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J. mt. area res., Vol. 7, 2022 

   

               Journal of Mountain Area Research 
  
          

 

 

PETROGRAPHIC AND SEM-EDX CHARACTERIZATION OF MAFIC-FELSIC 

PLUTONIC ROCKS OF WASHAPI KAUR WESTERN RASKOH ARC, PAKISTAN 
Jafer Iqbal1, Inayat Ullah1,*, Razzaq Abdul Manan1, Abdul Ghaffar1, Fida Murad1, Jalil Ahmed2 

1. Centre of Excellence in Mineralogy, University of Balochistan, Quetta 87550, Pakistan 

2. Department of Geology, University of Balochistan, Quetta 87550, Pakistan 

 

ABSTRACT 

The Washapi Kaur plutonic rocks is located at the western part of the Ras-Koh arc, Pakistan, and 

intruded in the Cretaceous to Paleocene rock sequences. This complex consists of two main magma 

series, mafic to intermediate, forming small gabbro and diorite intrusions and felsic comprising 

granitic rock units. Gabbro consists of clinopyroxene, plagioclase, amphibole, and biotite and 

displays in-equigranular poikilitic texture. Diorites present porphyritic texture and mainly composed 

of plagioclase, K-feldspar, amphibole, quartz, and biotite with minor constituents of clinopyroxene. 

Granites are comprised of quartz, K-feldspar, plagioclase, biotite and muscovite. The field features, 

petrographic and SEM (Scanning Electron Microscopy) suggest that the magmatic activity in the 

Washapi Kaur formed as the initial mantle-melt magma derived from mafic to the intermediate 

source. Later, the melt interacted with slab-derived hydrous fluids in a continental arc setting. 

 

KEYWORDS: Igneous intrusions, Calc-alkaline, Ras-Koh arc, Pakistan 

 
*Corresponding author: (Email:  inayat.cem@um.uob.edu.pk)

1. INTRODUCTION 

Igneous intrusions with mafic to silicic 

composition composed of gabbro, diorite, 

granodiorite and granite are formed by the 

mantle magma and partial melting of 

continental crust (1, 2, 3). These igneous 

complexes tectonically occur in the crustal 

extension, rifting zone, hot spot within the plate, 

along the subduction zone and orogenic belt. 

The petrological and geochemical 

characteristics of felsic igneous intrusions are 

conclusively described by mixing mafic magma 

with the crustal melt. Therefore, the diorite and 

granitic rock units are predominant in the mafic-

silicic layer intrusion, indicating the evidence of 

upward fractional crystallization of the episodic 

variation of gabbroic intrusion (4, 5, 6, 7). 

Granitic intrusion formed by the partially melting 

of continental crust is a basic process that 

physically stabilizes and chemically 

discriminates the continental crust. Evaluating 

the temperature and pressure of the partially 

melt of continental crust plays a key role in 

understanding the genesis of granitic intrusion 

(8, 9). According to Clemens et al. (2020), the 

granitic intrusions are formed by the residual 

melting of granulitic rock units, and 

emplacements form the shallow continental 

crust (10).  

The Chagai and Raskoh magmatic arcs are 

Jurassic to Paleocene in age and are theolitic, 

which developed in response to Neo-Tethyan 

intra-oceanic subduction to continent-arc 

collision in western Pakistan. Whereas post-

Paleocene intrusive rocks generated in an 

Andean-arc system (12).  Raskoh intrusions are, 

well developed composed of mafic to felsic 

rock units (13). These intrusive formed batholiths 

(Raskoh and Koh-i-Kambran Batholiths), several 

laccoliths, small intrusive stocks, dikes and sills. 

These intrusive structures intruded older 

(Cretaceous) rock sequences, i.e., Kuchaki and 

Vol. 7, 2022 

https://doi.org/10.53874/jmar.v7i0.152 

Full length article 



 

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J. mt. area res., Vol. 7, 2022 

Rakshani Formations in the Raskoh range. 

Previously, there were no detailed petrographic 

or geochemical studies on these intrusive 

bodies. This situation hinders understanding the 

magmatic and petrographic evolution of 

Raskoh intrusions and more specifically Washapi 

Kaur plutonic rocks. This article is focused on the 

geological field features, petrography, and 

major geochemical characteristics of the 

Washapi Kaur intrusions. 

