- Email: [email protected]
Greenstone belts and their mineral endowment: Preface
Accepted Manuscript Greenstone belts and their mineral endowment: Preface Sohini Ganguly, Qiong-Yan Yang PII:
S1674-9871(17)30191-3
DOI:
10.1016/j.gsf.2017.11.001
Reference:
GSF 622
To appear in:
Geoscience Frontiers
Please cite this article as: Ganguly, S., Yang, Q.-Y., Greenstone belts and their mineral endowment: Preface, Geoscience Frontiers (2017), doi: 10.1016/j.gsf.2017.11.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
ACCEPTED MANUSCRIPT 1
Editorial
2 3
Greenstone belts and their mineral endowment: Preface
RI PT
4 5
The granite-greenstone terranes nested in Archean cratonic nuclei of
7
continents over the world are composed of variably metamorphosed igneous and
8
sedimentary remnants of ancient ocean basins. These rocks preserve distinct
9
geological and geochemical imprints of mantle evolution and differentiation of
10
primordial crust, varying conditions of magmatism and fluid generation, plume-arc
11
interaction, subduction-accretion, tectonic cycles of ocean closure and continent
12
generation; hydrothermal fluid activity, remobilization and mineralization of precious
13
metals over geological time. The notion of mineral endowment of Archean
14
greenstone belts invokes a conjunction of magmatic, sedimentary and metamorphic
15
processes that operated in different geodynamic settings and collectively contributed
16
towards the nature and diversity of mineralization. The spatial and temporal
17
distribution of metallogenic associations in greenstone belts is marked by a
18
heterogeneity as recorded by (i) Pb- and sulphate- rich volcanogenic massive
19
sulphides (VMS), porphyry-style Mo–Cu and evaporative barite deposits of 3.5–3.3
20
Ga and 3.0–2.7 Ga greenstone sequences conforming to shallow marine to
21
subaerial environments and (ii) komatiite-associated Ni–Cu deposits, VMS, base
22
metal and gold mineralization associated with greenstones formed in deeper
23
basins. Iron and manganese mineralization have been attributed to hydrothermal
24
processes associated with mid-oceanic ridge-rift system. In contrast, gold, Cu
25
porphyry and VMS Cu–Zn deposits show prominent affinity towards metallogenic
AC C
EP
TE D
M AN U
SC
6
2
ACCEPTED MANUSCRIPT 26
processes operative in Archean subduction environments. Hence, diverse
27
geodynamic conditions including mantle plume activity, divergent and convergent
28
margin processes substantiate the heterogeneous mineral endowment of Archean
29
greenstone belts. In this special issue of Geoscience Frontiers on “Greenstone belts and their
31
mineral endowment”, we assemble seven scholarly contributions addressing the
32
intriguing questions on Archean plate tectonics and mantle dynamics, fluid-crust-
33
mantle interactions and tectonic control on greenstone hosted mineralization thereby
34
providing cutting-edge perceptions towards understanding of the evolution of
35
asthenosphere-lithosphere system over geological time and its involvement in crustal
36
growth and metallogenic processes associated with Archean greenstone belts. The
37
relative influence of plate and stagnant lid tectonics in the thermotectonic evolution of
38
the earth has triggered debatable issues and invoked a geodynamic transition from
39
early Hadean stage stagnant-lid convection tectonics to a short-term episodic style of
40
subduction tectonics during Archean consistent with gradual decrease of mantle
41
temperature and thickening of lithosphere. It has been
42
subduction tectonics during Archean was marked by intermittent plate motions and
43
flat subduction of hot young oceanic lithosphere where frequent slab break-off
44
events prevented a modern-style long-lived subduction system and resulted in
45
frequent cessation and re-initiation of the subduction process. The first two articles
46
of this issue address the contentions on the magmatic and geodynamic processes
47
that sketched the evolutionary history of the earth including existence of subduction-
48
driven plate tectonics during Archean.The first paper of this issue by de Witt et al.
