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Table of Contents - Special Paper 354

Petrologic and Structural History of Tobago, West Indies: A Fragment of the Accreted, Mesozoic Oceanic Arc of the Southern Caribbean

ABSTRACT 1

INTRODUCTION 3

GEOLOGIC FRAMEWORK 4

NORTH COAST SCHIST 4

Rock units 5

Parlatuvier Formation 5

Mount Dillon Formation 7

Metasedimentary and metatuff unit 8

Metamorphic conditions 8

Depositional environment 11

Structural fabric elements 11

Synmetamorphic structures 11

Late metamorphic structures 11

Postmetamorphic structures 12

Possible broad correlations 12

TOBAGO VOLCANIC GROUP
14

Stratigraphic sequence and depositional environment 14

Argyle Formation 17

Goldsborough Formation 17

Bacolet Formation 17

Volcanogenic sedimentary rocks 20

Undifferentiated part of the Tobago Volcanic Group 20

Metamorphism 21

Possible broad correlations 21

TOBAGO PLUTONIC SUITE AND ASSOCIATED ROCKS
23

Deformed volcanic-plutonic complexes 23

Ultramafic rocks 24

Field characteristics and lithologic variations 24

Petrography 24

Gabbro-diorite 26

Field characteristics and lithologic variations 26

Petrography 29

Tonalitic rocks 29

Field characteristics and lithologic variations 29

Petrography 31

Dike swarm 31

ROCKS OF THE DYNAMOTHERMAL AUREOLE
32

Field relationships and lithologic variations 32

Structural fabric 32

Metamorphism 34

Protolith of the amphibolite facies aureole 35

MACROSCOPIC STRUCTURAL FEATURES OF TOBAGO
35

Boundary between the plutonic suite and North Coast Schist 35

Central Tobago fault system 36

North-northwest–striking cross faults 38

Upper Courland fault zone 39

Black Rock fault zone 39

Southern Tobago fault system 40

Bending of structural and lithic boundaries 40

DEVELOPMENTAL MODEL FOR THE TOBAGO FRAGMENT OF THE MESOZOIC OCEANIC ARC OF THE SOUTHERN CARIBBEAN 40

Mesozoic age relationships for Tobago 40

Penetrative deformation and metamorphism of the North Coast Schist 40

Pluton subsidence, extensional shear zone, and superposed normal faulting 42

Strike-slip history 44

Evaluation of some alternative interpretations 44

STRUCTURAL POSITION OF TOBAGO IN THE SOUTHEASTERN CARIBBEAN
45

COMPARISON WITH ROCKS OF THE CARIBBEAN-COLOMBIAN CRETACEOUS IGNEOUS PROVINCE 47

TOBAGO, WEST INDIES, AS A MODEL EXAMPLE OF A CROSS SECTION THROUGH INTRAOCEANIC-ARC CRUST 49

Acknowledgments 50

References cited 50

ABSTRACT			1
INTRODUCTION			3
GEOLOGIC FRAMEWORK			4
NORTH COAST SCHIST			4
	Rock units		5
		Parlatuvier Formation	5
		Mount Dillon Formation	7
		Metasedimentary and metatuff unit	8
	Metamorphic conditions		8
	Depositional environment		11
	Structural fabric elements		11
		Synmetamorphic structures	11
		Late metamorphic structures	11
		Postmetamorphic structures	12
	Possible broad correlations		12
TOBAGO VOLCANIC GROUP			14
	Stratigraphic sequence and depositional environment		14
		Argyle Formation	17
		Goldsborough Formation	17
		Bacolet Formation	17
		Volcanogenic sedimentary rocks	20
		Undifferentiated part of the Tobago Volcanic Group	20
	Metamorphism		21
	Possible broad correlations		21
TOBAGO PLUTONIC SUITE AND ASSOCIATED ROCKS			23
	Deformed volcanic-plutonic complexes		23
	Ultramafic rocks		24
		Field characteristics and lithologic variations	24
		Petrography	24
	Gabbro-diorite		26
		Field characteristics and lithologic variations	26
		Petrography	29
	Tonalitic rocks		29
		Field characteristics and lithologic variations	29
		Petrography	31
	Dike swarm		31
ROCKS OF THE DYNAMOTHERMAL AUREOLE			32
	Field relationships and lithologic variations		32
	Structural fabric		32
	Metamorphism		34
	Protolith of the amphibolite facies aureole		35
MACROSCOPIC STRUCTURAL FEATURES OF TOBAGO			35
	Boundary between the plutonic suite and North Coast Schist		35
	Central Tobago fault system		36
	North-northwest–striking cross faults		38
	Upper Courland fault zone		39
	Black Rock fault zone		39
	Southern Tobago fault system		40
	Bending of structural and lithic boundaries		40
DEVELOPMENTAL MODEL FOR THE TOBAGO FRAGMENT OF THE MESOZOIC OCEANIC ARC OF THE SOUTHERN CARIBBEAN			40
	Mesozoic age relationships for Tobago		40
	Penetrative deformation and metamorphism of the North Coast Schist		40
	Pluton subsidence, extensional shear zone, and superposed normal faulting		42
	Strike-slip history		44
	Evaluation of some alternative interpretations		44
STRUCTURAL POSITION OF TOBAGO IN THE SOUTHEASTERN CARIBBEAN			45
COMPARISON WITH ROCKS OF THE CARIBBEAN-COLOMBIAN CRETACEOUS IGNEOUS PROVINCE			47
TOBAGO, WEST INDIES, AS A MODEL EXAMPLE OF A CROSS SECTION THROUGH INTRAOCEANIC-ARC CRUST			49
Acknowledgments			50
References cited			50