petrogenesis of metapelitic rocks exposed in ka ka-naung pein-...

The Second Myanmar National Conference on Earth Sciences (MNCES, 2018) 113

November 29-30, 2018, Hinthada University, Hinthada, Myanmar

Department of Geology, Monywa University, Monywa, Sagaing Region, Myanmar

[email protected]

Petrogenesis of Metapelitic Rocks Exposed in Ka Ka-Naung Pein-

Man Hlwe Area, Katha Township, Sagaing Region

Aung Khin Soe

Abstract

The study area lies in Katha Township, northeastern part of Sagaing Region. It is situated between Latitude 24° 17′ to 24° 25′ N and Longitude 96° 16′ to 96° 24′ E. The presence of the

distinctive mineral assemblages such as chlorite-muscovite-quartz, biotite-muscovite-chlorite-

quartz and garnet-muscovite-biotite-quartz in metapelite point out that the study area falls

within the lower greenschist facies to amphibolites facies. Some textural features and

lithologic characters indicate that the metamorphic rocks of the Katha-Gangaw Range of the

study area may probably be metamorphosed from the mixture of pelitic and psammitic rocks

with subordinate amount of basic rocks of Late Jurassic to Early Cretaceous age. Three

metamorphic zones such as chlorite, biotite and garnet zones are recognized. Although

equilibrium is difficult to attain and P-T conditions are not certain, the chlorite zone is to be in

the 350 to 450°C range. The equilibrium conditions of biotite zone are 420°C at about 0.35

GPa. The porphyroblasts of almadine garnets do not occur until the temperature of 460-500°C

in typical pelites and the metamorphic grade starts to enter the lower amphibolites facies. There is neither precise time of metamorphism nor available radiometric dating for the

metamorphic rocks of the study area. The time of metamorphism of the present study area can

be ascertained with the neighbouring area and some establish area especially on the basis of

lithologic similarity and lateral continuity. So, the time of metamorphism of the Katha-

Gangaw Range (including study area) could be assigned tentatively to Late Cretaceous to

Early Oligocene. The sequence of metamorphic conditions encountered could be compared to

the medium P/T (intermediate pressure and intermediate temperature) facies series of

Barrovian Type.

Keywords: pelitic and psammitic rocks, equilibrium, Barrovian Type

Introduction

The study area lies in Katha Township, northeastern part of Sagaing Region. It is

situated between Latitude 24° 17ʹ to 24° 25ʹ N and Longitude 96° 16ʹ to 96° 24ʹ E of

UTM map sheet No. 2496 07. It can readily be approached by car and by ship from

Mandalay, Katha and Banmaw throughout the year. The location map of the study area is

shown in (Fig.1). The main ridge comprises in the study area is east of Katha-Gangaw Range.

Although there are some previous geologic accounts on the study area, petrogenesis of

metamorphic rocks and progressive metamorphism deduced from mineral isograds on

metamorphic rocks have not been documented yet. Thus, I was carried out this present

research work.

Regional Geologic Setting

Mitchell (1981) divided the Myanmar region into four plates, viz., (1) Indian Plate

lying west of the Indo-Burman Ranges; (2) The Eastern Burma Plate extending from the

Indo-Burman Ranges to the Sagaing-Namyin Fault; (3) The Shillong Plate lying north of the

Naga Hills and (4) The Asian Plate lying east of the Sagaing-NamyinFault.The study area lies

within the northern part of Central Cenozoic Belt (Central Lowland) and it is located in the

west of the western margin of Sino-Myanmar Ranges (Kachin-Shan-Tanintharyi Highlands

or Eastern Highlands) (Bender, 1983).According to Mitchell (1981)’s divisions, the study

area falls in the eastern part of Eastern Burma Plate and western part of Asian Plate. The

Sagaing Fault passes through the western part of this area.

