Complexity and Changing Pattern of Tectonics in Hydrocarbon Bearing Basin of South East Asia

Manu Rastogi

University of Petroleum and Energy Studies, India

manurastogi1991@gmail.com

E ast and South-east Asia is a giant ‘jigsaw puzzle’ of allochthonous continental lithospheric blocks and fragments (terranes) that are bounded by suture zones or by geological discontinuities such as major strike-slip faults. The complex assemblage of South-east Asian continental terranes, accretionary complexes, ophiolites, volcanic arcs, and marginal ocean basins occurs in the zone of convergence between the Eurasian, Indo-Australian, and Pacific plates. In this region, two important biogeographical boundaries are recognized, the extant Wallace’s Line and the Late Palaeozoic Gondwana–Cathaysia Divide. Both of these biogeographical boundaries are the result of convergent plate-tectonic processes bringing together allochthonous continental lithospheric terranes on which had developed contrasting faunas and floras owing to their prior geographical separation, different palaeoclimates, and biogeographical isolation. Multidisciplinary data shows that in the Early Palaeozoic all of the principal East and South-east Asian continental terranes were located on the margin of eastern Gondwana, where they formed an Indo-Australian ‘Greater’ Gondwana. The regional geology of South-east Asia is thus characterized by Gondwana dispersion and Asian accretion of terranes and the subsequent collisions of India and Australia with these terranes following the breakup of Gondwana and their northwards drift. A variety of multidisciplinary data is used to constrain the origins of the terranes, their times of rifting and separation from the parent cratons, the timing, directions, and amount of drift, and the timing of suturing (collision and welding) of the terranes to each other. Significant oil and gas accumulations occur widely in East and South-east Asia, generally in Cenozoic. Sedimentary basins and these have contributed markedly to the economies of South-east Asian countries. The oil and gas accumulations are commonly associated with rocks of Middle and Upper Miocene age, with locally significant Oligocene and Pliocene occurrences. This paper focuses mainly on the complexity and changing pattern of Gondwanaland of south-east Asian continent and the hydrocarbon bearing basins of the region.

References:

1. Fraser AJ, Matthews SJ, and Murphy RW (eds.) (1997) Petroleum Geology of Southeast Asia. Special Publication 126. London: Geological Society.

2. Hall R and Blundell D (eds.) (1996) Tectonic Evolution of Southeast Asia. Special Publication 106. London: Geological Society.

3. Hall R and Holloway JD (eds.) (1998) Biogeography and Geological Evolution of South East Asia. Amsterdam: Backhuys Publishers.

Tectonic patterns of the Yenisey Ridge: a review and kinematic data from major faults

Matushkin N.Yu.

A.A. Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Russia,

Novosibirsk State University, Russia

MatushkinNY@ipgg.nsc.ru

The Yenisei Ridge is a fold-and-thrust belt in the western framing of the Siberian platform. It has been studied since the beginning of the XX century, and during the 60s–70s its main geological features were described more or less in detail (reviewed in [1]). This orogen was believed to be an ancient geosyncline separated by large faults from adjacent geological domains. The orogen’s structure was considered a combination of NNW trending synlinoria and anticlinoria dislocated by many long faults of the same NNW strike. It was estimated that this orogen evolved from the Archean to the Paleozoic.

Geologists were particularly interested in two major faults: Yenisei and Ishimba. They stretch for the entire length of the orogen and are marked by positive anomalies in the magnetic and gravitation fields, which are caused by multiple mafic intrusions. It was also observed that the Yenisei fault separates rock complexes of very different composition, level of deformation and metamorphism. Ishimba fault separates the main part of the Yenisei Ridge (containing many granitic intrusions) from the deformed sediments of the margin of the Siberian platform, which is totally devoid of igneous rocks. Later it was suspected that the large NNW trending faults of the Yenisei Ridge apparently control the arrangement and orientation of magmatic bodies. The major faults were mostly described as upthrows and thrusts.

