『Abstract
China contains three major Precambrian blocks, the North China,
South China and Tarim cratons, separated and sutured by Phanerozoic
orogenic belts. The North China Craton (NCC) contains rocks as
old as 3.8 Ga, but is dominated by Neoarchean igneous rocks that
were formed during two magmatic events at 2.8-2.7 Ga and 2.55-2.50
Ga. The 2.8-2.7 Ga magmatic pulse is considered as a major phase
of juvenile crustal growth in the craton, though exposure of these
rocks is limited. The 2.55-2.50 Ga rocks make up 〜80% of Archean
basement in the NCC, but their rock associations,structural patterns,
and metamorphic age and P-T paths in the eastern and western parts
(Eastern and Western blocks) are different from those in the central
part (Trans-North China Orogen). In the Eastern and Western blocks,
the end-Neoarchean rocks are exposed as gneissic domes and dominated
by tonalitic-trondhjemitic-granodioritic (TTG) gneisses and mafic
to komatiitic rocks that were metamorphosed at 〜2.5 Ga, , along
anticlockwise P-T paths involving isobaric cooling, that is interpreted
to reflect underplating of mantle-derived magmas. In the Trans-North
China Orogen, the end-Neoarchean rocks occur as linear structural
belts and are composed of arc-related granitoids and volcanic
rocks that formed in a supra-subduction zone setting and were
metamorphosed at 〜1.85 Ga along a clockwise P-T paths involving
isothermal decompression in a continent-continent collisional
setting. Although magmatic arc models can explain the origin of
the 2.55-2.50 Ga TTG rocks in the Eastern and Western blocks,
a mantle plume model is favored because it best explains Paleoproterozoic
rocks in the Trans-North China Orogen exhibit the sample structural
and metamorphic characteristics that typify continental margin
arcs and collisional belts. Spatially, Paleoproterozoic rocks
in the NCC are related to collisional assembly of the disparate
parts of the Eastern and Western blocks including a 〜1.95 Ga collisional
event that led to amalgamation of the Yinshan and Ordos blocks
to form the Western Block, which then collided with the Eastern
Block to form the Trans-North China Orogen at 〜1.85 Ga. Following
the final assembly at 〜1.85 Ga, the interior of the NCC underwent
ongoing extension, leading to widespread emplacement of 1.80-1.75
Ga mafic dyke swarms, 1.75-1.68 Ga anorthosite-mangerite-granite-rapakivi
suites, and deposition of Mesoproterozoic and Neoproterozoic strata.
Meanwhile, a large Paleo-Mesoproterozoic volcanic belt (Xiong'er
Group) developed on the southern margin of the NCC, and is variously
interpreted as an intracontinental rift zone or an Andean-type
continental margin arc. In the late Mesoproterozoic, the northern
margin of the NCC underwent rifting (Zhaertai-Bayan Obo rift zone),
coincident with breakup of the Columbia (
Nuna) supercontinent.
The South China Craton consists of the Yangtze and Cathaysia
blocks, which are considered to have collided along the Jiangnan
Belt in the Neoproterozoic. Archean and Paleoproterozoic basement
rocks in the Yangtze Block are only locally exposed. The late
Mesoproterozoic to early Neoproterozoic folded belts in the Yangtze
Block are divided into the Jiangnan Belt in the southeast and
the Panxi-Hannan Belt in the west and north. The former is dominated
by early Neoproterozoic metamorphosed volcanic-sedimentary strata
intruded by middle Neoproterozoic peraluminous (S-type) granites
and unconformably overlain by the middle Neoproterozoic Banxi
Group and its equivalents. The Panxi-Hannan Belt consists of late
Mesoproterozoic to early Neoproterozoic metamorphosed volcanic-sedimentary
units and plutonic complexes. A number of mutually exclusive models
(e.g. plume-rift, slab-arc, plate-rift, etc.) have been proposed
for these belts. The Cathaysia Block is composed predominantly
of Neoproterozoic basement rock with Paleoproterozoic rocks only
exposed in southwest Zhejiang and north Fujian, and Mesoproterozoic
rocks limited to Hainan Island. The Paleoproterozoic rocks consists
of 1890-1830 Ma granitoids and 1850-1815 Ma supracrustal rocks,
which were metamorphosed at 1.89-1.88 Ga and locally reworked
at 250-130 Ma. Neoproterozoic rocks make up 〜90% of the Precambrian
basement in the Cathaysia Block and mainly consist of volcanic-sedimentary
strata metamorphosed from greenschist to granulite facies. Some
of the volcanic rocks have arc affinities, suggesting the existence
of a Neoproterozoic magmatic arc in the Cathaysia Block. The Neoproterozoic
rocks were metamorphosed at 460-420 Ma. The tectonic setting of
this event has been related to both intracontinental orogeny and
continental margin subduction and collision.