  2. REGIONAL GEOLOGY 

The Raskoh arc strikes from north-east to 

southwest direction about 250 km long, and 50 

km wide zone mainly consist of accretionary 

complex mélange, ophiolitic rock unit, volcanic-

sedimentary sequence, intra-oceanic arc unit 

associated with granodioritic intrusion covered 

by the tertiary to quaternary sedimentary rock 

units (Fig.1; 14). This arc is well-known as the 

frontal arc of the Chagai arc (12, 15). 

Regionally, the Ras-Koh arc is part of the 

Makran-Trench arc system. Both Chagai and 

Ras-Koh formed a double-arc (Chagai-Raskoh 

arc) system, which is separated by Dalbandin 

Trough (13, 11). Ras-Koh arc develops south of 

the Chagai arc, whereas its eastern boundary 

ends at the Noshki-Chaman transform fault 

system. The northward subduction of the Neo-

Tethyan ocean extensively develops the Ras-

Koh arc underneath the southern part of the 

Afghan block (16, 17, 18), whereas, considered 

as the accreted mass of an oceanic island arc 

(19, 20, 21, 14).  

 

 
Figure1. Regional geology and tectonic map of Ras-

Koh arc, representing the various lithological units 

and Ras-Koh ophiolite in the region (13). 

 

The Bunap mélange is the oldest rock unit (late 

Jurassic to early Cretaceous) in the Ras-Koh arc, 

which has thrusted contact with the overlying 

Ras-Koh ophiolite (Bunap Massif in Bunap area), 

an early to middle Jurassic Radiolarian chart unit 

and late Jurassic Sedimentary complex (22). This 

mélange unit was emplaced on the Neo-

Tethyan Oceanic floor between the passive 

northern margins of Gondwana landmass and 

the southern part of the Afghan block (22). The 

overlying Bunap massif of Raskoh ophiolite is 

comprised of metamorphic sole rock, 

peridotite, dunite, pyroxenite, gabbro 

cumulates, and pillow lava basalt with minor 

chert (21, 14). The Late Cretaceous Kuchaki 

Formation is most exposed lithological unit in the 

study area, mainly consisting of basaltic to 

andesitic lava flows and their pyroclastic 

equivalents, with thin-bedded limestone, 

sandstone, mudstone, and chert (13). The 

Paleocene Rakshani Formation is comprised of 

sandstone and shale, with minor basalts. The 

lower and of Rakshani Formation is 

disconformable with the Ras-Koh Ophiolite. The 

Raskoh intrusion was dated 40Ar-39Ar, the 

dating results of biotite and hornblende 

indicated the Ras-Koh intrusions were cooled 

about ~48 – 46 Ma (21). The Eocene Kharan 

Limestone predominantly consists of thick-

bedded to massive bioclastic limestone 

intercalated with argillaceous limestone and 

has conformable contact with overlying 

Oligocene Nouroz Formation (13). 

3. GEOLOGY OF THE WASHAPI KAUR 

 3.1. PLUTONIC COMPLEX      

The Washapi Kaur plutonic complex is located 

in the western part of the Ras-Koh arc, 

approximately 15 to 20 km southwest of 

Dalbandin town. These intrusions are widely 

dispersed as a small stock and have intrusive 

contact with the Late Cretaceous Kuchaki 

Formation (Fig.2. The Washapi Kaur intrusion is 

composed of gabbro, diorite, and granitic. 

Gabbro and diorite are formed in the central 

part of the intrusion, whereas granitic units are 

formed as dyke and lenticular sills (Fig.3). 



 

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J. mt. area res., Vol. 7, 2022 

 
Figure 2. Geological map of the study area. 

 

Granitic intrusions are present in small stock, 

dyke and sill in the study area (Fig.3). Granite has 

coarse grain texture; the fresh color is light 

reddish weather’s reddish-brown to dark brown. 

The granitic unit is mainly in contact with the 

dioritic, basaltic unit and the biotite pegmatite 

(Fig.3). These units display intense fractures with 

the spheroidal type of weathered surface (Fig. 

4a, b). Biotite pegmatite in the study area 

intruded within the granitic intrusion (Fig. 4c, d). 

 

 
Figure 3. Generalized cross-section showing the 

mafic-felsic intrusive rocks of Washapi Kaur are. 

 

Biotite pegmatite in the study area intruded 

within the granitic intrusion (Fig. 4c, d). The 

shape of biotite pegmatite in the study area 

looks like a dome shape (Fig.4c, d). Gabbro and 

dioritic intrusion mainly consist of 

ferromagnesian minerals like pyroxene, 

amphibole and biotite. Very coarse grains of 

biotite and plagioclase with laths crystal 

structure visible with a naked eye are mainly 

predominant in these intrusions. The peripheral 

part of these intrusions shows a significant 

variation in texture and composition because of 

intense weathering; the chlorite and epidote 

alteration is pervasive (Fig.4e, f).  

