Lithospheric mantle density structure of the North China Craton

Earth and Planetary Science Letters, 2002

Re^Os data for peridotite xenoliths carried in Paleozoic kimberlites and Tertiary alkali basalts confirm previous suggestions that the refractory and chemically buoyant lithospheric keel present beneath the eastern block of the North China craton (and sampled by Paleozoic kimberlites) is indeed Archean in age and was replaced by more fertile lithospheric mantle sometime after the Paleozoic. Moreover, lithospheric mantle beneath the central portion of the craton (west of the major gravity lineament) formed during the last major Precambrian orogeny, around 1900 Ma ago. This age is significantly younger than the overlying crust (2700 Ma), suggesting that the original Archean lithosphere was replaced in the Proterozoic. The timing of lithospheric replacement in the eastern block of the North China Craton is constrained only to the Phanerozoic by the Re^Os results. Circumstantial geologic evidence suggests this new lithosphere is Jurassic or Cretaceous in age and formed after collision of the Yangtze and North China cratons in the Triassic, an event that was also responsible for the subduction and uplift of ultrahigh-pressure metamorphic rocks. Collectively, these data suggest that lithosphere replacement occurred in response to two continent collisional events widely separated in time (V1900 and V220 Ma). Coupled with observations from other Archean cratons we suggest that wholesale replacement of lithospheric mantle ( þ lower crust) may require large-scale continental collision. ß

Journal of Earth Science, 2011

A detailed knowledge of the thickness of the lithosphere in the North China craton (NCC) is important for understanding the significant tectonic reactivation of the craton in Mesozoic and Cenozoic. We achieve this goal by applying the newly proposed continuous wavelet transform theory to the Gravity Field Model (EGM 2008) data in the region. Distinct structural variations are identified in the scalogram image of profile Alxa-Datong (大同)-Qingdao (青岛)-Yellow Sea (profile ABC), transversing the main units of NCC, which we interpret as mainly representing the Moho and lithosphereasthenosphere boundary (LAB) undulations. The imaged LAB is as shallow as 60-70 km in the southeast basin and coastal areas and deepens to no more than 140 km in the northwest mountain ranges and continental interior. A rapid change of about 30 km in the LAB depth was detected at around the boundary between the Bohai (渤海) Bay basin (BBB) and the Taihang (太行) Mountains (TM), roughly coincident with the distinct gravity decrease of more than 100 mGal that marks the North-South Gravity Lineament (NSGL) in the region. At last we present the gravity modeling work based on the spectral analysis results, incorporating with the observations on high-resolution seismic images and surface topography. The observed structural differences between the eastern and western NCC are likely associated with different lithospheric tectonics across the NSGL. Combined with seismic tomography results and geochemical and petrological data, this suggests that complex modification of the lithosphere probably accompanied significant lithospheric thinning during the tectonic reactivation of the old craton. KEY WORDS: EGM 2008 geopotential model, continuous wavelet transform, Bouguer gravity anomaly, constrained gravity field modeling, North China craton (NCC).

