Paulo, Rua doLago562,05508-080, São Paulo, Brazil. tuto de Geociências (GMG-IGc), Universidade de São 97187, Luleå, Sweden. Technology,tal Engineering, Luleå University of SE Geosciences andEnvironmen sources, Divisionof Avenida 80# 65-223, 050034,Medellín, Colombia. Facultad de Minas, Universidad Nacionalde Colombia, lona, Spain. ket 251, 9410, Ushuaia, Tierra del Fuego,ket 251,9410,Ushuaia,Tierra Argentina. versidad del Fuego-CONICET, de Tierra Fueguia Bas license(https://creativecommons.org/licenses/by-nc-sa/4.0/) is anopenaccess article undertheCCBY-NC-SAThis Universidad Nacional Autónoma de México. Peer Reviewing under the responsibility of Manuscript June accepted: 20,2020 Corrected manuscript received: June 11,2020 Manuscript received: 9,2020 April org/10.18268/BSGM2020v72n3a120620 Mexicana, 72(3),A120620.http://dx.doi. Colombia: Boletín de la Sociedad Geológica the Medellin Metaharzburgitic Unit (MMU), high-Al chromitites from geochemistry of J.M., Proenza, J.A., 2020,Petrology and Blanco-Quintero, I.F., González-Jiménez, M., Escayola, M., Ramírez-Cárdenas, C., Pujol-Solà, N., Aiglsperger, T., Weber, J.S.,Hernández-González, Butjosa,L., How tocitethisarticle: 7 6 5 4 3 2 1 Juan S. Hernández-González (UMM), Colombia Petrología y geoquímica de cromititas ricas enAlde la Unidad Metaharzburgitic Unit(MMU),Colombia Petrology and geochemistry ofhigh-Al José María Marion Weber de Barcelona, C/Martí iFranquès s/n,08028,Barce FacultatAplicada, de Ciències de laTerra, Universitat [email protected] * Corresponding author: (N. Pujol-Solà) enueva s/n,18002,Granada,Spain. de Ciencias, Universidad de Granada,Avda. Fuent Vicente del Raspeig s/n,03690,Alicante, Spain. Ambiente, Universidad de Alicante, Carretera de San Instituto de Ciencias Polares yAmbientales ICPA, Uni Departamento de Ciencias de la Tierra ydel Medio de Ciencias de laTierra Departamento Departamento de Mineralogía y Petrología,Departamento Facultad Departamento de Mineralogia e Geotectônica, Insti Departamento Departament de Mineralogia, PetrologiaDepartament iGeologia eateto CivilEngineering andNatural Re of Department Departamento de Geociencias yMedio Ambiente,Departamento González-Jiménez 4 , Mónica Escayola Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín 1,2 7 ------, Joaquín A.Proenza , Lídia 5 , Car spinel with anAl-rich core, ii)porous, Cr-Fe into three groups: i)partially altered chromian spinel inthe metaperidotites canbe classified positional variations, chromian the accessory ophiolites. According to textural andcom supra-subduction peridotites from those of dotites ranges from 0.58to 0.62andoverlaps chromianprimary spinel inthe metaperi the accessory [Cr/(Cr+Al) atomic ratio] of Cr# the unit. The evolution of the thermal chromian during secondary spinel, formed minerals, magnetite,serpentine-group and recrystallized olivine,talc, fine-grained assemblage composed by tremolite, chlorite, pyroxene, mineral andalater metamorphic olivine, chromian spinel andminorortho mantle-derived rocks contain relicts of and San Pedro ultramafic ore The deposits). dunites andchromitite bodies (Patio Bonito metaharzburgites, minormeta consists of Colombiaand in the Central Cordillera of Pangea duringTriassic time, is locatedgin of continental mar emplaced onto the western Medellin MetaharzburgiticThe Unit (MMU), ABSTRACT spinel, and iii) homogeneous Fe enriched chromian andAl-Mg-depleted supra-subduction zone, Colombia. mian spinel, chromitite, ophiolite, Keywords: Metaperidotite, chro tholeiitic magma (back-arc basin basalt type). and that the chromitites crystallized from a zone (back-arc basin/incipient arc scenario), spheric mantle related to asupra-subduction asuboceanic litho- at shallow levelsformed of ites andchromitites indicate that the MMU characteristics preserved inthe metaperidot- petrological primary The andgeochemical ppb). <41 (ΣPGE elements group platinum Al-rich (#Cr <0.6) andstrongly in depleted chromian spinel andchlorite. Chromitites are ferrian surrounded by thin alteration rimsof nel crystals, which show large unaltered cores chromian spi textures, and mainlyconsist of peridotites have massive andsemi-massive Chromitite bodies associated with the meta that reached amphibolite facies (ca.600ºC). to superimposed medium-T metamorphism variationsmian spinel. These canbe related Butjosa los Ramírez-Cárdenas 1 , Núria 1 Pujol-Solà 3+ chromitites -rich chro- 1 , IdaelF 1,* 2+ ------, T /72(3)A1206202020 homas . Blanco-Quintero Metaharzburgítica Cr-espinela homogéneaFe rica en de suprasubducción, Colombia. cromitita,Cr-espinela, ofiolita, zona Palabras clave: Metaperidotita, (cuenca de trasarco/arco incipiente). ceánico relacionado conunazona de suprasubducción somerosrepresenta niveles del manto litosférico subo (tipo basalto de cuenca de trasarco) yque la UMM toleítico últimas cristalizaron a partir de unmagma y las cromititaslas metaperidotitas indican que estas características petrológicas y geoquímicas primarias de Las ppb). <41 (ΣPGE platino de grupo del mentos primaria <0.6) yuncontenido total muybajo de ele refractario:ricas enAl(grado #Cr enla Cr-espinela y clorita.de Cr-espinela Las cromititas férrica son núcleos de Cr-espinela inalterada rodeados por bordes tienen texturas masivas ysemi-masivas y comprenden cuerpos de cromitita asociados a las metaperidotitas que alcanzó facies anfibolita (ca. 600ºC).Los de unmetamorfismo superpuesto sorias son evidencia texturales y composicionales de las Cr-espinelas acce quecida enCr-Fe con unnúcleo rico enAl,ii)Cr-espinela porosa, enri composicionales: i)Cr-espinela parcialmente alterada sus variaciones texturales y según en tres grupos ducción. La Cr-espinela accesoria sepuede clasificar los valores de las peridotitas de zonas de suprasub #Cr [Cr/(Cr+Al)] entre 0.58 y 0.62, similar a de esta unidad. La Cr-espinela primaria tiene térmica durante losprocesos de evolución secundaria, formada yCr-espinela de la serpentina, magnetita del grupo talco, fino,olivino recristalizado de grano minerales metamórfica posterior compuesta por tremolita, clorita, proporciónortopiroxeno, además de unaasociación contienen olivinomantélico, Cr-espinela yenmenor de Patio(depósitos BonitoySan Pedro). Estas rocas menor proporción metadunitas y cuerpos de cromitita de Colombia, comprende metaharzburgitas y en el Triásico, localizada enla Cordillera Central continental de Pangeaemplazadael margen en durante La Unidad Metaharzburgítica de Medellín (UMM), RESUMEN Aiglsperger from 2+ yempobrecida enAl-Mg, yiii) the Medell 3 , 6 , de 3+ . Las variaciones Medellín ín 1 - - - - -
High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) ABSTRACT High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) INTRODUCTION 1. Introduction The locationof the studiedsamplesisshown inthemap. 2007; Gómez Figure 1 2 2 Valley, the Central Cordillera, the CaucaRiver Cordillera, the Magdalena Riverwest: the Eastern ranges separated by valleys, namely from east to South America, are divided intothree mountain of ColombianAndes,The located inthe northwest pre-hispanic andcolonialtimes. (PGE), this region hasbeen largely explored since mainly gold,silver andPlatinum-Group Elements 2003). Due to its highpotential for precious metals, et al Colombia region called “ Range make up the geographic River Valley, the Western Cordillera, andthe Baudó Cauca the Cordillera, Central the of flank western Valley, andthe Western Cordillera (Figure 1A).The / / (A)Distribution map ofperidotite bodiesand mafic-ultramafic rockassociationsin Colombia (modified from Correa-Martínez, Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ., 1987;Moreno-Sánchez andPardo-Trujillo, et al ” (Restrepo andToussaint, 1973;Bourgois ., 2015).