Title Stratigraphy and Petrographic Investigation of the Rock Units

Home , Shwegu, Shwegu Township

Stratigraphy and petrographic investigation of the rock units exposed along Title Banmaw-Shwegu car road (Zinbon Range), Shwegu Township, Kachin State

KhinKhin Lin, Myo Min, and Win Khant All Authors

Local Publication Publication Type

Publisher Universities Research Journal, Vol.7, No.4 (Journal name, issue no., page no etc.) This area is located around ZinbonTaung between Shwegu and Banmaw in the southern Kachin state. Regionally, this area is mainly composed of Quaternary sediments, Irrawaddy Formation and equivalents, flysch-types sediments and limestones, ultrabasic rocks (peridotite and sepertinite). Stratigraphically, four main rocks units were occurred in this research area. These units are; ultramafic and associated rocks, Cretaceous rocks, Tertiary sediments, and Quaternary sediments. Samples are collected from conglomerate rocks (Irrawaddy Formation) on road side at ZinbonTaung located between Shwegu and Banmaw motor road. Abstract Selected samples are analyzed to know their mineral composition and to identify their ages from crystallization processes of apatite and zircon minerals. Selected samples are analyzed to identify their ages using zircon and apatite minerals via apatite fission-track (AFT) analysis, (U-Th/He) (AHe and ZHe). Based on the dating processes from apatite and zircon minerals, most of samples are between 7 Ma and 16 Ma in ages. Pebbles of the Irrawaddy Formation of NE-Myanmar, likely Late Miocene-Pliocene coarse fluvial deposits of the Paleo-Irrawaddy, cooled 5-10 Ma later through 60-100°C than the adjacent Mogok belt rocks. fission-track, Tertiary, stratigraphy, petrography Keywords

Citation

2014 Issue Date

151 Universities Research journal 2014, Vol.7, No. 4

Stratigraphy and petrographic investigation of the rock units exposed along Banmaw-Shwegu car road (Zinbon Range), Shwegu Township, Kachin State Khin Khin Lin1, Myo Min2, Win Khant3

Abstract This area is located around Zinbon Taung between Shwegu and Banmaw in the southern Kachin state. Regionally, this area is mainly composed of Quaternary sediments, Irrawaddy Formation and equivalents, flysch- types sediments and limestones, ultrabasic rocks (peridotite and sepertinite). Stratigraphically, four main rocks units were occurred in this research area. These units are; ultramafic and associated rocks, Cretaceous rocks, Tertiary sediments, and Quaternary sediments. Samples are collected from conglomerate rocks (Irrawaddy Formation) on road side at Zinbon Taung located between Shwegu and Banmaw motor road. Selected samples are analyzed to know their mineral composition and to identify their ages from crystallization processes of apatite and zircon minerals. Selected samples are analyzed to identify their ages using zircon and apatite minerals via apatite fission-track (AFT) analysis, (U-Th/He) (AHe and ZHe). Based on the dating processes from apatite and zircon minerals, most of samples are between 7 Ma and 16 Ma in ages. Pebbles of the Irrawaddy Formation of NE- Myanmar, likely Late Miocene-Pliocene coarse fluvial deposits of the Paleo-Irrawaddy, cooled 5-10 Ma later through 60-100°C than the adjacent Mogok belt rocks

Introduction This area is located around Zinbon Taung between Shwegu and Banmaw in the southern Kachin state and is covered by the map sheet 92- D/15 of the one inch to one mile topographic map. This area is highly mountainous area between Shwegu plain and Banmaw plain (Fig. 1). Regionally, this area is mainly composed of ultramafic and their equivalents, Irrawaddy group and equivalents, flysch-type sediments and limestones, peridotite and sepertinite rocks.

