Sedimentary Origin of Calcareous Intrusions in the ~1 Ga Oaxacan Complex, Southern Mexico: Tectonic Implications

International Geology Review Vol 46 2004 p 528ndash541Copyright copy 2004 by V H Winston amp Son Inc All rights reserved

0020-681404740528-14 $2500 528

Sedimentary Origin of Calcareous Intrusions in the ~1 GaOaxacan Complex Southern Mexico Tectonic Implications

J DOSTAL1

Department of Geology Saint Maryrsquos University Halifax Nova Scotia B3H 3C3 Canada

J D KEPPIE Instituto de Geologia Universidad Nacional Autonoma De Mexico 04510 Mexico DF Mexico

H MACDONALD Department of Geology Saint Maryrsquos University Halifax Nova Scotia B3H 3C3 Canada

AND F ORTEGA-GUTIEacuteRREZ

Instituto de Geologia Universidad Nacional Autonoma De Mexico 04510 Mexico DF Mexico

Abstract

Intrusive calcareous bodies marbles and calc-silicate rocks are a distinctive feature of the high-grade metamorphic suites of the ~1 Ga northern Oaxacan Complex They typically form dike-likeintrusions up to 4 m thick which cut across the surrounding high-grade granulite- and upper-amphibolite facies metamorphic rocks Various protoliths are possible for these carbonate bodies (1)sediments including evaporites (2) metasomatic skarns and (3) carbonatites An evaporitic pro-tolith is supported by the predominance of scapolite low abundances of incompatible trace elements(including Nb and rare-earth elements) relative to carbonatites and the presence of a sharp contactwith host rocks without a significant contact metamorphic aureole or fenitization It is inferred thatlimestones and related rocks were remobilized under granulite-facies conditions and intruded intothe host rocks The widespread distribution of such evaporites in the Oaxacan Complex is consistentwith deposition after the worldwide ~13 Ga oxygenation event that increased the marine sulfatereservoir Intrusion of rift-related plutons into the sediments at ~1157ndash1130 Ma provides a youngerlimit on the age of protholiths of the metamorphic suites Modern analogues for such evaporitesare rifts associated with passive margins (eg Red Sea) and active margins (eg Gulf of California)The presence of evaporites implies a paleolatitude of 10ndash35deg a conclusion consistent with a paleo-geographic provenence for the Oaxacan Complex adjacent to either Amazonia or eastern Laurentiain Rodinia reconstructions

Introduction

THE COMPOSITION OF metasedimentary rocks canprovide important clues to the provenance and tec-tonic settings of their deposition It is particularlyimportant in deciphering the origin of high-grademetamorphic rocks in Precambrian areas wheredeformation and metamorphism have destroyedmost of the features used to constrain their genesisSuch is the case for the calcareous rocks in the ~1Ga Oaxacan Complex of southern Mexico Two ori-gins have been proposed for these rocks (1) a sedi-mentary origin as part of an evaporite sequencedeposited in a passive-margin tectonic setting(Ortega-Gutieacuterrez 1984) and (2) an igneous origin

as carbonatites (Melgarejo and Prol-Ledesma1999) The rocks could also have originated throughmetasomatic processes The geochemical andmineralogical signatures and field relations of suchprocesses are distinctive To determine theserelations and constrain the origin of the Oaxacancalcareous rocks they were studied along the twohighways connecting Nochixtlan and Oaxaca insouthern Mexico (Figs 1ndash3)

Geological Setting

The Oaxacan calcareous rocks (containing 10 togt90 vol carbonates) have been subdividedaccording their modal composition by Ortega-Gutieacuterrez (1984) into marbles (gt 50 vol carbon-1Corresponding author email jardadostalstmarysca

OAXACAN COMPLEX MEXICO 529

ates) and calc-silicates (10ndash50 vol carbonates)They form concordant layers (lt200 m thick) anddiscordant bodies up to 4 m thick that are an inte-gral part of the high-grade metamorphic sequence(Ortega-Gutieacuterrez 1984) The discordant calcare-ous rocks are the dike-like intrusions which cutacross the surrounding metamorphic rocks Thesediscordant bodies are mostly marbles with xenolithsof calc-silicate andor host rocks whereas the con-cordant bodies are both calc-silicates and marbles

The calcareous bodies occur in the upperldquoparagneissrdquo thrust slice of the northern OaxacanComplex (Figs 2ndash3) This slice was intruded bywithin-plate ge1140 Ma charnockite and meta-syen-ite (Keppie et al 2003) before being involved in twotectonothermal events the ~1100 Ma Olmecanevent and the ~1005ndash980 Ma Zapotecan event(Solari et al 2003) The latter involved polyphasedeformation under granulite-facies metamorphicconditions (Solari et al 2003) Peak granulite-facies metamorphism reached 700degndash750degC and72ndash82 kbar (Mora et al 1986) The concordantcalcareous lenses contain Zapotecan foliations andfolds and although the discordant bodies cut acrossthese ductile structures they record the granulite-facies metamorphism indicating that the high-grademetamorphism outlasted the deformation Titaniteand phlogopite from these discordant calcareousbodies have yielded ages of 968 plusmn 9 Ma (concordantU-Pb age) and 945 plusmn 10 Ma (40Ar39Ar laser fusion

analyses) respectively which have been interpretedas dating cooling through 660ndash700degC and ~450degC(Keppie et al in press)

The host rocks range in compositions from maficto felsic The main mineral assemblages of most ofthe thrust slice are of granulite facies The assem-blages of the rocks are mostly anhydrous andinclude quartz plagioclase (commonly antiper-thitic) hypersthene clinopyroxene garnet alkalifeldspar (perthite and mesoperthite) opaque min-eral (ilmenite) and a variable amount of titaniferoushornblende and biotite Hydrous phases includinghornblende and biotite are in textural equilibriumwith the anhydrous minerals (Mora et al 1986) Inplaces the rocks are composed of mineral assem-blages containing biotite amphibole plagioclaseand opaques indicative of only upper amphibolite-faciesndashgrade metamorphism Phase equilibria werereported by Prakash et al (1991) for some of thesecalc-silicates with emphasis on the rare assemblageof wollastonite-quartz-graphite

Petrography and Mineral Chemistry

The calcareous rocks both marbles and calc-silicate rocks typically contain calcite diopsidescapolite and phlogopite as essential minerals withminor to accessory amounts of dolomite forsteritewollastonite pargasitic amphibole spinel garnettitanite sulfides Fe-Ti oxides clinozoisite and

FIG 1 Simplified geological map of Mexico with inset showing the location of Figure 2 Oaxaquia and its possibleextension is after Ortega-Gutieacuterrez et al (1995) TMVBndashTrans-Mexican volcanic belt MXndashMexico City

530 DOSTAL ET AL

humite minerals such as chondrodite Quartzplagioclase and alkali feldspar occur in variableamounts In addition accessory apatite vivianiteiron phosphate cancrinite and anhydrite (mostlypseudomorphed to gypsum) occur in some of theserocks Retrograde minerals include numeroushydrated phases such as chondrodite serpentinetalc brucite zoisiteclinozoisite epidote tremolitegypsum and Mg-Fe chlorite which indicate a highflux of water-rich fluids during retrogression

MarbleThe marble is white to light grey massive and

composed principally of equant calcite In additionto carbonates (gt50 vol) the marbles typically con-tain forsterite diopside phlogopite scapolite rareamphibole chondrodite spinel apatite sulfidestitanite quartz and feldspars (Tables 1 and 2) The

marble without dolomite also contains wollastoniteTexturally all of these minerals seem to represent anequilibrium assemblage

Carbonate minerals have a grain size typicallyranging between 02 and 1 mm and exceptionallyreaching up to 15 cm in diameter Dolomite typicallyaccounts for lt10 of the modal composition Cli-nopyroxene is slightly pleochroic light green diop-side (Table 1) which forms prismatic grains rangingin size from ~1 to 10 mm Olivine (~Fo92) partiallyserpentinized was found only in marbles Brownishpleochroic amphibole (Table 2) occurs in marbles inassociation with clinopyroxene Phlogopite (with low~1 wt TiO2) is present in some marbles as a majorconstituent (5ndash10 vol) Minerals present in minor toaccessory amounts include (1) spinel which occursonly in marbles with dolomite (2) chondrodite whichforms along the grain boundaries of the dolomite as an

FIG 2 Geological map of the northern Oaxacan Complex (modified after Solari et al 2003) showing the locations ofsampled calcareous intrusions


alteration feature (3) feldspars including calcic pla-gioclase nearly pure albite An2 and K-feldspar(Table 2) (4) scapolite and (5) titanite Rare anhy-drite mostly pseudomorphed to gypsum was likely intextural equilibrium with the other mineral phasesGrains of sulfides apatite and other phosphateminerals (probably vivianite and heterosite) occur intrace proportions

