreaaaa in value, leading to a relative enrichment of Rb in tha raaidual malt* Shaw (1968), in a review of K^Rb fractionation trenda, aummariaed evidence advanced by many authora both for and againat the fraction ation of K and Rb, Ha concluded that, in the main trend, the R/Rb ratio doea deoraaae during fractionation, Thua during magmatlo fractional cryatalliiation, rubidium, prob ably owing to ita larger ionic radiua, can ba expected to become relatively concentrated with reapeot to potaaaium, and lead to dacreaaing R/Rb ratioa. When oonaidering individual mineral phaaaa, it haa baan found tha relative incorporation of potaaaium and rubidium 11 1« different for #moh phaoo* Tmueon (1965) provided K-Rb dot* for ooixieting biotite end mlkmli feldepmr in eeverml rook typee. In emoh omme the biotite hmd m lower Vftb rmtiot genermlly by m fmotor of two or three. The relmtivmly h i ^ oonoentrmtion of rubidium in biotite with reepeot to potmeeium ie probmbly due to m Imrger mlkmli mite in biotite. In mlkmli feldepmr the potmeeium site ie m little tighter end more ridgid, Thue the Imrger rubidium ie more oomfortmble in the mlkmli eite of biotite,

Bmrium Of the common omtione preeent in m mmgmm, bmrium eubetitutee prinoipmlly for potmeeium mnd to m leeeer ex tent for omloium mnd medium, Bm*^ ie mbout the mmme mime mm but, probmbly beomuee of it# double ohmrge, it hme been obeerved to be preferentimlly Inoorpormted into emrly formed potmeh phmeee, Tmylor (1965) etmted thmt mlthough bmrium tende to be omptured by emrly formed potmeeium minermlm, it oeomeionmlly hme been obeerved to be enriohed toward the end of the differentiation mequenoe in the roeid- uml melt mnd euggeated thmt bond type, owing to differenoee in eleotronegmtivity of potmeeium mnd barium, may exert eome influence, Thie enrichment might be more emeily ex plained in terme of the order in whioh minermlm are observed to oommonly orystmlliee out of a magma, Plmgioolmse is often the first major phase to appear# and einoe it incorporâtes little bmrium eubetituting for omloium mnd sodium, its oontinued oryetmlliaation may enrich the 12 r##iduml m*lt in barium* Btrlln and H#nd«rmon (1969) hmv# found thmt in porphyritic trmehytoi and phonolltam tha •nriohmant of barium in tha raaidual magma la directly dapandant on tha amount of plagioelaaa to cryatalliia* Tha graatar tha amount oryatallltad tha graatar tha barium contant of tha aanldinaa whan thay atart to oiyatallita* Korringa and Nobla (197I)» in a atudy of a wida variety of porphyritic volcanic rocka, found barium to ba enriched in tha groundmaaa over tha plagioelaaa phanoovyata, with a dia* trlbution ratio of from about 0.42 to 0*16. Haiar (1962) noted, largely from a atudy by Haiar and Taylor (1959) on aoutham Norwegian Pre*Cambrian alkali feldapara, the tendency for barium to ba enriched in early formed alkali feldapara. Kerriek {1969) made an electron mioroprobe analyala of the Oathedral Peak quarte monionita of Oalifomia and found the microoline phenooryata to be diatinot from the groundmaaa microoline by having a higher barium content. The phenooryata were alao found to be toned, with a high barium core and a relatively lower barium rim. From thia Kerriok auggeated that the phenooryata ware formed earlier in tha malt than the groundmaaa microoline * Boattohar at al (I967) found potaah feldapar phenooryata in a porphyritic trachyte dike aaaooiatad with tha Rainy Oraak oomplam alao to be toned, having high barium oorea and low barium rima. Littla data on tha bahavior of barium in plagioelaaa ia available. In a raatricted atudy, Haiar (1962) noted that plagioolu« app«ftr«d to aeotpt inortafitig amount» of bar!ua, at laait with roipaot to orthoolaso» aa differentiation ppooeeded. Korringa and Noble (1971) have found that the amount 6f barium aooepted into plagioolaee inoreaaee aa the An content deoreaaee*

Strontium During magmatie oryatalliiation atrontium tende to oompete mainly with oaleium» potaaaium# and aodium for atruotural poritiona* While all available evidenoe in- diomtea that atrontium ia preferentially captured in place of potaaaium in alkali feldapar# oauaing the element to be aomewhat enriched in early formed fraction## there ia acme queation aa to Ita behavior in plagioolaao# Taylor (1965) indicated that calcium waa incorporated preferentially over atrontium in cxyatallising plagioolaao# Thia would oauae the Sr/Oa ratio of the reaidual melt to inoreaae and be reflected in higher Sr/Oa ratioa in later formed plagioolaee becauae of the enrichment of the melt in atrontium# Taylor reoommended the Sr/Oa ratio of plagioolaee to be a uae- ful and aenaitive guide to fractionation prooaaaaa# Berlin and Henderaon (1969) found the oppoaite trend for plagie- olaae phenooryata in traohytea and phonolitea# with the 8r/0a ratio deoreaaing on fractionation# XOrrlnga and Noble (1971)# in a atudy of atrontium and barium dietrlbution between feldapar and ignaoua melt in porphyritic vcloanio rook# concluded the aeparation of a calcic plagioelaaa from mafic and intermediate melta raiaed the Sr/Oa ratio of the 14 rtiiduil whll* ■•paration of aodlo plagioolaao from mor# allioio molt# loworod the Sr/Oa ratio* Thua aa plagioolaao hooomoa inoroaoingly oodio during oryotalliaation atrontium ia moro oaaily able to enter the atnioture* The interpretation of atrontium bohavior In plagioolaao oryatal" liming from ailloio nagmaa ia no doubt oomplioatod by the eO"Oxyatalliiation of other phaaaa* aa orthoolaao* whioh will atrongly tend to deplete the melt in atrontium*

Rtlrtlv B«h«vlor of Bmrlu». Strontium, n d Omloium Ba, Sr, and Oa are all preferentially captured into potaaaium poaitiona by oxyatalliiing alkali feldapar* Heier and Taylor (1939) found that aa the abaolute amount# of theae element# deoreaaed in alkali feldapar# upon fractionation* their ratio# change# It wa# found that the relative rate of deoraaae wee in the order Ba* Sr* Oa* Thua the B#/5r ratio deoreaaee and the C#/Sr ratio Inoreaaee with fractionation* % i a relative behavior ie contrary to what might be ofpeeted from either ooldaohmidt*# or Nookolda* rulaa for aubatitution* Rather than viewing the placement of Sr* Oa# and Ba into potaaaium aitea in the alkali feld apar «truoture from the etandpoint of how aimilar they are in propertiea to potaaaium* perhap# the aubatitution ahould be taken from the viewpoint of the aite* Potaaaium certainly i# not the optimum ion for the aite* or elae the other ion# would not be preferentially replacing it* Thia behayior goea to point out the lack of generality of 15 pr«ftnt sutatltutlon rwl*## sueh ma Ooldmohmidt'm or Nookoldm", and why ohamrvation* from nature are extremely valuable«

Bmrlwa/Rubldlun Ratio Taylor and Heier (i960) have found the Ba/Rb ratioa of potaah phaaae to provide a critical index of fraotionation, Aa haa already been noted» Ba tende to be perferentially incorporated into early formed potaah phaaea, while Rb haa a alight tendency to be enriched in later forming potaah phaaea. Thua the Be/Rb ratio can be expected to deoreaae in phaaea auoh aa alkali feldapar on fractional ciyatalliiatlon. Taylor (1965) provided a plot of rubidium veraua barium for alkali feldapara ahowlng the fraotionation trend.

Dietribution of Traoe^lemente Between Ooexiatina Peldanara In trying to interpret trace element behavior during magmatic oryatalliiatien* it ia important to keep in mind that the degree of equilibrium achieved can aeriouely affect the concentration of a given trace element in a phaae. In igneoua prooeeeea equilibrium can rarely be aaaumed. Thia become# particularly aiffiificant when attempting to determine the partitioning of a trace element between two ooexiating phaaea, aa the partitioning of Sr and Ba between ooexiating 16 and alkali faldapar» Tha theory of alanant partitioning hatwatn ooexiating phaaea haa been diecuaaed in detail by Molntir# (1963) and will therefore be given only a review here. Under oonditiona of Ideal oheaioal equilibrium the ohem-> ioal potential of eaoh component» whether major or trace» la homogeneoua throughout eaoh individual phaae and between the varioue different phaaea preaent. For ooexiating feldapara one would aaaume that upon oryatalliiatlon eaoh phaae oontinuoualy remote with the realdual melt to eatabliah a oontinuoua ohemioal equilibrium» with chemioal adjuatmenta to ohanging temperature» preaaure and oonoentrationa being carried to completion. The reaulting eryatala ahould be totally unioned» either in major or trace elementa. In the oaae of Sr partitioning between ooexiating plagioolaae end alkali feldapar» the ohemioal potential of Sr for eaoh phaae would bet Uj^ • u{ 4 RT ln(a]g) (K^apar) Up K RT In(ap) (plagioolaae) where u* ia the ohemioal potential of Sr In a atandard atate» R ia the gaa eonatent» T la the abaolute temperature and (a) the activity of the component. At equilibrium the ohemioal potential of Sr in K-apar la equal to the ohemioal potential of Sr In plagioolaae. Since u{ and u{ are oon- atanta» at fixed temperature and preaaure» it ahould follow that# 17 Up - m #%p .I.. — ... m OOnStUlt (K}* •p RÏ

