Confession of Wugong Mountain: What kind of geological changes have I experienced when I was born 800 million years ago?

Speaking of Wugong Mountain, we may know that it is located in Jiangxi Province and is a national 5A-level tourist attraction. The main peak of Wugong Mountain, Baihe Peak (Jinding), is the highest peak in Jiangxi Province. It is famous for its four-layer three-dimensional geological landscape, including alpine meadows, peak forests and steep cliffs, steep slope waterfalls, low hills and hot spring chains. However, we may not know how such a unique geological landscape of Wugong Mountain was formed. Today, we will travel through the long river of geological time and space, return to the Proterozoic Era, and see the vicissitudes of the earth through the past and present of Wugong Mountain.

The interior of the earth is not uniform. In the long time since the formation of the earth, multiple layers have been formed inside the earth. The structure of the earth's interior can be likened to a boiled egg. The yolk in the center is the "core", the egg white wrapped around the yolk is the "mantle", and the outermost eggshell is equivalent to the "crust". Although the mantle is solid, it can move extremely slowly. The hot rocks deep in the earth become lighter after heating, slowly rise, and reach the shallow part of the earth. The crust "floats" on the mantle like a thin plate. During the movement of continental plates/oceanic plates, due to compression or tension, they collide or split at their edges or inside, forming ridges, rift valleys, trenches, archipelagos, mountains, etc.

The Earth has a history of 4.6 billion years since its formation. This 4.6 billion-year history is divided into several geological eras: Hadean (4.6 billion years ago to 4 billion years ago), Archean (4 billion years ago to 2.5 billion years ago), Proterozoic (2.5 billion years ago to 541 million years ago), and Phanerozoic (541 million years ago to the present). Wugong Mountain in the Paleozoic Era: from the Cambrian to the Permian.

Our story starts from the Proterozoic Eon. 800-570 million years ago, due to the collision between the Yangtze and Cathaysia landmasses, the Wugongshan area was in a deep-sea-sub-deep-sea environment. At that time, the entire Earth was in the "Snowball Earth" ice age.

About 500 million years ago, the Earth, which had experienced a "cold winter", ushered in the Cambrian "explosion" of life. Due to the rise of the earth's crust, the sea water was relatively shallow, and the Wugong Mountain area was in a shallow sea-continental slope environment. At this time, the depth and temperature of the sea water were very suitable for the reproduction of ancient marine life, and the Wugong Mountain area opened up a paradise for marine animals and the era of trilobites. After these animals died, their remains were preserved in the Cambrian sedimentary strata of the shallow sea-continental slope phase to form fossils.

450 million years ago, after nearly 100 million years of stable sedimentation, the thickness of the Cambrian strata reached about 2,000 meters. At this time, the Cathaysia Plate in the area was in a compression tectonic environment, and the weak Cambrian strata were folded and deformed (rock strata bend under the action of tectonic movement, and a bend is called a fold. If a series of wavy bending deformations occur, it is called a fold). At the same time, the deep earth also became unstable, and the molten magma in the deep welled up, pushing up the Cambrian strata into an arch. As the magma continued to well up, the strata were lifted higher and higher and exposed to the sea surface.

However, the force of the magma failed to pass through the folded and thickened Cambrian strata to reach the surface, and the deep magma gradually calmed down and cooled and condensed, forming Silurian granite. At this moment, the shape of the Wugongshan area is like the "bump" on the skin caused by mosquito bites.

We can't help but ask, why did the "bulge" form here, and where did this "bulge" go afterwards? Then let's get on the spaceship again and start the journey of time, going back to about 900 million years ago. The collision between the Yangtze Block and the Cathaysia Block was mentioned earlier. After the collision, the two continental blocks will be spliced ​​together. The narrow strip of land spliced ​​together is geologically called a suture zone, or a tectonic zone, just like a zipper on clothes, which combines the two continental blocks into a larger plate, the Cathaysia Plate. When clothes are worn for a long time, in most cases, the first place to be damaged is the zipper or near the zipper, and the same is true for the plate. The area where Wugong Mountain is located is located near the ancient suture zone. As a structural weak point inside the plate, the suture zone is very easy to rise along this part when the plate is squeezed or stretched. This is also the reason why the "bulge" was formed in the area in the Silurian period.

After being squeezed, the plate is often accompanied by long-term tension, just like a spring, which is compressed and then released. At a certain stage, it will become more slender than before compression. In the next 250 million years, the area was first submerged by the ocean again, and the Devonian system (about 420 million years ago-360 million years ago) was deposited in the marine-shallow marine phase, followed by hundreds of millions of years of Carboniferous, Permian, and Triassic coastal-shallow marine phases.

