Abstract:Abstract：After 1309 days of hard work, the Chinese Continental Scientific Drilling (CCSD) project drilled a total depth of 5118.20 m and reached its target depth by January 23th, 2005. The well completion is a new landmark in the development of China′s drilling technology. A comprehensive on-going study is being carried out and great advances have been made in the following aspects：precise dating of deep subduction of voluminous continental materials, UHP deep subduction and exhumation, setting of formation of protoliths of UHP rocks, upper mantle rheology, discovery of special, new mantle minerals and discovery of subsurface fluid anomalies and subsurface microorganisms.

Abstract:Abstract：This paper introduces the operation of China′s first deep hole, hard rock continuous coring project, CCSD-1 drilling project, concerning the drilling technical design, hole structure and casing program , as well as the techniques used in core drilling, hole reaming and directional drilling. In addition, the drilling process of CCSD-1 and the technical problems encountered in drilling and the measures adopted to solve the problems are described, and the main technical and economic indices are presented. Many special and new drilling technologies have been used in the drilling operation of CCSD-1, and high-efficiency, good-quality and low-cost drilling results have been achieved.

Abstract:Abstract：Sm-Nd ages of from eclogites in the mainhole of the Chinese Continental Scientific Drilling (CCSD) Project and outcrops in the southern ultrahigh-pressure terrane were determined. The data points of whole rock, garnet and omphacite of each sample all plot on a line. Except for sample B210R186, the other five samples eclogites give very close Sm-Nd isochron ages, ranging between 202.6 and 219 Ma. These Sm-Nd ages are similar to those (SHRIMP U-Pb ages 200 - 220 Ma) of zircon retrogressive rims from the country rock——gneisses, suggesting that the Sm-Nd isotope system of garnet in eclogites analyzed in the study might be reset during the isothermal decompressional retrogressive stage and close during the retrograde transition to amphibolite facies. Therefore the Sm-Nd whole rock-mineral isochron ages of 202.6-219 Ma determined in this paper should be interpreted as representing the retrograde ages of the isothermal decompressional retrogressive stage during exhumation of the South Sulu eclogite, rather than the ultrahigh-pressure metamorphic ages of the Sulu terrane.

Abstract:Abstract：The drill site of the 5000 m deep main hole of the Chinese Continental Scientific Drilling Project (CCSD) is located in the southern Sulu ultrahigh-pressure (UHP) metamorphic belt. The 0 to 2000 m interval of the CCSD main hole consists of eclogite, gneiss, garnet peridotite and minor schist and quartzite. The eclogites with a cumulative thickness of about 1000 m have different mineral assemblages and model contents, as well as variable petrochemical compositions. They can be divided into five types：Si-rich quartz eclogite, Ti-rich rutile eclogite, Al-rich phengite and kyanite eclogite, Mg-rich two-mineral eclogite and normal eclogite. Protoliths of eclogites include layered mafic to ultramafic cumulates and supracrustal rocks. The whole-rock composition of eclogites has an apparent controlling effect on the contents of some components in garnet, omphacite and phengite and directly influences the P-T estimates of UHP metamorphism. The extensive development of diffusional compositional zoning in the eclogitic garnet, omphacite and phengite indicates that these UHP minerals were re-equilibrated during the early-stage retrograde metamorphism. This fact and the existence of garnet porphyroblasts with growth zoning suggest that the eclogites formed at higher temperature (940℃) and pressure (>4.5GPa) than those estimated by previous workers.

Abstract:Abstract：The main hole of the Chinese Continental Scientific Drilling (CCSD) Project is located in the eastern part of the Dabie-Sulu ultrahigh pressure (UHP) metamorphic belt. In the 0–2000 m long core, all kinds of eclogites account for >50 percent and most of them have experienced different degrees of retrograde metamorphism. According to the retrograde degrees of the dominant minerals garnet and omphacite in the eclogites, the process of the retrograde metamorphism may be divided into two major stages and four substages：the first major stage, which may be further divided into the substages of weak retrograde metamorphism and partial retrograde metamorphism，and the second major stage, which may be further divided into the substages of retrograde metamorphism and strong retrograde metamorphism. The general trend of retrograde process is as follows: garnet was gradually replaced by pargasite or epidote+biotite and omphacite was replaced by symplectitic coronas of amphiboles and plagioclase; the jadeite content of omphacites decreases gradually in the retrogression and part of omphacites are transformed to aegirine-augites. The P-T conditions of eclogites are as follows: the peak stage, 697–831℃ and ~3.0 GPa; the substage of partial retrograde metamorphism, 629–776℃ and 1.2-1.6 GPa; the substage of retrograde metamorphism, 550–650℃ and 0.5-0.7 GPa; the substage of strong retrograde metamorphism, 300–400℃ and 0.30-0.35 GPa. According to an integrated study of the petrological and mineralogical characteristics and P-T conditions, it is deduced that eclogites underwent a process of two-stage exhumation: the first major stage witnessed nearly isothermal decompression, suggesting fast exhumation (eclogites experienced retrograde metamorphism of the first major stage during this stage) and the second major stage saw decrease in temperature and pressure due to slow uplift (during this stage, eclogites underwent retrograde metamorphism of the second major stage). The complete retrograde metamorphism of omphacites is not only the marker of distinguishing the two major stages of retrograde metamorphism but also a marker of distinguishing the two major stages of exhumation.

