Open access peer-reviewed chapter

Mineral Chemistry of Chalki Basalts in Northern Iraq and Their Petrological Significance

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Mohsin M. Ghazal, Ali I. Al-Juboury and Sabhan M. Jalal

Submitted: March 15th, 2019 Reviewed: September 23rd, 2019 Published: October 26th, 2019

DOI: 10.5772/intechopen.89861

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Abstract

Chalki basalts as a small body of volcanic rocks have green to grayish green color due to their nearly complete alteration to chlorite. The essential minerals of Chalki basalt to andesitic basalts are plagioclase (labradorite, An51–61; andesine, An35 to An42; and oligoclase, An22). Moreover, there is sodic plagioclase (albite, An0.1 to An04) whose coexistence with the other more calcic plagioclase means that albitization had occurred. The other essential mineral is pyroxene (endiopside, en66–68 wo27–28 fs05–06; and subcalcic augite, en72 wo14 fs14). Olivine (Fo80–81) is also present. According to the NiO content (0.11–0.12 wt%) in olivine grains, they are interpreted to be originated tectonically. The prevalent chlorite in all the samples is mainly diabantite and penninite, indicating chloritization after the ferromagnesian olivine and pyroxene. Serpentine (type lizardite and chrysotile) is also recorded as lesser alteration product after the forsteritic olivine. Rare secondary hornblende (type magnesiohornblende) is also found. The spinel group as accessory minerals is defined as magnetite, chromian magnetite, and chromian spinel giving the imprints of their metamorphic origin due to low temperature sub-sea metamorphism and also of alpine type.

Keywords

  • petrography
  • mineral chemistry
  • electron microprobe
  • Chalki basalts
  • Iraq

1. Introduction

The Paleozoic Chalki volcanic rocks crop out in a restricted part of the northern Thrust Zone of Iraq close to Iraqi-Turkish border and are considered as integral part of the upper part of Pirispiki Red Beds (late Devonian) Formation [1, 2, 3]. Chalki Formation was defined by Wetzel (unpublished report, 1952 in [1]) (which has no synonyms) who named it after the Chalki village (Figure 1).

Figure 1.

Geological map of northern Iraq showing the Paleozoic succession including Chalki volcanics within Pirispiki formation in Ora section (A) and the studied section (Chalki Nasara, section B) (modified after [8]).

Lithologically, they represent dull green and grayish green, red- and white-speckled, altered olivine-rich basaltic rocks (flow or intrusions) alternating with intercalations of bright red, ash-containing soft siltstones and shale.

They are undated and their origin is uncertain. Outcrop is typically not diagnostic. They are considered to be extrusive by [4] based on their identification of ash layers (not observed in this study). Petrographically, the bulk of the material consists of olivine basalts or fine-grained dolerites, with hematite-magnetite-rimmed pseudomorphs, in chlorite, replacing the olivine. There are albitized plagioclase laths and considerable amounts of chlorite and ankeritic carbonates in the groundmass. Locally the basalts are crossed by numerous veins of white ankerite with fibrous chalcedony.

The Chalki volcanic rocks probably had suffered severe sub-sea alterations. Therefore, this work aims to study mineral chemistry using electron probe microanalyzer (EPMA) in order to distinguish the various phases of minerals resulted from the alteration on basaltic rocks of the Chalki volcanics and interpret their petrologic significance.

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2. Geologic setting

The Chalki volcanics located near Kaista (Khabour valley, Amadia district, N. Iraq) occur as basalt intercalations, of 2–5 m in thickness within the Pirispiki Formation. The type section lies at Chalki village (Figure 1) in which the basaltic beds are associated with ash-containing shales and siltstones occupying most of the uppermost 20 m of the section. The type section is 16 m thick in aggregate [4].

Sharland et al. [5] interpreted the Chalki volcanics to represent back-arc rift volcanics associated with the initiation of subduction along the Tethyan margin of the Arabian Plate. They interpreted the initiation of subduction to have caused the so-called Hercynian orogeny in the late Devonian times. The age of the “Hercynian orogeny” in the Arabian Plate has been reported to range from pre-Late Devonian to middle Carboniferous [6].

Subduction along the southern margin of the Palaeo-Tethys is supported by the occurrence of Devonian-Carboniferous volcanic and metamorphic rocks found in the Kuh-Sefid area of the Sanandaj-Sirjan Zone [7]. However, the central part of the Arabian plate was probably not significantly affected by this subduction.

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3. Materials and methodology

The petrography of 15 samples collected from Chalki volcanics section at Chalki Nasara section (Figure 1) was determined using petrographic microscope at the Earth Science Department of Mosul University, Iraq. A Swift Polarized microscope is used in the petrographic description.

Electron microprobe analyses of minerals were performed using a Cameca SX-50 in the Department of Geology and Geophysics at the University of Utah, USA. Analyses were conducted using PC1, TAP, PET, and LiF crystals on four wavelength-dispersive spectrometers, with an accelerating voltage of 15 keV, a beam current of 30 nA, and a spot size of 10 mm. Peak intensities were measured for 20 s and background intensities for 10 s on both sides of the analytical peaks. Na was measured first, and analytical times were reduced by half in order to minimize sodium loss under the electron beam. The analytical routine for feldspars included Si, Al, Fe, Ca, Sr, Ba, Na, and K, and a separate analytical routine for mafic and other minerals added Ti, Cr, Mn, Ni, Zn, Mg, F, and Cl (K, Sr and Ba excluded). Mineral standards include fluorite (F-Kα), tugtupite (Cl-Kα), sanidine (Si-Kα, Al-Kα, K-Kα), albite (Na-Kα), plagioclase (Ca-Kα), barite (Ba-Lα), celestite (Sr-Lα), chrome diopside (Mg-Kα), hematite (Fe-Kα), rutile (Ti-Kα), rhodonite (Mn-Kα), chromite (Cr-Kα), nickel silicide (Ni-Kα), and zinc sulfide (Zn-Kβ). Rounds of standard analyses were performed prior to and after the suite of thin sections. Concentrations are calculated using the PAP matrix correction factors. Correction for “excess” F by interference of the Fe-Lα peak with F-Kα peak was accomplished by measuring an F-free Fe-bearing standard (hematite) and calculating a correction factor of 0.029.