During investigations in the 80s the orogen began to be viewed as a fold-and-thrust belt [2,3]. The study of the Yenisei Ridge on the basis of Plate Tectonics started only in the early 90s [4,5]. The major faults were considered as large thrusts separating continental, island arc and ophiolitic rock complexes. Later studies concentrated on petrological typification of granites and isotopic-geochronological (U-Pb, Ar-Ar, Rb-Sr, Sm-Nd) investigations. These studies culminated in the creation of a tectonic model for the formation of the Yenisei Ridge based on the concept of terrane analysis [6,7]. Thus the Yenisei Ridge is considered an accretionary-collisional belt and the major faults mentioned above are considered as tectonic sutures between terranes. In the model the Yenisei Ridge is divided into five terranes of various origins and age [6,7]: Angara-Kan and Predivinsk in the south and East Angara, Central Angara and Isakovka in the north. The Angara-Kan terrane is a Paleoproterozoic cratonic block, consisting of gneisses, granulites and granites. The East Angara terrane is a passive continental margin terrane, composed by Meso-Neoproterozoic terrigenous and carbonate sediments, which were thrust towards the Siberian platform. The Central Angara terrane is a composite block made of deformed Meso-Neoproterozoic passive continental margin sediments, accreted sheets of Mesoproterozoic ophiolites, and Neoproterozoic collisional granites and active continental margin igneous rocks. This terrane collided with Siberia 760–720 Ma, according to U-Pb dating of collisional granites, which led to the formation of the Tatarka-Ishimba suture zone. The Isakovka and Predivinsk terranes are fragments of a Middle-Late Neoproterozoic (700–630 Ma) island arc with ophiolite fragments that accreted to the Siberian margin 630–600 Ma via the Yenisei suture zone.

The organized structure of the Yenisei Ridge reveals its tectonic evolution. For example the Tatarka-Ishimba and Yenisei fault zones are not just marked by ophiolite fragments. Aside from the island arc terranes in the western part of the orogen they are the only structures with known Meso-Neoproterozoic tectonic sheets of mafic rocks, which confirm their role as sutures. The collisional granites that were emplaced during the “Central Angara terrane – Siberia” collision have been geochemically classified into syn-collisional (760–750 Ma) and post-collisional (750–720 Ma) [7]. Syn-collisional granites are located strictly within the Tatarka-Ishimba suture zone. Post-collisional plutons also intruded systematically: the earliest were emplaced in the north-west of the Central Angara terrane, while each following intrusion took place further to the south-east. The sequential intrusion and cooling (according to Ar-Ar dating) of post-collisional granites played an important role in creating a complex thermal situation in the Central Angara terrane, which impacted the following magmatic events [8]. The NNW elongation of post-collisional plutons and their association with co-directional faults clearly indicates their syn-tectonic emplacement. In contrast, earlier granites (880–860 Ma) of the Central Angara terrane, which are believed to have formed before its collision with Siberia [7], have no systematic orientation and were clearly deformed multiple times. Another consistent pattern can be found in the location and ages of gold deposits. In the Yenisei Ridge most of them are located within the Tatarka-Ishimba suture zone. An analysis of geochronological data from multiple methods for these deposits shows that they were probably formed during the first collisional event [9,10]. In general the age values for the gold deposits also form a NW-SE trend from earliest to latest.

Despite poor exposure in the northern (Transangarian) Yenisei Ridge the long NNW trending faults have always been regarded mostly as upthrows and thrusts. This has usually been confirmed by geophysical investigations for the last 40 years (reviewed in [1]). Most interpretations of the orogen’s deep morphology indicate an imbricate “mushroom”-type structure with thickened crust and fan-like orientation of NNW trending steep thrusts. Geological maps of the region show that long thrusts and upthrows in the western and eastern parts of the Central Angara terrane have an opposite dip direction. Detailed structural and microstructural studies in the middle and southern parts of the Ishimba suture zone showed overturned and recumbent folds associated with west, south-west dipping thrusts as well as ductile deformations observed in outcrops and thin sections. Investigations results confirm the vertical motions in the faults. However a lot of kinematic indicators indicate a sinistral strike-slip component. Thus the deformations in the Central Angara terrane are consistent with a palm-tree structure, which typically forms in transpressional tectonic settings. The structure of the East Angara terrane is characterized by asymmetrical degree of deformation. The northern half shows signs of significantly more intense lateral compression from the Central Angara terrane with linear folds of NNW strike associating with multiple faults. The southern half of the terrane is characterized by brachyaxial folds, which are much less disturbed by faults.

The NW-SE trend in the emplacement of post-collisional granites, in gold mineralization formation, the asymmetrical intensity of lateral compression, as well as the sinistral transpressional tectonic setting of the deformation could be an indication of oblique collision and clockwise rotation. Clockwise rotation of the Central Angara terrane during its collision with the Siberian craton has been confirmed by paleomagnetic data for the older “pre-collisional” granites (880–860 Ma) [11].

