Magna geological processes and tourist observation routes in Zushan Scenic Area

1. Teaching Purpose

Route: Internship Base—East Gate of Zushan Scenic Area—Depot—Qiuziyu—Internship Base.

(1) Observe the Early Cretaceous Xiangshan granite batholith and granite landforms.

(2) Observe contact metamorphism and structural phenomena near the contact zone between rock mass and formation.

(3) Observe the geological processes of rivers in the bedrock area and the characteristics of Cenozoic sediments.

(4) Observe the lithology and primary structure of the Cambrian strata.

(5) Observe the Qiuziyu anticline structure and conduct structural movement analysis.

(6) Zushan Natural Scenic Area and Ming Dynasty Great Wall Tourism.

2. Teaching Arrangement and Teaching Content

No.1

Located about 200m west of the microwave tower (Weiziyu Forest Farm) in the east gate of Zushan Scenic Area North side.

(1) Observe the Xiangshan granite rock mass and its secondary structures and landforms.

Geologically, Zushan Natural Scenic Area is part of the Xiangshan granite batholith of the Early Cretaceous. The exposed area of ??this rock base is about 217km2, which is produced in an irregular elliptical shape on the plane (the long axis extends to 25km in the north-northeast direction, and the exposed width reaches 15km). The exposed location is the intersection of two sets of faults. Under the continuous action of tectonic movements, the Xiangshan rock mass continued to expand, forming two phases of magma intrusion. The contact boundary between the rock mass and the surrounding rock is irregular and jagged, the interior of the rock mass has no directional fabric, and surrounding rock xenoliths are common near the contact zone. This observation point is located at the eastern edge of the rock mass, and its lithology is early intrusive medium-coarse-grained alkali feldspar granite.

Medium-coarse-grained alkali feldspar granite: light flesh red, medium-coarse-grained unequal grain structure, local porphyry-like structure, massive structure, mineral directionality is not obvious, and local geode structures are developed. Main mineral composition and content: quartz 20% to 25%, histological granular shape, size 1 to 8mm; potassium feldspar greater than 65%, flesh red, semi-hedral to euhedral, size 2 to 10mm, mostly 3 to 6mm, large Those form "phenocrysts"; plagioclase 5% to 10%, off-white, euhedral-semi-euhedral, size 4-9mm. The minor minerals are hornblende and biotite, both of which contain less than 5%.

The primary structure of rocks is the structure produced during the formation of rocks. The primary structures of the Xiangshan rock base are mainly geode structures and primary joint structures. Nearly circular, oval or irregular primary holes in intrusive rocks are called geodes. Geodes vary in size, from a few centimeters to tens of centimeters in diameter. Late or later magma (or hydrothermal fluid) seeps into the geode, and quartz and feldspar crystals with intact crystal shapes often develop on the walls of the geode. Quartz crystals that grow well are called crystals and generally grow perpendicular to the geode walls. The Xiangshan granite geode structure is relatively developed, indicating that the rock mass was formed in an extensional tectonic environment. Primary joints are more developed in the early intrusions of the Xiangshan batholith, and three groups of mutually perpendicular primary joints can be seen in the same outcrop. The occurrence of primary joints is controlled by the tectonic stress field during magma emplacement.

(2) Observe granite landforms.

Many nearly vertical cracks in different directions are developed in the Xiangshan rock mass, including primary joints and secondary joints. Under the action of surface geology, especially weathering and surface water erosion, the Xiangshan rock mass has formed landform features of deep valleys, strange peaks, and steep terrain. Two or three groups of secondary joints cutting the rock can also be seen on the outcrop (345°∠64°, 5°∠80°～89°).

No.2

It is located on both sides of the east gate of Zushan Scenic Area.

(l) Understand the natural scenery of Zushan, receive patriotism and professional ideological education, and enhance environmental protection awareness.