These things happened billions of years ago. How do geologists know that it was a change in the sedimentary environment from land to coastal to shallow sea? The mystery is largely due to paleontology. There are various animal and plant fossils in the strata, and the growth environment of these ancient organisms represents the sedimentary environment at that time. In the late Paleozoic era, there were large tracts of lush forests growing on land, and primitive ferns could be as high as 30 meters, equivalent to the height of a 10-story building.

In the forest lived giant dragonflies, with wingspans of more than 70 centimeters, which was several dozen centimeters wider than the wingspan of today's pigeons. In addition, in the shallow sea lived fish with scales more than 1 meter long, as well as brachiopods, corals and other animals. After all, these animals and plants have their own specific survival periods. By identifying different combinations of animal and plant fossils in the strata, we can not only determine the sedimentary environment of the strata, but also determine the formation era of the strata.

The good times did not last long, only about 200 million years, until the Late Triassic (about 230 million years ago), when "the wind blows north and the plate drifts north". Of course, the northward sea breeze was not enough to drive the Huaxia Plate to move northward, but the north-south compression stress field. The Huaxia Plate encountered the obstruction of the huge and stable Yangtze Plate to the north, and this collision lasted for hundreds of millions of years. The weak strata wrinkled and arched again, struggling to stand up from the sea, fell, stood up again, fell again, and stood up again, opening the Late Triassic-Early Jurassic marine-continental interphase deposition.

The long-planned deep magma surged up again, shaking the earth for a while. The South China Dragon said to the Jiangxi Dragon: "Let's run quickly, otherwise the volcano will erupt!" This run lasted for 30 million years. During this period, the volcano did not erupt. The Jurassic magma only invaded the Silurian granite and failed to reach the surface. They just slid from the slope of Wugong Mountain to the foot of the mountain. However, this slide detached the sedimentary strata covering the rock mass along the fault.

In the early Cretaceous period (about 140 million years ago), the intrusion of magma and the uplift of the mountain caused another earthquake. The South China Dragon said to the Jiangxi Dragon: "Let's run quickly, or the volcano will erupt!" This run lasted for 80 million years. During this period, the volcano did not erupt again. They just fell into the joints and cracks of the Jurassic granite again and again. They struggled to climb out of the joints, kicked the granite angrily, and ran away. Little did they know that this kick would add another set of vertical joints to the granite. Joints are a very common tectonic geological phenomenon, which are the cracks we see on rock outcrops, or rock cracks.

One day 66 million years ago, the ground shook again, and the mountains trembled again. The South China Dragon said to the Jiangxi Dragon: "Let's run quickly, or the volcano will erupt!" This time, they failed to run away. Far across the ocean in Mexico, an asteroid with a diameter of about 10,000 meters fell from the sky and hit the Yucatan Peninsula. The thick cloud of toxic gas and dust formed by the impact covered the sky for several years. The South China Dragon and the Jiangxi Dragon starved to death in Yichun, and the dinosaurs became extinct.

Near the southwest edge of the Eurasian Plate, the Indian Plate gradually approached and collided, and the Earth entered the vigorous Himalayan period, forming the world's tallest and most majestic mountain system - the Himalayas and the world's highest peak - Mount Everest. Affected by the collision, the South China Plate (called the South China Plate after the collision and splicing of the Yangtze Plate and the Huaxia Plate) was squeezed in an east-west direction, and Wugong Mountain further rose to an altitude of about 2,000 meters. After that, external forces gradually prevailed (geological forces can be divided into internal forces and external forces according to the source of energy. Internal forces are divided into crustal movement, magmatic activity and metamorphism; external forces are mainly weathering, erosion, transportation, etc.). The soil formed after the weathering of the Silurian granite on the top of the mountain is suitable for the growth of herbaceous plants, thus forming an alpine meadow; the Jurassic granite on the mountainside is controlled by two sets of vertical joints, and weathering and erosion form steep cliffs; the granite on the hillside becomes high, steep and slippery due to uplift, faults and erosion, thus forming steep slope waterfalls; near the fault zone at the foot of the mountain, atmospheric precipitation that penetrates into the ground along the faults absorbs deep heat rising along the faults to become hot water, and then rises along the faults to reach the surface to form a hot spring chain around Wugong Mountain.

The Himalayas are folded mountains formed by the collision of two continental plates, but Wugong Mountain is a dome mountain formed by the orogenic belt within the plate - the Wugong Mountain granite dome. (Some pictures are from the Internet)