  
 Figure 4 (a – f). The field photographs represent the    

 Different intrusions with numerous features. (a and b)  

Spheroidal weathering of granitic intrusions with the 

intensely light and dark brown color weathered 

surface of granite and fresh surface of granite is a 

light color with a coarse grain texture. (c and d) The 

dome shape of biotite pegmatite intruded within the 

granitic rock units, the biotite pegmatite has coarse 

grain well developed flaky or sheet-like crystal 

structure. (e) Light color dioritic intrusion has a coarse 

grain texture with black biotite and amphibole well-

developed grain cut across the green epidote vein. 

(f) Dark grey to grey color weathered surface of 

gabbro to gabbro diorite intrusion has coarse grain 

texture with green color intense chlorite alteration. 

 

4. ANALYTICAL METHODS 

Thin sections were prepared and examined with 

an optical (Leica DM 500) binocular 

microscope, which was further refined with 

Scanning Electron Microscope at the Centre of 

Excellence in Mineralogy, University of 

Balochistan CEM-UOB, Quetta. A Scanning 

Electron Microscope – Energy Dispersive X-ray 

spectrometer (SEM-EDX) equipped with a Back 

Scattered Electron (BSE) imaging unit were used 

to study the major mineralogical composition 

and texture of the samples at the laboratory of 

CEM-UOB, Quetta. The SEM analysis of ten least 



 

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J. mt. area res., Vol. 7, 2022 

altered samples were selected and performed 

in a SEM Model: JSM- IT 200 coupled with EDS for 

major oxides. Small chips were taken out from 

the rock, subsequently polished and coated 

with gold to obtain BSE imaging and EDX results. 

For the operational conditions we used an 

electron current = 90 µA, a constant 

acceleration voltage = 18 kV, and a work 

distance = 15 mm. We analyzed seven spots on 

feldspar, seven spots on clinopyroxene, ten 

spots on amphibole and ten spots on biotite. The 

result of major oxides are presented in Table.1 

and mineral analysis in Table. 2.  

 

5. PETROGRAPHY 

Gabbro rock units are mainly composed of 

essential minerals calcium-rich plagioclase 

(anorthite) (44.03 vol. %), clinopyroxene (21.12 

vol.  %), amphibole (11.02 vol. %), biotite (10.03 

vol. %) and the presence of minor constituents 

of k-feldspar (2.58 vol. %). The accessory 

minerals comprised of zoisite, rutile, chrome-

spinal and opaque, whereas low-grade 

metamorphic minerals include prehnite and 

pumphilite. The secondary minerals are 

predominantly enriched with chlorite, epidote 

and sericite, these are alteration product of 

clinopyroxene, amphibole, biotite, plagioclase 

and k-feldspar. The gabbro-diorites have sub-

ophitic to interlocking texture among the 

clinopyroxene and plagioclase grains. In Wk-04, 

Wk-11-1 and Wk-13-2 the plagioclase, biotite 

and clinopyroxene have coarse grain texture 

with laths crystal structure bounded by the 

chlorite and sericite. Some samples display in-

equigranular, poikilitic texture. (Figs. 5a – f and 

9a – h). 

 
 

Figure 5. (a – d); a and c XPL, b and d PPL; 2.5X) 

Photomicrograph showing the petrographic feature 

of the gabbro rock unit is chiefly composed of 

clinopyroxene, calcium-rich plagioclase (anorthite), 

amphibole and biotite with equigranular and poikilitic 

texture. (e – f) BSE images illustrate the texture and 

compositional variation of gabbro.  Abbreviations: 

Cpx, Clinopyroxene; Plg, Plagioclase; Amp, 

Amphibole; Bi, Biotite; Ap, Apatite; Opq; Opaque; 

Mag, Magnetite; Cross Polarized Light; PPL, Plane 

Polarized Light. 

 

Diorites are predominantly composed of quartz 

(44 vol. %), plagioclase (26 vol. %), k-feldspar (12 

vol. %), biotite (11 vol. %) and amphibole (8 vol. 

%) with minor clinopyroxene (4 vol. %) 

constituents and accessory apatite, zircon, 

ilmenite, sphene and opaque minerals. This rock 

unit has a porphyritic texture with phenocrysts of 

quartz, plagioclase, k-feldspar, clinopyroxene 

having groundmass of the same minerals (Fig. 6 

a – f).    