1 Lecturer, Geology Department, Shwebo University 2 Lecturer and Head, Geology Department, Shwebo University 3 Assistant Lecturer, Geology Department, Shwebo University Universities Research journal 2014, Vol.7, No. 1 152

Generally, the ages of rock units are ordered from younger to older as Quaternary sediments, Tertiary sediments, Cretaceous rocks, and older ultramafic and related rocks. The purpose of this paper is to investigate the stratigraphy, petrographic condition and age of the sedimentary rocks exposed at Zinbon Taung along Shwegu-Banmaw car road.

97° 00'

Banmaw

Shwegu Ayeyarwaddy River

Naungmo

5' 5'

0 0 Zinbon 24° 24°

97° 00'

Banmaw

Shwegu Ayeyarwaddy River

Zinbon Taung

Figure 1. Landsat image and topographic image map of around Zinbon Taung area, Shwegu Township.

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Regional Geology This area is a part of the easternmost ophioite belt in Burma and is dominated by strongly serpentinized to ultramafic rocks belonging to the mantle tectonite, with rare occurrences of dunite. The rocks at the first and second Defiles of the Ayeyarwady River are composed of the Cretaceous limestones, arenaceous sediments and extrusives (Myint Myint Yee, 2011). Associated volcanites range from olivine tholeiite to dacitic and quartz porphyritic rocks. Emplacement of the ultramafic rocks in a marine basin was followed by local deposition of sandstone, composed of ultramafic gabbroic, and volcanic clasts in a calerous matrix, red and green radiolarian cherts and a thick sequence of clastic sediments and fossiliferous carbonates, for which a Cretaceous age has been established (Einfalt et.al, 1989). After folding and partial erosion of this sequence, fluviatile late Tertiary Irrawaddy Group sediments of silty to conglomeratic composition covered this area at least up to an elevation of 330 m. Stratigraphy and petrography of Irrawaddy Group sediments of conglomeratic will be mainly focused and investigated in this research. Regional geological map of the study area is shown in figure (2). Stratigraphically, four main rocks units were occurred in this research area. These units are; ultramafic and associated rocks, Cretaceous rocks, Tertiary sediments, and Quaternary sediments. These rock units are briefly described as follows; Ultramafic and associated rocks Ultramafic and associated rocks of ophiolitic origin cover about 40% of the area. They form an incomplete opiolite sequence or suite. Sediments (red and green radiolarian cherts), volcanites (olivine tholeites to andesites), plagiogranites, gabbroic dykes, and ultramafic rocks (serpentinites and dunites) are regarded as belonging to the ophiolite suite. These rocks are mainly occurred in the area of Naungmo (Taung Nyo and Lamwa Taung), Taung Kadon, Minye Taung, and Shwe Taung. Cretaceous rocks Cretaceous rocks consist of a thick, folded sequence of clastic and biogenic sediments with a predominant strike to the ENE. Massive, gray, fine-grained limestone with abundant mollusk shells forms the more prominent outcrops and high cliffs along the Irrawaddy River. The whole sequence is indurated, the micritic limestone shows moderate Universities Research journal 2014, Vol.7, No. 1 154 recrystallization. These sediments are unconformably overlain by clastic Tertiary sediments.

Q1 Q1 Q2 MositChaung Q2 Shwegu

Ub Q1 Ayeyarwaddy River Naungmo Loc.2 Ir Ub Zinbon Ub Loc.1 Loc.3 Nampa Chaung Q1 b Ir Ir Ub b

Explanation

Q2 Younger Alluvium

Q1 Older Alluvium and Gravels

Ir Irrawaddy Formation and its equivalents b Gabbro and related rocks Ophiolite Assemblages (serpentinite, peridotite, pyroxenite, gabbro and Ub pillow lavas)

River and stream (Chaung) Motor-road Town and village Sample locations Figure 2. Regional geological map of the study area (Myanmar Geosciences Society, 2014). 155 Universities Research journal 2014, Vol.7, No. 4

Tertiary sediments This rock unit is mainly composed of a sequence of sandstones, siltstones, shales, and interbedded conglomerates (Fig. 3). They were found up to an elevation of 290 m along the western slopes and the streams of Taung Kadon and up to 330 m on the southern slope of Taung Nyo. Sandstone is the predominant sediment in this sequence; siltstones and shales are also present. Sandstone is usually grayish brown, rarely yellowish brown, the grain size varies from fine- to coarse-grained with abundant pebbly layers a few m in thickness. Sandstone is mostly massive. Well- bedded sandstone was observed opposite of Zinbon village.

