Jack Hills
| Jack Hills | |
|---|---|
 Physical card |
|
.jpg) Satellite image ( Landsat 5 , true color) |
|
| Highest peak | Mount Hale ( 697 m ) |
| location | Western Australia |
| Coordinates | 26 ° 7 ′ S , 117 ° 9 ′ E |
| Type | Rump Mountains |
| rock | Metasediments |
| Age of the rock | Paleoarchean |
| particularities | contains the oldest known geological evidence of the early "primeval earth" |
The Jack Hills are a mountain range up to approximately 700 meters above sea level ( AHD ) in the Mid-West region of Western Australia . In the archaic rocks that there are pending that were previously oldest world were mineral found grains of earth. This more than 4000 million year old detrital zircons allow so-called geoarchives the reconstruction of geological processes in the Hadean , the earliest section of the Earth's history .
Geographical location and morphology
The Jack Hills are in the border area between the Shire of Murchison and the Shire of Meekatharra , about 800 kilometers north of Perth . They stretch for around 70 kilometers in a southwest-northeast direction between the Murchison River in the north and Whela Creek, a southern tributary of the Murchison, in the south.
The mountain range can be roughly divided into three morphologically relatively clearly separated sections: a southwest, a middle and a northeast. The middle section has both the largest area and the greatest terrain height. It increases in height to the northeast and forks into two approximately parallel ridges rising well over 500 meters above sea level (AHD). In the northwest of these two ridges is Mount Hale, the highest point in the Jack Hills. Its height is 697 meters above sea level. This corresponds to a height of around 300 to 350 meters above the surrounding area.
geology
Geologically, the Jack Hills belong to the Narryer Gneiss Terran and thus to the Yilgarn Craton in Western Australia. They are part of a belt of folds 80 kilometers long, trending in a northeast direction and made up of supracrustal metasediments .
The east-north-east trending and almost vertical metasediments consist mainly of siliciclastic rocks that are interpreted as alluvial fans or river deltas . This interpretation is based on repetitive layers of layers that become finer towards the hanging wall with a base conglomerate, medium-grain and finally fine-grain sandstone . Their degree of metamorphism can be assigned to the green schist to lower amphibolite facies based on the presence of andalusite , thistle and chloritoid . Mafic and ultramafic rocks as well as ribbon ores also occur subordinately . The metasediments are embedded in granulite facial gneisses that have been deformed and metamorphosed several times. The gneisses provide different educational ages, but are generally older than 3600 million years BP.
Detritic zircons
A number of detritic zircons more than 4,000 million years old have been discovered in the Jack Hills metasediments. On Erawandoo Hill even a crystal found with an age of 4404 ± 8 million years ago. The latter thus comes from the Jack Hillsium or the zirconium of the Hadaic era . The host rocks of the zircons are metaconglomerates , which are dated to around 3000 million years BP. Since the zircons are detritic, they must have been eroded from older precursor rocks before they were incorporated into the metaconglomerates.
Various geochemical parameters of the zircons provide evidence of the existence of a continental crust during the Hadaic era. This finding contradicts previous notions about the earliest part of the earth's history . The sometimes very high oxygen isotope ratios (δ 18 O to 7.5 ‰ SMOW - the earth's mantle value is 5.3 ‰ SMOW in comparison) in the zirconia show the presence of liquid water on the earth's surface and it is quite possible that this is possible At this point in time there was already a primeval sea. The theory wetter and cooler climatic conditions before the onset of major bombings is called Cool Early Earth ( Engl. Cool Early Earth or abbreviated CEE ).
Deposit
The band ores were mined as hematite- bearing iron ore and shipped via the port of Geraldton . The dismantling has now been stopped again.
Web links
Individual evidence
- ↑ AJ Cavosie, inter alia: Internal zoning and U-Th-Pb chemistry of Jack Hills detrital zircons: a mineral record of early Archean to Mesoproterozoic (4348-1576 Ma) magmatism . In: Precambrian Research . tape 135 , 2004, pp. 251-279 .
- ^ SA Wilde, RT Pidgeon: Geology of the Jack Hills Metasedimentary Rocks . In: SE Ho, et al. (Ed.): Proceedings of the Third International Symposium . University of Western Australia, Perth, WA 1990, p. 82-89 .
- ↑ SA Wilde, among others: Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago . In: Nature . tape 409 , no. 6817 , 2001, p. 175-178 .
- ↑ Rebecca Lindsey: Ancient Crystals Suggest Earlier Ocean . NASA Earth Observatory, 2006.
- ↑ JW Valley, among others: A cool early Earth . In: Geology . tape 30 , 2002, pp. 351-354 .