Mesozoic intrusive rocks

(1) Mesozoic Indosinian intrusive rocks

Intrusive rocks in this period are relatively developed in Jiaodong area, mainly exposed in Wendeng, Weihai, Rongcheng Shidao, Zhaoyuan Fushan and the southern part of Laizhou, with an area of about 56 1km2. It appears in the form of composite bedrock with different shapes, rock strain or Oedolgae strain. It intruded into Rongcheng suite and was penetrated by Mesozoic Yanshanian intrusive rocks. A relatively complete magmatic cycle consists of basic → neutral → acidic → alkaline rocks. There are three intrusive rocks in the area: Liulinzhuang, Ningjinsuo and Chashan.

1. Liulinzhuang diorite

It is distributed in Liulinzhuang in Wendeng Shazi Township, Zhouguan and Beixiazhuang in Laizhou, with an area of about 20km2. Small-scale, elliptical, lenticular, irregular rock plants and rock tumors in the north-south direction, a very small amount of composite rock mass, irregular doping between units, flexible boundary, and the distribution direction is opposite to the regional tectonic line. It intruded into Jingshan Group and Rongcheng Gneiss Group, and was cut by Ningjinsuo late granite and Mesozoic Yanshanian intrusive rocks. In Jiaodong area, only five units, namely Beixiazhuang, Zhouguan, Sanpan Tashi, Roof and Tianshui Shore, are exposed.

Lithology is diorite, diorite and quartz monzonite. Geochemical research shows that Liulinzhuang diorite is a type I granite with crystallization differentiation of basaltic magma in the early upper mantle, and a type I granite with crystallization differentiation of regenerated magma formed by metasomatism of molten crust source materials by basaltic magma in the middle and late stage.

2. Ningjin syenite

Ningjinsuo-Shidao area, which is only exposed in the south of Rongcheng, is also seen in Wendeng's grandson. The scale is relatively small, with a total area of 1 16km2. It is a compound rock plant distributed in Northeast China. Porphyries in rocks are directional, and their distribution patterns are in harmony with regional tectonic lines. It intruded into Rongcheng gneiss group and Liulinzhuang diorite body and was cut by Chashan and Laoshan granites.

The rock is alkaline syenite, with unequal grain structure, porphyritic structure and massive structure. The phenocryst is potash feldspar, and the matrix is mainly potash feldspar, followed by plagioclase, and a small amount of dark minerals. From the early unit to the late unit, the rock types evolved from amphibole syenite → pyroxene syenite → syenite, and the rock structure changed from fine to coarse, reflecting that this kind of granite is a dual evolution sequence of mineral composition and structure.

Geochemical research shows that the superunit belongs to the Mediterranean-type K-Ca-alkaline rock series, which is a highly differentiated acidic and alkaline rock. Its material comes from the rich lithospheric mantle source area. Due to different stages of melting, different degrees of crystallization differentiation and assimilation and contamination of the lower crust, intrusive rock units with different compositions were formed.

3. Chashan granite

It is distributed in Chashan, Renhe, Wendeng Xizhuang, Balizhuang and Zhangjiachan in the south of Rongcheng, with an area of about 108km2. The occurrence of composite rock strain is nearly east-west irregular belt. It invaded Rongcheng gneiss suite and Ningjin syenite, and was invaded by late Weideshan granite, which is a set of syenite.

From the early unit to the late unit, the mineral composition of Chashan granite changed little except that the time increased slightly and plagioclase decreased slightly. The structure shows obvious changes from medium grain to medium coarse grain and coarse grain to variegated medium coarse grain, which reflects the evolution sequence dominated by structure. Magma comes from the mantle source region rich in lithosphere and belongs to A-type granite.

(2) Mesozoic Yanshanian intrusive rocks

In the late Mesozoic, there was a strong tectonic transformation in Jiaodong area, forming a complex geological structure pattern, which was generally characterized by intracontinental extension and large-scale lithospheric thinning, accompanied by mantle uplift. The ancient metamorphic rock series with crystalline basement was rapidly heated in a certain depth and partially melted to form granitic magma. Deep mantle-derived materials are also partly involved, and with the uplift of asthenosphere, large-scale intense magmatism is caused (Figure 2-3).

