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Highland-Vijayan complex boundary.Final

Boundry related to publications and researched based on mineral deposits and thermal springs

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Highland-Vijayan complex boundary.Final

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  1. Highland-Vijayan Complex Boundary ESM 32211 Geology of Sri Lanka

  2. Group Members S.M.K. Wijesinghe P.H.M.S.R. Pahathkumbura-SEU/IS/18/BS/017 K.L.A.A.R.Liyanage K.S. Wetthasinghe -SEU/IS/18/BS/053 -SEU/IS/18/BS/092 -SEU/IS/18/BS/098 02

  3. Content 1) Introduction 2) Structural features 3) Mineralogy & Lithology 4) History of Origin 5) Specific Features 6) Conclusion 7) References 03

  4. 1.Introduction • The Highland Complex- Vijayan complex thrust boundary is the major lithotectonic boundary which represents the Gondwana suture in Sri Lanka. • The boundary separates granulite grade HC rocks from the amphibolite grade VC rocks. 4

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  6. 2.Structural settings • There is no clear structural boundary between HC and WC, • The thrust boundary between HC and VC is a tectonic contact with strong shearing and high strain (micro continents) . • Tectonic inliers of Highland Complex rocks are infolded inside the Vijayan Complex in the southernmost region of Sri Lanka. 6

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  8. 1. 2. 3. 4. 5. Small rootless folds (F1) Isoclinal folds (F2) lineation L2 flattening foliation (S2) partial melting and migmatization 8

  9. 3. Mineralogy & Lithology Cpx - Opx - Grt - Pl - Qtz ± Kfs Hbl – Bt – Pl – Qtz – Kfs ±Grt Dominat - Charnockitic gneiss Dominat-Hornblende biotite gneiss Minor - Garnet biotite gneiss Minor-Granitic gneiss 9

  10. • The mineral assemblage Cpx - Opx - Grt - Pl - Qtz ± Kfs present in almost all the charnockitic gneisses in the area is consistent with metamorphism under granulite-facies conditions of ~850-900֯ C and ~8-10 kbar. • The assemblage Hbl – Bt – Pl – Qtz – Kfs ±Grt in the Vijayan area is consistent with metamorphism under amphibolite-facies conditions. • The boundary separates granulite grade HC rocks from the amphibolite grade VC rocks. • Field observations suggest that rocks between HC and VC have undergone intense deformation, migmatization under the granulite facies conditions caused for mineralization of rocks along the boundary. partial melting and 10

  11. Boundary Zone Rocks Table 01: Observation summary of field samples 11

  12. Boundary Zone Rocks • Pegmatites and migmatites are common intrusions close to the boundary. • Pegmatites have very coarse grains of hornblende, quartz, and biotite. • Migmatites enriched in biotite, quartz, feldspar are abundant and generally mapped as ‘Augen gneiss’. • Abundant of silica-poor, pegmatitic syenites with hornblende in a broad zone between the HV-VC thrust boundary. both biotite and Figure: Augen Gneiss 12

  13. Minerals • Biotite and garnet are the most common minerals and a well developed fabric is typical. • Quartz shows a strong stretching lineation giving a very high length to width ratio. Grain size varies from fine to coarse. Figure A,B,C: Gt- bt-qtz-flds gneiss 13

  14. Major mineralization along the HC-VC thrust boundary • serpentinite bodies near the southeastern part of the country • Gold mineralization • magnetite deposits • corundum deposits • calcite deposits • Vein quartz • Feldspar • magnesite 14

  15. Garnets • The garnet formation reactions were noted in this boundary rocks. • The charnockitic gneisses show the reaction, Hyp + Pl = Grt + Qtz • Retrogression under amphibolite grade during thrusting is supported by hornblende and biotite replacement of syn- kinematic garnets. 15

  16. 04 04. History of Origin . History of Origin • Sri Lankan Gondwana fragment was consisting at least three crustal units (micro continents), namely Wanni Complex, Highland Complex and Vijayan Complex. • During the latter part of Proterozoic eon, these crustal units were brought into contact by tectonism at two distinct stages, and juxtaposed during Pan African Collisions. • The nature and the mechanism of the amalgamation of these litho- tectonic units are yet to be understood. 16

  17. With the passage of time, this Highland-Wanni system was amalgamated The researches evident that this Vijayan is an igneous unit with less chemical variations. Rather, its origin has similarities to an island arc with oceanic sediments. According to Kehelpannala (1997),Wanni and Highland crustal units were first amalgamated with concurrent metamorphism in both complexes. with the Vijayan crustal unit, with a giant collision. With this collision, specific ductile deformations occurred in both units in addition to the metamorphism in Earth material. Dominantly associated with the boundary. 17

  18. ●The HC-VC boundary which denotes the contact between the two complexes, is reported to be a major low angle thrust zone. This contact has formed under regional upper Amphibolite facies conditions during 591-456 Ma. This is accompanied with a widespread migmatization in the thrust zone. During later event, the boundary has been folded in to some open, plunging upright folds, still under Amphibolite facies conditions. (Kleinschrodt,1994) 18

  19. 05. Specific Features 05. Specific Features • There are specific geological features evidencing the behavior of the boundary between Highland and Vijayan complex. 1) Paired metamorphic belts containing Granulitic facies and Amphibolite facies. 2) Basic and ultra basic rocks. 3) Copper, Magnetite, Apatite bodies and related rocks. 4) Thermal springs 19

