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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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