If th# eonovntrmtion of Sr In tho foldsparo 1« low# Henry*# lew for dilute solution# would apply* and so the aotiwity of Sr would be proportional to its oonoentration* thus I

oonofntxation of gr in K-snar ____ ^ oonoentration of Sr in plagloolmse ^

would be the equilibrium distribution coeffieient of Sr between alkali feldspar and plagioolaae for some speoifio environmental eondition* The numerical value of is not constant but depends on such factors as temperature# pres* sure* and the compostion of the phases. The partitioning of Sr between coexisting feldspars has been discussed by Barth (1956# 1961)# Heier (1962)# and Hall (196?). It is generally felt that the ratio for Sr decreases with temperature# with typical values ranging from about 0*5 to 2#o* end that major element concentrations also have an affect on this ratio. Neuman at ml (195b) are generally pessimistic about the usefulness of partitioning coefficients# feeling that the concentration of trace elements in melt and solid during crystallisation is generally a non-equilibrium condition# with the trace elements being distributed in a logarithmic manner. The crystallisation of a given phase from a magma will tend to deplete or enrich the residual melt In various IB depending on their affinity for the phaae* For example the orystalliiation of orthoclaae would tend to deplete the realdual melt in barium and enrich it in rubidium. Such depletion or oonoentration ahould be evidenced by elemental icnatlon within the phaae if later homogeniaation haa not taken place, Kerrick (1969) and Boettcher at al (1967) have found orthoclaae phenocxyata to be monad with high barium corea and low barium rime. The point here ia# according to Neuman at al (195^)# that the enrichment or depletion of an element in the melt produced by the oryatalliiation of a given phaae will affect the extent of that elementa concentration in later oryatal- llaing phaaea. The ctyatalliaation of caloic-plagioclaae will enrich a melt in barium# ao that when the field of orthoclaae la finally reached thia new phaae will have more barium available to it than if it had actually oo-oryatal^ limed with the plagioolaae. The reaulting aaaemblage would be non«equilibrium in two reapectai 1) due to elemental lonlng within the individual phaaea 2) due to a lack of chemical equilibrium between the ooexiating phaaea. Mo Intire (1963) atated that the dietribution of trace elementa in a oryatallialng magma fall aomewhere inbetween the extremea of complete equilibrium and logarithmic die* tributicn# probably leaning toward the latter. OSOLOOIO SBTTINO OP INTROSIV: BOOIK

Introduotlo» Thr## Intruflv* bodi## looatvd in th# Park Oity-Llttl# Oottonwood-An#rioan Pork mrem of th# c#titrml Wumtch Rang# hav# b##n oho«#n for th# pr#«#nt trao# #l#m#nt atudy* fh#a# bedifls ar# allgn#d in a n#ar #aat-##at dirootion along th# ajcia of a u j o r antiolinal foatur# of th# ar#a. Prom #a#t to w#at th# bodi#a ■uoe##siv#ly inoroaa# in p#ro#ntag# ailica» in av#rag# grain aim## and in ar#a of ontorop. Th# matamnoat body ia th# Littl# Oottonaood atoek and oonaiata largely of porphyritio quart# monmonit#. Approaimatoly two nilaa #aat ia th# Alta a took of granodiorit#, Th# #aat#m- moat intruaiv## th# Clayton Peak ateek# ia alao a grano* diorit# and ia in oontaot with th# Alta atook, Baoaua# of th# proximity of th# thr## intruaiv### th#ir alignm#nt along a major antiolinal foatur# of th# aroa# th# d#er#aa# in mafic phaaea# and the oonaiat#nt change in ailioa oontent with direction# it appeara that them# bodi*a may hav# aom# common origin from a d##p#r central magma aouro#. Further evideno# of auoh a relatlonahip la pro vided by th# relative age# of th# intruaiv### with th# moat mafic body being th# oldeat of th# three and th# moat ailioio body th# young##t (Crittenden and Xlatler# 1969)# 19 20 Bvldtno* of # common «ourco» based on minor slsmont dls^ tribution* will bo prosontod Imtor.

Location Tho Llttlo Cottonwood, Alta, and Clayton foak stocks aro located in the central Wasatch Range# approximately twenty miles southeast of Salt Lake City* Utah# The Little Cotton* wood stock lies within the Draper, Dromedary Peak, Lehi, and Timpanogos Cave quadrangles. The dimensions of the body in outcrop are approximately seven by nine miles, the Alta and Clayton Peak intrusive# lie almost com* pletely within the Brighton quadrangle# Access is provided by Utah Highway 152 to the head of Big Cottonwood Canyon where the resort area of Brighton is located# From Brighton the Alta stook is easily reached by foot, while freash outcrops of the Clayton Peak stook are most easily reached by means of an improved dirt road crossing Ouardsman's Pass# The Alta stock is approximately two miles by three miles# Taken together the Alta and Clayton Peak stocks outcrop over an area less than one*third that of the Little Cottonwood stock# 21 R#«lonml Structure Th# thr## Intniiiv# hodi## 11# n##r th# int#r##otion of two mmjor tootonio #l#m#nt# of th# w##t#m Unitod St#t##« Th# first of th### #l#n#nt# 1# a #a#t-w##t trending upwarp# th# #ut#m m o # t #xten#ion giving ria# to th# Uinta Mountains ind th# weatommost #xt#nsion forming th# Cottonwood uplift, along th# Uinta aroh* Th# sooond taotonio #l#m#nt is a north-south trending arouat# bolt of fold# and thrust faults extending from southern Nevada to Montana and Idaho* A portion of these two elements is shown on the map in Figure 1* A feature important to th# understanding of th# west fso# of the central Wasatch Range is th# Wasatch fault* This major fraotur# is part of th# mid-Tertiaiy Basin and Rang# faulting and. runs parallel to th# west side of th# Wasatoh Rang# for approximately 115 miles and is responsible for muoh of the present relief of the range* It is a dip-slip normal fault which dips at 50 to 70 degrees to th# wost* Vertical displacement is estimated at 1000 to 10,000 feet (Bardley, 1951)• The Wasatoh fault is a olassio example of block faulting* The downthrown block underlies the Salt Lake valley while the upthrown block, slightly tilted eastward, forms the west front of th# Wasatoh Range* This period of faulting occurred after the emplacement of the intrusives under study* Thrust faulting has been reoognised in the oentral Wasatch Range* Overthrusting is well exposed Just west of 22

Pigur# 1# Mnvralltcd geologic sotting of Intruaiv* atoelca. Oonpllod from Orlttondon (196tf)* Orangor and Sharp (1952) t Orlttondon et al (1952), Crittonden (1965), and Baker *t al (1966). 23 th# Alt# itock in th# Alt# thrust* This thrust pr#d#t#s folding and ignsous intrusion in th# mrs# and has bssn son#* what obscured by the later events. The Alta thrust is out by th# Alta stook and is offset in several places by normal faults* The Charleston*Nebo thrust* just south of the Little Cottonwood stook* nay have had a displaoement of nearly 40 miles (Crittenden* 1961)# These thrusts are all part of a broad son# of originally eastward moving thrust faults. The east-west trending upwarp* the Uinta arch* is made up of Preoambrian* Paleosoio* Mesosoio and early Tertiary sediments and metas#diments. This broad anticline inter sects the north-south trending central Wasatch Bang# at nearly right angles. Though modified by later regional falulting and local folding* the aroh is the dominant geo logic feature in this portion of the range* Its western most end is truncated by the Wasatoh fault system* with the area immediately to the east of this truncation known as the Cottonwood uplift. Here the axis of the fold is exposed at the front of the Wasatch Range* Just north of the mouth of Little Cottonwood Canyon. The north limb of the aroh is exposed in Big Cottonwood Canyon* The south limb of the arch has been replaced by the Little Cottonwood stock* The axis of the arch plunges at about 30 degress to the east toward Brighton and Alta to a point just beyond Park City* where the fold rises again to form the Uinta Mountains. Beeson (1925) was the first to point out that the axis of 2k th# Uinta# projaot# to th# Oottonmod uplift and that th# pluton# in thl# ar#a, th# Intruaiv## und#r atudy in thia pap#r# ar# in approxinat# alignmant along thia antiolinal foatur# and an imaginary lin# #xt#nd#d through thorn point# waatward to th# Bingham atook in th# Oqulrrh Mountain#• Pigur# adaptod from Eardloy (1968), ia a g#n#ralis#d, diagrammatio goologio map ahowlng thia alipmant. It ia thought that thia alignmont ia mor# than ooinoldantal and ia ralatad to a major raglonal foatur# of th# aroa, Approximataly tan mil## to th# north of th# Uinta aroh ia an adjoining downfold, th# Parlay# Canyon aynolina, Thia aynolin# ia actually a doubla fold, with on# aynolin# in Emigration Canyon and th# othor in Parloya Canyon, Thaaa two aynolin## ar# aaparatad by th# tightly foldad Spring Canyon antiolin#, Th# ax#a of thaa# two fold# ar# ahown in Pigur# 1* Th# aignifioano# of th# Parloya Canyon aynolin# to th# proaont atudy lia# in an obaorvation mad# by Orangar and Sharp (1952), Thay hav# ahown that thr## oonglomarat## of Lat# Orataoaoua to aarly Tertiary ag# involvod in th# Parlay# Canyon aynolin# war# auooaaaivaly foldad about alightly différant ax#a, Thia indioataa that th# aynolin#* aa wall aa th# Uinta aroh, underwent at laaat three auo- oeaaiv# period# or pula#a of oruatal oonpreaaion from Lat# Orataoaoua to aarly Tertiary, Granger and Sharp (1952) not# that thia period of oruatal oompreaaion ooinoidaa well with th# eatimatad time# of intruaion of th# Littl# Cottonwood, 23

m *

i l

fkSAîCH Vf m o u n t a i n s

o q u ir r h C P Altai and Olayton Peak atooka* Orittandan (1964) haa aatlaatad tha tlmaa of thaaa pulaaa* Tha flrat ia aatinatad to hava ooourrad around 65 to 90 ■lllion yaara ago, tha saeond about 75 a i U i o n yaara ago, and tha third 60 to 70 ■illion yaara ago, Thaaa oompraaaional pulaaa probably not only eoinoida cloaaly in tima with tha intruaiona# but ara diraotly raaponaibla for thaa. A oantral parant magma aouroa, uadargoing fractional oiyatalliaation, may hava baan aotad upon by thaaa pulaaa, with aaoh pulaa forcing raaidual malt matarial into tha eora of tha nawly forming Uinta aroh. PREVIOUS WORK ON INTRUSIVES

