2006 Vol. 31, No. 4
Display Method:
2006, 31(4): 427-436.
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Abstract:
By the construction for the HP-UHP metamorphic rocks,containing eclogite,feldspar amphibolite,paragneiss and granitic gneiss,it is revealed that their protoliths were continental basaltic rocks,gabbros,supracrustal rocks and granites formed under extensional environment at the Yangtze passive continental margin. New zircon SHRIMP U-Pb dating for the protoliths of the south Sulu UHP metamorphic rocks reflects the Neoproterozoic (700—800 Ma) granitic-marie magmatism events induced by the Rodinia supercontinental breakup. Detailed zircon SHRIMP U-Pb dating for granitic gneiss in the N. Sulu (Qingdao-Weihai) area shows its oldest metamorphic basement being age of〉2 400 Ma and was overprinted by metamorphisms of 1 700-1 800 Ma and to 200 Ma. Therefore,above-mentioned age dating together with previous chronologic data led us to conclude that the Sulu HP-UHP nappes have two basements: the Early-Middle Protrozoic (≥2 400 Ma) basement in the N. Sulu and the Neoprotrozoic (700-800 Ma) basement in the S. Sulu. The basement ages in the N. Sulu together with its western part of the no-UHP metamorphic area (Laiyang-Penglai) are similar and named by the Jiao-Liao- Korea block (JLKB) belong to the NCP. Besides,the boundary between both of the S. Sulu UHP area and JLKB is along north Wulian and south Haiyangsuo. New zircon SHRIMP U-Pb dating for coesite-bearing quartzite of the N. Sulu shows the UHP peak metamorphism being age of 238 Ma and retrograde metamorphism being age of 215 Ma,which indicates both basements of the Sulu UHP metamorphic terrain have undergone UHPM simultaneously. Based on occurrences of the two different basements of the Sulu HP-UHP metamorphic terrain,a new dynamic model of deep subduction erosion for continent-continent collision is proposed in this study. That means during the deep subduction of YZP at 240-220 Ma,the part of JLKB had been dragged downward to be 100 kM depth and a wedge subduction erosion body was formed on the upper part of the Yangtze subducted slab. Then both of them were exhumed rapidly.
By the construction for the HP-UHP metamorphic rocks,containing eclogite,feldspar amphibolite,paragneiss and granitic gneiss,it is revealed that their protoliths were continental basaltic rocks,gabbros,supracrustal rocks and granites formed under extensional environment at the Yangtze passive continental margin. New zircon SHRIMP U-Pb dating for the protoliths of the south Sulu UHP metamorphic rocks reflects the Neoproterozoic (700—800 Ma) granitic-marie magmatism events induced by the Rodinia supercontinental breakup. Detailed zircon SHRIMP U-Pb dating for granitic gneiss in the N. Sulu (Qingdao-Weihai) area shows its oldest metamorphic basement being age of〉2 400 Ma and was overprinted by metamorphisms of 1 700-1 800 Ma and to 200 Ma. Therefore,above-mentioned age dating together with previous chronologic data led us to conclude that the Sulu HP-UHP nappes have two basements: the Early-Middle Protrozoic (≥2 400 Ma) basement in the N. Sulu and the Neoprotrozoic (700-800 Ma) basement in the S. Sulu. The basement ages in the N. Sulu together with its western part of the no-UHP metamorphic area (Laiyang-Penglai) are similar and named by the Jiao-Liao- Korea block (JLKB) belong to the NCP. Besides,the boundary between both of the S. Sulu UHP area and JLKB is along north Wulian and south Haiyangsuo. New zircon SHRIMP U-Pb dating for coesite-bearing quartzite of the N. Sulu shows the UHP peak metamorphism being age of 238 Ma and retrograde metamorphism being age of 215 Ma,which indicates both basements of the Sulu UHP metamorphic terrain have undergone UHPM simultaneously. Based on occurrences of the two different basements of the Sulu HP-UHP metamorphic terrain,a new dynamic model of deep subduction erosion for continent-continent collision is proposed in this study. That means during the deep subduction of YZP at 240-220 Ma,the part of JLKB had been dragged downward to be 100 kM depth and a wedge subduction erosion body was formed on the upper part of the Yangtze subducted slab. Then both of them were exhumed rapidly.
2006, 31(4): 437-456.
