[China Geo University (Wuhan)]
1999, when celebrating the 50th anniversary of the founding of new China, the author once wrote a review of the progress of metamorphic petrology in China in the past 50 years [1]. 2 1 century, traditional geology is turning to modern geology with "earth system science" as its core content. Under the situation of global geological integration, China Geological Survey not only carried out a new round of1:250,000 regional geological survey in the mainland, but also vigorously carried out1:250,000 regional geological survey in Qinghai-Tibet, Xinjiang and other places in the western region, and carried out detailed mapping of some important metamorphic areas in southern Tibet, Kunlun and Tianshan Mountains, and obtained many valuable firsts. This paper intends to observe the achievements and prospects of metamorphic petrology from the perspective of petrology development.
I metamorphism under extreme conditions
From the development of metamorphic petrology itself, researchers have paid more and more attention to the study of metamorphism under extreme conditions in recent years. The so-called "extreme conditions" mean that the external factors such as metamorphic temperature and pressure are different from those of conventional metamorphism (that is, t = 250 ~ 800℃, p = 1 ~ 2.5 GPA). Metamorphism under extreme conditions, such as ultra-high pressure metamorphism, ultra-high temperature metamorphism, ultra-low grade metamorphism and impact metamorphism, has made great progress in China in recent years.
1.UHP metamorphism
In metamorphic geology, it is customary to divide the types of metamorphism by the geothermal gradient of metamorphism. Ultra-high-pressure metamorphism refers to metamorphism with extremely low geothermal gradient (less than 10℃/km) and metamorphic pressure greater than 2.5GPa, which makes high-pressure minerals such as coesite and diamond appear in garnet, zircon and other metamorphic rocks.
Ultra-high pressure metamorphism discovered in Dabieshan-Sulu area since 1980s is a kind of metamorphism under extreme conditions. It is characterized by fine inclusions of ultra-high pressure marker minerals diamond and coesite, which generally exist in eclogite and gneiss associated with eclogite. It has become the largest ultra-high pressure metamorphic belt with the best exposed conditions in the world, which has attracted the attention of scholars at home and abroad. The research in recent 10 years proves that this kind of rocks have regional distribution, starting from Tianshan Mountain in the west and extending to Altun-Qilian Mountain and East Qinling-Dabie Mountain-Sulu in the east, forming a "central structural belt" across China. The existence of ultrahigh pressure metamorphic rocks reveals that continental crustal materials can dive deep into the mantle. In order to explore the deep structure of this abnormal orogenic belt, with the support of the Ministry of Land and Resources, the Institute of Geology of the Chinese Academy of Geological Sciences conducted the first Chinese mainland scientific drilling (drilling) in the East China Sea of Jiangsu since 200 1, which lasted for 4 years, and the final hole depth was more than 5,000 meters. Full core drilling, combined with geophysical and other interdisciplinary research, has achieved the following results: (1) the three-dimensional structure, composition and geophysical properties of the Dabie-Sulu convergence plate boundary; Explore the nature and age of ultrahigh pressure metamorphism; Exploring crustal dynamics and crust-mantle interaction during the formation and exhumation of ultrahigh pressure metamorphic rocks; Study the fluid circulation process and mineralization of the crust and mantle; Establish a long-term observation laboratory to study crustal dynamics and deep evolution of continental crust [4].
Ultra-high pressure metamorphism has become the focus of international geological science research, and the research on various ultra-high pressure metamorphic areas that have been discovered at present is deepening day by day, and new achievements are constantly emerging; Exploring the subduction depth of lithospheric plate by experimental petrology; The research on major scientific issues such as the relationship between crust and mantle and fluid circulation is in-depth development.