 

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J. mt. area res., Vol. 7, 2022 

 
Figure 6. (a – d); a and c XPL, b and d PPL; 2.5X) 

Photomicrograph showing the petrographic feature 

of the diorite rock unit is chiefly composed of 

clinopyroxene, calcium rich plagioclase (anorthite), 

amphibole, biotite and accessory minerals apatite 

with inequigranular and ophitic texture. (e – f) BSE 

image illustrate the texture and compositional 

variation of diorite.  Abbreviations:  Zr, Zircon; other 

abriviations in Fig. 5. 

 

 

Figure 7. (a – d); a and c XPL, b and d PPL; 2.5X) 

Photomicrograph showing the petrographic feature 

of the granitic rock unit consists of quartz, k-feldspar, 

albite plagioclase, biotite and muscovite with fine to 

medium grain texture because of micro-granular 

texture indicated the micro-granite. (e – f) BSE image 

illustrates the texture and compositional variation of 

granite. Abbreviations: Kfs, K-feldspar; Mu, Muscovite; 

Qtz, Quartz, other abriviations in Figs.5 and 6. 

 

Granite consist of quartz (69 vol. %), k-feldspar 

(13 vol. %), albite plagioclase (8 vol. %), biotite 

(7 vol. %) and muscovite (3 vol. %) associated 

with accessory minerals, apatite, zircon and 

opaque minerals. This rock unit has medium 

grain texture of quartz, plagioclase, k-feldspar, 

biotite and muscovite because of fine to 

medium grain texture, the granitic rock is called 

micro-granite (Figs. 7a – f and 8 i – p). 

 

 
Figure 8. (a – b) Plagioclase has a type of calcium-

rich anorthite plagioclase, thin lamella coarse grain 

texture, and euhedral well developed elongated 

laths crystal structure. (c – d) Clinopyroxene has pale 

brown, brown, pale green and pink color, medium to 

coarse grain texture with sample and a lamellar twin 

along the composition plane and moderate to high 

relief. (e – f) Amphibole has high order interference 

figure with pale green to pale brown color, medium 

to coarse grain texture and double set perfect 

cleavages. (g – h) Biotite has pale brown to green 

color, medium to coarse grain texture, flaky crystal 

structure with highly perfect cleavages and highly 

pleochoric and moderate relief. (i and j) K-feldspar 

has white interference color, medium to coarse grain 

texture, euhedral to subhedral crystal shape with 

sample twining. (k – l) Muscovite has pale green to 



 

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J. mt. area res., Vol. 7, 2022 

pink color, a medium to coarse grain texture, and a 

flaky crystal structure with perfect cleavage. (m – n) 

Plagioclase has medium to coarse grain texture, 

subhedral to euhedral crystal shape and 

polysynthetic albite twining with medium to thick 

lamellas. (o – p) Quartz has coarse grain 

inequigranular texture, subhedral to euhedral 

prismatic crystal structure with undulose extinction. 

Abbreviations: An, Anorthite; Alb, Albite, other 

abriviations in Figs.5, 6 and 7. 

 

5.1 Petrographic/textural variations in 

Washapi Kaur intrusions 

The significant constituents of gabbro are 

calcium-rich anorthite plagioclase and 

clinopyroxene. Therefore, the calcium-rich 

plagioclase (anorthite) is characterized by the 

thin lamella that occurred along the twining 

plane and section no Wk-11-1 consists of thin 

percales-albite type polysynthetic twinning. 

Anorthite plagioclase has characterized by 

coarse grain texture, euhedral well developed 

elongated laths crystal structure with white to 

first-order interference color in cross-polarized 

light and plane-polarized light anorthite 

plagioclase has colorless interference figure 

with moderate to low relief (Fig.9 a, b). 

Clinopyroxene has second to third order high 

interference figure with pale brown and brown, 

pale green and pink color, medium to coarse 

grain texture, subhedral to euhedral crystal 

shape with sample and a lamellar twin along 

the composition plane, perfect cleavage and 

irregular fracture with incline extinction along 

the cleavage plane in cross-polar light. 

Clinopyroxene has high interference color 

greenish to light brownish pleochroic image with 

moderate to high relief (Fig. 8c, d).   

The diorite units are highly dominant amphibole, 

biotite and sodium rich plagioclase. Amphibole 

has second to third-order interference figure 

with pale green to pale brown color, medium to 

coarse grain texture, double set perfect 

cleavage with subhedral to euhedral well 

developed prismatic crystal structure. 