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4. Results

4.1 Petrography

The volcanic rocks are olivine-basalt, sometimes doleritic, or even andesitic-basalt. They are of greenish to greenish gray color due to high chloritization after olivine. They are associated with little phyllites and pyroclasts of volcano-sedimentary rocks. They contain also veins of carbonate minerals and quartz.

Texturally, the rocks of Chalki volcanics are porphyritic basaltic in general, cut by microscopic veins of carbonate minerals (calcite) in addition to minute quartz veins.

Mineralogically, the pseudomorphs after olivine phenocrysts are identified microscopically, such as chlorite, iddingsite, and iron oxides (Figure 2). Another essential mineral is plagioclase (sometimes albitized), which sometimes slightly altered to sericite and kaolinite. No individual pyroxene grains have been identified, but they probably present as fine grains in the groundmass.

Figure 2.

Representative photomicrograph for Chalki basalt showing (A) dumpy prismatic olivine with rim alteration to black iron oxide and reddish brown iddingsite (arrows), chlorite (Chl), and white fine laths of plagioclase. (B) Plagioclase laths (arrows), altered olivine to iddingsite, iron oxide. Under-crossed nicols. Scale bar is 0.2 mm.

4.2 Mineral chemistry

4.2.1 Plagioclase

The calcic plagioclase (labradorite, An51 to An61) is the essential mineral of Chalki basalt resembling the basaltic type. Some grains are less calcic (andesine, An35 to An42). Moreover, there is sodic plagioclase (albite, An0.1 to An04) as a result of albitization process (Table 1 and Figure 3).