Th# Intrusion of th# Littl# Cottonwood■ Alts# snd Olayton P#ak stocks into foldad Precanbrian to jurmssio shalast quartsit*s, and liaostonas has produoad load, lino# silver# gold# and ooppar mlnersllsmtion# primarily in th# limastonas, Pravious work on thasa intrusive bodies has baan cantered largely around tha oharaeteriaation of tha bodies as ore producers• Tha aaount of both replacement and vein mineralisation decreases from the Olayton Peak to tha Little Cottonwood stook. Consequently# the Olayton Peak and Alta stocks hava received the most attention# with little work being dona on tha Little Cottonwood stock. As a result of tha ore mlnarallsatlon# three dominant mining areas developed around tha turn of tha century* These are the Park City# Little Cottonwood# and tha American Fork districts. Tha geology and mineral deposits of tha Park City district# which includes the eastern portion of the Clayton Peak stock# has baan described by Boutwell {1912). The general geology and ore deposits of the Little Oottonwood-Amarican Fork area# which includes tha eastern portion of the Little Cottonwood stock# the Alta stock# and the western portion of the Olayton Peak stook# has baan described in some detail by Calkins and Butler (1943). In 27 26 th#ir paper Cmlkln# end Butler included a compilation of whole rook chemioal analyaea performed cn the three in- truaivee* Table 3 ie taken directly from thia compilation* From thia table it ia aeen that ailioa inoreaaea weatward from the Olayton Peak atook to the Alta and Little Cotton wood atooka, whereaa calcium, magneaium, and iron deoreaae in thia direction* Thia ia aa would be expected in a general fraotionation trend, Crittenden, Sharp, and Oalkina (1952) updated the work of Galkina and Butler (19^3)* providing a regional map* Recently the U,S* Geological Survey haa mapped aeverml quadranglea in the oentral Waaatoh of intereat in thia atudyi aee Baker et al (1966), Baker and Crittenden (I96I), Bromfield et al (I967), and Crittenden (1965)* Slawaon (1953) atudied by apeotrochemloal analyaea the dietribution of lead in alkali feldapara from the Little Cottonwood, Alta and Olayton Peak Intrualvea* Lead ahowa aa muoh variability within each atook aa in auooeaalve in- truaivea. Parry (1961) apectroohemically analyied blotitea from the intrualvea for copper, lead, and mine, Wilaon (1961) analyied aeveral mineral aeparatea from the Alta Intruaive for Ou, Pb, Zn, Ag, Co, Ml, and Sn and mapped textural changea of the body in detail* He concluded the Alta magma was intruded in two phaaea, the later phaae having a porphyritio texture, and that Ou, Pb, and Sn were alightly more abundant in the later phaae* Kamil (196?) examined magnetitem from the intrualvea by x-ray apeotro- 29 TABLE 3 ANALYSES OP SPECIÏŒNS PROM LITTLE COTTONWOOD* ALTA, AND CLAYTON PEAK STOCKS* (from Calkins and Butler, 19^3)

little dlayton Cottonwood Alta Alta Alta Peak S1Ô2 67.02 65,2ÿ 6^,46 62.16 5^.i5 AlgOj 15.78 15.75 15.93 17.17 16,36 Fe|0 3 1.56 2.31 2,61 2.26 2.90 PeO 2,80 1,65 2,31 2,78 3.36 MgO 1,09 1*62 2,27 1.81 3.08 CaO 3.31 4,09 4.33 4,70 5.03 Na20 3.85 3.92 3.66 3.96 3.73 KgO 3.67 3*25 3.49 3.58 3.85 H2O- .29 $21 .27 ,03 ,28 HgO+ .63 .53 .74 ,60 $64 TÎ02 .55 ,62 .53 .87 ZrOo III • 02 ,03 ,01 P O ,26 2 5 .25 • 16 •17 S .03 m — ,o4 — MnO • 02 ,10 .09 ,06 iO? CO2 traoe trace . traoe BaO ■ .13 ,11 .15 .17 • 16 Cl ,01 .05 • 05 PeS2 - • 02 . .02 SrO - .05 - ,05 100,85 99.91 100.17 100,03 100,29

* for details of sample locations and analysts refer to Calkins and Butler (19^3)* 30 •oopy for traoe notalo* Orlttondtn and Klatlar (I968) hava provided absolute age determinations for the Olayton Peak, Alta, and Little Cottonwood stocks by Pbecsnd K-Ar* Dates by the two methods are discordant (Table 4). Crittenden end Mistier offer two interpretations of the data* The first is that the aireon dates represent the period of intrusion and the K-Ar dates represent cooling history or a later thermal event* They comment that this interpretation fits best into the regional structural setting* The second interpretation offered is that the sircon dates are partly relict, in which case accepted structural relations would need re* vision* Belt (1969) has made whole rook analyses for Ou, Zn, and Pe of the Alta and Olayton Peak stocks by atomlo absorption* He concluded from his data that each stock was emplaced in a series of events* 31

TABLB 4 , ABSOLUTS AGE DETERMINATIONS OP INTRUSIVES IN MILLIONS OP YEARS (from Grltitndon wid Klotlor, 1968)

K-Ar k-Ar K-Ar Intnuivo ilreon muooovito biotito homblondo

Olmyton Ftmk 70 36i? Altm 60 32.5 33.7 32.5 31,0 32.5 34.7 Llttlo Cottonwood 50 25#8 25.5 31.1 28.1 PBTROLOOr OF INTRUSIVES

Tht Clayton- f»mk Stock Spmùlm#n# from th* Olayton P*ak atook ar* typically dark to medium gray, fin# t#atur#d, «qtiigranular rookm. Avorag* grain aim* is about 1 mm* 3p*oin*na ar* mad* up of approx* imataly 60 to 70 percent plagioolaae* 5 to 20 percent alkali feldspar# 5 to 10 percent quarts# and 15 to 20 percent mafic minerals* The mafio minerals include various amounts of augite# hornblende# biotite# and minor hyperthene. Acces sory phases preaent include magnetite# apatite# sircon# and sphene* The Olayton Peak stock has been described as a quarts dicrite by Boutwell (1912)# a diorit* by Galkins and Butler (1943), a granediorite by Bromfield (1966) and a hypersthen* biotite diorit* by Belt (1969)# Owing to the relatively high# t h c u ^ variable, alkali feldspar content# the body is probably more correctly termed a granediorite* Plagloclase occurs as subhedral laths 0*5 to 1*5 mm in sis* which show slight sonatioh* Oomposition as determined by atomic absorption is about An^g to Ani^* Albite# Carlsbad# and pericline twinning of the plagloclase is common, as shown in Figure 3# Some of the plagloclase laths are slightly serioitised. The structural state of the 32 33

Pigur# 3« Photomiorograph ahowlng typical texture of Olayton Peak atook, 34X*

Figure 4. Photomicrograph ahowing aubhedral alkali feldapar ciyatal* 34X* 34 alkali feldapara waa determined by uatng the two peak# 060 and ?04# x^ray method of Wright (I96B) and waa Identi fied aa orthoelaae* Nearly all the orthoclaae ia interatitial and ia generally optically non-perthitlo« Oo- caaionally a aubhedral alkali feldapar oryatal# crowded with inoluaiona of plagioolaae and mafio phaaea# ia en countered* One auoh oryatal ia ahown in Figure 4# Bio tite ia generally anhedral to aubhedral and alightly ohloritiled* Augite la commonly found to be altered# the produo ta being hornblende and chlorite* quart# ia interatitial* Sample location# for the Olayton Peak atook are ahown in Figure 5*

T h f A M # Speoimena from the Alta intruaive are diatinotly lighter gray in color than thoae from the Olayton Peak# coaraer grained* and contain no pyroxene* The Alta atock exhibit# two principal lithologie aapeota# whioh differ mainly in texture* The predominant lithologie aapeot ia a granitic texture# while the other la a porphyritio texture# Bie porphyritio portion oooupiea the core of the atock acuth- weat of Brighton and an arm extending northeaat from the main body. The regional relatlonahip of the two lithologie# ia ahown in Figure 5« The nonporphyritio lithology grade# Clayton

■ ■ ■ Æ Peak m m Stock

« Sompk Locotion Cbytaih^

ein ml tes pOV^fflflC figure 5. Sample locations for the Alta and Clayton Peak stocka.