Calc-silicate rocksThe calc-silicate rocks are medium to coarse

grained (mostly lt ~2 mm in size) and consist pre-dominantly of a granoblastic-polygonal mineralassemblage composed of significant amounts ofdiopsidic clinopyroxene (~15ndash90 vol) and scapo-lite (up to 45 vol) Scapolite is Ca-rich with themeionite component ranging from 053 to 097 Thecontents of carbonates principally calcite arehighly variable averaging around 15 vol Theserocks may also contain graphite quartz plagioclasealkali feldspars (K-feldspar and albite) wollasto-nite hedenbergite andradite and phlogopite Incalc-silicate samples amphibole (magnesiohasting-site Table 2) typically occurs in association withscapolite Titanite is evenly distributed as an acces-

sory mineral but in some cases forms prismaticcrystals gt 25 cm in size Clinozoisite might reach upto 5 vol Apatite iron phosphate zircon Fe-Tioxides and sulfides are other accessory phases

Contact aureoleThe amphibole-biotite mafic gneisses that gener-

ally host the carbonates show a narrow typically lt5cm wide contact aureole The host gneisses aremedium grained (05ndash1 mm in size) composed pre-dominantly of brown amphibole biotite and plagio-clase (An~30) In the 2ndash3 cm wide contact zonesurrounding the cross-cutting carbonate intrusionsthe host gneisses were converted into fine-grainedrocks (typically 03ndash05 mm in grain size) contain-ing mainly plagioclase K-feldspar quartz stronglyaltered mafic minerals (chiefly biotite and clino-pyroxene) opaques and sulfides Mafic mineralswhich are less abundant than in the mafic gneisseswere replaced by a mixture of fibrous minerals andTi-magnetite

XenolithsXenoliths in the marble intrusions are typically

cms to dms in size and are composed of amphibole-

FIG 3 Structural section of the northern Oaxacan Complex (modified after Solari et al 2003) showing the locationof the sampled calcareous intrusions Symbols are the same as in Figure 2 AMCG = anorthosite-mangerite-charnockite-granite suite Huitzo El Catrin and El Marquez refer to three thrust sheets of the Oaxacan Complex (Solari et al 2003)

532 DOSTAL ET AL

biotite gneisses amphibole-clinopyroxene granu-lites and calc-silicate rocks Amphibole-biotitegneiss xenoliths are rimmed by a thin contact zonecomposed of plagioclase-clinopyroxene-biotiterock whereas the granulite xenoliths are sur-rounded by clinopyroxene-plagioclase-titanite rims

Analytical Methods

Samples were analyzed for major and some trace(Rb Sr Ba Zr Nb Y Cr Ni Sc V Ga and Zn)elements by X-ray fluorescence spectrometry at theRegional Geochemical Center at Saint Maryrsquos Uni-versity Halifax Nova Scotia The precision andaccuracy of the data have been reported by Dostal etal (1986) Representative samples were then cho-sen for analyses of rare-earth elements (REE) ThTa Nb and Hf (Table 3) by inductively coupledplasma-mass spectrometry (ICP-MS) at the Geo-science Laboratories of the Ontario Geological Sur-vey Precision and accuracy are given by Ayer andDavis (1997) and are generally within 5 Mineral

compositions were determined at the Department ofEarth Sciences of Dalhousie University (HalifaxNova Scotia) using a JEOL Superprobe 733 with awavelength-dispersive spectrometer and operatedwith a beam current of 15 kV at 5nA

Geochemistry

The calcareous rocks show a spectrum of mineraland element concentrations ranging from relativelypure marbles to calc-silicate rocks The two groupsof the Oaxacan calcareous rocks (marbles and calc-silicates) defined by Ortega-Gutieacuterrez (1984) aredistinct not only in modal proportions of forsteritediopside scapolite feldspars and carbonates butalso on the basis of their chemical compositions(Table 3)

MarblesThe marbles have high contents of CaO (gt30

wt) and loss on ignition (LOI) but low SiO2 (lt30wt) reflecting the dominance of calcite in these

TABLE 1 Representative Analyses of Minerals from the Calcareous Intrusions1

Clinopyroxene Olivine

Marble Calc-silicate Marble

Sample OX-5 OX-5 OX-50 OX-3 OX-3 OX-45 OX-45 OX-47

SiO2 (wt) 5319 5284 5157 5291 5288 4183 412 4075

TiO2 032 039 066 037 031

Al2O3 252 23 522 194 231

FeO 193 28 318 739 718 69 706 867

MnO 027 037 042

MgO 1645 1578 144 127 1335 5168 518 4986

CaO 2502 2481 2464 2414 2305

Na2O 038 046 074 061 073

Σ 9981 9938 10068 10006 10018 10041 10006 997

XMg 094 091 089 075 077 093 093 091

Wo 051 051 052 051 049

En 046 045 043 037 039

Fs 003 004 005 012 012

1End-member components Wo = wollastonite En = enstatite Fs = ferrosilite mineral compositions were determined using a JEOL Superprobe 733 at Dalhousie University (Halifax Nova Scotia) Data were reduced using ZAF corrections


TAB

LE 2

Rep

rese

ntat

ive

Ana

lyse

s of

Min

eral

s fr

om th

e C

alca

reou

s In

trus

ions

1

Spin

elPh

logo

pite

Am

phib

ole

Feld

spar

Scap

olite

Mar

ble

Mar

ble

Mar

ble

CS

Mar

ble

Mar

ble

CS

Sam

ple

OX

-45

OX

-45

OX

-5O

X-5

OX

-5LS

-53

OX

-7O

X-7

OX

-49

OX

-1LS

-62

SiO

2 (w

t)

410

040

89

441

643

76

627

863

82

688

950

10

502

1

TiO

21

251

101

051

38

Al 2O

369

24

686

013

60

136

513

67

152

919

05

188

419

85

250

025

34

FeO

665

652

252

238

258

153

MnO

MgO

232

322

80

245

124

64

179

419

73

CaO

128

713

13

035

132

513

37

Na 2O

041

038

207

223

075

024

103

45

775

81

K2O

104

110

33

196

201

156

516

30

093

089

BaO

106

ZnO

117

131

Cl

132

123

Σ10

029

992

393

70

933

796

30

990

699

29

992

099

43

963

796

85

XM

g0

860

860

950

950

930

96

Me

053

054

Or

093

098

Ab

007

002

098

An

002

1 Abb

revi

atio

ns C

S =

calc

-sili

cate

roc

k E

nd-m

embe

r co

mpo

nent

Or

= or

thoc

lase

Ab

= al

bite

An

= an

orth

ite M

e =

mei

onite

534 DOSTAL ET AL

TABLE 3 Representative Analyses of Calcareous Rocks from the Oaxaca Complex1

Marble Calc-silicate Gneiss

OX-45 OX-47 OX-49 OX-50 98-2-2 98-3-1 S-2-2 98-2-1 S-2-9 98-1-4 98-1-1

SiO2() 1198 784 753 1466 2620 4907 4456 5179 5014 5046 6876

TiO2 001 012 012 017 020 063 101 045 040 143 074

Al2O3 175 117 128 176 486 1248 1389 663 770 1712 1393

Fe2O3 338 111 105 149 272 741 440 434 798 985 471

MnO 019 016 014 010 013 017 012 034 020 014 006

MgO 1520 713 212 505 308 588 898 1175 916 649 073

CaO 3354 4424 4737 4417 3596 1413 2209 2192 2184 610 195

Na2O 038 025 001 033 099 224 077 159 141 390 251

K2O 101 042 033 098 164 193 105 029 033 258 557

P2O5 002 002 005 002 006 020 001 003 002 040 018

LOI 3370 3720 3920 3110 2358 612 346 152 126 170 128

Σ 10116 9966 9920 9983 9942 10026 10034 10065 10044 10017 10042

Cr (ppm) 19 9 13 25 4 117 32 14 27 115 10

Ni 16 3 4 6 4 21 19 3 6 97 7

V 10 17 24 28 42 107 141 80 80 183 80

Zn 246 23 41 34 57 127 56 165 217 139 44

Rb 4 12 8 5 50 59 52 7 9 90 80

Ba 29 50 89 50 653 742 84 28 25 506 1464

Sr 220 116 702 404 762 497 126 138 124 583 206

Ga 2 3 0 6 5 22 13 12 15 18 22

Ta 002 005 041 004 058 065 079 073 055 099 156

Nb 04 11 12 03 44 70 12 75 59 120 304

Hf 003 050 051 167 115 449 274 706 557 582 968

Zr 1 25 17 66 39 170 128 223 186 228 453

Y 40 14 22 56 27 34 7 12 15 31 32

Th 022 036 139 015 180 391 032 433 186 130 017

La 7564 808 2452 1022 3526 2434 623 557 903 2622 1764

Ce 1329 1473 3891 1895 5901 5342 1340 1378 2215 5705 3903

Pr 1470 197 503 2224 703 736 170 209 329 764 579

Nd 4940 801 1854 7747 2559 3121 665 857 1360 3171 2688

Sm 783 174 322 1288 444 658 131 199 310 665 633

Eu 120 041 080 174 117 228 046 048 055 217 470

Gd 667 202 306 1083 384 616 112 188 266 635 646

Tb 098 030 047 153 058 093 017 032 042 095 096

Dy 585 185 275 921 355 548 107 197 249 566 578

Ho 125 039 057 186 074 111 022 044 050 111 117

Er 359 122 177 531 208 327 060 127 147 321 329

Tm 052 016 024 077 031 048 008 021 023 048 048

Yb 337 104 145 476 194 309 050 154 196 290 324

Lu 056 016 022 072 032 055 006 030 036 042 050

1Sample 98-1-1 = host rock at the contact with discordant carbonate intrusion 98-1-4 = host rock ~5 cm away from the con-tact and from sample 98-1-1


rocks As with most carbonate rocks CaO correlatesnegatively with SiO2 and Al2O3 suggesting that therocks are admixtures of carbonate and silicate com-ponents Correlations between modal abundances ofminerals and chemical compositions are in agree-ment with observations of other carbonate rocks(eg Condie et al 1991 Rock et al 1987) whichshow that most major and trace elements are con-tained in non-carbonate chiefly silicate phases The

marbles are poor in iron with respect to magnesiumand MgOFeO ratios display a negative correlationwith SiO2 The rocks also have a wide range of theMgCa ratio from 001 to 09 reflecting changes inthe proportions of dolomite and Mg-rich silicatesrelative to calcite Titanium Zr and REE are vari-able and Ti shows a positive correlation with ZrThe varying concentrations of these elements mayindicate an irregular distribution of heavy minerals