Zushan Scenic Area is a national scenic spot, national geological park, rare plant and endangered wild animal and plant protection zone. It is located in the Xiangshan-Laoling area of ??Qinglong County, about 25km northwest of Qinhuangdao City, covering an area of ??approximately 118km2, and the highest peak, Xiangshan Mountain, is 1421m above sea level. The peaks north of the Bohai Sea and east of the Yanshan Mountains are all formed by the development of Xiangshan Mountain, so they are named after the "ancestor of the mountains".

Zushan Mountain has five major scenic spots and hundreds of natural landscapes, including the Natural Geology Museum (Shili Langgu), rare plants left from the original (Tiannu Mulan), peaks that play music in the wind (Xiangshan), Changing Mountain The impermanent six pine trees (phantom pines), primeval forests, meadows, waterfalls and the Ming Dynasty stone Great Wall are even more fascinating. Zushan Scenic Area is not only a rare mountain forest park in the north, but also a good natural laboratory for geological, biological, environmental and other research.

Tiannu Mulan, also known as Tiannvhua, Tianlan, Mountain Peony, etc., belongs to the genus Magnolia of the Magnoliaceae family. It is a broad-leaved sub-arbor. It is listed as the second level in the national list of rare and endangered plants. It is a world-famous precious tree species. The flowering period of the goddess magnolia is between June and July. The petals are milky white, the stamens are red with yellow, which is extremely cool. The leaves are green and plump, and the branches are smooth and grainless. The overall appearance is a beautiful fairy image. Celestial magnolia is very selective about the environment. It can only bloom and survive in areas above 1000m above sea level. Once the environment is damaged, it will grow poorly and even wither and die. At present, this tree species is found in only a few areas in my country, and there are 1,500 trees in Zushan, growing in patches, which is even more rare. In late June every year, the goddess magnolia blooms in full bloom, with its long flower stalks fluttering in the wind and fragrant, just like the goddess scattering flowers, which is breathtaking and unforgettable.

On the steep hillsides on both sides of the gate of the scenic area, the Weiziyu Great Wall winds and undulates from northeast to south-west. It was built in 1381 AD (the fourteenth year of Hongwu in the Ming Dynasty) by Xu Da, the founding father of the Ming Dynasty. In 1567 AD (the first year of Longqing in the Ming Dynasty), it was rebuilt under the leadership of the national hero Qi Jiguang and became the Great Stone Wall. It is a world historical and cultural heritage.

(2) Observe the geological characteristics of mountainous rivers.

The tributary of Shihe River on the south side of the east gate of the scenic spot originates from Xiangshan. Due to the downward erosion of the river, the upper reaches of the valley takes on a "V" shape; the composition of the alluvial material is relatively simple, mainly medium-coarse-grained granite and medium-fine-grained granite. Granite, quartz syenite, etc. are poorly sorted, angular to sub-circular, and locally the gravels are arranged in an imbricated manner; floodplains and shoals are developed, and locally I and II level river erosion terraces or concave banks can be distinguished The phenomenon of erosion and convex bank sedimentation.

(3) Observe the medium-fine-grained granite in the late Xiangshan pluton.

On the steep walls on both sides outside the east gate of the scenic area, you can see the medium-fine-grained alkali feldspar granite on the edge of the Xiangshan rock mass. The rock is light flesh red, with medium-fine-grained granite structure, porphyry-like structure, and massive structure. The main mineral is quartz, with a content of about 25%. It is in the shape of granular particles with a size of 0.5-2mm. The content of potassium feldspar is greater than 65%. It is semi-euhedral, with a size of generally 0.5-2mm. Some of them are 2-4mm and constitute "phenocrysts". The secondary mineral content is 5% to 10%, mainly biotite, with a small amount of plagioclase. The intrusion time of this granite is slightly later than that of the medium-coarse-grained alkali feldspar granite at the previous observation point. The former intruded into the latter in the form of veins. The contact relationship between the two can be seen on the steep wall about 150m east of the foot of the Great Wall on the south side.

(4) Observe joints.