49
(2018) presents a comparative account of different crust generation processes
50
construed
further envisaged that
AC C
EP
TE D
M AN U
SC
RI PT
30
from
geological,
structural,
geochemical,
geochronological
and
3
ACCEPTED MANUSCRIPT geophysical data for seven ultramafic-mafic-felsic complexes of Barberton
52
greenstone belt, South Africa and constrains the validity of plume or plate tectonic
53
models in a Paleoarchean environment. These magmatic complexes, separated by
54
gold-hosted major shear systems of southern Makhonjwa Mountains, collectively
55
preserve subduction signatures resembling modern style intraoceanic arc-back arc
56
systems and records of crustal growth by horizontal tectonics controlled by
57
subduction-accretion processes as observed in Phanerozoic convergent margin
58
settings. In this article, the authors corroborate subduction-driven plate tectonic
59
genes in Paleoarchean earth and suggest that plate convergence and plate tectonic
60
processes were operative by 3.6–3.2. The inferences and ideas emerging from this
61
comprehensive study reinforce the consensus for plate tectonics in early Archean. In
62
the next paper, Agangi et al. (2018) evaluate Paleoarchean felsic magmatism and
63
crustal evolution of Kaapval Craton, South Africa. Bulk chemical analyses, zircon U–
64
Pb ages and Hf-in-zircon systematics of igneous clasts from a conglomerate of the
65
3.2 Ga Moodies Group of the Barberton Greenstone Belt attest to the presence of a
66
differentiated felsic continental crust at >3.5 Ga that imply mantle processes and
67
melt extraction episode dating back to Eoarchean. The authors propose a unified
68
model for plutonic and volcanic magmatic suites suggesting coeval, multiple pulses
69
of sodic and potassic magmatism during 3.5–3.2 Ga that resulted into gradual
70
progression from tonalite-trondhjemite-granodiorite (TTG) to granite-monzogranite-
71
syenogranite (GMS) lithologies.
AC C
EP
TE D
M AN U
SC
RI PT
51
72
Archean ultramafic-mafic complexes, as attributed either to extrusive
73
magmatism of mantle origin or to layered intrusions of subvolcanic magma chamber
74
crystallization, are associated with a wide variety of tectonic settings ranging from
75
intraoceanic (oceanic crust or oceanic plateau) to oceanic ridge, forearc basin,
4
ACCEPTED MANUSCRIPT marginal back arc basin and active continental rift environments and provide
77
significant clues for understanding dynamic mantle processes during early stages of
78
the earth. These magmatic bodies are important source for several types of ores like
79
chromite (source of Cr), magnetite (source for Fe, V, Ti), gold (Au), Ni–Cu sulphides,
80
base metal sulphides (BMS; Cu–Pb–Zn) and platinum group of elements (PGE). In
81
accordance with these, the third paper by Szilas et al. (2018) elucidate the
82
geochemical characteristics and petrogenetic evolution of layered dunite-peridotite
83
and stratiform chromitites of 2.97 Ga Seqi Ultramafic Complex from southwest
84
Greenland. Highly forsteritic olivine compositions and Platinum Group Element
85
(PGE) fractionations indicate in situ olivine-spinel dominated cumulus crystallization
86
of melts derived by >40% partial melting of a highly magnesian, anhydrous,
87
refractory mantle. The authors infer that the peridotite-dunite cumulates of Seqi
88
ultramafic complex represents an ultra-depleted cratonic keel beneath Archean
89
North Atlantic Craton and provide insights into the melt generation processes and
90
geodynamic conditions of primitive Archean mantle that served as precursor to
91
continent generation and subcontinental lithospheric mantle (SCLM) evolution in
92
early earth. Furthermore, this type of chromitite-bearing ultramafic layered intrusive
93
complexes provide potential evidence for Ni–Cu ores, PGE, Fe, Ti, V and chromite
94
mineralization.