FIG 4 Chondrite-normalized rare-earth element abundances in calcareous intrusions and related rocks Normalizingvalues after Sun and McDonough (1989) A Marbles B Calc-silicate rocks C Host rocks 98-1-4 (~5 cm away fromthe contact) and 98-1-1 (at the contact) Carbonatite from Oka Complex (USGS geochemical reference standard rockCOQ-1) is shown for comparison

536 DOSTAL ET AL

in the original protolith A wide range of SrY ratios(4ndash35) in the marbles supports the important role ofaccessory phases in the distribution of trace ele-ments in these rocks The chondrite-normalizedREE patterns of the marbles (Fig 4) are similarthey are light REE-enriched have a relatively flatheavy REE segment with (GdYb)n between 16 and19 The absolute concentrations are variable withLan ranging between 24 and 310 times chondrites (Fig4) Some patterns exhibit Eu anomalies

The abundances of some critical elements in theOaxacan marbles and calc-silicate rocks normalizedto an average Phanerozoic marine limestone ofCondie et al (1991) are shown in Figure 5 Asequence of elements in the graph is arrangedaccording to increasing concentrations in the aver-age Oaxacan marble In general the Oaxacan mar-bles resemble Phanerozoic limestones Relative to

average Phanerozoic marine limestone the ele-ments Ni through Rb are depleted while Sr throughLa are progressively enriched in the marble (Fig 5)The pattern is also similar to those of other marblesfrom high-grade terranes including those of the Pre-cambrian Lewisian marbles (Fig 5) from Scotland(Rock et al 1987) which are of sedimentary originThe patterns differ however from those of carbon-atites which are distinctly enriched in Nb Sr andREE (Fig 5)

Calc-silicate rocksThe chemical composition of the calc-silicate

rocks reflects an admixture of carbonate and silicatecomponents Compared with the marbles theycontain a significantly higher proportion of silicatecomponents and higher concentrations of oxides ofmost major elements including SiO2 Al2O3 FeOtot

FIG 5 Normalized element distributions in (A) average marble (ldquomarblerdquo average of six samples) and average calc-silicate rock (ldquocalc-silicaterdquo average of four samples) from the Oaxacan Complex B Carbonatite from the Oka Complex(USGS geochemical reference standard rock COQ-1) and average of Lewisian marble (Rock et al 1987) are shown forcomprison Normalizing values for average Phanerozoic marine limestone are from Condie et al (1991) and are as follows(in wt) MnO = 0084 Fe2O3 (total) = 054 Al2O3 = 10 TiO2 = 02 (in ppm) Rb = 20 Cr = 15 Ni = 15 Y = 5 Zr =20 Eu = 02 La = 5 Ba = 85 Sr = 400 Nb = 15


TiO2 Na2O but lower CaO (Table 3) Higher con-centrations of some trace elements in the average ofthe Oaxacan calc-silicate rocks compared tothe marbles and Phanerozoic limestones (Fig 5)confirm the presence of these elements mainly insilicates Negative anomalies of Mn and Sr in thepatterns of the calc-silicates indicate that theseelements occur chiefly in carbonates The chon-drite-normalized REE patterns of the calc-silicaterocks show an enrichment of light REE but arehighly variable in their shapes (Fig 4) They alsohave variable REE concentrations with Lan ~5ndash90but in general lower than those of marbles Inas-much as metamorphic minerals are similar in bothcalc-silicates and marbles it appears that the differ-ences in REE patterns were inherited from the pro-tholiths which compositionally are similar to thoseof sedimentary rocks (Taylor and McLennan 1985)The REE patterns resemble patterns of various clas-tic sedimentary rocks (Lentz 2003)

Contact aureole

The host rocks at the immediate contact with thecarbonate intrusions have significantly higher con-tents of SiO2 K2O Ba Zr Hf Nb and Ta but arelower in Al2O3 FeOtot MgO MnO CaO Na2OTiO2 Sr Th Cr Ni Zn and light REE than the hostrocks farther away from the contact (Table 3) TheREE pattern of the contact rock (98-1-1) is similarto those of the gneiss but also shows a positive Euanomaly (Fig 4) consistent with the enrichment ofsecondary feldspars observed in the contact rocksHowever the rocks at a distance of about 5 cm fromthe contact (98-1-4) do not show an Eu anomaly

Discussion

Various hypotheses have been invoked to explainthe origin of calcareous rocks in high-grade meta-morphic terranes They include derivation from (1)metasomatic calcareous skarns (2) carbonatitesand (3) metamorphosed sediments includingevaporites The available data for the Oaxacan car-bonates are now evaluated in the context of thesedifferent hypotheses

Skarn origin

This hypothesis essentially assumes that calc-silicate rocks and impure marbles were produced bymetasomatic introduction of silica and otherelements into pure carbonate rocks Metasomaticcalcareous skarns are granoblastic rocks that gener-

ally occur at or near an intrusive igneous body andare typically characterized by the presence of calc-silicate minerals such as wollastonite garnet(andradite or grossularite) epidote and vesuvian-tite with or without calcite (Blatt and Tracy 1996Easton 1995 Lentz 1998) In the Oaxacan Com-plex the absence of associated intrusive bodies andthe absence of zonations in the calcareous bodiesare inconsistent with a skarn genesis The intrusiveand crosscutting nature of some of the calcareousbodies and the relatively sharp contacts betweenthe calcareous intrusions and host rocks are alsoincompatible with metasomatism

Carbonatite origin

Melgarejo and Prol-Ledesma (1999) suggestedthat the calcareous bodies may be carbonatite intru-sions Several features are consistent with thismodel (1) their intrusive nature and (2) their post-peak of metamorphism emplacement However car-bonatite intrusions are typically characterized by(1) extensive fenitization of the surrounding rocksmarked by K-metasomatism (2) an unusual miner-alogy including monazite perovskite scapoliteapatite and zircon and (3) very high contents ofREE as well as highly fractionated patterns (Fig 4)and high-field-strength elements (HFSE) particu-larly Nb (Wall and Mariano 1996 Wyllie et al1996 Hornig-Kjarsgaard 1998) The Oaxacan cal-careous bodies differ from carbonatites in havinglow contents of HFSE and REE (Fig 5) Fenitizationis absent in the host rocks and several key mineralsof carbonatites such as perovskite zircon bariteand magnetite are absent or present only in traceamounts

Sedimentary origin

This model postulates that the intrusive calcare-ous rocks are isochemically metamorphosed lime-stones and related rocks remobilized undergranulite facies and intruded into the host rocks(Ortega-Gutieacuterrez 1984) However a questionarises about the nature of the protholith The car-bonates could be either marine limestones or a partof an evaporite sequence

The Oaxacan calcareous bodies differ fromPhanerozoic marine limestones (Taylor and McLen-nan 1985) due to the presence of significantamounts of scapolite (Cl and Na rich) alkali-richminerals including alkali feldspar and phlogopiteand Mg-rich minerals such as clinopyroxene for-sterite dolomite and phlogopite These features

538 DOSTAL ET AL

particularly the presence of scapolite (Moine et al1981 Tysdal and Desborough 1997) suggest anevaporite precursor Elevated concentrations ofchlorine alkalis calcium magnesium and sulfurare principal characteristics of sedimentary rocksassociated with evaporites (Moine et al 1981) Infact Ortega-Gutieacuterrez (1984) suggested that therocks are metamorphosed carbonates from anevaporite sequence that originally formed in apassive-margin environment

Evaporites are produced by the extensive if notcomplete evaporation of water from saline solutionsPrecipitated minerals include calcite dolomitehalite sulfates (gypsum and anhydrite) and boraxInasmuch as high-grade metamorphism destroysmost of the evaporite minerals scapolite and otherminerals containing Na Cl S F and B (Hietanen1967 Serdyuchenko 1975) such as tourmaline