Abstract:Abstract： How radiogenic heat-producing elements (HPE) are distributed as a function of depth in the Earth is critical to determine the thermal and rheological structure of continental crust and to constrain geochemical, petrological, and tectonic models of crustal evolution. Our knowledge of HPE distribution within the crust has been derived predominantly from studies of large-scale granitic batholiths. The HPE distribution within high-grade metamorphic terrains are not well studied and thus poorly understood. The Chinese Continental Scientific Drilling (CCSD) Project provides us an unparallel opportunity to characterize the vertical HPE distribution in a type example of high- to ultrahigh-pressure metamorphic terrains worldwide. U, Th, and K2O contents have been measured on 734 core samples taken at intervals of 2 to 5 m and used to determine the distribution pattern of radiogenic heat production. Preliminary results show that： (1) the granitic gneisses have the highest heat production with an average of 1665×10-11W/kg; (2) the paragneisses have the intermediate heat production values; (3) the rutile eclogites and garnet peridotites have the lowest and similar values at about 17~20×10-11W/kg；(4) radiogenic HPE concentrations and heat production change stepwise as lithology changes downward. These data reveal a sandwich-like structure for the HPE in the drilling core in which relatively high heat production sections are enclosed by relatively low heat production sections. Such a pattern is not consistent with the downward-decreasing exponential distribution predicted from modeling of surface heat flow data. However, it may represent a typical structure in UHP metamorphic terrains as a result of deformation during or after the exhumation which resulted in the juxtaposition of mafic to ultramafic blocks with felsic blocks.

Abstract:Abstract：The Ground Core Gamma Eye was used to test the natural gamma values of cores (2000 m) in the main hole of the Chinese Continental Scientific Drilling (CCSD) Project. The peak and valley of the gamma curve and their corresponding petrological, structural and mineralization features were recorded. Through systematic logging, a 2000 m long natural gamma value profile was constructed. The gamma value of eclogite is low and gets high progressively from eclogite through amphibolite to granite gneiss. There is a distinct correspondence between the gamma values and the lithology of metamorphic rocks. Concentrations of the radioactive elements K, U and Th for different types of rock are varied. The genesis of metamorphic rocks is discussed in the context of the radioactivity of these elements in rocks. It is proposed that the genesis of rocks reflected by the protoliths of eclogites and meta-basic (-intermediate) rocks different from that of metapelitic sedimentary rocks. These rocks are orthometamorphites and high Th/U ratios of the rocks are related to the action of near-surface weathering or hydrothermal alteration. The systematic measurements of the natural gamma values of high-grade metamorphic rocks in the main hole are helpful to homing the depth and orientation of cores and studying the genesis of rocks, thermal state of the lithosphere and tectonic evolution.

Abstract:Abstract：The magnitude of the maximum principal stress is determined by using acoustic emission measurements of cores at 301, 598, 1003, 1258 and 1531 m depth in the main borehole of the Chinese Continental Scientific Drilling (CCSD) Project, and the measurement results of acoustic emission are compared with the measurement results of borehole breakouts. It is shown that the results from two methods are in good agreement. The results of stress measurement are reliable. The magnitude of stress in the main borehole increases with depth. The maximum principal stress is 13.4 MPa at 301 m depth and 55.2 MPa at 1655 m depth. The increase rate with depth is 0.0279 MPa/m. The direction of the maximum principal stress is N 54.2°±3.3°E and does not change with depth. It is considered that acoustic emission combined with borehole breakouts is an economic and effective method for deep in-situ stress measurement.