Song Mingchun et al. (20 10b) studied the isotopic age data of Mesozoic magmatic rocks 177 K-Ar and12 u-Pb in Shandong Province (including some 39Ar-40Ar, Rb-Sr isochrons and Sm-Nd isochrons). Three age-concentrated segments were formed, namely, 230~200Ma, 160 ~ 135~90Ma and 135~90Ma, indicating that Shandong Province experienced three stages of magmatic activity: Triassic, Jurassic and Cretaceous. The peak age of Cretaceous magmatic activity is about 120Ma, indicating that the lithospheric thinning in Jiaodong reached its strongest at this time.

Figure 2-3 Distribution Map of Mesozoic Intrusive Rocks in Jiaodong Area

(According to Song Mingchun in 2008, it has been revised)

1-Liulinzhuang diorite; 2- Wendeng granite; 3- Ningjin syenite; 4- Chashan granite; 5-Duogushan granodiorite; 6- Linglong granite; 7- guojialing granite; 8- Weideshan granite; 9- Laoshan granite

Figure 2-4 Statistical Histogram of Isotopic Age of Mesozoic Magmatic Rocks

(According to Song Mingchun et al. 20 10b)

K-Ar isotopic age; Isotopic ages of boron, uranium, lead, 39Ar-40Ar, rubidium, strontium and samarium and neodymium.

1. Jurassic Duogushan granodiorite

Dagu Mountain and Guduo Mountain, which are exposed in the east of Rushan, cover an area of about 140km2. Irregular composite bedrock occurs on the Kunyushan-Rushan fault uplift, which is northeast-oriented, with a large west and a small east. From the early stage to the late stage, the units are arranged from east to west, and the overall distribution orientation is consistent with the regional tectonic line, and there is directional fabric in the rock mass. It invaded the junction of Jingshan Group and Haiyang College, and was invaded by Linglong granite and Mesozoic Yanshanian intrusive rocks. It is a set of intermediate-acid granodiorite with weak gneiss structure. From morning till night, it is divided into three units: riding Longshan, Tiger Nest and Dagushan.

Porphyry crystals are mostly directionally arranged potash feldspar, which is an intrusive rock with tectonic evolution sequence. From the early stage to the late stage, the unit is from medium grain to mottled medium grain to mottled medium grain. Geochemical research shows that the Duogushan granodiorite belongs to type I granite, and its source region comes from the basic lower crust between high-pressure granulite facies and eclogite facies.

2. Jurassic Wendeng granite

It is concentrated in Wendengying and Wangtuan in Wendeng City, Yekou-Haobo in Weihai City, Fushan, Bashan and Panjiadian in Zhaoyuan City, with an area of 427km2. Granite in Wendeng-Weihai area is produced in olive composite bedrock, distributed in north-south direction, intruded into Rongcheng gneiss suite, and was cut by Mesozoic Yanshanian intrusive rocks. Granite in Zhaoyuan area is an irregular compound bedrock with NW distribution, which intruded into Qixia gneiss suite, contacted with Linglong granite fault and was cut by Mesozoic Yanshanian intrusive rocks.

The units that make up the composite rock mass are arranged in disorder and have surging or pulsating intrusion relationship with each other. The boundary is curved and changeable, and the distribution direction is not in harmony with the regional tectonic line. Rock branches penetrate into the compound rock mass, and xenoliths are often found around the rock mass. It is a set of adamellite series, which is divided into seven units from morning till night: Guniangfen, Bashan, Fushan, Yekou, Xiaoqikou, Shimending and Caomiaozi. Among them, Yekou (187.5km2) and Fushan (1 15km2) units are larger, while others are smaller.

From the early stage to the late stage, the mineral composition of intrusive rocks changed little, and the rock structure changed from fine grain to porphyritic medium grain, coarse medium grain to fine medium grain, porphyritic medium grain to giant porphyritic medium grain, reflecting the evolution sequence dominated by structure. Geochemical research shows that the magma of Wendeng granite comes from the crust and belongs to S-type granite remelted in continental crust.