(Abraham et al 1972) alkali feldspars and Mg-rich carbonates have been used as indicators inher-ited from ancient evaporite piles High abundanceof meionitic scapolite dolomite phlogopite albiteand K-feldspar in the Oaxacan carbonate bodiessupports this genesis The marialitic nature of thescapolite minerals implies the presence of Cl andNa in the system Albite K-feldspar phlogopite andcancrinite contain elevated concentrations of alka-lis whereas dolomite forsterite clinopyroxene andamphibole are rich in Mg and sulfides are rich in SOn the other hand tourmaline which is also consid-ered to be an important indicator of the evaporiteprecursor is absent in Oaxacan rocks As boratesare some of the last minerals to precipitate from seawater it is possible that the evaporites associatedwith these rocks never reached the stage of precipi-tating borates An alternative explanation for the

FIG 6 1100 Ma reconstruction of Rodinia showing the location of Oaxaquia Mexico as part of a 1 Ga belt on themargin of Amazonia (modified after Keppie et al 2003) Note that carbonates in Oaxaquia lie between 10deg and 35degSwhich are the limits for the formation of Phanerozoic evaporites The barbed line is a subduction zone with triangles onthe upper slab


absence of tourmaline in the Oaxacan Complex maybe thermal instability of the tourmaline under thelow water pressures characteristic of granulitefacies Boron if originally present probablymigrated with the fluid and melt phases to lower-temperature and wetter zones of the orogen Lowcontents of boron may also indicate that the sourceof the Oaxacan carbonate rocks was non-granitic

The marbles were probably derived from impurelimestones and evaporites whereas the protholith ofcalc-silicate rocks were calcareous sediments withhigher contents of silicates The common presenceof spinel may indicate some silica-poor bauxiticcomponent in the clay fraction and thus probablyhighly weathered source rocks

Conclusions

Based on the evidence presented here it is con-cluded that the carbonate rocks of the OaxacanComplex best fit the model of an evaporite-lime-stone precursor (Ortega-Gutieacuterrez 1984) Precam-brian evaporites became widespread after the ~13Ga limited oxygenation event which increased themarine sulfate reservoir (Kah et al 2001) Thistogether with the intrusion of rift-related plutonsinto the sediments at ~1157ndash1130 Ma (Keppie etal 2003) brackets deposition of the Oaxacan sedi-ments between ~13 and 116 Ga

In the Phanerozoic evaporites generally occurbetween 10deg and 35deg (McKerrow et al 1992) Sim-ilar paleolatitudinal constraints appear to apply to~13ndash10 Ga evaporites which have been recorded(1) in the 13ndash115 Ga evaporites at Balmat in theAdirondack Lowlands (Whelan et al 1990) (2) inthe 12 Ga carbonate-evaporite of Baffin and BylotIslands (Kah et al 2001) (3) at McArthur River inAustralia (Williams and Ray 1974) (4) at Outo-kumpo in Finland (Makela 1974) and (5) in the~11 Ga Upper Roan Group in Zambia (Strauss1993) The Oaxacan evaporites would also lie withinthese paleolatitudes if Oaxaquia is placed neareither Amazonia or eastern Laurentia in ~1 Gareconstructions of Rodinia (Fig 6 eg Keppie etal 2003) The apparent absence of similar-agedevaporites in Siberia (Bartley et al 2001) may sup-port the hypothesis of Sears and Price (2000) thatRodinia lay off western Laurentia at 1 Ga

Evaporites are typically found in rifts associatedwith passive margins such as the Red Sea and riftsassociated with active margins such as the Gulf of

California and intra-arc rifts and backarc basinsPotentially correlative ~13ndash115 Ga metasedi-ments in the southern Oaxacan Complex are associ-ated with arc volcanic rocks (Keppie et al 2001)and the ~1157ndash1130 Ma rift-related plutons thatmay have been intruded during associated rifting(Keppie et al 2003)

Acknowledgments

Funding for various aspects of this project wasprovided by CONACyT grants (0255P-T9506 and25705-T) PAPIIT grants (IN116999 and IN10799)to JDK and FOG and a NSERC Discovery grant toJD We are grateful to AK Chatterjee for enlighten-ing discussions and Drs Brian Fryer and JohnGreenough for their constructive reviews

REFERENCES

Abraham K Mielke H and Povondra P 1972 On theenrichment of tourmaline in metamorphic sediments ofthe Arzberg Series NE Bavaria Neues Jahrbuch furMineralogie Monatshefte v 5 p 14

Ayer J A and Davis D W 1997 Neoarchean evolutionof differing convergent margin assemblages in theWabigoon Subprovince Geochemical and geochrono-logical evidence from the Lake of the Woods green-stone belt Superior Province northwestern OntarioPrecambrian Research v 8 p 155ndash178

Bartley J K Kaufman A J Semikhatov M A KnollA H Pope M C and Jacobsen S B 2001 Globalevents across the MesoproterozoicndashNeoproterozoicboundary C and Sr isotopic evidence from SiberiaPrecambrian Research v 111 p 165ndash202

Blatt H and Tracy R J 1996 Petrology Igneous sedi-mentary and metamorphic San Francisco CA W HFreeman and Company 529 p

Condie K C Wilks M Rosen DM and Zlobin V L1991 Geochemistry of metasediments from the Pre-cambrian Hapschan Series eastern Anabar ShieldSiberia Precambrian Research v 50 p 37ndash47

Dostal J Baragar W R A and Dupuy C 1986 Petro-genesis of the Natkusiak continental basalts VictoriaIsland NWT Canadian Journal of Earth Sciences v23 p 622ndash632

Easton R M 1995 Regional geochemical variation inGrenvillian carbonate rocks Implications for mineralexploration in Summary of field work and other activ-ities 1995 Ontario Geological Survey MiscellaneousPaper 164 p 6ndash18

Hietanen A 1967 Scapolite in the Belt Series in St JoendashClearwater region Idaho Geological Society of Amer-ica Special Paper 86 1ndash56

540 DOSTAL ET AL

Hornig-Kjarsgaard I 1998 Rare earth elements insovitic carbonatites and their mineral phases Journalof Petrology v 39 p 2105ndash2120

Kah L C Lyons T W and Chelsey J T 2001Geochemistry of a 12 Ga carbonate-evaporite succes-sion northern Baffin and Bylot Islands Implicationsfor Mesoproterozoic marine evolution PrecambrianResearch v 111 p 203ndash234

Keppie J D Dostal J Cameron K L Solari L AOrtega-Gutieacuterrez F and Lopez R 2003 Geochro-nology and geochemistry of Grenvillian igneous suitesin the northern Oaxacan Complex southern MeacutexicoTectonic implications Precambrian Research v 120p 365ndash389

Keppie J D Dostal J Ortega-Gutierrez F and LopezR 2001 A Grenvillian arc on the margin of Amazo-nia Evidence from the southern Oaxacan Complexsouthern Mexico Precambrian Research v 112 p165ndash181

Keppie J D Solari L A Ortega-Gutieacuterrez F Ortega-Rivera A Lee J W K and Hames W E in pressU-Pb and 40Ar39Ar constraints on the cooling historyof the northern Oaxacan Complex southern MexicoTectonic implications in Tollo R P CorriveauL McLelland J B and Bartholemew G eds Prot-erozoic tectonic evolution of the Grenville Orogenin North America Geological Society of AmericaMemoir

Lentz D R 1998 Mineralized intrusion-related skarnsystems Mineralogical Association of Canada ShortCourse 26 664 p

______ 2003 Geochemistry of sediments and sedimen-tary rocks evolutionary considerations to mineraldeposit-forming environments Geological Associationof Canada Geotext 4 184 p

Makela M 1974 A study of sulfur isotopes in the Outo-kumpo ore deposit Finland Geological Survey of Fin-land Bulletin 267 45 p

McKerrow W S Scotese C R and Brasier M D 1992Early Cambrian continental reconstructions JournalGeological Society of London v 149 p 599ndash606

Melgarejo J C and Prol-Ledesma R M 1999 Th andREE deposits in the Oaxaca Complex in southernMexico in Stanley C J Mineral deposits Processesto precessing Rotterdam Netherlands Balkema p389ndash392

Moine B Sauvan P and Jarousse J 1981 Geochemis-try of evaporite-bearing series A tentative guide forthe identification of metaevaporites Contributions toMineralogy and Petrology v 76 p 401ndash412

Mora C I Valley J W and Ortega-Gutieacuterrez F 1986The temperature and pressure conditions of Grenville-age granulite-facies metamorphism of the OaxacanComplex southern Meacutexico Revista del Instituto Mex-icano del Petroleo v 5 p 222ndash242

Ortega-Gutieacuterrez F 1984 Evidence of Precambrianevaporites in the Oaxacan granulite complex of south-ern Meacutexico Precambrian Research v 23 p 377ndash393

Ortega-Gutieacuterrez F Ruiz J and Centeno-Garcia E1995 Oaxaquia a Proterozoic microcontinentaccreted to North America during the late PaleozoicGeology v 23 p 1127ndash1130

