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GEOCHEMICAL AND PETROLOGICAL CHARACTERIZATION OF THE CAJAMARCA

COMPLEX IN THE RIO CLARO AREA: METAMORPHIC IMPLICATIONS

By:

Nataly Pulido Fernández

Undergraduate Thesis for Geosciences FACULTY OF SCIENCES

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GEOCHEMICAL AND PETROLOGICAL CHARACTERIZATION OF THE CAJAMARCA

COMPLEX IN THE RIO CLARO AREA: METAMORPHIC IMPLICATIONS

NATALY PULIDO FERNÁNDEZ

Ungraduated thesis to opt for the title of:

Geoscientific

Supervisor:

IDAEL FRANCISCO BLANCO QUINTERO, PhD.

Universidad de los Andes

Faculty of Sciences

Department of Geosciences

Bogotá - 2017

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Table of contents 1. Abstract ....................................................................................................................................................................................... 7

2. Introduction ............................................................................................................................................................................ 8

3. Conceptual Framework .................................................................................................................................................. 11

3.1. Barrovian regional metamorphism ............................................................................................................................................. 11

4. Geological Setting ............................................................................................................................................................. 15

5. Methodology and Analytical techniques ........................................................................................................... 18

6. Results ....................................................................................................................................................................................... 21

6.1. Petrography ...................................................................................................................................................................... 21

6.2. SEM - BSE Images and EDS analyses ..................................................................................................................................... 24

6.3. Geochemistry ................................................................................................................................................................................................ 29

7. Discussion ............................................................................................................................................................................... 33

7.1. Tectonic implications ............................................................................................................................................................................ 33

7.2. P-T metamorphic conditions .......................................................................................................................................................... 36

8. Conclusions ........................................................................................................................................................................... 39

9. Acknowledgements ......................................................................................................................................................... 40

10. References ......................................................................................................................................................................... 41

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1. Abstract

The Cajamarca Complex, widely distributed along the Northern Central Cordillera of

Colombia, was formed in a tectonic setting dominated by Permian subduction, volcanic-arc

magmatism, basin development and closure and accretion of terrenes. Outcrops of the

Cajamarca Complex sequence were studied in Rio Claro and Abejorral municipalities of

Colombia. The rocks area metapelite samples which were analyzed by a petrographic

microscopy, scanning electron microscope (SEM) and geochemical data using major and trace

elements. This study focuses on discussing the tectonic implications by the analysis of tectonic

discrimination diagrams and the P-T metamorphic conditions calculated in the

THERMOCALC software. Bulk geochemistry of metapelites shows an inverse relation to the

atomic number in rare earth elements (REE) normalized to chondrite. In addition, the N-

MORB analysis shows a depleting of the high-field strength elements (HFSEs) as well as an

enrichment on the large-ion Lithophile Elements (LILE). The samples are mainly formed by

garnet, amphibole, plagioclase, muscovite, epidote, chlorite and biotite, with rutile, ilmenite,

titanite, apatite as accessory phases. The P-T conditions yield a pressure of 8.4 ±3.4 kbar and a

temperature of 629 ±83℃. These represent a metamorphic gradient of medium to high

pressure and medium temperature metamorphism indicating amphibolite facies conditions,

corresponding to Barrovian-type metamorphism. This type of regional metamorphism led

toward a depth approximately of 27 km. The tectonic implications across the Colombian

Central Cordillera in the present work suggest rifted continental margins developed on

continental crust at the edges of continent triggered a oceanic sedimentary basins under a

compressive regime. These data suggest that the Jurassic collision previously reported to the

south could be extrapolated more to the north in the Cajamarca Complex (Central Cordillera).

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2. Introduction

The northwest margin of South America (Colombia-Ecuador) is related to a collisional

process of subduction of palaeo-Pacific plate (Figure 1). Therefore, events of accretion of

oceanic terranes, extensive magmatism (island arc and plateau) and continental margin

growth are the result of this interaction (Bayona et al. 2006, 2010). The Permian collision

trigged these tectonic scenarios of subduction, volcanic-arc magmatism, basin development

and closure, and accretion of terrenes (Blanco-Quintero et al., 2014; Restrepo and Toussaint

1982; Bayona et al. 2006, 2010; Vinasco et al. 2006; Kennan and Pindell 2009) in the Central

Cordillera of Colombia. Therefore, this terrane is composed of a metamorphic basement that

has been Permo-Triassic (Restrepo et al., 1991; Vinasco et al., 2006). The metamorphism during

this time interval affected granites, basalts and sedimentary rocks of the Cajamarca Complex

(Restrepo et al., 2011).

The multiple tectonic events that are related to this Colombian margin, cause the formation

of ophiolite structures, Barrovian metamorphic belts, medium- to high-pressure and medium-

temperature metamorphism (Ramos, 1999; Ramos and Aleman, 2000; Kerr et al., 1997, 2002;

Giunta et al., 2002). The mineral associations of metapelitic rocks of the Cajamarca Complex

indicated a sedimentary protolith, this metamorphic evolution and the geochemical

composition of the metapelites may have essential information of the tectonic model,

suggesting a deep-marine environment possibly a mid-ocean ridge (Bustamante et al., 2011).