Amphibole grains look like a biotite grain 

elsewhere the major difference is cleavage 

angle, the amphibole has double set perfect 

cleavage and biotite has single set parallel 

cleavage (Fig.7. e and f). Biotite has pale brown 

to green interference color, medium to coarse 

grain texture, and a flaky crystal structure with 

perfect cleavages. Lath crystals of biotite have 

bird eye extinction with highly pleochroic and 

moderate relief in the plane-polarized light (Fig. 

8g, h).  

The granitic rock unit mainly consists of quartz, k-

feldspar, sodium rich plagioclase albite, biotite 

and muscovite.  Muscovite has pale green to 

pink interference color, medium to coarse grain 

texture, and a flaky crystal structure with perfect 

cleavages. The orthoclase type of k-feldspar is 

chiefly dominant in this rock units. Frist order to 

white interference color, medium to coarse 

grain texture, euhedral to subhedral crystal 

shape with sample twining in cross-polarized 

light, colorless interference figure, and low 

moderate relief in plane-polarized light. 

Sericitization is more common in Wk 02-1 and Wk 

05-3, therefore, the sericitization is an alteration 

product of orthoclase feldspar (Fig.8 i, j). Lath 

crystals of muscovite is highly pleochroic and 

moderate relief in the plane polarized light. 

Muscovite is commonly altered into chlorite in 

Wk 12 and Wk 05-3 section (Fig.8 k, l). 

Plagioclase has medium to coarse grain texture, 

subhedral to euhedral crystal shape, 

polysynthetic albite twinning with medium to 

thick lamellas and laths crystal structures with 

low interference color in cross-polarized light. In 

Wk 03-2, Wk 10-2 and Wk 19-2, the core of 

plagioclase grains are partly altered into sericite 

and epidote. The fine grain sphene and apatite 

grains are included within the plagioclase grains 

(Fig.8 m, n). Quartz is highly dominant in the 

granitic rock unit. Quartz has fine to coarse grain 

inequigranular texture, subhedral to euhedral 

prismatic crystal structure with undulose 

extinction and colorless to low interference 

color with negative relief. (Fig.8 o, p). 

 

6. RESULTS 

6.1 Major Elements Geochemistry 

SEM-EDX results for major oxides of intrusive 

rocks of Washapi Kaur intrusions are slight variant 

in SiO2 (51.19-77.75 wt%), Al2O3 (14.21- 18.9 wt %), 

K2O (0.56 – 1.67 wt%), Na2O (2.03 – 4.4. wt %), 



 

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J. mt. area res., Vol. 7, 2022 

CaO (0.2 – 12.97 wt%), MgO (0.2 – 6.98 wt%), FeO 

(0.45 – 9.89 wt%), MnO (0.03 – 0.23 wt%), P2O5 

(0.24 wt% - 0.93 wt%) and TiO2 (0.06 – 0.95 wt%) 

(Table.1).  

In the discrimination diagram, the intrusive 

rocks are classified as gabbro-diorite, diorite, 

and granite in the silica versus total alkalis 

diagram (Fig. 9; 24). In the SiO2 versus K2O (25), 

both mafic and felsic intrusion of Washapi Kaur 

complex fall in the calc-alkaline field, which 

indicates calc-alkaline type magmatism for 

Washapi Kaur complex (Fig. 9). 

 

 
Figure 9. Discrimination binary diagram illustrate the 

total alkali versus SiO2 of studied rocks in the study 

area (24; 25). 

 

7. DISCUSSION     

7.1 Petrographyical evidence for magma 

evolution 

Petrographically the Washapi Kaur the intrusive 

rocks are composed of mafic to felsic and 

identified as gabbro, diorite and granite. The 

plutonic contact between dioritic and granitic 

rock units are intensively sharp with visible 

effects of chilling (Fig. 4), which is indicate the 

late phase of magmatic intrusion of granite 

within the dioritic intrusion. The gabbro to 

gabbro-diorite and diorites are consist of high 

constituents of hydrous minerals such as 

amphibole and biotite, tectonically which is 

indicated that the starting of early phase of 

oceanic plate subduction beneath the 

continental plate with high contamination of 

the oceanic plate and the granitic rock units 

having dominant felsic phases such as quartz, 

alkali feldspar and plagioclase, tectonically that 

is indicate the genesis of granitic rock units are 

linked with high involments of continental plate.  