Prakash G O Murillo M G Grajales N J M TorresV R and Bosh G P 1991 A rare wollastonite-quartz-graphite assemblage from a high-grade regionalmetamorphic terrain of late Precambrian age in Oax-aca Mexico Revista del Instituto Mexicano del Petro-leo v 13 p 5ndash13

Rock N M S Davis A E Hutchison D Joseph Mand Smith T K 1987 The geochemistry of Lewisianmarbles in Park R G and Tarney J eds Evolutionof the Lewisian and comparable Precambrian highgrade terrains Geological Society (London) SpecialPublication 27 p 109ndash126

Sears J W and Price R A 2000 New look at the Sibe-rian connection No SWEAT Geology v 28 p 423-426

Serdyuchenko D P 1975 Some scapolite-bearing rocksevolved from evaporites Lithos v 8 p 1ndash7

Solari L A Keppie J D Ortega-Gutieacuterrez F CameronK L Lopez R and Hames W E 2003 990 Ma and1100 Ma Grenvillian tectonothermal events in thenorthern Oaxacan Complex southern Mexico Roots ofan orogen Tectonophysics v 365 p 257ndash282

Strauss H 1993 The sulfur isotopic record of Precam-brian sulfates New data and a critical evaluation of theexisting record Precambrian Research v 63 p 225ndash246

Sun S S and McDonough W F 1989 Chemical andisotopic systematics of oceanic basalts Implicationsfor mantle composition and processes in SaundersA D and Norry M J Magmatism in the oceanbasins Geological Society (London) Special Publica-tion 42 p 313ndash345

Taylor S R and McLennan S M 1985 The continentalcrust Its composition and evolution Oxford UKBlackwell Scientific 328 p

Tysdal R G and Desborough G A 1997 Scapoliticmetaevaporite and carbonate rocks of Proterozoic Yel-lowjacket Formation Moyer Creek Salmon RiverMountains central Idaho US Department of the Inte-rior U S Geological Survey Open File Report 97-268

Wall F and Mariano A N 1996 Rare earth minerals incarbonatites A discussion centred on Kangankundecarbonatites Malawi in Jones A P Wall F andWilliams C T eds Rare earth minerals Chemistryorigin and ore deposits London UK Chapman andHall p 193ndash225

Whelan J F Rye R O deLorraine W and OhmototH 1990 Isotopic geochemistry of a mid-Proterozoic


evaporite basin American Journal of Science v 290p 396ndash424

Williams N and Ray D M 1974 Alternative interpre-tation of sulphur isotope ratios in the McAuthur lead-zinc-silver deposit Nature v 247 p 535ndash537

Wyllie P J Jones A P and Deng J 1996 Rare earthelements in carbonate-rich melts from mantle to crustin Jones A P Wall F and Williams C T eds Rareearth minerals Chemistry origin and ore depositsLondon UK Chapman and Hall p 77ndash103


ates) and calc-silicates (10ndash50 vol carbonates)They form concordant layers (lt200 m thick) anddiscordant bodies up to 4 m thick that are an inte-gral part of the high-grade metamorphic sequence(Ortega-Gutieacuterrez 1984) The discordant calcare-ous rocks are the dike-like intrusions which cutacross the surrounding metamorphic rocks Thesediscordant bodies are mostly marbles with xenolithsof calc-silicate andor host rocks whereas the con-cordant bodies are both calc-silicates and marbles

The calcareous bodies occur in the upperldquoparagneissrdquo thrust slice of the northern OaxacanComplex (Figs 2ndash3) This slice was intruded bywithin-plate ge1140 Ma charnockite and meta-syen-ite (Keppie et al 2003) before being involved in twotectonothermal events the ~1100 Ma Olmecanevent and the ~1005ndash980 Ma Zapotecan event(Solari et al 2003) The latter involved polyphasedeformation under granulite-facies metamorphicconditions (Solari et al 2003) Peak granulite-facies metamorphism reached 700degndash750degC and72ndash82 kbar (Mora et al 1986) The concordantcalcareous lenses contain Zapotecan foliations andfolds and although the discordant bodies cut acrossthese ductile structures they record the granulite-facies metamorphism indicating that the high-grademetamorphism outlasted the deformation Titaniteand phlogopite from these discordant calcareousbodies have yielded ages of 968 plusmn 9 Ma (concordantU-Pb age) and 945 plusmn 10 Ma (40Ar39Ar laser fusion

analyses) respectively which have been interpretedas dating cooling through 660ndash700degC and ~450degC(Keppie et al in press)

The host rocks range in compositions from maficto felsic The main mineral assemblages of most ofthe thrust slice are of granulite facies The assem-blages of the rocks are mostly anhydrous andinclude quartz plagioclase (commonly antiper-thitic) hypersthene clinopyroxene garnet alkalifeldspar (perthite and mesoperthite) opaque min-eral (ilmenite) and a variable amount of titaniferoushornblende and biotite Hydrous phases includinghornblende and biotite are in textural equilibriumwith the anhydrous minerals (Mora et al 1986) Inplaces the rocks are composed of mineral assem-blages containing biotite amphibole plagioclaseand opaques indicative of only upper amphibolite-faciesndashgrade metamorphism Phase equilibria werereported by Prakash et al (1991) for some of thesecalc-silicates with emphasis on the rare assemblageof wollastonite-quartz-graphite

Petrography and Mineral Chemistry

The calcareous rocks both marbles and calc-silicate rocks typically contain calcite diopsidescapolite and phlogopite as essential minerals withminor to accessory amounts of dolomite forsteritewollastonite pargasitic amphibole spinel garnettitanite sulfides Fe-Ti oxides clinozoisite and

FIG 1 Simplified geological map of Mexico with inset showing the location of Figure 2 Oaxaquia and its possibleextension is after Ortega-Gutieacuterrez et al (1995) TMVBndashTrans-Mexican volcanic belt MXndashMexico City

530 DOSTAL ET AL

















532 DOSTAL ET AL


Analytical Methods



Geochemistry








SiO2 (wt) 5319 5284 5157 5291 5288 4183 412 4075

TiO2 032 039 066 037 031

Al2O3 252 23 522 194 231

FeO 193 28 318 739 718 69 706 867

MnO 027 037 042

MgO 1645 1578 144 127 1335 5168 518 4986

CaO 2502 2481 2464 2414 2305

Na2O 038 046 074 061 073

Σ 9981 9938 10068 10006 10018 10041 10006 997

XMg 094 091 089 075 077 093 093 091

Wo 051 051 052 051 049

En 046 045 043 037 039

Fs 003 004 005 012 012



TAB

LE 2

Rep

rese

ntat

ive

Ana

lyse

s of

Min

eral

s fr

om th

e C

alca

reou

s In

trus

ions

1

Spin

elPh

logo

pite

Am

phib

ole

Feld

spar

Scap

olite

Mar

ble

Mar

ble

Mar

ble

CS

Mar

ble

Mar

ble

CS

Sam

ple

OX

-45

OX

-45

OX

-5O

X-5

OX

-5LS

-53

OX

-7O

X-7

OX

-49

OX

-1LS

-62

SiO

2 (w

t)

