evolucion cretacica snsm. zuluaga 2011

7/27/2019 Evolucion Cretacica SNSM. Zuluaga 2011

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Late CretaceousePaleocene metamorphic evolution of the Sierra Nevada de SantaMarta: Implications for Caribbean geodynamic evolution

Carlos Zuluaga a,*, Harold Stowell b

a Dpto de Geociencias, Universidad Nacional de Colombia, Cr 30 45-03 Edif. Manuel Ancizar, Of. 301, Bogot, Colombiab Geological Sciences, The University of Alabama, Tuscaloosa, AL, USA

Keywords:

Caribbean plate

Santa Marta massif

Late CretaceousePaleocene metamorphism

PeT path

a b s t r a c t

A Late CretaceousePaleocene metamorphic event in the Santa Marta massif (northern Colombia) is

characterized by a PeTpath with a pressure increase after an initial temperature increase or temperature

increasing simultaneously with pressure. In either case, this path indicates loading of pre-heated crust in

agreement with the proposed models for the origin of the Caribbean plate and with the current

configuration of the CaribbeaneSouth America plate boundary. The PeT path constructed in a pelitic

schist from the inner Santa Marta metamorphic belt indicates that garnet grew during a loading event

that caused a pressure increase of up to 1.5 kbar in a subduction setting. Sample PeT path and Santa

Marta massif tectonic features are compatible with metamorphism on an accretionary wedge with

heating prior to loading or synchronous loading and thermal relaxation during thickening of the wedge,

this could result from a sedimentary pile accumulated in an anomalously hot oceanic crust. PeT path is

also compatible with low angle subduction similar to the current configuration of the subduction of the

Caribbean plate below the South America plate and to extensive retrograde metamorphism most likely

related to exhumation.

2011 Elsevier Ltd. All rights reserved.

1. Introduction

The Sierra Nevada de Santa Marta massif is an isolated

triangular-shaped mountain range in northern Colombia that is

separated from the rest of the Colombian Andes by extensive

sedimentary basins dominated with Tertiary infill. Two fault

Systems bound the massif and the adjacent basins, the Oca fault

bounds the block toward the north and the Santa Mar-

taeBucaramanga fault bounds the block toward the west. The most

striking tectonic feature of Santa Marta massif is the high elevation,

since the block is located at the edge of the continent and lacks an

appropriate continental root to support such high elevation as

indicated by strong positive Bouguer anomalies (Case andMacDonald, 1973; Ceron, 2008). Understanding the evolution of

this block is crucial for making reasonable interpretations for the

Cretaceous and younger interactions between the Caribbean and

South American plates. The evolution of the Santa Marta massif is

also important for unraveling the geologic history of the adjacent

petroleum-rich sedimentary basins. For example, it is crucial to

know whether the Santa Marta massif is cogenetic with the rest of

the Colombian Andes or originated elsewhere and is only related to

the Caribbean plate. In either case, the origin and evolution of this

tectonic block is particularly important for understanding interac-

tions between the Caribbean and the South American plates. There

are several interpretations for the tectonic evolution of this plate

boundary; however, all infer oblique convergence, diachronous

accretion of blocks, and formation of orogenic belts along the South

American plate edge. For example, Ostos et al. (2005) argue that

oblique convergence caused migration of the Lesser Antilles

volcanic arc, which collided with South America since the Late

Cretaceous. Similarly, James (2000) suggests that oblique conver-

gence of the Caribbean plate with northern South America

produced diachronous accretion of terranes to the northwesternborder of the continent and that this accretion caused episodic

orogeny between Upper Cretaceous and early Eocene times. This

orogeny caused metamorphism in the Mesozoic sedimentary

sequence, which was later exhumed as a coast mountain belt in

northwestern South America (Caribbean episode). Creta-

ceousePaleocene biotite AreAr cooling ages reported by Cardona

et al. (2006) from Paleozoic metamorphic rocks seem to be

related to Late Cretaceous orogeny probably related to evolution of

the Caribbean plate. Guth (1991) inferred that the metamorphic

belts along the Caribbean coast originated west of their present

position and that eastward movement of the Caribbean plate* Corresponding author.

E-mail address: [email protected] (C. Zuluaga).