The Precambrian basement of the Tarim Craton consists of Neoarchean
and Paleoproterozoic rocks and late Mesoproterozoic to early-middle
Neoproterozoic sedimentary and volcanic strata metamorphosed at
greenschist and blueschist facies, which are unconformably overlain
by unmetamorphosed late Neoproterozoic (Sinian) cover. The Neoarchean
and Paleoproterozoic rocks are exposed in the Kulukatage and Dunhuang
complexes on the northern and northeastern margins of the craton,
respectively. The Neoarchean rocks consist of granitoid rocks
and minor supracrustal rocks, including TTG gneisses, calc-alkaline
granites and Kf-granites, most of which were emplaced at 2.6-2.50
Ga. The Paleoproterozoic basement rocks are also composed of granitoid
and supracrustals rocks (Xingditage and Dunhuang groups), of which
the granitoids were emplaced in two stages at 2.45-2.35 G and
〜1.9 Ga. In the Kulukatage Complex, the Neoarchean and Paleoproterozoic
rocks underwent metamorphic events at 1.9-1.8 Ga and 1.1-1.0 Ga
that are related to assembly of the Columbia (Nuna) and Rodinia
supercontinents, respectively. In the Dunhuang Complex, Archean
rocks underwent metamorphic events at 〜2.5 Ga and 1.9-1.8 Ga,
similar to two major metamorphic events occurring in the Western
Block of the NCC, leading to speculation that the complex is the
western extension of the Alax Complex of the NCC. Late Mesoproterozoic
to early-middle \\Neoproterozoic metamorphosed strata are exposed
on the peripheral margins of the Tarim Craton and are considered
to have formed in Andean-type continental margins that were deformed
and metamorphosed between 1.0 Ga and 0.9 Ga, probably related
to the assembly of Rodinia. During middle Neoproterozoic to Cambrian
time, the Tarim Craton became a stable platform overlain by middle-late
Neoproterozoic to Cambrian unmetamorphosed cover, of which the
middle-late Neoproterozoic units contain four sequences of tillite
correlated with the global snowball Earth events. Widespread middle
to late Neoproterozoic ultramafic-mafic complexes and mafic dyke
swarms with the Tarim Craton are related to a mantle plume event
that led to the final breakup of Rodinia.
Keywords: Cathaysia block; North China Craton; Precambrian geology;
Tarim Craton; Yangtze Block』
1. Introduction
2. Precambrian geology of the North China Craton (NCC)
2.1. Tectonic subdivision of the NCC
2.2. Eastern block
2.3. Western block
2.4. Trans-North China Orogen
2.5. Paleo-Neoproterozoic unmetamorphosed rock assemblages in
the NCC
3. Precambrian geology of the South China Craton
3.1. Yangtze Block
3.1.1. Archean-Paleoproterozoic crystalline basement in the
Yangtze Block
3.1.2. Late Mesoproterozoic to early Neoproterozoic folded belts
in the Yangtze Block
3.1.2.1. Jiangnan Belt
3.1.2.2. Panxi-Hannan Belt
3.1.3. Tectonic models for late Mesoproterozoic to early Neoproterozoic
folded belts in the Yangtze Block
3.2. Cathaysia Block
3.2.1. Archean crustal record in Cathaysia
3.2.2. Paleoproterozoic basement in Cathaysia
3.2.3. Mesoproterozoic basement in Cathaysia
3.2.4. Neoproterozoic basement in Cathaysia
3.2.5. Tectonic nature of early Paleozoic metamorphic event
in Cathaysia
3.3. Where, when and how did Yangtze and Cathaysia collided to
form the Jiangnan Belt?
3.3.1. Where is the suture zone in the Jiangnan Belt?
3.3.2. When did collision between the Yangtze and Cathaysia
blocks occur?
3.3.3. How did the Yangtze and Cathaysia blocks collided to
form the Jiangnan Orogen?
4. Precambrian geology of the Tarim Craton
4.1. Archean basement of the Tarim Craton
4.2. Paleoproterozoic magmatic events in the Tarim Craton
4.3. Later Mesoproterozoic to Neoproterozoic metamorphosed strata
in the Tarim Craton
4.4. Middle Neoproterozoic unmetamorphosed rocks in the Tarim
Craton
5. Summary
Acknowledgements
References
Fig. 1. Schematic tectonic map of China showing the major Precambrian blocks connected by Phanerozoic fold belts (Zhao et al., 2001a). Zhao and Cawood(2012)による『Precambrian geology in China』から |