\j» 36 mlmomt inparotptibly Into tho porphyritio• Sanplo location# for tho Alta atook aro alao ahorni in figuro 5* fho nonpbrphyritio lithology oonaiata of approximately

40 to 60 poroont plagioolaao, 10 to 20 poreont orthoolaao, 10 to 20 poroont quarto» 5 to 20 poroont homblondot 5 to 15 poroont biotito* 2 to 5 poroont magnotito* and accoaaory aphono* apatite* and lireon* Grain aito ia approximately 2 to 5 mm* Figure 6 ahowa tho general texture* Plagioolaae* An^O to An^y in oompoaition aa determined by atomio abaorption* ia aonod* oeoura in aubhedral to anhedral lathe* com monly ahowa albite* Oarlabad* and pericline twinning* and ia commonly aerioitiied along odgea and fraeturea* Ortho- olaao ia quite variable in amount and habit* even within a aingle aootion* Moat orthoclaae ia interatitial to the other phaaea, Oeoaaionally aome large anhedral and aub hedral graine* crowded with inoluaiona* are preaent* whioh may ahow porthitio atruoture. Interstitial* non-porthltio orthoclaae ia ahown in Figure 6, Hornblende and biotite are generally aubhedral* 2 to 3 mm in aise* and commonly marginally ohloritised* Quarts ia interatitial to the other phaaea* Figure 7 ahowa the texture of the poj^hyritio lithology. Here the phenooiyata are approximately the aame aise* 2 to 5 mm* and node aa the phaaea of the nonporphyritio rook. The groundmaaa ia composed mostly of orthoclaae and quarts* 0*1 to 1 mm in aise* with minor plagioolaae* hornblende* and biotite. 37

Figure 6, Fhotozniorûgraph ahowlng texture of nonporphyritio feoies of Alta stock* 34X*

Figure 7* Photomicrograph ahowlng texture of porphyritio faoiea of Alta stock* 34X. 38 Th« littl# Cottonwood StoBk

Th* littl# Oottonwood intruaiv# ia a quarti nonsonit# porphyry in which th# ahoundanoo of phonooryata varioa aignificantly throughout th# body ov#r amall diatano##, Th# majority of th# phonooryata ar# aubhedral aingl# eryatala of orthoolaa# which vary from 1 to 8 cm in aim#, Larg# aub hedral eryatala of plagioclaa# ar# praaant, but ralativaly uncommon* Th# taztur# of th# groundmaaa ia medium to ooara# grained» with anhedral to aubhedral plagioolaae, orthoclaae, quart! and biotite ranging from 1 to 10 mm in aim#, out^ crop# of the quart! non!onit« ar# light gray In color and where aeverely weathered ahow the phonooryata of orthoclaae protruding above the groundmaaa, Speoimena from the Little Cottonwood vary oonaidarably in minéralogie oompoaition but typically average 40 to ^0 per cent plagioolaae, 30 to 40 percent orthoolaa#, 10 to 20 percent quart!, 2 to 5 percent hornblende, 10 to 15 percent biotite, and contain aooeaaory aphene, magietit#, apatite, and airoon, Plagioolaae ia anowy white in hand apeoimen, An2c to An^o in oompoaition * aonod, typically anhedral, ahowa albite* Oarlabad, and pericline twinning, and ia alightly aerieitiaed. Orthoclaae ocoura in two forma, lntej> atitially and aa aubhedral phenooryata. The interatitial orthoclaae ia generally porthitio, with atringera of ex- aolved albite, whioh may ahow twinning, and uaually con tain# inoluaiona of other phaaea. Figure 8 ahowa the typical 39 intermtitiml mode. Th# phtnoory#t# of orthoolu# mr# trftnolveont with #ith#r a light gray or pink oatt in hand apaoimon, art porthitio with atrlngora and patohta of alblt## contain inoluaiona» and oft«n «xhibit twinning# Pigur# 9 ahowa a portion of a Oarlahad-twlnnod orthoolaa# phono* eryat which contain# inoluaiona of plagioolaao and horn* blond# togothor with oxaolvod patch## and atrlngora of albito# Biotito and homblondo aro gonorally aubhedral and partially ohloritiaod. Samplo location# for tho Littl# Oottonwood quart# monmonit# aro ahown in Pigur# 10» 4 0

Figure 6* fhotoniorogrmph showing interetiti«l orthooleee in the Little Cottonwood quarts aonionite* 34x#

Figure 9# Photomicrograph showing a portion of a twinned orthoolaae phenocryst. N littift

Little Cottonwood Stock

* Sample Locatîoa

icaTe in miles

Figmr* 10m Sample locations for the Little Cottonwood quarts monsonite. BXFSRIMENTAL DETERMINATION OP DISTRIBUTION OOEPPIGIENTS

It w«s th« original intent of thlo otudy to oxporimontmlly emtmblloh tho partitioning ooaffioianta of barium and • atrontium botwaan ooaxlating alkali and plagioolaaa fold- apar for varioua tamparaturaa* It warn hopad that auoh data eould ba uaad to da tormina tha tamparatura of last a^ui* librium for tha intrualva bodlaa* Tha approach dacidad upon waa to try to datarmina tha partitioning of Ba and Sr batwaan aquaoua aolution and aaoh of tha ooaxlating faldapara at varioua tamparaturaa and 0«5 Kbar, Kara a glvan amount of faldapar* pravioualy •nalysad* was aaalad in a gold tuba with a givan amount of HgO (0.1 normal HOI). Whan hold at an alavatad tamparatura it waa axpaotad that major and minor ooaponanta would go into aolution until an aquilibrium atata waa raaohad for aaoh of tha componanta. Upon analyiing thia aquilibrium aolution for Ba and Sr* ona oould maka anothar run with tha aana faldapar# at tha aama tamparatura# but uaing a aolution mora conoantratad in Ba and Sr than tha pravloua aquilibrium aolution. If hold undar tha aama P-T oonditiona# aoma of tha axoaaa Sr and Ba in aolution ahould go into aolid aolution in tha faldapar. Ona would not axpaot tha raaulting ooneantration in tha aquaoua aolution to ba tha aama aa tha 42 43 initial run bmomua# tha eonoantratlona or aotivitiaa of Sr and Ba in the faldapar wara inoraaaad# Ona would a%- poet, however# that plots of oonoantrations in aquaoua aolution versus ooneantration in solid solution would he linearfl so long as both solutions mot aa dilute solutions* Whan oarriad out at various tamparaturaa* this procedure might yield a family of lines» one for aaoh tamparatura, relating the oonoentration of Sr and Ba in aqueous solution to oonoentration of Sr and Ba in the feldspar* This family of curves would ba unique to the in, Ab, Or content of the feldspar, since major element ohemlstry affects tha activities of the trace components. Thus several families of curves would need to ba established in order to determine the extent of the compositional dependence. If one were to then determine the partitioning of Ba and Sr between aqueous solution and the other coexisting feldspar in a similar fashion, another family of curves would be obtaindd* Then» for some particular temperature, to determine the partitioning coefficient one would simply find from the several plots the oonoantrations in the two feldspars, of some An» Ab, Or composition, which have a common aqueous solution concentration* By using natural coexisting feldspars from the intrusIves it was hoped that something conclusive about temperature of last equilibrium could be said. Unfortunately the ex change of trace elements between aqueous solution and feld spar is an extremely slow process# probably rate limited by 4 4 diffusion of Ba and Sr in tha faldapar atruotura* Evan aftar run# of thraa watka duration» tha eonoantrmtlon of Sr and Ba in aolution was undateotabla by tha analytical mathod anployad (atomic abaorption). In light of analytical dataminationa on tha natural faldapara» it is doubtful If auoh partitioning data oould hava baan uaad for gaotharmo- matry on tha intruaivaa* Thia la bacauaa» aa will ba shown latar* thara ia fair avidanoa that tha partitioning of Ba and Sr batwaan tha natural ooaxlating faldapara ia not an aquilibrium partitioning* AHALyTIOAL KETKODS

Smmpl# Pr#D#rmtion Mineral aepmrate# of alkali ftldspar# plagioolaaa■ and kiotlta vara obtained from the rook aamplaa by a oomblnation of haavy-liquida» electronagnetio aeparatlon# and hand picking# Approximately 500 grama of aaoh rook apeoimen waa brokan into 1/6 inoh alia or anallar partiolea# Thia natarial waa coned and quartered twlea to obtain approxi mately 125 grama of material# Obvioua partiolea of quart# and blotlta were then hand picked from thia material. Next the rook material waa oruahed in a tungaten carbide mill to minuB 100 meah. Fine# were then removed by élutriation# A twenty-five gram aplit of the reaulting material waa then paaaed through a Pranti iaodynamio aeparator to remove the mafioa# Separation of the phaaea compriaing the non-magnetio fraction, mainly alkali feldapar, plagioolaae, and quarts, waa aooompliahed by heavy liquida# Hix- turea of bromofoxn and dimethylformamlde were used for the heavy liquid media# Specimens from the Little Cottonwood quarts monionite porphyry required special attention in that it was desired to separate the phenocxyats of orthoolaae from the groundmass orthoolaae# This separation waa aooompliahed In the 45 4 6 initial fracturing of tha rook apaeiman# with fragmanta of tha phanooxyata hting aortag hy hand.

Prooaduraa for Atomic Ahaorption Analvaia A Farkin-Slnar Modal 303 atomic ahaorption apaetrophoto- matar waa uaad for tha quantitative elemental deteminationa* The following ia a brief diaouaaion of tha taohniqua uaad# Mineral aeparataa and U»S,0,S* rook atandarda were taken into aquaoua aolution for atomic abaorption analyaia by watting approximately 1 gram of material in a platinum oruoibla with 7 3*65C perohlorio acid and following thia with approximately 30 ml of 48# hydrofluoric acid. Tha aample waa alowly evaporated to dtynaaa on a hotplate at about 300^F, Reaction of tha hydrofluoric acid with tha ailicatea yielded gaaaoua ailleon tatrafluorida. Upon evaporation the oationa precipitated aa parohloratea* To the dried raaidue 50 ml of 1 H HOI waa added to bring the perohlorataa back into aquaoua aolution, Thia aolution waa reduced in oonoentration by a aeriea of volumetric dilutiona in order to bring tha oationa into the analytical range of the atomie abaorption apaotro- photometar, Tha elementa quantitatively analymad for were potaaaium* aodium, rubidium# calcium# barium# and atrontium, Potaa>* alum# aodium# and rubidium are relatively aimple elementa to analyte for by A.A. and may be dond uaing an air- 4? ■sttylim flani» Omlolum, t#rlum, and atronttugi» hawavar, « art not totally diaiooiatod» or fraed# In the low temperature air-aoetylene flame# but require a aomewhat higher temp* erature flame* Accordingly* a nitroua oxide-acetylene gaa mixture waa uaad for theae elementa* Although thia gaa mixture did diaaooiate the calcium, barium# and atrontium# it alao apparently produced appreciable ion* iiation of theae elementa* An element in the ionic atate cannot abaorb characteriatic atomic radiation beoauae of the altered outer electron ahell* To control thia# about Ig of eaaily ioniiable potaaalum waa added to both aamplea and atandarda* Prom the analyaia of the U*9*0*s* rook atandarda# thia addition appeared to inoreaae the number of atoma in the neutral atate and hence the abaorption of characteriatic radiation*

teeufev mnd Prtolaion of A.A. i n l v M * In order to provide an indication of the accuracy achieved in the A,A* analyaea three U,8,G,S* atandard rocka# 0-2# GSP-lf and AVO-1# were analymad along with the aamplea* The data obtained for theae atandarda ia given in Table 5 together with acme well accepted# publiahed valuea* An eatimate of the preeiaion of the analyaea waa ob tained by analyiing three aliquota of one of the alkali feldapar aeparataa. The three analyaea are given in 46

