How is Jade Formed
(Image Credits: Field and raw jade photos: courtesy of George Harlow and colleagues)
The formation conditions of jade are extremely special and complicated. Most of them come from the molten magma at a depth of tens of kilometers underground. This high-temperature slurry rushes from the underground along the cracks to the surface of the earth, and after cooling, it becomes a hard rock. In this process, only certain elements slowly crystallize into hard jade or gems, and their formation time is very far away from us.
The process of jade formed can be divided into the following 4 important periods according to the sequence:
1. The depositional stage of dolomite
In the late Mesoproterozoic (about more than a billion years ago), the southern margin of the Tarim ancient land, which is where the northern margin of the Kunlun Mountains is today, was once a shallow sea area with a large number of carbonate deposits, among which the dolomite containing magnesium is one of the main material sources of jade.
2. The metamorphic stage of jade in the dolomite area
In the Sinian period at the end of the Proterozoic, the Tarim movement caused strong folds and faults in the whole area, which finally formed the Tarim continent. In extensive regional metamorphism, dolomite is metamorphosed into dolomite marble. Since then, the landmasses in this area have uplifted and become one of the earliest land exposed to the sea in my country, and there is no original layer of sediment covering it.
3. Metasomatic alteration stage of dolomite
More than 200 million years ago, from the late Paleozoic to the late Carboniferous to the Late Permian, a worldwide crustal movement occurred, which was called the Valissian movement. In the late Valissian period, on the southern margin of the Tarim continent, there were strong faults and magmatism in the continental margin of the ancient land block and the middle block of the active zone. The intermediate-acid intrusive rocks intruded into the dolomite marble along the fault zone. After the remaining dolomite marble traps or tongue-like bodies on the top of the intrusions are in contact with the magma intrusions and hydrothermal fluids, they will form diopside, forsterite, and tremolite, which become one of the material conditions for jade formation.
4. The stage of becoming jade
When the shallow intermediate-acid dikes derived from the late Valissian intrusions intrude into the dolomite marble alteration zone, contact metasomatism occurs again. Under appropriate geological conditions (about 300350 degrees Celsius, 2.5 kbar or less and a certain torsional compression Under stress), Hetian jade finally formed.
The above four stages can be summarized as follows:
- A. Late Mesoproterozoic continental margin marine sediments/sedimentary dolomites (one of the sources of jade-forming materials)
- B. Tarim movement at the end of the Proterozoic, regional metamorphism/Dolomite metamorphism into dolomite marble (material structure of jade. Transformation)
- C. The mid-acid intrusive activity in the late Valissian period, contact metasomatism/formation of dolomite marble alteration zone (material basis for jade formation)
- D. In the late Valissian period, the contact metasomatism of the intermediate-acid dikes derived from the intrusive body/the formation of the King of Hetian