(a) (b)

Figure 3. Outcrop views of sandstone and conglomerate layers from Irrawaddy Formation and equivalents at Zinbon Taung.

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A finely laminated variety occurs along the Thabeik Chaung. Conglomeratic layers up to 2 m thick were observed in the Naungmo area and on the western slope of Taung Kadon. They consisted of pebbles up to 20 cm in diameter. Clegg (1937) mentioned some folding of the Tertiary strata, e.g. between Zinbon and Naungmo. He also mentioned another occurrence of lignite in late Tertiary sandstones about 4 miles south of Zinbon near the village of Lagatyan. The whole sequence is regarded as fluviatile sediment and an equivalent of the late Tertiary Irrawaddy Group. Quaternary rocks Quaternary sediments occur mainly in the Shwegu and the Banmaw plains, low-level alluvial plains (probably a Holocene terrace). Terrace remnants are also present in some places along the present course of Irrawaddy River in the area around the Naungmo and Zinbon. They are also expected to veil Tertiary rocks in the hilly foreland of Minye Taung and Shwe Taung. Remnants of gravel beds were encountered at an elevation of about 340 m on top of Taung Kadon. Genetically, most of the sedimentary pebbles and boulders, as well as the ultramafic rocks and some of the volcanites, are derived from lithological units in the surround area. High-grade metamorphic rocks (schists and gneisses) and granites north of Banmaw and Precambrian belt of metamorphic rocks were assumed the origin of these sediments.

Sampling and Analytical Methods Samples are collected from conglomerate rocks of Irrawaddy Formation at Zinbon Taung. 23 samples are collected from three locations. List of collected samples are shown in table (1). 14 samples are collected from loc.1 (N 24.09225° and E 96.86852°) and among them, 9 samples are granite pebbles. 4 samples are from loc.2 (N 24.13380° and E 96.86075°) and 5 samples from loc.3 (N 24.08425° and E 96.88897°). Sandstones from Irrawaddy Formation are loosely cemented and friable. We cannot date directly from these rocks. So, we collected the conglomerates and dated. Firstly, samples are cut and polished to make thin-sections. Thin-sections are investigated under polarized microscope to know the detailed mineral compositions and their descriptions. Selected samples are also analyzed to identify their ages from crystallization processes of zircon and apatite 157 Universities Research journal 2014, Vol.7, No. 4 minerals via apatite fission-track (AFT) analysis, (U-Th/He) (AHe and ZHe). Table 1. Collected pebble samples from conglomerate of Irrawaddy Formation.

Sample No. Location Latitude (N) Longitude (E) Sample descriptions 1 5377A 24.09225 96.86852 granite 2 5377B 24.09225 96.86852 mylonite granite 3 5377C 24.09225 96.86852 biotite gneiss 4 5377D 24.09225 96.86852 rhyolite 5 5377E 24.09225 96.86852 aplite gneiss intermediate volcanic 6 5377F 24.09225 96.86852 rock

7 5377G 24.09225 96.86852 subvolcanic rock

8 5377H Loc.1 24.09225 96.86852 epidote granite 9 5377I 24.09225 96.86852 biotite granite 10 5377J 24.09225 96.86852 hb mega fsp granite 11 5377K 24.09225 96.86852 foliated granite 12 5377L 24.09225 96.86852 biotite granite 13 5377M 24.09225 96.86852 rhyolite 14 5377N 24.09225 96.86852 Kfsp biotite granite 15 5378A 24.13380 96.86075 dolerite

16 5378B 24.13380 96.86075 mylonitic qtz-fsp- augengneiss 17 5378C 24.13380 96.86075 mylonitic qtz-gneiss