TABLE 5 OOMPAAISON OP VALUES OBTAINED ON U,S*O.S« KOOK STANDARDS WITH PUBLISHED VALUES

R w n i Q-g qs m i Z Z Æ ^ \ .

nSsoijll # 1 % OftO (H) 1.68 1.96 ».98 this work Bm (ppm) 2260 1305 1605 Sr (ppm) 410 221 5?4 Rb (ppm) 191 302 84 % 0 (#) 4.51 5 52 2.92 Mmzof# 3.96 2.72 4.13 Omrmlohmml CmO (m) 2.00 2.06 4*96 #t ml (196?)Bm (ppm) 2350 1600 1550 Sr (ppm) 465 230 640 Rb (ppm) 175 260 70 KgO ()() 4.51 5.48 2.69 Nm20(jC) 4.15 2.88 4.33 Flmnmmtn OmO (m) 1.96 2.03 4.96 ( « « ? ) 6Bm. (pp.)(ppm Igk igo ijlO Sr (ppm Kb (ppm 23. 343 69 49 T#ble 6 for eomporlion* Oonorally tho onalyooo mre roproduolblo within 3 or 4 peroont*

8100tron Ktoroprobo Analvoio A MAO olootron mloroprobo woo uiod to dotermin# lonation of bmrium in the olkmli foldopar phonooryat# of tho liittio Cottonwood quorti nonionito« Th# phonooryot# wor# ««otionod mo nomr to thoir oontoro mo poooiblo# mountod in bmkollto, poliohod# mnd oomtod with m omrbon lmy#r to nmko thorn eonduotivo* Point onmlyooo w*r# mod* with m 3 nioron dimnotor olootron boom mt 500 mioron otopo mlong m lino trmvoroo, from odgo to odgo of tho phonooryot#* BmTio^ wmo uood mo tho bmriun otondmrd for tho micro* onmlyooo* Boomuoo omoh point wmo onmlyood for bmriun mlono, no oorroetion oould bo mppliod to tho dmtm* Tho prinoipml information dooirod wmo rolmtivo barium ooncontrmtion throughout omoh phonooryot# honeo oxmot omounto wor# of oocondmry importonoo* Tho mloroprobo onmlyooo do# howovor# oomparo fmwormbly# within 25)(# to tho A*A*S* onmlyooo of tho phonooryoto# Aoproduoibility on tho mioron oemlo with thio typo of nmtoriml (inoluolono and porthitio otruoturo) ia impootiblo* Suoooooivo point count trmvorooa moroom tho phonooryot# mt 500 mioron otopo# will invariably hmvo olightly difforont pointa analytod omoh timo* 50

TABLE 6 ' DUPLICATE ANALYSIS OP ALKALI FELDSPAR SEPARATE TO DETERMINE REPRODUCIBILITY

Aliquot Element 1 3 X (^) 10,26 10.29 1 0 ,3 2 Mm (#) 1.42 1*49 1*38 Ok (ppm) 1283 1245 1310 Bm (ppm) 4360 4210 4275 Sr (ppm) 360 372 351 Rb (ppm) 340 333 355 A*A.S. ANALÏTIOAL RESULTS

Th# #n#lytio#l r##ult# obtained for the alkali feld apar# alkali feldapar phenocryata# plagioolaaa# and blotite aeparataa are given# reapeotivaly# in Table# 7# 6# 9# and 10. Selected whole rook analyaea for Ba and Sr are given in Table 11. Mineral aeparataa from the Clayton Peak atook are labled OPS# thoae from the Alta atook AS# and thoae from the Little Cottonwood atook LOW. Mole percent Or# Ab# An# and On waa calculated for the alkali faldapara# while mole percent Ab and An waa calculated for the plagioolaae.

51 52

TABLE 7 A.AtS. RESULTS FOR ALKALI FELDSPARS mol# ^ S w w l # #Mm Ca DPP B* 1)1» Sr pwi Rb pom Or Ab An On CPS-1 9*55 1.92 4073 17320 2156 203 69,7 23.8 2.9 3*6 OPS-2 9*65 1.66 4275 18550 2235 193 70.2 23,0 3*0 3*6 OFS-3 9.70 1,79 4217 17642 2053 199 71,2 22.2 3*0 3*6 OPS-4 9*62 1.89 3871 16923 2180 2l4 70*3 23*5 2.7 3*5

AS-46 11.08 1.69 2550 5523 380 342 77*4 20.2 1.8 0.8 AS-47 10.97 1*72 2361 6213 312 325 76*7 20.5 1*6 1.2 AS-48 10.26 1.42 126) ^ 6 0 380 340 29*4 18.7 1*0 0.9 AS^49 11*36 1,41 2324 5455 428 346 80.4 16.9 1*6 1 .1 AS*50 11*10 1.65 2123 533 349 326 77*6 19*7 1*4 1.1 AS-51 10.87 1*78 2025 5340 340 331 76*3 2 1 .2 1.4 1 .1

LOW 4 11*31 1*44 1292 2648 141 379 81.1 17*5 0.9 0.5 L0V12 l U Z Z 1.48 1553 3642 252 370 80.2 16.0 1.1 0.7 L0W23 11.34 1*39 1372 3160 I83 385 81.5 17*0 0.9 0 .6 LOW40 i n 28 1.44 1464 2913 185 367 60*9 17*5 1.0 0.6 L0W42 1 1 .30 1 .4 3 1223 3164 252 386 8 1 .0 1 7 ,4 0.9 O.7 L0W45 11*42 1.28 1112 2465 248 392 62.9 15*8 0.8 0.5 L0W46 11.24 1.46 1096 3640 267 370 80.6 17.8 0.7 0.7 L0W47 11.18 1 .5 2 1474 3784 214 403 79*7 18.4 1.0 0.8 L0V46 11.27 1.46 1183 2851 289 396 8I.I 17.6 0.6 0.7 L0W49 11.40 1 .3 0 1221 2370 254 4ll 82.7 1 6 ,0 0 .8 0.5 10*50 1 1 .31 1.42 1460 3097 318 376 81.1 1 7 ,3 1,0 0.6

TABLE 8 A.A.S RESULTS FOR ALKALI FELDSPAR PHENOORYSIS m oi# Jl S«wai4

TABIS 9 A.A.S. RBSULTS FOR FLAOIOCLASB

mol# % % M# _ Ba ppm _ Br imm m . OFS-1 4.88 6.24 738 57.5 W . 5 GPS-2 6.44 760 OPS-3 OFS-lf 5.42 f i U k 63.7 36.3

W - 4 6 4.66 708 1 0 9 67.4 32.6 î : n 467 *W 52.5 37.5 5.95 409 AS-49 5.02 m A8-50 1 : 1 1 É ! M i l AS-31 5.52 g ; 66.6 33.4

LOtf-4 6.68 3.22 322 78.3 2 1 .7 LOtf-12 6.00 3i75 364 7 3 .6 26*4 IOW-23 3.07 1870 282 79.8 20.2 LOtf-40 l : H 7 4 .3 25.7 LOW-42 6.08 I p l 7 0 .9 29.1 LOW-45 6.36 1850 7 5 .6 24.2 LOW-46 6.36 I960 7 9 .2 20.8 LOW-47 6.58 i .51 7 6 .3 23.5 LOW-48 6.17 I .00 7 2 .9 2 7 .1 LOW-49 6 .1 3 4.11 1716 7 2 .2 2 7 .8 LOW-50 6.06 4.58 1490 6 9 .6 3 0 .2 y»

TABUS 10 A.A.S. RBSULT3 FOR BIOTIIBS

Bniil» % K Bm mom &r nnm up pwi 0P8-1 6.07 4)6? 171 269 OPS-2 5.8? 4150 163 231 OPS-3 5.1) 4263 152 249 OPS-4 5.71 4038 161 252

AS-46 6.50 5240 31 335 AS-47 6.07 4874 42 jog AS-48 4.67 4175 60 226 AS-49 6.57 5700 52 338 AS-50 4.90 5361 55 259 AS-51 5.97 4243 45 309

&0V-4 7*51 3961 27 691 liOW-12 7.38 4260 23 609 UW -2 3 6 .6 0 4042 30 641 l0«r-40 6.66 4212 19 652 U3S-42 7.11 3981 32 670 lOW-4 5 6 .3 5 3960 25 665 162-46 6.15 4230 41 625 162-47 6.22 41)2 35 648 162-48 6.88 3420 39 564 162-49 6 .5 8 3832 24 612 161^50 6.44 3741 29 638 55

TABLE 11 ' WHOLE ROCK ANALYSES FOR B« AND Sr

Suroît Bft o»m_ sr Don OPS-1 3620 900 OFS-2 5505 810 AS-46 2050 510 AS-50 2130 540 AS-51 I960 485 LOW-46 1885 IOW-46 1770 ISS LCW-45 LOW-42 KM INTERPRETATION AND DISCUSSION 'OP ANALYTICAL RESULTS