The estimation of metamorphic conditions, considering the distinct types of tectonic

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scenarios, can be considered a useful focus of investigation to understand the complex tectonic

evolution to the northwestern Colombian margin.

In this project, I present a geochemical and petrographic characterization of different samples

of metapelites from Rio Claro and Abejorral municipalities as part of the Cajamarca Complex.

The results are used to determine the metamorphic implications and relate them to the

tectonic evolution of the northwestern margin of Colombia. For an improved understanding

of the type of metamorphism, the analysis of geochemical and petrological data, the protoliths

of the rocks and the pressure and temperature conditions were used. The methodology of this

project consists on, first, doing the fieldwork and subsequently analyzing petrology and

geochemical results, where the tectonic implications and the conditions of pressure and

temperature are discussed. This works is based on the analyses of several metapelite samples.

Petrographic analyses, X-ray fluorescence (XRF), inductively coupled plasma mass

spectrometry (ICP-MS), back-scattered Electro (BSE) images and X-ray spectroscopy (EDS)

using a scanning electron microscope (SEM) allowed to stablish the chemical composition,

the analysis of compositional changes that suffered each sample from the metamorphism and

the origin of the protolith. The results are presented in transmitted-light microscopy photos

of thin sections and BSE images from the scanning electron microscope (SEM) with a detailed

analysis respectively and Harker and REE diagrams for geochemical results. Finally, discussion

and conclusion comprise tectonic discrimination diagrams with the analysis of the provenance

to the tectonic environments and lastly the study of the results of pressure and temperature

conditions.

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Figure 1. A 130 Ma reconstruction of the circum-Gulf of Mexico and Caribbean region (Pindell and Kennan, 2009). An oceanic back-arc basin is inferred to separate the trans-American arc from southern Colombia and Ecuador and to be the source of many of the 140–130 Ma ultramafic and mafic rocks that separate the Arquia and Quebradagrande terranes in Colombia from the rest of the Central Cordillera. (Pindell and Kennan, 2009 p. 11)

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3. Conceptual Framework

3.1. Barrovian regional metamorphism

The Barrovian metamorphism series, identified/mapped by George Barrow (1893) from his

orogenic regional metamorphism study in the Scottish Highlands (Figure 2), considered the

variations in rock types and mineral associations with progressive metamorphism (Winter,

2001). Intense deformation and metamorphism in the Scottish Highlands occurred during the

Caledonian orogeny and its maximum intensity was about 500 Ma ago (Winter, 2001). This

Barrow-type sequence is medium- to high-pressure, and medium-temperature metamorphism.

So as for the presence of minerals, kyanite and sillimanite are the index minerals used in these

high-grade rocks. (Winter, 2011; Gillen, 1982).

Barrovian sequences ranging from Archean to Cenozoic (Jamieson et al., 2012) represent

significant and systematic mineralogical changes in the pelitic rocks (Tilley, 1925) and can be

subdivided into a series of metamorphic zones given the presence of the new mineral as

metamorphic grade increase (Gillen, 1982)

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(a) Metamorphic Zones of the Scottish Highlands

An isograd (a line in the field) separates the zones and represent the first appearance of

metamorphic index mineral.

(i) Zone of Chlorite

Chlorite is in the lowest area, and is divided in two (a) zone of clastic mica and (b) zone of

digested clastic mica. (Tilley, 1995).

Figure 2. Regional metamorphic map of the Scottish Highlands, showing the zones of minerals that develop with increasing metamorphic grade (Gillen, 1982)

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(ii) Zone of Biotite

Slates change to phyllites and schists, with biotite, chlorite, muscovite, quartz, and albite.

(Tilley, 1925; Winter, 2001).

(iii) Zone of Garnet

Schists with distinguished red almandine garnet, frequently with biotite, chlorite, muscovite,

quartz, and albite or oligoclase. (Tilley, 1925; Winter, 2001).

(iv) Zone of Staurolite

Schists with staurolite, biotite, muscovite, quartz, garnet, and plagioclase, ±chlorite. (Tilley,

1925; Winter, 2001).

(v) Zone of Kyanite

Schists with kyanite, biotite, muscovite, quartz, plagioclase, and generally garnet and

staurolite. (Winter, 2001).

(vi) Zone of Sillimanite

Schists and gneisses with sillimanite, biotite, muscovite, quartz, plagioclase, garnet, ±staurolite,

± kyanite. (Winter, 2001).

The pelitic rocks have high amount of silicate minerals (Table 1) that can be used as indicators

of metamorphic grade.

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Mineral assemblage produced

Grade Mineral Zone

(rock name) (for pelitic rocks) Mudstones and shales Limestones Basic igneous

rocks

(slate, phyllite) chlorite

chlorite, quartz, muscovite, plagioclase

chlorite, calcite or dolomite, plagioclase

chlorite, plagioclase

low

(schist)

Biotite biotite, quartz, plagioclase

medium garnet garnet, mica, quartz, plagioclase

garnet, epidote, hornblende, calcite

garnet, chlorite, epidote, plagioclase

(schist)

staurolite

staurolite, mica, garnet, quartz, plagioclase

garnet, hornblende, plagioclase hornblende,

plagioclase

high Kyanite kyanite, mica, garnet, quartz, plagioclase

(gneiss) Sillimanite sillimanite, garnet, mica, quartz, plagioclase

garnet, augite, plagioclase

Table. 1 Regional metamorphic zones and mineral assemblages in different original rock types (index mineral). (Gillen 1982).