Loc.2 fsp rich foliated 18 5378D 24.13380 96.86075 granitoid 19 5385A 24.08425 96.88897 biotite granite 20 5385B 24.08425 96.88897 rhyolite

21 5385C 24.08425 96.88897 granite gneiss

22 5385D Loc.3 24.08425 96.88897 aplite granite sanidine-bearing 23 5385E 24.08425 96.88897 subvolcanic rock Universities Research journal 2014, Vol.7, No. 1 158

Results and discussion Above twenty three samples from the area were selected for apatite fission-track (AFT) analysis. We calculated the fission-track ages with the stand based Z, ζ, and ζ0 methods and the independent (absolute)  method (Jonckheere, 2003); the ages with 1σ errors are summarized in Table (2), which also specify sample location and lithology. The ages obtained from the four different methods agree. In the following, we use  ages. Eva Enkelmann analyzed the apatite samples for apatite and zircon ages (U- Th/He) (AHe and ZHe). Some selected samples are discussed detail in below.

No.1-5377A: Granite Petrology: Biotite granite showing tectonic overprint, which resulted in dynamic recrystallisation of quartz. The retrograde overprint coupled with this deformation led to a chloritisation of biotite, mobilisation of carbonate and sericitisation of feldspar. Age: AFT 11.5  0.7 Ma

Figure 4. Photomicrographs of sample 5377A and 5377B (Under XN)

No.2-5377B: Mylonitic granite Petrology: Granite mylonite showing penetrative mylonitic foliation with growth of white mica and small new biotite flakes (later chloritized). Prismatic green tourmaline crystals are observed and large orthoclase clasts with inclusions of plagioclase and 159 Universities Research journal 2014, Vol.7, No. 4

brown biotite represent part of the protolithic mineral assemblage. Age: ZHe: 13.51 ± 2.01 Ma; AFT 14.1  0.6 Ma

No.3-5377C: Biotite gneiss Petrology: Biotite orthogneiss showing a foliated texture with thorough dynamic recrystallization of quartz. Large clasts of quartz and orthoclase including euhedral plagioclase crystals are present. Biotite shows alignment into the foliation and in part late chloritisation. Carbonate appears on joints. Age: AFT 9.4  0.4 Ma; AHe: 12.1 ± 2.4 Ma No.4-5377D: Undeformed subvolcanic rhyolite Petrology: Subvolcanic, pristine rhyolite with sanidine and pseudomorphs of quartz.

Figure 5. Photomicrographs of sample 5377C and 5377D (Under XN)

No.5-5377E: Undeformed aplite gneiss Age: ZHe 21.3 ± 2.4 Ma; AFT 20.9 ± 1.6 Ma No.7-5377G: Weakly foliated subvolcanic rock Age: AFT 11.7 ± 0.6 Ma No.9-5377I: Foliated biotite gneiss Universities Research journal 2014, Vol.7, No. 1 160

Age: AFT 12.6 ± 0.6 Ma No.10-5377J: Hornblende-bearing mega-feldspar granite Age: AFT 26.1 ± 1.9 Ma

Figure 6. Photomicrographs of sample 5377E and 5377G (Under XN) No.11-5377K: Foliated granite Age: AFT 23.1 ± 1.7 Ma No.12-5377L: Coarse biotite granite Petrology: Biotite granite with coarse grained, subhedral texture and porphyric euhedral orthoclase crystals. Minerals are quartz, plagioclase, orthoclase, biotite and alkali-amphibole (small green crystals, resemble chlorite). Age: ZHe: 34.51 ± 5.75 Ma; AFT, 16.5  0.7 Ma, AHe: 21.8  2.8 Ma No.13-5377M: Rhyolite No.14-5377N: Kfeldspar-biotite-gneiss Age: AFT 14.1 ± 0.7 Ma No.15-5378A: Dolerite No.16-5378B: Mylonitic quartz-feldspar-augengneiss Petrology: Garnet-biotite gneiss, fine-grained, distinctly foliated, well equilibrated mineral assemblage of garnet, biotite, muscovite, plagioclase (oligoclase), cordierite, and quartz. Accessories are opaques, zircon and apatite. Age: AFT 7.8  0.3 Ma 161 Universities Research journal 2014, Vol.7, No. 4