SC
M AN U
TE D
EP
AC C
95
RI PT
76
The Neoarchean period (2.8–2.7Ga), marked by a peak in crustal growth,
96
enhanced crustal thinning and extension, development of thick komatiite-basalt and
97
felsic volcanic sequences, large scale deposition of banded iron formations (BIFs),
98
cratonization, regional deformation and metamorphism, and development of shear
99
zone systems represents an important timeframe in greenstone metallogenesis.
100
Mishra et al. (2018) provide a detailed account of the nature and source of ore-
5
ACCEPTED MANUSCRIPT forming fluids contributing to the genesis of Neoarchean orogenic gold deposits
102
associated with the granite-greenstone belts of Dharwar Craton, southern peninsular
103
India. Orogenic gold mineralization associated with Archean granite–greenstone
104
terranes is primarily controlled by structural style, tectonic setting, metamorphism of
105
host and associated rocks, shear zones, hydrothermal system involving physico-
106
chemical processes and flow of hydrothermal fluids for mobilization, transportation
107
and deposition of gold. The authors interpret geochemistry of sulphide, tourmaline
108
and other minerals, and also evaluate fluid inclusion microthermometric and Raman
109
spectroscopic data to address the source of ore fluid, nature of gold transport and
110
mechanism of gold ore formation in the Dharwar Craton. This study corroborates
111
uniform ore fluid compositions in orogenic gold deposits of Dharwar Craton and
112
suggests their origin from low salinity, reduced aqueous-gaseous fluids derived by
113
hydrothermal alteration and metamorphic devolatilization of mafic rocks and
114
interlayered sediments of Dharwar greenstone belts. The authors suggest that gold
115
precipitation occurred by fluid-rock sufidation reactions in narrow P–T regime and
116
fluid phase separation driven by fluid pressure fluctuation.
SC
M AN U
TE D
EP
117
RI PT
101
The next paper by Yakymchuk and Szilas (2018) highlights the prospects of
119
kyanite and sillimanite hosted corundum (ruby–sapphire) mineralization in high-
120
grade Archean granite-greenstones terranes of southwest Greenland comprising
121
aluminous gneisses of sedimentary origin and amphibolite facies metaperidotites.
122
The authors deduce a phase equilibria model to evaluate the geochemical,
123
metamorphic and tectonic parameters that principally govern genesis and
124
mineralization of corundum in Archean greenstone belts and thereby suggest
125
amphibolite- to granulite-facies metamorphic conditions, desilicification inducing
AC C
118
6
ACCEPTED MANUSCRIPT 126
breakdown of sillimanite and kyanite at elevated temperatures and ruby formation,
127
juxtaposition of low-silica ultramafic rocks and high-silica aluminous metapelite
128
triggering a chemical potential gradient to stabilize corundum in metapelites, addition
129
of alumina by mica-rich metasomatic reactions
130
corundum exploration.
RI PT
as the essential vectors for
The arc-style and non-arc style magmatic records of Archean greenstone
132
belts have propounded bottom-up mantle upwellings through plume ascent and top-
133
down oceanic slab subduction processes as principal mechanisms that initiated
134
continent generation, lithospheric evolution and crustal growth in early earth.