(B)Geological mapoftheMedellín region (modified from García-Casco http://dx.doi.org/10.18268/BSGM2020v72n3a120620 Western /72(3)A1206202020 /72(3)A1206202020 peridotites metamorphosed at amphibolite facies peridotites metamorphosed by Antioquia; Figure 1A) and is formed ment of Medellín (Depart Central Cordillera, northeast of the of flank western the in located is It 1987). rez, Dunite ( historically knownColombia is the Medellin as the Centralmain Cordilleraultramafic of body of (Nivia, 1987;Kerr the Caribbean-Colombian oceanic plateau of Correa-Martínez, 2007) and(2) mantle portions saint, 1973;Álvarez, 1987; Bourgois ophiolite mantle sequence (Restrepo and Tous 1A), an as: (1) fragments of them interpreted (Figure some of bodies ultramafic several of rence Westerncharacterized Colombiais bythe occur García-Casco (ca. 600ºC, <6 conditions kbar; Restrepo, 2008; e . g ., Restrepo and Toussaint, 1984; Álva Toussaint,1984; and Restrepo ., et al ., 2020andreferences therein). et al et al ., 1996;Serrano, 2009). The ., 2020and references therein). et al ., 1987; - - - - and references therein). Proenza Correa-Martínez, 2007; García-Casco 2003; Proenza 2008; 1986, Álvarez, 1987;Correa-Martínez and Nilson, Restrepo, 1984; 1973, Toussaint, debate for various decades ( Cr-PGE mineralization hasbeen a matter of 2007). (Al-rich;Proenza chromian containsrefractory grade deposit spinel ore This 1B). (Figure body ultramafic the of area Patio Bonito, located in the southern of deposit Colombia, including the large mineralization of the best-known MMUhosts chromian The spinel ate than the historical “Medellin Dunite” term. Metaharzburgitic Unit (MMU)ismore appropri mainly harzburgitic, Medellin and that the term et al element geochemical approach, García-Casco (Correa-Martínez, 2007). Usingabulk-rockmajor the so-called Aburrá Ophiolite mantle section of the as interpreted been has body ultramafic This 1B and2). (Figures body ultramafic the of sections northern and San Pedro, which cover and the southern metaperidotites from Las Palmas, Patio Bonito chromitites andassociated ical characteristics of studied mineralogical, petrological andgeochem mitite bodies hosted inthe MMU. We have its alteration. the MMU, aswell chromian as accessory spinelof the textural characteristicsand compositional of the less, to date, there are nodetailed studies of rock. the host Neverthe about thepetrogenesis of information valuable provides rocks ultramafic in spinel andpentlandite. chromian Accessory spinel the PGE content, chromian magmatic origin of a primary Pt, Pd, andRh,suggesting of mainly metadunite (up to 1.2 ppm), tent in two samples of Pereira in asupra-subductionenvironment.tle formed oceaniclithosphericman represents afragment of thatCorrea-Martínez (2007) suggested the MMU The origin of the MMU and itsassociated the MMU originof The hspprfcsso h td fthe chro paper focusesThis on the study of . (2020) inferred that this ultramafic body is body ultramafic this that inferred (2020) . et al . (2006)documented a highPGE con et al et al , 04; Pereira 2004a; ., ., 2004a; Correa-Martínez, 2004a; ., Boletín de la Sociedad Geológica Mexicana Mexicana Mexicana Geológica Geológica Sociedad Sociedad la la de de Boletín Boletín http://dx.doi.org/10.18268/BSGM2020v72n3a120620 e . g et al ., Restrepo and . (2004a) and (2004a) . et al et al ., 2006; ., 2020 ------THE COLOMBIAN ANDES 2.1. MAFIC/ULTRAMAFIC ROCK ASSOCIATIONS IN 2. Geologicalsetting (Feininger ages, ranging from the Triassicto the Neogene different of plutons by intruded successions tary overlain byMesozoic andCenozoic sedimen basement Cordillera) comprises a metamorphic the Colombian Andes (Central central part of The morphic continental basement to the east, called morphic oceanic crusttothe west andthe Paleozoic meta betweenimportant tectonic boundary Cretaceous the Central Cordillera, there is an part of western 07 Fgr 1) s n o h mafic-ultramafic the of one is 1B) Figure 2007; al and Toussaint,1973; Álvarez, 1987;Bourgois ophioliticorigin(Restrepo asof are interpreted and complexes theCauca-Almaguer fault located to theeastof bodies mafic-ultramafic the of spheric Province. Onthe other hand, the majority these bodiesintotheWesternCretaceous Litho et al taceous oceanicplateau (Nivia, 1987,1996;Kerr aCre areconsidered mainly tobefragments of and affinity oceanic rocksvolcano-sedimentaryof the Cauca-Almaguer fault are associated with of Moreno-Sánchez andPardo-Trujillo, 2003). Toussaint,1973; Bourgois ofthe Cauca-Almaguer fault (Figure 1A) (Restrepo and sides onboth lie ages different of bodies López 2001; Moreno-Sánchez andPardo-Trujillo, 2003; the Central Cordillera (Nivia, 1996, basement of Paleozoic the and affinity oceanic of rocks ceous betweento be the tectonic boundary the Creta Cauca-Almaguer faultconsideredis 1995). The jao andCauca-Almaguer (Maya andGonzález, main faults(from EtoW):San Jerónimo, Silvia-Pi three complex2019). This shear zoneof consists 1971; McCourt the Romeral Shear Zone (Figure 1A; Case ., 1987;Correa-Martínez andMartens, 2000). The AburráThe Ophiolite (Correa-Martínez, The mafic-ultramafic bodies located to the west ., 1996;Serrano,(1993) grouped 2009).Nivia et al et al , 09. sre o mafic-ultramafic of series A 2009). ., /72(3)A1206202020 / 72(3)A1206202020 ., 1972;Vinasco et al ., 1984; Nivia, 1996; Vinasco,1996; Nivia, 1984; ., et al ., 1987;Nivia,1993; et al ., 2006).Inthe et al 3 3 et ., ------
INTRODUCTION / GEOLOGICAL High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) SETTING High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) GEOLOGICAL SETTING 2.2. MEDELLINMETAHARZBURGITIC UNIT(MMU) 4 4 Metaharzburgitic Unit (MMU) and several mafic several and (MMU) Unit Metaharzburgitic comprises ultramafic rocks that the Medellin form paleo-continental margin. Aburrá Ophiolite The (Maya andGonzález,1995)that represents the the Cajamarca Complex rocksof metamorphic thelow-grade maguer fault. It liestothewest of the Cauca-Al units that crops out to the east of intruding the El Picacho metagabbros, which was Triassic) inzirconsfrom dike aplagiogranite 216.6± 0.36 Ma(Late (2007) obtained an age of al and Paul,2016; Spikings 2019;García-Casco debate (see Rodríguez remainsa subjectof still the ophiolite formation geodynamicsetting of Triassic back-arc basin.However, the age and the can berelated the MMU to a that the origin of subduction zone environment, andsuggested (2003) considered thisunittohave ina formed an obducted ophiolite. Correa-Martínez and Nilson of part as MMU the of rocks ultramafic the 1987). Restrepo andToussaint (1973) interpreted Hall, 1945; ro-Restrepo, were exploited over various decades ( chromitite that a hostfor several small bodiesof for chromiumand explorationmining it is since al bolites (Figure 1B;Restrepo, 2008;Rodríguez Sajonia mylontic gneissesandCretaceous amphi (Figure 1B), which isinfault contact with Jurassic Cordillera Central Colombian the in affinity ophiol itic of body ultramafic main the represents covers MMU The approximately 71km 1973; Rodríguez amphibolites (Figure 1B) (Restrepo andToussaint, the MMU overthrusts the Espadera-Chupadero the Aburrá Ophiolite are tectonic and ent units of differ the between contacts The Restrepo,2008). et al rea-Martínez and Nilson,2003;Correa-Martínez (Correa-Martínez and Martens, 2000;Cor and theEspadera-Chupadero Amphibolites units, which include the El Picacho Metagabbros / / ,21) hsui a eno specialinterest been of unit has ., 2016).This ., 2020andreferences therein). Correa-Martínez Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín , 04 20; oraMríe, 2007; Correa-Martínez, 2005; 2004, ., et al ., 2016). et al ., 1970;Álvarez, http://dx.doi.org/10.18268/BSGM2020v72n3a120620 e . g ., Bote 2 and et al et et ., /72(3)A1206202020 ------/72(3)A1206202020 2.3. THECHROMITITE BODIES spinel andorthopyroxene ( magmatic olivine, chromian phyllite and relicts of spinel, andto a lesser extent, carbonates, antho ser olivine, pentine group minerals, magnetite, andchromian recrystallized fine-grained chlorite, and minormetadunites, containingtremolite, talc, Correa-Martínez, 2007;Rodríguez Batholith (Figure 1B) (Feininger and Botero, 1982; the Cretaceous Antioquia several apophysisof of pre-Cretaceous age constrained byis the intrusion the continent still unknown,is but aminimum the Aburrá ophiolite onto emplacement of age of the ophiolite oceanic crust.Inaddition,the of as the minimuminterpreted age for the formation ern and southern bodies(Correa-Martínez, 2007). and southern ern inthe north small minesandquarries opening of reactivateding activitywas the 2000’sin with the and upto 7 mwidth(Álvarez, 1987). Artisanal min the largest was deposit in the area, with 30mlength Patiotries (Correa-Martínez, 2007). The Bonito the 1970’s-1980’s by metallurgical indus and glass ore. They were exploited during ~20000 tonsof of are small, containing a maximum tonnage estimate mafic rock (Correa-Martínez, 2007).The ore bodies ultra thehost to subconcordant withthefoliation of pentinized dunite (metadunite) and are concordant contactswiththe enclosing strongly ser sharp to disseminated textures. Chromitites usually show inated schlieren (Álvarez, 1987),showing massive metric pods, but also asdikes, lenses, anddissem Chromitite bodies occurmainlyascentimetric to the MMU(García-Casco whichphism, a newtectonic supposes scenario for ii) intra- back-arc subduction-initiation metamor ( metamorphism ocean-floor i) metabasites: associated and MMU the of tings inorder to explain the metamorphism et al (ca. 600ºC). García-Cascoconditions metamorphic 2007; Restrepo, 2008),indicating medium-grade Correa-Martínez, 1984; Toussaint, and Restrepo The MMU comprisesmainlymetaharzburgitesThe . (2020) analyzed two possible geodynamicset e . g ., Correa-Martínez, 2007), and et al ., 2020). e . g ., Álvarez, 1987; et al ., 2016). ------(B) Metaperidotite outcropcrosscutbyamaficdike orsillinthePatioBonitolocality.(C)and (D)Metaharzburgite outcropsintheLas Figure 2 General view ofthePatioBonitoMine.(H)Zoom onthemassivechromitite inthePatioBonitolocality. Palmas locality. (E)Chromitite bodyintheSanPedro locality. (F)Massivechromitite hand-specimen fromtheSanPedro locality. (G) Fieldphotographs of SanPedro, PatioBonito, and Las Palmaslocalities.(A)Metaperidotite outcropintheSan Pedro locality. Boletín de la Sociedad Geológica Mexicana Mexicana Mexicana Geológica Geológica Sociedad Sociedad la la de de Boletín Boletín http://dx.doi.org/10.18268/BSGM2020v72n3a120620 /72(3)A1206202020 / 72(3)A1206202020 5 5