Figure 7. Photomicrographs of sample 5378B (Under XN)

No.17-5378C: Deformed mylonitic quartz-gneiss Petrology: Ortho-mylonite with fine grained to dense, mylonitic layers and penetrative foliation. Mylonitization took probably place under greenschist facies conditions (biotite zone) and was later retrogressed. Age: AFT 7.6  0.7 Ma No.18-5378D: Feldspar rich foliated granatoid No.19-5385A: Biotite granite No.20-5385B: Dark crystal bearing rhyolite

Figure 8. Photomicrographs of sample 5385B (Under XN)

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Petrology: Rhyolite with magmatic flow texture bears b-quartz pseudomorphs, sanidine and small alkali-amphiboles (probably richterite with green color, resembles chlorite); further minerals are saussuritized plagioclase (epidote-filled) and epidote aggregates on joints as well as chloritized biotite. Accessories are zircon, apatite and opaques. No.21-5385C: Granite gneiss No.22-5385D: Apalite granite No.23-5385E: Sanidine-bearing subvolcanic rock

Figure 9. Comparison of AFT and AHe ages between pebbles from Irrawaddy Formation of study area and Mogok Belt.

Deformation The Irrawaddy Formation exhibits NNW-SEE extension by faulting and pebble fracturing; the Pliocene deformation (post dating cooling as recorded in the pebbles) is related to the stress field of the Sagaing fault zone. NW-SE extension (not long after deposition) by faulting and fracturing of pebbles.

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Figure 10. Structural data from Irrawaddy Formation.

Depositional Environment They are deposited in proximal fluviatile, channels and levees, examples of syn-sedimentary extension. Pebbles of the Irrawaddy formation of NE-Myanmar, likely late Miocene-Pliocene coarse fluvial deposits of the Paleo-Irawaddy, cooled 5-10 Ma later through 60-100°C than the adjacent Mogok belt rocks. This suggests derivation of these conglomerates from the E-syntaxis region, supporting speculations of a paleodrainage link with the Yarlung Tsangpo drainage of Tibet (Clark et al., 2004).

Universities Research journal 2014, Vol.7, No. 1 2014,Vol.7, Universities No. journal Research Table (2) Apatite fission-track data, rock description and sample locations ρD ϕ(10* Z z Latitude Longitude Elv. Gr P ϕ-age Z-age z-age z0-age Sample Lithology Ns i (10*6 15 (10*6 (year N E [m] . (x*2) (Ma) (Ma) (Ma) (Ma) cm-2) cm-2) year) cm*2) 11.7± 12.9±0. 12.7± 5377A granite 24° 05.535' 96° 52.111' 267 64 380 2472 0.473 2.500 167.43 350.3 0.000 11.5±0.7 0.6 8 0.8 mylonitic 14.4± 15.9±0. 15.6± 5377B 24° 05.535' 96° 52.111' 267 32 1022 5455 0.477 2.527 169.80 350.3 0.057 14.1±0.6 granite 0.5 8 0.7 biotite 9.5± 10.6±0. 10.3± 5377C 24° 05.535' 96° 52.111' 267 44 1006 8182 0.480 2.554 172.17 350.3 0.000 9.4±0.4 gneiss 0.3 5 0.4 aplite 0.303 ± 241.4 20.9 5377E 24° 05.535' 96° 52.111' 267 20 390 680 13.30 gneiss 0.009 ± 8.4 ± 1.6 Kfsp 0.311 ± 241.4 11.7 5377G biotite 24° 05.535' 96° 52.111' 267 60 2595 8335 0.00 0.009 ± 8.4 ± 0.6 granite biotite 0.310 ± 241.4 12.6 5377I 24° 05.535' 96° 52.111' 267 64 2069 6144 0.00 granite 0.009 ± 8.4 ± 0.6 hb mega 0.307 ± 241.4 26.1 5377J 24° 05.535' 96° 52.111' 267 22 478 677 0.00 fsp granite 0.009 ± 8.4 ± 1.9 foliated 0.309 ± 241.4 23.1 5377K 24° 05.535' 96° 52.111' 267 14 441 711 1.20 granite 0.009 ± 8.4 ± 1.7 biotite 16.8± 18.7±0. 18.0± 5377L 24° 05.535' 96° 52.111' 267 14 1009 4769 0.487 2.609 176.92 350.3 0.045 16.5±0.7 granite 0.6 9 0.8 Kfsp 0.304 ± 241.4 14.1 5377N biotite 24° 05.535' 96° 52.111' 267 56 2316 6007 0.00