410

040

89

441

643

76

627

863

82

688

950

10

502

1

TiO

21

251

101

051

38

Al 2O

369

24

686

013

60

136

513

67

152

919

05

188

419

85

250

025

34

FeO

665

652

252

238

258

153

MnO

MgO

232

322

80

245

124

64

179

419

73

CaO

128

713

13

035

132

513

37

Na 2O

041

038

207

223

075

024

103

45

775

81

K2O

104

110

33

196

201

156

516

30

093

089

BaO

106

ZnO

117

131

Cl

132

123

Σ10

029

992

393

70

933

796

30

990

699

29

992

099

43

963

796

85

XM

g0

860

860

950

950

930

96

Me

053

054

Or

093

098

Ab

007

002

098

An

002

1 Abb

revi

atio

ns C

S =

calc

-sili

cate

roc

k E

nd-m

embe

r co

mpo

nent

Or

= or

thoc

lase

Ab

= al

bite

An

= an

orth

ite M

e =

mei

onite

534 DOSTAL ET AL



OX-45 OX-47 OX-49 OX-50 98-2-2 98-3-1 S-2-2 98-2-1 S-2-9 98-1-4 98-1-1

SiO2() 1198 784 753 1466 2620 4907 4456 5179 5014 5046 6876

TiO2 001 012 012 017 020 063 101 045 040 143 074

Al2O3 175 117 128 176 486 1248 1389 663 770 1712 1393

Fe2O3 338 111 105 149 272 741 440 434 798 985 471

MnO 019 016 014 010 013 017 012 034 020 014 006

MgO 1520 713 212 505 308 588 898 1175 916 649 073

CaO 3354 4424 4737 4417 3596 1413 2209 2192 2184 610 195

Na2O 038 025 001 033 099 224 077 159 141 390 251

K2O 101 042 033 098 164 193 105 029 033 258 557

P2O5 002 002 005 002 006 020 001 003 002 040 018

LOI 3370 3720 3920 3110 2358 612 346 152 126 170 128

Σ 10116 9966 9920 9983 9942 10026 10034 10065 10044 10017 10042

Cr (ppm) 19 9 13 25 4 117 32 14 27 115 10

Ni 16 3 4 6 4 21 19 3 6 97 7

V 10 17 24 28 42 107 141 80 80 183 80

Zn 246 23 41 34 57 127 56 165 217 139 44

Rb 4 12 8 5 50 59 52 7 9 90 80

Ba 29 50 89 50 653 742 84 28 25 506 1464

Sr 220 116 702 404 762 497 126 138 124 583 206

Ga 2 3 0 6 5 22 13 12 15 18 22

Ta 002 005 041 004 058 065 079 073 055 099 156

Nb 04 11 12 03 44 70 12 75 59 120 304

Hf 003 050 051 167 115 449 274 706 557 582 968

Zr 1 25 17 66 39 170 128 223 186 228 453

Y 40 14 22 56 27 34 7 12 15 31 32

Th 022 036 139 015 180 391 032 433 186 130 017

La 7564 808 2452 1022 3526 2434 623 557 903 2622 1764

Ce 1329 1473 3891 1895 5901 5342 1340 1378 2215 5705 3903

Pr 1470 197 503 2224 703 736 170 209 329 764 579

Nd 4940 801 1854 7747 2559 3121 665 857 1360 3171 2688

Sm 783 174 322 1288 444 658 131 199 310 665 633

Eu 120 041 080 174 117 228 046 048 055 217 470

Gd 667 202 306 1083 384 616 112 188 266 635 646

Tb 098 030 047 153 058 093 017 032 042 095 096

Dy 585 185 275 921 355 548 107 197 249 566 578

Ho 125 039 057 186 074 111 022 044 050 111 117

Er 359 122 177 531 208 327 060 127 147 321 329

Tm 052 016 024 077 031 048 008 021 023 048 048

Yb 337 104 145 476 194 309 050 154 196 290 324

Lu 056 016 022 072 032 055 006 030 036 042 050






536 DOSTAL ET AL









Contact aureole


Discussion


Skarn origin



Carbonatite origin


Sedimentary origin



538 DOSTAL ET AL








Conclusions





Acknowledgments


REFERENCES









540 DOSTAL ET AL






























530 DOSTAL ET AL

















532 DOSTAL ET AL


Analytical Methods



Geochemistry








SiO2 (wt) 5319 5284 5157 5291 5288 4183 412 4075

TiO2 032 039 066 037 031

Al2O3 252 23 522 194 231

FeO 193 28 318 739 718 69 706 867

MnO 027 037 042

MgO 1645 1578 144 127 1335 5168 518 4986

CaO 2502 2481 2464 2414 2305

Na2O 038 046 074 061 073

Σ 9981 9938 10068 10006 10018 10041 10006 997

XMg 094 091 089 075 077 093 093 091

Wo 051 051 052 051 049

En 046 045 043 037 039

Fs 003 004 005 012 012



TAB

LE 2

Rep

rese

ntat

ive

Ana

lyse

s of

Min

eral

s fr

om th

e C

alca

reou

s In

trus

ions

1

Spin

elPh

logo

pite

Am

phib

ole

Feld

spar

Scap

olite

Mar

ble

Mar

ble

Mar

ble

CS

Mar

ble

Mar

ble

CS

Sam

ple

OX

-45

OX

-45

OX

-5O

X-5

OX

-5LS

-53

OX

-7O

X-7

OX

-49

OX

-1LS

-62

SiO

2 (w

t)

410

040

89

441

643

76

627

863

82

688

950

10

502

1

TiO

21

251

101

051

38

Al 2O

369

24

686

013

60

136

513

67

152

919

05

188

419

85

250

025

34

FeO

665

652

252

238

258

153

MnO

MgO

232

322

80

245

124

64

179

419

73

CaO

128

713

13

035

132

513

37

Na 2O

041

038

207

223

075

024

103

45

775

81

K2O

104

110

33

196

201

156

516

30

093

089

BaO

106

ZnO

117

131

Cl

132

123

Σ10

029

992

393

70

933

796

30

990

699

29

992

099

43

963

796

85

XM

g0

860

860

950

950

930

96

Me

053

054

Or

093

098

Ab

007

002

098

An

002

1 Abb

revi

atio

ns C

S =

calc

-sili

cate

roc

k E

nd-m

embe

r co

mpo

nent

Or

= or

thoc

lase

Ab

= al

bite

An

= an

orth

ite M

e =

mei

onite

534 DOSTAL ET AL



OX-45 OX-47 OX-49 OX-50 98-2-2 98-3-1 S-2-2 98-2-1 S-2-9 98-1-4 98-1-1

SiO2() 1198 784 753 1466 2620 4907 4456 5179 5014 5046 6876

TiO2 001 012 012 017 020 063 101 045 040 143 074

Al2O3 175 117 128 176 486 1248 1389 663 770 1712 1393

Fe2O3 338 111 105 149 272 741 440 434 798 985 471

MnO 019 016 014 010 013 017 012 034 020 014 006

MgO 1520 713 212 505 308 588 898 1175 916 649 073

CaO 3354 4424 4737 4417 3596 1413 2209 2192 2184 610 195

Na2O 038 025 001 033 099 224 077 159 141 390 251

K2O 101 042 033 098 164 193 105 029 033 258 557

P2O5 002 002 005 002 006 020 001 003 002 040 018

LOI 3370 3720 3920 3110 2358 612 346 152 126 170 128

Σ 10116 9966 9920 9983 9942 10026 10034 10065 10044 10017 10042

Cr (ppm) 19 9 13 25 4 117 32 14 27 115 10

Ni 16 3 4 6 4 21 19 3 6 97 7

V 10 17 24 28 42 107 141 80 80 183 80

Zn 246 23 41 34 57 127 56 165 217 139 44

Rb 4 12 8 5 50 59 52 7 9 90 80

Ba 29 50 89 50 653 742 84 28 25 506 1464

Sr 220 116 702 404 762 497 126 138 124 583 206

Ga 2 3 0 6 5 22 13 12 15 18 22

Ta 002 005 041 004 058 065 079 073 055 099 156

Nb 04 11 12 03 44 70 12 75 59 120 304

Hf 003 050 051 167 115 449 274 706 557 582 968

Zr 1 25 17 66 39 170 128 223 186 228 453

Y 40 14 22 56 27 34 7 12 15 31 32

Th 022 036 139 015 180 391 032 433 186 130 017

La 7564 808 2452 1022 3526 2434 623 557 903 2622 1764

Ce 1329 1473 3891 1895 5901 5342 1340 1378 2215 5705 3903

Pr 1470 197 503 2224 703 736 170 209 329 764 579

Nd 4940 801 1854 7747 2559 3121 665 857 1360 3171 2688

Sm 783 174 322 1288 444 658 131 199 310 665 633

Eu 120 041 080 174 117 228 046 048 055 217 470

Gd 667 202 306 1083 384 616 112 188 266 635 646

Tb 098 030 047 153 058 093 017 032 042 095 096

Dy 585 185 275 921 355 548 107 197 249 566 578

Ho 125 039 057 186 074 111 022 044 050 111 117

Er 359 122 177 531 208 327 060 127 147 321 329

Tm 052 016 024 077 031 048 008 021 023 048 048

Yb 337 104 145 476 194 309 050 154 196 290 324

Lu 056 016 022 072 032 055 006 030 036 042 050






536 DOSTAL ET AL









Contact aureole


Discussion


Skarn origin



Carbonatite origin


Sedimentary origin



538 DOSTAL ET AL








Conclusions





Acknowledgments


REFERENCES









540 DOSTAL ET AL








































532 DOSTAL ET AL


Analytical Methods



Geochemistry








SiO2 (wt) 5319 5284 5157 5291 5288 4183 412 4075

TiO2 032 039 066 037 031

Al2O3 252 23 522 194 231

FeO 193 28 318 739 718 69 706 867

MnO 027 037 042

MgO 1645 1578 144 127 1335 5168 518 4986

CaO 2502 2481 2464 2414 2305

Na2O 038 046 074 061 073

Σ 9981 9938 10068 10006 10018 10041 10006 997

XMg 094 091 089 075 077 093 093 091

Wo 051 051 052 051 049

En 046 045 043 037 039

Fs 003 004 005 012 012



TAB

LE 2

Rep

rese

ntat

ive

Ana

lyse

s of

Min

eral

s fr

om th

e C

alca

reou

s In

trus

ions

1

Spin

elPh

logo

pite

Am

phib

ole

Feld

spar

Scap

olite

Mar

ble

Mar

ble

Mar

ble

CS

Mar

ble

Mar

ble

CS

Sam

ple

OX

-45

OX

-45

OX

-5O

X-5

OX

-5LS

-53

OX

-7O

X-7

OX

-49

OX

-1LS

-62

SiO

2 (w

t)