114 The Second Myanmar National Conference on Earth Sciences (MNCES, 2018)


Wuntho-Banmauk uplift (United Nations, 1978) is situated in the western part of the

area and it comprises chlorite, actinolite and mica schists and phyllites overlain by the

Mawgyi basalt (early Cretaceous), pillow lavas and volcaniclastics beneath Upper Albian

limestone. Pre-Albian rocks are intruded by andesite sills, by the early Upper Cretaceous

granodioritic Kanza Chaung Batholith, and by Tertiary minor intrusions. Post-Oligocene,

Miocene sediments and some carbonate rocks are exposed between this uplift and Sagaing

Fault. The Katha-Gangaw Range is made up of pelitic metamorphic rocks and the first defile

of Ayeyarwady lies between the Katha-Gangaw Range and Tagaung-Myitkyina Belt

including Tagaung Taung Ultrabasic rocks (Cretaceous) (Aung Kyaw Thin, 2006).

The southern part of the study area is covered by Pleistocene gravels, Irrawaddy

Formation and Pondaung Formation (Myint Thein, et.al., 1982), Cenozoic volcanic and

ultrabasic volcanic rocks (serpentinite), Mayathein complex (schist, gneiss, marble and

migmatites), Katha Methamorphics (phyllite, talc schist, green schist, garnet-mica schist,

quartz-mica schist and amphibolites), Ngapyawdaw Chaung Formation (Triassic) (Myint

Thein et.al., 1982; L.Laja,1983), (Late Jurassic-early Cretaceous) (Maung Maung et.al.,2006)

and Wabo Chaung Formation (Oligocene) (DGSE,1976 in Nyan Win, 2008).

Jade Mines Belt, northern part of the area, is consisting of hornblende schist,

glaucophane schist, chlorite schist, kyanite schist and graphite schist (Chhibber, 1934). The

metamorphic rocks are generally trending NE-SW. The regional geologic setting of the study

area and its environs are shown in (Fig.2).

LEGEND

Figure (1). Location map of the study area

Study area

95°50ʹ 96°15ʹ 96°40ʹ

95°50ʹ

24°

0ʹ

96°15ʹ 96°40ʹ

24°

20

ʹ

24°

40

ʹ

24°

40

ʹ

24°

20

ʹ

24°

0ʹ

N

0 28 km



Figure (2). Regional geologic setting of the study area and its environs. (Source: MGS, 2014)

Study area



Distribution of Rock Units

The present study area is made up chiefly of metamorphic rocks. The metamorphic

rocks are of Late Jurassic -Early Cretaceous Katha Metamorphics rock units. They occupy

the entire bulk of the east of Katha-Gangaw Range and the metamorphic rocks are low to

medium grade. It is noteworthy that the metamorphic units pass into one another in a

gradational manner. The Katha Metamorphics rock units cover two-third of the study area.

The Katha Metamorphics are subdivided into three informal units: lower Unit I,

middle Unit II and upper Unit III. Based on the minerals, mineral assemblages and

lithologies, the units are arranged in orderly. The lower Unit I is chiefly composed of garnet

biotite schist, garnet muscovite schist and garnet quartzite. The middle Unit II is essentially

composed of sericite schist, micaceous quartzite, graphite mica schist, biotite schist and

muscovite schist. The upper Unit III is mainly composed of chlorite schist.

Based on the field observation, lithologic trends and mineral variation, the

stratigraphic succession of the investigated area can be described in Table (1) and the

distribution of rock units is shown in Fig. (3).

Table (1). Stratigraphic succession of the study area

Stratigraphic Units Age

Sedimentary Unit

Alluvium

-unconformity

Recent

Ultramafic Rocks

Serpentinite

Metamorphic Unit

Unit III

Chlorite schist

Unit II

Sericite schist

Micaceous quartzite

Graphite mica schist

Biotite schist

Muscovite schist

Unit I

Garnet biotite schist

Garnet muscovite schist

Garnet quartzite

Late Cretaceous-Early Eocene

Katha

Metamorphics

Late Jurassic-Early Cretaceous



EXPLANATION

Sedimentary Unit

Unconformity

Metamorphic Unit

(Katha Metamorphics)

Vertical Scale 0.8 ʺ = 1000 m

Horizontal Scale 1ʺ = 1250 m

Unit I Garnet biotite schist, garnet muscovite

schist and garnet quartzite

Unit II Quartz sericite schist, micaceous

quartzite, graphite mica schist,

biotite schist and muscovite schist

Unit III Chlorite schist

Alluvium Recent

Late Jurassic-

Early

Cretaceous

Village

1 km

Figure (3). Map showing the distribution of various rock units in the Ka Ka-Naung Pein –

Man Hlwe area



Petrogenesis of Metamorphic Rocks

Types of Metamorphism

The type of metamorphism of study area is regional metamorphism and locally

dynamic metamorphism according to the mineralogical and textural criteria. The regional

metamorphic rocks of the present area consisting of platy or prismatic minerals, like micas

and chlorite, therefore exhibit strong schistosity.