2. Ultrahigh temperature metamorphism.
It belongs to the category of granulite facies metamorphism, but it is different from ordinary granulite in that the metamorphic temperature is greater than 800℃. It is characterized by the appearance of high-temperature minerals, such as pseudosapphire and olivine. At present, it has been found in Antarctica, India and other places, and only Mashan Group in Heilongjiang Province has reported fake sapphire in China. In recent years, Peking University cooperated with Santosh of Kochi University to re-study the Kongziyan Belt in Inner Mongolia. Based on metamorphic mineral assemblage, fluid inclusion characteristics, monazite and zircon isotopic chronology, it is determined that the following ultra-high temperature mineral assemblage has been found in the known granulite facies rock assemblage:
False sapphire+timely; Low zinc /Fe3+ spinel+time; High alumina orthopyroxene+sillimanite+timely and high temperature medium striped feldspar. By using the conventional mineral thermometer, the phase equilibrium simulation is carried out according to the latest research false profile, and it is found that the metamorphic temperature in this area can reach 1000℃ and the metamorphic pressure is about 1.0 GPa. After the peak metamorphism, it is followed by a near-isobaric cooling process, and then it turns back to form a near-isothermal decompression path. Microstructure, mineral reaction and phase equilibrium simulation show that the rock has experienced counterclockwise pT trajectory.
Paleofluid exists in ultra-high temperature metamorphic minerals, and its composition is CO2, which is consistent with the anhydrous mineral assemblage widely existing in rocks. According to the chemical and isotopic dating of monazite and zircon single mineral samples, the age of ultra-high temperature event is 1.92Ma, which belongs to Proterozoic high temperature metamorphism. It is found that from west to east, the age of ultra-high temperature metamorphism event changed from 1.95Ma to 1.92Ma, obviously showing a new trend. Based on this, the author speculated that the ultra-high temperature metamorphism of the suture zone in Inner Mongolia was caused by the oblique collision and scissor-like closure of the Ordos block in the south and Yinshan block in the north when the Proterozoic North China Craton was welded into columbia supercontinent [5].
The determination of ultra-high temperature metamorphic belt in Inner Mongolia is a great progress in metamorphic geology in China.
3. Very low-grade metamorphism.
Extremely low-grade metamorphism refers to metamorphism with metamorphic temperature conditions between diagenesis and low-grade metamorphism. Using low-temperature metamorphic minerals such as zeolite, clay minerals and chlorite and their mineral combinations, drawing isoparametric lines of extremely low-grade metamorphism and revealing their thermal structure can play a certain role in predicting the prospect of oil and gas resources, because it is generally believed that if the ground temperature reaches the metamorphic category, the prospect of oil and gas resources will be greatly reduced.
In the extremely low metamorphic area, due to the low metamorphic temperature, the mineral crystal size is very fine, which is difficult to be identified by general rock microscope. Illite crystallinity is an important method to quantitatively divide the metamorphic degree of rocks in extremely low-grade metamorphic areas, and X-ray diffraction analysis is the most effective method to measure illite crystallinity. Since 1962, different illite crystallinity indexes have appeared in western literature, such as Weaver index, Weber index and Kubler index. Wang He and Jin of Peking University determined the relationship between these indexes from the perspective of X-ray theory, and improved the determination method and accuracy of illite crystallinity.
The study of extremely low-grade metamorphism in China is weak. In the late 1990s, Suo Shutian and others studied the Youjiang low-temperature gold deposit in Guangxi by means of extremely low-grade metamorphism. 2 1 century, the study of extremely low-grade metamorphism in China has been gradually combined with the study of oil and gas geology, and remarkable progress has been made. Bi Xianmei and others have discussed the relationship between extremely low-grade metamorphism and mineralization [7]. Wang Hejin and Zhu Mingxin discussed the relationship between the structural changes of layered silicates and metamorphic temperature and pressure conditions, such as the crystallinity of illite and chlorite, illite polymorphism and crystal axis b0. Value and strain characteristics, etc. Lower Paleozoic shale and Triassic flysch widely distributed in Hunan and northwest Sichuan are analyzed and studied [8, 9]. Among them, the vertical planes of the four sections of eastern Hunan and western Hunan should change along the sections. At the same time, using internationally comparable illite crystallinity data, it is determined that the regional low-temperature and extremely low-grade metamorphic temperature of Mesoproterozoic-Lower Paleozoic is 250 ~ 400℃, but the metamorphic pressure changes from time to time. Mesoproterozoic is of medium pressure type, and Neoproterozoic-Lower Paleozoic is of medium and low pressure type. All these have deepened the geological community's understanding of these ancient rocks of the Yangtze Platform.
