Exploring the secrets of Cenozoic continental plate activity in Xinjiang

1. The Tarim Basin has a long geological history

The Tarim Basin between the Tianshan Mountains and the Kunlun Mountains is the largest inland basin in my country. The Taklimakan Desert is located in the middle of the basin and is the largest mobile desert in my country and the second largest in the world (Figure 1-6-1). The Tarim River is about 2,100 kilometers long and is the longest inland river in my country (Figure 1-6-2).

The basement of the Tarim Basin is an ancient block composed of Precambrian crystalline rocks. It is called the Tarim Block, Tarim Platform, Tarim Craton, Tarim Block, etc. by scholars with different academic views. Since the Proterozoic Eon, the Tarim plate has experienced many ups and downs in the evolution of paleogeography. Among them, the Sinian, Silurian-Devonian, and Permian periods were generally in an ancient continent state and were the peak of the development of the Tarim ancient continent. period. During the Carboniferous, marine transgression occurred in the west, shrinking the scope of the ancient continent. In the Mesozoic Era, inland basins with varying ranges gradually appeared. During the Cretaceous Period, there was seawater intrusion at the southwest edge. Since the Cenozoic Era, with the uplift of the surrounding mountains, the Tarim Basin of today's scale has appeared.

The edge faults of the Tarim Basin are very developed. The vertical differential movement of the fault edge is very significant. Its fault width often reaches several thousand meters and decreases toward the east. In the Quaternary Period, the fault distance is generally 200 to 500 meters. Throughout the neotectonic period, with the strong collision of the Eurasian plate and the Indian plate The overall rise was another 600 to 1,000 meters. According to the differences in internal activities of Tarim, it can be further divided into five sub-units.

(1) Shaya Depression area. Located to the north of the Tarim River, Shayabei was the center of the depression during the Quaternary Period. The depression was 300 meters wide, and a small Quaternary dome-shaped uplift was found in it, reflecting the unevenness of the bottom of the depression itself. Drilling in 1984 confirmed that there was an ancient buried hill uplift in the area. This uplift was related to the current uplift of the Tarim Central Uplift, and caused the Tarim River to move more than 80 kilometers northward.

(2) Tarim central uplift area. It was caused by the re-uplift of the depression before the late Pliocene. The uplift amplitude is 800 meters and the altitude is 1560-1635 meters. This makes the Quaternary system in the surrounding areas of the exposed uplift of the Paleogene and Neogene systems of Rostag and Mazatag be thinner (only 20~40 meters). Like the strong uplift of the South Tianshan Mountains, there was magma and volcanic activity in the Maigaiti and Shakongkala Mountains during the Quaternary, and it is related to deep structures. It is a crustal uplift with a shell thickness of 42 kilometers.

(3) Lop Nur weak depression area. It is a depression that separates the uplift area of ??the Kuruktag and Altyn Fault Blocks. The maximum depression amplitude in the Quaternary is 60 meters. It is an approximately circular asymmetric depression. The depression is quite slow and looks like a helix when viewed from satellite images. It is also a 42-kilometer-thick crustal uplift.

(4) Yarkand strongly faulted area. In the late Miocene, the fault depression entered the continental sedimentation period from marine sedimentation. During the Pliocene, the fault width was 4000-5000 meters, during the Early Pleistocene, the fault width was 200-3400 meters, and since the middle Pleistocene, the fault width has been 50-900 meters. The Holocene fault width is only 5 to 10 meters. Since the Middle Pleistocene, the fault center has moved southeastward. With the strong uplift of the West Kunlun Mountains in the late Pliocene, this fault depression formed a series of anticline uplifts in the south of Yingjishan, southwest of Moyu, and south of Luopun, such as the Piyaman anticline.

(5) Qiemo fault depression area. It is a stepped fault depression. In the early Pleistocene, the fault width was 500 meters, and since the middle Pleistocene, the fault width has been 300 to 500 meters. It uplifted along with the fault block of the Altyn Mountains in the southeast, and also formed some new anticline uplifts in the east of Qiemo and west of Ruoqiang (such as the Jianggasayi anticline uplift).