Contents lists available at SciVerse ScienceDirect

Journal of South American Earth Sciences

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j s a m e s

0895-9811/$ e see front matter 2011 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jsames.2011.10.001

Journal of South American Earth Sciences 34 (2012) 1e9
mailto:[email protected]://www.sciencedirect.com/science/journal/08959811http://www.elsevier.com/locate/jsameshttp://dx.doi.org/10.1016/j.jsames.2011.10.001http://dx.doi.org/10.1016/j.jsames.2011.10.001http://dx.doi.org/10.1016/j.jsames.2011.10.001http://dx.doi.org/10.1016/j.jsames.2011.10.001http://dx.doi.org/10.1016/j.jsames.2011.10.001http://dx.doi.org/10.1016/j.jsames.2011.10.001http://www.elsevier.com/locate/jsameshttp://www.sciencedirect.com/science/journal/08959811mailto:[email protected]


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caused their accretion to the continent. The effects of Car-

ibbeaneSouth American plate interaction probably extend beyond

the continental coastal areas, as indicated by Kellogg and Bonini

(1982), who argue that the Cenozoic uplifts and adjacent depres-

sions in the Santa Marta massif, the Perija mountains, and the

Venezuelan Andes result from more than 500 km of shortening

associated with subduction of Caribbean oceanic lithosphere below

the overriding South American plate.

The Santa Marta massif is divided into several NEeSW meta-

morphic belts separated by two regional lineaments (Cesar and

Sevilla) and by abrupt changes in metamorphic grade. Toward the

northwest of the triangular block, the two youngest belts (Sevilla

and Santa Marta metamorphic belts) are probably associated with

a subduction zone (Tschanz et al., 1974). The Santa Marta meta-

morphic belt (SMMB) is the outer and younger of the two and it

consists of pelitic and psammitic schist and metabasites effected by

low to medium grade metamorphism (greenschist to amphibolite

facies), which occurred between Late Cretaceous and Paleocene

(Restrepo-Pace et al., 1997; Tschanz et al., 1974). Inward to the core

of the block, the next metamorphic belt (Sevilla belt) contains

mostly medium to high-grade mafic gneisses of probable Paleozoic

age (Cardona et al., 2006). In the core of the Santa Marta massif, the

Sierra Nevada belt contains late Precambrian granulite facies pel-itic, quartzo-feldspathic, and mafic gneisses and Jurassic magmatic

rocks (Tschanz et al., 1974; Restrepo-Pace et al., 1997; Ordonez-

Carmona et al., 2002; Cordani et al., 2005; Cardona et al., 2006).

Low-grade metasedimentary rocks (schist and phyllite) of the

southeastern belt (Perija belt) are similar to those observed in the

Eastern Cordillera of the Colombian Andes (Tschanz et al., 1974).

The SMMB contains two bands,the inner, eastern band, contains

amphibolite facies metapelites (micaceous schist with garnet and

sillimanite) while the outer, western band, contains greenschist

facies rocks (Tschanz et al., 1974). This contribution presents new

PeTestimates and interpretations for the metamorphic history of

metapelites from the inner band of the SMMB, subsequently

referred to as the Inner SMMB.

2. Methodology

Two samples were analyzed to study the metamorphic evolu-

tion of the inner SMMB. The goal was to determine metamorphic

peak pressures and temperatures and to constrain the possible PeT

paths followed by the samples during burial and exhumation. Both

samples were collected in a metapelitic interval in the central

portion of the study area (Fig. 1).

Whole-rock compositions used for pseudosection construction

were determined by X-ray fluorescence from fused glass discs. First

0.8 g of the sample were mixed with a flux (a mixture of lithium

tetraborate and lithium metaborate) in a 1:10 ratio and then a non-

wetting agent was added (lithium iodide). Sample was heated past

the melting point of theflux in a 95% platinum and 5% goldcrucible.The analysis was performed with the Universidad Nacional de

Colombia Philips MagixPro PW e 2440 X-ray fluorescence spec-

trometer equipped with a Rh X-ray tube with a maximum power of

4 kW. Quantitative mineral analyses and X-ray maps were collected

with the JEOL 8600 electron probe microanalyzer at The University

of Alabama using wavelength dispersion spectrometry (1e20 mm

beam diameter, 20 nA current, a 15 kV accelerating potential, and

count times from 30 to 45 s). Operating conditions for collection of

X-ray maps were 15 kV accelerating potential, 75e300 nA beam

current, and a 1 mm beam. Count times ranged from 50 to 100 ms

per pixel.

The PeT paths integrate rim thermobarometry and pseudo-

sections following the techniques presented by Vance and Mahar

(1998), Stowell et al. (2001), and Stowell and Tinkham (2003).

Fig. 1. Generalized geologic map of the western Santa Marta massif, showing sample

localities mentioned in the text. A NWeSE interpretative cross section is shown below

the map (redrawn from Tschanz et al., 1969). The top figure is a generalized tectonic

map of northern Colombia showing the location of the Santa Marta massif (SNSM

Block). SM-B Santa MartaeBucaramanga Fault, CM Fault System CaucaeAlmaguer

(Romeral) Fault System.

