Zhao,G. and Cawood,P.A.(2012): Precambrian geology of China. Precambrian Research, 222-223, 13-54

『中国の先カンブリア時代の地質』


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


戻る