Overview of the Tarim Basin, as previous people have said: "The foothills are rich in water and grass, livestock are everywhere, and the cultivated fields are like weaving. It is a quiet but busy production base for herdsmen, farmers, and weavers; Shuifeng Road on the edge of the basin The basin is adjacent to the basin and oases, and is densely populated; in the center of the basin is a saline-alkali land, a desert, and a sand sea, where drinking water is difficult and inaccessible. There are often violent storms, flying sand and rocks, and many historical monuments are submerged in it" (Lolan Kingdom, etc.).

2. The backbone of Central Asia - the ups and downs of the Tianshan Mountains

The Tianshan Mountains are a large mountain system in the hinterland of Central Asia, separating the two major basins of the Tarim and Junggar basins.

The mountain range extends from east to west for 2,500 kilometers, is 250 to 300 kilometers wide, and has an altitude of 3,000 to 5,000 meters. It is composed of a series of east-west broken mountains. The famous peaks include Tomur Peak (7443.8 meters) and Khan Tengri Peak (6995 meters). ) and Bogda Mountain (5445 meters). It is an ancient and young mountain range. The ancient Tianshan Mountains were formed as early as 300 million years ago. It was reduced by erosion to a 200-meter-high planar surface and numerous platforms of different sizes. Later, the neotectonic movement resurrected the faults and strongly uplifted them, forming the current layers of mountains. Intermountain basins and valleys formed by overlapping peaks, majestic and straight mountains and local collapse (Figure 1-6-3), such as Turpan Basin, Hami Basin, Ili Basin, etc. The lake level of Aydin Lake in the Turpan Basin is higher than the sea level. It is 154 meters lower and is the lowest point on land in my country.

The Tianshan Mountains have risen rapidly since the Neogene, with an amplitude of about 4,000 meters and a maximum height of 7,000 to 8,000 meters. The uplift amplitude since the Pleistocene has reached 1,000 to 2,000 meters. Due to the strong activity of active faults within the Tianshan Mountains, relative depressions occurred during the general uplift process. The Tianshan Mountains can be further divided into six sub-units.

(1) North Tianshan uplift. Refers to the Tianshan Mountains west of Urumqi and north of the Nalati active fault. The uplift amplitude during the neotectonic period is 2,000 to 2,500 meters. The amplitude of the uplift since the Pleistocene is generally 100 to 450 meters. The axis of the uplift is around the main peak of the Tianshan Mountains, and the degree of uplift gradually decreases toward the north, so the planation tilts gently towards the Junggar area. There are also three larger intermountain basins with very strong neotectonic activity. For example, the Ili River fault valley has a fault depth of 3,500 meters since the Neogene and 150 meters since the Pleistocene; Tekes -The fault amplitude of the Zhaosu Depression has been about 500 meters since the Neogene; the fault amplitude of the Bortala fault valley is generally only 50 to 60 meters, but in Lake Aibi, the maximum fault amplitude reaches 800 meters, and this It is only the extent of faulting since the Pleistocene.

Another important characteristic of neotectonic activity is high heat flow values. Along the active faults of southern Junggar Basin and Boroholo and other active fault depressions, at least 23 hot springs are exposed from Wenquan, Zhaosu and Tekes to Wusu, Shawan, Hutubi and Changji. The general temperature ranges from 33 degrees Celsius to 60 degrees Celsius, with the highest temperature reaching over 90 degrees Celsius. In addition, there are collapse structures, landslides, seismic cracks, etc. caused by large tilt-slip earthquakes. This area was the epicenter of the 1812 Nilek earthquake, and the epicenter of the 1906 Manas magnitude 8 earthquake is not uncommon.

(2) The East Tianshan block is uplifted. Tianshan is located east of Urumqi and south of the active fault in the East Tianshan piedmont. There are two large faulted uplifts: one is the Bogda faulted uplift and the other is the Hallik Mountain faulted uplift. During the neotectonic period, the uplift amplitude of the East Tianshan block fault was about 2,200 meters, and the uplift time was relatively late, mostly starting from the Pliocene to Early Pleistocene. The uplift was very strong in the middle Pleistocene. It is estimated that the uplift amplitude of the block fault in the middle Pleistocene was between About 260 meters. The intersection of mainly east-west active faults and a series of northwest-trending active faults divides the uplift into large and small fault blocks, and diverts the Urumqi River, Sangong River and Gongbei ditch that flows into Barkol Lake eastward. The differential activity of fault blocks has formed many fault basins (Qijiaojing, Barkol, Chaiwobao, etc.). The Barkol fault basin has been faulted with an amplitude of 100 to 500 meters since the Pleistocene, from north to south. The collapse amplitude increased sharply. These fault basins were uplifted with the block uplift of the East Tianshan Mountains during the neotectonic period. In the case of the Barkol fault depression, they were uplifted by 1,200 meters.