C. Zuluaga, H. Stowell / Journal of South American Earth Sciences 34 (2012) 1e92


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Garnet rim thermobarometry was used to estimate PeT at peak

metamorphic conditions with the average PeT routine of THER-

MOCALC (Powell and Holland, 1988; Powell et al., 1998) using

externally calculated activities. Estimates for peak pressures and

temperatures were integrated with pseudosection fields following

the technique presented in Zuluaga et al. (2005). Garnet core

compositions were plotted as the compositional variables spes-

sartine, grossular, and iron number (Fe# Fe/FeMg) in PeT

pseudosections (isopleths). Pseudosections were constructed

using the computer program THERMOCALC and the thermody-

namic database of Holland and Powell (1998) with the silicate

melts model extension (Holland and Powell, 2001; White et al.,

2001; tcds55 produced on 22 Nov 2003). All thermodynamic

models used the nine-component oxide system: MnO, Na2O, CaO,

K2O, FeO, MgO, Al2O3, SiO2, and H2O (MnNCKFMASH), activity

models used here are the same as those used and discussed in

Tinkham et al. (2001), Holland and Powell (2001) and White

et al. (2001).

3. Geology of the inner SMMB

The inner SMMB contains amphibolite, amphibole schist,

quartzo-feldspathic schist, quartzite and pelitic schist that are

grouped into three units: San Lorenzo Schist, Gaira Schist and

Undifferentiated Schist (Doolan, 1970; MacDonald et al., 1971;

Tschanz et al., 1974). The western contact of the inner SMMB

band with the Santa Marta batholith is characterized by the pres-

ence of metamorphic enclaves in the pluton (roof pendants and

xenoliths trapped during pluton emplacement) and the eastern

contact is with higher grade metamorphic rocks of the Sevilla belt.

Since all three units have similar lithologies and the contacts

between them are in most cases gradational they could correspond

to a single sequence that underwent the same metamorphic and

deformational history. All lithologies are locally mylonitic and show

evidences of retrograde metamorphism (see Table 1 for a summary

of lithologies and their characteristics). Amphibolite and amphibole

schist predominate toward the north while quartzite and quartzschist are the most abundant lithologies in the central part of the

band. Metapelites and metapsammites are observed locally at the

north and central zones of the band. Migmatite is also present

locally in the north portion of the Inner SMMB and is characterized

by the presence of quartzo-feldspathic and amphibole gneiss with

numerous cross-cutting tonalite leucosomes. The origin of the

leucosomes (e.g., external versus internal derivation) and the

relationships between this migmatite and the other lithologies in

the Inner SMMB is unknown because migmatites are separated

from the other lithologies by El Carmen Fault and associated fault

systems in a complex tectonic setting (Fig. 1).

Metapelitic intervals are best exposed in the central portion of

the Inner SMMB (La Tagua, Fig.1), where a thick quartzite sequence

overlies metapelites interlayered with amphibolite, amphibole

schist, and quartzo-feldspathic schist. These metapelites locally

contain garnet and sillimanite (Table 1).

4. Characterization of metamorphism in the inner SMMB

This manuscript describes two samples of medium grained

schist, sample 07CZCT18d has a parageneses of quartz

plagioclase

biotite

garnet

sillimanite and sample 07CZCT21ewith a parageneses of quartzplagioclase biotite garnet

sillimanite muscovite. The mineral assemblage differences bet-

ween the two samples reflect the different chemical composition,

e.g., sample 07CZCT21e contains more SiO2 and less Al2O3 than

sample 07CZCT18d (Table 2). Retrograde chlorite is present in both

samples cutting across foliation and/or replacing other phases;

however, the proportion of retrograde chlorite is low in sample

07CZCT21e where the main retrograde mineral is muscovite.

Retrograde muscovite is not seen in sample 07CZCT18d. Retrograde

muscovite occurs as small irregularly shaped crystals commonly

intergrowth with chlorite as pseudomorphs after sillimanite and

biotite.Accessory phases in bothsamples are tourmaline, zircon and

apatite. Identification of an aluminum silicate (kyanite or silli-

manite) in sample 07CZCT18d was only possible in the electron

microprobe since the crystals are less than 100 mm in maximum

dimension, this aluminum silicate is interpreted to be sillimanite.