410

040

89

441

643

76

627

863

82

688

950

10

502

1

TiO

21

251

101

051

38

Al 2O

369

24

686

013

60

136

513

67

152

919

05

188

419

85

250

025

34

FeO

665

652

252

238

258

153

MnO

MgO

232

322

80

245

124

64

179

419

73

CaO

128

713

13

035

132

513

37

Na 2O

041

038

207

223

075

024

103

45

775

81

K2O

104

110

33

196

201

156

516

30

093

089

BaO

106

ZnO

117

131

Cl

132

123

Σ10

029

992

393

70

933

796

30

990

699

29

992

099

43

963

796

85

XM

g0

860

860

950

950

930

96

Me

053

054

Or

093

098

Ab

007

002

098

An

002

1 Abb

revi

atio

ns C

S =

calc

-sili

cate

roc

k E

nd-m

embe

r co

mpo

nent

Or

= or

thoc

lase

Ab

= al

bite

An

= an

orth

ite M

e =

mei

onite

534 DOSTAL ET AL



OX-45 OX-47 OX-49 OX-50 98-2-2 98-3-1 S-2-2 98-2-1 S-2-9 98-1-4 98-1-1

SiO2() 1198 784 753 1466 2620 4907 4456 5179 5014 5046 6876

TiO2 001 012 012 017 020 063 101 045 040 143 074

Al2O3 175 117 128 176 486 1248 1389 663 770 1712 1393

Fe2O3 338 111 105 149 272 741 440 434 798 985 471

MnO 019 016 014 010 013 017 012 034 020 014 006

MgO 1520 713 212 505 308 588 898 1175 916 649 073

CaO 3354 4424 4737 4417 3596 1413 2209 2192 2184 610 195

Na2O 038 025 001 033 099 224 077 159 141 390 251

K2O 101 042 033 098 164 193 105 029 033 258 557

P2O5 002 002 005 002 006 020 001 003 002 040 018

LOI 3370 3720 3920 3110 2358 612 346 152 126 170 128

Σ 10116 9966 9920 9983 9942 10026 10034 10065 10044 10017 10042

Cr (ppm) 19 9 13 25 4 117 32 14 27 115 10

Ni 16 3 4 6 4 21 19 3 6 97 7

V 10 17 24 28 42 107 141 80 80 183 80

Zn 246 23 41 34 57 127 56 165 217 139 44

Rb 4 12 8 5 50 59 52 7 9 90 80

Ba 29 50 89 50 653 742 84 28 25 506 1464

Sr 220 116 702 404 762 497 126 138 124 583 206

Ga 2 3 0 6 5 22 13 12 15 18 22

Ta 002 005 041 004 058 065 079 073 055 099 156

Nb 04 11 12 03 44 70 12 75 59 120 304

Hf 003 050 051 167 115 449 274 706 557 582 968

Zr 1 25 17 66 39 170 128 223 186 228 453

Y 40 14 22 56 27 34 7 12 15 31 32

Th 022 036 139 015 180 391 032 433 186 130 017

La 7564 808 2452 1022 3526 2434 623 557 903 2622 1764

Ce 1329 1473 3891 1895 5901 5342 1340 1378 2215 5705 3903

Pr 1470 197 503 2224 703 736 170 209 329 764 579

Nd 4940 801 1854 7747 2559 3121 665 857 1360 3171 2688

Sm 783 174 322 1288 444 658 131 199 310 665 633

Eu 120 041 080 174 117 228 046 048 055 217 470

Gd 667 202 306 1083 384 616 112 188 266 635 646

Tb 098 030 047 153 058 093 017 032 042 095 096

Dy 585 185 275 921 355 548 107 197 249 566 578

Ho 125 039 057 186 074 111 022 044 050 111 117

Er 359 122 177 531 208 327 060 127 147 321 329

Tm 052 016 024 077 031 048 008 021 023 048 048

Yb 337 104 145 476 194 309 050 154 196 290 324

Lu 056 016 022 072 032 055 006 030 036 042 050






536 DOSTAL ET AL









Contact aureole


Discussion


Skarn origin



Carbonatite origin


Sedimentary origin



538 DOSTAL ET AL








Conclusions





Acknowledgments


REFERENCES









540 DOSTAL ET AL






























532 DOSTAL ET AL


Analytical Methods



Geochemistry








SiO2 (wt) 5319 5284 5157 5291 5288 4183 412 4075

TiO2 032 039 066 037 031

Al2O3 252 23 522 194 231

FeO 193 28 318 739 718 69 706 867

MnO 027 037 042

MgO 1645 1578 144 127 1335 5168 518 4986

CaO 2502 2481 2464 2414 2305

Na2O 038 046 074 061 073

Σ 9981 9938 10068 10006 10018 10041 10006 997

XMg 094 091 089 075 077 093 093 091

Wo 051 051 052 051 049

En 046 045 043 037 039

Fs 003 004 005 012 012



TAB

LE 2

Rep

rese

ntat

ive

Ana

lyse

s of

Min

eral

s fr

om th

e C

alca

reou

s In

trus

ions

1

Spin

elPh

logo

pite

Am

phib

ole

Feld

spar

Scap

olite

Mar

ble

Mar

ble

Mar

ble

CS

Mar

ble

Mar

ble

CS

Sam

ple

OX

-45

OX

-45

OX

-5O

X-5

OX

-5LS

-53

OX

-7O

X-7

OX

-49

OX

-1LS

-62

SiO

2 (w

t)

410

040

89

441

643

76

627

863

82

688

950

10

502

1

TiO

21

251

101

051

38

Al 2O

369

24

686

013

60

136

513

67

152

919

05

188

419

85

250

025

34

FeO

665

652

252

238

258

153

MnO

MgO

232

322

80

245

124

64

179

419

73

CaO

128

713

13

035

132

513

37

Na 2O

041

038

207

223

075

024

103

45

775

81

K2O

104

110

33

196

201

156

516

30

093

089

BaO

106

ZnO

117

131

Cl

132

123

Σ10

029

992

393

70

933

796

30

990

699

29

992

099

43

963

796

85

XM

g0

860

860

950

950

930

96

Me

053

054

Or

093

098

Ab

007

002

098

An

002

1 Abb

revi

atio

ns C

S =

calc

-sili

cate

roc

k E

nd-m

embe

r co

mpo

nent

Or

= or

thoc

lase

Ab

= al

bite

An

= an

orth

ite M

e =

mei

onite

534 DOSTAL ET AL



OX-45 OX-47 OX-49 OX-50 98-2-2 98-3-1 S-2-2 98-2-1 S-2-9 98-1-4 98-1-1

SiO2() 1198 784 753 1466 2620 4907 4456 5179 5014 5046 6876

TiO2 001 012 012 017 020 063 101 045 040 143 074

Al2O3 175 117 128 176 486 1248 1389 663 770 1712 1393

Fe2O3 338 111 105 149 272 741 440 434 798 985 471

MnO 019 016 014 010 013 017 012 034 020 014 006

MgO 1520 713 212 505 308 588 898 1175 916 649 073

CaO 3354 4424 4737 4417 3596 1413 2209 2192 2184 610 195

Na2O 038 025 001 033 099 224 077 159 141 390 251

K2O 101 042 033 098 164 193 105 029 033 258 557

P2O5 002 002 005 002 006 020 001 003 002 040 018

LOI 3370 3720 3920 3110 2358 612 346 152 126 170 128

Σ 10116 9966 9920 9983 9942 10026 10034 10065 10044 10017 10042

Cr (ppm) 19 9 13 25 4 117 32 14 27 115 10

Ni 16 3 4 6 4 21 19 3 6 97 7

V 10 17 24 28 42 107 141 80 80 183 80

Zn 246 23 41 34 57 127 56 165 217 139 44

Rb 4 12 8 5 50 59 52 7 9 90 80

Ba 29 50 89 50 653 742 84 28 25 506 1464

Sr 220 116 702 404 762 497 126 138 124 583 206

Ga 2 3 0 6 5 22 13 12 15 18 22

Ta 002 005 041 004 058 065 079 073 055 099 156

Nb 04 11 12 03 44 70 12 75 59 120 304

Hf 003 050 051 167 115 449 274 706 557 582 968

Zr 1 25 17 66 39 170 128 223 186 228 453

Y 40 14 22 56 27 34 7 12 15 31 32

Th 022 036 139 015 180 391 032 433 186 130 017

La 7564 808 2452 1022 3526 2434 623 557 903 2622 1764

Ce 1329 1473 3891 1895 5901 5342 1340 1378 2215 5705 3903

Pr 1470 197 503 2224 703 736 170 209 329 764 579

Nd 4940 801 1854 7747 2559 3121 665 857 1360 3171 2688

Sm 783 174 322 1288 444 658 131 199 310 665 633

Eu 120 041 080 174 117 228 046 048 055 217 470

Gd 667 202 306 1083 384 616 112 188 266 635 646

Tb 098 030 047 153 058 093 017 032 042 095 096

Dy 585 185 275 921 355 548 107 197 249 566 578

Ho 125 039 057 186 074 111 022 044 050 111 117

Er 359 122 177 531 208 327 060 127 147 321 329

Tm 052 016 024 077 031 048 008 021 023 048 048

Yb 337 104 145 476 194 309 050 154 196 290 324

Lu 056 016 022 072 032 055 006 030 036 042 050






536 DOSTAL ET AL









Contact aureole


Discussion


Skarn origin



Carbonatite origin


Sedimentary origin



538 DOSTAL ET AL








Conclusions





Acknowledgments


REFERENCES









540 DOSTAL ET AL































TAB

LE 2

Rep

rese

ntat

ive

Ana

lyse

s of

Min

eral

s fr

om th

e C

alca

reou

s In

trus

ions

1

Spin

elPh

logo

pite

Am

phib

ole

Feld

spar

Scap

olite

Mar

ble

Mar

ble

Mar

ble

CS

Mar

ble

Mar

ble

CS

Sam

ple

OX

-45

OX

-45

OX

-5O

X-5

OX

-5LS

-53

OX

-7O

X-7

OX

-49

OX

-1LS

-62

SiO

2 (w

t)

