Page 6 - Sumatra Geology, Resources and Tectonic Evolution

Contents

Preface vii Geochemistry of the Silungkang and
Palepat Formations 67
Contributors ix Metavolcanics and serpentinites in the
Medial Sumatra Tectonic Zone 68
Chapter 1. Introduction and previous research Bentong-Billiton Accretionary Complex 68
A. J. BARBER, M. J. CROW & J. S. MILSOM West Sumatra Triassic Plutonic-Volcanic Arc 71
History of geological research in Sumatra Pahang Volcanic Belt 71
before WWII Jurassic-Cretaceous Plutonic-Volcanic Arcs 71
Post-WWII research Volcanics in the Woyla Accretionary Complex 72
SEATAR Programme Oceanic volcanic arc fragments 77
Indonesian Petroleum Association Origins of the volcanic units and their environments
British and Indonesian Geological Surveys of formation 79
University of London Southeast Asian Research
Group, BGS and LEMIGAS Chapter 7. Tertiary stratigraphy 86
M. E. M. DE SMET & A. J. BARBER
Southern Sumatra Project
Stratigraphic review 86
Chapter 2. Seismology and neotectonics Pre-Rift stage (Eocene) 87
Horst and graben stage
J. S. MILSOM
(latest Eocene-Oligocene) 88
Shallow seismicity 9
Transgressive stage
The Wadati-Benioff Zone (WBZ) 9
(Late Oligocene-Mid-Miocene) 91
Toba seismicity 10
Maximum transgression (Mid-Miocene) 94
Relative horizontal movements 11
Regressive stage (Mid-Miocene-Present) 95
GPS data, the Enggano and Simeulue earthquakes
Summary 95
and Mentawai Fault 13
Vertical movements 15
Chapter 8. Tertiary volcanicity 98
Chapter 3. The gravity field 16 M. J. CROW
J. S. MILSOM & A. S. D. WALKER Radiometric dating of volcanism and plutonism
Data sources 16 in Sumatra 98
Regional gravity patterns 16 Tertiary volcanic stratigraphy 98
Toba-Tawar gravity low 19 Major and trace element geochemistry of the
Eastern Sumatra 19 Tertiary volcanic rocks 109
Gravity effects of sedimentary basins 19 Volcanism, plutonism and subduction beneath
The forearc basin 20 Sumatra during the Tertiary: summary of
Seismic tomography and the long-wavelength Tertiary volcanism and tectonic overview 110
gravity field 22
Chapter 9. Quaternary volcanicity 120
Chapter 4. Pre-Tertiary stratigraphy 24 M. GASPARON
A. J. BARBER • M. J. CROW Quaternary volcanic arc and its relationship with
Pre-Carboniferous basement 24 main tectonic features of Sumatra 120
Tapanuli Group (Carboniferous - ?Early Permian) 25 Pyroclastic deposits 123
Peusanguan Group (Permo-Triassic) 35 Quaternary arc volcanoes 124
Woyla Group (Jurassic-Cretaceous) 40 Quaternary backarc volcanics 125
Volcanic hazard 130
Chapter 5. Granites 54
E. J. COBBING Chapter 10. Fuel resources: oil and gas 131
Isotopic ages of Sumatran granites 54 J. CLURE
The granite suites 56 North Sumatra Basin 131
Conclusions 61 Central Sumatra Basin 135
South Sumatra Basin 137
Chapter 6. Pre-Tertiary volcanic rocks 63 Other Sumatran basins 140
M. J. CROW
Carboniferous volcanism 63 Chapter 11. Fuel resources: coal 142
East Sumatra Plutonic-Volcanic Belt L. P. THOMAS
(Permian volcanism) 63 Geology and coal deposits in Sumatra 142
West Sumatra Permian Plutonic-Volcanic Belt Coal quality 145
(Early-Mid-Permian volcanism) 64 Coal resources and production 145