135
Petrological, geochemical and geochronological studies of Archaean greenstone
136
belts over the last three decades from all major cratons of the world have
137
documented two major types of volcanic rock associations: (i) an oceanic plateau
138
association composed of compositionally relatively uniform komatiites and Mg- to Fe-
139
rich tholeiitic basalts erupted from mantle plumes and (ii) a compositionally diverse
140
intra-oceanic island arc association, dominated by ‘normal’ tholeiitic to calc-alkaline
141
basalts, andesites, dacites, and rhyolites (BADR). These diverse magmatic suites
142
are juxtaposed in most of the greenstone terranes through plume-arc interaction and
143
subduction-accretion processes. In their paper, Tang et al. (2018) present a
144
comprehensive overview of crustal growth and cratonization of the North China
145
Craton (NCC) linked with amalgamation of microblocks welded by 2.75–2.6 Ga and
146
~2.5 Ga mineralized granite-greenstone belts. The authors integrate lithological
147
characteristics, petrological, geochemical and geochronological data to address two
148
distinct episodes of granite-greenstone generation and associated gold, BIF-hosted
149
iron, VMS type Cu–Zn mineralization in NCC. Tang et al. (2018) infer plume-arc
150
interaction processes generating the early Neoarchean (2.75–2.6 Ga) greenstone
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131
7
ACCEPTED MANUSCRIPT belts and associated mineralization and propose subduction-accretion-collision
152
processes for the generation of their late Neoarchean (~2.5 Ga) counterparts and
153
their mineralization. This paper deciphers the transitional geodynamic conditions for
154
the Neoarchean greenstone belt evolution and crustal growth in NCC substantiated
155
by plume-arc interaction to oceanic slab subduction tectonics and accretionary
156
processes that provide insights into the tectonic control on spatial and temporal
157
diversity of greenstone-hosted mineralization in NCC.
RI PT
151
The last paper in this issue is by Singh et al. (2018) who present the
159
geochemical systematics of the Mauranipur- Babina greenstone belt from
160
Bundelkhand Craton, Central India and identify a komatiitic basalt-island arc tholeiitic
161
BADR association that corroborates plume-back arc- arc accretion tectonics for
162
Neoarchean crustal evolution in Bundelkhand Craton.
M AN U
SC
158
We hope that the contents of this issue will generate interest among our
164
readers in the earth science community, and will provide impetus for further scientific
165
probe on this topic. We sincerely thank all the authors for their insightful contributions
166
to this volume and all the referees for providing constructive peer reviews. We are
167
grateful to Prof. M. Santosh, Editorial Advisor, Geoscience Frontiers for all the
168
motivation and guidance. We also thank the editorial staff of Geoscience Frontiers
169
and in particular Dr. Lily Wang for their assistance and support towards this special
170
issue.
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171 172
References:
173 174 175
Agangi, A., Hofmann, A., Elburg, M. A., 2018. A review of Palaeoarchaean felsic volcanism in the eastern Kaapvaal craton: Linking plutonic and volcanic records. Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.08.003
176 177 178
de
Wit ,M., Furnes, H., MacLennan, S., Doucouré, M., Schoene,B., Weckmann, U., Martinez, U., Bowring S., 2018. Paleoarchean bedrock lithologies across the Makhonjwa Mountains of South Africa and Swaziland linked to geochemical, magnetic
8
ACCEPTED MANUSCRIPT and tectonic data reveal early plate tectonic genes flanking subduction margins, Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.10.005 Mishra, B., Pruseth, K. L., Hazarika, P., Chinnasamy, S. S., 2018. Nature and source of the ore-forming fluids associated with orogenic gold deposits in the Dharwar Craton. Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.09.005
185 186 187 188
Singh, S. P., Subramanyam, K. S. V., Manikyamba, C., Santosh, M., Singh, M. R., Kumar, B. C., 2018. Geochemical systematics of the Mauranipur-Babina greenstone belt, Bundelkhand Craton, Central India: Insights on Neoarchean mantle plume-arc accretion and crustal evolution. Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.08.008
189 190 191 192
Szilas, K., van Hinsberg, V., McDonald, I., Næraa, T., Rollinson, H., Adetunji, J., Bird, D., 2018. Highly refractory Archaean peridotite cumulates: Petrology and geochemistry of the Seqi Ultramafic Complex, SW Greenland. Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.05.003
193 194 195
Tang, L., Santosh, M., 2018. Neoarchean granite-greenstone belts and related ore mineralization in the North China Craton: An overview. Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.04.002
