CN #1. Post - North China craton geology and mineralisation. Research using seismic tomography. For detailed paper see geotreks.com.au website

Paper 1. Pilot study of plan seismic tomography from 70 through 195 km depth, one EW, and two NS seismic tomographic sections. ? Bob Watchorn - August 2019.

1.   Summary

This paradigm changing pilot study research examines the structural geology of North China by comparing the surface geology, the plan tomography from 70 through 195 km depth, an EW and two NS tomographic sections with the lunar mares – they look identical! This suggests the craton is ~ 4 Ga in age and formed by impact during the Late Heavy Bombardment 

Mineralisation closely follows the boundary of the change between high and low velocity rocks. This suggests that the mineralisation source and control is mainly influenced by the lithosphere and not the crust as currently believed by most explorers.

2.   Interpreted seismic tomography from 70 through to 195 km depth

Interpreted structurally enhanced seismic tomography of the North China craton from 70 to 195 km depth. The grey areas represent the greater North China Hadean/Archaean Craton and the brown represents sediments and lavas entrained in the cratonic structure.

Note the concentric circular morphology that typifies an impact structure. This structure is 2000 km in diameter!

3.   Comparison of North China craton to the Lunar mares – probable genesis.

Concentric giant ring structures of a similar size and density to the Lunar mares were outlined by tomography from 70 to 195 km depth.

Comparison of North China cratons at 90 km depth with Lunar Mares. Interpreted North China cratons and Lunar craters (yellow) are of a similar size and density.

The largest impact structures (X and A) are 1000 – 2000km in diameter and form the core of the North China craton and the Lunar mare areas (with Australia superimposed for scale).

4.   Geochronology of the Lunar mares - its implication to the North China craton genesis and timing.

Structurally enhanced seismic tomography of the North China craton at ~ 90 km depth. The inset shows lunar mares and geochronology from NASA landing sites.

The moon mares were formed during and after the Late Heavy Bombardment (LHB) that engulfed the inner solar system from 4.1 – 3.8 Ga with more minor impacts through to 2.6Ga.

There was probably up to 100 km thickness of heavier mafic rocks extruded during the intense Late Heavy Bombardment (LHB) period. The LHB extended over 300 million years from > 4.1 – 3.8 Ga. Volcanism, vertical tectonics, Rayleigh–Taylor flow and subsequent (post Archaean) erosion would give great buoyancy to these cratons. It is suggested that most of the largest LHB impact created cratons still exist on Earth in the lithosphere because of this great buoyancy.

The YHR and SSR rifts (green), which are located in the annulus of giant ring structure X, may follow these Trans-Lithospherical structures and have a similar geochronology to the moon lavas. Plate tectonics didn't commence for another 1 billion years at ~2.6 Ga

5.   Interpreted seismic tomographic cross sections through the North China Craton - genesis and timing.

Structurally interpreted enhanced seismic tomographic sections A, B and C of the North China craton from the surface to 195 km depth. The original un-enhanced seismic tomography was from Wang et al. 2016.

The three tomographic cross-sections showed a series of stacked bowl-shaped structures which correspond to the giant ring structure rings on each plan level. Uplift dome structures occurred under the giant ring structure centres. These are ideal for mineralisation.

The timing of these structures is before the Hadean (> 4 Ga) based on their stratigraphic position beneath the crust and Moho. They most likely formed during the Late Heavy Bombardment (4.1 – 3.8 Ga). There has been no comparable world – wide, high density, giant ring structure forming event since that time.

6.   Interpreted Seismic tomographic plan at 90 km depth.

Enhanced Image of seismic tomography of upper-mantle shear velocity at 90 km beneath the North China craton and along section A-A’. The blue/grey areas represent the North China Craton.

The ring structure morphology, both in section and plan, is that of giant impact structures and the only period of dense impacts was the Late Heavy Bombardment from 4.1 – 3.8 Ga. All evidence points to their formation by LHB impacts. The lithosphere that they impacted into has to be older and would have formed between the separation of the Earth and moon at 4.5 Ga and the earliest LHB impacts at 4.1 Ga.

The ring structures however show no fragmentation (in plan or section) since their formation in the LHB. The GRS are still circular suggesting the Lithosphere at least has been rigid since ~ 3.8 Ga.

Interpreted enhanced seismic tomography cross sections A-A’, B-B’ and C-C’ of the North China continent from surface to 200 km depth (original data Wang et al. 2016). The plan shows the extent of the North China craton and the YHR and SSR rift systems at the surface.

The north China craton geochronology has been estimated as follows;

Plan. The North China craton surface Archaean crustal age ranges from 0.22 to ~ 2.6 Ga and forms a series of NS – NNE trending deformed orogens over the centre of the craton and approximately EW orogens on the north and south boundaries. The more upthrust areas in the east are the oldest. Conventional geology principles suggest that older lithologies lie underneath.

There are several circular topographical features in the NW of the craton corresponding with ring structures at the 90 km depth. The Huang He river follows the west and north boundary of giant ring structure X. The Huanglu Gaoyuan massif lies over the centre of X. This may be similar to the deeply buried giant ring structures in Australia that exert an influence on the surface geology right through to the present by Trans-Lithospherical structures. The centres are uplifted and the annulus is more fractured allowing magmatism up the fractures and more rapid erosion, forming basins and river systems, following the annulus.

Section. The seismic tomographic sections show the vertical Archaean geological structure and the probable geochronology of the geological layers in the crust and Lithosphere.

The above morphology strongly indicatives that the giant ring structures were formed by impacts during the LHB.

7. Mineralisation surface pattern Comparison of the surface mines with the geology at 70 km depth.

Enhanced Image of seismic tomography of upper-mantle shear velocity 70 km beneath the North China craton. The North China Craton interpretation is in yellow and the mines are shown.

A high percentage of the mines follow the boundary between the fast (dark grey) and slow Dark Brown/grey) lithologies in the lithosphere. This is also the case in Australia and North America and suggests the strong influence the lithosphere and giant ring structures have on mineralisation content and pathways. This concept has not been documented in the current research literature. This is an important paradigm change to use for exploration planning.