 

7.1.1 Feldspar: Types and Origin 

The plagioclase grains change from calcium-

rich plagioclase (An) to sodium-rich plagioclase 

(Alb) in gabbro-diorite to granites (Table. 2). The 

plagioclase grains core in gabbro-diorite and 

diorite rock mainly consists of calcium-rich 

plagioclase (Anorthite-Bytownite), while rims 

with andesine compositions. These 

compositional changes represents hybrids 

mafic to felsic magma types; typically, the 

patchy zone anorthite and bytownite core are 

resorbed and overgrowth by the Ca-Na rich 

plagioclase andesine rims. The Ca-rich core 

plagioclase (An) is crystallized from the mafic 

type magma and the early phase of felsic 

magma feeds from the acidic magma 

chamber (26, 27). 

Strong undercooling in the mafic magma 

infiltrated the more acidic magma may have 

led to the formation of unusual dendritic and 

boxy-cellular calcic plagioclase crystals with 

patchy zoning (5, 28, 29). Rare crystals of 

andesine (early-formed crystals acquired from 

the acidic magma) would have been melted 

and partially resorbed in the hybrid dioritic 

magma before being overtaken by a limited 

zone of Ca-rich plagioclase. Crystallization 

would have evolved slowly after mixing and 

thermal readjustment, changing the 

plagioclase from thin calcic zones to broad 

zoned andesine rims. At the same time, the 

comparatively sodic core would have 

overgrown the more typical calcic cores, while 

tiny, unzoned plagioclase of similar composition 

nucleated and formed in the groundmass (30, 

31). The Ca-rich, Ca-Na rich and Na rich 

plagioclase were observed in the gabbro-

diorite, diorite and granitic rock units in Washapi 

Kaur intrusive complex (Fig. 10 a, b). Therefore, 

the compositional variation of plagioclase 

feldspar generally describes the feeding of the 

magma chamber with new pulses of magma in 

Washapi Kaur intrusion.  



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J. mt. area res., Vol. 7, 2022 

Table 1. Major Oxides of mafic-felsic rocks from Washapi Kaur Complex, Ras-Koh arc. 

Elements 

Major Elements Geochemistry Results 

Granite Diorite Gabbro Diorite 

wk2-

1 

wk5-

3 

wk5-

4 
wk12-1 wk03-2 wk19-1 wk03-1 wk15-2 wk10-1 wk15-1 wk19-2 wk00-2 wk01-1 wk13-1 wk11-1 

wk4-

1 

SIO2% 77.75 76.51 75.06 74.54 62.98 61.28 60.88 57.95 57.45 57.3 57.23 52.63 52.06 51.3 51.23 51.19 

Al2O3% 14.21 16.79 15.91 17.82 14.85 16.24 18.9 15.65 15.24 14.85 15.84 15.62 17.74 14.36 17.6 17.16 

K2O% 1.5 1.2 1.67 1.54 1.19 1.61 1.11 1.2 1.16 1.13 1.16 0.87 0.73 0.56 0.9 0.86 

Na2O% 3.03 3.72 3.92 3.02 4.1 4.23 4.42 4.4 4.27 4.14 4.1 2.03 2.23 2.13 2.16 2.42 

CaO% 0.9 0.2 1.08 1.13 4.57 5.84 4.13 8.7 7.35 8.88 6.42 12.97 11.85 12.29 11.97 11.86 

MgO% 0.5 0.2 0.9 0.42 3.5 3.92 3.14 3.91 4.19 5.11 5.44 5.83 5.95 6.98 6.94 5.63 

FeO% 0.65 0.48 0.45 0.37 6.85 5.27 6.03 5.74 8.25 7.01 8.19 8.02 7.17 9.89 6.74 9.04 

MnO% 0.21 0.03 0.06 0.05 0.18 0.08 0.03 0.11 0.23 0.08 0.15 0.21 0.27 0.09 0.21 0.21 

P2O5% 0.26 0.24 0.35 0.36 0.45 0.41 0.53 0.56 0.66 0.46 0.43 0.77 0.64 0.93 0.67 0.66 

TiO2% 0.08 0.16 0.06 0.07 0.59 0.56 0.34 0.79 0.9 0.74 0.46 0.95 0.73 0.71 0.58 0.76 

Total 99.09 99.53 99.46 99.32 99.26 99.44 99.51 99.01 99.7 99.7 99.42 99.9 99.37 99.24 99 99.79 

 

 



 

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7.1.2 Pyroxene: Types and Origin 

Ca-rich (Di-Fs-Hd) pyroxene series is identified 

by the SEM-EDX analysis in the gabbro-diorite 

and dioritic rock units in Washapi Kaur intrusion 

(Fig. 10 c, e, Table. 2). The complete solid 

solution between CaMgSi2O6-CaMgFeSi2O6-

CaFe2Si2O6 forms the Ca-rich Diopside-

Ferosalite-Hedenbergite pyroxene series. 