CV-32
Wt% 1 2 3 4 5 6 7 8
SiO2 54.59 56.20 57.15 66.91 65.28 67.76 58.82 55.16
Al2O3 27.44 26.06 26.25 19.41 20.81 19.65 25.04 27.56
FeO* 0.59 0.92 0.87 0.91 0.56 0.92 0.77 0.77
CaO 10.32 8.56 8.49 0.34 0.88 0.15 7.25 10.15
SrO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.03
BaO 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00
Na2O 5.33 6.24 6.07 10.70 10.20 11.23 6.63 5.16
K2O 0.35 0.24 0.50 0.10 0.91 0.13 0.58 0.27
Total 98.6 98.2 99.3 98.4 98.6 99.8 99.1 99.1
apfu
Si 2.501 2.575 2.587 2.979 2.914 2.976 2.657 2.511
Al 1.481 1.407 1.400 1.018 1.095 1.017 1.333 1.478
Fe2+ 0.023 0.035 0.033 0.034 0.021 0.034 0.029 0.029
Ca 0.507 0.420 0.412 0.016 0.042 0.007 0.351 0.495
Sr 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
Ba 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
Na 0.473 0.554 0.533 0.924 0.883 0.956 0.580 0.456
K 0.021 0.014 0.029 0.006 0.052 0.007 0.034 0.016
Ab 47.30 56.07 54.75 97.67 90.34 98.52 60.16 47.17
An 50.63 42.48 42.31 1.73 4.33 0.71 36.35 51.21
Or 2.07 1.45 2.94 0.60 5.33 0.77 3.49 1.61
Labradorite Andesine Andesine Albite Albite Albite Andesine Labradorite
CV-25
Wt% 1 2 3 4 5 6
SiO2 57.80 53.20 52.54 62.32 52.91 57.66
Al2O3 25.46 28.77 29.17 22.97 29.20 26.26
FeO* 1.20 0.68 0.86 0.71 0.67 0.55
CaO 7.52 11.68 12.08 4.71 11.64 8.36
SrO 0.00 0.02 0.00 0.06 0.00 0.00
BaO 0.00 0.00 0.00 0.05 0.01 0.03
Na2O 6.60 4.61 4.15 8.64 4.29 6.32
K2O 0.56 0.19 0.33 0.63 0.52 0.52
Total 99.1 99.1 99.1 100.1 99.2 99.7
apfu
Si 2.621 2.433 2.408 2.774 2.419 2.597
Al 1.361 1.551 1.576 1.205 1.573 1.394
Fe2+ 0.046 0.026 0.033 0.026 0.026 0.021
Ca 0.365 0.572 0.593 0.225 0.570 0.404
Sr 0.000 0.000 0.000 0.000 0.000 0.000
Ba 0.000 0.000 0.000 0.000 0.000 0.000
Na 0.580 0.408 0.369 0.745 0.380 0.552
K 0.032 0.011 0.019 0.036 0.030 0.030
Ab 59.35 41.18 37.58 74.12 38.76 56.01
An 37.35 57.72 60.45 22.34 58.13 40.94
Or 3.30 1.10 1.97 3.54 3.11 3.05
Andesine Labradorite Labradorite Oligoclase Labradorite Andesine
CV-37
Wt% 1 2 3 4 5
SiO2 57.32 54.96 58.70 56.93 55.49
Al2O3 25.85 27.08 24.96 24.40 27.90
FeO* 1.00 1.19 0.87 1.65 0.98
CaO 8.10 9.94 7.05 6.76 10.06
SrO 0.00 0.00 0.00 0.00 0.00
BaO 0.00 0.00 0.03 0.02 0.01
Na2O 6.13 5.28 6.79 6.25 5.46
K2O 0.48 0.27 0.61 0.61 0.39
Total 98.9 98.7 99.0 96.6 100.3
apfu
Si 2.604 2.516 2.656 2.647 2.502
Al 1.384 1.461 1.331 1.337 1.482
Fe2+ 0.038 0.046 0.033 0.064 0.037
Ca 0.394 0.487 0.342 0.337 0.486
Sr 0.000 0.000 0.000 0.000 0.000
Ba 0.000 0.000 0.000 0.000 0.000
Na 0.540 0.469 0.595 0.563 0.477
K 0.028 0.016 0.035 0.036 0.022
Ab 56.14 48.23 61.26 60.16 48.43
An 40.99 50.14 35.14 35.98 49.31
Or 2.87 1.64 3.61 3.86 2.26
Andesine Labradorite Andesine Andesine Labradorite
CV-41
Wt% 1 2 3 4 5 6 7 8 9
SiO2 68.13 67.84 68.02 67.77 68.20 66.15 67.24 67.39 67.87
Al2O3 19.45 19.34 19.25 19.59 19.56 20.09 19.51 19.46 19.59
FeO* 0.47 0.56 0.77 0.95 0.54 1.55 0.77 0.71 0.63
CaO 0.04 0.04 0.03 0.10 0.07 0.41 0.32 0.08 0.12
SrO 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
BaO 0.00 0.01 0.00 0.00 0.00 0.37 0.00 0.00 0.00
Na2O 11.16 11.13 11.24 11.18 11.43 10.42 11.04 11.09 11.14
K2O 0.03 0.04 0.02 0.07 0.05 0.29 0.07 0.17 0.09
Total 99.3 99.0 99.3 99.7 99.9 99.3 98.9 98.9 99.4
apfu
Si 2.996 2.995 2.996 2.980 2.988 2.940 2.977 2.983 2.985
Al 1.008 1.006 0.999 1.015 1.010 1.053 1.018 1.015 1.016
Fe2+ 0.017 0.021 0.028 0.035 0.020 0.058 0.028 0.026 0.023
Ca 0.002 0.002 0.001 0.005 0.003 0.020 0.015 0.004 0.006
Sr 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
Ba 0.000 0.000 0.000 0.000 0.000 0.001 0.000 0.000 0.000
Na 0.951 0.953 0.959 0.953 0.971 0.898 0.948 0.952 0.950
K 0.002 0.002 0.001 0.004 0.003 0.016 0.004 0.010 0.005
Ab 99.59 99.59 99.72 99.11 99.39 96.15 98.03 98.61 98.90
An 0.21 0.19 0.14 0.50 0.32 2.10 1.59 0.37 0.60
Or 0.21 0.22 0.13 0.39 0.30 1.75 0.39 1.02 0.51
Albite Albite Albite Albite Albite Albite Albite Albite Albite

Table 1.

Chemical composition (wt%) and atom per formula unit (apfu) of plagioclase on the basis of 8 O (samples CV-32, CV-25, CV-37, CV-41).

Figure 3.

An-Ab-Or plot for Chalki basalt plagioclase showing the composition variation from labradorite, andesine, oligoclase, to albite (modified from [9]).

4.2.2 Olivine

Chalki olivine is forsteritic (Fo80 to Fo81) and consequently high Mg# (80–81) (Table 2). It contains NiO (0.11–0.12 wt%), which is plotted against (Fo%) revealing its tectonic origin (Figure 4).

Figure 4.

Fo vs. NiO for Chalki basalt olivines shown as type tectonic (adapted from [10]).

Figure 5.

En-Fs-Wo triangular diagram for Chalki basalt pyroxene shown as endiopside and subcalcic augite (after [11]).

4.2.3 Pyroxene

The pyroxene of Chalki basalt is endiopside to subcalcic augite as shown in Table 3 and Figure 5.

Wt% 1 2 3 4
SiO2 39.29 40.01 38.52 39.34
TiO2 0.02 0.04 0.02 0.04
Al2O3 0.19 0.24 0.19 0.24
Cr2O3 0.02 0.06 0.02 0.06
FeO* 17.20 18.01 16.86 17.71
MnO 0.37 0.48 0.36 0.47
NiO 0.12 0.12 0.12 0.11
ZnO 0.54 0.00 0.53 0.00
MgO 43.03 41.35 42.19 40.66
CaO 0.01 0.64 0.01 0.63
Na2O 0.04 0.01 0.04 0.01
F 0.05 0.07 0.05 0.07
Cl 0.00 0.00 0.00 0.00
Total 100.88 101.03 98.90 99.34
apfu
Si 0.992 1.010 0.992 1.010
Al 0.006 0.007 0.006 0.007
Ti 0.000 0.001 0.000 0.001
Cr 0.000 0.001 0.000 0.001
Fe 0.363 0.380 0.363 0.380
Mn 0.008 0.010 0.008 0.010
Mg 1.620 1.556 1.620 1.556
Ca 0.000 0.017 0.000 0.017
Na 0.002 0.001 0.002 0.001
K 0.000 0.000 0.000 0.000
Ni 0.001 0.001 0.001 0.001
Zn 0.004 0.000 0.004 0.000
Fo 81.361 79.946 81.361 79.946
Fa 18.639 20.054 18.639 20.054
Mg# 81.686 80.367 81.686 80.367

Table 2.