4. Impact metamorphism
Meteorites hit the earth or other celestial bodies, creating craters. The surrounding rock is under the conditions of extremely high strain rate (106 ~109s-1), instantaneous high temperature (1000 ~ 1000℃) and dynamic high pressure (10). Judging from the photos interpreted by the data sent back by Chang 'e 1, the surface of the moon is covered with craters of all sizes. Unlike the moon and other celestial bodies, the earth has an atmosphere about 1000km thick, so smaller celestial bodies that hit the earth after falling into the atmosphere burn due to strong friction. So there are few craters left on the earth. According to statistics, there are more than 160 known craters in the world. Many large craters are home to world-famous metal deposits, such as sudbury, and most small craters have been developed into tourist attractions, such as Reese in southern Germany and Meteor Crater in Arizona, USA [10].
Because of the cover of surface sediments, it needs a lot of research work to determine a crater. At present, the confirmed crater in China is Baisha, Hainan, which is publicly reported in1997 [11]; Xiuyan crater in Liaoning Province was discovered in 1970s and was once considered as a rotating structure. After 40 years of repeated research, Guangzhou Institute of Geochemistry recently cooperated with Liaoning Metallurgical Geology Company to conduct scientific drilling with a depth of 307 meters. At the depth of 107 ~ 149 meters, a series of impact effects caused by shock waves such as timely shear foliation, multi-phase conglomerate containing molten glass and glass impact were found. And the properties of the impact structure are determined. This achievement was published in 2009 [12], which is a significant progress in the study of impact metamorphism in China.
Second, teaching of metamorphic petrology
Due to the great progress in various fields of metamorphic petrology, the teaching of metamorphic petrology in China has also made great progress. The concrete manifestations are as follows: ① Many China scholars' research results have been adopted by major foreign metamorphic petrology textbooks; (2) China Geo University (Wuhan) took the lead in the English teaching of metamorphic petrology and achieved success.
1. The achievements of many domestic scholars in metamorphic petrology have entered foreign textbooks.
For a long time, foreign scholars know very little about the research situation in China, so that the textbooks of metamorphic petrology published abroad generally refer to the achievements of foreign scholars. In recent years, with the pace of reform and opening up, academic exchanges between China and the West have been frequent. Now the achievements of China scholars have gradually appeared in textbooks published abroad.
Taking "The Rock Genesis of Metamorphic Rocks" (8 the D.) published by Kurt Bucher and Rodney Grapes in Springer-Verlag 2011as an example, the achievements of 12 domestic scholars are cited.
1) Professor Wu Chunming's paper on geological thermometers in high-grade metamorphic rocks from 2004 to 2007 was cited in the fourth chapter of Metamorphic Degree.
2) Professor Zhang (2003) published the combination of extremely low geothermal gradient when the ultra-high pressure metamorphic rock series in the western Tianshan Mountains subducted to 150km, and dolomite reacted to generate magnesite+aragonite, which belongs to the "forbidden zone" in metamorphic rocks. This paper has been cited many times. The third chapter "Metamorphism Process" is the designated reference for readers to read, and the sixth chapter "Metamorphism of Dolomite and Limestone" is listed as "cited reference".
3) In Chapter 9, "Metamorphic basic rocks", seven papers on ultrahigh-pressure metamorphism by China scholars are also cited. I won't list them all here.
2. English teaching of metamorphic petrology
The teaching of metamorphic rock petrology in China has always been a part of petrology, and the teaching hours are as high as 40 hours. After 200 1, petrology will be reduced from 220 hours to 150 hours, and metamorphic rocks will be reduced accordingly. In order to speed up the integration of China's higher education with the international community and speed up the training of international professionals, the bilingual teaching of metamorphic rock petrology in the science base class of China Geo University (Wuhan) was reformed. Since 10, with the efforts of Professor Sang Longkang and others, British geologist roger mason has played a very good role in teaching metamorphic rock petrology in English, overcome many difficulties and made great achievements.