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4. Geological Setting

The Colombian mountain system consists of three mountain ranges in N-S direction: The

Western, Central and Eastern cordilleras; that are separated by the Cauca-Patia graben and

Magdalena valley. These three independent ranges suffer processes of subduction, collision

and accretion since Late Paleozoic (Restrepo and Toussaint, 1982; Vinasco et al., 2006;

Villagómez et al., 2011).

The Western Cordillera consists of marine sediments of Upper Cretaceous and Cenozoic age,

intruded by igneous rock of Cenozoic age and oceanic sequences of basic volcanic rocks.

(Gonzalez et al., 1988; Aspden et al., 1987). The Eastern Cordillera, comprises polydeformed

continental Precambrian and Paleozoic igneous and metamorphic rocks covered by

sedimentary sequences of Paleozoic to Mesozoic age (Gonzalez et al., 1988).

The Central Cordillera, includes continental, oceanic and volcanic-arc of Paleozoic to

Cretaceous magmatic rocks likewise, pre-Mesozoic polymetamorphic basement interfered by

plutonic rocks of Meso-Cenozoic age (Restrepo and Toussaint 1982; Aspden et al. 1987; Maya

and González 1995) and this complex is limited by Otú-Pericos and Cauca-Almanguer strike-

slip faults (Figure 3). It basement is mainly composed of low- to medium-grade metamorphic

rocks of the Cajamarca Complex (Maya and González, 1995) and high-grade rocks of El Retiro

Group and Las Palmas gneiss (González, 2001). This complex includes pelitic schist,

quartzites, marbles, and amphibolites (e.g. Maya and González, 1995; González, 2001, Blanco-

Quintero et al., 2014). Serpentine bodies have been described too (e.g. Gomez-Tapia and

Bocanegra-Gomez, 1999).

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Figure 3. (A) Regional geological map showing the principal units of the Colombian Central Cordillera The figure shows the location of the study area. (B) Geological map of the study area with the location of the samples. (modified from Mapa Geológico Colombiano (SGC), 2015).

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The first described age of metamorphism of the Cajamarca Complex was in a Permian age but

it was also dated as Mid to Late Triassic age (ca. 240-230 Ma). Blanco-Quintero et al., 2014,

through analytical techniques of 𝐴𝑟 40 − 𝐴𝑟

39 age of amphibolites and pelitic schist samples,

suggest that metamorphism occurred in a Late Jurassic age (ca. 157-146).

The rocks that are exposed in the study area, belong to the area of Rio Claro and Abejorral in

the Antioquia department. In these areas, geological studies are very limited due to geographic

and political situations. This zone, in located in the structural part of the Central Cordillera in

the Cajamarca complex. Is composed of quartz-feldspar gneiss, quartz-sericite schist,

quartzites, amphibolites ad marble in which the caves are form. The marble is limited by

Palestina fault and places in contact with micaceous-schist and limestones (Toussaint et al.,

1989; González, 1980; Toussaint, 1993; Restrepo et al., 1991).

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5. Methodology and Analytical techniques

Seven samples were selected from Rio Claro and Abejorral municipalities located in the

Cajamarca Complex (Figure 4), during a field of structural and tectonic geology in the

department of Antioquia (Table 2). The samples collected were analyzed to determine content

and mineral composition elements likewise whole-rock mayor and trace.

From the following samples, seven thin sections were made (30μm), where two of them were

sections polished-thin to make a petrology analysis which was performed using a polarized

light petrographic microscope with the help of the OLYMPUS CX31 instrument at

Universidad de Los Andes.

Whole-rock major elements analysis and Zr components for two samples, were determined

applying glass beads of 0.6% of powered sample diluted in 6g of 𝐿𝑖2𝐵4𝑂7 by a PHILIPS Magix

Pro (PW-2440) X-ray fluorescence (XRF) at the Centro de Instrumentación Científica (CIC)

of University of Granada in Spain. Zr and LOI precision it was in a range of ±4% at 100 ppm

concentration and the results of the analyses were recalculated to an anhydrous 100 wt.% basis.

Sample Longitud Latitud

RC-4A -74.876933333 5.964133333

RC-7 -74.860783333 5.937516667

RC-8 -74.863366667 5.91595

RC-9 -74.859766667 5.91145

RC-23 -74.860466667 5.890866667

FL-22 -75.4733 5.710083333

RC-25 -74.856683 5.89338 Mica.schist, high content of biotite, presence of quartz veins

Hand Sample Identification

Outcrop of metamorphic heavily altered, Qz + Ms partial fusion

Fine-grained metasediments - foliation

Quartzite outcrops

Metasediments

Green schist, Qz veins (after metamorphism)

Graphitic schist, slickenside, quartz-vein banding (indicates effort),

lineage goes with striae (355N)

Table 2. Description of the hand samples with their respective coordinates

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Using the method of inductively coupled plasma mass spectrometry (ICP-MS). Subsequent

HNO3+HF digestion of 0.1000 g of sample powder in a Teflon-lined vessel at ̴ 180 °C and ̴

200 °C p.s.i for 30 minutes’ evaporation to dryness, and subsequent dissolution in 100 ml of 4

vol.% HNO3 trace elements analysis were determinate. Blanks and international standards

PMS, WSE, UBN, BEN, BR and AGV (Govindaraju, 1994) were run during analytical sessions.