Four groups of joints can be seen in the rock, with the occurrences being 320°∠74°, 12°∠76°, 265°∠85°, and 115°∠85°. They are mainly secondary structures and joint cutting. Rocks that make granite form steep walls. These joints indicate that the rock mass was damaged by later tectonic movements after its formation.

No.3

It is located on the steep wall on the southeast side of Dalaoyu Village about 1.5km east of the east gate of Zushan Scenic Area.

(1) Observation and discrimination of macroscopic characteristics of sedimentary rocks and igneous rocks.

The surrounding rocks of the eastern edge of the Xiangshan rock mass are Middle to Late Cambrian sedimentary rocks. The separated rock mass is distributed from west to east in the Middle Cambrian Xuzhuang Formation, Zhangxia Formation and Upper Cambrian Gu The Shan Formation, Changshan Formation, and Fengshan Formation are a set of rock combinations of carbonate rock, argillaceous rock intercalated with quartz sandstone, and contain bioclastic limestone. This observation point is mainly the Middle Cambrian strata. Macroscopically, the rocks are well stratified and have well-developed bedding structures. The colors are mainly gray, light brown gray, and dark gray. The main lithology is mica-containing silty shale, Oolitic limestone, bioclastic limestone, feldspathic quartz coarse sandstone, and algae-containing argillaceous banded limestone. The strata are distributed in medium-thin layers on top of the rock mass and develop fold structures, indicating that the rock mass intrusion or later tectonic activities caused plastic deformation of the strata.

(2) Observation of contact metamorphism and characteristics of contact metamorphic zones.

The rocks at the edge of the rock mass are fine-grained alkali feldspar granite and syenite porphyry. Macroscopically, it is mainly light brown and gray brown, with a massive structure. There is no clear boundary between the two. It is a transitional relationship. The closer the rock particles are to the surrounding rock, the finer the grains. It changes from a fine-grained granite structure to a porphyry structure to a porphyry structure. Cryptocrystalline or glassy structure, that is, there are obvious fine-grained edges or condensed edges at the edge of the rock mass. This is formed when magma intrudes into the stratum and the edges of the magma body are quenched, indicating the intrusive contact relationship between the Xiangshan rock mass and the Middle Cambrian.

Syenite porphyry is light yellowish brown, with a porphyry structure and a massive structure. The phenocryst components are orthoclase and hornblende. The former is flesh-red, with a content of 5% to 10%, euhedral, and a size of 1 to 4 mm; the latter is dark green, with a content of less than 5%, and is semi-euhedral, with a size of 1 to 3 mm. . The matrix is ??cryptocrystalline. False flow structures develop locally. Xenoliths of surrounding rocks can be seen in the rock mass.

Due to the baking of magma, the surrounding rock undergoes contact metamorphism, forming contact metamorphic rock, which makes limestone, mudstone, etc. with low hardness become hard. Away from the magma, the degree of metamorphism of the rock body becomes shallower, until it reaches normal sedimentary rock. In the surrounding rocks of different ages, contact metamorphic zones with a width of 1 to 10 cm are developed, with irregular boundaries. The lithology is mainly marble, silicified rock, hornfels, and skarn and pyrite are locally developed.

(3) Understanding and observation of fold structures.

Under the guidance of teachers, observe and analyze contact metamorphism and the characteristics of contact metamorphic rocks, analyze the causes of condensation edges and baking edges, and discuss the role of condensation edges and baking edges in determining the contact relationship between intrusive rocks and sedimentary rocks. effect. Measure the contact surface occurrence and stratigraphic occurrence, and make a sketch of the intrusion contact relationship profile.

No.4

It is located on the roadside next to the residential houses in the southwest of Chechang Village.

(1) Observe loose accumulations and analyze their formation environment.

Quaternary loose accumulations about 20m wide are developed in syenite porphyry and Cambrian medium-thin limestone and marl. It is mainly composed of gravels of fine-grained granite, medium-coarse-grained granite, and syenite porphyry, as well as sand and soil. Limestone, marl, and mudstone have less gravel content, loose structure, and poor sorting properties.