196 197 198
Yakymchuk, C., Szilas, K., 2018. Corundum formation by metasomatic reactions in Archean metapelite, SW Greenland: Exploration vectors for ruby deposits within high-grade greenstone belts. Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.07.008
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Sohini Ganguly* Department of Earth Science Goa University, Taleigao Plateau Goa 403206 India
EP
Corresponding author e-mail: [email protected] Qiong-Yan Yang School of Earth Sciences and Resources China University of Geosciences Beijing, 29, Xueyuan Road, Beijing 100083 China
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199 200 201 202 203 204 205 206 207 208 209 210 211 212 213
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179 180 181 182 183 184
S1674-9871(17)30191-3
DOI:
10.1016/j.gsf.2017.11.001
Reference:
GSF 622
To appear in:
Geoscience Frontiers
Please cite this article as: Ganguly, S., Yang, Q.-Y., Greenstone belts and their mineral endowment: Preface, Geoscience Frontiers (2017), doi: 10.1016/j.gsf.2017.11.001. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
ACCEPTED MANUSCRIPT 1
Editorial
2 3
Greenstone belts and their mineral endowment: Preface
RI PT
4 5
The granite-greenstone terranes nested in Archean cratonic nuclei of
7
continents over the world are composed of variably metamorphosed igneous and
8
sedimentary remnants of ancient ocean basins. These rocks preserve distinct
9
geological and geochemical imprints of mantle evolution and differentiation of
10
primordial crust, varying conditions of magmatism and fluid generation, plume-arc
11
interaction, subduction-accretion, tectonic cycles of ocean closure and continent
12
generation; hydrothermal fluid activity, remobilization and mineralization of precious
13
metals over geological time. The notion of mineral endowment of Archean
14
greenstone belts invokes a conjunction of magmatic, sedimentary and metamorphic
15
processes that operated in different geodynamic settings and collectively contributed
16
towards the nature and diversity of mineralization. The spatial and temporal
17
distribution of metallogenic associations in greenstone belts is marked by a
18
heterogeneity as recorded by (i) Pb- and sulphate- rich volcanogenic massive
19
sulphides (VMS), porphyry-style Mo–Cu and evaporative barite deposits of 3.5–3.3
20
Ga and 3.0–2.7 Ga greenstone sequences conforming to shallow marine to
21
subaerial environments and (ii) komatiite-associated Ni–Cu deposits, VMS, base
22
metal and gold mineralization associated with greenstones formed in deeper
23
basins. Iron and manganese mineralization have been attributed to hydrothermal
24
processes associated with mid-oceanic ridge-rift system. In contrast, gold, Cu
25
porphyry and VMS Cu–Zn deposits show prominent affinity towards metallogenic
AC C
EP
TE D
M AN U
SC
6
2
ACCEPTED MANUSCRIPT 26
processes operative in Archean subduction environments. Hence, diverse
27
geodynamic conditions including mantle plume activity, divergent and convergent
28
margin processes substantiate the heterogeneous mineral endowment of Archean
29
greenstone belts. In this special issue of Geoscience Frontiers on “Greenstone belts and their
31
mineral endowment”, we assemble seven scholarly contributions addressing the
32
intriguing questions on Archean plate tectonics and mantle dynamics, fluid-crust-
33
mantle interactions and tectonic control on greenstone hosted mineralization thereby
34
providing cutting-edge perceptions towards understanding of the evolution of
35
asthenosphere-lithosphere system over geological time and its involvement in crustal
36
growth and metallogenic processes associated with Archean greenstone belts. The
37
relative influence of plate and stagnant lid tectonics in the thermotectonic evolution of
38
the earth has triggered debatable issues and invoked a geodynamic transition from
39
early Hadean stage stagnant-lid convection tectonics to a short-term episodic style of
40
subduction tectonics during Archean consistent with gradual decrease of mantle
41
temperature and thickening of lithosphere. It has been
42
subduction tectonics during Archean was marked by intermittent plate motions and
43
flat subduction of hot young oceanic lithosphere where frequent slab break-off
44
events prevented a modern-style long-lived subduction system and resulted in
45
frequent cessation and re-initiation of the subduction process. The first two articles
46
of this issue address the contentions on the magmatic and geodynamic processes
47
that sketched the evolutionary history of the earth including existence of subduction-
48
driven plate tectonics during Archean.The first paper of this issue by de Witt et al.