Chemical composition (wt%) and atom per formula unit (apfu) of olivine on the basis of 4 O (sample CV-67).

Figure 6.

Si vs. Mg/(Mg + Fe2+) diagram for Chalki basalt amphiboles shown as magnesiohornblende (after [12]).

The chemical formula of pyroxene is XYZ2O6 [11].

4.2.4 Hornblende

The rare mineral in Chalki basalt is hornblende, whose composition resembles the magnnesiohornblende as shown in Figure 6 after representation of its chemical composition given in Table 4.

Figure 7.

Chalki basalt chlorite shown as mainly diabantite and less penninite (after [13]).

Wt% 1 2 3 4 5
SiO2 56.54 56.43 56.53 57.31 50.47
TiO2 0.08 0.07 0.03 0.06 0.05
Al2O3 1.92 2.05 1.58 1.11 0.88
Cr2O3 0.09 0.12 0.19 0.08 0.11
FeO* 3.28 3.22 3.12 3.39 9.99
MnO 0.13 0.03 0.08 0.09 0.21
NiO 0.05 0.05 0.03 0.02 0.04
ZnO 0.21 0.00 0.00 0.00 0.02
MgO 22.27 22.33 22.91 22.75 29.19
CaO 13.17 13.03 12.79 12.75 8.18
Na2O 0.23 0.29 0.19 0.10 0.12
F 0.01 0.00 0.00 0.00 0.05
Cl 0.00 0.01 0.01 0.01 0.01
Total 98.0 97.6 97.5 97.7 99.3
apfu
Si 2.028 2.027 2.033 2.055 1.850
Aliv −0.028 −0.027 −0.033 −0.055 0.150
Alvi 0.109 0.114 0.100 0.101 −0.112
Ti 0.002 0.002 0.001 0.001 0.001
Cr 0.002 0.003 0.006 0.002 0.003
Fe2+ −0.314 −0.316 −0.335 −0.324 −0.495
Mn 0.004 0.001 0.000 0.003 0.006
Mg 1.191 1.196 1.229 1.216 1.595
Ni 0.002 0.002 0.001 0.000 0.001
Zn 0.006 0.000 0.000 0.000 0.001
Fe2+ 0.412 0.413 0.429 0.426 0.801
Ca 0.506 0.502 0.493 0.490 0.321
Na 0.016 0.020 0.014 0.007 0.008
K 0.000 0.000 0.000 0.000 0.000
Z 2.000 2.000 2.000 2.000 2.000
Y 1.002 1.002 1.001 1.000 1.001
X 0.934 0.935 0.936 0.923 1.131
Xmg 0.924 0.925 0.929 0.923 0.839
fs 5.478 5.386 5.177 5.626 13.776
en 66.322 66.659 67.675 67.277 71.777
wo 28.199 27.955 27.148 27.097 14.447

Table 3.

Chemical composition (wt%) and atom per formula unit (apfu) of pyroxene on the basis of 6 O (sample CV-67).

The general formula of amphiboles is W (0–1) X 2 Y 5 Z 8O22(OH,F)2 [11].

4.2.5 Chlorite

The chlorite of Chalki basalt is the predominant secondary mineral in all samples giving the greenish color of the hand specimen samples. The huge number of analysis for many samples as given in Table 5 reveals the prevalence of diabantite with less abundant penninite, in addition to few grains of clinochlorite, pyenochlorite, and ripidolite (Figure 7).

Wt% 1 2 3
SiO2 45.77 44.9 45.8
Al2O3 11.09 11.45 11.45
TiO2 0.91 1.1 0.77
Cr2O3 1.08 0.96 0.67
FeO* 7.03 7.99 8.02
MnO 0.06 0.03 0.01
MgO 17.04 16.55 16.87
CaO 12.14 12.4 12.66
Na2O 1.45 0.88 0.6
Total 96.6 96.3 96.9
(apfu)
Si 6.600 6.522 6.592
Aliv 1.400 1.478 1.408
Alvi 0.483 0.482 0.534
Ti 0.099 0.120 0.083
Cr 0.123 0.110 0.076
Fe2+ 0.627 0.701 0.685
Mn 0.007 0.004 0.001
Mg 3.662 3.584 3.620
Fe2+ 0.221 0.270 0.280
Ca 1.874 1.930 1.952
Na −0.095 −0.199 −0.232
K 0 0 0
Z 8 8 8
Y 5 5 5
X 2 2 2
W 0 0 0
Mg# 0.812 0.787 0.789

Table 4.

Chemical composition (wt%) and atom per formula unit (apfu) of hornblende on the basis of 23 O (sample CV-67).

Figure 8.

Cr-Al-Fe plot of Chalki basalt spinels shown as magnetite, chromian magnetite, and chromian spinel (after [14]).

4.2.6 Spinel group

The chemical data (Table 6) and their representation (Figure 8) for the few measured points of spinel group display that they are magnetite, chromian magnetite, and chromian spinel. Moreover, the plot of their Cr# against Mg# (Figure 9) gives an important and clear sign for their metamorphic origin as a result of low-grade metamorphism and of alpine type.