Precision was better than ±2% and ±5% for concentrations of 50 and 5 ppm.

Given the minerology or geochemical analysis, five of the remaining samples were analyzed

by X-ray fluorescence (XRF) with Oxford Instrument X-MET 7500 – Mining Analyzer that

combines Oxford Instruments’ 45 kV X-Ray tube and high count rate, high resolution large

area Silicon Drift detector (SDD) with precision for elements major elements than 5-10% to

determinate the concentration of major and trace.

For the determination of the chemical composition of a sample volume and for the analysis of

compositional changes, a scanning electron microscope (SEM) was performed. Back-scattered

Electro (BSE) images and X-ray spectroscopy (EDS) were obtained using this method. To this

end, a JEOL microscope, model JSM 6490-LV was used, worked at an accelerating voltage of

20-30 kV and 0.5 to 3000.000X magnification, with a 3.0 nm spatial resolution, which belongs

to Universidad de Los Andes.

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Figure 4. Detailed geological map of the study area with principal lithological units. The map shows all the studied samples (Servicio Geológico Colombiano, 2015).

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6. Results

6.1. Petrography

The metamorphic samples are medium to coarse-grained and can be classified as metapelites.

The sample FL-22 is mainly composed of sericite 17% + quartz 45.3% + garnet 2.2% + chlorite

3.3% + biotite 26.6% + muscovite 5.6%, plus clinozoisite + epidote + ilmenite+ zircon as

accessory phases. This sample shows an alteration of sericitization of plagioclase, consumption

of anorthite produced fine-grained zoisite and sericite (Figure 5A, B). The garnet

phenocrystals show irregular edges, stretched form and a high presence of fractures, replaced

by clinozoisite and sericite, giving place an inclusions of this two minerals (Figure 5B). Quartz

crystals are xenoblastic with undulatory extinction, also these crystals have a stretched shape

by aggregates of the same mineral phase through dynamic recrystallization mechanisms. There

are sutured contacts between the crystals and many of the crystals are fractured.

The sample RC-7 is mainly composed of sericite 13.1% + quartz 23,93% + garnet 10.3% +

chlorite 7.3% + biotite 9.96% + muscovite 35.5%, plus ilmenite + plagioclase + apatite + titanite

+ zircon as accessory phases. The original banding of the sample went through a deformation

S1 producing a more penetrative foliation, which can be determined by the muscovite and a

second crenulation S2 foliation (Figure 5C). The deformed banding, surrounds phases like

garnet and albite. The rotation of the equidimensional minerals, as well as the stretching of

grains is due to phenomena of dissolution by pressure and intracrystalline deformation of

grains. Plagioclases have a composition that varies between albite and anorthite, according to

extinction angle method (EAM) and the Michel-Levy table. Quartz crystals have intense

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undulatory extinction. Likewise, the shape of quartz crystals is associated with the

development of crenulation foliations and mechanism of dissolution by pressure.

Porphyroblasts of garnet show irregular edges with the presence of fractures that were

included by chlorite and biotite. The rock shows an intergrowth of muscovite with biotite,

thus, the biotite is overgrown by the muscovite. As shown in Figure 5D, the biotite is in the

nucleus and the muscovite is surrounding and altering it.

The sample RC-25 is mainly composed of sericite 7% + quartz 15.96% + chlorite 3% +

muscovite 41.66% + graphite 31.4%, plus zoisite-clinozoisite + sillimanite. This sample can be

classified as a slickenside, the foliation is highlighted by the muscovite and the graphite, it is

inferred two cinematic indicators, the graphite is defined as S1 and the muscovite as S2, which

shows a sinistral displacement (Figure 5E, F). The quartz is recrystallized forming bands with

variable size and intense undulatory extinction by in addition, the crystals are elongated

forming ribbons in distinct parts of the rock. The sample also presents a metamorphic quartz

sub-grains with heterogeneous extinction (Figure 5F), giving an idea of a ductile deformation

and showing a reaction aureole where magnesium-rich chlorite is located.

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Figure 5. Transmitted-light microscopy photos of thin sections. A) Metapelite with alteration of sericitization of plagioclase. B) Garnet phenocrystals with a high presence of fractures, replaced by clinozoisite and sericite. C) Deformation S1 which can be determined by the muscovite and a second crenulation S2 foliation. D) Garnet and intergrowth of muscovite with biotite (parallel polars). E) Sinistral displacement of muscovite and garnet. F). Metamorphic quartz sub-grains with heterogeneous extinction.