Abstract:
The Zhimafang ultramafie body in the Sulu ultrahigh pressure (UHP) metamorphic belt is a block of unusual mantle composed of highly depleted peridotite,which has been enriched in REE and LILE by metasomatism. It consists of interlayered garnet peridotite and garnet-free peridotite,which have many common compositional features and formed under the same p-T conditions. The rocks record several geological events; however,evidence of progressive metamorphism has not been confirmed. Calculated p-T conditions from equilibrium mineral pairs suggest pressures of 6-7 GPa. Partial melting of the sequence in the Mesoproterozic was probably responsible for the interlayering of the two rock types. AU-Pb zircon age of 220 Ma records the collision between Yangtze and North China blocks,but this age may not represent the time of peak UHP metamorphism. More likely,it records exhumation of the block from the deep portion of the subduction zone. The available data suggest that the garnet was exsolved from enstatite as rocks rose from the deep mantle.
The Zhimafang ultramafie body in the Sulu ultrahigh pressure (UHP) metamorphic belt is a block of unusual mantle composed of highly depleted peridotite,which has been enriched in REE and LILE by metasomatism. It consists of interlayered garnet peridotite and garnet-free peridotite,which have many common compositional features and formed under the same p-T conditions. The rocks record several geological events; however,evidence of progressive metamorphism has not been confirmed. Calculated p-T conditions from equilibrium mineral pairs suggest pressures of 6-7 GPa. Partial melting of the sequence in the Mesoproterozic was probably responsible for the interlayering of the two rock types. AU-Pb zircon age of 220 Ma records the collision between Yangtze and North China blocks,but this age may not represent the time of peak UHP metamorphism. More likely,it records exhumation of the block from the deep portion of the subduction zone. The available data suggest that the garnet was exsolved from enstatite as rocks rose from the deep mantle.
2006, 31(4): 457-474.
Abstract:
The Chinese pre-pilot hole (PP1) is located at Zhimafang Village,Donghai County in the Sulu UHP terrane,east China. Ultrahigh-pressure peridotites of 115 m thick within gneiss recovered from the PP1 are composed of abundant lherzolite,harzburgite,and minor wehrlite and dunite. Peridotite near to the contacts with gneiss is strongly serpentinized. More than 90 vol% peridotites contain garnet and phlogopite; some contain magnesite and Ti-clinohumite. All peridotites contain lower "fertile elements" compared with primitive mantle,their Mg# numbers range from 90.3 to 92.6,and MgO content (36.61%-49.15%,averagely 45.17%) has negative correlation with Na2O (0.01%-0.25%),Al2O3 (0.07%-3.71%,most < 2.0%,averagely 1.46%) and CaO (0.12%-2.53%,one up to 3.30%,averagely 1.00%) contents. In contrast to major element depletion feature,the PP1 peridotites show light rare earth element-enriched and slight to moderately fractionated REE pattern of nearly parallel curves and roughly identical pattern with (La/Lu) N ratios of 3.18-33.05. Most of the peridotites contain high Ba (higher than 92 times of primitive mantle) and LREE and low HFSE,and are characterized by negative Rb,Nb,Ta,Zr,Hf and Sr anomalies (e.g.,C39-157-81) in spidergrams. Ti/Eu ratios are lower than ca. 1 300. The lack of correlation between refractory degree and enrichment of incompatible elements documents effect by metasomatism after mantle melting. Petrographic characteristics show multiple metasomatism of phlogopite and magnesite. Phl-rich peridotites (such as samples C25-143-61,C32-149-71) have the K2O enrichment trend and good correlations between K2O and some LILE such as Rb,Ba and Th. No positive correlations between K2O and REE and between Sr and Ca are seen. These signatures show that peridotites were metasomatised by hydrous,silicic,aluminous and alkaline melts containing some LILE,and then severely overprinted by metasomatism of magnesite melt containing high Ba and low Rb and HFSE which modified Ba content drastically and endued REE patterns of mantle carbonatite melt. Whole rock has heterogeneously high radiogenic Sr (87 Sr/86 Sr=0.708 4-0.720 1) and low radiogenic Nd (ε_ Nd (t) =-1.14 to-8.55),which indicates the peridotites from PP1 hole was probably derived from long-term enriched mantle by agents from depth,especially combined with oxygen isotope compositions of anhydrous and hydrous minerals reported by previous studies.