In the study area, the characteristics features of regional metamorphism and dynamic

metamorphism in the field and petrographic studies are as follows:

(1) Texturally, the rocks of the study area show foliation and it is one of the most prominent

features of regional metamorphism;

(2) Successive mineral zones are formed, and appearance and disappearance of minerals from

zone to zone are taken into account the regional metamorphism;

(3) The deformation features of grain granulation, suture boundary, undulatory extinction and

intensely fractured grains are present locally and it provide the evidences of dynamic

metamorphism.

Mineral Assemblages, Metamorphic Facies and Zone

Six representative mineral assemblages are recognized in the study area based on the

petrographic analysis. They are as follows;

(1) chlorite -muscovite -quartz,

(2) biotite-muscovite- quartz,

(3) biotite-muscovite-chlorite-quartz,

(4) garnet-biotite-muscovite-quartz-graphite,

(5) garnet- muscovite -quartz,

(6) garnet- biotite-quartz,

The facies classification, nomenclature and representative mineral assemblages used

in this research work was mainly based on Turner (1968), Yardley (1989), Bucher and Frey

(1994), Winter (2010) and Bucher and Grapes (2011).

The mineral assemblage of Chl-Ms-Qtz is typical assemblage of chlorite schist. The

occurrence of this mineral assemblage in chlorite schist clearly indicates that the rock

develops in chlorite zone of lower greenschist facies.

The Bt-Ms-Qtz assemblage is developed in the biotite schist and Bt-Ms-Chl-Qtz in

muscovite schist. These assemblages are the characteristic of biotite zone of upper

greenschist facies.

Grt-Bt-Qtz assemblage is common in garnet biotite schist, Grt-Ms-Qtz assemblage in

garnet muscovite schist and Grt-Bt-Ms-Qtz assemblage in garnet quartzite. These

assemblages are typically developed in the metapelite of garnet zone of lower amphibolites

facies.



Table (2). Mineral assemblages and metamorphic facies of the study area

Type of

Metamorphism

Rock Group Representative

Rock

Mineral

Assemblage

Metamorphic

Facies

Regional

Metamorphism

Metapelites

Chlorite schist

chlorite,

muscovite,

quartz Greenschist

Facies Biotite schist

biotite, muscovite,

quartz

Muscovite schist biotite, muscovite,

chlorite, quartz

Garnet biotite

schis

garnet, biotite,

quartz

Amphibolite

Facies

Garnet

muscovite schist

garnet,

muscovite,quartz

Garnet quartzite garnet,biotite,

muscovite, quartz

Reaction-Isograds

Chlorite zone

Pelites in the chlorite zone are typically slates and they contain chlorite and muscovite

with variable amounts of quartz and albite. In the study area, metapelites of the chlorite zone

are mainly composed of chlorite, muscovite and quartz. This assemblage is plotted on the

AKF diagram shown in (Fig. 4) (in Winter, 2010). Most of the analyzed pelite compositions

contain quartz, chlorite and phengitic muscovite in the two-phase field in (Fig. 4). In this

figure, Chl-Ms tie-lines connect coexisting chlorite and mica compositions. These

compositions are governed by the substitution of Al with Fe, Mg and Si, as a function of the

Al-content of the rock. Equilibrium is difficult to attain in experiments at these low

temperatures, so that P-T conditions are not certain, but they are believed to be in the 350 to

450°C range (Winter, 2010). The development of mineral assemblage and above

considerations, the chlorite zone is placed below the biotite isograd in P-T space.