Journal of Geodynamics, 2010

We investigate the mantle dynamics beneath the North China Craton (NCC) and surrounding regions based on a synthesis of recent P-wave mantle tomographic data down to depths of 600–800km and their correlation with the surface geological features, with particular reference to the Paleoproterozoic tectonic events associated with the incorporation of the NCC within the Columbia supercontinent amalgam. From the tomographic images, we identify a hot corridor in the mantle transition zone beneath the central region of the Western Block of the NCC sandwiched between two cold corridors. This scenario is similar to the donut-shaped high-velocity anomaly surrounding a region of low-velocity anomaly in the lowermost mantle under the Pacific and suggests that the cold regions might represent slab graveyards which provide the fuel for the plumes rising from the center. A tomographic transect along the collisional suture of the NCC with the Columbia supercontinent, covering the Yinshan-Ordos Blocks in the Western Block through the Central Orogenic Belt and into the Eastern Block of the NCC reveals a ca. 250km thick lithospheric keel below the Ordos Block defined by a prominent high-velocity anomaly. We identify slab break-off and asthenospheric upwelling in this region and suggest that this process probably initiated the thermal and material erosion of the tectosphere beneath the Eastern Block from the Paleoproterozoic, which was further intensified during the Mesozoic when a substantial part of the sub-continental mantle lithosphere was lost. We visualize heat input from asthenosphere and interaction between asthenosphere and overlying carbonated tectosphere releasing CO2-rich fluids for the preservation of ultra-high temperature (ca. 1000 ◦C) metamorphic rocks enriched in CO2 as well as high-pressure mafic granulites as a paired suite in this region. We also identify a hot swell of the asthenosphere rooted to more than 200km depth and reaching up to the shallow mantle in the tomographic section along 35◦N latitude at a depth of 800 km. This zone represents a cross-section through the southern part of the NCC. The surface distribution of Paleoproterozoic Xiong’er lavas and mafic dykes in this region would indicate that this region might have evidenced similar upwellings in the past. Our study has important implications in understanding the evolution of the NCC and suggests that the extensive modification of the mantle architecture and lithospheric structure beneath one of the fundamental Precambrian nuclei of Asia had a prolonged history probably dating from the Paleoproterozoic suturing of the NCC within the Columbia supercontinent amalgam.

Contributions to Mineralogy and Petrology, 2019

The eastern North China Craton (NCC), where an initially diamondiferous deep cratonic mantle root was lost during Paleozoic and Mesozoic time, represents a prime natural laboratory to study the processes and mechanisms of continental lithospheric mantle destruction and replacement, which remain, however, controversial. In this study, detailed petrography, whole-rock and mineral compositions of spinel-facies peridotite xenoliths from Cenozoic basalts in the Huinan area, northeastern NCC, are presented to provide new constraints on the transformation of the subcontinental lithospheric mantle (SCLM). These xenoliths define two groups based on textural observation and mineral modes: Group 1 peridotites show protogranular textures and consist of harzburgites and dunites. They have low Al 2 O 3 contents in whole-rock and orthopyroxene (0.53-1.06 wt.% and 2.10-3.21 wt.%, respectively), high olivine modes (79-96%), whole-rock MgO (44.8-47.9 wt.%) and Mg# (100 Mg/(Mg + Fe T) molar: 90.1-90.7), suggesting that they were derived from moderately refractory SCLM. In contrast, Group 2 xenoliths display porphyroclastic to protogranular textures and consist of lherzolites and harzburgites with rare spinel-pyroxene intergrowths. They have overall higher Al 2 O 3 (1.48-3.23 wt.% and 3.02-4.65 wt.%, respectively) in wholerock and orthopyroxene, lower olivine modes (64-83%), MgO (38.6-44.5 wt.%) and whole-rock Mg# values 87.6-90.1, and they may represent fertile SCLM. Peridotites of both groups have similar equilibration temperatures (i.e., 923-977 °C and 881-1110 °C, respectively), which are not correlated with Mg# in olivines, suggesting that they coexist over a range of depths. However, clinopyroxenes in the Group 1 xenoliths display LREE-enriched and convex-upward REE patterns, whereas those in Group 2 mainly show LREE-depleted and spoon-shaped REE patterns, with minor LREE-enriched and convex-upward ones. In addition, spinel-pyroxene intergrowths indicative of garnet destabilization are ubiquitous in Group 1, consistent with variable Al 2 O 3 over a narrow range of Mg# in some opx and low HREE in some cpx, but rare in Group 2 peridotites. Interaction of the fertile mantle with melts similar to the Cenozoic basalts at high melt-rock ratios eradicated most signatures of their origin in the garnet stability field, whereas the refractory peridotites, which reacted with residual melts or fluids at low melt/fluid-rock ratios, retained evidence for the former presence of garnet. We suggest that, combined, these observations are best reconciled if portions of ancient refractory lithosphere, which were partly delaminated during multiple subduction episodes affecting the eastern NCC, were re-accreted together with fertile mantle during asthenospheric upwelling driven by extension.