High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) GEOLOGICAL SETTING STUDIED SAMPLES AND ANALYTICAL High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) TECHNIQUES techniques 3. Studiedsamplesandanalytical Table 1.Whole rock analysesof theMedellin Metaharzburgitic(MMU) metaperidotites. Unit 6 6 chromian spinel alteration andthe mineralogical the Pedro and Patio Bonito. textural The study of Pedro andPatio Bonito also chromitites at San burgites andmetadunites from LasPalmas, San metaharz include These light). reflected and ted thin sections using optical microscopy (transmit (Figure 2)were selected to be studied onpolished Palmas, San Pedro andPatio Bonito outcrops 19 representative samples from Las A total of / / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín
b.d.l. = below detection limit. b.d.l. =belowdetection Type SiO Li Locality Sample Sample Fe Al Na MnO MgO Total P TiO CaO
K LOI 2 (ppm) Cu Rb Co Cr Ba Be Cs Ni Sc Sr 2 2 V of (wt%) 2 2 O O 2 O O
O
2 5 3T rock 3
Metaharzburgite http://dx.doi.org/10.18268/BSGM2020v72n3a120620 Las 0.071 99.14 41.20 39.59 LP LP b.d.l. b.d.l. 2241 2231
28.9 1.49 0.19 0.80 8.17 0.01 0.57 0.13 8.61 0.84 0.02 101 Palmas 1.3 6.2 2.7 1.1 - - 1 1
Metaharzburgite /72(3)A1206202020 Las - - /72(3)A1206202020 12771 40.36 40.60 122.5 0.008 99.50 LP LP b.d.l. b.d.l. 3593
0.01 0.74 0.12 8.02 0.96 0.06 0.46 0.19 0.37 8.63 129 113 Palmas 7.3 0.9 0.9 - - 4 4
using the analyzing crystals: LiFforusing the analyzing crystals: Fe, Mn, and elements were 20 nA. The acquired current of 20kV anda beam to anacceleration voltage of same institution. Operating conditions were set JXA-8230 electron microprobe wasused at the For the mineral chemistry analyses, the JEOL (CCiTUB), Universitatnològics de Barcelona. i Tec Científics Serveis the at 325/D8395 XTE (SEM-EDS) usingthe ESEM Quanta 200 FEI, with Energy-Dispersive X-Ray Spectroscopy was phases grain out with Scanning Electroncarried Microscopy fine the of characterization
Las Metadunite 37.20 10.80 31.18 0.037 94.74 LP LP b.d.l. b.d.l. 1927 1488
0.01 0.07 0.12 5.27 0.30 30.5 0.47 0.19 0.38 9.79 Palmas 2.6 8.4 2.8 2.3 98 - -
7 7
Metaharzburgite San 39.92 38.93 0.027 99.19 11.29 b.d.l. b.d.l. SP 2260 1558 SP 0.01 0.53 0.12 7.58 0.77 0.04 28.6 0.83 0.19 0.60 109 7.4 1.7 1.5
19 Pedro - - 1 1
- Table 1.(Continuation) Whole rockanalysesof theMedellin Metaharzburgitic(MMU)metaperidotites. Unit iníia CC, nvria deGranada. Universidad (CIC), Científica out inthe Centrocarried de Instrumentación wollastonite (Ca), andorthoclase (Si, K). (Ni), rutile (Ti),metallic vanadium (V),albite (Na), Fe), periclase (Mg), rhodonite oxide (Mn),nickel standardsThe used were chromian spinel (Cr, Al, Ni; TAP for Mg and Al;PET for Cr, V, andTi. hl okaaye fperidotite samples were Whole rock analyses of Type Zr Zr Locality
Sample (ICPMS)
Tm Mo Sm (XRF) Gd Yb Ho Nd Nb Yb Ga Lu Dy Tb Eu Th Zn Ce La Pb
Hf Er Sn Ta Pr Tl U of
rock
Boletín de la Sociedad Geológica Mexicana Mexicana Mexicana Geológica Geológica Sociedad Sociedad la la de de Boletín Boletín
Metaharzburgite http://dx.doi.org/10.18268/BSGM2020v72n3a120620 Las 0.008 0.061 0.043 0.013 0.063 0.008 0.052 0.019 0.047 0.143 0.027 0.174 0.084 0.203 0.016 0.005 LP
0.52 0.01 0.49 0.36 0.14 0.14 0.45 0.48 P 1.1 8.8 0.7 44 almas - 1
Las Metadunite 0.003 0.016 0.002 0.007 0.002 0.007 0.001 0.007 0.002 0.007 0.031 0.078 0.043 0.054 0.008 0.007 0.011 LP
0.34 0.18 0.28 0.08 0.37 0.15 0.11 134 P 0.6 5.8 5.3 almas - 4
been described by Lázaro the analytic protocols have (ICP-MS). Details of Zr) were obtained by ICP MassSpectrometry Fluores Ray cence (XRF).Trace elements abundances (except X (PW-2440) Pro Magix Philips Major elements andZrwere analyzed usinga analyses were performed byanalyses were performed ICP-MS method at are shown inTable 1.Platinum-Group Elements Metaharzburgite Las 0.015 0.098 0.017 0.072 0.026 0.124 0.017 0.088 0.016 0.085 0.183 0.039 0.239 0.080 0.041 0.009 0.003 LP
0.31 0.13 0.12 0.79 0.39 0.19 0.11 P 4.5 5.6 0.9 33 almas - 7
/72(3)A1206202020 / 72(3)A1206202020
Metaharzburgite San 0.008 0.045 0.007 0.023 0.009 0.027 0.004 0.019 0.006 0.020 0.072 0.014 0.098 0.056 0.024 0.006 0.004 S 0.32 0.16 0.09 0.26 0.31 0.29 0.11 0.6 7.0 0.7 42 P Pedro - 1
et al
(04. Results (2014). . 7 7 -
STUDIED SAMPLES AND ANALYTICAL High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) TECHNIQUES High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) RESULTS 4.1.1. ULTRAMAFIC ROCKS 4.1. PETROGRAPHY 4. Results b.d.l. = below detection limit. b.d.l. =belowdetection (ppb). the MMUchromitites of analyses (PGE) elements platinumgroup rock Whole 2. Table
8 8 Sample ary fine-grained olivine, tremolite, chlorite, talc, chlorite, tremolite, olivine, fine-grained ary eral assemblage andincludes second issecondary minor orthopyroxene. However, the min much of mantle-derived olivine, chromian spinel, and of relicts contain rocks ultramafic The kink-bands. tures, andminerals show undulose extinction and predominantly porphyroclastic/granoblastic tex mantle tectonites, texturesprimary are typical of (Figures preserved 3Ato 3D).The serpentinized partially both Ol), (>90% metadunites and Opx) >5% and Ol (>40% metaharzburgites to spond metaperidotite samples (FigureThe 2)corre shown inTable 2. found inGervilla the analytical procedure can be details of The ppb for Rhand2ppbfor Os, Ir, Ru, Pt, andPd. dington (Australia). detection limits were The 1 Genalysis Laboratory Services Pty. Ltd. inMad / ΣPGE / Rh Ru Pd Os Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Pt Ir
b.d.l. SP2 28 17 2 1 4 4 San
Pedro et al SP1 41 18 . (2005)andthe results are 2 3 2 8 8
OF12 b.d.l. b.d.l. 27 14 Patio 4 2 7 http://dx.doi.org/10.18268/BSGM2020v72n3a120620
Bonito OF12A b.d.l. b.d.l. 14 3 1 7 3
/72(3)A1206202020 - - - - - /72(3)A1206202020 in pyroxene Non-pseudomorphic pseudomorphs. kink-bands, andisalsofound asrelict inclusions and oriented, showing undulose extinction and grains rounded μm) 20 (Figure olivine isvariably 3B).Primary deformed (< smaller forms that clasts, recrystallized andsecondary olivine (Ol2) porphyro μm 100-500 forms which (Ol1), olivine olivine: primary There are two generations of by andtremolite (Figure 3Aand3B). serpentine iddingsite alongrimsandfractures, andpyroxene mantle olivine isreplaced by and serpentine mesh andbastite textures,pseudomorphic where 2020 andreferences therein). carbonates andanthophyllite (García-Casco chromianserpentine, secondary spinel, andminor (Figure 3C). veinlets thin filling and serpentine in overgrowths as found are talc and Tremolite crystals. μm) 20 smaller (~10 to size olivine forms and secondary in μm ~100 crystals forms olivine mantle Primary boundaries andfractures (Figurealong grain 3C). olivine porphyroclasts replaces primary serpentine mesh textures,ites show pseudomorphic where as envelopes around chromitite bodies. Metadun ities (Figure 1B).InSan Pedro, metadunites occur been observed inLasPalmas andSan Pedro local than metaharzburgites inthe MMU, andhave rounded by adecussate chlorite corona. I andIIchromian spinel inthe MMUare sur types Both 4F). and 4E (Figures spinel chromian homogeneous III type and 4D), and 4C (Figures contains abundant chlorite within the porosity chromian spinel, which is completely altered and porous II type 4B), and 4A (Figures spinel mian Gervilla classified according to be the textural classification proposed by can and petrographically, guished chromian spinel canbe distin Three types of phase in the MMU metaperidotites.accessory mainly serpentine. observed (Figure 3A).Talc andchlorite replace gorite, tremolite olivine are andsecondary also anti textures, characterized by intergrowths of hoin pnl 6080 m i a common a is μm) (600-800 spinel Chromian Metaharzburgites: Metadunites: et al . (2012):type Ipartially altered chro Metadunites are less abundant Metaharzburgites show et al ., ------4.2.1. METAPERIDOTITES 4.2. WHOLEROCK GEOCHEMISTRY 4.1.2. CHROMITITES pull-apart textures. Semi-massive chromitites are rite (Figureinclusions 3G), also showing typical chromian ferrian spinelwithabundant chlo of unaltered cores surrounded by thinalteration rims chromian aggregates, which spinelcrystal have textures. spinel) chromian large (0.5-0.8 cm) Massive chromitites of consists vol. (60–80% sive semi-mas and spinel) chromian vol. (>80% sive Bonito localities(Figures 3Eto3H)exhibit mas Chromitite samples from SanPedro andPatio after pyroxenepseudomorphs are observed. pyroxenenor primary neither and size in μm 500 spinel (Figure reach 3D).Chlorite crystals upto chlorite corona surrounds the type IIchromian Gervilla of classification spinel corresponds