3. Jurassic Linglong Granite

Linglong granite is one of the most developed intrusive rocks in Jiaodong, with large scale and wide distribution, which constitutes Linglong and Kunyu Mountain. It is distributed in the south of Longkou Imperial City, the north of Pingdu, the east of Laizhou, the west of Laixi Nanshu, the east of Qixia Kou Tie and Mupingbu, the west of Rushan Feng Jia and Wendeng Shaizi, the south of Muping Longquan and the north of Rushan, and it is also exposed in Biguo, Zhaoyuan, with a total area of about 3733km2. Linglong granite is a series of adamellite intrusive rocks, which are weak gneissic garnet-bearing adamellite in the early stage and massive light-colored adamellite in the late stage. The former accounts for about 38% of the total area of Linglong granite.

The main rock masses of Linglong granite are Linglong rock mass, Kunyushan rock mass, Queshan rock mass and Biguo rock mass. Linglong complex batholith is distributed in NNE, and its core part is Buguojiadian rock mass, followed by Cuizhao, Fanggoushan, Jiuqu and other rock masses in turn, showing a symmetrical arrangement pattern with new middle and old sides. On the profile, the high-altitude part is completely occupied by the early Yunshan rock mass, and the relatively low part is the late rock mass (Guojiadian rock mass or Cuizhao rock mass). On the north side of bedrock, there are a large number of residual inclusions in Qixia gneiss suite at the contact between Guojiadian and Cuizhao rock. Its east side is controlled by Zhaoping fault; The west side is restricted by Tangtian fault and Longkou-Laizhou fault. The geochemical characteristics of Linglong granite are similar to those of adakite, mainly high strontium and low yttrium granite, belonging to S-type granite with remelted continental crust.

Many researchers have come to different conclusions about the diagenetic age of Linglong granite. According to the measured isotopic age, it can be roughly divided into three types: Neoproterozoic diagenetic theory (Shi et al.,1981; Qiu,1988; Wang Jizan, 2000; Song Mingchun et al., 2003), Mesozoic diagenetic theory (Wen Zi,1985; Luo Wancheng et al.,1987; Yu Hanmao,1987; Wang Henian et al.,1988; Zhaolong Li et al.,1993; Miao Laicheng,1998; Chen Yanjing et al., 2004) and Neoproterozoic, Paleozoic and Mesozoic granites constitute a composite batholith (,1989). Linglong granite belongs to high-potassium calc-alkaline rock series, and its geochemical characteristics show that it is continental crust remelted granite (Song Mingchun, 2008 a). Gao Jinghui et al. (2003) studied the zircon SHRIMP U-Pb age of Kunyushan complex, indicating that zircon generally has a double-layered structure, and there are two kinds of zircon in the core, namely magmatic zircon and metamorphic zircon. The age of inherited zircon from magma is mostly 800 ~ 700 Ma, and that from metamorphic zircon is mostly 230 ~ 200 Ma, and the individual occurrence is 1.9 ~ 65438.

In the late Mesozoic, there was a strong tectonic system transformation in the northwest of Jiao Jiao, which was generally characterized by intracontinental extension and large-scale lithospheric thinning, accompanied by mantle uplift, leading to strong magmatic activity. Linglong granite is a granite body formed in the earliest stage of Jurassic-Cretaceous large-scale magmatism in Jiaodong area. The zircon SHRIMP U-Pb age is 160 ~ 150 Ma (Miaolaicheng et al., 1998), which indicates the beginning of tectonic system transformation. Since then, the eastern part of China has entered an era of unified dynamic background dominated by tension.