410

040

89

441

643

76

627

863

82

688

950

10

502

1

TiO

21

251

101

051

38

Al 2O

369

24

686

013

60

136

513

67

152

919

05

188

419

85

250

025

34

FeO

665

652

252

238

258

153

MnO

MgO

232

322

80

245

124

64

179

419

73

CaO

128

713

13

035

132

513

37

Na 2O

041

038

207

223

075

024

103

45

775

81

K2O

104

110

33

196

201

156

516

30

093

089

BaO

106

ZnO

117

131

Cl

132

123

Σ10

029

992

393

70

933

796

30

990

699

29

992

099

43

963

796

85

XM

g0

860

860

950

950

930

96

Me

053

054

Or

093

098

Ab

007

002

098

An

002

1 Abb

revi

atio

ns C

S =

calc

-sili

cate

roc

k E

nd-m

embe

r co

mpo

nent

Or

= or

thoc

lase

Ab

= al

bite

An

= an

orth

ite M

e =

mei

onite

534 DOSTAL ET AL



OX-45 OX-47 OX-49 OX-50 98-2-2 98-3-1 S-2-2 98-2-1 S-2-9 98-1-4 98-1-1

SiO2() 1198 784 753 1466 2620 4907 4456 5179 5014 5046 6876

TiO2 001 012 012 017 020 063 101 045 040 143 074

Al2O3 175 117 128 176 486 1248 1389 663 770 1712 1393

Fe2O3 338 111 105 149 272 741 440 434 798 985 471

MnO 019 016 014 010 013 017 012 034 020 014 006

MgO 1520 713 212 505 308 588 898 1175 916 649 073

CaO 3354 4424 4737 4417 3596 1413 2209 2192 2184 610 195

Na2O 038 025 001 033 099 224 077 159 141 390 251

K2O 101 042 033 098 164 193 105 029 033 258 557

P2O5 002 002 005 002 006 020 001 003 002 040 018

LOI 3370 3720 3920 3110 2358 612 346 152 126 170 128

Σ 10116 9966 9920 9983 9942 10026 10034 10065 10044 10017 10042

Cr (ppm) 19 9 13 25 4 117 32 14 27 115 10

Ni 16 3 4 6 4 21 19 3 6 97 7

V 10 17 24 28 42 107 141 80 80 183 80

Zn 246 23 41 34 57 127 56 165 217 139 44

Rb 4 12 8 5 50 59 52 7 9 90 80

Ba 29 50 89 50 653 742 84 28 25 506 1464

Sr 220 116 702 404 762 497 126 138 124 583 206

Ga 2 3 0 6 5 22 13 12 15 18 22

Ta 002 005 041 004 058 065 079 073 055 099 156

Nb 04 11 12 03 44 70 12 75 59 120 304

Hf 003 050 051 167 115 449 274 706 557 582 968

Zr 1 25 17 66 39 170 128 223 186 228 453

Y 40 14 22 56 27 34 7 12 15 31 32

Th 022 036 139 015 180 391 032 433 186 130 017

La 7564 808 2452 1022 3526 2434 623 557 903 2622 1764

Ce 1329 1473 3891 1895 5901 5342 1340 1378 2215 5705 3903

Pr 1470 197 503 2224 703 736 170 209 329 764 579

Nd 4940 801 1854 7747 2559 3121 665 857 1360 3171 2688

Sm 783 174 322 1288 444 658 131 199 310 665 633

Eu 120 041 080 174 117 228 046 048 055 217 470

Gd 667 202 306 1083 384 616 112 188 266 635 646

Tb 098 030 047 153 058 093 017 032 042 095 096

Dy 585 185 275 921 355 548 107 197 249 566 578

Ho 125 039 057 186 074 111 022 044 050 111 117

Er 359 122 177 531 208 327 060 127 147 321 329

Tm 052 016 024 077 031 048 008 021 023 048 048

Yb 337 104 145 476 194 309 050 154 196 290 324

Lu 056 016 022 072 032 055 006 030 036 042 050






536 DOSTAL ET AL









Contact aureole


Discussion


Skarn origin



Carbonatite origin


Sedimentary origin



538 DOSTAL ET AL








Conclusions





Acknowledgments


REFERENCES









540 DOSTAL ET AL






























534 DOSTAL ET AL



OX-45 OX-47 OX-49 OX-50 98-2-2 98-3-1 S-2-2 98-2-1 S-2-9 98-1-4 98-1-1

SiO2() 1198 784 753 1466 2620 4907 4456 5179 5014 5046 6876

TiO2 001 012 012 017 020 063 101 045 040 143 074

Al2O3 175 117 128 176 486 1248 1389 663 770 1712 1393

Fe2O3 338 111 105 149 272 741 440 434 798 985 471

MnO 019 016 014 010 013 017 012 034 020 014 006

MgO 1520 713 212 505 308 588 898 1175 916 649 073

CaO 3354 4424 4737 4417 3596 1413 2209 2192 2184 610 195

Na2O 038 025 001 033 099 224 077 159 141 390 251

K2O 101 042 033 098 164 193 105 029 033 258 557

P2O5 002 002 005 002 006 020 001 003 002 040 018

LOI 3370 3720 3920 3110 2358 612 346 152 126 170 128

Σ 10116 9966 9920 9983 9942 10026 10034 10065 10044 10017 10042

Cr (ppm) 19 9 13 25 4 117 32 14 27 115 10

Ni 16 3 4 6 4 21 19 3 6 97 7

V 10 17 24 28 42 107 141 80 80 183 80

Zn 246 23 41 34 57 127 56 165 217 139 44

Rb 4 12 8 5 50 59 52 7 9 90 80

Ba 29 50 89 50 653 742 84 28 25 506 1464

Sr 220 116 702 404 762 497 126 138 124 583 206

Ga 2 3 0 6 5 22 13 12 15 18 22

Ta 002 005 041 004 058 065 079 073 055 099 156

Nb 04 11 12 03 44 70 12 75 59 120 304

Hf 003 050 051 167 115 449 274 706 557 582 968

Zr 1 25 17 66 39 170 128 223 186 228 453

Y 40 14 22 56 27 34 7 12 15 31 32

Th 022 036 139 015 180 391 032 433 186 130 017

La 7564 808 2452 1022 3526 2434 623 557 903 2622 1764

Ce 1329 1473 3891 1895 5901 5342 1340 1378 2215 5705 3903

Pr 1470 197 503 2224 703 736 170 209 329 764 579

Nd 4940 801 1854 7747 2559 3121 665 857 1360 3171 2688

Sm 783 174 322 1288 444 658 131 199 310 665 633

Eu 120 041 080 174 117 228 046 048 055 217 470

Gd 667 202 306 1083 384 616 112 188 266 635 646

Tb 098 030 047 153 058 093 017 032 042 095 096

Dy 585 185 275 921 355 548 107 197 249 566 578

Ho 125 039 057 186 074 111 022 044 050 111 117

Er 359 122 177 531 208 327 060 127 147 321 329

Tm 052 016 024 077 031 048 008 021 023 048 048

Yb 337 104 145 476 194 309 050 154 196 290 324

Lu 056 016 022 072 032 055 006 030 036 042 050






536 DOSTAL ET AL









Contact aureole


Discussion


Skarn origin



Carbonatite origin


Sedimentary origin



538 DOSTAL ET AL








Conclusions





Acknowledgments


REFERENCES









540 DOSTAL ET AL


































536 DOSTAL ET AL









Contact aureole


Discussion


Skarn origin



Carbonatite origin


Sedimentary origin



538 DOSTAL ET AL








Conclusions





Acknowledgments


REFERENCES









540 DOSTAL ET AL






























536 DOSTAL ET AL









Contact aureole


Discussion


Skarn origin



Carbonatite origin


Sedimentary origin



538 DOSTAL ET AL








Conclusions





Acknowledgments


REFERENCES









540 DOSTAL ET AL
































Contact aureole


Discussion


Skarn origin



Carbonatite origin


Sedimentary origin



538 DOSTAL ET AL








Conclusions





Acknowledgments


REFERENCES









540 DOSTAL ET AL






























538 DOSTAL ET AL








Conclusions





Acknowledgments


REFERENCES









540 DOSTAL ET AL

































Conclusions





Acknowledgments


REFERENCES









540 DOSTAL ET AL






























540 DOSTAL ET AL


































Documents

Sedimentary Origin of Calcareous Intrusions in the ~1 Ga Oaxacan Complex, Southern Mexico: Tectonic Implications