to type Ispinel according to the chromian altered partially This 4B). and 4A ure chromian planes (Fig spinel (111)crystallographic chromian spinel with chlorite following the altered porous unaltered cores surrounded by rimsof chromianAccessory spinel (0.6- 1mm)shows range from 8.17 to 11.29 wt% (Table 1). The The 1). (Table Al wt% 11.29 to 8.17 from range the metaperidotites MMU LOIThe values of voids (Figures 4Ato4D). havecrystals irregular or acicular-shaped coarse (Figure 3H),whereas the ones inthe more altered less altered chromian are spinel crystals rounded the in rims alteration the within voids The fides. sul minor and chlorite by filled are voids the and chromian spinelalterationare rims porous highly rutile, andamphibole. In both chromitite bodies, nel include olivine, chlorite, serpentine, ilmenite, Mineral observedinclusions within chromian spi by minor serpentine, rutile, ilmenite, andtitanite. predominant intergranular mineral accompanied brecciated textures.locally forming Chlorite is the chromianalong rims to ferrian spinel(Figure 3H), to 0.2cm)that are strongly fractured andaltered smaller chromian (up spinel grains made upof 2 O 3 contents (0.84 - 0.96 wt%) are rather low rather are wt%) 0.96 - (0.84 contents Boletín de la Sociedad Geológica Mexicana Mexicana Mexicana Geológica Geológica Sociedad Sociedad la la de de Boletín Boletín et al . (2012).Adecussate http://dx.doi.org/10.18268/BSGM2020v72n3a120620 ------4.2.2. CHROMITITES: PGEGEOCHEMISTRY negative Eranomaly. One metaharzburgite sample Pedro (SP-1) shows apositive Hoanomalyanda or flat almost are metaharzburgiteU-shaped. The sample from San 5A) (Figure patterns (REE) and Fe TiO contents of highest the and respectively), wt% 0.07 and wt% SiO showsthe lowest contentsof One metadunite fromPalmasLas (sampleLP-7) (Table1). respectively) wt% 0.30 - 0.02 and wt% and CaO and TiO wt%, 41.20 to 37.20 between MgO wt%, 10.80 Fe wt%, 40.60 and 31.18 (except for sample LP-7), SiO (Proenza the Al-rich chromitites from Tehuitzingo, México are similartothosefrom patterns 1991). These chromititesis typical for podiform ( alies, andanegative slopefromRu toPd,which comparableand Irvalues, Os positive Ru anom (Figureized 6) are PGE patterns characterized by content than inSan Pedro. chondrite-normal The element (7 - 14 ppb), but with a significantly lower ΣPGE < 37 ppb, Ru also being the most abundant Patio(17 -18ppb).The Bonitochromitites have element abundant most the being Ru ppb, 41 < ΣPGE have chromitites Pedro San The values. arounddepletion, 100timeslower than chondritic with the MMU (Figure 6) show ageneral PGE dritic values for the massive chromitites associated tochonWhole rockPGE contentsnormalized and Pbanomalies. elements (HFSE). Allsamplesshow positive Th strength field high in enriched slightly and (LILE) in large-iontypically depleted lithophile elements primitive mantle (Figure 5B) metaperidotites are to the In the multielemental normalized diagram anomaly, not observed inthe other samples. majorelements, shows anoticeable negative Eu of dunite (LP-7), which isalready particular interms when compared to the other samples. meta The from Las Palmas (LP-4) is clearly depleted in REEs Chondrite-normalized rare earth element Chondrite-normalized 2 O et al 3 (10.80wt%)(Table 1). /72(3)A1206202020 / 72(3)A1206202020 ., 2004b). 2 03 w%, Al wt%), (0.30 2 contents are low (0.07 - 0.74 - (0.07 low are contents 2 O 3 between 7.58 and 2 2 ranges between andCaO (31.18 2 O 3 e 52 wt%), (5.27 . g ., Leblanc, 9 9 - - - -
High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) RESULTS High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) RESULTS alteration rimsin chromianspinel( strongly alteredand fractured chromianspinel( chlorite matrix( decussate chlorite( olivine ( with Metadunite (D) nicols. andcrossed light magmatic olivine( olivine ( olivine ( andrelict Figure 3 10 10 / / Ol1 Microphotographsof metaharzburgites, and fromtheMMU.(A)Metaharzburgite metadunites chromitites withtremolite( Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín ), secondary olivine( Chl Ol1 Ol1 ). Transmittedlightand parallelnicols.(F)SameasE in transmittedlightand crossednicols.(G)Chromitite showing Chl ) replaced by serpentine and chlorite ( serpentine andby chlorite ) replaced ) alteredtoserpentine( ) corona.Transmittedlightand parallel nicols.(E)Chromitite withcoarsechromian spinel( Ol2 ), chlorite( Spl ) crystalsinchromitite. Reflected light. http://dx.doi.org/10.18268/BSGM2020v72n3a120620 Chl Srp ) and latecarbonateveins.Transmittedlight and crossednicols.(C)Metaduniteshowing ) and iddingsite. Talc( Spl ) crystalssurrounded bychlorite( Ol1 ) partially altered to serpentine. Chromian( serpentine. spinel to altered partially ) Chl /72(3)A1206202020 ). Transmitted light and crossed nicols. (B) Metaharzburgite with relict Metaharzburgiteandwith crossed nicols.(B) light Transmitted ). /72(3)A1206202020 Tlc ) and accessory spinel( ) and accessory Chl ). Reflected light.(H)Chromitite showing Spl ) arealsoobserved.Transmitted Spl ) is surroundeda is by ) Spl ) crystalsina Tr ) in metaperidotite. Chlorite( Figure 4 chlorite halo surroundingchlorite thespinel.(E) and (F)TypeIII chromian spinel(Fe (Cr-Fe chromian spinel Type IIsurrounding and(D) corona (C) a the spinel. as Back-scattered electron images (BSE) of the accessory chromian spinel in MMU. (A) and (B) Type I chromianI( Type spinel (B) and (A) in MMU. chromian spinel accessory the of (BSE) electron images Back-scattered Chl ) ispresentasinclusionswithin thechromianspinelthatfollow the(111)crystallographicplanesand Boletín de la Sociedad Geológica Mexicana Mexicana Mexicana Geológica Geológica Sociedad Sociedad la la de de Boletín Boletín http://dx.doi.org/10.18268/BSGM2020v72n3a120620 3+ -rich) intergrown withtremolite( 2+ -rich, and Al-Mg-depleted) with chlorite inclusions anda inclusions chlorite with andAl-Mg-depleted) -rich, /72(3)A1206202020 / 72(3)A1206202020 Tr ). Spl ) (Al-rich) ) 11 11
High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) RESULTS High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) RESULTS projected for comparison.Normalizing valueswere takenfrom McDonough and Sun(1995). Deschamps Himalaya, Morari, (Tso serpentinites wedge mantle andhydrated 2008) REE patterns.(B)Multi-elementaldiagramnormalized tothe primitivemantle.Thefieldsfor (Godard abyssalmantleperidotites Figure 5 4.3.1. CHROMIAN SPINEL 4.3. MINERALCHEMISTRY 12 12 • and Table 3). 7B,8 7A, (Figures petrographically defined cation contents are directly related to the textural classifi positional variations regarding the Fe has been divided into 3 textural groups. com The chromian Accessory the metaperidotites spinelin / / Whole rockgeochemistryoftheLas Palmas(LP-1, LP-4 and LP-7) and (A)Chondrite-normalized SanPedro (SP-1)metaperidotites. Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín cores are characterized by Cr# [Cr/(Cr+Al) representcomposition. These the primary Al-rich cores (FiguresTable 7Aand8A, 3) that Type I chromian spinel(partially altered) has http://dx.doi.org/10.18268/BSGM2020v72n3a120620 3+ , CrandAl /72(3)A1206202020 - - /72(3)A1206202020 • ags rm .4 o .6 M# rm .3 to 0.13 from Mg# 0.96, to 0.84 from ranges composition ischaracterizedThe by Cr# that whenMn, compared toType Ichromian spinel. and enrichedMg-depleted in Cr, Fe Type IIchromianspinel (porous) Al and is netsky mantle rocksat supra-subductionzones (Kame spinelin accessory is typical of composition This wt%. 0.87 to 0.68 from ZnO and wt%, TiO Fe 0.44, to 0.42 from ratio] atomic [Mg/(Mg+Al) atomic ratio] ranging from 0.58to 0.62, Mg# 3+ et al # [Fe 2 03 w% MO rm .2 o 0.42 to 0.32 from MnO wt%, 0.36 ≤ et al ., 2010; Mariana Forearc, Savov Forearc, Mariana 2010; ., 3+ ., 2001)(Figure 7A). /(Fe 3+ +Cr+Al) atomic ratio] ≤ 0.03, et al 2+ ., 2005) are 2005) ., , Tiand et al ., - patterns fortheSanPedro andPatioBonito chromitites. Figure 6 Proenza (1980). Thefield for theTehuitzingo(México) isfrom chromitites Normalizing chondriticvalues arefromand Naldrett Duke higher Cr# (0.51 -0.63)andMg# (0.67-0.80), sim spinel cores from Patio Bonito chromitites exhibit chromian unaltered contrast, In Table4). 7D, 7C, (Figures wt% 0.23 < NiO and wt%, 0.17 < ZnO Fe 0.58, to Mg# from 0.54 0.43 to 0.68, TiO from ranging Cr# has chromitites Unaltered chromian spinelcores from San Pedro • 3+ Chondrite-normalized platinumgroupelement (PGE) et al # <0.035, MnO < 0.27 wt%, V ZnO from 0.04 to0.28wt%. to 0.45 wt%, MnO from 0.16 to 0.58 wt%, and to 0.22, Fe that rangesfrom0.98 to1.00,Mg#from 0.09 rich (Figures 7Band8B, Table 3) andhasCr# Type IIIchromianFe spinel(homogenous)is 3). Table7B, (Figure wt% 0.66 to 0.37 from ZnO to 1.57 wt%, MnO from 0.39 to 0.76 wt%, and 0.27, Fe . (2004b). 