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6.2. SEM - BSE Images and EDS analyses

Using the scanning electron microscope (SEM), back-scattered Electron (BSE) images and

mineral chemistry compositions (by EDS) were obtained. Therefore, the mineral association

of the two samples was analyzed. Additionally, with the information of the EDS the

composition of cations per formula unit of each sample was calculated (Table 3A, B). The BSE

imaging of the RC-7 sample, revealed that a very few crystals of muscovite and biotite are

intergrowth among themselves (Figure 6A). The image shows that the biotite is in the nucleus

and the muscovite is around it (it confirms the observation in the petrographic microscope),

indicating that the biotite crystalized before the muscovite and is overgrown by it. One could

also observe that porphyroblasts of garnet that has inclusions of chlorite, biotite and ilmenite

(Figure 6B). Biotite has high content of Fe and Mg. Garnet can be classified as almandine by

chemical composition of weight percent of oxides, which are: SiO2 (41.91%), Al2O3 (19.82%),

FeO (23.93%), MnO (13.98%), MgO (2.21%) and CaO (1.52%), the Ca content in the garnet is

low. Chemical composition of plagioclase is, SiO2 (65.69%), Al2O3 (22.92%), MgO (1.19%), CaO

(1.15%), Na2O (6.86%) and K2O (3.51%) confirming the results obtained with angle method

(EAM) and the Michel-Levy method. The foliation of the rock is denoted around the garnet

crystal. The content of ilmenite in the sample is quite highs.

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Backscattered electron imaging of the FL-22 sample, showing that garnet is in very irregular

forms and has inclusions of biotite, muscovite and epidote (Figure 6C). The garnet can be

classified as almandine by chemical composition of weight percent of oxides: SiO2 (47.05%),

Al2O3 (22.81%), FeO (27.13%), MnO (3.57%), MgO (2.44%) and CaO (12.16%). The size of

apatite crystal varies between ( ̴0,1 – 0,4 mm) and the content of this mineral is high (Figure

6D). In terms of epidote content, the sample shows two different subgroups: clinozoisite and

allanite SiO2 (44.45%), Al2O3 (27.64%), FeO (8.68%), and CaO (23.95%). Chemical composition

of plagioclase shows a solution of albite-anorthite: SiO2 (76.05%), Al2O3 (23.9%), FeO (1.52%),

MgO (1.14%), Na2O (7.97%) and K2O (2.53%). According to the chemical composition of

Sample

Mineral Chl Grt Bt Ms Ilm Pl Ap Zrn

37.67 41.91 31.85 53.95 0 65.69 0 29.86

0 0 0 0 54.23 0 0

20.71 19.82 19.51 30.38 0 22.92 0 4.95

24.19 23.93 21.38 0 40.3 0 0 0

0 13.98 0 0 7.04 0 0 0

14.34 2.21 12.94 1.67 0 1.19 0 0

0 1.52 0 0 0 1.15 15.07 0

0 0 0 0 0 6.86 0 0

5.52 0 9.54 10.48 0 3.51 0 0

0 0 0 0 0 0 1.74 0

0 0 0 0 0 0 0 55.67

17.61 19.59 14.89 25.22 0 30.7 0 13.96

0 0 0 0 32.51 0 0 0

10.95 10.49 10.325 16.08 0 12.13 0 2.62

18.8 18.6 16.62 0 31.325 0 0 0

0 10.83 0 0 5.45 0 0 0

8.64 1.33 7.805 1.01 0 1.185 0 0

0 1.08 0 0 0 0.082 4.56 0

0 0 0 0 0 5.09 0 0

4.56 0 7.92 8.7 0 2.91 0 0

0 0 0 0 0 0 0.54 0

0 0 0 0 0 0 0 41.21

RC-7

SiO2

iO2

Al2O3

FeO

MnOMgO

CaO

Na2O

K2O

Si

i

Al

Fe

Mn

Mg

Ca

Na

K

2O

O2

Table 3A. Representative analyses of metapelite, sample RC-7

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amphibole, SiO2 (50.16%), Al2O3 (24.82%), FeO (12.89%), MnO (0.34%), MgO (5.8%), CaO

(10.68%) and Na2O (2.78), it was determined that this amphibole can be classified as

hornblende.

Mineral chemical formula for garnet, apatite, biotite, chlorite, muscovite, plagioclase and

zircon were normalized to 12, 5, 11, 14, 11, 8 and 4 oxygens, respectively. For the ilmenite and

apatite of the sample RC-7 were normalized to 3 oxygens also epidote and allanite of the FL-

22 sample were normalized to 12 and 13 oxygens respectively. The chemical formulas of the

minerals mentioned above are shown in table 4 and 5.