Sample 07CZCT21e contains prismatic sillimanite and fibrolite, and

kyanite was identified as relicts surrounded by muscovite, chlorite

and sillimanite (Fig. 2). Euhedral biotite contains abundant zircon

inclusions and is locally replaced by chlorite, note that in sample

07CZCT18d results of biotite microprobe analysis show a trend

toward the retrograde chlorite composition (Fig. 4). Garnets in

sample 07CZCT18d are up to 5 mm in diameter, euhedral to sub-

hedral and poikiloblastic, while in sample 07CZCT21e garnets are

smaller (up to 0.5 mm),more euhedraland poorer in inclusions than

in sample 07CZCT18d. Inclusions in garnet are mostly quartz,

plagioclase,and biotite.In bothsamples, garnet is locallyreplaced by

chlorite. Compositional zoning in garnet shows typical bell-shape

profiles of spessartine and grossular components that are rela-tively high in the core and low at the rims; however, the composi-

tional cores are not at the geometric center of the grains. This

compositional zoning is best observed in sample 07CZCT18d

because of the size of the garnet crystals, where the difference in

mole fraction between rim and core is ca. 0.07 mole fraction for

spessartine and ca. 0.04 mole fraction for grossular (Fig. 3). Garnets

in sample 07CZCT18d alsoshow inverse zoning towardthe rimswith

a slight increase in spessartine (ca. 0.03 mole fraction) andgrossular

content (ca. 0.01 mole fraction). For sample 07CZCT21e, less than

0.3 mm garnets have compositional differences between core and

rim that range from 0.04 mole fraction for almandine to less than

0.02 for grossular, pyrope, and spessartine. The compositional

zoning in the last mentioned sample is actually well preserved in

spite of the small crystal size.

Table 1

Summary of characteristics of main lithologies in the inner SMMB, Sierra Nevada de Santa Marta, Colombia.

Lithology Microstructure Paragenesis Observations

Pelitic schist Schistose Quartzplagioclasebiotite garnet

sillimanitemuscovite

More than 20 mode% of biotite. Accessories: rutile, tourmaline,

apatite and zircon. Retrograde chlorite and epidote.

Psammitic schist Schistose Quartzplagioclasebiotite garnet

sillimanitemuscovite

More than 50 mode% of quartz and less than 10 mode% of biotite.

Accessories: rutile, apatite and zircon. Retrograde chlorite and epidote.

Quartzite Schistose Mostly quartz Variable amounts of plagioclase and biotite

Migmatite Gneissic Mesosome: Amphibole and quartzfeldspathic schist

Leucosome: tonalite and quartzeplagioclase lenses

Amphibolites and

amphibole schist

Schistose Quartzplagioclasehornblende. Accessories: Epidote and actinolite. Retrograde chlorite.

C. Zuluaga, H. Stowell / Journal of South American Earth Sciences 34 (2012) 1e9 3


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4.1. Prograde path and metamorphic peak

The general topology of the pseudosections for samples

07CZCT18d and 07CZCT21e (Figs. 5 and 6) facilitates interpretation

of mineral textures and constrain the PeTevolution for the Inner

SMMB. Textural observations and microprobe data indicate that thepeak mineral assemblage in 07CZCT18d is Grt Bt SilQtz Pl,

the pseudosection stability field for this parageneses is in the range

ca. 6e8.5 kbar and 610e675 C. Similarly, the stable peak mineral

assemblage in sample 07CZCT21e is predicted between 3.7 and

7 kbar and 575e670 C (Fig. 6), a much wider range than that for

sample 07CZCT18d. However, relict kyanite constrains pressures

reached before peak conditions to ca. 5e7 kbar. In sample

07CZCT21e, peak pressures and temperatures are also constrained

by average PeTusing six reactions (Table 4; Fig. 6), to a temperature

of 612109 C and a pressure of 5.61.3 kbar. The pseudosection

field for the peak mineral assemblage of sample 07CZCT21e

(Grt Bt SilQtz PlMs) and the presence of relict kyanite

further constrain peak PeT to ca. 6e7 kbar and 640e670 C.

Thermobarometry and pseudosection PeT predictions for the

two samples allow for two possible PeTpath interpretations. These

paths are well constrained in sample 07CZCT21e (Fig. 6) by initial

garnet growth PeTconditions, peak metamorphic conditions and

the presence of kyanite relicts. One possible scenario is a path with

continuous PeT increase, the alternative interpretation is a path

with initial pressure increase followed by an isobaric heating

(Fig. 6).

4.2. Retrograde path

The retrograde chlorite and lack of retrograde muscovite in

07CZCT18d are predicted by the pseudosection (Fig. 5) which

shows the chlorite-in line at ca. 620e630 C in the range 5e8 kbar,

just 20 C below the field of the stable paragenesis. The muscovite-

in line is predicted more than 50

C below the field of the stableparagenesis at 5 kbar. In contrast, the pseudosection for sample

07CZCT21e predicts muscovite stable in the paragenesis field and

the chlorite-in line at lower temperatures than those of sample

07CZCT18d, the chlorite-in line is predicted in the range

580e630 C and 5e8 kbar. Pseudosection topology is in agreement

with the observed textures in sample 07CZCT21e that has musco-

vite as the main retrograde mineral with minor retrograde chlorite.