CV-32 CV-67
Wt% 1 2 3 4 5 6 1 2
SiO2 32.02 32.76 33.26 34.05 34.88 35.47 32.24 30.38
TiO2 0.09 0.00 0.04 0.05 0.00 0.02 0.02 0.03
Al2O3 13.58 14.80 13.44 13.81 13.75 13.32 13.90 18.68
Cr2O3 0.03 0.01 0.04 0.01 0.03 0.00 1.14 0.16
FeO* 17.25 14.75 16.25 14.52 13.18 13.46 7.17 6.04
MnO 0.11 0.06 0.05 0.02 0.03 0.03 0.03 0.06
NiO 0.08 0.09 0.09 0.07 0.09 0.07 0.05 0.10
ZnO 0.00 0.23 0.07 0.37 0.24 0.11 0.06 0.00
MgO 21.66 21.64 22.48 22.76 23.76 23.54 31.03 30.76
CaO 0.48 0.47 0.38 0.39 0.31 0.32 0.26 0.03
Na2O 0.02 0.05 0.06 0.04 0.07 0.12 0.01 0.05
F 0.07 0.04 0.06 0.04 0.08 0.10 0.08 0.03
Cl 0.01 0.00 0.01 0.00 0.01 0.03 0.02 0.01
Total 85.4 84.9 86.2 86.1 86.4 86.6 86.0 86.3
Apfu
Si 6.611 6.689 6.742 6.836 6.916 7.020 6.309 5.861
Aliv 1.389 1.311 1.258 1.164 1.084 0.980 1.691 2.139
Alvi 1.914 2.251 1.954 2.103 2.128 2.126 1.513 2.108
Ti 0.013 0.000 0.007 0.008 0.000 0.003 0.003 0.005
Cr 0.004 0.002 0.006 0.002 0.004 0.000 0.177 0.024
Fe 2.979 2.518 2.755 2.437 2.184 2.227 1.174 0.974
Mn 0.020 0.010 0.008 0.004 0.006 0.004 0.006 0.010
Ni 0.013 0.015 0.015 0.012 0.015 0.012 0.007 0.016
Zn 0.000 0.035 0.010 0.054 0.035 0.017 0.008 0.000
Mg 6.667 6.587 6.794 6.811 7.024 6.945 9.054 8.848
Ca 0.107 0.103 0.084 0.083 0.066 0.068 0.054 0.005
Na 0.008 0.018 0.022 0.015 0.026 0.046 0.003 0.019
CV-25
Wt% 1 2 3 4 5 6 7
SiO2 23.44 25.96 27.76 31.42 33.24 36.69 37.34
TiO2 0.72 0.24 0.33 0.19 0.05 0.00 0.04
Al2O3 11.42 13.15 13.84 15.31 16.19 19.58 21.16
Cr2O3 0.01 0.11 0.04 0.01 0.00 0.03 0.08
FeO* 34.69 30.38 26.27 17.29 14.32 12.79 11.40
MnO 0.03 0.04 0.04 0.07 0.09 0.01 0.00
NiO 0.08 0.08 0.10 0.11 0.09 0.08 0.06
ZnO 0.12 0.00 0.10 0.11 0.00 0.34 0.33
MgO 17.16 18.73 19.86 22.71 23.52 20.32 18.84
CaO 0.11 0.13 0.12 0.11 0.24 0.27 0.26
Na2O 0.04 0.02 0.04 0.01 0.04 0.07 0.06
F 0.02 0.04 0.07 0.11 0.11 0.10 0.10
Cl 0.02 0.02 0.01 0.02 0.01 0.01 0.01
Total 87.9 88.9 88.6 87.5 87.9 90.3 89.7
apfu
Si 5.332 5.624 5.868 6.334 6.524 6.862 6.947
Aliv 2.668 2.376 2.132 1.666 1.476 1.138 1.053
Alvi 0.394 0.981 1.315 1.972 2.269 3.179 3.587
Ti 0.124 0.039 0.053 0.029 0.007 0.000 0.005
Cr 0.002 0.018 0.007 0.002 0.001 0.005 0.012
Fe 6.598 5.504 4.642 2.914 2.350 2.000 1.773
Mn 0.005 0.007 0.007 0.013 0.014 0.002 0.000
Ni 0.014 0.014 0.017 0.018 0.013 0.011 0.009
Zn 0.020 0.000 0.016 0.017 0.000 0.048 0.046
Mg 5.818 6.050 6.260 6.826 6.883 5.666 5.226
Ca 0.027 0.030 0.027 0.025 0.049 0.053 0.051
Na 0.018 0.010 0.017 0.005 0.017 0.026 0.023
CV-37
Wt% 1 2 3 4 5 6 7 8
SiO2 32.18 32.68 32.69 32.85 32.87 32.95 32.96 33.09
TiO2 0.02 0.04 0.00 0.05 0.09 0.01 0.06 0.00
Al2O3 15.68 15.55 15.56 15.66 13.92 15.62 15.48 15.16
Cr2O3 0.13 0.18 0.09 0.08 0.00 0.15 0.02 0.04
FeO* 14.75 14.29 14.47 14.77 17.19 14.96 15.08 14.87
MnO 0.01 0.03 0.04 0.03 0.09 0.04 0.04 0.04
NiO 0.05 0.11 0.06 0.11 0.07 0.06 0.06 0.12
ZnO 0.00 0.18 0.00 0.00 0.43 0.39 0.26 0.18
MgO 23.81 24.67 24.61 24.21 22.20 24.20 23.55 23.70
CaO 0.12 0.20 0.12 0.15 0.39 0.16 0.18 0.20
Na2O 0.04 0.02 0.03 0.01 0.01 0.03 0.05 0.03
F 0.06 0.10 0.04 0.11 0.05 0.09 0.12 0.10
Cl 0.01 0.01 0.01 0.01 0.00 0.01 0.01 0.01
Total 86.9 88.1 87.7 88.0 87.3 88.7 87.9 87.5
apfu
Si 6.421 6.429 6.429 6.465 6.629 6.459 6.516 6.558
