Definition of North China craton

The North China craton (NCC) occupies

about one million square miles (1.7 million km2) in northeastern

China, Inner Mongolia, the Yellow Sea, and North

Korea. It is bounded by the Qinling–Dabie Shan orogen to the

south, the Yinshan-Yanshan orogen to the north, the Longshoushan

belt to the west and the Qinglong-Luznxian and Jiao-

Liao belts to the east. The North China craton includes a large

area of intermittently exposed Archean crust, including circa

3.8–2.5 billion-year-old gneiss, tonalite, trondhjemite, and granodiorite.

Other areas include granite, migmatite, amphibolite,

ultramafite, mica schist and dolomitic marble, graphitic and

sillimanitic gneiss (khondalites), banded iron formation (BIF),

and metaarkose. The Archean rocks are overlain by the

1.85–1.40 billion-year-old Mesoproterozoic Changcheng

(Great Wall) system. In some areas in the central part of the

North China Craton, 2.40–1.90 billion-year-old Paleoproterozoic

sequences deposited in cratonic graben are preserved.

The North China craton is divided into two major

blocks separated by the Neoarchean Central orogenic belt in

which virtually all U-Pb zircon ages fall between 2.55 billion

and 2.50 billion years old. The Western block, also known as

the Ordos block, is a stable craton with a thick mantle root,

no earthquakes, low heat flow, and a lack of internal deformation

since the Precambrian. In contrast, the Eastern block

is atypical for a craton in that it has numerous earthquakes,

high heat flow, and a thin lithosphere reflecting the lack of a

thick mantle root. The North China craton is one of the

world’s most unusual cratons in that it had a thick tectosphere

(subcontinental lithospheric mantle) developed in the

Archean, which was present through the Ordovician as

shown by deep xenoliths preserved in Ordovician kimberlites.

However, the eastern half of the root appears to have delaminated

or otherwise disappeared during Paleozoic, Mesozoic,

or Cenozoic tectonism. This is demonstrated by Tertiary

basalts that bring up mantle xenoliths of normal “Tertiary

mantle” with no evidence of a thick root. The processes

responsible for the loss of this root are enigmatic but are

probably related to the present-day high-heat flow, Phanerozoic

basin dynamics, and orogenic evolution.

The Central orogenic belt includes belts of tonalite-trondhjemite-

granodiorite, granite, and supracrustal sequences

metamorphosed from granulite to greenschist facies. It can be

traced for about 1,000 miles (1,600 km) from west Liaoning

to west Henan. Widespread high-grade regional metamorphism

including migmatization occurred throughout the Central

orogenic belt between 2.6 billion and 2.5 billion years

ago, with final uplift of the metamorphic terrain at 1.9–1.8

billion years ago associated with extensional tectonism or a

collision on the northern margin of the craton. Amphibolite to

greenschist-grade metamorphism predominates in the southeastern

part of the Central orogenic belt, but the northwestern

part of the orogen is dominated by granulite facies to amphibolite

facies rocks, including some high-pressure assemblages

(10–13 kilobars at 850±50°C). The high-pressure assemblages

can be traced for more than 400 miles (700 km) along a linear

belt trending east-northeast. Internal (western) parts of the

orogen are characterized by thrust-related horizontal foliations,

flat-dipping shear zones, recumbent folds, and tectonically

interleaved high-pressure granulite migmatite and

metasediments. It is widely overlain by sediments deposited in

graben and continental shelf environments and intruded by

several dike swarms (2.4–2.5 billion and 1.8–1.9 billion years

ago). Several large anorogenic granites with ages of 2.2–2.0

billion years are identified within the belt. Recently, two linear

units have been documented within the belt, including a highpressure

granulite belt in the west and a foreland-thrust fold

belt in the east. The high-pressure granulite belt is separated

by normal-sense shear zones from the Western block, which is

overlain by thick metasedimentary sequences (khondalite,

younger than 2.4 billion years, and metamorphosed at 1.86

billion years).