Fig. 2. Photomicrographs in PPL of samples 07CZCT21e (a, b, and c) and 07CZCT18d (d). Note in b and c the kyanite relicts within sillimanite and muscovite. Note also the difference

in garnet sizes between sample 07CZCT21e (a) and sample 07CZCT18d (d). Mineral abbreviation after Kretz (1983).

Table 2

Whole-rock chemical analysis of samples mentioned in the text, Sierra Nevada de

Santa Marta, Colombia.

07CZCT18d 07CZCT21e

SiO2 65.16 74.06

TiO2 0.93 0.69

Al2O3 15.59 12.02

Fe2O3 5.2 5.9

MnO 0.11 0.22MgO 2.81 2.29

CaO 3.64 0.47

Na2O 2.5 0.77

K2O 1.64 2.37

P2O5 0.117 0.06

LOI 2.01

Total 99.71 98.85

Fe2O3 indicates total Fe.



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For this sample, the prograde path favors consumption of musco-

vite, which will grow again in the retrograde part of the path.In any case, re-equilibration of paragenesis with growth of

retrograde chlorite and muscovite in both samples constrain the

retrograde path to that shown in Fig. 6. Note that, in both samples,

a retrograde path without a significant isothermal pressure

decrease will favor the growth of retrograde chlorite more than

a path with isothermal pressure decrease after the metamorphic

peak, since the chlorite-in line will be crossed by the path at lower

temperatures.

5. Discussion and tectonic implications

A preliminary interpretation indicates that during garnet

growth, pressure may have increased by up to 1.5 kbar. Tempera-

ture likely was high prior to the loading event or increased

simultaneously with the pressure increase as indicated by pseu-

dosection of sample 07CZCT21e. The last observation probably

indicates that garnet grew during a loading event in pre-heated

crust, this PeT path signature is different from most common

clockwise PeT paths associated with thrust loading where initial

isothermal pressure increases is followed by thermal relaxation

(e.g., England and Thompson, 1984). The age of this event, i.e., the

age of metamorphism, has not been directly determined. A prov-

enance study reported in Cardona et al. (2010a) constrains the

oldest age for sedimentation in the SMMB by detrital Ue

Pb zirconsfrom schist in the outer band as Late Cretaceous. The youngest age

is constrained by the Santa Marta batholith that intrudes the

metamorphic belt. The batholith age rangesup tow56 Ma based on

zircon LA-ICPMS UePb ages (Duque, 2010). Data of Cardona et al.

(2010b) points to a episodic development of the massif with

a metamorphic event related to a caribbean arc collision at ca.

65 Ma. These data constrain the age of metamorphism to the range

Late CretaceousePaleocene. Amphibole, biotite and heavy fraction

KeAr ages reported by Tschanz et al. (1974) in the inner SMMB

range between 36 Ma and 51 Ma, these ages were interpreted as

the result of plutonic activity or cooling during exhumation and not

as a direct result of the metamorphic event (Tschanz et al., 1974).

Older amphibole, biotite and whole-rock KeAr ages are reported in

the outer band of the belt (MacDonald et al., 1971) and from

Fig. 3. Compositional zoning of garnet in samples 07CZCT21e and 07CZCT18d. (a)

Garnet compositional profile, sample 07CZCT21e. (b) Garnet compositional profile,

sample 07CZCT18d. (c) Mn X-ray map, sample 07CZCT18d, the white line crossing the

garnet shows the location of compositional profile in b. Observe compositional zoning

with high Ca and Mn content and low Mg and Fe content at the core of garnet in

sample 07CZCT18d (b and c). Note also that compositional zoning in sample

07CZCT21e (a) is weak for Ca and Mg, but more pronounced in Mn and Fe.

07CZCT18d

07CZCT21e

Grt

Sil

Bt

A

MF

Grt

Sil

Bt

A

MF

Bulk rock

Chlorite

Biotite

Garnet rim

Garnet core

Bulk rock

Biotite

Garnet rim

Garnet core

Fig. 4. AFM compatibility diagrams projected from quartz, muscovite, and water.

Diagrams show mineral compositions from microprobe analysis (Table 3) and bulk

rock compositions from X-ray fluorescence analysis (Table 2). Note that projection

from muscovite is not strictly correct for sample 07CZCT18d; however, the diagramhelps to understand variations in biotite compositions for sample 07CZCT18d due to

extensive retrograde re-equilibration.



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Table 3

Electron microprobe analysis of garnet, biotite, muscovite, chlorite, and plagioclase of samples mentioned in the text, Sierra Nevada de Santa Marta, Colombia. All analyses were

sample 07CZCT18d.