Blfatnt»! B#hKvior in th# Alkmli P#ld#omM

Potmolum/Rubldlua R&tlo Th# analytleal data for tho oon oentration of potaioium end rubidium in the alkali feldepare for the Clayton Peak» Alta» and Little Cottonwood atook# la preaented graphically in Figure 11* Superinpoaed on the plot are daahed linea for apeoifie ratio# of l^Rb* The reaulta are quite aignifioant for it oan be readily aeen on thia plot that aa we proceed from the Clayton Peak to the Alta and to the Little Cottonwood atook# the known ohronologioal aequenee of intrusion# the K/Rb ratio falla from about 500 to 300* The K/Rb ratio of each of the alkali feldapar aeparataa ia given in Table 12. Thus in thia aequenoe Rb beoomea eonoentrated relative to K* Shaw (1968) haa ahown that rubidium ia expected to concentrate relative to potaaaium in the reaidual melt during magmatio fractionation and thereby produoe lower K/Rb ratioa. The regular trend ahown ia perhaps the atrongeat evidenoe found in thia study suggesting each of the atooka to be derived from a common deep seated parent magma, fractionally oryatalliaing with time* Thought to be a very significant finding for this study S6 57

500-

o ' ______

# # # * 300- • I --- \ g 200t - 300----

_ @=CM loof-Osicw h- #siCW ptwwcryit

J ...... I I t i I I ...... fis ICO io5 no rii K In IXripar, wt. p*f c«nt

Figura 11* Plot of potaaaium varsua rubidium for tha alkali faldapara* %

w*w*a>

I& *8gg33>:gS3$8 S S 9 , fSS-SRfl I J J é s é s DOOO ! S 3 S 9 â asaaassaass aaa 59 la tha raXatlva poaition of tha alkali faldapar phanooryata from tha Llttla Cottonwood quart* nonionlta on tha K-Rb plot* It la quita apparent that tha phanooryata ara dlatlnot from tha groundmaaa faldapara. Th* relative poaition of the phanooryata on tha plot auggaata thay graw not only aarllar than tha groundmaaa faldapar of tha Llttla Cottonwood atook, but aarllar than tha alkali faldapar of tha Alta atook as wall. Thia la provided, of coups*, thay ara In fact derived from a common magma.

Barium Barium can hardly ba oonaldarad a trace alamant in tha alkali faldapara from this study. In all thraa atooka tha alkali feldspars are oharmctarlsad by unusually high barium contents, aa compared to tha values glvan by Halar (1962). Tha groundmasa K-apar In tha Littl* Cottonwood atook contains about 0*5)1, tha Alta stock 0*5)1, and tha Clayton Peak atook about 1,7# Ba* In aaoh oasa tha barium axoaada tha oalolum* Th* ralatlonahlp of barium to mole percent Or In tha alkali faldapar la given In Figure 12. Hare It la seen that aa th* potassium content of th# alkali faldapara In- craaa## from Or^Q in th# Clayton Peak stock, through Oryy In tha Alta stock, to Crg2 In tha Little Cottonwood atook, tha barium content drops. It has baan pointed out aarllar that barium la known to ba prafarantlally captured by aarly 1 0

* ##

L _ | JL L 74 76 M o l % Or

Pigur* 12. Plot of ««l^t pozcsnt 'barlon vontis mol* percent Or for the elkali feldspars. 61 formed poteeh pheeee. Thle* at lemet in part, ia the ex* planatlon offered for the deoreaae obaerved here. Aa the alkali feldapar oryatalliaed In the parent magma it in- oremaingly depleted the reaidual melt in barium* In the previous section it waa shown that the orthoolaae phenocryata were different from the groundmasa orthoolaae of the Little Cottonwood atook by having a h l ^ e r f^Ab ratio* Prom Figure 12 it is apparent that the phenoorycta are diatlnot from the groundmasa by having a much higher barium content* The phenocryata have about 1*3^ Ba while the groundmasa orthoolaae haa about 0*3#, Beoauae barium is preferentially captured by early formed alkali feldapar and depleted in the reaidual melt, it ia suggested that the phenocryata grew much earlier than the groundmasa orthoolaae. It will be remembered an earlier time of oryetalliaatlon waa alao suggested by the k/Ab ratio, it ahould be noted from Figure 12 that the phenooiyat valuea plot between the valuea for the Clayton Peak and Alta atooka, indicating the phenocryata grew sometime after the intrusion of the Clayton Peak granodiorite, but before the intrusion of the Alta granodiorite. This same sequence of growth ia alao in* dioated by the K*Ab plot in Figure 11, Evidence for the degree of equilibrium achieved during cry#talliaatlon of the phenocryata la provided by the die* tribution of barium throughout the phenocryata* Successive points across sections of three phenocryata, in 0*3 mm steps from rim to center to rim, were analysed for barium 62 ty an electron mloroprobo. The roeulte of theee anelyeee are presented graphically In figures 13« 14# and 15* Although suooessive plots are somewhat Irregular# the trend is quite apparent. As we proceed from edge to edge# the barium content of each phenocryst first increases# reaches a maximum in the core and then decreases again aa we approach the opposite edge. It is thus suggested that these early formed feldspars began crystallising in a melt relatively high in barium# preferentially incorporating barium into their structure. As crystallisation proceeded# because of the preferential capture# barium became relatively depleted In the residual melt, with the later additions to the growing phenoorysts having less barium available for incorporation than the core material. In such a manner the phenoorysts grew and became elementally soned in barium and probably other elements yet undetermined. It should be noted here that the barium content of the cores is comparable with barium in the Clayton Peak stock alkali feldspar. This remnant soning gives conclusive evidence that elemental equilibrium was not achieved# at least for the barium# otherwise it would be homogeneously distributed. Although at the high temperatures of growth# it is likely that at least some attempt to homogenise was made in response to the activity gradient present. The main point is that the logarithmic distribution described by Neuman et al (1954) and Molntire (1963) is here believed M 1 8 L C W 45

W - • • •

a - I 1 i. i ■ ' ' i ■ ' ■ I ‘ ■ i ■ ’ ■ A ■ ■ il- ■ ‘ ■ A ‘ ■ Distonc», nun

Pigur* 13* Plot shoidng the distribution of bsrius morose en elkmli feldspar phenocryst from ssmple LCV-45 of the Little Cottonwood qumrt* monsonite porphyry*

. « Km U - LCW 46

U wt.X U9 Ko

TÏT Di*tonc«, m m

Fignr# 14. Plot showing the distritnition of barium a- cross an alkali feldspar phenocryst ffoa sample^ IÆ4-46,

0» l e w 50

1.4 W t . Z Bo

Figure 15» Plot showing the dietrlbutien of hmrlum ecross en elkmli feldspmr phenocryst from sample LCV-50* 66 to b# mppromohed. Whothor tho logmrlthmlo dlotribution hold# true for tho other olomont# !#• of oour##, unknown* It may bo that alnoo barium io oapturod Into potaaaium alto# in praforonoa to potaaaium itaalf * tha barium ion# ara vary tightly hold and hava aueh a high activation energy to ovareona to ohanga aitaa* that thay hava little thermodynamic motivation to move and honoganima* Slananta ■*admittad** to tha potaaaium aitaa, auoh a# rubidium* would probably hava amallar anargy barrier# preventing than from leaving their aita# and miitht on this account roach a greater degree of homoganiiation*

Barium/hubidium Ratio Taylor and Kaiar (i960) and Taylor {1965) have concluded that tha Ba/Rb ratio of alkali fald- •par provides a critical index of magmatio fractionation* This i# bacauaa Ba ha# a tandanoy to become depleted in a fractionating magma while Rb become# relatively concentrated * A plot of rubidium varsu# barium for tha alkali faldapara in the three atook# studied 1# given in Figure 16 , The plotted Ba/Rb ratio# are given in Table 1). Buperimposed on the plot is the Ba/Rb fractionation trend given by Taylor (1965)* the left portion of the curve was obtained by Taylor from pegmatio alkali faldapara* Tha plot# from this study* in the order Clayton Peak* Alta* little Cottonwood* follow the fraotionation trend perfectly* in the sequence of known •»8. at

I I I I I ml I I I I 11 III I I I I I ml I I I 1 Ml I 10 too 1000 10000 Ba in K-tpor, p p m

Figure 16* Plot of rubidium versus barium for the alkali feldspars* Ok 6S

TABUS 13 Ba/kb RATIO OP ALKABI FBLDSPAR SEPARATES

SZSE 0PS.1 OPS-2 OPS-3 OPS-4 &v#rag# 1 AS-46 16 A8-47 19 A8-48 A8-49 ÏÎ AS-50 16 AS-51 -4J- U W - 4 I0W*12 d IOW-23 8 LOW-40 8 LOW-42 8 L0W*45 6 LOW-46 10 LOW-47 9 LOW-48 LOW-49 Î LOW-50 mv#r#g# + LOW-45 phffnoosyst LOW-46 " LOW-50 ** 5? mvermge 69 Intrusion* Thus strong suggestion for m common psrsnt of the stocks is sgsln msds* It should be noted on Figure 16 thst the phenoorysts from the Little Cottonwood stock are distinct from the groundaass orthoolase* and their values plot between those for the Alta and Clayton Peak stocks.

Strontium The relative concentration of strontium in the alkali feldspars from each of the three stocks is shown plotted against mole percent Or in Figure 1?, The ground* mass orthoclase of the Little Cottonwood quarts monsonite contains approximately 200 ppm Sr and the orthoclase of the Alta granodiorite about 350 ppm. From the compilation of trace element data on feldspars given by Keier (1962) these values are typical. The relatively high value of 2200 ppm Sr for the alkali feldspar of the Clayton Peak stook, however* is somewhat rarer, with few analysed feld spars approaching this value. The large difference in values between the Clayton Peak granodiorite and the Alta granodiorite would suggest that if the two were derived from the same parent source* then the strontium became rapidly depleted in the melt before the intrusion of the Alta stock. This rapid depletion* followed by a more gentle decrease is reminiscent of a logarithmic type curve. From Neuman et al (1954) and MeIntire (1963)# this would be the expected behavior of an element in which g 1000-

74 76 M o t % Or

Figure 17* Flot of strontium versus noie percent Or for the mlkmli feldspars* o 71 (oono* In solld)/(eono« in n«lt) i n gr*mt«r thin unity* Strontium ii known to bo cipturod in tho alkili sito in proforonoo to potiooium in orthoolooo and it# oryitiXlisation in tho molt could loeount for tho Sr dooroast obaorvod* Kotoin piguro 17 that tho phonoopyata of orthoolaao in tho Littlo Cottonwood atook aro onriohod in atrontium rolativo to tho groundmaaa orthoolaao.