(3) Turpan-Hami Depression. As an inherited depression, it was a unified depression until the Neogene and Early Pleistocene. After the Early Pleistocene, it was divided into two depressions by the north-south Kumtag uplift. From the Pliocene to the Early Pleistocene, the Turpan Depression had a depression width of more than 1,000 meters in the west. Since the Pleistocene, the depression has reached 220 meters. It is still depressed, forming the lowest depression in my country - Aydin Lake (located in the sea). 154 meters below the plane, the lowest point is -161 meters). Due to the intense neotectonic activity, there are east-west and northwest-trending anticlinal uplifts, with an amplitude of nearly 170 meters only since the Middle Pleistocene.

The general depression amplitude of the Hami Depression is within 60 meters, and the amplitude becomes smaller and smaller from north to south. It may have been formed in the early middle Pleistocene. Since the late middle Pleistocene, the depression has experienced a jump uplift phenomenon. , there are local fault block uplifts, the amplitude of which is mostly 50 to 70 meters, and this uplift can reach 110 to 150 meters during the entire neotectonic period.

(4) The South Tianshan Mountains are strongly uplifted. Located south of the Nalati active fault, it is the area with the strongest uplift in the Tianshan Mountains in China. Since the Neogene, the uplift has been at least 2,500 meters and up to 4,500 meters, and the crust is 48 to 50 kilometers thick.

The neotectonic uplift in this area is strong. For example, the Neogene planation surface of Huoranda Ban was uplifted to an altitude of 3,500 to 4,000 meters above sea level. The gravel layer of the Western Region (Lower Pleistocene) in the adjacent Pamir area is also at an altitude of 3,000 meters. Above, it is more than 1,000 meters above the local river bed. At the same time, it also created a unique high-level rift basin (large and small Rondus Basin) and a series of longitudinal rifts. Such as Yanqi Fault Depression (1048-1500 meters), Kumish Fault Depression, Toshgan Valley Fault Depression, etc. Since the Quaternary, the Kumish fault depression has moved northward, and the center of the fault depression has moved 30 kilometers northward. At the same time, the Cenozoic sediments in the fault depression are generally folded.

It is precisely due to the strong uplift of the South Tianshan Mountains and the strong activity of active faults that the largest earthquake in Xinjiang has occurred so far, namely the 1902 Atushi 8.25 magnitude earthquake, which resulted in the emergence of large-scale seismic gravity structures. And more hot springs, with higher heat flow value.

Others: For example, Kuruktag-Beishan is slightly uplifted, formed in the Quaternary Period, with an uplift amplitude of more than 50 meters, and is now becoming quasi-plain; the Kalping fault block is uplifted, and the new structure is uplifted. It is more than 900 meters long, and also forms some small fault depressions and small intermountain basins. Its internal uplift is an oblong short-axis anticline, several thousand meters long and hundreds of meters wide. The active fault has alkaline gabbro intruding and cutting through the Paleogene and Neogene strata; the Kuqa Depression is an inherited depression, with a depression length of 7,000 meters in the Pliocene Epoch, and a depression amplitude of nearly 4000 meters, and formed a series of anticlines and some active faults. For example, the Qiulitage anticline near Kancun has an elevation of 1900-2400 meters. It was uplifted at least 900-1400 meters in the neotectonic period and at least 200 meters in the late Pleistocene. (Becoming a unique tectonic new mountain).

Overview of the Tianshan Mountains: “The tops of high mountains are often covered with snow-capped glaciers all year round” (Figure 1-6-4) (Since the Pleistocene, from oldest to newest, Danangou, Urumqi, Qian Five ice ages including Xiaxia, Wangfeng and the Holocene Little Ice Age).

“There are many strange peaks and ridges pointing to the blue sky, caressing the flowing clouds. The waist of the mountain system is full of deep canyons, jagged cliffs, rapid water flow, no birds can cross, and difficult passage; however, the dense forests and stripes are Thousands of miles, antelopes galloping and deer roaring, clouds covering the fog, it is the most attractive and charming scenic spot. It is said that the residence of the Queen Mother of the West - Gongque Yaotai is hidden in the Tianshan Mountains (Tianchi)" (Figure 1-6-5).