3+ # from 0.05to 0.16, TiO 3 # from 0.30to 0.79, TiO Boletín de la Sociedad Geológica Mexicana Mexicana Mexicana Geológica Geológica Sociedad Sociedad la la de de Boletín Boletín 2 from 0.02 to 0.5 wt%, http://dx.doi.org/10.18268/BSGM2020v72n3a120620 2 O 3 < 0.22 wt%, 2 2 from 0.42 from from 0.27 3+ - - 4.3.2. OLIVINE 4.3.4. CHLORITE 4.3.3. TREMOLITE all the analyzed show similarcomposition crystals olivine,rived metamorphic olivine andsecondary mantle-de possibleit was primary to distinguish hashi mantle olivine ( is withinthe range of Fo of ranges fromits composition Fo Olivine isonlypresent in the metaperidotites and ZnO (<0.37wt%)(Figures 7C,7DandTable 4). V wt%), (0.11-0.49 MnO but lower Fe ilar TiO 3.37 wt% (up to 0.49 Fe0.49 to (up wt% 3.37 to 1.79 fromFeO and a.p.f.u.) Si 6.7 to (up wt% SiO (1954). Hey by classification the to according 9C) (Figure to clinochlorecorresponds andhigh-Si pennantite the metaharzburgitesChlorite in composition position Aisbetween 0.69and1.00a.p.f.u. (0.001 -0.19)contents(Table vacancyin 6). The Fe4.96), Si (7.20 - 8.02), Al K (<0.007 a.p.f.u.) contents, andhave variable low Ti(<0.02 a.p.f.u.),(<0.06 a.p.f.u.) Mn and as tremolitesify (Figure 9B). yielded Analyses very (Ca 0.95 to 0.99 (Table calcium amphiboles 6). These Mg# [Mg/(Mg+Fe Hawthorne tion scheme of classifica the to according 2014) Locock, lowing belong to the calcium subgroup (calculations fol Type-III chromian studied crystals spinel.The moreand itis abundantsamples that in contain Amphibole isonlypresent in the metaharzburgites peridotite fields(Ishii (Moghadam betweencompositions the abyssalperidotites olivine (Table 5). Figure 9Ashowsa scattering of B = 1.196 - 2 a.p.f.u; Na 90.5 et al ), and NiO from 0.19 to 0.51 wt%, which wt%, 0.51 to 0.19 from NiO and ), 2 TOT (0.05 to 0.5 wt%) and NiO (<0.21 wt%) (<0.21 NiO and wt%) 0.5 to (0.05 ., 1987).Even thoughpetrographically (0.14 - 0.39), Ca (1.19 - 2.00), and Na and 2.00), - (1.19 Ca 0.39), - (0.14 2 /72(3)A1206202020 3 content ranges from 27.91to 35.21 / 72(3)A1206202020 et al +# (<0.018 wt%) and slightly higher ., 2015) and the supra-subduction TOT 2+ ) atomic ratio] ranging from et al (0.016 - 0.131), Mg (3.76 - 2+ ., 1992). a.p.f.u.). Fe/(Fe The + 2 O B et al = 0.001 - 0.19) clas 3 <.6 t) and wt%), (<0.26 89.7 . (2012),andhave to Fo 93.7 e . g (average ., Taka 13 13 - - - - -
High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) RESULTS High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) RESULTS for boninites andfor boninites MORBarefrom Arai(1992),references arethesameasin(C). al Proenzafrom is and theMoaBaracoaand Nicolas(1992)respectively, SaguadeTánamo(Cuba) fields arefrom Proenza andchromitites, primarychromian spinelfor Thepodiform themetaperidotites. and stratiform fields areafter Irvine (1967)and Leblanc Mg# [Mg/(Mg+Fe)]diagramforchromian spinelof chromian theMMU.(C)Cr#[Cr/(Cr+Al)]vs. spinelof theSanPedro and PatioBonito Kamenetsky Al (wt%) vs. Figure 7 14 14 . (2020). (D) Cr# vs. TiO vs. Cr# (D) (2020). . / / Mineral chemistry of accessory chromian spinel in the metaperidotites and in the chromitite bodies of the MMU. (A) TiO (A) MMU. the of bodies chromitite andin the metaperidotites in the chromian spinel accessoryof Mineralchemistry Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín 2 O et al 3 (wt%)diagramfor typeIchromian spinel.Fieldsfor supra-subduction and zone are (SSZ) MORB-typeperidotites from et al . (2001),and thefield for thePuerto RicoPeridotite isfromMarchesi . (2004b), Los Guanacos (Argentina) is from Proenzafrom is (Argentina) Guanacos Los (2004b), . 2 (wt%) for the San Pedro and Patio Bonito chromitites, and type I chromian spinel in the metaperidotites. Fields metaperidotites. in the chromian spinel I andtype chromitites, Bonito Patio andSan Pedro the for (wt%) http://dx.doi.org/10.18268/BSGM2020v72n3a120620 /72(3)A1206202020 /72(3)A1206202020 et al . (2008), and Cerro Colorado (Venezuela) is from Mendifrom (Venezuela)is ColoradoandCerro (2008), . et al . (2011).(B)Cr, Fe et al . (1999), Tehuitzingo. (1999),(México) 3+ and Alcompositionsfor et 2
Table 3.Representative chromianspinel electronmicroprobeanalysesof inthemetaperidotites. accessory also low (<2.61 wt%). foundmetaperidotites.in Cr The valuesThese are lower than those from chlorite and Fe/(Fe +Mg)ratio between 0.02and0.03. wt% 1.79 to 1.22 FeOfrom wt%, 32.61 to 27.07 clinochlore (Figure 9C), with SiO Cr Mg) ratio ranges between 0.03 and0.05,alsothe 2 Chlorite the chromititesin to corresponds O 3 contentislow (<3.2wt%)(Table 6). b.d.l. = below detection limit. b.d.l. =belowdetection
SiO
Ti Sample
Cr (a.p.f.u.) Fe Al Total MnO Fe MgO V ZnO TiO Area Mg# 2 FeO NiO Fe Fe Cr# Mn Mg
Zn Cr Ni Al (wt.%) V 2 2 2 2 3+ O O O 2+ 3+ O
# 2
3
3 3 3
Palmas 98.96 21.44 41.91 19.97 LP 0.00 0.43 0.02 0.01 0.55 0.06 0.00 1.12 0.80 0.01 0.12 8.44 0.87 0.34 5.37 0.16 0.29 0.05 0.03 0.44 0.58 Las Boletín de la Sociedad Geológica Mexicana Mexicana Mexicana Geológica Geológica Sociedad Sociedad la la de de Boletín Boletín
-7
http://dx.doi.org/10.18268/BSGM2020v72n3a120620 Palmas Type Type Type 99.11 21.54 42.76 19.03 b.d. LP 0.03 0.43 0.60 0.00 0.43 0.02 0.01 0.55 0.06 0.00 1.15 0.76 0.01 0.05 8.39 0.68 0.36 5.77 0.17 0.35 Las -7 l
.
2
I I I
2
ranging from
O 3 contentis Palmas 99.27 21.86 44.09 18.29 LP 0.00 0.41 0.02 0.01 0.57 0.05 0.00 1.19 0.73 0.01 0.05 8.10 0.79 0.32 5.26 0.14 0.30 0.07 0.03 0.42 0.62 Las
-7
Palmas 32.69 52.42 99.15 b.d. LP 0.50 0.58 0.25 6.82 0.78 0.12 0.27 0.84 0.00 0.26 0.01 0.02 0.72 0.24 0.01 1.44 0.28 0.02 0.04 5.08 Las -
-7 l
.
4.3.5. SERPENTINE Type Type Type Palmas 34.88 54.54 99.14 b.d. LP 0.57 0.62 0.33 3.67 0.88 0.10 0.12 0.19 0.91 0.19 0.02 0.02 0.80 0.24 0.01 1.54 0.15 0.02 3.54 Las - -
-7 l
. II II II
15 t 4.8 t o SiO of wt% 45.98 to 41.54 (Figurecomposition 9D) ranges fromSerpentine spinel, where chlorite israre. chromianmetaperidotites with type III accessory est SiO Cr Al wt%, 4.51
2 O San SP 38.16 53.73 99.58 0.63 0.70 0.33 2.19 1.13 0.07 0.16 0.14 0.94 0.00 0.14 0.02 0.02 0.84 0.31 0.01 1.53 0.09 0.03 0.09 2.55 3
Pedro -001 from 0.03 to 0.47 wt% (Table 6). The high -
2
values are from observed in serpentine
/72(3)A1206202020 / 72(3)A1206202020 COL Bonito 27.40 39.22 28.67 99.55 Patio 0.24 0.58 0.16 0.24 0.29 0.08 0.30 0.20 0.99 0.02 0.19 0.01 0.03 0.76 0.60 0.01 1.34 0.02 0.01 0.48 2.19 2
O -6
3 rm .3 o .0 t, and wt%, 2.50 to 0.53 from Type Type Type COL Bonito 28.17 50.72 17.49 99.89 Patio 0.07 0.32 0.16 0.10 0.31 0.08 0.48 0.20 0.99 0.04 0.20 0.00 0.02 0.77 0.94 0.01 1.00 0.01 0.02 0.66 1.81
-7 III III III
2 COL Bonito 28.92 56.79 11.03 99.52 , FeO from 2.85 to Patio b.d. 0.08 0.26 0.11 0.29 0.05 0.63 0.16 1.00 0.05 0.15 0.00 0.02 0.80 1.22 0.01 0.73 0.00 0.02 0.81 1.18
l -6 .
15 15 -
High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) RESULTS High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) DISCUSSION PERIDOTITES 5.1. TECTONIC SETTINGOFTHEMMU 5. Discussion 16 16 Table 4.Representative electronmicroprobechromianbodies spinelanalysesfromthechromitite intheMMU. and Furnes, 2014 and references therein). In gen In therein).references and 2014 Furnes, and tectonic settings (Dilek andFlower, 2003;Dilek oceanic lithosphere (“ophiolites”) invarious of types different of development the control cesses, magmatic events,global which, and together with mantle pro tectonic first-order with related Ophiolitic peridotites are spatially and temporally / / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín b.d.l. = below detection limit. b.d.l. =belowdetection
SiO Ti Locality
Cr Fe (a.p.f.u.) Al Total MnO Fe MgO V TiO ZnO 2 Mg# NiO FeO Fe Fe Cr# Mn Mg
Cr Ni Al (wt.%) V 2 2 2 2 3+ O
O O 2+ 3+ O
# 2 3
3 3 3
100.89 15.70 13.40 36.56 32.74 chr1 chr1 chr1 0.13 0.68 0.43 0.00 0.68 0.00 0.32 0.05 0.00 0.83 1.11 0.00 0.08 0.00 0.14 2.07 0.09 0.03 0.09
100.89 15.51 13.54 36.28 32.49 b.d. chr2 chr2 chr2 0.15 0.67 0.43 0.67 0.01 0.33 0.06 0.00 0.83 1.11 0.00 0.02 0.20 2.63 0.13 0.04 0.03 -
l .
http://dx.doi.org/10.18268/BSGM2020v72n3a120620 San 100.94 15.13 13.92 38.01 31.33 chr3 chr3 chr3 0.11 0.66 0.45 0.00 0.66 0.01 0.34 0.04 0.00 0.87 1.07 0.00 0.11 0.05 0.19 1.87 0.19 0.05 0.07
Pedro
100.47 15.05 13.89 37.53 31.31 chr4 chr4 chr4 0.02 0.15 0.16 2.15 0.10 0.07 0.03 0.12 0.66 0.45 0.00 0.66 0.00 0.34 0.05 0.00 0.87 1.08 0.00
/72(3)A1206202020 - - /72(3)A1206202020 100.93 15.09 14.02 37.71 31.23 chr5 chr5 chr5 0.05 0.08 0.18 2.26 0.19 0.08 0.06 0.13 0.66 0.45 0.00 0.66 0.00 0.34 0.05 0.00 0.87 1.07 0.00
mantle and/or at levels. deeper heat advection and melting in the asthenospheric plumes), which are linked to mantle diapirism, unrelated ophiolites (oceanic ridges, MORor metasomatized peridotites, and(ii) subduction of partial melting cesses, andrepetitiveof episodes the subducting plate, associated metasomatic pro dehydration of the by influenced be might which duction zone orvolcanic arc) related ophiolites, can be classified as: (i) subduction zone (supra-sub affinity ophiolitic ultramafic of oceanic eral, rocks 100.20 15.10 13.11 43.38 27.06 b.d. chr1 chr1 chr1 0.16 0.17 0.82 0.12 0.14 0.14 0.05 0.67 0.52 0.00 0.67 0.00 0.33 0.00 0.00 1.03 0.95 0.00 l .