Garnet Biotite Plagioclase

Near Rim-15 anal.(1) 20 anal. 20 anal. 8 anal.

Rep. Average Rep. Average Rep. Average Rep. Average

Oxide(2) Oxide s.d. Cations(3) Oxides Oxides s.d. Cations Oxides Oxides s.d. Cations Oxides Oxides s.d. C

Sample 07CZCT18d

SiO2 37.88 37.82 0.13 2.98 37.41 37.21 0.34 2.97 37.23 37.57 1.98 2.77 52.52 53.96 2.95 2

TiO2 1.81 1.76 0.26 0.10

Al2O3 22.13 21.85 0.16 2.04 21.44 21.83 1.00 2.05 19.09 19.81 1.30 1.72 29.63 28.76 2.19 1

FeO 28.49 28.8 0.23 1.90 27.04 26.74 0.44 1.78 15.91 1 5.11 1.61 0.93

MgO 4.64 4.71 0.07 0.55 3.06 3.14 0.14 0.37 12.62 12.24 1.39 1.35

MnO 2.28 2.41 0.10 0.16 5.27 5.34 0.15 0.36 0.12 0.13 0.03 0.01

CaO 4.24 4.37 0.07 0.37 5.55 5.58 0.21 0.48 0.01 0.16 0.58 0.01 11.59 10.62 2.43 0

Na2O 0.11 0.1 0.05 0.01 4.71 5.52 1.50 0

K2O 7.35 8.08 1.32 0.76 0.06 0.06 0.03 0

Total 99.66 99.94 99.77 99.85 94.25 94.95 98.51 98.92

Garnet Biotite Plagioclase

Near Rim-10 anal.(1) Core-14 anal. 14 anal. 25 anal.

Rep. Average Rep. Average Rep. Average Rep. Average

Oxide(2) Oxide s.d. Cations(3) Oxides Oxides s.d. Cations Oxides Oxides s.d. Cations Oxides Oxides s.d. C

Sample 07CZCT21e

SiO2 36.74 36.62 0.32 2.95 37.29 37.12 0.21 2.96 35.38 35.52 0.37 2.66 60.44 60.16 0.56 2

TiO2 2.03 2.38 0.20 0.13

Al2O3 22.1 22.33 0.34 2.12 22.04 22.21 0.14 2.09 19.98 20.3 0.54 1.79 25.02 25.13 0.50 1

FeO 31.57 31.63 0.36 2.13 30.56 30.6 0.35 2.04 18.27 18.16 0.76 1.14

MgO 3.09 3.03 0.11 0.36 3.4 3.34 0.06 0.40 9.85 9.38 0.61 1.05

MnO 4.42 4.49 0.14 0.31 5.2 5.32 0.11 0.36 0.16 0.17 0.04 0.01

CaO 1.55 1.55 0.07 0.13 1.77 1.95 0.21 0.17 0 0.01 0.01 0.00 5.88 6.12 0.34 0

Na2O 0.23 0.21 0.07 0.03 8.67 7.98 0.69 0K2O 10.89 11.01 0.31 1.05 0.11 0.14 0.09 0

Total 99.47 99.64 100.26 100.53 96.8 97.13 100.12 99.53


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possible correlative lithologies in the basement of adjacent sedi-

mentary basins (Tschanz et al., 1974). These ages suggest that the

metamorphic event could be as old as 130 Ma. However, these

reports conflict with the more robust detrital UePb zircons ages

summarized above and the older KeAr ages are considered

dubious.

The PeT path constructed for sample 07CZCT21e of the inner

SMMB is most compatible with interpretation of the Late Creta-

ceousePaleocene metamorphic belt of the Santa Marta massif as an

accretionary prism of a subduction zone related to the interactionbetween the Caribbean and South American plates according to the

tectonic plate reconstruction for this region during the age range

Late CretaceousePaleocene (Pindell and Kennan, 2009). Further-

more, the interpreted age range for this belt is similar to the age of

the metamorphic belt in the Alta Guajira region (Etpana Meta-

morphic Suite and Jarara Schist) interpreted also to be Late Creta-

ceousePaleocene (Weber et al., 2010). Both belts belong to a larger

metamorphic belt in northwestern South America that records the

interaction of the mentioned tectonic plates.