0.009 ± 8.4 ± 0.7 granite 7.9± 8.5± 5378B mylonitic 24° 08.028' 96° 51.645' 277 22 1022 10310 0.490 2.636 179.29 350.3 0.002 8.9±0.4 7.8±0.3 augengneiss 0.3 0.4 mylonitic 7.7± 8.2± 5378C 24° 08.028' 96° 51.645' 278 20 139 1460 0.494 2.663 181.67 350.3 1.000 8.6±0.8 7.6±0.7 gneiss 0.7 0.8 Note: Ns: number of spontaneous tracks; Ni: number of induced tracks; ρD: track density on dosimeter; f: neutron flux density; Z: Z-calibration factor; z: z- calibration factor; P(x)*2 is the probability of obtaining X*2 value for v degrees of freedom (where v = number of grains - 1).

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Conclusion Stratigraphically, four main rocks units were occurred in this research area; namely, ultramafic and associated rocks, Cretaceous rocks, Tertiary sediments, and Quaternary sediments. Samples are collected from Tertiary sediments (Irrawaddy Formation and its equivalents) of pebbles. Samples are analyzed to identify their ages from crystallization processes of zircon and apatite minerals via apatite fission-track (AFT) analysis, (U- Th/He) (AHe and ZHe). Based on the dating processes from apatite and zircon minerals, most of samples are between 7 Ma and 16 Ma in ages. Pebbles of the Irrawaddy Formation of NE-Myanmar, likely Late Miocene-Pliocene coarse fluvial deposits of the Paleo-Irrawaddy, cooled 5-10 Ma later through 60-100°C than the adjacent Mogok belt rocks. This suggests derivation of these conglomerates from the E-syntaxis region, supporting speculations of a paleo drainage link with the Yarlung Tsangpo drainage of Tibet. Acknowledgements We would like to thank to Rectors Profs. Dr. Sein Htun and Dr. Tin Tun Myint, Banmaw University and Shwebo University, for their kind permission to submit this research paper. We thank Eva Enkelmann, University of Cincinnati, USA, for determining apatite and zircon (U-Th/He) ages of numerous samples. This research has been supported by Department of Higher Education (Upper Myanmar), Ministry of Education.

References Clark, M.K., L.M. Schoenbohm, L.H. Royden, K.X. Whipple, B.C. Burchfiel, X. Zhang, W.Tang, E.Wang, and L. Chen (2004), Surface uplift, tectonics, and erosion of eastern Tibet from large scale drainage patterns, Tectonics, 23, TC1006, doi:10.1029/2002TC001402. Clegg, E.L.G. (1937), Notes on geology of the second defile of the Irrawaddy River. Reg.Geol.Surv. India, vol.71, 350-358 p. Einfalt, H.D., T. Htay, M. Htut, T. Lwin, Z.W. Nyunt, N. Sein (1989), Mineral Prospecting in the Bhamo-Shwegu Area, ECAMS Final report, vol.4. pp.1-64.

Jonckheere, (2003), Myint Myint Yee (2011), Stratigraphy and sedimentary facies of the Mesozoic and Tertiary units in the Nga-O area, Mabein Township, Northern Shan State. Ph.D. (Thesis), University of Mandalay, p.123.