Journal of Petrology, 2009

Gondwana Research, 2012

The structure and rheology of the lithosphere can provide constraints on our understanding of the geodynamic processes in the Earth's interior. The lateral heterogeneity of the strength and rheological structure of the lithosphere are closely correlated with the lateral variation in the thickness of the seismogenic layer. It is still unclear how geodynamic process(es) are linked with this lateral variation in the geophysical properties of the lithosphere. In order to understand the possible links between geodynamical process and lateral variation of lithosphere strength, we compiled crustal velocity and density structure, the elastic thickness of the lithosphere, and the temperature field, and then construct a northeast-southwest transect of the lithosphere across the eastern part of the North China Craton (NCC) with an overall length of 1660 km. Along the lithosphere-scale transect, we observe that (a) a thinner (80-120 km) Archean lithosphere at the North China Plain (NCP), (b) a lateral variation of the seismogenic brittle layer, which is about 15 km thick beneath the Qinling-Dabie orogenic belt (QDOB) and the Yanshan orogenic belt (YSOB), and about 25 km thick under the NCP. Together, these characteristics represent an excellent illustration of the scale of geodynamic processes necessary to accommodate lateral variations in lithospheric strength and the contribution of these to the mechanism of disruption of the Archean NCC. The thick seismogenic layer beneath the NCP can be formed due to: (1) deeper fault penetration beneath the NCP than beneath the QDOB and the YSOB; (2) the thick brittle layer is preserved after delamination of the lower part of the thickened crust; (3) thickening by changes to brittleness of the brittle/ductile transition layer (BDTL). With constraints of above mentioned geophysical properties of the lithosphere, we propose that (1) only the first and third processes can successfully explain the lateral variation of the thickness of the seismogenic layer across the eastern part of the NCC, and (2) the extensional tectonics and thermal erosion (notwithstanding the delamination of the lithosphere) play their significant roles in the disruption of the NCC.

Journal of Asian Earth Sciences, 2003

The Archean North China Craton consists of two major blocks, separated by the Central Orogenic Belt. The age of collision of the two blocks along the Central Orogenic Belt is controversial. Some models suggest that the Archean blocks collided at 1.8 Ga, during the Luliang Orogeny (1.7-1.9 Ga). In this model, high-pressure granulite facies metamorphism accompanied collision at 1.8 Ga. Other models have suggested that the Eastern and Western Blocks collided at 2.5 Ga, soon after 2.6 -2.5 Ga ophiolitic and arc rocks throughout the orogen were formed. We synthesize the geology, geochronology, and tectonics of the Neoarchean through Mesoproterozoic evolution of the North China Craton. We suggest that the Eastern and Western Blocks collided at 2.5 Ga 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 a 1400 km long orogen known as the Inner Mongolia -Northern Hebei Orogen. A 1600 km long granulite-facies terrain formed on the southern margin of this orogen, representing a 200 km wide uplifted plateau formed by crustal thickening. The orogen was converted to an Andean-style convergent margin between 2.20 and 1.85 Ga, 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 Ga 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 basel Changcheng Series in a foreland basin along the north margin of the craton. At 1.85 Ga 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 and 1.8 Ga, 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 Ga.

Geological Society, London, Special Publications, 2007

The North China Craton contains one of the longest, most complex records of magmatism, sedimentation, and deformation on Earth, with deformation spanning the interval from the Early Archaean (3.8 Ga) to the present. The Early to Middle Archaean record preserves remnants of generally gneissic meta-igneous and metasedimentary rock terranes bounded by anastomosing shear zones. The Late Archaean record is marked by a collision between a passive margin sequence developed on an amalgamated Eastern Block, and an oceanic arc-ophiolitic assemblage preserved in the 1600 km long Central Orogenic Belt, an Archaean-Palaeoproterozoic orogen that preserves remnants of oceanic basin(s) that closed between the Eastern and Western Blocks. Foreland basin sediments related to this collision are overlain by 2.4 Ga flood basalts and shallow marine-continental sediments, all strongly deformed and metamorphosed in a 1.85 Ga Himalayan-style collision along the northern margin of the craton. The North China Craton saw relative quiescence until 700 Ma when subduction under the present southern margin formed the Qingling-Dabie Shan-Sulu orogen (700-250 Ma), the northern margin experienced orogenesis during closure of the Solonker Ocean (500-250 Ma), and subduction beneath the palaeo-Pacific margin affected easternmost China (200-100 Ma). Vast amounts of subduction beneath the North China Craton may have hydrated and weakened the subcontinental lithospheric mantle, which detached in the Mesozoic, probably triggered by collisions in the Dabie Shan and along the Solonker suture. This loss of the lithospheric mantle brought young asthenosphere close to the surface beneath the eastern half of the craton, which has been experiencing deformation and magmatism since, and is no longer a craton in the original sense of the word. Six of the 10 deadliest earthquakes in recorded history have occurred in the Eastern Block of the North China Craton, highlighting the importance of understanding decratonization and the orogen-craton-orogen cycle in Earth history.