Aliv 1.579 1.571 1.571 1.535 1.371 1.541 1.484 1.442
Alvi 2.110 2.033 2.033 2.097 1.938 2.067 2.123 2.098
Ti 0.003 0.006 0.006 0.008 0.013 0.001 0.008 0.000
Cr 0.020 0.029 0.029 0.013 0.000 0.023 0.003 0.007
Fe 2.462 2.351 2.351 2.430 2.898 2.451 2.493 2.464
Mn 0.001 0.005 0.005 0.005 0.015 0.006 0.007 0.006
Ni 0.008 0.018 0.018 0.017 0.011 0.010 0.010 0.019
Zn 0.000 0.027 0.027 0.000 0.065 0.056 0.039 0.027
Mg 7.084 7.235 7.235 7.102 6.675 7.070 6.941 7.000
Ca 0.026 0.042 0.042 0.032 0.085 0.033 0.037 0.043
Na 0.016 0.006 0.006 0.004 0.005 0.012 0.018 0.010
CV-41
Wt% 1 2 3 4 5 6 7 8
SiO2 33.06 32.54 32.39 32.62 32.58 32.06 31.82 33.02
TiO2 0.05 0.04 0.04 0.04 0.01 0.01 0.00 0.00
Al2O3 14.98 15.00 15.02 15.04 15.26 15.40 15.44 15.45
Cr2O3 0.09 0.21 0.20 0.08 0.08 0.03 0.02 0.05
FeO* 16.38 16.66 16.62 16.96 15.84 16.38 17.11 16.05
MnO 0.02 0.06 0.01 0.02 0.05 0.09 0.11 0.06
NiO 0.02 0.03 0.05 0.11 0.09 0.11 0.06 0.10
ZnO 0.00 0.00 0.06 0.17 0.37 0.02 0.05 0.61
MgO 22.77 22.67 22.57 22.45 22.46 22.28 21.63 22.80
CaO 0.20 0.19 0.20 0.21 0.22 0.29 0.61 0.19
Na2O 0.03 0.02 0.03 0.03 0.05 0.02 0.00 0.01
F 0.06 0.07 0.09 0.07 0.00 0.09 0.09 0.06
Cl 0.01 0.02 0.02 0.01 0.00 0.01 0.02 0.00
Total 87.7 87.5 87.3 87.8 87.0 86.8 87.0 88.4
apfu
Si 6.579 6.512 6.501 6.519 6.532 6.465 6.440 6.529
Aliv 1.421 1.488 1.499 1.481 1.468 1.535 1.560 1.471
Alvi 2.092 2.049 2.052 2.061 2.139 2.126 2.122 2.130
Ti 0.007 0.006 0.006 0.006 0.002 0.001 0.000 0.000
Cr 0.014 0.033 0.032 0.012 0.013 0.005 0.004 0.008
Fe 2.726 2.787 2.789 2.834 2.655 2.763 2.894 2.653
Mn 0.004 0.011 0.002 0.003 0.008 0.016 0.020 0.010
Ni 0.002 0.004 0.009 0.018 0.014 0.018 0.010 0.016
Zn 0.000 0.000 0.008 0.025 0.054 0.003 0.007 0.088
Mg 6.755 6.763 6.754 6.688 6.713 6.701 6.527 6.719
Ca 0.042 0.040 0.043 0.044 0.047 0.063 0.132 0.041
Na 0.010 0.007 0.012 0.013 0.020 0.009 0.001 0.005
CV-41
Wt% 9 10 11 12 13 14 15 16
SiO2 32.62 31.97 32.53 31.62 31.35 34.42 32.19 30.87
TiO2 1.22 0.08 0.00 0.04 0.01 0.05 0.01 0.01
Al2O3 15.50 15.56 16.13 16.15 16.31 16.46 16.71 17.19
Cr2O3 0.14 0.13 0.11 0.12 0.15 0.10 0.17 0.18
FeO* 15.25 16.67 14.47 14.18 14.59 13.95 14.87 14.53
MnO 0.04 0.05 0.04 0.04 0.02 0.03 0.03 0.07
NiO 0.05 0.11 0.19 0.09 0.11 0.11 0.11 0.06
ZnO 0.25 0.01 0.10 0.00 0.14 0.02 0.28 0.32
MgO 23.17 21.61 24.06 21.94 22.74 20.25 23.35 22.42
CaO 0.17 0.40 0.11 0.21 0.13 0.60 0.13 0.12
Na2O 0.01 0.02 0.05 0.01 0.03 0.93 0.05 0.04
F 0.07 0.11 0.10 0.00 0.08 0.08 0.08 0.01
Cl 0.02 0.01 0.00 0.02 0.00 0.01 0.02 0.01
Total 88.5 86.7 87.9 84.4 85.7 87.0 88.0 85.8
apfu
Si 6.414 6.467 6.410 6.469 6.352 6.803 6.353 6.243
Aliv 1.586 1.533 1.590 1.531 1.648 1.197 1.647 1.757
Alvi 2.006 2.175 2.156 2.362 2.246 2.637 2.239 2.342
Ti 0.181 0.012 0.000 0.006 0.001 0.008 0.002 0.001
Cr 0.021 0.020 0.017 0.019 0.023 0.016 0.026 0.029
Fe 2.508 2.819 2.384 2.425 2.471 2.306 2.454 2.458
Mn 0.007 0.008 0.007 0.006 0.004 0.004 0.004 0.012
Ni 0.008 0.017 0.030 0.014 0.018 0.018 0.018 0.010
Zn 0.036 0.002 0.015 0.000 0.021 0.003 0.040 0.048
Mg 6.792 6.514 7.067 6.689 6.870 5.967 6.869 6.761
Ca 0.036 0.086 0.024 0.045 0.029 0.126 0.027 0.025
Na 0.005 0.008 0.018 0.004 0.013 0.357 0.019 0.015