The Hengshan high-pressure granulite belt is about 400

miles (700 km) long, consisting of several metamorphic terrains,

including the Hengshan, Huaian, Chengde, and west

Liaoning complexes. The high-pressure assemblages commonly

occur as inclusions within intensely sheared tonalitetrondhjemite-

granodiorite (2.6–2.5 billion years) and granitic

gneiss (2.5 billion years) and are widely intruded by K-granite

(2.2–1.9 billion years) and mafic dike swarms (2.40–2.45 Ga,

1.77 billion years). Locally, khondalite and turbiditic slices

are interleaved with the high-pressure granulite rocks, suggesting

thrusting. The main rock type is garnet-bearing mafic

granulite with characteristic plagioclase-orthopyroxene corona

around the garnet, which show rapid exhumation-related

decompression. An isothermal decompressive pressure-temperature-

time path can be documented within the rocks, and

the peak pressures and temperatures are in the range of

1.2–1.0 GPa, at 1,290°F–1,470°F (700°C–800°C). At least

three types of geochemical patterns are shown by mafic

rocks of the high-pressure granulites, indicating a tectonic

setting of active continental margin or island arc. The highpressure

granulites were formed through subduction-collision,

followed by rapid rebound-extension, recorded by

2.5–2.4 billion-year-old mafic dike swarms and graben-related

sedimentary sequences in the Wutai Mountain–Taihang

Mountain areas.

The Qinglong foreland basin and fold-thrust belt is

north to northeast-trending and is now preserved as several

relict folded sequences (Qinglong, Fuping, Hutuo, and

Dengfeng). Its general sequence from bottom to top can be

further divided into three subgroups of quartzite-mudstonemarble,

turbidite, and molasse, respectively. The lower subgroup

of quartzite-mudstone-marble is well preserved in

central sections of the Qinglong foreland basin (Taihang

Mountain), with flat-dipping structures, interpreted as a passive

margin developed prior to 2.5 Ga on the Eastern block.

It is overlain by lower grade turbidite and molasse type sediments.

The western margin of Qinglong foreland basin is

intensely reworked by thrusting and folding and is overthrust

by the overlying orogenic complex (including the

tonalitic-trondhjemitic-granodiorotic gneiss, ophiolites, accretionary

sediments). To the east its deformation becomes

weaker in intensity. The Qinglong foreland basin is intruded

by a gabbroic dike complex consisting of 2.4 billion-year-old

diorite and is overlain by graben-related sediments and flood

basalts. In the Wutai and North Taihang basins, many ophiolitic

blocks are recognized along the western margin of the

foreland thrust-fold belt. These consist of pillow lava, gabbroic

cumulates, and harzburgite. The largest ophiolitic

thrust complex imbricated with foreland basin sedimentary

rocks is up to five miles (10 km) long, preserved in the

Wutai-Taihang Mountains.

Several dismembered Archean ophiolites have been identified

in the Central orogenic belt, including some in Liaoning

Province, at Dongwanzi, north of Zunhua, and at Wutai

Mountain. The best studied of these are the Dongwanzi and

Zunhua ophiolitic terranes. The Zunhua structural belt of

the Eastern Hebei Province preserves a cross section through

most of the northeastern part of the Central orogenic belt.

This belt is characterized by highly strained gneiss, banded

iron formation, 2.6–2.5 billion-year-old greenstone belts and

mafic to ultramafic complexes in a high-grade ophiolitic

melange. The belt is intruded by widespread 2.6–2.5 billionyear-

old tonalite-trondhjemite gneiss, 2.5 billion-year-old

granites, and is cut by ductile shear zones. The Neoarchean

high-pressure granulite belt (Chengde-Hengshan HPG)

strikes through the northwest part of the belt. The Zunhua

structural belt is thrust over the Neoarchean Qianxi-Taipingzhai

granulite-facies terrane, consisting of enderbitic to

charnockitic gneiss forming several small dome-like structures

southeast of the Zunhua belt. The Zunhua structural

belt clearly cuts across the dome—like Qian’an-Qianxi structural

patterns to the east. The Qian’an granulite-gneiss dome

(3.8–2.5 billion years old) forms a large circular dome in the

southern part of the area and is composed of tonalitic-trondhjemitic

gneiss and biotite-granite. Mesoarchean (2.8–3.0 billion

years old) and Paleoarchean (3.50–3.85 billion years

old) supracrustal sequences outcrop in the eastern part of the

region. The Qinglong Neoarchean amphibolite to greenschist

facies supracrustal sequence strikes through the center of the

area and is interpreted to be a foreland fold-thrust belt,

intruded by large volumes of 2.4 billion-year-old diorite in

the east. The entire North China craton is widely cut by at

least two Paleoproterozoic mafic dike swarms (2.5–2.4 and

1.8–1.7 billion years old), associated with regional extension.