100.68 18.16 43.21 26.81 chr2 chr2 chr2 0.14 0.05 0.11 8.65 3.13 0.11 0.22 0.09 0.25 0.81 0.52 0.00 0.81 0.00 0.19 0.02 0.00 1.02 0.94 0.00
Patio 101.00 15.93 11.98 43.03 26.63 chr3 chr3 chr3 0.14 0.07 0.20 2.64 0.15 0.15 0.08 0.17 0.72 0.52 0.00 0.71 0.01 0.28 0.02 0.00 1.02 0.94 0.00
Bonito
15.07 12.89 43.37 26.58 99.82 chr4 chr4 chr4 0.18 0.12 0.19 0.95 0.21 0.16 0.10 0.06 0.68 0.52 0.00 0.68 0.00 0.32 0.01 0.01 1.03 0.94 0.00
100.18 17.25 43.99 26.49 chr5 chr5 chr5 0.20 0.11 0.13 9.74 1.85 0.14 0.18 0.10 0.15 0.77 0.53 0.00 0.77 0.00 0.23 0.01 0.00 1.04 0.93 0.00
- - LP-7). Note the highAl,Fe,andLP-7).gradually decreasestowards therims. NoteCr TheAl-richcores contents inthecorethat aresurrounded by Figure 8 depletion, whereasabsent. Alisalmost the Cr with related enrichmentis The Fe (Sample CO-7). metaperidotite Palmas Las the fromIII chromian spinel Type (B) halo. high-V a Elementdistributionmapsfor chromianspinelintheMMU. (A)TypeI accessory chromian spinel from Las Palmas(Sample Boletín de la Sociedad Geológica Mexicana Mexicana Mexicana Geológica Geológica Sociedad Sociedad la la de de Boletín Boletín http://dx.doi.org/10.18268/BSGM2020v72n3a120620 /72(3)A1206202020 / 72(3)A1206202020 17 17
High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) DISCUSSION High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) DISCUSSION Table 5.Representative electronmicroprobeanalysesof olivineinthemetaperidotites. 18 18 Mineral Ol-1 Ol-1 Ol-1 Ol-1 Ol-2 Ol-2 Ol-2 Ol-1 Ol-1 Ol-2 Ol-2 Ol-1 Ol-1 Ol-2 Ol-2 Ol-1 Ol-1 Ol-1 Ol-2 Ol-2 Ol-1 Ol-2 Ol-2 Ol-2 Ol-2
Locality Las Palmas San Pedro Patio Bonito / / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Type of rock dun dun dun dun dun dun dun dun dun dun dun dun dun per per per per per per per dun dun dun dun dun Mexicana Geológica Sociedad la de Boletín
Sample LP-1 LP-1 LP-1 LP-1 LP-1 LP-1 LP-1 LP-7 LP-7 LP-7 LP-7 LP-7 LP-7 SP-1 SP-1 SP-1 SP-1 SP-1 SP-1 SP-1 CO-7 CO-7 CO-7 CO-7 CO-7
SiO2 (wt.%) 40.72 40.87 41.30 40.86 41.03 41.04 41.14 41.45 41.21 40.91 40.96 40.98 40.72 41.04 40.60 41.08 40.97 40.89 40.94 40.79 41.39 40.94 41.07 41.21 40.96
TiO2 b.d.l. 0.04 b.d.l. 0.02 b.d.l. 0.02 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.04 b.d.l. 0.02 b.d.l. b.d.l. 0.03 0.02 b.d.l. b.d.l. 0.02 0.03 b.d.l. b.d.l. 0.05
Al2O3 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l.
Cr2O3 0.03 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.02 0.02 b.d.l. 0.02 b.d.l. b.d.l. 0.02 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.02 b.d.l. 0.02
V2O3 b.d.l. 0.02 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.03 b.d.l. 0.02 0.02 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.04 b.d.l. b.d.l. b.d.l.
FeO 9.52 9.55 9.69 9.69 9.73 9.65 9.69 8.98 8.41 9.57 9.40 9.98 9.65 9.22 9.47 8.48 8.56 8.71 9.52 9.59 8.66 8.81 8.79 8.68 8.76
MnO 0.15 0.18 0.18 0.12 0.17 0.15 0.17 0.12 0.17 0.13 0.16 0.12 0.11 0.15 0.15 0.13 0.12 0.14 0.16 0.16 0.17 0.18 0.16 0.18 0.17 http://dx.doi.org/10.18268/BSGM2020v72n3a120620 ZnO 0.02 0.05 b.d.l. b.d.l. b.d.l. 0.02 b.d.l. 0.04 0.03 b.d.l. b.d.l. 0.05 0.08 b.d.l. 0.02 b.d.l. 0.03 b.d.l. 0.04 b.d.l. b.d.l. 0.03 b.d.l. b.d.l. 0.03
MgO 48.67 48.71 48.55 48.33 48.70 48.62 48.42 49.97 49.90 49.29 49.08 48.93 48.98 49.48 49.33 49.83 49.84 49.83 48.93 49.09 49.70 49.74 49.59 49.53 49.46
NiO 0.33 0.34 0.37 0.34 0.32 0.29 0.34 0.26 0.29 0.34 0.32 0.19 0.26 0.38 0.37 0.37 0.38 0.36 0.35 0.33 0.38 0.37 0.38 0.38 0.42
CaO b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.04 b.d.l. b.d.l. b.d.l. 0.03 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.02 b.d.l. b.d.l. 0.02
Na2O b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.02 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.03 b.d.l. 0.02 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. /72(3)A1206202020 /72(3)A1206202020
K2O b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l.
Total 99.46 99.77 100.11 99.36 99.98 99.81 99.78 100.84 100.08 100.29 99.96 100.29 99.87 100.33 99.97 99.94 99.94 100.00 99.98 100.00 100.32 100.17 100.04 100.01 99.89
Mineral Ol-1 Ol-1 Ol-1 Ol-1 Ol-2 Ol-2 Ol-2 Ol-1 Ol-1 Ol-2 Ol-2 Ol-1 Ol-1 Ol-2 Ol-2 Ol-1 Ol-1 Ol-1 Ol-2 Ol-2 Ol-1 Ol-2 Ol-2 Ol-2 Ol-2
Si (a.p.f.u.) 1.003 1.004 1.010 1.007 1.005 1.007 1.010 1.003 1.003 0.999 1.003 1.002 0.999 1.000 0.994 1.002 1.000 0.998 1.003 0.999 1.006 0.998 1.002 1.005 1.001
Ti - 0.001 - 0.000 - 0.000 - - - - - 0.001 - 0.000 - - 0.000 0.000 - - 0.000 0.000 - - 0.001
Al ------
Cr 0.001 ------0.000 0.000 - 0.000 - - 0.000 ------0.000 - 0.000
V - 0.000 ------0.001 - 0.000 0.000 - - - - - 0.001 - - -
Fe2+ 0.196 0.196 0.198 0.200 0.199 0.198 0.199 0.182 0.171 0.194 0.192 0.204 0.198 0.188 0.182 0.173 0.175 0.173 0.195 0.194 0.176 0.177 0.179 0.177 0.179
Mn 0.003 0.004 0.004 0.003 0.004 0.003 0.003 0.002 0.003 0.003 0.003 0.002 0.002 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.003 0.004 0.003 0.004 0.004
Zn 0.000 0.001 - - - 0.000 - 0.001 0.001 - - 0.001 0.001 - 0.000 - 0.001 - 0.001 - - 0.001 - - 0.000
Mg 1.787 1.783 1.770 1.776 1.779 1.778 1.771 1.803 1.811 1.795 1.791 1.783 1.792 1.798 1.800 1.812 1.813 1.812 1.787 1.793 1.801 1.808 1.804 1.801 1.803
Ni 0.006 0.007 0.007 0.007 0.006 0.006 0.007 0.005 0.006 0.007 0.006 0.004 0.005 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.007 0.008
Ca ------0.001 - - - 0.001 ------0.001 - - 0.000
Na ------0.001 ------0.002 - 0.001 - - - - -
K ------
O=4 ------
Fo 0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.91 0.91 0.90 0.91 0.90 0.90 0.91 0.91 0.91 0.91 0.91 0.90 0.90 0.91 0.91 0.91 0.91 0.91
b.d.l. = below detection limit. Mineral Amp Amp Amp Amp Amp Amp Amp Amp Chl Chl Chl Chl Chl Chl Chl Chl Srp Srp Srp Srp Srp Srp Srp Srp Table 6.Representative electronmicroprobeanalysesof tremolite,chloriteand serpentine and inthemetaperidotites chromitites.
Locality Las Palmas San Pedro Patio Bonito Las Palmas San Pedro Patio Bonito Las Palmas San Pedro Patio Bonito
Type of rock dun dun dun per per dun dun dun dun dun dun dun per per chr per dun dun dun dun per per dun dun
Sample LP-1 LP-1 LP-1 SP-1 SP-1 CO-7 CO-7 CO-7 LP-1 LP-1 LP-7 LP-7 SP-1 SP-1 CO-4 CO-6 LP-7 LP-7 LP-7 LP-7 SP-1 SP-1 CO-7 CO-7
SiO2 (wt.%) 58.17 57.73 57.68 57.73 57.77 57.61 56.72 58.48 33.62 33.15 32.26 32.38 34.41 34.20 27.91 27.91 35.54 35.15 34.83 35.12 38.87 36.28 36.85 36.15
TiO2 0.05 0.08 0.05 b.d.l. b.d.l. b.d.l. b.d.l. 0.02 0.06 0.04 0.10 0.09 b.d.l. b.d.l. 0.07 0.07 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.04
Al2O3 0.22 0.38 0.33 0.36 0.33 0.43 0.49 0.25 14.09 14.59 16.16 16.23 12.75 13.22 22.17 22.17 0.02 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l.
Cr2O3 0.02 0.08 0.36 0.05 0.10 0.03 0.07 0.04 2.67 2.15 1.81 1.71 1.71 1.43 1.24 1.24 b.d.l. 0.02 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l.
V2O3 b.d.l. b.d.l. 0.02 b.d.l. b.d.l. b.d.l. b.d.l. 0.02 0.05 0.05 0.02 b.d.l. 0.02 0.04 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.02 b.d.l. b.d.l.