Qnloium In Piguro 16 tho oaloium oontont of tho alkali foldapara from tho throo intruaivoa la plettod againat nolo poroont Or. Unliko tho logarlthmio-llko bohmvior of 6a and Sr# oaloium dooroaaoa aomowhat moro linoarly* Althoui^ oaloium la oapturod Into tho alkali alto of orthoolaao* ita docroaao In abundanoa la duo aa wall to ita doplotion in tho molt by tho oryatalliiation of plagioolaao. Aa warn tho oaao for Rb, Ba, and Sr, tho phonooryata of orthoolaao in tho Littlo Cottonwood atook aro again dif* foront from tho groundmaaa orthoolaao by having a highor oaloium oontont. Thia auggoata thoy grow boforo tho groundmaaa. I 2 0 0 0 - o u CO D V

Figure 18* Flot of calcium versus mol# percent Or for the alkali feldspars* 73

Bl«w>nt«l Behavior In th« H m Io o Im »»

Strontium Pigur* 19 thorn that at mol# ptroant An da* optattt from Clayton Peak to Littl# Cottonwoodp atrontium alto dooroatot* Plagloolatt from th# Clayton Paak atook hat a fairly high atrontium laval# about 725 ppm» with tha valua of atrontium in plagioolata for tha tuooaading pluton» tha Alta atook# dropping to about 450 ppm# Strontium in plagioolata from tha Littla Cottonwood atook ovarlapt that from tha Alta atook but ganarally avaragat 360 ppm. A timilar daoraaaa warn alto notad for tha atrontium oontant of tha alkali faldapara. Togathar thaaa might indioata a logarithmic typa daplatlon of atrontium in tha parant magma# with latar formad faldapara having lata atrontium availabla to tham.

Barium An unaxpaotad faatura in tha diatribution of barium in tha plagioolaaaa from tha thraa atook# ia ahown in Figura 20. Barium inoraaaaa in tha ordar Clayton Paak granodiorita# Alta granodiorita# Littla Cottonwood quart# monaonita* This ia contrary to tha bahavlor of barium in alkali faldapar# which ahowa a daoraaaa in tha aama diraotion# and oontrary to tha whola rook abundanoa of barium# which also daoraaaa# in thia diraotion (Tabla 11). ?»

I a 700-

100-

W 20 30 io C o tn plogloclos*, mol por cont A n

Figura 19* Plot of atrontium varaua mol# paroant An for tha plagioolua faldapara* 75

2000 -

1500-

1000-

5 0 0 -

Co in plogiocloi*, mol por ctnt An

Figura 20, Plot of barium varaua mol# paroant An for tho plagioolaea faldapara* 76 If th# thr## b#di#t ar# related to a alngl# parent magma* then thie obaerved enrichment in plagioolaea muet be due to a change in the ability of the plagicolaae to incorporate barium* That ie* {Ba in plag*)/(Ba in melt) inoreaeee with fractionation, Keier (1962) has also suggested that barium inoreases In concentration in plagioolase with re spect to alkali feldspar during magmatio crystallisation* KCrringa and Noble (1971) have found for porphyritic volcanic rooks that the barium content of plagioolase phenoorysts increases with Increase in Ab content* with respect to the groundmass* indicating that as fractionation pro ceeds plagioolase can be expected to consume sn increasing proportion 6f the barium*

Partltlonln» of Barium lad Strontium Co,«litlng PlMloel— « Mid Orthoelm

t Barium It will be recalled that barium was found to be scned in the orthoclase phenoorysts of the Little Cotton wood quarts monsonite* This suggested that chemical equi librium was not achieved during crystallisation* but rather more closely approached the logarithmic* non equilibrium type of elemental distribution described by Neuman et al (195^> and Kclntire (1963), This type of 77 distribution would mmk# partitioning data vary inaeourata* Thus aarioua doubt la oaat upon tha following plot in Figura 21t which gives a graphic rsprasantation of tha partitioning data for barium. For instanoa# from tha texture of tha Clayton Paak granodiorita# It appears that plagioolase crystallised before tha Interstitial orthoclase. Comparing tha barium content of the plagioolase# about 330 ppm# with the barium content of the whole rock# which is taken here to be representative of the barium content Of tha melt# about 3600 ppm (Table 11)# it appears (Ba in plag, )/(Ba in melt) » 0*09* Thus barium was enriched in the residual melt by the crystallisation of plagioolase, When the field of alkali feldspar was finally reached during crystallisation# the melt was greatly anrlohed in barium. This lad to the high Ba oon* tent now observed in the alkali feldspar# about 1,8^* Here# incidentally# it is seen that (Ba in K^spar}/(Ba in melt) ■ 5# thus showing crystallisation markedly depleted the residual melt in barium. Tha outer rim of plagioolase which grew on the existing crystals shortly before the orystalllsaticn of orthoclase was no doubt# If this hypothesis is correct# forced to accommodate increasing amounts of barium due to ita in- ore as Ing abundance in the melt. Thus one might expect the plagioolase to be soned# with low barium cores and high barium rims. An electron mlcroprobe analysis would be needed to confirm this* Probably the only part of the 76

g 500-f

6 o In K-mpor, w t. p*r c*nt

Figura 21. Plot of barium in ooaxiating alkali and plagioolase faldspar. 79 plmgloolw# «tiioh 1# in «qiiilibrliia with orttioolut i# th* hypoth*slt*d high bmriim rimm, which aetiawlly co- oryctallitid wixh th# mlkmli fmldmpmr. Th* point h*r* ifl thmt m bulk mnmlymic of th* plmgioolma* probably giv*m a valu* for barium which ia lower than th* tru* *qui* librium value* In apit* of tha fact that th* partitioning valuta ob* tained ar* probably inaoourat* owing to non-equilibrium# th* plot of barium concentration in plagioolaao varaua barium in alkali faldapar ia informativ*# In th* Clayton Paak atook (Ba in K-apar)/(Ba in plag*) ■ 53# ahowing, at leaat qualitatively# that alkali faldapar la tha much praferrad hoat for barium* In th* Alta atook tha ratio haa baan reduced aharply to about 9*9# while th* barium oon tant of the whola rook haa gone from about ]600 to 2000 ppm* It ia aaan that the alkali faldapar undargoea over a three fold deoraaaa in barium# while plagioolaao inoraaaaa ita barium oontant by a factor of about 1*6. In accounting for thia relative change# part of it ia real# that plagioolaea ia able to take more barium into it# atruotura# and part oiroumatantial# beoauaa barium wâa enriched in tha Clayton Paak orthoolaaa by tha maohaniam explained* In tha Littla Cottonwood atook tha ratio of (Ba in K-apar)/(Ba in plag*) ia reduced to about 1*7# indicating that plagioolaao took an inoraaaing portion of tha total barium* Whola rook barium rangea from about 2000 ppm in th* Alta atook to about IflOO ppm in tha Littla 60 Cottonwood otookt In tho order Cloyton Peek. Alto, end Little Cottonwood, the generml trend le apperent, Aa the total. Whole rook, barium deoreaaee, plagioolaee ooneumed an Inoreaeing pro portion of the barium relative to alkali faldapar* Barth (1961) haa deduced that below about 250^C plagioolaao will contain a greater portion of the total barium than the alkali faldapar. Holer (1962) noted that, in a reatrioted itudy* the ratio (Ba in K-apar)/(Ba in plag.) aeemed to approach unity with decreaaing temperature.

Strontium Prom Table 11 it ia evident that total whole rook atrontium in the intruaivoa daoreaaed in the order Clayton Peak (650 ppm), Alta (520 ppm). Little Cotton wood (220 ppm). In the a erne order the ratio (Sr in K-apar)/ (Sr in plag.) daoreaaed from 2.97 to 0.82 to 0.61, indicating that plagioolaao beoame Increaalngly the pre ferred hoat of the atrontium upon differentiation* It ahould be kept in mind, however, from the logarithmic dia tribution behavior believed to have operated with barium, that too much faith oannot be put Into theae ratioa and that they are probably only qualitative. The ratio of (sr in plag.)/(Sr in rook) - 0.86 for the Clayton Peak atook, and from thia it ia believed that atrontium wma oonoentrated in the reaidual melt by initial cryatalliaation 61 of plmgioolM# and that thia glvaa a higher valua of atrontium in tha orthoolaaa than tha aqullihrium valua. Thia waa alao tha oaaa for barium. Tha dteraaaing ratio of (Sr in K*apar)/(Sr in plag.}. praaantad graphically in Figura 22. of aueoaaaiva atooka ia wall in accord with praaant viawa on atrontium bahavlor. It will ba raeallad from an aarllar diaouaaion that tha ratio la ganarally thought to daoraaaa with tamparatura. although thara la a great naad for additional data.

FotM.lun/HuDidliw Ratio of ±h. Blotlf.

Tmbl# 14 s It *. th# V R b rbtie for biotit# .«pMatoo from tha Olay ton Paak. Alta and Littla Cottonwood atocka. Tha ratio daoraaaaa in that order, aa waa tha oaaa for alkali faldapar. and indlcataa that Rb inoraaaad in coneantration ralativa to potaaaium. Thia ia tha axpaotad bahavlor for a diffarantiatlng magma.