Abstract:Abstract：The lithologic section of the upper 2000 m core from the main hole of CCSD reveals that the granitic gneiss unit of the 1113-1600 m interval of core is the downward extension of granitic gneisses of the Shihu slice of the North Sulu ultrahigh-pressure metagranitic gneiss imbricate tectonic slice at the surface. The upper and lower boundaries of this unit are ductile shear zones, and in the interior of this unit minor ductile shear deformation is developed. The shear sense markers (rolled porphyroclastic structure, etc.) are only seen locally. They, mainly located in interbeds of weakness, are dominated by the SE-NW thrust shear sense with subordinate NW-SE normal-slip shear sense. The latter is new evidence for the existence of extensional dome structure in the Sulu area. In the 1140-1280 m lithologic interval there occurs discontinuous, weak stretching lineation, which generally plunges SE at angles of 10-36. Some quartz in granitic gneisses occurs as polycrystalline quartz bands. The dominant mineral feldspar in the granitic gneisses essentially shows no phenomenon of dynamic recrystallization and has only the feature of weak stretching (X∶Y=2 or so); foliation of the granitic gneiss unit generally dips 170°E at 20°on the average, which is notably different from the attitude of foliation the other lithologic units. Foliation of the granitic gneiss unit probably represents E-W-directed structure before exhumation and deformation; whereas other lithologic units are greatly influenced by exhumation and deformation. The foliation mainly represents NE-NNE structure formed in the exhumation phase. EBSD analysis of the quartz fabric and comparison of the analytic results with the results obtained by the Fedorov stage indicate that the granitic gneiss unit in the 1113-1600 m core has undergone medium- to low-temperature deformation, with the high-temperature fabric survived locally. The shear sense is mainly the vergence of thrusting from SE to NW. The high-temperature fabric and medium-temperature fabric both indicate the SE-NW thrusting shear sense, reflecting the consistency of the senses of relative shear of the slice in the early stage and main stage of exhumation. The weak deformation in the interior of the granitic gneiss unit is due to the fact that rocks of the granitic gneiss unit were so competent during exhumation and deformation that they were deformed difficultly. Brittle deformation in the late stage is mainly marked by tenso-shear faulting.

Abstract:Abstract：The determination of the contact relationship between the high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic belts at the southern margin of the Sulu HP-UHP metamorphic terrane has great significance for establishing the tectonic framework of the area. The basal conglomeratic bed of the Jingping Group in the HP metamorphic belt at the southern margin of the Sulu HP-UHP metamorphic terrane unconformably overlies the Qushan granite-gneiss in the southern part of the UHP metamorphic belt. The gravels in the conglomeratic bed underwent late-stage plastic deformation but their geological characteristics still display the unique properties of sedimentary gravels in the lower part of the strata. In addition, isotope chronological study has revealed that the protoliths of the Qushan granite-gneiss and Jinping Group metamorphic rocks formed at 859 Ma and 814 Ma respectively, indicating that the contact between the Qushan granite-gneiss and Jinping Group metamorphic rocks is unconformable. They together underwent HP-UHP metamorphism-deformation in the process of the late-stage tectonic movement. During their exhumation the Jingping Group metamorphic rocks were subducted toward the WNW, forming a ductile shear zone on the unconformity.

Abstract:Abstract：The characteristics of the Nangang-Gaogongdao ductile shear zone in the south Su-Lu high-pressure metamorphic belt were studied on the basis of the geological section survey. The results reveal that： rocks in the upper part of the shear zone are deformed weakly, in which the S-C fabric and stretching lineation are developed; rocks in the central part are deformed intensely, in which asymmetric folds, S-C fabrics and σ- and δ-type rolled porphyroblasts, as well as domino structure of plagioclase are developed; and rocks in the lower part are deformed most intensely, in which mylonitized grains accounts for up to 80%-90% and congruous tight folds can also be found. EBSD fabric analysis shows that： mylonitized quartz grains in the upper part are characterized by the low- to medium-temperature rhombohedral face fabric and medium-temperature prismatic face fabric, those in the central and lower parts are characterized by low-temperature basal face fabric and low- to medium-temperature rhombohedral face fabric, and banded quartz grains in the shear zone are dominated by medium-temperature prism face fabric, which indicates that the shear zone experienced a complex deformation process from medium-temperature through low-medium temperature to low temperature deformations. The shear sense of the quartz fabrics is mainly from SE to NW and subordinately from NW to SE, reflecting that thrusting shear deformation is dominant, while ductile déollement shear is subordinate in the shear zone. No apparent trend of variations exists in chemical composition and REE patterns of the rocks from the upper part to lower part of the shear zone, so the composition may be determined mainly by the primary compositions of the rocks. 39Ar-40Ar ages of muscovite and biotite from the shear zone indicate that intensive metamorphism and deformation took place in the period of 253.8-214.2 Ma.