FeO 1.81 1.98 1.86 1.89 1.68 1.37 1.50 1.28 2.44 2.47 2.56 2.68 2.29 2.35 1.79 1.79 5.92 6.35 6.13 5.66 4.98 5.95 5.66 6.03 Boletín de la Sociedad Geológica Mexicana Mexicana Mexicana Geológica Geológica Sociedad Sociedad la la de de Boletín Boletín
MnO 0.09 0.12 0.06 0.11 0.06 0.04 0.03 0.07 0.03 0.02 0.03 0.04 0.02 b.d.l. b.d.l. b.d.l. 0.11 0.12 0.13 0.09 0.07 0.07 0.08 0.05
ZnO 0.04 0.02 0.08 b.d.l. b.d.l. b.d.l. 0.04 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. 0.03 0.02 0.03 b.d.l. 0.04 0.03 http://dx.doi.org/10.18268/BSGM2020v72n3a120620
MgO 23.36 23.57 23.11 23.44 23.41 23.90 25.00 23.10 33.55 33.13 32.80 32.39 34.21 33.99 33.56 33.56 39.40 40.20 41.37 40.84 39.13 38.82 40.96 40.60
NiO 0.05 0.08 0.07 0.06 0.11 0.12 0.09 0.07 0.13 0.14 0.13 0.15 0.21 0.21 b.d.l. b.d.l. 0.17 0.20 0.21 0.22 0.13 0.34 0.36 0.35
CaO 12.74 12.27 12.41 11.96 12.88 13.41 12.89 13.43 b.d.l. 0.02 0.03 0.02 b.d.l. b.d.l. b.d.l. b.d.l. 0.05 0.04 0.02 b.d.l. 0.04 0.03 b.d.l. 0.05
Na2O 0.27 0.34 0.35 1.05 0.49 0.32 0.24 0.22 0.02 b.d.l. b.d.l. b.d.l. 0.05 0.04 b.d.l. b.d.l. b.d.l. b.d.l. 0.02 b.d.l. b.d.l. 0.03 b.d.l. b.d.l.
K2O b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l.
H2O 2.18 2.18 2.17 2.18 2.18 2.19 2.18 2.19 12.65 12.54 12.56 12.53 12.56 12.54 12.75 12.75 11.78 11.87 11.94 11.87 12.19 11.85 12.19 12.07
Total 99.01 98.82 98.54 98.85 99.02 99.42 99.25 99.16 99.31 98.31 98.47 98.23 98.24 98.02 99.51 99.51 92.99 93.95 94.70 93.84 95.46 93.40 96.14 95.37
Mineral Amp Amp Amp Amp Amp Amp Amp Amp Chl Chl Chl Chl Chl Chl Chl Chl Srp Srp Srp Srp Srp Srp Srp Srp
Si (a.p.f.u.) 7.997 7.950 7.975 7.954 7.951 7.905 7.807 8.018 6.375 6.341 6.161 6.196 6.573 6.542 5.249 5.249 3.617 3.552 3.498 3.550 3.825 3.672 3.626 3.593
Ti 0.005 0.008 0.005 - - - - 0.002 0.008 0.006 0.014 0.013 - - 0.010 0.010 ------
Al 0.036 0.062 0.054 0.058 0.054 0.070 0.079 0.040 3.149 3.289 3.637 3.660 2.871 2.980 4.914 4.914 0.003 ------
Cr 0.002 0.008 0.039 0.006 0.011 0.003 0.007 0.004 0.400 0.325 0.273 0.259 0.258 0.217 0.184 0.184 - 0.001 ------
V - - 0.002 - - - - 0.002 0.007 0.008 0.004 - 0.003 0.005 ------0.002 - - /72(3)A1206202020 / 72(3)A1206202020
Fe3+ 0.020 0.063 0.024 0.071 0.029 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.282 0.282 0.504 0.537 0.515 0.478 0.350 0.504 0.466 0.501
Fe2+ 0.188 0.165 0.191 0.147 0.165 0.157 0.173 0.147 0.387 0.395 0.409 0.429 0.366 0.376 0.000 0.000 0.000 0.000 0.000 0.000 0.059 0.000 0.000 0.000
Mn 0.011 0.014 0.007 0.013 0.007 0.004 0.004 0.009 0.005 0.004 0.005 0.006 0.004 - - - 0.009 0.010 0.011 0.008 0.006 0.006 0.006 0.005
Zn 0.005 0.002 0.008 - - - 0.004 ------0.002 0.002 0.002 - 0.003 0.002
Mg 4.787 4.839 4.763 4.814 4.803 4.889 5.130 4.722 9.483 9.448 9.338 9.240 9.743 9.692 9.409 9.409 5.978 6.057 6.194 6.153 5.740 5.857 6.009 6.015
Ni 0.006 0.009 0.007 0.007 0.012 0.013 0.009 0.008 0.020 0.022 0.020 0.023 0.033 0.033 - - 0.014 0.016 0.017 0.018 0.010 0.028 0.028 0.028
Ca 1.877 1.810 1.838 1.766 1.899 1.971 1.901 1.973 - 0.003 0.005 0.004 - - - - 0.005 0.004 0.003 - 0.004 0.003 - 0.005
Na 0.073 0.091 0.094 0.280 0.129 0.085 0.063 0.057 0.008 - - - 0.017 0.013 - - - - 0.004 - - 0.005 - -
K ------
H 2 2 2 2 2 2 2 2 16 16 16 16 16 16 16 16 8 8 8 8 8 8 8 8
O 24 24 24 24 24 24 24 24 36 36 36 36 36 36 36 36 18 18 18 18 18 18 18 18 19 19
Mg# 0.962 0.967 0.961 0.970 0.967 0.969 0.967 0.970 0.961 0.960 0.958 0.956 0.964 0.963 1.000 1.000 1.000 1.000 1.000 1.000 0.990 1.000 1.000 1.000
High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) DISCUSSION High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) DISCUSSION Al, Fe+Mgdistributiondiagram for serpentine of theMMUmetaperidotites. Sia.p.f.u.classificationdiagramfor chloriteaccordingMg) vs. toHey(1954),for andoftheMMU.(D)Si, themetaperidotites chromitites Hawthorne accordingto classification diagram Figure 9 Takahashi 20 20 ur-udcin oe de o oaierc fluid volatile-rich to due zones supra-subduction tent with melt percolation reactions,in common REE patterns (almost flat or U-shaped) are consis positive LREEto HREE slopes(Figure 5A). The (MOR-type) (Godard peridotites abyssal of those from differ and 2010) 2005; Marchesi supra-subduction zone peridotites (Savov idotites compare well with those related with 2000; Marchesi peridotites from ophiolites (Figure 7A; Pearce supra-subduction from the MMU overlap those of unaltered coresfrom Type-I chromianspinel) chromian spinelinmetaperidotites (0.58 - 0.62, the accessory tion zone peridotites. Cr# of The similar to abyssalocean ridge and supra-subduc gites and dunites with tectonite textures andare MMUprotolithsThe are predominantly harzbur / / (A) NiO (wt%) vs. Forsterite content (Fo) in olivine from the metaperidotites ofcontent (Fo)inolivinefromthemetaperidotites theMMU.Fieldsfor Forsterite (A)NiO(wt%)vs. mantleolivineare from Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín h E atrso the studied metaper of REEpatterns The et al . (1987),fore-arc peridotite from Ishii et al et al ., 2016andreferences therein). et al ., 2006;Deschamps ., 2008), characterized by http://dx.doi.org/10.18268/BSGM2020v72n3a120620 et al . (2012), variations of variations (2012), . et al et al et al . (1992)andabyssalperidotite from Moghadam et al ., ., ., /72(3)A1206202020 - - - - /72(3)A1206202020 A (Na + K + 2Ca) a.p.f.u. vs. vs. a.p.f.u. 2Ca) + K + (Na formed byformed expansion processes related to asub signatures but have oceanic cruststructures clearly setting, where ophiolites show typical island arc probably in asupra-subduction zone formed Medellín in rocks ultramafic the Consequently, Jiménez Roberts, 1988;Proenza supra-subduction zone settings (Pearce chromitites within are predominantly formed Several have authors that suggested podiform chromian described for spinel deposits Colombia. fore-arc (Savov duction zone peridotites from the Tso Morari MMU metaperidotites are similar to supra-sub the studied (Figure 5B)of trace element patterns 2006, 2016). Also, primitive mantle-normalized et al infiltration produced by slab dehydration (Proenza On the otherthe hand,the major MMU hosts ., 1999;Pearce et al ., 2012, 2014a and references therein). et al ., 2005). C (Al + Fe + (Al et al ., 2000;Marchesi et al et al 3+ + 2Ti) a.p.f.u. (C) Fe/(Fe + Fe/(Fe (C) a.p.f.u. 2Ti) + ., 1999;González- . (2015).(B)Amphibole et al ., 1984; et al ., - - MINERALIZATION 5.2. ORIGINOFTHECHROMIAN SPINEL (MORB; Dick and Bullen, 1984) and boninite-like for chromian spinelfrom mid-ocean ridge basalts defined fields the between plot that compositions mitite bodies associated with the exhibitMMU chromian the chro spinelforming coresmary of Jiménez and Violette, 1983;Proenza the crust inophiolite complexes (Leblanc base of layered gabbros at the Zone (MTZ), near levels of mantle-crust transition zone, orMohoTransition Al-rich chromitites are usually found withinthe and 7D)strongly (Figure PGE-depleted 6). and SanPedroare deposits Al-rich (Figures 7C studiedchromititeThe samples from Patio Bonito emplaced duringJurassic time. duringthe Triassicformed and later tectonically the Aburrá Ophiolite an oceanicback-arc basin work by Correa-Martínez (2007), who considers withthe arc agrees interpretation This basins). duction zone ( 1.5 t, TiO wt%, 15.75 = Al calculationsThe give average values of 0.64Fe# ln(FeO/MgO) (TiO (Al (Maurel andMaurel, 1982;Zaccarini has been calculated using the following equations the Patio Bonito andSan Pedro chromitites of with unaltered (magmatic) chromian spinelcores zuela (Mendi (Proenza (Proenza Cuba (Proenza region (Figures 7C and 7D)such asMoa-Baracoa, America andtheCaribbean central and southern are to otherAl-rich similar ophioliticchromitites in lavas (Figure compositions 7D) (Arai, 1992). These 2 h opsto fthe melt in equilibrium composition of The O 2 3
melt
melt spinel et al ) =0.708·ln(TiO et al ) =4.1386·ln(Al et al +ln(FeO/MgO) ., 2014a; Mendi 2014a; ., ., 2008),andCerro Colorado, Vene ., 2004b), Los Guanacos, Argentina Guanacos, Los 2004b), ., et al spinel e . et al g .,: fore-arc, intra-arc, andback- ., 2020). 0.47–1.07Al# = ., 1999), Tehuitzingo, México 2melt 04w% n (FeO/ and 0.41wt% = Boletín de la Sociedad Geológica Mexicana Mexicana Mexicana Geológica Geológica Sociedad Sociedad la la de de Boletín Boletín 2 2 O
spinel et al melt et al 3