The PeTpath constructed here for the amphibolite facies schist

of the Santa Marta Belt differs from the commonly inferred paths of

thrustingethermal relaxation cycles characteristic of collision

tectonics. Other types of tectonic mechanisms inferred to have an

important role in the evolution of metamorphic belts are subduc-tion initiation, triple-junction interactions, initiation and shut off of

arc volcanism, subcontinental delamination, and hot spot migra-

tion (Wakabayashi, 2004). The continue increase in pressure and

temperature in the PeT path with interpreted medium P/T ratio

could be related to a lowangle subduction zone, consistent with the

current configuration of the CaribbeaneSouth America plate

boundary, obtained at the end of the Cretaceous (Giunta and

Oliveri, 2009; Pindell and Kennan, 2009; and references therein).

The difficulty in relating this medium P/T hairpin path with

a subduction zone is the lack of published similar PeT paths.

Although the initially anticlockwise part of the PeT path is still

speculative, we offer here an interpretation for this part of the PeT

path (initial heating and then rapid buriale initially anticlockwise).

The tectonic regime for the development of the anticlockwise part

of the PeTpath could be related to thickening of a pre-heated crust

in a hot spot or incipient rift environments (e.g. Sandiford and

Powell, 1986; Bohlen, 1987; Harley, 1989; Bohlen, 1991) in agree-

ment with the two current models for the origin of the Caribbean

plate (e.g., in situ origin: Klitgord and Schouten, 1986; Donnelly,

1989; James, 2006, 2009a,b; Giunta and Oliveri, 2009; pacific

origin: Pindell and Dewey, 1982; Burke et al., 1984; Pindell andBarret, 1990; Pindell and Kennan, 2009). In this scenario, it is

probable that the sedimentary pile accumulated in an anomalously

hot oceanic crust; however, it remains uncertain if the amount of

heat available and the efficiency of heating the sedimentary pile on

top of the oceanic crust are enough to explain the initial temper-

ature increase in the proposed PeT path.

Retrograde phases (chlorite and muscovite) could have grown

during exhumation of the rocks. Retrograde metamorphism during

exhumation is possible in conjunction with the exhumation rates

proposed by Villagmez (2010) for the Santa Marta massif during

the Paleogene (generally in excess of 0.3 km/My) because would

likely have been water available in the tectonic setting. Although it

has been proposed that the most effective mechanisms for

exhuming metamorphic rocks are synorogenic erosion and normal

Prp = 0.123

Sps = 0.122

Grs = 0.159

Temperature (C)

Pressure(kbar)

475 500 525 550 575 600 625 650 675

3

3.5

4

4.5

5

5.5

6

6.5

7

7.5

8

8.5

9

9.5

10Solidus

Grt Bt Ms Chl

Qtz Pl H2O

Ms Chl Bt

Qtz Pl H2O

Grt Bt Ms Ky

Qtz Pl H2O

Grt Pg Ms Chl

Qtz Pl H2O

Grt Bt Ky

Qtz Pl H2O

Grt Bt Sil

Qtz Pl H2O

Grt Bt Cd

Qtz Pl H2O

Grt Bt Chl Cd

Qtz Pl H2O

Grt Bt St

Chl Qtz

Pl H2O

Grt Bt Chl Sil

Qtz Pl H2O

Fig. 5. 07CZCT18d MnNCKFMASH Pe

Tpseudosection. There is no clear intersection of

garnet core compositional isopleths, therefore it was not possible to predict the PeT

conditions of initial garnet growth. The location of the peak mineral assemblage field,

is shaded in gray, assuming the aluminum silicate present is sillimanite.

450 500 550 600 650 7003

3.5

4

4.5

5

5.5

6

6.5

7

7.5

8

8.5

9+Qtz +H2O

Grt Bt Pl

Ms Chl

Grt Bt PlMs Chl Zo

Grt Pl MsChl Zo

Grt Pl Ms

Chl Pa Zo

Grt Bt MsChl Pa Zo

Grt Bt Ms

Chl Pa

Grt Bt PlMs Chl Pa

Grt Bt Pl

Ms Ky

Grt Bt Pl

Ms Chl PaGrt Bt Pl

Ms Pa

Grt Bt Pl

Ms Pa Ky

Grt Bt PlMs St

Grt Bt PlMs Sil

Grt Bt PlMs And Cd

Grt Bt Pl

Ms CdGrt Bt PlKfs Cd

Grt Bt Pl

Ms Sil Cd

Grt Bt Pl

Ms And

Grt Bt Pl

Ms St Ky

Grt Bt PlMs St Sil

Grt Bt PlMs St Chl

Grt Bt Pl

Ms Ky

Pl

450 500 550 600 650 7003

3.5

4

4.5

5

5.5

6

6.5

7

7.5

8

8.5

9 Grt Bt Pl MsSil Qtz H2O

Fe # = 0.837

450 500 550 600 650 7003

3.5

4

4.5

5

5.5

6

6.5

7

7.5

8

8.5

9

Sps = 0.121

Grs = 0.056

Temperature (C)

Pressure

(kbar)

Solidus

Temperature (C)

Pressure

(kbar)

Temperature (C)

Pressure

(kbar)

Fig. 6. 07CZCT21e MnNCKFMASH PeT pseudosection. The top figure shows the

general topology of the pseudosection, the intersection of garnet core compositionalisopleths (used to predict the PeTconditions of initial garnet growth e black ellipse),

the peak mineral assemblage field in gray, and the assemblage kyanite (relict phase)

with a horizontal lines pattern. Average pressureetemperature determination for peak

metamorphic conditions is shown with its uncertainty ellipse in broken lines in the

lower left figure. The two possible PeTpaths are shown by gray and black curves in the

lower right figure.