Mesozoic-Cenozoic granite, diorite, gabbro, and ultramafic

plugs occur throughout the NCC and form small intrusions

in some of the belts.

The largest well-preserved sections of the Dongwanzi

ophiolite are located approximately 120 miles (200 km)

northeast of Beijing in the northeastern part of the Zunhua

structural belt, near the villages of Shangyin and Dongwanzi.

The belt consists of prominent amphibolite-facies mafic-ultramafic

complexes in the northeast sector of Zunhua structural

belt. The southern end of the Dongwanzi ophiolite belt near

Shangyin is complexly faulted against granulite-facies gneiss,

with both thrust faults and younger normal faults present.

The main section of the ophiolite dips steeply northwest, is

approximately 30 miles (50 km) long, and is 3–6 miles (5–10

km) wide. A U/Pb-zircon age of 2.505 billion years for two

gabbro samples from the Dongwanzi ophiolite shows that

this is the oldest, relatively complete ophiolite known in the

world. However, parts of the central belt are intruded by a

mafic/ultramafic Mesozoic pluton with related dikes.

The base of the ophiolite is strongly deformed and is

intruded by the 2.391 billion-year-old Cuizhangzi dioritetonalite

complex. The Dongwanzi ophiolite is associated with

a number of other amphibolite-facies belts of mafic plutonic

and extrusive igneous rocks in the Zunhua structural belt.

These mafic to ultramafic slices and blocks can be traced

regionally over a large area from Zunhua to West Liaoning

(about 120 miles or 200 km). Much of the Zunhua structural

belt is interpreted as a high-grade ophiolitic mélange, with

numerous tectonic blocks of pillow lava, BIF, dike complex,

gabbro, dunite, serpentinized harzburgite, and podiform

chromitite in a biotite-gneiss matrix, intruded extensively by

tonalite and granodiorite. Cross-cutting granite has yielded

an age of 2.4 billion years. Blocks in the mélange correlate

with the Dongwanzi and other ophiolitic fragments in the

Zunhua structural belt. This correlation is supported by Rhenium-

Osmium (Re-Os) age determinations on several of these

blocks, revealing that they are 2.54 Ga old.

The Eastern and Western blocks of the North China craton

collided at 2.5 billion years ago during an arc/continent

collision, forming a foreland basin on the Eastern block, a

granulite facies belt on the Western block, and a wide orogen

between the two blocks. This collision was followed rapidly

by post-orogenic extension and rifting that formed mafic dike

swarms and extensional basins along the Central orogenic

belt and led to the development of a major ocean along the

north margin of the craton. An arc terrane developed in this

ocean and collided with the north margin of the craton by

2.3 Ga, forming an 850-mile (1,400-km) long orogen known

as the Inner Mongolia–Northern Hebei orogen. A 1,000-mile

(1,600-km) long granulite-facies terrain formed on the southern

margin of this orogen, representing a 120-mile (200-km)

wide uplifted plateau formed by crustal thickening. The orogen

was converted to an Andean-style convergent margin

between 2.20 billion and 1.85 billion years ago, recorded by

belts of plutonic rocks, accreted metasedimentary rocks, and

a possible back arc basin. A pulse of convergent deformation

is recorded at 1.9–1.85 billion years across the northern margin

of the craton, perhaps related to a collision outboard of

the Inner Mongolia–Northern Hebei orogen and closure of

the back arc basin. This event caused widespread deposition

of conglomerate and sandstone of the basal Changcheng

Series in a foreland basin along the north margin of the craton.

At 1.85 billion years the tectonics of the North China

craton became extensional, and a series of aulacogens and

rifts propagated across the craton, along with the intrusion of

mafic dike swarms. The northern granulite facies belt underwent

retrograde metamorphism and was uplifted during

extensional faulting. High-pressure granulites are now found

in the areas where rocks were metamorphosed to granulite

facies and exhumed two times, at 2.5 billion and 1.8 billion

years ago, exposing rocks that were once at lower crustal levels.

Rifting led to the development of a major ocean along the

southwest margin of the craton, where oceanic records continue

until 1.5 billion years ago.

See also ARCHEAN; OPHIOLITES.

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