  20. a) Paired metamorphic belts containing Granulite facies and Amphibolite facies. • • Highland complex rocks have mainly metamorphosed under Granulite facies. Vijayan complex rocks have metmorphosed under Amphibolite facies. • In comparison with the rocks of the Vijayan series, the rocks of Highland series are well bedded, banded and run continuously miles along the strike with little variation and hardly any dislocation. The Vijayan rocks are seldom uniform. 20

  21. b) Basic and ultra basic rocks. ● There are basic and ultra basic rocks located along the boundary of Highland and Vijayan complex Sri Lanka. ● few medium grained basic rocks are also observed at a number of places in Vijayan series. The basic rocks are fine grained quartz dolerites and albite dolerites. A very ● The basic rocks are of two diagnostic mineral assemblages. a) Apatite , Ilmenite± Olivine, Clinopyroxeneand Plagioclase b) IlmeniteClinopyroxene and Plagioclase (Dominant) ● These type of minerals assemblages are found in the greenstone belt in South West England. 21

  22. c) Copper, Magnetite, Apatite bodies and related rocks • The occurrence of Copper-Magnetite deposits at Seruwila lies in the Northern part of the HC-VC boundary, was discovered in 1971. 22

  23. • Basic and ultra basic rocks and anorthosite rocks are found to be erupted closer to the magnetite deposit. They represent a reworked material intruded along the faulted contact zone. • The carbonatite (apatite) complex at Eppawala falls within the Western Vijayan series. This may have resulted due to the subduction of Vijayan oceanic crust and partial melting of the crust at depth, which has later series.(Pathirana,1980) intruded in to the Highland • The Serpentinite body at Udawalawe surrounded by Migmatitic gneisses and crystalline limestone considered as the ultra mafic belt located in the South East Quadrant of Sri Lanka near the Highland Vijayan Boundary. • There are possible Gold occurrences in Seruwila Copper-Magnetite deposit, hosted in an ultramafic intrusion located in the HC-VC boundary. These non-ore grade Pyrite/chalcopyrite serve as targets of gold occurances, being a potential site of gold mineralization in the context of East Gondwana.(Samarakoon and Malviarachchi, 2021) veinlets of gold bearing 23

  24. d) Thermal springs • There are ten thermal springs with temperature between 40◦C and 61◦C along a narrow, approximately N-S running belt in Sri Lanka, near to the HC-VC boundary. 24

  25. • Deep through regional fractures, acquire heat from still hot dolerite bodies at depth and emerge at surface forming the majority of thermal springs of Sri Lanka. percolating ground water • Based on the findings of present study, it is proposed that thermal spring, is a result of deep percolation of ground water through a regional fault zone, heated up by Hot Dry Rock beneath the Dimbulagala mountain and then returning to the surface along a NE-SW trending regional vertical fault plane in the area.(Kumara and Dharmagunawardhane,2014) Ex:- the Nelumwewa 25

  26. 06. Conclusion ● Sri Lanka's Highland-Vijayan Complex Boundary is a crucial lithotectonic feature indicating the Gondwana suture.It Separates granulite-grade rocks (Highland Complex - HC) from amphibolite-grade rocks (Vijayan Complex - VC). ● Tectonic contact with strong shearing and high strain,small folds (F1), isoclinal folds (F2), lineation (L2),flattening foliation (S2) and evidence of partial melting and migmatization are some characteristics of this boundary. ● Mineralogical differences of this boundary are; ➢ Charnockitic gneisses dominate HC. ➢ Hornblende biotite gneisses prevalent in VC. ➢ Presence of garnet, biotite, and pegmatites/migmatites near the boundary. 26

  27. ● This boundary originate from amalgamation of Highland and Wanni units and later collision with Vijayan unit, causing ductile deformations along the boundary. ● It has low-angle thrust zone with a westward dip and it spans Sri Lanka from NE to SW. ● Paired metamorphic belts,basic and ultrabasic rocks,occurrences of copper, magnetite, apatite deposits and thermal springs are some specific features of this boundary. ● Mineralization in this boundary includes serpentinite, gold, magnetite, corundum, calcite, vein quartz. ● It is a complex geological zone providing insights into tectonic evolution and geological history. 27

  28. 07. References ● Adams,F.D. (1929). The Geology of Sri Ceylon,Canad. J. Research, vol1:pp.411-525 ● Coates, J.S., (1935). The Geology of Ceylon. Spolia Ceylanica. 19 (2): pp101-187. ● Cooray, P.G., (1963). The Erunwala Gravel and the probable significance of its ferricrete ● cap. The Ceylon Geographer, 17: pp39-48. ● Cooray, P.G., (1967). An Introduction to the Geology of Sri Lanka. Ceylon National ● Museum Publication, Colombo, pp 184-176. ● Cooray, P.G., (1968). A note in the occurrence of beachrock along the west coast of ● Ceylon. Jour. of Sedimentary Petrology, 38: pp650- 654. 28

  29. ● Cooray, P.G., (1968): The geomorphology of the part of the northwestern coastal plain of ● Ceylon. Zeitschrift fur Geomorphologie, NF Supplement 7,pp95-113. ● Cooray P.G., 1984. An Introduction to the Geology of Sri Lanka. 2nd Revised Edition. ● Ceylon National Museum Publication, Colombo, pp 140- 142. ● Cooray, P.G. and Katupotha, J., 1991. Geological evolution of the coastal zone of Sri Lanka. ● Proc. Symposium on "Causes of Coastal Erosion in Sri Lanka", CCD/GT7., Colombo, Sri ● Lanka, 9-11, Feb. 1991 ● Cooray P.G., (1984).The geology of Sri Lanka,Natn.Museums.Sri Lanka, pp.340 29

  30. Thank you. 30

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