Sample

Mineral Grt Bt Ms Pl Ep Ap Am Aln Zrn

47.05 41.86 48.07 76.05 45.14 0 50.16 44.45 32.13

0 2.33 2.05 0 0 0 0 0 0

22.81 18.85 23.86 23.9 30.01 0 24.82 27.64 0

27.13 22.44 15.58 1.52 6.23 0 12.89 8.68 0

3.57 0 0 0 0 0 0.34 0 0

2.44 9.68 7.13 1.14 0 0 5.8 0 0

12.76 0 0 0 26.49 55.08 10.68 23.95 0

0 0 0 7.97 0 0 2.78 0 0

0 10.52 11.76 2.53 0 0 0 0 0

0 0 0 0 0 48.38 0 0 0

0 0 0 0 0 0 0 0 75.94

0 0 0 0 0 0 0 0 2.04

21.99 19.57 22.47 35.55 21.1 0 23.45 0 15.02

0 1.39 1.23 0 0 0 0 0 0

12.07 9.97 12.63 12.65 15.88 0 13.13 0 0

21.09 17.44 12.11 1.18 4.84 0 10.02 0 0

2.76 0 0 0 0 0 0.26 0 0

1.47 5.84 4.31 0.69 0 0 3.5 0 0

9.12 0 0 0 18.93 39.36 7.63 0 0

0 0 0 5.91 0 0 2.06 0 0

0 8.73 9.76 2.1 0 0 0 0 0

0 0 0 5.91 0 0 0 0 0

0 0 0 0 0 0 0 0 56.22

FL-22

SiO2

iO2

Al2O3

FeO

MnO

MgO

CaONa2O

K2O

Si

i

Al

Fe

Mn

Mg

Ca

NaK

2O

O2

CeO2

Table 3B. Representative analyses of metapelite, sample FL-22

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Sample

Mineral

Chlorite

Garnet

Biotite

Muscovite

Ilmenite

Plagioclase

Apatite

Zircon

Chemical Formula

RC-7

2 4 2 0 7𝐴 247)( 𝑖3 0)(𝑂 0 𝑂 4

0 42 739 029 0 2 𝐴 0 𝑖3 4 𝑂 2

0 03 9 0 77 3 𝐴 39 𝑖3 𝑂 0 𝑂 2 0 23 0 4 0 334𝐴 40 𝑖4 22 𝑂 𝑂 )

0 34 𝑖 009𝑂3

0 303 0 0 𝑖3 3 4𝐴 0 7 4𝑂

0 772 0 49 3 𝑂

𝑟0 𝐴 0 90 𝑖0 973𝑂4

Sample

Mineral

Garnet

Biotite

Muscovite

Plagioclase

Epidote

Apatite

Amphibole

Allanite

Zircon

FL-22

Chemical Formula

043 73 0 23 0 277 𝐴 02 𝑖3 90𝑂 2

0 2 4 4 3 𝐴 0 974 𝑖3 𝑂 0 𝑂 2

0 23 0 92 0 0𝐴 40 𝑖4 22 𝑂 𝑂

0 342𝐴 0 23 𝑖3 3 4𝑂

2 2 𝐴 4 0 4 𝑖3 0 𝑂 2 𝑂

42 2 230 3 𝑂

𝑟 07 𝑖0 929𝑂4

2 27 0 0 3𝐴 444 0 44 𝑖3 04 𝑂 2 𝑂 𝑂

27 229 32 𝑖 𝐴 2 079 𝑂22 𝑂 2

Table 4. Calculation of mineral formula of sample RC-7

Table 5. Calculation of mineral formula of sample FL-22

28

Figure 6. BSE images for metapelites samples. A) Intergrowth texture of muscovite and biotite minerals. B) Inclusions of chlorite, biotite and ilmenite in garnet crystal. C) Garnet highly fractured, biotite, epidote, muscovite and quartz D) Crystals of apatite, biotite, plagioclase and amphibole.

29

6.3. Geochemistry

Bulk-rock geochemistry was performed for all the samples (Table 6) using XRF for mayor

elements and ICP-MS for trace and rare earth elements (REE).

Harker diagrams for metapelites are presented in Figure 7. The rocks have high Al2O3, MgO

and K2O showing negative covariances between SiO2. Additionally, iO2 − SiO2 shows a

negative tendency and it is relative low (Figure 7). Conversely,CaO shows an irregular rise with

the ascending in SiO2 content. The Na2O, is only present in two samples due to the analytical

method used and is reached- to medium in each sample.

Normalized to chondrite (McDonough and Sun 1995), rare earth elements (REE) patterns in

the metapelites shows an inverse relation to the atomic number (Figure 8A and Table 7) and

are almost parallel so, the patterns are significantly similar. Light rare earth elements (LREE)

have a greater or steeper slope in both samples and are more fractionated than heavy rare

earth elements (HREE). The graphic shows a negative anomaly in Eu. Heavy rare earth

Sample RC-7 RC-8 RC-9 RC-25 RC-23 4A FL-22

Mineral 72.72 71.78 96.25 60.40 73.25 92.69 83.19

13.68 13.71 1.39 29.35 14.22 3.90 10.58

0.68 0.68 0.03 0.85 0.56 0.17 0.46

13.68 13.71 1.39 29.35 14.22 3.90 10.58

5.23 5.22 0.16 4.22 2.21 0.39 1.86

0.25 0.29 0.00 0.09 0.02 0.01 0.04

2.41 2.17 0.00 0.36 4.68 0.00 0.54

0.46 1.16 2.08 1.05 4.16 2.30 1.91

1.73 2.58 0.00 0.00 0.00 0.00 0.00

2.73 2.61 0.09 3.50 0.30 0.52 1.32

0.11 0.10 0.00 0.17 0.60 0.02 0.11

159.70 171.80 0.00 0.00 0.00 0.00 0.00

100 100 100 100 100 100 100

SiO2

iO2

Al2O3

2𝑂3

MnO

MgO

CaONa2O

K2O

2O

(ppm)

S M

Table 6. Results of analysis of mayor (wt%) elements of all the

30

Figure 7. Harker variation diagrams - iO2, Al2O3, MgO, CaO, Na2O and K2O versus SiO2

elements (HREE) still present a decreasing behavior. In general, the pattern of samples RC-7

and RC-8 is above 10 in concentration regarding normalized chondrite.