3. The triangular Junggar Basin is squeezed and depressed

The Junggar Basin is a roughly triangular inland area located between the Altai Mountains, the East-West Junggar Mountains and the Tianshan Mountains. basin. The basement nature of this basin has been controversial, with opinions including the Precambrian crystalline rock series and its Paleozoic cover, the basement of the Paleozoic orogenic belt, and the basement of the residual oceanic crust. But in fact, the basin has a composite nature, with the orogenic belt in the north and the ancient continent and its cover or residual oceanic crust in the south. As a complete basin, its final pattern was finalized after the uplift of the North Tianshan Mountains. In this sense, the caprock of the basin was formed at the end of the Paleozoic, including the lacustrine sediments of the Permian and Triassic, the coal-bearing formations of the Jurassic, the muddy red beds of the Cretaceous, and the Paleogene and Neogene , Quaternary molasse construction. The basin, including the eastern and western Junggar boundary mountains, can be divided into the following structural units.

(1) Arched uplift area in the western Junggar Mountains. Located to the west of the Dalabut Fault. Since the late Neogene, the western Junggar Mountains have been uplifted by at least 300 to 1,100 meters, and the vault has been uplifted by 1,200 to 1,800 meters. The uplift amplitude since the Pleistocene is only 100 meters, and the degree of uplift has gradually weakened since the early Pleistocene.

Among them, the settlement amplitude of the Hebuxel Depression is 31 to 48 meters; the settlement of the Tacheng Depression is at least 300 meters, and the deepest depth can reach 1,000 to 2,000 meters.

(2) Almantai-Kramaili uplift. It is the middle uplift that separates the Irtysh River-Ulungu River depression and the Santang Lake-Naomao Lake depression. The largest uplift since the Cenozoic has reached 1,100 meters. It now forms low mountains and residual hills, developing towards the peneplain. It is a relatively stable area.

(3) Santang Lake-Naomao Lake depression. It is a depression sandwiched between the Altai dome-like uplift area and the Tianshan strong uplift area, and forms two asymmetric depression centers. The depression amplitude is 1,000 to 2,000 meters. Affected by the strong uplift of the Tianshan Mountains after the Early Pleistocene, the southern uplift was larger than the northern one. However, the Altai dome uplift has continued to be active since the late Pleistocene, thus tilting the surface of the northern part of the depression by 10 to 15 degrees, a large amount of coarse clastic material has been accumulated; while the surface of the southern depression is inclined at 5 to 8 degrees, and the accumulated debris is finer, extending gently to the center of the depression for 30 kilometers, which is twice the width of the northern alluvial fan.

(4) Junggar subsidence area. It is equivalent to the Junggar Basin and has generally subsided since the Pliocene. The tectonic activity in the first half of the Pleistocene was relatively obvious, especially in the southern area adjacent to the Tianshan Mountains, which experienced greater changes due to the rapid uplift of the Tianshan Mountains. It can be divided into three sub-units according to the subsidence amplitude since the Pliocene.

① Slight uplift of Zhunbei: exposing large areas of Paleocene, Eocene and lower Pliocene red beds. The uplift amplitude gradually decreases from north to south. It is the area with the highest crustal uplift in Xinjiang, with a crust thickness of 40 kilometers.

② Quanzhong Depression: Formed in the late Neogene, the depression amplitude is 1000-2000 meters. The depression becomes deeper and deeper from north to south. The subsidence amplitude since the Pleistocene is 160-350 meters.

③ Urumqi Depression: It is an inherited fault depression controlled by the Jungnan active fault and the Manas active fault. The faulting amplitude has increased significantly since the Pleistocene. In the early Miocene, the fault center was located in the northeast of Anjihai, with a fault amplitude of 1,000 meters; in the late Miocene, the fault center extended westward to the northeast of Wusu, with a fault amplitude of 1,000 meters; in the Pliocene, the fault activity became more intense It is so strong that the area from Dushanzi to Manasan is faulted for 3,500 meters. After the Early Pleistocene, affected by the strong uplift of the Tianshan Mountains, the nature of the new structure changed fundamentally, and the southern part of the fault depression gradually evolved into part of the northern Tianshan uplift. There are 3 to 4 rows of right-moving echelon-shaped anticline uplifts and the longitudinal valley depressions sandwiched between them in the front of the Tianshan Mountains. The maximum uplift amplitude reaches about 200 meters, and the new depression amplitude reaches 400 to 500 meters. The current depression is still very strong.