Table 5.

Chemical composition (wt%) and atom per formula unit (apfu) of chlorite on the basis of 28 O (samples CV-32, CV-67, CV-25, CV-37, CV-41).

Figure 9.

Cr# vs. Mg# of Chalki basalt spinels indicating their metamorphic origin as a result of low-grade greenschist metamorphism and alpine type (after [15]).

Figure 10.

Chalki basalt serpentines shown as type lizardite and chrysotile (after [16]).

4.2.7 Serpentine

Another less abundant secondary mineral after olivine in Chalki basalt is the serpentine. Their chemistry (Table 7) and plot (Figure 10) reveal clearly that they are mostly of lizardite and chrysotile types.

S 25 S 41 S 67
Wt% 1 2 3 1 1 2
SiO2 0.25 0.08 1.08 0.12 0.11 0.19
TiO2 10.93 0.61 1.72 0.50 0.81 0.97
Al2O3 4.19 36.74 20.12 41.11 0.42 0.26
Cr2O3 21.07 22.96 30.26 23.03 2.03 2.50
FeO* 55.68 28.02 36.84 17.66 89.91 89.06
MnO 0.01 0.00 0.00 0.00 0.09 0.08
NiO 0.10 0.13 0.08 0.20 0.19 0.17
ZnO 1.81 0.00 0.29 0.03 0.44 0.35
MgO 0.17 10.87 5.49 15.45 0.43 0.38
CaO 0.02 0.00 0.02 0.52 0.02 0.01
Na2O 0.03 0.03 0.00 0.02 0.01 0.00
F 0.00 0.02 0.00 0.10 0.00 0.00
Cl 0.00 0.00 0.01 0.01 0.00 0.00
Total 94.3 99.5 95.9 98.8 94.5 94.0
apfu
Si 0.0101 0.0024 0.0374 0.0035 0.0053 0.0095
Al 0.2022 1.3019 0.8213 1.3889 0.0242 0.0154
Ti 0.3367 0.0138 0.0448 0.0108 0.0301 0.0362
Cr 0.6827 0.5457 0.8287 0.5219 0.0793 0.0978
1.2317 1.8639 1.7321 1.9250 0.1388 0.1590
Fe 1.9083 0.7045 1.0670 0.4233 3.7136 3.6864
Mn 0.0004 0.0000 0.0000 0.0000 0.0037 0.0035
Ni 0.0034 0.0031 0.0022 0.0047 0.0075 0.0069
Zn 0.0547 0.0000 0.0074 0.0007 0.0160 0.0127
Mg 0.0106 0.4875 0.2834 0.6601 0.0315 0.0284
Ca 0.0007 0.0001 0.0008 0.0160 0.0013 0.0007
Na 0.0020 0.0017 0.0000 0.0010 0.0012 0.0000
1.9801 1.1969 1.3607 1.1058 3.7747 3.7387
Fe2+ * 0.6361 0.2348 0.3557 0.1411 1.2379 1.2288
Fe3+ * 1.4121 0.5213 0.7896 0.3132 2.7481 2.7279
Cr# 0.771 0.295 0.502 0.273 0.766 0.864
Mg# 0.017 0.675 0.443 0.824 0.025 0.0226
Cr-magnetite Cr-spinel Cr-spinel Cr-spinel magnetite magnetite

Table 6.

Chemical composition (wt%) and atom per formula unit (apfu) of spinel group on the basis of 4 O (samples CV-25, CV-41, CV-67).

Calculated stoichometrically.


Wt% 1 2 3 4 5 6 7
SiO2 47.36 46.75 40.64 41.80 41.84 42.52 41.36
TiO2 0.03 0.00 0.00 0.00 0.06 0.00 0.03
Al2O3 0.48 0.63 0.17 0.35 0.86 0.60 0.38
Cr2O3 0.01 0.00 0.01 0.02 0.01 0.03 0.00
FeO* 9.88 11.22 10.50 15.14 13.84 13.71 11.09
MnO 0.20 0.10 0.19 0.21 0.25 0.18 0.26
NiO 0.27 0.13 0.23 0.14 0.10 0.19 0.01
ZnO 0.14 0.24 0.58 0.21 0.27 0.00 0.30
MgO 33.21 30.50 36.36 28.77 29.53 29.35 31.96
CaO 0.27 0.42 0.11 0.98 0.32 0.37 0.14
Na2O 0.07 0.05 0.03 0.03 0.04 0.00 0.03
F 0.01 0.09 0.09 0.09 0.05 0.09 0.09
Cl 0.02 0.02 0.02 0.02 0.02 0.01 0.00
Total 92.0 90.2 88.9 87.8 87.2 87.1 85.6
apfu
Si 4.298 4.354 3.911 4.141 4.132 4.190 4.107
Ti 0.002 0.000 0.000 0.000 0.004 0.000 0.002
Al 0.052 0.069 0.019 0.041 0.100 0.070 0.044
Cr 0.001 0.000 0.001 0.001 0.001 0.002 0.000
Fe 0.750 0.874 0.845 1.255 1.143 1.130 0.921
Mn 0.016 0.008 0.015 0.018 0.021 0.015 0.022
Ni 0.020 0.010 0.018 0.011 0.008 0.015 0.001
Zn 0.009 0.017 0.041 0.015 0.019 0.000 0.022
Mg 4.493 4.234 5.216 4.249 4.347 4.312 4.732
Ca 0.027 0.042 0.011 0.104 0.034 0.039 0.015
Na 0.012 0.009 0.006 0.005 0.007 0.000 0.005
9.679 9.616 10.082 9.840 9.817 9.774 9.871