spinel http://dx.doi.org/10.18268/BSGM2020v72n3a120620 ) +1.6436[2] [3] ., 1999,González- ., 2020). The pri ., 2020).The )+ 2.2828[1] et al spinel ., 2011): 2 + O 3melt - - - parental PGE-richmagma composition: Cr-rich content in chromitite is strongly related with the the parental magmas. PGE BABB compositionof chromitites is alsoconsistentwiththe MORB/ Casco (Correa-Martínez, 2007; Restrepo, 2008;García- the hostperidotites is basedonthe study of the MMU by that other authors ical setting of consistent withthe previously proposed geolog for back-arc basins, ageodynamicenvironment MORB/BABB magmasare characteristic of (Figure types 10). These diagram (melt) binary (MORB or BABB) in the FeO/MgO magmas (melt) vs. Al tholeiitic for described field MgO) 2011, 2014aand references therein). massive bodies(González-Jiménez to form and Ballhaus, 2002),inaself-sustained process (Matveev melt hydrous relatively the in flotation al mian spinel(Arai and Yurimoto, 1995;Melcher supersaturation in Cr in order to crystallize chro SiO different with melts of ing/mingling Cr-rich pyroxene from the host peridotite. Mix isprovidedtite formation by the dissolution of BABB melt, while Cr for the necessary chromi MORB/ differentiated more a with equilibrium thehost with harzburgite, generatingdunite in secondary reacts melt infiltrating model, González-Jiménez Robinson,1997; Proenza Yurimoto, 1995;Melcher fractionation within dunite channels (Arai and of degrees different with melts MORB/BABB arc mantle may berelated of with the mingling chromitites withinthesupra-subductionback- et al which are S-saturated (Hamlyn higher PGE-contents thantholeiitic magmas, boninitic magmasare S-undersaturated and have tholeiitic magmas.relatedis This to thefactthat ( magmas, whereas PGE-poor Al-richchromitites chromitites crystallize fromusually boninitic e . ., 1997), which may be accumulated by bubble g ., Colombianchromitites)crystallize from h ehns f rsalzto fthe crystallization of mechanismThe of ., 1998;González-Jiménez melt et al = 0.72 wt%, and plot overlapping the overlapping plot and wt%, 0.72 = ., 2020). The low., 2020). The PGE content in the /72(3)A1206202020 / 72(3)A1206202020 et al , 01 21a. n this In 2014a). 2011, ., et al et al ., 1997; Zhou and ., 1997;Zhou et al et al , 99 2004b; 1999, ., ., 2014b). ., 1985;Zhou 2 drives et al 2 21 21 O et ., - - - - 3
High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) DISCUSSION High-Al ophiolitic chromitites of Medellin Metaharzburgitic Unit (MMU) DISCUSSION 5.3. CHROMIAN SPINELALTERATION 22 22 these variations an origin related suggest to the at mantle temperatures orpressures. Instead, explained by processes magmatic/metamorphic cannot be the MMU in the chromian spinelof Textural and compositional variations observed fSiO of presence the in and ºC 400 ~ and 700 ~ between According to these authors, at temperatures Jiménez with the following reaction proposed by González- chromianthis secondary spinelcan be represented 2013; Colás 2000;Saumurolite facies (Barnes, andHattori, chromian at amphib spinelmetamorphosed of composition (Mg# vs. TiO invariable. porous The chromian spinel (type II) is enriched in Cr, whereas the Fe Fe in AlandMgcoupled with anincrease in Cr and ischaracterizedtransformation byThis adecrease facies) during cooling (García-Casco imprint (amphibolite medium-T metamorphic recrystallized olivine, tremolite and talc indicate secondary spinel andthe systematic presence of itation. Chlorite coronassurrounding chromian bychromian and chlorite spineldissolution precip porous chromian spinel(type II), can be explained first The chromian spinel,which forms of transformation America. South of paleomargin zoic during the Permian-Triassicperiod in the Meso cyclecooling associated with ametamorphic studied chromian spinelcouldbe attributed to Casco ºC, at medium pressures upto 6 kbar(García- 550-700 talc +forsterite) indicate temperatures of tions inthe metaperidotites (chlorite + tremolite + associa mineral metamorphic The bodies. mafic theultra evolution post-mantle metamorphic of / / Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín 2+ Boletín de la Sociedad Geológica Mexicana Geológica Sociedad la de Boletín opstoa n etrlvrain fthe Compositional and textural variations of + 8H 4(Mg . At this stage, the residual chromian spinel et al 2 -rich fluids, primary Al-rich Al-rich chromian spi fluids, primary -rich et al 2 0.7 O 2Mg ., 2020). Fe . (2015): et al 0.3 )CrAlO ,21,21) h omto fof formation The 2019). 2014, ., 5 AlSi 3 4 AlO +4Mg Cr 2 2 O , MnO, ZnO) istypical 10 (OH) 4 [4] 2 SiO http://dx.doi.org/10.18268/BSGM2020v72n3a120620 3+ 8 +2(Fe content stays 4 +2SiO et al ., 2020). 0.6 Mg 2 (aq.) 0.4 /72(3)A1206202020 ------/72(3)A1206202020 ) Figure 10 et al using theequationsbyMaurel and Maurel (1982)and Zaccarini in equilibriumcalculated were Melts chromitites. Bonito Patio andin equilibriumwith the SanPedro the parentalmelt (wt%)] of . (2011).Fieldsare from Moghadam tion product between chromian primary spinel and asthe reac other hand,it hasalsobeen interpreted al between chromian spinel andantigorite (Merlini 2000),or magnetite (Barnes, spinel andsecondary preted asthe reaction product between chromian chromian ferrian spinel hasbeen inter mation of The for spinel. chromian ferrian as classified be 0.3 to 0.79,and,therefore, this chromian spinel can nel types (Figure Fe 7B).The rich in comparison to the other two chromian spi in CrandFe residual porous type II chromian spinel, enriched nel reacts withforsterite to produce chlorite and oln fanultramafic body. cooling of spinel andlizardite (Mellini olivine (Gervilla ., 2009) during prograde metamorphism. Onthe ., 2009)duringprograde metamorphism. Homogeneous chromian spinel (type III) is Fe Composition diagram [(FeO/MgO) Composition diagram 2+ . et al ., 2012)orbetween chromian et al 3+ et al # values from vary ., 2005)duringthe . (2015). melt vs. (Al vs. 2 O 3 ) 3+ melt et - - - - -
6. Conclusions Acknowledgements tures closeto 600 ºC and evolving to temperatures a late hydrothermal processstarting at tempera chromianAl-Mg-depleted spinel(type II) during magnetite to the porous through the addition of Cr-rich spinel,probably at oxidizing conditions alreadyformed tion impliesthe of dissolution chromian homogenous The spinelforma This research has been financially supported financially by been and theSpanishProjectsFEDER Funds has research This to thegreenschist faciesconditions. reached amphibolite facies andlater retrograded the MMU, which processes has of metamorphic the superimposed the MMU give evidence of of chromianaccessory spinel in the metaperidotites spinel. Textural variations andcompositional of spinel, and(iii) homogeneousFe Cr-Fe altered partially (i) chromian with Al-rich spinel cores, (ii)porous as: classified is peridotites chromianmagma. Accessory spinelinthe meta spinel crystallizesfrom aBABB-type tholeiitic isa back-arcformation basin,where the chromian favorable geodynamicsetting for such chromitite most strongly is PGE.The and in depleted grade) associated with the MMU isAl-rich (refractory chromianscenario). The spinel mineralization duction zone setting (back-arc basin/incipient arc anic lithospheric mantle related to a supra-sub the suboce that these represent shallow levels of themetaperidotites from the indicateMMU of petrologicalThe and geochemical characteristics at greenschist facies.spinel metamorphosed Colás 2000;Saumurfacies (Barnes, andHattori, 2013; chromianmetamorphosed spinel in amphibolite spinel (type III) from the MMU isalso typical for TiO ºC (Colás lower than 500ºC (Gervilla 2 n,adZO fhomogeneouschromian , MnO, andZnO)of 2+ et al -enriched chromian andAl-Mg-depleted et al ., 2019) with similarities to chromian ., 2019). The composition(Mg# vs.., 2019).The Boletín de la Sociedad Geológica Mexicana Mexicana Mexicana Geológica Geológica Sociedad Sociedad la la de de Boletín Boletín et al http://dx.doi.org/10.18268/BSGM2020v72n3a120620 3+ ., 2012)or350 -rich chromian - - - - - References constructive criticism that has helped to greatly areeditors profoundly acknowledged for their Two anonymousreviewers andthe special volume Barcelona)appreciated. highly is (Universityof i Tecnòlogics Científics Serveis the at Prats Eva by Dr. X.Llovetby and duringFESEMsessions Excellent technical support during EPMA sessions paper. this and feedbackduringthepreparation of thank Dr. Antonio García-Casco for his support dad NacionaldeColombia(project no. 6867).We ria para la Movilidad de la Universi Internacional Colombia (project no. 35671) and the Convocato was partly supported the Universidad Nacional de 105625RB-C21. Fieldwork for sample collection CGL2012-36263, CGL2015-65824 and PID2019- Bourgois, J., Toussaint, J.F., González, H., cromo de Yacimiento 1945. G.Botero-Restrepo, S.J.,Barnes 2000,Chromite in komatiites, II. chromian spinel Arai, S., of 1992,Chemistry Arai, S., Yurimoto, H.,1995,Possible sub- Álvarez, J.,de los 1987,Mineralogíaquímica y thepresent manuscript. improve thequalityof L.A., Acevedo, A.P., Parra, E., Tournon, J., Azéma, J., Calle, B., Desmet, A.,Murcia, 321-334. Bogotá. 6, Tomo CEGOC, Antioquía). (Municipiode Envigado,“El Carmelo” https://doi. 387-409. org/10.1093/petrology/41.3.387 41, Petrology, of to Mid- Amphibolite FaciesJournal Metamorphism: Greenschist during Modification https://doi.org/10.1180/ minmag.1992.056.383.04 173–184. 56, magma chemistry: Mineralogical Magazine, in volcanic rocksas apotential guide to https://doi. 104-111. 4(2), org/10.1111/j.1440-1738.1995.tb00135.x Arc, Island chromitites: podiform The arc originof 28, 1-3,33-46. Colombia: Boletín Geológico Ingeominas, deAntioquia, de Medellín, Departamento de las dunitas de cromitadepósitos podiforme /72(3)A1206202020 / 72(3)A1206202020 23 23 - -
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