4. Metamorphic uplift of the Altai Mountains

The Altai Mountains run from northwest to southeast, with a total length of more than 2,000 kilometers, and lie across the borders of China, Kazakhstan, Russia, and Mongolia. 1000 to 3500 meters, the mountain rises steeply from the foothills to the ridge, with distinct layers and strong cuts. The Irtysh River, which develops on the southern slope of the main ridge of the Altai Mountains, is the only river in my country that flows into the Arctic Ocean water system: the "beautiful and magical" Hanas Lake lies quietly among the high mountains near the main peak of the Altai Mountains (Figure 1-6 -6), is a crescent-shaped alpine glacier lake in the north-northeast direction. The lake is 24 kilometers long and 1500-2900 meters wide. The lake surface is 1370 meters (1374 meters) above sea level. The average water depth is 90 meters and the deepest is 188.5 meters. It is the largest lake in my country. One of the best alpine deep water lakes.

The dome-shaped uplift area of ??the Altai Mountains. Located at the junction of China, Kazakhstan, Russia and Mongolia, the northwest section is about 300 kilometers wide, and the southeast section gradually narrows to only 50 to 80 kilometers. It is approximately fish-shaped in plane and was mainly formed in the Oligocene. It rose slowly from the Miocene to the early Pleistocene, and rose sharply from the middle Pliocene to the early Pleistocene. The faulting activity was intense, and the total amplitude of the uplift was 3000 to 3200 meters, forming an asymmetrical elbow-shaped water system. This is in the north-northeast- Reflection of right-lateral strike-slip along the Irtysh fault under south-south-west horizontal compression. It is estimated that the right-lateral strike-slip amplitude in the Altai Mountains is generally several kilometers, with a maximum length of 210 kilometers.

The Middle Pleistocene was an important period when the dome-shaped uplift of the Altai Mountains was rapidly uplifted, and the stepped landform features displayed by multi-level planations gradually became more prominent. Can be further divided into 2 sub-units.

(1) Dome-shaped uplift of the Altai Mountains. It and the Beitashan uplift form two important uplifts in the area. The two are located between the Irtysh Fault and the Kuphuo Fault. They are the southwest wing of the dome-shaped uplift area. From the perspective of Xinjiang, it seems to be an tilted structure. As its edge ruptures, it appears to have levels 3 to 4. Construct the stairs and tilt them to the sides. Since the Oligocene, the maximum tilt has been 1,900 meters. Since the Pleistocene, the tilt has continued, causing some alluvial layers to rise by more than 900 meters. Since the middle Pleistocene, the uplift has generally been 120 to 150 meters, and since the late Pleistocene, the lift has been 50 to 50 meters. 90 meters.

At the same time as the uplift, the inherited fault activity was extremely intense, especially the north-northwest active faults. During the process of dextral strike-slip, a series of bead-shaped fault depressions were formed in the extension section behind. Basins (thousands of meters deep) are embedded in low mountains and hills on the edge of the uplift (such as Qilti, Keketuohai, Turhong, etc.). The most important new tectonic feature here is along the cross-sectional Keketuohai-Ertai active fault. During the 1931 magnitude 8 earthquake, the famous Fuyun earthquake fault zone was formed in China and abroad and interrupted the water system. The earthquake fault zone is 176 kilometers long and is accompanied by a series of structural micro-landforms, such as Duansetang, Meiji, Duantougou, etc. At the same time, seven hot springs with a temperature of more than 50 degrees in the Alashan Summer Pasture in Fuhai County show geothermal anomaly areas. , indicating that modern tectonic activities in the Altai Mountains are still ongoing.

(2) Irtysh River-Ulungu River Depression. This depression is controlled by the Irtysh Valley fault and is a famous elbow-shaped water system depression. Affected by the dextral strike-slip of the Irtysh active fault, in the process of its southwest plate moving northwestward, it moved in the southeast direction. As a result, the Zaisan Depression, the Irtysh Depression, and the Brento Sea Depression were formed in sequence. They were separated by a series of weak uplifts. Among them, the Zaisan Depression and the Irtysh Depression were about 1,000 meters deep, and the Brento Sea Depression was about 1,000 meters deep. Only 100 meters.