8/9

faulting (e.g., Ring et al., 1999), in a subduction setting, the

subduction channel provides an alternative way for the exhuma-

tion of the rocks after or synchronous with the retrograde event. As

Platt (1993) pointed out, exhumation is at least partly a result of

tectonic processes and a potential tectonic mechanism in

a subduction zone is the flow of low-viscosity material trapped

between the upper and lower plates (flow-channel model; Cloos,

1982; Platt, 1993). The active flow, with rates on a time scale of

a few million years is restricted to a narrow channel confined

between thesubducting slab anda rigid wedgeof lithosphere in the

hanging wall, can cause upward flow of deeply buried rock (Cloos,

1982). Numerical simulations testing such a process shows that the

development of a subduction channel forces a return flow of low-

viscosity material and progressive widening by hydration of the

mantle wedge (Gerya et al., 2002). In this scenario, the retrograde

metamorphism can be explained because the thermal regime is

similar during the prograde and retrograde parts of the PeT path

(see for example Cloos, 1982) as shown by sample 07CZCT21e.

The alternative explanation is that retrograde metamorphismcould be related to a younger lower-grade metamophic event also

related to subduction of the Caribbean plate below the South

American plate (see for example Bustamante et al., 2009; Cardona

et al., 2010b). However, the interpretation of the age of the lower-

grade metamorphism based in tectonic position with constraints

from detrital zircon ages, a zircon metamorphic rim age, and

intrusive relations with Paleogene granitoids (Cardona et al., 2010a)

and the interpreted age of the amphibolite facies metamorphism

are not enough well constrained to allow for a interpretation of

a time interval separating the two events. There are not data to

support the interpretation of retrograde metamorphism related to

Paleogene plutonism other than the interpretation of resetting of

the KeAr ages reported by MacDonald et al. (1971) and Tschanz

et al. (1974).

6. Conclusions

The Late CretaceousePaleocene metamorphic belt of the Santa

Marta massif is part of a Late CretaceousePaleocene accretionary

prism of a subduction zone related to the interaction between the

Caribbean and South American plates in northwestern South

America. The low angle subduction of the Caribbean plate below

the South America plate may have predominated also during the

time of formation of the metamorphic belt as suggested by the PeT

path presented here with a interpreted medium P/T ratio and

continue pressure and temperature increase. It is no yet clear what

caused the extensive retrograde metamorphism observed in the

belt, but the shape of the PeT path and the likely mechanism of

exhumation in the subduction zone environment could point to

retrograde metamorphism related to exhumation because of

similar thermal regimes during the upward and downward

segments of the path.

Acknowledgments

This manuscript benefitted from helpful reviews from Antonio

Garcia-Casco and an anonymous reviewer, their comments are

greatly appreciated; however, all typos and mistakes are ours. This

work had financial support from a INGEOMINAS-INVEMAR-ICP

project and from the Universidad Nacional de Colombia. We want

to express gratitude to Georgina Guzman and German Yuri Ojeda

for their support at the beginning of the project. Microprobe

analysis was performed at the analytical facilities of the University

of Alabama.

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Activities, calculated at 610 C, 5.0 kbar Prp Alm Grs Phl Ann East Sill

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a sd(a) b c ln_K sd(ln_K)

1) GrsQtz2 Sill3 An 26.53 0.58 0.11522 5.335 6.457 0.853

2) 3 East6 QtzPrpPhl 2 Ms 14.11 1.23 0.01247 3.533 0.685 1.324

3) 7 Phl12 Sill5 Prp3 East4 Ms 200.66 2.16 0.03414 7.145 17.625 4.354

4) Phl East6 QtzPrp 2 Cel 59.39 1.08 0.03636 4.141 9.270 2.398

5) 2 AnnMs6 QtzAlm3 Fcel 63.64 2.19 0.03697 4.864 9.758 4.749

6) AnnQtz2 SillAlmMs 8.9 1.00 0.01003 2.070 1.742 0.412

Average PT P 5.6 1.3 kbar

T 612109 C



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