Abstract:Abstract：The author presents the main results of the latest geophysical investigations in the Dabie-Sulu ultrahigh-pressure (UHP) metamorphic belt, analyzes the general characteristics of the lithospheric structures in the Dabie-Sulu terrane, and makes a comparison of these characteristics with those beneath the East Qinling and Tongbai terranes observed by previous workers. The crustal structure in the eastern segment of the Central orogenic belt reflects the northward deep intracontinental subduction of the Yangtze craton. The continental crust was subducted at angles of about 20°-30°. As the subduction angles were gentle, an open backland basin developed in the eastern segment of the orogenic belt, and the basement structure below the basin still has the characteristics of the plate convergence of the orogenic plate. The manifestations of large-scale magmatic intrusions occurring in the upper-mid crust in the cores of the orogenic belt were related to post-orogenic geological processes. The Early Mesozoic Dabie-Sulu UHP metamorphic belt might still exist at the deep levels of the crust below the East Qinling and will not be exposed on the surface today.

Abstract:Abstract：Analysis of 3-D P-wave velocity structure shows that the crustal velocity structure below the Sulu-Dabie ultrahigh-pressure metamorphic belt has the following basic features: the upper crust has a markedly high velocity and is upwarped, the middle crust thickens, the lower crust is deeply buried and the Moho is downwarped. Compared with the Dabie area, the upper crust below the Sulu-Dabie ultrahigh-pressure metamorphic belt has a high P-wave velocity，and the area of the high-velocity region at the surface and volume of the high-velocity body of the upper crust are large. However, the Moho beneath the Dabie orogen is more deeply downwarped than that beneath the Sulu UHPM terrain, and the mountain root of the crust beneath the Sulu region gradually wore away. All these indicate that more intense subduction and exhumation took place in the Sulu terrain, and more UHP metamorphic rocks with higher velocity and density were exhumed to the crust and surface in the Sulu orogen than in the Dabie region. However, in Sulu, orogeny and UHP metamorphism started later but ended earlier. The orogeny in Sulu probably underwent a relatively short but intense evolution process. The formation and evolution of the orogeny and UHP metamorphic belt in Sulu may probably be related to the large-scale sinistral strike-slip motion of the Tanlu fault belt and the effects of the NW-SE extensional stress field in North China. Especially, the effects of the regional-scale extensional stress field in the North China region since the Mesozoic is probably an important tectonic cause for the exhumation of voluminous UHP metamorphic rocks subducted into the mantle to the upper crust or the surface.

Abstract:Abstract：In operations of Nos. 153 to 166 runs of core drilling in the 4820 to 4930 m interval of the CCSD main hole, very obvious gas abnormities were monitored from drilling mud by the fluid geochemistry laboratory. According to the concentrations of gas components, the abnormities can be divided into two corresponding intervals: 4820 to 4860 m and 4869 to 4930 m. Both intervals showed strong CO2 and H2, with maximum concentrations of 3.6% for CO2 and 12.1% for H2 in the first interval and 24.8% and 18.7% in the second interval respectively. At 4906 m depth, in addition to abnormally high CO2 and H2 concentrations, a short, obvious He increase was also observed with a maximum concentration of 17×10-6, which is about 3 times the normal value. Analysis of the drilling process and off-line experiments on drill mud and additives showed that the decomposition of drill mud additives by microbes could be one of the major causes of the abnormities and that the loss of circulation additives promoted the increase and continuation of CO2 and H2 abnormalities. The existence of both subsurface gases and gases resulting from mud decomposition by microbes contributes to the gas abnormities in this study.

Abstract:Abstract：Two earthquakes of ML 3.9 occurred near the CCSD main hole on November 30 and December 25, 2001 respectively. The daily mean variation maps show that a pronounced anomalous phenomenon existed on the curves of fluid compositions in mud of the CCSD main hole before and after the earthquakes. Analysis of the maximum correlation coefficient of the fluid components indicates that all the fluid components are well correlated except Ar and CO2 which are poorly correlated (with a mean maximum correlation coefficient of 0.632 and a mean square deviation of 0.223). Distinct anomalous fluctuations of the maximum correlation coefficient took place both before and after the earthquakes. The daily mean values and anomalous maximum correlation coefficients suggest that the fluid anomalies appearing in the CCSD main hole might have a certain relation to seismic activities in the area.

Abstract:Abstract：The Chinese Continental Scientific Drilling (CCSD) is a national key scientific and engineering project of China. During the project work, partnering researchers from all over the world work together at remote drill sites and in laboratories at their institutions. There are three different but connected computer networks located in Beijing and the Donghai drilling site, Jiangsu Province. This article briefly introduces the demand analysis, network topology and management information system of this project, proposes an integrated plan for the management information system based on the mixed C/S and B/S structure and sums up related experience in the design, building and maintenance of this complicated network.