It ahould ba notad from comparing tha K/Rh ratio of tha alkali faldapara in Tabla 12 with thair ooaxiating biotita oountarparta in Tabla I k that tha biotita ratioa ara lowar. Ihua it ia aaan that not only ara rubidium-potaaa ium fraotionatad ganarally in a oryatallising m a ^ . but ara alao fraotionatad by individual phaaaa diffarantly. 62

2000 -

£ 1 5 0 0 “

900 1000 1500 2000 Sr in K-fpor, ppm

V im irB 22* Plot of strontium In ootxlstlng mlksll ana plmgloolmss feldspar. B8BBBBBS888 I • LLLL i p i rrrffffffff m % £ £ > j S f r W N M @

% @ g M g w n o 3 5 ! 8 e a I n ü MM m m m m m MMMMMM MM 0>0«OOOMO OMO * n 84

Vl»u»lU»d 3»au«ne« ef Cwnt#

A v#ri#ty of «vldonoo h w b«#n profontod to oub- «tontiato that tha Olayton Paak granodiorita, Alta grano* diorita, and Littla Cottonwood quarta monaonita ara all ralatad to a aingla parent magma, differentiating with time. Tha avidanea haa takan tha form of traoe and minor elamant trends, relative ages of intrusion, variation in major element ohamistry, relation to local taotonio avants in tha area, and tha linaation of tha stocks along a large anti* olinal feature in their known ordar of intrusion. The following is an attempt to put together eaoh pièce of evidenoa to give tha vlsuaiitad sequence of events in ohronologioal ordar* 1) At some time during Mid to Lata Orataoeous time, tectonic forces, acting in a north-south diraotion* caused an east- west buckling of the orustal sedimentary rooks in the area and initiated the formation of tha Uinta arch* Con* temporanaoue with tha formation of tha arch was the generation of an intermediate mapia in the vicinity of tha arch. Prom tha h i ^ l ^ b ratios of the mineral separates, this maffna was somehow depleted in rubidium. The magma may hava baan generated from sediments by the heat derived from rising basalt, as suggested by Bardlay (1968), or perhaps the release of pressure along tha arch axis caused malting of sediments, In any event, once 65 g#n#r»ted, th* toagm* b*g#n to fraetionally eryatal* à lia*» beginning with th* oryatalliiation of plagloclaa** 2) During Lat* Or*tao*oua« th# aan* n irth-aouth taotonio fore** whioh formed th* Uinta aroh, alao oroatad th* firat of thr** new oompraaaional pulaea* Th*a* pulaea ar* recorded in th* aedimantary record of Parley* Ganyon aynoline* Since the intruaion of th* Olayton Peak granodiorit* occurred at about thia time, and allowing bob* leeway in iaotop* dating of th* atooka and the age determination of th* folded oonglomeratea# it ia thought that thia pula* acted upon the magma generated below the Uinta aroh and forced a portion of the differentiating melt up into th* relatively weak aroh aaia. Thia melt# brought into relatively cooler aedimantary roexa# began to oryatalliie. From the texture of the granodiorite# plagioolaea waa th* firat major phaae to oryatalliie# Ita oryatalliiation reaulted in barium# rubidium# and to a leaaer extent atrontium becoming relatively en riched in the reaidual melt. The amount* of barium and atrontium inoorporated into the plagioolaae atruotura were probably dlatributed logarithmically# with low oonoentrationa in the interior and relatively higher oonoentratlona outward# When alkali feldapar finally began to oryatalliie# it had been provided with a high barium# high atrontium environment in the melt# and beoame itaelf enriched in theae element*# Continued fractional oryatalliiation in th* parent magma reaulted in early 66 orystalXiiing plmgloolmm# oonotntrating bmrlum ttid •trontiiuQ her# me well. When the eryetmlllimtion field ef mlkmli feldepmr wme remohed thee# element#, in relmtive high ooneentrmtion, begin to be omptured into the mlkmli poeitione end be depleted in the reeiduml melt. Rubidium mleo began to be freotionmted, with reepeot to potmeelum, in the melt fraction, fieemuae the oonoentrmtion of theee element# in the reeiduml milt wme being reduced, the growing cry#tele could be expeoted to be xoned. It i# at thie point that the phenooryat# of the Little Cottonwood etook, being high in barium, atrontium# and K/Ab ratio, are thought to have grown and provide the evidenoe of the non^equilibrium, logarithmic type, diatribution during oryatmlliemtion. Continued oryetal* Illation led the reeiduml melt to beoome depleted in barium and atrontium and enriched in rubidium, 3) During Late Oretaeeoue to Early Paleooene the eaoond of the three pulaea occurred end, acting on the magma chamber, forced more melt into the overlying folded eedimentary rooke of the Cinta aroh# Whole rock anmlyeee ehow thia material to have a lower oonoentrmtion of barium and atrontium, owing to their capture by early alkali feld- epar# relative to the Olayton Peak# The lower level# of theee element# in the alkali feldapar alao refleot# the relative depletion. The alkali feldapar and biotita# ehow a lower V'Rb ratio# indicating rubidium to have become oonoentrated relative to potaaaium# Here plagio- 8? olMi b#omm* th# pr#f#rr#d ho#t for strontium r#l#tlv# to orthoolu#* Plsgioolss# slso gsln«d a largsr portion of th# barium with r#sp#ct to orthoolas#, 4) During Mid Pal#oo#n# th# third of th# thr## pul##s ocourrod* and again acting of th# parent magma, which by now was quit# silielo owing to fractional orystallliatlon, produced the intrusion of th# Little Cottonwood quarts monsonite* Whol# rook analyses show this stock to be •v#n more depleted in strontium and barium than the Alta stock, the alkali feldspars show lower strontium and barium and have a lower K/Rb ratio than th# Alta stock. Relative to the orthoclase, plagioolase consumed still a lairger proportion of th# total strontium and barium. Orthoclase phenoorysts formed early in the crystal lisation of the parent magma were included with the silicic melt. The mechanism for their inclusion is not yet understood. That they are chemically distinct from the groundmass orthoclase has been definitely established.

The distinction of the phenoorysts from the groundmass orthoolas# is perhaps the most interesting feature found in this study* They provide what is thought to be the strongest evidence for a common parent magma source for the Olayton Peak, Alta, and Little Cottonwood stocks* 88

BIBLIOGRAPHY

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Hall* A.* 1967* The distribution of oomo major and trao# olamanta in faldapara from tha Roaaaa and Ardara granit# complex##* Donegal* Ireland1 Oeoohim. #t Ooamoohim* Aota V. 31* p. 835-847. Hamil* B.M.* 1967* Trace element# in aooeaaory mapietite from Baa in and Range quart# nonaoniteai Univeraity of Utah Ph.D. thesia* 229 P* Heier* K*S.* and B.R. Taylor* 1959a* Dlatribution of 11* Ha* Ki Rb* Ca* Pb* and T1 in aouthem Norwegian pro- Cambrian alkali feldaparai oeoohlm. at Coamoohim* Aota* V. 1 5# p. 284, Heier* X.S.* and S.R. Taylor* 1959b* Dlatribution of Oa« Sr* and Ba in aouthem Norwegian pre-Cambrian alkali ' feldaparai Qeoohim. at Coamoohim# Aota# v# 17» p. 286 Heier* K.8.* 1962, Trace elements in feldapara-A review# Norak# Qeol# Tidaakr. v, 42* p. 415-454# Kerriok* D.M.* 1969* K-feldapar megacryata from a per# phyritio quarts monionlte* central Sierra Nevada* California# Amer# Mineral#, v# 54* p. 839-646. Korringa* M.K. # and D.C. Noble* 1971* Distribution of Sr and Ba between natural feldspar and igneous melt# Earth and Planetary Sol# Letters# v# 11* p# 147-151* Mo Intire* W.L.* 1963# Trace element partition coeffi- eienta-a review of theory and applications to geo logy t oeoohim# at Coamoohim# Aota* v. 27* p# 1209-1264# Naaaau# K## 1964# On the distribution of minor components during the formation of mineralst Amer# Mineral## V. 49# p. 321.325. Neumann# H.* J. MSad* and 0#J. Vltaliano* 1954* Trace element variation during fractional crystallisation as calculated from the dlatribution law# Oeoohim. at Coamoohim# Aota# v. 6* p# 98* Nockolds* S.R## 1966# The behavior of some elements during fractional oryatallisaticn of magma# Oeoohim# at Coamoohim# Aota* v#38# p# 267 -276 * Ringwood* A.B.* 1955# The principles governing traoe- element distribution during magmatie differentiation Part II Oeoohim# at Coamoohim# Acta# v# 7# p# 189-202# 91 * 8haw» D,M## 19^6 f A rwvlaw of K-Rb frootionotion tronds by oovarlanoo wiolyolii Gooohim, #t Ooomoohlm. Aota» T* 32» p« 373,601 $ Slawaon» tf$P$» 1938# l#ad in Potmiaiun faldapara from Baain and Rang# quarts monsonitaat Univareity of Utah Ph$D* thosia. Tmuaon» L$V$» 1963» Paotora in the dlatribution of the trace elements during the oryatallisatlon of magmas 1 Phys, and Ohem, Earth» v$ 6» p, 213,230$ Taylor» 3$R$» and K$S$ Heier» 1938» Alkali elements in potash feldspar from the pre-Cambrian of aouthem NorwayI Oeoohim# et Coamoohim# Aota» v$ 13» p# 293> Taylor» 3$R$» and K$S. Heier» 1958» Rubidium depletion in feldspars I Nature (London)» v. 162» p. 202$ Taylor» S$R$» and K.S. Heier» I960» The petrological aig- nifiosnoe of trace element variations in alkali feld spars# Report 21at Intern# Oeol# Oongr.» Norden» pt# 14» p$ 47# Taylor» S$R$» 1963» The application of trace element data to problems in petrology1 Phys# and Ohem# Barth» V# 6» p$ 133-213$ miittafcer» E$J$N$» 1967» Paotora affooting element ratios in the crystallisation of minerals 1 Oeoohim# et Coamo- chim# Acta» v# 3I» p$ 2273*2288#

Wilson» JiW#» 1961» Geology of the Alta stock# California Institute of Technology Ph,D# thesis» 236p#