In the N-MORB-normalized element diagram (N-MORB after Sun and McDonough 1989)

the metapelites show negative slope with a semi-horizontal tendency for the high-field

strength elements (HFSEs) (Figure 8B), both samples tend to parallel behavior, therefore their

patterns are very similar. The diagram exhibits an anomaly in Eu; at this point, the slope tends

to be more negative, generating an inflection point. The samples show enrichment on the

large-ion Lithophile Elements (LILE). The samples are above 0.1 in concentration of chondrite

normalized and are in a range between ±10 and ±100.

31

Sample RC-7 RC-8

Li 59.247 47.649

Rb 95.211 69.415

Cs 5.474 5.623

Be 3.05 2.318

Sr 101.178 194.533

Ba 1285.729 1167.073

Sc 15.133 14.223

V 91.669 95.438

Cr 64.575 76.198

Co 18.391 31.116

Ni 40.252 26.749

Cu 69.396 61.181

Zn 85.715 77.436

Ga 19.214 17.256

Y 20.497 21.122

Nb 12.766 13.486

Ta 1.033 1.146

Zr 139.02 146.43

Hf 3.284 3.172

Mo 1.946 7.064

Sn 2.876 1.873

TI 0.596 0.669

Pb 15.446 63.647

U 1.802 1.732

Th 9.196 8.163

La 25.719 21.062

Ce 65.958 53.215

Pr 6.033 5.166

Nd 22.401 19.971

Sm 4.605 4.174

Eu 0.803 0.664

Gd 3.973 3.735

Tb 0.616 0.596

Dy 3.56 3.508

Ho 0.759 0.756

Er 2.029 1.994

Tm 0.345 0.355

Yb 2.113 2.29

Lu 0.346 0.362

Table 7. Analysis results of trace elements and rare earth elements of all

32

Figure 8. A) REE and B) element abundance of the studied samples normalized to the

chondrite (McDonough and Sun 1995) and N-MORB (Sun and McDonough 1989),

33

7. Discussion

7.1. Tectonic implications

During the Middle and Late Jurassic, Colombia and Ecuador suffer a subduction of Palaeo-

Pacific plates. The northwestern margin of South America was affected by different

continental rifting events related with the opening of the Proto-Caribbean (Pindell and

Kennan, 2009). The tectonic model of the Cajamarca complex, based on palaeomagnetic data

of (Bayona et al. 2006,2010) inferred that, until Early Cretaceous time, Jurassic terranes moved

from south to north along de Andean margin relating the distribution of Triassic marine

sedimentary basins (Bayona et al. 2006, 2010). The Jurassic volcanic arc emerged from an

extensional to a compressive system throughout the dextral slip of Ibague Batholith and other

northern Colombian blocks (Aspden et al. 1992; Noble et al. 1997).

The provenance to the tectonic environments for two samples, major elements chemistry was

used. According to the K2O/Na2O 𝑣𝑠 SiO2 sandstone − mudstone disc imination diag am

(Roser an Korsch 1986) we can observe that the studied samples correspond to Passive

Continental Margin (Figure 9A) indicating that provenance characteristics of the sample can

be assigned as the following tectonic settings: (1) rifted continental margins developed on

continental crust on the edges of continent, (2) sedimentary basins on the trailing edge of a

continent.

In the discriminant function diagram for the provenance signatures of sandstone-mudstones

using major elements and major elements ratios (Roser and Korsch 1988) (Figure 9B and 9C);

it was determinate that it is primarily quartzose sedimentary. This analysis was based on the

34

composition of Al2O3/SiO2, K2O/Na2O and Fe2O3 tot + MgO. For the first two determinant

functions, the oxides of Ti, Al, Fe, Mg, Ca, Na and K determined and differentiated the origin

of the samples (Figure 9B). Additionally, using ratio plots, which discriminant functions are

based of iO2 Fe2O3 tot MgO Na2O and K2O all to Al2O3, ratios (Figure 9C) also determined

the provenance of the samples. That shows, that probably during this period, the Central

Cordillera was in a rift system where was formed an oceanic basing. This basin accumulated a

sedimentary protolith that suffered different tectonic events (Blanco-Quintero et al., 2014).

35

Figure 9. A) The log (K2O/Na2O discrimination diagram of Roser and Korsch (1986) for sandstones-mudstones suites and shows observed that studied samples correspond to Passive Continental Margin. B) Discriminant function diagram for the provenance signatures of sandstones-mudstones suites using major elements (Roser and Korsch, 1986), where it is exhibited the field for a quartzose sedimentary provenance. C) Discriminant function diagram for the provenance signatures of sandstones-mudstones suites using major elements ratios (Roser and Korsch, 1986), and the field is rectified by a quartzose sedimentary provenance.