Aluminum is poor constituent in diopsides and 

ferosalite type pyroxene (CaMgSi2O6), and 

typically, aluminum is enriched in the 

hedenbergite type of pyroxene (CaFe2Si2O6). 

The crystallization temperature Ca-rich 

pyroxene series (Di-Fs-Hd) is 1200 to 900 ˚C in 

binary system (34, 35). Ca-rich pyroxene series 

is chiefly crystalized with Ca-rich plagioclase 

(An) with approximately same temperature. 

Paragenesis of Ca-rich pyroxene series 

crystalized in the early stage of mafic type of 

magma, elsewhere the disposed type 

pyroxene is crystalized in strongly alkaline-rich 

magma and Hedenbergite type pyroxene is 

formed by the high aluminum and silica rich 

basic to intermediate type of magma (36, 37). 

7.1.3 Amphibole 

The SEM-EDX study of amphibole 

predominantly consists of Na constituents with 

Fe, Mg, K, Al, and Ti elements in gabbro and 

dioritic rock units in Washapi Kaur intrusion (Fig. 

10 f, Table.2). The amphibole is highly 

pleochroic with brown color (Fig. 8 e, f). 

Amphibole from mafic magma, crystalized in 

shallow depth with high temperature about 

900 ˚C (38, 39). High temperature is 

theoretically possible because they fall within 

the magmatic amphibole stability field, and 

their effect would explain the cores 

consistently higher Ti and Al (40). The 

constituents of Ti content in amphiboles group 

minerals increases with temperature and is the 

minute consequence of pressure. The 

presence of Ti element could be indicate the 

primary source of brown color amphiboles 

(41, 42). The brown color amphibole typically 

crystalized in the gabbro-diorite and dioritic 

rock units in Washapi Kaur intrusion suggest 

that mafic magma crystallized before the 

infuse pulses of acidic magma in the magma 

chamber. Continuously magma quenching 

and cooling in the acidic type magma, green 

type of amphiboles common in granites.  

7.1.4 Biotite 

In petrographic study identified the two types 

of biotite (Green biotite and Brown biotite) 

concerning their physical properties; 

furthermore, in SEM-EDX compositional 

variation from the gabbro-diorite, diorite and 

granite rock units in the Washapi Kaur 

intrusion. The green biotite chiefly consists of 

magnesium (Mg), and the brown biotite 

mainly consists of iron (Fe) (Fig. 8 g, h and Fig. 

9 g, Table. 2). Magnesium (Mg) rich biotite 

associated with gabbro-diorite and iron (Fe) 

rich biotite is with diorite and granites. The Mg 

enrichment in mafic-intermediate magmas 

indicates these rocks formed from early mafic 

rocks, while the Fe-rich biotite indicates the 

substantial subduction inputs and subsequent 

felsic magmatism in Washapi Kaur enriched 

the Fe-contents in magma. 

   



32 
J. mt. area res., Vol. 7, 2022 

Table 2. Elements mass % of rock forming minerals from Washapi Kaur Complex, Ras-Koh arc. 

 
  

Sample# Minerals O (Mass %) Si (Mass %) Al (Mass %) K (Mass %) Na (Mass %) Fe (Mass %) Mg (Mass %) Ca (Mass %) Ti (Mass %) Mn (Mass %)