Figure (4). AKF diagram showing mineral assemblage developed in chlorite schist (source:

Winter, 2010)



Biotite zone

Many reactions can produce biotite. One biotite isograd reaction that can affect pelites

is encountered at point 2 in (Fig.7). The first prograde biotite taking places in common pelite

can be described by the reaction;

3Chl + 8Kfs = 5Bt + 3Ms + 9Qtz + 4H2O

Because chlorite is more plentiful than K-feldspar in most pelites, the above reaction

typically marks the loss of Kfs toward higher grade. This reaction can be demonstrated

geometrically by resorting to the AKF projection (Fig.5). At grades below this biotite-isograd

reaction, Chl and Kfs are stable together, as indicated in (Fig.5 a) by the tie-lines connecting

them. Above the isograd (Fig. 5 b), the new Bt-Ms tie line separates Chl and Kfs, so that Bt

+ Ms are stable together and Chl + Kfs are not, as this reaction indicates (in Winter, 2010).

According to Winter (2010), the metamorphic grades above the tie line flip reaction in

(Fig. 5), the composition of the white mica that coexists with biotite and chlorite gradually

becomes less phengitic via continuous reactions by which the most Al-poor white mica

breaks down, and the amount of chlorite and biotite increases. Biotite begins to appear in

progressively more aluminous pelites compositions as a result of the continuous reaction such

as the above reaction.

Near 400°C, the first biotite appears in Al-poor metapelites. Biotite forms at the

expense of Kfs and Chl. The reaction has equilibrium conditions of 420°C at about 0.35 GPa

in pure KFASH system. The equilibrium conditions of this reaction in the pure KFMASH

system are shown in (Fig.6) (Bucher and Grapes, 2011).

Figure (5). AKF diagrams illustrating the mineral assemblages developed in biotite zone

(source: Winter, 2010)



Figure (6). P-T-X diagram representing the Kfs-Ms-Bt-Chl assemblage (Source: Bucher and

Grapes, 2011)

Figure (7). Petrogenetic grids showing the location of selected reaction isograds appropriate

for the study area. (Source: Winter, 2010)

Garnet zone

Garnet may become stable in the Mg-free KFASH system due to any of several

reactions. Garnet-isograd reaction giving way to produce assemblage, if Fe-chlorite is less

aluminous it may break down to almadine plus a small amount of Fe-biotite;

3Chl + 1Ms + 3Qtz = 4Grt + 1Bt + 12H2O



This reaction has been suggested by Thompson and Norton (1968) and they described

this reaction is common in more typical pelites (in Winkler, 1979). This assemblage is

illustrated by means of AFM diagram as shown in (Fig.8).

Figure (8). AFM diagram showing the mineral assemblage occurred in garnet zone (Source:

Winter, 2010)

The first garnet appears in metapelites at temperature of around 450°C. This

temperature is in conflict with the formation provided by the pure FASH system. But, a

significant spessartine and grossular components in almadine garnet has the effect of

lowering temperature of first formation. Therefore, the Mn-Fe garnet appears at significantly

lower temperatures than pure almadine garnet. The porphyroblasts of almadine garnets do not

occur until the temperature of 460-500°C in typical pelites.

Fe-rich chlorite begins to be replaced by garnet + biotite between 500°C and 520°C.

The new assemblage Grt + Bt remains stable to very high grade and the P-T condition of this

garnet isograd reaction can be observed in (Fig.8). So, this reaction takes place at about

520°C and the metamorphic grade starts to enter the lower amphibolites facies.

Original Rock Sequence and Age

In general, various mineral assemblages, lithologic characters and some textural

features suggest that the metamorphic rocks in the study area may probably be

metamorphosed from mixture of pelitic and psammitic rocks. Following points are taking

into account the above conclusion.

(1). Characteristic minerals of greenschist facies include the chlorite, muscovite, biotite,

garnet and quartz. Greenschist derived from pelites have much more quartz and white

muscovite, less chlorite.

(2). Garnet bearing quartzite derived from the quartzose sandstone or quartzite.

(3). Graphite schist may come from organic rich sediment. The presence of graphite is

generated during the metamorphism of black shale and marls.



(4). The abundant constituents of garnet in schists indicate rich in Fe and Mn component in

parent rock.