In the lecture, Professor roger mason not only introduced the genesis of typical metamorphic rocks in China, but also introduced the contact metamorphism of Scottish Barrow Belt, Norwegian Suligerma metamorphic belt and British Skidow granite contact belt in detail, which greatly broadened students' horizons and mastered the working methods of metamorphic geology. Metamorphic Geology, edited by Sang Longkang and roger mason, was also published as the 11th Five-Year Plan textbook of China Geo University in 2007, and won the second prize of Hubei Teaching Achievement in 2009 [14].
The advent of metamorphic geology and the achievements of bilingual teaching of metamorphic petrology have laid a good foundation for improving the teaching quality of metamorphic petrology in the future.
Reviewing the research progress of metamorphic petrology in recent 10 years, we can find that: ① combining with solving major problems of social and economic development, finding and solving problems in production practice is the driving force for the further development of metamorphic petrology; (2) Paying close attention to the frontier of discipline development, grasping hot issues and investing in research strength are the only way to improve the theoretical level of discipline; Strengthening international academic exchanges and broadening research horizons are necessary means to ensure the level of disciplines and enhance international competitiveness.
At present, China's geological research is moving from a geological power to a geological power. Strengthening the study of metamorphic petrology, crystalline petrology and metamorphic geology is one of the keys to the development of geological science in China.
refer to
[1] You Zhendong. 50 years of metamorphic petrology in China. Join: Wang Hongzhen, editor. Fifty years of geological science in China. Wuhan: China Geo University Press, 1999, 144 ~ 152.
[2] You Zhendong. A new era of regional geological research. See: 20th Annual Academic Meeting of geological society of china Geological History Professional Committee, 2008, 70 ~ 72.
[3] Meng Xianlai. Speech at the opening ceremony of1:250,000 regional geological survey report meeting and "Eleventh Five-Year Plan" key seminar in the blank area of Qinghai-Tibet Plateau. Geological Bulletin, 2006, (2)
[4], Yang Jingsui. Deep drilling in Dabie-Sulu ultrahigh pressure metamorphic belt, Journal of China Geo University, AGU, February 22, 2005, 86(8):77~78.
Liu Shijie Chu Jiatai. Proterozoic UHT metamorphic granulites in the North China Craton: a tectonic model of extreme crustal metamorphism. Precambrian studies, 20 1 1
Suo, Bi Xianmei, Zhou. Extremely low-grade metamorphism: taking Youjiang Mesozoic tectonic belt as an example. Beijing: Geological Publishing House, 1999.
Bi Xianmei, Mo Metaphysics. Diagenesis-ultra-low grade metamorphism and related minerals. Frontier of Earth Science, 2004, 1 1 (4)
Wang Hong, M, Tao Xiaofeng, et al. Diagenesis and metamorphism of Triassic flysch in northwest Sichuan. Journal of Geology, 2008,82:17 ~ 926.
Zhu Mingxin, Wang Hejin. Extremely low-grade metamorphism of Lengjiaxi Group and Banxi Group in Changsha-Liling-Liuyang area. Acta petrolei sinica, 200 1, 17 (2)
[10] You Zhendong, Liu Rong. Research status and prospect of meteorite impact tectonism. Journal of Geomechanics, 2008, 14 (1): 22 ~ 36.
[1 1] Wang Daojing. Hainan Baishakeng. Haikou: Hainan Publishing House, 1997.
Chen Ming, Xiao Wansheng, Xie Xiande. Confirmation of Xiuyan crater. Science bulletin, 2009, 54: 2777 ~ 2780.
Yang, Gong, Sang Longkang, et al. Main course construction and personnel training of geology major in China Geo University. Wuhan: China Geo University Press, 20 12.
[14] Sang Longkang, roger mason. Metamorphic geology (English version) Wuhan: China Geo University Press, 2007.