Wk- 01.2 Amphibole 56.34 16.26 5.55 1.09 1.45 8.31 4.84 5.34 0.52 0.28

Wk- 01.3 55.6 17.81 12.24 0.49 2.13 2.9 1.44 6.88 0.18

WK- 01.4 56.34 16.26 5.55 1.09 1.45 8.31 4.84 5.34 0.52 0.28

WK- 03.2 40.9 18.88 9.64 7.76 0.97 11.78 7.31 0.99

WK- 03.3 44.94 11.95 6.8 3.055 2.37 4.87 2.84 1.68 0.4

WK- 10.4 48.63 17.65 8.37 6.43 1.53 7.56 8.19 1.65

WK- 11.3 37.53 18.95 8.33 8.62 4.15 12.93 7.38 1.84

WK- 11.4 51.58 14.68 8.88 1.47 3.25 8.76 9.3 1.53 0.55

WK- 15.6 51.09 21.15 6.4 4.87 1.02 5.86 7.51 1.55 0.55

WK- 19.1 18.79 8.64 3.68 0.47 1.43 45.77 1.5 10.36 7.95

WK- 03.1 Biotite 37.82 16.42 4.31 1.55 1.38 35.09 1.45 0.97

WK- 03.4 43.28 14.14 7.95 3.32 1.96 21.42 7.47

WK- 10.4 48.63 17.65 8.37 6.43 1.53 7.56 8.19

WK- 11.3 37.53 18.95 8.33 8.62 4.15 12.93 7.38

WK- 15.2 59.69 27.19 0.35 0.52 0.84 0.26

WK- 15.3 51.84 12.66 10.57 15.52 9.41

WK- 15.5 51.98 13.7 10.48 1.47 1.69 11.23 9.28

WK- 19.2 52.96 20.41 15.11 6.59 1.82 2.09 1.03

WK- 19.3 50.58 20.71 17.35 7.87 0.46 2.03 0.21

WK- 19.4 53.48 20.48 14.95 6.45 1.87 2.2 0.57

WK- 10.2 Clinopyroxene 52.28 21.08 1.32 0.63 4.99 6.86 12.49

WK- 10.5 32.34 3.87 1.13 0.55 1.9 55.81 1.56 2.85

WK- 11.2 52.16 20.26 2.04 0.45 5.91 7.61 11.56

WK- 11.4 51.58 14.68 8.88 1.47 3.25 8.76 9.3 1.53

Wk- 13.2 56.73 19.95 0.84 0.64 4.05 7.22 10.57

WK- 13.3 48.56 23.19 1.3 0.47 4.72 7.29 14.25

WK- 13.4 49.6 22.74 0.85 5.57 6.76 14.19

WK- 10.8 Plagioc lase 54.73 21.82 13.39 4.05 6.01

WK- 10.11 27.35 39.05 16.46 3.62 2.15 0.13 11.24

WK- 10.9 57.16 20.86 12.31 0.26 4.91 4.49

WK- 15.1 48.86 25.6 15.01 2.33 4.15 0.49 0.22 3.34

WK- 10.8 54.73 21.82 13.39 4.05 6.01

WK- 10.6 61.02 19.72 10.64 6.15 2.48

WK- 01.5 59.87 19.81 10.99 0.35 5.19 3.48



 

Iqbal et al., J. mt. area res. 07 (2022) 23-36 

33 
J. mt. area res., Vol. 7, 2022 

 
Figure 10. (a-h) SEM-EDX and BSE image showing the numerous rock forming mineral elemental composition 

of Gabbro-diorite, Diorite and Granite rock units in Washapi Kaur intrusions. (a – c) Plagioclase series (An – 

Alb - Kfs); (d – f) Pyroxene series (Di – Hd); (g) Biotite; (h) Hornblende. 

 



 

Iqbal et al., J. mt. area res. 07 (2022) 23-36 

34 
J. mt. area res., Vol. 7, 2022 

CONCLUSIONS 

1. Washapi Kaur Intrusion intruded within the 

older Cretaceous Kuchaki Formation 

sequences are composed of gabbro-diorite, 

diorite, and granite.  

2. The mineralogical composition of gabbro-

diorites is clinopyroxene, calcium-rich 

plagioclase (anorthite), amphibole, and 

biotite. Major constituents of diorite rock units 

are predominantly composed of quartz, 

plagioclase, k-feldspar, biotite and 

amphibole with minor constituents of 

clinopyroxene. Granitic rocks consist of quartz, 

k-feldspar, albite plagioclase, biotite and 

muscovite.  

3. The compositional variations in feldspar, 

clinopyroxene, and biotite depict the magma 

evolution from the oceanic-arc environment 

to the island arc setting. 

4. The gabbro-diorite and diorite rock 

represent oceanic island arc and granitic rock 

are continental calc-alkaline arc origin. 

Conflicts of interest/Competing interests: The 

authors declare no any conflict of 

interest/competing interests.  

Authors’ contributions: 

Jafer Iqbal: Field investigation, sampling, data 

processing, map drawing and draft 

writing. Inayat Ullah: Program designing, draft 

writing, revision. Razzaq Abdul Manan: 

Conceptualization, revision and editing. 

Abdul Ghaffar: Field investigation, Draft 

writing, revision and editing. Fida Murad: 

Laboratory Analysis, Draft writing, Raw data 

acquisition and data processing. Jalil Ahmed: 

Field investigation and sampling, draft writing. 

 

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Received: 17 Feb. 2022. Revised/Accepted: 24 March 2022.