(5). Sequential interlayered nature of schist and quartzite indicates that the original rock

sequence may probably be alternative sequence of pelitic and quartzose sandstone.

(6). Continuous changing of mineral zoning in present area suggests that sediments are

homogeneous in composition and clay rich pelite.

These facts collectively suggest that the metamorphic rocks in study area may

probably be derived from pelite and psammite.

There are no radiometric ages available for any of the rocks described in present area,

so that original age of rock is not fixed. Form the various point of views, correlation with

other established area and similarity of metamorphic rock units exposed in the surrounding

area, the age of the metasediments in present area is equivalent to the Ngapyawdaw Chaung

Formation of Late Jurassic to Early Cretaceous.

Time of Metamorphism

There is not available precise time of metamorphism for the metamorphic rocks of

study area. Radiometric dating was carried out the metamorphic rocks exposed in some parts

of Katha and Kumon Range by GIAC project. Therefore, the time of metamorphism of the

present area can be ascertained to correlate with the neighboring area and some established

area concerning with this.

(1). The Jade Mine area, northwestern part of the study area, glaucophane bearing schist

associated with ultrabasic rocks is overlain by the Tertiary clastic sediments (Chhibber,

1934; Soe Win, 1960 in Aung Win, 2008).

(2). Mitchell (1998) established that the metamorphic rocks in Katha-Gangaw Range may be

Pre-Triassic rocks equivalent to the lower part of the Mergui Nappe or Chaungmagyi

Turbidities to the east.

(3). The metamorphosed rocks associated with ophiolite suite including radiolarian chert in

Tagaung- Myitkyina belt is derived from Ngapyawdaw Chaung Formation assigned the

age of Late Jurassic to Early Cretaceous from the analysis of radiolarian (Aung Kyaw

Thin, 2007) so that the age of the metamorphism of the area is later than assigned age.

(4). Radiometric dating were performed on metamorphic rocks, using Ar39

/Ar40

methods for

muscovite and biotite, in Katha and Kumon Ranges that indicate the time of

metamorphism took place in 37 to 32 Ma (G.I.A.C, 1999 in Aung Win, 2008).

(5). The earliest Alpine regional metamorphism in Himalaya Mountain chain is Late

Cretaceous in age (90-65 Ma). This event was responsible for the formation of eclogite

and blueschist in both continental and oceanic basement and Mesozoic sediments. The

peak of the Alpine metamorphism is usually interpreted as having ended in the early

Oligocene; younger, many Miocene ages have been obtained (Yardley, 1989 ).

Based on the above mentioned criteria, the time of metamorphism of the study area

could be assigned tentatively to Cretaceous to Early Eocene.



Table(3). Comparison of petrogenetic criteria and age of metamorphism of the rocks occurred

in the study area with those of other areas.

Previous Authors

Rock Type

(of which

geothermobarometric

calculation is

performed)

Peak

Metamorphic

Condition

Age of

Metamorphism

Aung Kyaw Thin

(2006)

Tagaung-Twinnge

Area

Basic Rock 1.1 GPa/ 650°C Late Cretaceous

Searl et al., (2007),

Mogok Metamorphic

Belt, Kyanigan and

Kyaukse Area

Gneisses 0.49 GPa/680°C

Late Jurassic-Early

Cretaceous/

Paleocene-Early

Eocene/

Late Eocene-Oligocene

Aung Win (2008)

Mogaung Area Basic Schist 2.3 GPa/493°C

Cretaceous-Early

Eocene

Nyan Win (2008)

Hopin-Mohnyin

Area

Pelitic Schist 1.9 GPa/750°C Late Eocene-Early

Oligocene

Chatterjee & Ghose

(2010)

Naga Hill

Basic Schist, Pelitic

Schist 2 GPa/610°C Eaerly Eocene

Thaire Phyu Win,

Indaw-Katha Area, Basic Schist 1.59GPa/583°C

Late Eocene-Early

Oligocene

Aung Khin Soe

(2018) KaKa-Naung

Pein-Man Hlwe area,

Katha Township

Pelitic Schist 0.35GPa/520°C Cretaceous to Early

Eocene

Conclusion

The occurrence of Chl-Ms-Qtz mineral assemblage in chlorite schist clearly indicates

that the rock develops in low-grade metamorphism of lower greenschist facies condition.