4. Cretaceous guojialing granodiorite.

It is mainly distributed in Laizhou, Qixia and Penglai, with Shangzhuang, Beijie and Jia Cong in Zhaoyuan, Wang Nan, guojialing and Cunji in Penglai and Wendengze in the east, with an area of about 5 14km2. Granites in guojialing are distributed discontinuously, and the compound rock masses with a certain scale from west to east include Cangshang rock mass, Shangzhuang rock mass, northern rock mass, Jia Cong rock mass, Qujia rock mass, guojialing rock mass and Fanjiadian rock mass. Its lithology is syndiorite-quartz diorite-granodiorite adamellite series intrusive rocks, mainly porphyritic medium-grained amphibole adamellite (accounting for about 53% of the total granite area in guojialing). The rock is characterized by porphyritic structure, and there are many particulate diorite inclusions in the rock mass. From the early unit to the late unit, the chronological and potash feldspar gradually increased, while the plagioclase and dark components gradually decreased. Rock structure has experienced the evolution process from porphyritic to porphyritic and then to rough, showing the dual evolution characteristics of structure and composition.

The isotopic ages of guojialing granites obtained by conventional dating methods are mostly concentrated in 200.6 ~ 102 Ma. The SHRIMP U-Pb age of magmatic zircon determines its emplacement age as 130 ~ 126Ma (Wang et al.,1998; Luo Zhenkuan et al., 2002), Early Cretaceous.

Guojialing granite is sodic granite, belonging to a series of high-K-Ca alkaline rocks, with the characteristics of type I granite (Song Mingchun et al., 20 10b). There are many dark diorite inclusions in granite. Petrology, geochemistry and accessory mineral assemblage of these inclusions indicate that mantle-derived materials participated in diagenesis (Xu Jinfang et al., 1989).

5. Cretaceous Weideshan granite

Widely distributed in Rongcheng Wade, Wendeng Sanfo Mountain, Muping Yuangezhuang, Qixia Yashan, Ai Shan, Haiyang Zhaohushan, Longwangshan and other places, with a large scale. In addition, there are outcrops in southern Jiangsu, Laizhou and Daze Mountain in Pingdu, with an area of about 1435km2. On the whole, it is a compound bedrock and rock-plant occurrence in the northeast and northeast direction, which is the strongest magmatic intrusion activity in Cretaceous, and is mainly composed of a set of neutral-intermediate acid intrusive rocks. From the early unit to the late unit, it has experienced the evolution of diorite → monzodiorite → Shi Ying monzogranite → granodiorite → monzogranite (Table 2-3), in which the distribution area of monzogranite accounts for about 5 1% of the total area, and that of Shi Ying monzogranite accounts for about 46%. It often constitutes a large complex rock mass, including Yuangezhuang rock mass, Sunan rock mass, Yashan rock mass and Ai Shan rock mass. From the early stage to the late stage, plagioclase and dark minerals decreased, while potash feldspar and quartz increased. The rock structure changes rhythmically from fine to porphyritic, medium to fine. It reflects the dual evolution sequence of Weideshan granite, which is dominated by mineral composition evolution and supplemented by tectonic evolution.

Statistical isotope ages range from196.4 to 75.55 Ma (Table 2-4), mostly in 135 ~ 85ma, and concentrated in 127 ~ 105 Ma (Song Mingchun et al., 2003), indicating that the Weideshan granite is the main body.

The chemical composition of the main elements of Weideshan granite belongs to high-potassium calc-alkaline series and olivine andesite series, showing the characteristics of I-type granite and the evolution characteristics of calc-alkaline rocks (Song Mingchun et al., 20 10 b). Geochemical characteristics show that the Weideshan granite has dual characteristics of mantle source and crust source. Granite contains a large number of diorite inclusions, showing traces of magma supercooling and magma mixing (Zhang Huafeng et al., 2006). It shows that the rock mass has the genetic characteristics of magma mixing, which is formed by mixing acidic magma from the crust and basic magma from the mantle.

Table 2-3 Division Table of Rock Genealogy Units of Weideshan Granite

Weideshan granite has a long formation time, complete evolution and wide distribution area, which can provide heat source for a long time. The surface is mainly distributed in the middle and east of Jiaodong, but it is often produced as a small rock plant in the northwest of Jiaodong, so its relationship with mineralization is often ignored.