49
(2018) presents a comparative account of different crust generation processes
50
construed
further envisaged that
AC C
EP
TE D
M AN U
SC
RI PT
30
from
geological,
structural,
geochemical,
geochronological
and
3
ACCEPTED MANUSCRIPT geophysical data for seven ultramafic-mafic-felsic complexes of Barberton
52
greenstone belt, South Africa and constrains the validity of plume or plate tectonic
53
models in a Paleoarchean environment. These magmatic complexes, separated by
54
gold-hosted major shear systems of southern Makhonjwa Mountains, collectively
55
preserve subduction signatures resembling modern style intraoceanic arc-back arc
56
systems and records of crustal growth by horizontal tectonics controlled by
57
subduction-accretion processes as observed in Phanerozoic convergent margin
58
settings. In this article, the authors corroborate subduction-driven plate tectonic
59
genes in Paleoarchean earth and suggest that plate convergence and plate tectonic
60
processes were operative by 3.6–3.2. The inferences and ideas emerging from this
61
comprehensive study reinforce the consensus for plate tectonics in early Archean. In
62
the next paper, Agangi et al. (2018) evaluate Paleoarchean felsic magmatism and
63
crustal evolution of Kaapval Craton, South Africa. Bulk chemical analyses, zircon U–
64
Pb ages and Hf-in-zircon systematics of igneous clasts from a conglomerate of the
65
3.2 Ga Moodies Group of the Barberton Greenstone Belt attest to the presence of a
66
differentiated felsic continental crust at >3.5 Ga that imply mantle processes and
67
melt extraction episode dating back to Eoarchean. The authors propose a unified
68
model for plutonic and volcanic magmatic suites suggesting coeval, multiple pulses
69
of sodic and potassic magmatism during 3.5–3.2 Ga that resulted into gradual
70
progression from tonalite-trondhjemite-granodiorite (TTG) to granite-monzogranite-
71
syenogranite (GMS) lithologies.
AC C
EP
TE D
M AN U
SC
RI PT
51
72
Archean ultramafic-mafic complexes, as attributed either to extrusive
73
magmatism of mantle origin or to layered intrusions of subvolcanic magma chamber
74
crystallization, are associated with a wide variety of tectonic settings ranging from
75
intraoceanic (oceanic crust or oceanic plateau) to oceanic ridge, forearc basin,
4
ACCEPTED MANUSCRIPT marginal back arc basin and active continental rift environments and provide
77
significant clues for understanding dynamic mantle processes during early stages of
78
the earth. These magmatic bodies are important source for several types of ores like
79
chromite (source of Cr), magnetite (source for Fe, V, Ti), gold (Au), Ni–Cu sulphides,
80
base metal sulphides (BMS; Cu–Pb–Zn) and platinum group of elements (PGE). In
81
accordance with these, the third paper by Szilas et al. (2018) elucidate the
82
geochemical characteristics and petrogenetic evolution of layered dunite-peridotite
83
and stratiform chromitites of 2.97 Ga Seqi Ultramafic Complex from southwest
84
Greenland. Highly forsteritic olivine compositions and Platinum Group Element
85
(PGE) fractionations indicate in situ olivine-spinel dominated cumulus crystallization
86
of melts derived by >40% partial melting of a highly magnesian, anhydrous,
87
refractory mantle. The authors infer that the peridotite-dunite cumulates of Seqi
88
ultramafic complex represents an ultra-depleted cratonic keel beneath Archean
89
North Atlantic Craton and provide insights into the melt generation processes and
90
geodynamic conditions of primitive Archean mantle that served as precursor to
91
continent generation and subcontinental lithospheric mantle (SCLM) evolution in
92
early earth. Furthermore, this type of chromitite-bearing ultramafic layered intrusive
93
complexes provide potential evidence for Ni–Cu ores, PGE, Fe, Ti, V and chromite
94
mineralization.