Table 7.

Chemical composition (wt%) and atom per formula unit (apfu) of serpentines on the basis of 14 O (CV-67).

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5. Petrological significance

  1. Olivine alteration to chlorite, serpentine, iddingsite, amphibole, and iron oxide as shown petrographically is a good evidence to low-grade metamorphism.

  2. The variation of the plagioclase in Chalki basalt from labradorite (An51–61) to andesine (An35–41) to andesine (An22) reflects the andesitic variety of these volcanic rocks in addition to basalt, while the coexisting albite composition (An0.1-04) indicates clearly that the rocks had suffered albitization due to low-grade sub-sea metamorphism.

  3. The NiO content (0.11–0.12 wt%) in the Chalki forsteritic olivine (Fo80–81) reflects the tectonic origin of this extrusion.

  4. The enrichment of Chalki pyroxene in MgO causes its shifting from diopside-augite trend of the layered igneous rocks to endiopside (en66–68 wo27–28 fs05–06) and subcalcic augite (en72 wo14 fs14).

  5. The prevalent chlorite (mainly type diabantite and penninite) in all the Chalki samples represents its suffering from chloritization process after the ferromagnesian olivine and pyroxene.

  6. Serpentine (type lizardite and chrysotile) is recorded as an alteration product after the forsteritic olivine, in addition to another rare amphibole secondary mineral of type magnesiohornblende.

  7. The spinel group as accessory minerals in Chalki basalt is classified as magnetite, chromian magnetite, and chromian spinel confirming the metamorphic origin (low-temperature sub-sea metamorphism and also of alpine type).

References

  1. 1. Dunnington HV, Wetzel R, Morton DM. Mesozoic and Paleozoic. In: van Bellen RC, Dunnington H, Wetzel R, Morton DM, editors. Lexique Stratigraphique International. Paris: Centre National recherché Scientifique Fasc 10a, Iraq; 1959. p. 333
  2. 2. Seilacher A. Kaledonischer Unterbau der Irakiden. Neases Jahrb. Geol. Palent. Abt. A. Monatshefte No 10, Stuttgart. 1963
  3. 3. Buday T. The Regional of Iraq. Stratigraphy and Palaeogeography. Vol. 1. Baghdad, Iraq: State Organization for Minerals; 1980. p. 445
  4. 4. van Bellen RC, Dunnington H, Wetzel R, Morton DM. Lexique Stratigraphique International. Paris: Centre National Recherché Scientifique Fasc 10a, Iraq; 1959. p. 333
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  7. 7. Davoudzadeh M, Weber-Diefenbach K. Contribution to the paleogeography, stratigraphy and tectonics of the upper Paleozoic of Iran. Neues Jahrbuch für Geologie und Paläontologie Abhandlungen. 1987;175(2):121-146
  8. 8. Sissakian VK. Geological Map of Iraq. Baghdad: Geological Survey; 2000
  9. 9. Tröger WE. Optische Eigenschaften und Bestimmung der Wichtigsten Gestein-bildenden Minerale, (Feldspata). In: Freund H, editor. Handbuch der Mikroskopie in der Tecknik. Vol. 4. 1st ed. Frankfurt: Umschau Verlag; 1955. pp. 79-119
  10. 10. Leblanc M, Dupuy C, Merlet C. Nickel content of olivine as discriminatory factor between tectonite and cumulate peridotite in ophiolites. Sciences Géologiques. Bulletin. 1984;37(2):131-135
  11. 11. Harlbut JCS. Klein C. Manual of Mineralogy (after Dana, J.D.). 19th ed. New York: John Wiley and Sons; 1977. p. 532
  12. 12. Leake BE, Wooley AR, Arps CES, Gilbert MC, Grice JD, Hawthorne FC, et al. Nomenclature of amphiboles: Report of the subcommittee on amphiboles of the international mineralogical association, commission on new minerals and mineral names. The Canadian Mineralogist. 1997;35:219-246
  13. 13. Hey MH. A new revision of the chlorite. Mineralogical Magazine. 1954;30:277-292
  14. 14. Steven RE. Composition of some chromites of western hemisphere. American Mineralogist. 1944;26:1-34
  15. 15. Irvine TN. Chromian spinel as a petrogenetic indicator, part II. Petrological applications. Canadian Journal of Earth Sciences. 1967;4:71-103
  16. 16. Wickes FJ, Plant G. Electron microprobe and X-ray microbeam studies of serpentine textures. Canadian Mineralogist. 1979;17:785-830

Written By

Mohsin M. Ghazal, Ali I. Al-Juboury and Sabhan M. Jalal

Submitted: March 15th, 2019 Reviewed: September 23rd, 2019 Published: October 26th, 2019