Physics of the Earth and Planetary Interiors, 2006

We invert for the upper-mantle temperatures of the Chinese continent in the depth range of 70-240 km from a recent S-velocity model. The depth where temperatures intersect a mantle adiabat with a potential temperature of ∼1300 • C is in close correspondence with the top of the seismic low velocity zone for most regions. This correspondence implies that seismic lithosphere estimated from short-time scale seismic information may be equivalent to the long-time scale geodynamical lithosphere. Defining the 1300 • C adiabat as coinciding with the lithospheric base, we estimate the seismic-thermal lithosphere thickness. The estimated thickness shows obvious dependence on the tectonic settings. Beneath eastern China, which mainly belongs to the circum-Pacific tectonic domain, it has a thickness of ∼100 km; and beneath the Qinghai-Tibet plateau and south to the Tarim craton, which belong to the Tethyan tectonic domain it has a thickness of ∼160-220 km. The lithospheric thicknesses of the three large para-platforms/cratons range from ∼170 km for the western Yangtze, ∼140 km for Tarim, and ∼100 km for Sino-Korean. The three cratons may have been reshaped by Phanerozoic tectonic activities and are thinner than most cratons in other continents.

Gondwana Research, 2013

The North China Craton (NCC) consists of Archean to Paleoproterozoic basement overlain by Mesoproterozoic to Cenozoic cover. Minor Eoarchean to Mesoarchean basement rocks are locally present in the eastern part of the NCC, but little is known about their extent, nature and tectonic evolution due to widespread reworking by later events. The Neoarchean basement in the NCC was formed during two distinct periods: 2.8-2.7 Ga and 2.6-2.5 Ga, of which the former is considered as a major period of juvenile crustal growth in the NCC as evidenced by Nd and zircon Hf isotopic data, though the 2.8-2.7 Ga rocks are not widely exposed. The 2.6-2.5 Ga rocks make up~80% of the Precambrian basement of the NCC and can be divided into high-grade gneiss complexes and lowto medium-grade granite-greenstone belts that are widespread over the whole NCC, seeming to support a notion that the cratonization of the NCC occurred at~2.5 Ga. However, the 2.6-2.5 Ga rocks in the eastern and western parts of the NCC (Eastern and Western Blocks) are different from those similar-aged rocks in the central part (Trans-North China Orogen), with the former dominated by gneiss domes and metamorphosed at~2.5 Ga, characterized by anticlockwise P-T paths involving isobaric cooling, reflecting an origin related to the underplating of mantle-derived magmas, whereas the latter, which are defined by strike-slip ductile shear zones, large-scale thrusting and folding, and transcurrent tectonics locally with sheath folds, were metamorphosed at~1.85 Ga, characterized by clockwise P-T paths involving isothermal decompression, consistent with subduction and continent-continent collision settings. In addition, komatiites/komatiitic rocks are present in the granitegreenstone belts in the eastern and western parts of the NCC, but generally are absent in the central part. These differences imply that the 2.6-2.5 Ga basement rocks in the eastern and western parts of the NCC formed under different tectonic settings from those in the central part. Although both magmatic arc and mantle plume models can be used to explain the tectonic setting of the 2.6-2.5 Ga basement rocks in the eastern part of the NCC, a mantle plume model is favored as it can reasonably interpret: (1) the exceptionally large exposure of granitoid intrusions that formed over a short time period (2.55-2.50 Ga), without systematic age progression across a~800 km wide block; (2) generation of komatiitic magmas with eruption temperatures as high as 1650°C;