6. Cretaceous Yushan granite porphyry

The rock mass is undeveloped and small in scale, distributed in Yushan, Guajishan, Fushan, Yantai and Kou Tie, Qixia, with an area of 89km2. Oval and irregular strip-shaped rock plants, rock walls or dikes appear. Generally, it is distributed in northeast or nearly north-south direction, which is obviously controlled by northeast faults. The Cretaceous Qingshan Group and Weideshan granite invaded by Laoshan granite are high-grade hypabyssal intrusive rocks in the late Ai Shan. They are a set of neutral-acid porphyries or porphyries with secondary structure, and three units, Wangjiazhuang, Shuikuang and Hejiagou, are exposed.

Yushan granite porphyry evolved from early unit to late unit, from synbiotic porphyry to granodiorite porphyry to adamellite porphyry. The content of chronological and potash feldspar in rocks increases, while the content of plagioclase and amphibole decreases, showing a magmatic sequence dominated by mineral composition evolution. Its source rock comes from the same lava magma formed by assimilation of molten crust source materials during the upward migration of basaltic magma in the upper mantle, which has the characteristics of type I granite.

7. Cretaceous Laoshan granite

It is distributed in Laoshan, Jimo Aoshan, Haiyang Zhaohushan, Rongcheng Longxu Island and Pingdu Daze Mountain, with an area of about 7 10 km2. It was the last large-scale plutonic magma intrusion in the late Yanshan period, and it was produced in the form of northeast composite bedrock and rock strands. From early to late, it experienced the evolution of adamellite-syenite-alkaline granite, in which the distribution area of adamellite accounts for about 40% of the total area and syenite accounts for about 36%. Granites in alkali feldspar often contain alkaline dark minerals albite and aegirine. The isotopic age of diagenesis ranges from129.92 to 86.74 Ma, and most of the ages are concentrated in 1 15.4 ~ 90 Ma (Song Mingchun et al., 2003), indicating that the Laoshan granite was formed between the early Cretaceous and the late Cretaceous.

Table 2-4 Isotopic Age Table of Weideshan Granite

Laoshan granite belongs to the series of high potassium and calcium-alkaline, with high silicon (SiO270.43%~76.65% ~ 76.65%), alkali-rich (K2O+Na2O8.19% ~1.44%) and poor calcium (Cao 0.22). The geochemical composition of trace elements and rare earth elements also shows the characteristics of A-type granite. The rock mineral composition shows that the early unit of Laoshan granite is A 1 type granite, mainly adamellite and syenite granite, and the late unit is A2 type granite marked by alkaline minerals (Song Mingchun et al., 20 10b).

(3) Mesozoic dikes

The Mesozoic dikes in Jiaodong area are particularly developed, ranging from several meters to several hundred meters in width and from more than one hundred meters to several tens of kilometers in length, with a north-east direction and nearly a north-south direction. Most of the veins are related to Mesozoic intrusive rocks and distributed in intrusive rocks and their surrounding rocks. Vein rocks often form regular combinations according to lithology, age, region and occurrence, so they are named as three major vein rock belts.

1. Linglong-Zhaofeng dike rock belt

Mainly distributed in Linglong rock mass. It can be roughly divided into Tao Pan-Songjia pulse group, Sunan-Linglong pulse group and guojialing pulse group. The main dike types are diorite, diorite porphyry, synbiotic porphyry, granodiorite porphyry, granite porphyry, syenite, synbiotic syenite, lamprophyre and so on. Formed simultaneously with or after Jurassic intrusive rocks.

2. Jushan-Longmenkou vein rock belt

Widely distributed in the northwest of Jiaojiao, concentrated in Jushan-Longmenkou area. The main dike types are diorite, diorite porphyry, syenite porphyry, granite porphyry, adamellite porphyry, rhyolite porphyry and lamprophyre. The isotopic age of basic dikes is125 ~1100 Ma (Jinhui Yang et al., 2000).

3. Laoshan-Dazhushan vein rock belt

Associated with Laoshan granite, it is generally distributed in the northeast. The main types of dikes are syenite, syenite, granite, granite porphyry, syenite porphyry, granite microcrystal, porphyry, diorite and lamprophyre. The main types are syenite, syenite porphyry, granite porphyry and lamprophyre. Formed in the late Cretaceous.