SC
M AN U
TE D
EP
AC C
95
RI PT
76
The Neoarchean period (2.8–2.7Ga), marked by a peak in crustal growth,
96
enhanced crustal thinning and extension, development of thick komatiite-basalt and
97
felsic volcanic sequences, large scale deposition of banded iron formations (BIFs),
98
cratonization, regional deformation and metamorphism, and development of shear
99
zone systems represents an important timeframe in greenstone metallogenesis.
100
Mishra et al. (2018) provide a detailed account of the nature and source of ore-
5
ACCEPTED MANUSCRIPT forming fluids contributing to the genesis of Neoarchean orogenic gold deposits
102
associated with the granite-greenstone belts of Dharwar Craton, southern peninsular
103
India. Orogenic gold mineralization associated with Archean granite–greenstone
104
terranes is primarily controlled by structural style, tectonic setting, metamorphism of
105
host and associated rocks, shear zones, hydrothermal system involving physico-
106
chemical processes and flow of hydrothermal fluids for mobilization, transportation
107
and deposition of gold. The authors interpret geochemistry of sulphide, tourmaline
108
and other minerals, and also evaluate fluid inclusion microthermometric and Raman
109
spectroscopic data to address the source of ore fluid, nature of gold transport and
110
mechanism of gold ore formation in the Dharwar Craton. This study corroborates
111
uniform ore fluid compositions in orogenic gold deposits of Dharwar Craton and
112
suggests their origin from low salinity, reduced aqueous-gaseous fluids derived by
113
hydrothermal alteration and metamorphic devolatilization of mafic rocks and
114
interlayered sediments of Dharwar greenstone belts. The authors suggest that gold
115
precipitation occurred by fluid-rock sufidation reactions in narrow P–T regime and
116
fluid phase separation driven by fluid pressure fluctuation.
SC
M AN U
TE D
EP
117
RI PT
101
The next paper by Yakymchuk and Szilas (2018) highlights the prospects of
119
kyanite and sillimanite hosted corundum (ruby–sapphire) mineralization in high-
120
grade Archean granite-greenstones terranes of southwest Greenland comprising
121
aluminous gneisses of sedimentary origin and amphibolite facies metaperidotites.
122
The authors deduce a phase equilibria model to evaluate the geochemical,
123
metamorphic and tectonic parameters that principally govern genesis and
124
mineralization of corundum in Archean greenstone belts and thereby suggest
125
amphibolite- to granulite-facies metamorphic conditions, desilicification inducing
AC C
118
6
ACCEPTED MANUSCRIPT 126
breakdown of sillimanite and kyanite at elevated temperatures and ruby formation,
127
juxtaposition of low-silica ultramafic rocks and high-silica aluminous metapelite
128
triggering a chemical potential gradient to stabilize corundum in metapelites, addition
129
of alumina by mica-rich metasomatic reactions
130
corundum exploration.
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as the essential vectors for
The arc-style and non-arc style magmatic records of Archean greenstone
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belts have propounded bottom-up mantle upwellings through plume ascent and top-
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down oceanic slab subduction processes as principal mechanisms that initiated
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continent generation, lithospheric evolution and crustal growth in early earth.
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Petrological, geochemical and geochronological studies of Archaean greenstone
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belts over the last three decades from all major cratons of the world have
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documented two major types of volcanic rock associations: (i) an oceanic plateau
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association composed of compositionally relatively uniform komatiites and Mg- to Fe-
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rich tholeiitic basalts erupted from mantle plumes and (ii) a compositionally diverse
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intra-oceanic island arc association, dominated by ‘normal’ tholeiitic to calc-alkaline
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basalts, andesites, dacites, and rhyolites (BADR). These diverse magmatic suites
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are juxtaposed in most of the greenstone terranes through plume-arc interaction and
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subduction-accretion processes. In their paper, Tang et al. (2018) present a
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comprehensive overview of crustal growth and cratonization of the North China
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Craton (NCC) linked with amalgamation of microblocks welded by 2.75–2.6 Ga and
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~2.5 Ga mineralized granite-greenstone belts. The authors integrate lithological
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characteristics, petrological, geochemical and geochronological data to address two
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distinct episodes of granite-greenstone generation and associated gold, BIF-hosted
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iron, VMS type Cu–Zn mineralization in NCC. Tang et al. (2018) infer plume-arc
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interaction processes generating the early Neoarchean (2.75–2.6 Ga) greenstone
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ACCEPTED MANUSCRIPT belts and associated mineralization and propose subduction-accretion-collision
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processes for the generation of their late Neoarchean (~2.5 Ga) counterparts and
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their mineralization. This paper deciphers the transitional geodynamic conditions for
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the Neoarchean greenstone belt evolution and crustal growth in NCC substantiated
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by plume-arc interaction to oceanic slab subduction tectonics and accretionary
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processes that provide insights into the tectonic control on spatial and temporal
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diversity of greenstone-hosted mineralization in NCC.