From biotite schist, through muscovite schist, garnet biotite schist, garnet muscovite schist

and garnet quartzite, the metamorphic grade gradually increased through lower greenschist

facies to lower amphibolites facies conditions. Although equilibrium is difficult to attain and

P-T conditions are not certain, the chlorite zone is to be in the 350 to 450°C range. The

equilibrium conditions of biotite zone are 420°C at about 0.35 GPa. The porphyroblasts of

almadine garnets do not occur until the temperature of 460-500°C in typical pelites and the

metamorphic grade starts to enter the lower amphibolites facies. The type of metamorphism

of study area is regional metamorphism and locally dynamic metamorphism according to the

mineralogical and textural criteria. The metamorphic rocks of the study area may probably be

metamorphosed from mixture of pelitic and psammitic rocks of the Ngapyawdaw Chaung

Formation of Late Jurassic to Early Cretaceous and the time of metamorphism could be

assigned tentatively to Cretaceous to Early Eocene. According to comparison of petrogenetic

criteria, the metamorphic grade of the Katha-Gangaw Range decreases toward the east.



Acknowledgements

I would like to express my thanks to Dr Thura Oo, Rector of Monywa University, Dr Sein Sein Aung

and Dr Thet Naing Oo, Pro-rectors of Monywa University and Dr Zaw Myint Ni, Professor and Head of

Geology Department, Monywa University for their encouragement. Thanks are also due to all local people of

the Ka Ka, Naung Pein and Manhlwe villages for their valuable helps through the field trip. Finally, all teaching

staff members from Geology Department, Monywa University are highly thanked for their cooperation.

References

Aung Kyaw Thin, (2006). Petrogenetic study on igneous and metamorphic rocks of the Tagaung-Twinnge area,

Thabeikyin Township. PhD, (Dissertation), Geology Department, Mandalay University,

Unpublished Paper, 123 p.

Aung Win, (2008). Petrogenetic studies of metamorphic rocks in Mogaung area, Mogaung and Phakant

Township, Myitkyina District, Kachin State. PhD, (Dissertation), Geology Department,

Mandalay University, Unpublished Paper. 183p.

Barker, A.J., (1998). Introduction to Metamorphic Textures and Microstructures.2nd ed. Staley Thorners

(Publishers) Ltd. UK.

Best, M.G., (2003). Igneous and Metamorphic Petrology. CBS publisher and Distributors, New Delhi, India.

Bucher, K. and Frey, M., (1994). Petrogenesis of Metamorphic rocks. 6thed, Springer-Verlag Berlin Heidelberg, printed in Germany.

Bucher, K. and Grapes, R., (2011). Petrogenesisof Metamorphic rocks.8thed, Springer-Verlag Berlin Heidelberg,

printed in Germany.

Hyndman, D.W., (1985). Petrology of Igneous and Metamorphic rocks.2nded. Mc.Graw Hill, Inc, New York.

Kerr, R.E., (1959). Optical Mineralogy. Mc. Graw Hill, Inc, New York.

Philpotts, A.R., (2003). Petrography of Igneous and Metamorphic Rocks. Waveland Press, Inc, UAS.

Turner, F.J., (1968). Metamorphic Petrology (Field and Mineralogical Aspects). Mc. Graw Hill, Inc, New York.

William, H., Turner, F.J., and Gilbert, C., (1953). Petrography. Freeman and Co., Sanfransisco.

Winter, J.D., (2010). An Introduction to Igneous and Metamorphic Petrology.2nd ed. Prentice Hall, New Jersey.

Yardley, B.W. D., (1989). An Introduction to Metamorphic Petrology. Longman Group Ltd.

Yardley, B. W. D., McKenzie, W. S., and Guilford, C., (1990). Atlas of Metamorphic Rocks and their Textures.Longman Scientific and Technical, John Wiley and Sons, Inc. New York.

petrogenesis of metapelitic rocks exposed in ka ka-naung pein-...

Documents