In the vertical direction, the sediments have zoning characteristics: ① The lower part is a gravel layer. The particle size of the gravel is large, 5 to 45 cm, mainly 5 to 15 cm. The roundness is good, sub-angular to sub-round, and the content More than 60%, slightly arranged in an imbricated shape, and the rest is fine gravel and sand; ② The middle part is mainly brown-yellow sand and mud layer, in the shape of a long lens, with very little gravel, about 40-60cm thick; ③ The upper part is rounded A gravel layer with different degrees of gravity. The lower part of the gravel is mainly granite and syenite porphyry, and the upper part is mainly sedimentary rock. The particle size is small, about 3-30cm. The roundness is not good, and it is angular to sub-angular. , the content is greater than 65%, and the rest is loose sand.

(2) Analyze the source area based on the characteristics of the accumulation.

Under the guidance of the teacher, analyze the formation environment and provenance area of ??the Quaternary sediments at this point. This point contains less content and is observed and analyzed on the side of the highway. Teachers can make choices based on specific circumstances. In addition, please pay attention to traffic safety.

No.5

It is located in the quarry on the west side of the road 700m north of Qiuziyu Village.

(1) Observe folds and their associated structures.

The observation point is located on the west side of the Liujiang syncline and is an upright anticline (Figure 4-20). The exposed strata are the Xuzhuang Formation and Zhangxia Formation of the Middle Cambrian. The lithology is mainly limestone, oolitic limestone, bamboo leaf limestone, marl, mudstone and bioclastic limestone. Oolitic limestone is medium-thick layered-massive, gray, oolitic structure, particle size 1 ~ 2mm, round, content greater than 80%, mainly bright crystal cementation, spherical ooid grains are clearly protruding on the weathering surface on the rock surface. The bioclastic limestone is gray in color, has a bioclastic structure, a grain structure, and is medium-thin layered. The fossils contained are mostly paleontological fragments, with fewer intact ones, mainly bivalves.

There is a fold structure developed in the formation, which is an upright anticline. The anticline spreads in a north-northeast direction, with a hinge trend of 5° to 10°, and it dips to the northeast with a dip angle of about 10°. The exposure height is 6 to 8m and the width is about 30m. The core strata are gray from the Xuzhuang Formation. The rock is interbedded with marl, and the wings are composed of Zhangxia Formation limestone, oolitic limestone and bioclastic limestone; the stratigraphic occurrence in the west wing is 300°~302°∠22°~39°, and in the east wing it is 65°~ 82°∠30°～33°; developing positive fan-shaped joints and secondary folds. The joints near the anticline axis can often become good ore guide and ore storage structures. Regionally, this fold belongs to the northeastern section of the Shangpingshan sloping anticline. The strata on the west wing were damaged, eroded and incomplete by the Xiangshan rock mass, which indicates that the anticline was formed before the Xiangshan rock mass.

(2) Observe the fracture structure. In the direction of the vertical anticline, some fault structures develop, some with an opening width greater than 30cm, and they are filled with laterite and limestone breccia formed by weathering. They are tensional joints formed in directions parallel to the compression stress during fold formation.

(3) Primary structure and karst phenomenon of sedimentary rocks. The primary and secondary structures of the strata are developed, mainly including nodular structures, horizontal bedding, suture structures, feather cracks, etc. Observe and analyze the causes of these structures.

(4) Measure the stratigraphic occurrence, make a cross-section sketch of the anticline structure, and determine the fold type.

Figure 4-20 Cross-section sketch of Qiuziyu anticline (according to Lin Jianping, 2005)

3. Review and reflection

(1) How Distinguish sedimentary rocks and intrusive rocks from macroscopic characteristics in the field?

(2) How to identify condensation edges and baking edges? What significance do they have in studying the contact relationship between geological bodies?

< p>(3) What are the similarities and differences in the characteristics of sediments formed by rivers, torrents, and sheet flows?

(4) How to identify source areas based on sediment characteristics?

(5 ) Try to describe the origin of the anticline structure.

How to identify fold types? How to describe fold characteristics?