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The last paper in this issue is by Singh et al. (2018) who present the
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geochemical systematics of the Mauranipur- Babina greenstone belt from
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Bundelkhand Craton, Central India and identify a komatiitic basalt-island arc tholeiitic
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BADR association that corroborates plume-back arc- arc accretion tectonics for
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Neoarchean crustal evolution in Bundelkhand Craton.
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We hope that the contents of this issue will generate interest among our
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readers in the earth science community, and will provide impetus for further scientific
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probe on this topic. We sincerely thank all the authors for their insightful contributions
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to this volume and all the referees for providing constructive peer reviews. We are
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grateful to Prof. M. Santosh, Editorial Advisor, Geoscience Frontiers for all the
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motivation and guidance. We also thank the editorial staff of Geoscience Frontiers
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and in particular Dr. Lily Wang for their assistance and support towards this special
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issue.
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References:
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Agangi, A., Hofmann, A., Elburg, M. A., 2018. A review of Palaeoarchaean felsic volcanism in the eastern Kaapvaal craton: Linking plutonic and volcanic records. Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.08.003
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Wit ,M., Furnes, H., MacLennan, S., Doucouré, M., Schoene,B., Weckmann, U., Martinez, U., Bowring S., 2018. Paleoarchean bedrock lithologies across the Makhonjwa Mountains of South Africa and Swaziland linked to geochemical, magnetic
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ACCEPTED MANUSCRIPT and tectonic data reveal early plate tectonic genes flanking subduction margins, Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.10.005 Mishra, B., Pruseth, K. L., Hazarika, P., Chinnasamy, S. S., 2018. Nature and source of the ore-forming fluids associated with orogenic gold deposits in the Dharwar Craton. Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.09.005
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Singh, S. P., Subramanyam, K. S. V., Manikyamba, C., Santosh, M., Singh, M. R., Kumar, B. C., 2018. Geochemical systematics of the Mauranipur-Babina greenstone belt, Bundelkhand Craton, Central India: Insights on Neoarchean mantle plume-arc accretion and crustal evolution. Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.08.008
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Szilas, K., van Hinsberg, V., McDonald, I., Næraa, T., Rollinson, H., Adetunji, J., Bird, D., 2018. Highly refractory Archaean peridotite cumulates: Petrology and geochemistry of the Seqi Ultramafic Complex, SW Greenland. Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.05.003
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Tang, L., Santosh, M., 2018. Neoarchean granite-greenstone belts and related ore mineralization in the North China Craton: An overview. Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.04.002
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Yakymchuk, C., Szilas, K., 2018. Corundum formation by metasomatic reactions in Archean metapelite, SW Greenland: Exploration vectors for ruby deposits within high-grade greenstone belts. Geoscience Frontiers. doi.org/10.1016/j.gsf.2017.07.008
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Sohini Ganguly* Department of Earth Science Goa University, Taleigao Plateau Goa 403206 India
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Corresponding author e-mail: [email protected] Qiong-Yan Yang School of Earth Sciences and Resources China University of Geosciences Beijing, 29, Xueyuan Road, Beijing 100083 China
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