The terrane model for the Yenisei Ridge regards the Isakovka and Predivinsk terranes as fragments of the same paleo-island arc with the Isakovka terrane volcanic rocks being somewhat older (700 Ma) and the Predivinsk rocks – younger (637–628 Ma) [6,7]. The accretion/obduction time for both blocks also differs: 630–600 Ma for the Isakovka terrane and 600–564 Ma for the Predivinsk terrane. Most reported field observations of the contacts of the Isakovka and Central Angara terrane (reviewed in [1]) describe them as thrusts with up to 10 km of displacement amplitude. The contact between the Predivinsk and Angara-Kan terrane is a wide zone of brittle and ductile deformations indicating a sub-latitudinal lateral compression. Detailed structural studies in the Predivinsk terrane showed another palm-tree structure, which is visible in folds and faults orientation and a sinistral strike-slip component observed in outcrops and thin sections in all deformational structures [12,1]. Clockwise rotation of the Predivinsk island arc fragment during its accretion has been demonstrated by paleomagnetic investigations [13].

After their formation the major fault zones of the Yenisei Ridge became “permeable” areas for following events including: the formation of a late Neoproterozoic active continental margin igneous complex [14], Devonian tectonic-thermal and magmatic event and Triassic trap magmatism [15].

This work was supported by the RFBR (grants 10-05-00230, 10-05-00128) and the Earth Sciences Department of the RAS (project ОNZ-10.1).

References:

1. Matushkin N.Yu. (2010) Geology and kinematics of the Ishimba and Yenisei fault zones of the Yenisei ridge. Dissertation abstract. Novosibirsk: IPGG SB RAS, 16 p.

2. Постельников Е.С. Геосинклинальное развитие Енисейского кряжа в позднем кембрии // Тр. ГИН АН СССР, Вып. 341. М., 1980, 71 с.

3. Кузьмичев А.Б. Тектоника Исаковского синклинория Енисейского кряжа: Автореф. дис. ... канд. геол.-мин. наук. М., Ин-т литосферы окраинных морей РАН, 1987, 19 с.

4. Зоненшайн Л.П., Кузьмин М.И., Натапов Л.М. Тектоника литосферных плит территории СССР. Москва, Недра, 1990. т. 1, 326 c.; т. 2, 328 c.

5. Волобуев М.И. Рифейский офиолитовый комплекс Енисейского кряжа // Геотектоника, 1993, № 6, с. 82-87.

6. Vernikovsky V.A., Vernikovskaya A.E., Kotov A.B., Sal’nikova E.B., Kovach V.P. Neoproterozoic accretionary and collisional events on the western margin of the Siberian craton: new geological and geochronological evidence from the Yenisey Ridge // Tectonophysics, 2003, V. 375, P. 147-168.

7. Верниковский В.А., Верниковская А.Е. Тектоника и эволюция гранитоидного магматизма Енисейского кряжа // Геология и геофизика, 2006, т. 47, № 1, с. 35-52.

8. Vernikovskaya et al., 2011

9. Верниковский В.А., Верниковская А.Е., Метелкин Д.В., Матушкин Н.Ю. Формирование покровно-складчатых поясов в обрамлении Сибирского кратона: геодинамика, эволюция магматизма и рудообразования / Геологические процессы в обстановках субдукции, коллизии и скольжения литосферных плит: Материалы Всероссийской конференции с международным участием. Владивосток, 20-23 сентября 2011 г. Владивосток: Дальнаука, 2011. С. 20-22.

10. Nevolko P.A. (2009) Geologic and physical-chemical conditions of antimonial mineralization formation in gold deposits of the Yenisei Ridge. Dissertation abstract. Novosibirsk: IGM SB RAS, 16 p.

11. Верниковский В.А., Метелкин Д.В., Верниковская А.Е., Казанский А.Ю., Матушкин Н.Ю. К проблеме формирования западного обрамления Сибирского кратона: новые палеомагнитные и геохронологические данные по Центрально-Ангарскому террейну (Енисейский кряж) // Геодинамическая эволюция литосферы Центрально-Азиатского подвижного пояса (от океана к континенту). Вып. 9: Материалы науч. совещ. (Иркутск, 18-21 окт. 2011 г.). - Иркутск: Ин-т земной коры СО РАН, 2011. - С. 48-50.

12. Верниковский и др., 2009

13. Метелкин и др., 2004

14. Верниковский и др., 2008

15. Верниковская и др., 2010