36

7.2. P-T metamorphic conditions

The thermodynamic calculation software, THERMOCALC (Powell and Holland 1988) was

used in this project for the determination of pressure and temperature suffered by the rocks.

The chemical composition in the phases is strongly influence by these independent variables.

The thermobarometry calculation is based on the petrology of the rock, so it must be

considered a textural equilibrium of the metamorphic minerals (Powell and Holland 1988,

1994).

With the mineral chemistry data (Table 8), conditions in which the rock was equilibrated were

determined; using the average P-T method. This method was used for the metapelite sample

FL-22, where the minerals of garnet, muscovite, biotite, epidote and plagioclase were

considered.

Before using the THERMOCALC method the activity and uncertainties of the endmembers

of the solid solutions must be determined. This database was calculated with the AX program

and using the weigh percent of the minerals determined by the EDS analysis. Subsequently,

g

47.05 0 22.81 0 27.13 3.57 2.44 12.76 0 0

mu

53.95 0 30.38 0 0 0 1.67 0 0 10.48

bi

41.86 0 18.85 0 22.44 0 9.68 0 0 10.52

ep

45.14 0 30.01 0 6.23 0 0 26.49 0 0

fsp

80.5 0 23.34 0 0 0 0 1.57 9.53 0.94

𝑖𝑂2 𝑖𝑂2 𝐴 2𝑂3 2𝑂3 𝑂 𝑂 𝑂 𝑂 2𝑂 2𝑂

Table 8. Mineral chemistry data of metapelite sample Fl-22. Acronym of phases: garnet (g), muscovite (mu), biotite (bi), epidote (ep) and plagioclase (fsp).

37

these activities for the endmembers for P-T can be used for rock calculations in

THERMOCALC.

Based on the results of the data acquired in THERMOCALC program, the conditions

calculated correspond approximately 8.4 ±3.4 kbar and 629 ±83℃, cor =0.686, sigfit = 3.49. The

P-T metamorphic conditions are related to a tectonic depth, indicating that rocks where down

in the lithosphere to approximately 27 km (Figure 10). In the view of these conditions, a

metamorphic gradient of medium P/T was considered.

With these data, a Barrovian-type metamorphism is evidenced, similar to other outcrops of

the Cajamarca most to the south (Blanco-Quintero et al., 2014), and concerning the tectonic

implications of this area, this type of metamorphism can also be suggested. Barrovian facies

series, comprise an amphibolite facies rocks that shows a mineral association similar to the

metapelites recollected in the study zone. The sedimentary protolith came from an oceanic

basing environment, suggesting that the regional metamorphism occurred in areas that have

deformed during a collision event (i.e. orogenic event).

38

Figure 10. Explicative diagram which relates P-T conditions and with tectonic depth (Nelson, 2012).

39

8. Conclusions

This work presents a detailed analysis of the metamorphic conditions of the Cajamarca

Complex in the Rio Claro area (Antioquia Department). The tectonic scenario and the type

of metamorphism are linked considering the P-T metamorphic conditions. The chemical

composition of the protoliths, indicate that the provenance of the tectonic setting comprises

a model of rifted continental margins developed on continental crust triggered an oceanic

basin on the trailing of a continent.

The study area comprises a metapelitics rocks of Late Jurassic age (ca. 160; Blanco-Quintero

et al., 2015) where the pressure and temperature conditions were 8.4 ±3.4 kbar and 629 ±83℃

respectively. That suggests depths down to approximately 27 km. With these conditions and

with the origin of the protolith, it is concluded that the Cajamarca Complex suffered

extension, rifting and compression tectonic processes. Thus, the oceanic basin development

and closure can be classified as a medium-to high pressure, and medium temperature

metamorphism.

The petrography and the geochemistry analysis showed that the chemical composition of the

samples belongs to the field of amphibolite facies. Likewise, the thermobarometry presents

conditions in which these rocks are presented too. This means that, the mineral association of

the samples has the following mineral assemblage: amphibole, plagioclase (albite), epidote,

chlorite, ± biotite. In conclusion, the metapelites from the Cajamarca Complex suffered

collision-accretion process linked with a metamorphic gradient of medium P/T. Hence, it is

evident a Jurassic Barrovian-type metamorphism.

40

9. Acknowledgements

Quiero agradecer a mis papás por apoyarme en todo lo que sea necesario, por darme tanto amor y

compresión y asimismo por ser mi modelo a seguir en un futuro cercano. También a mi director de

tesis Idael Francisco Blanco Quintero por ser mi guía y ejemplo durante mi formación académica.

Gracias al Departamento de Geociencias, en especial a Ivette que fue un gran apoyo y ayuda para la

preparación de mis muestras al principio de este proyecto.

Virginia, muchas gracias por sacar tiempo para mí y apoyarme siempre que te necesité. Te aprecio

mucho y espero seguir compartiendo conocimiento juntas. Adriana Giraldo, Ana María Tobón, Karen

Angulo y Nicolás González ustedes son uno de mis mayores apoyos, gracias por tan linda amistad. A

mis colegas y grandes amigos Aura Cuervo, Andrés Rodríguez y Sebastián Ardila por la compañía

incondicional que me brindaron durante mi carrera. A Randy y Morita familia perruna que me anima,

¡muchas gracias!

41

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