The Chinese pre-pilot hole (PP1) is located at Zhimafang Village,Donghai County in the Sulu UHP terrane,east China. Ultrahigh-pressure peridotites of 115 m thick within gneiss recovered from the PP1 are composed of abundant lherzolite,harzburgite,and minor wehrlite and dunite. Peridotite near to the contacts with gneiss is strongly serpentinized. More than 90 vol% peridotites contain garnet and phlogopite; some contain magnesite and Ti-clinohumite. All peridotites contain lower "fertile elements" compared with primitive mantle,their Mg# numbers range from 90.3 to 92.6,and MgO content (36.61%-49.15%,averagely 45.17%) has negative correlation with Na2O (0.01%-0.25%),Al2O3 (0.07%-3.71%,most < 2.0%,averagely 1.46%) and CaO (0.12%-2.53%,one up to 3.30%,averagely 1.00%) contents. In contrast to major element depletion feature,the PP1 peridotites show light rare earth element-enriched and slight to moderately fractionated REE pattern of nearly parallel curves and roughly identical pattern with (La/Lu) N ratios of 3.18-33.05. Most of the peridotites contain high Ba (higher than 92 times of primitive mantle) and LREE and low HFSE,and are characterized by negative Rb,Nb,Ta,Zr,Hf and Sr anomalies (e.g.,C39-157-81) in spidergrams. Ti/Eu ratios are lower than ca. 1 300. The lack of correlation between refractory degree and enrichment of incompatible elements documents effect by metasomatism after mantle melting. Petrographic characteristics show multiple metasomatism of phlogopite and magnesite. Phl-rich peridotites (such as samples C25-143-61,C32-149-71) have the K2O enrichment trend and good correlations between K2O and some LILE such as Rb,Ba and Th. No positive correlations between K2O and REE and between Sr and Ca are seen. These signatures show that peridotites were metasomatised by hydrous,silicic,aluminous and alkaline melts containing some LILE,and then severely overprinted by metasomatism of magnesite melt containing high Ba and low Rb and HFSE which modified Ba content drastically and endued REE patterns of mantle carbonatite melt. Whole rock has heterogeneously high radiogenic Sr (87 Sr/86 Sr=0.708 4-0.720 1) and low radiogenic Nd (ε_ Nd (t) =-1.14 to-8.55),which indicates the peridotites from PP1 hole was probably derived from long-term enriched mantle by agents from depth,especially combined with oxygen isotope compositions of anhydrous and hydrous minerals reported by previous studies.
2006, 31(4): 475-487.
Abstract:
The ultramafic rocks in the CCSD-PP3 (China Continental Scientific Drilling) drill-hole consist of dunite and garnet peridotite with a gradual margin between them. The main minerals in the rocks are olivine,chromium spinel,diopside,endiopside,and/or garnet,orthopyroxene,amphibole and phlogopite. Chromium spinels in PP3 ultramafic rocks can be divided into 4 groups with a varied composition,Cr# (molar 100Cr/(Cr+Mg)) from 51 to 89,which consists of four evolution stages of the ultramafic rocks. The 4 stages are partial melting,eclogite facies,amphibole facies and greenschist facies. When the Cr# of chrome spinels increases,the Mg# (molar 100Mg/(Mg+Fe 2+)) of chromium spinels decreases,but oxygen fugacity rises. Compositions of the chromium spinels reflect that the rocks originating from the shallow mantle have subducted to a depth of over 100 km and have then been exhumed to the surface. During the subsequent greenschist-facies and amphibole- facies metamorphism,the chromium spinels lost some Cr,Mg and Al,but gained relatively more Fe.
The ultramafic rocks in the CCSD-PP3 (China Continental Scientific Drilling) drill-hole consist of dunite and garnet peridotite with a gradual margin between them. The main minerals in the rocks are olivine,chromium spinel,diopside,endiopside,and/or garnet,orthopyroxene,amphibole and phlogopite. Chromium spinels in PP3 ultramafic rocks can be divided into 4 groups with a varied composition,Cr# (molar 100Cr/(Cr+Mg)) from 51 to 89,which consists of four evolution stages of the ultramafic rocks. The 4 stages are partial melting,eclogite facies,amphibole facies and greenschist facies. When the Cr# of chrome spinels increases,the Mg# (molar 100Mg/(Mg+Fe 2+)) of chromium spinels decreases,but oxygen fugacity rises. Compositions of the chromium spinels reflect that the rocks originating from the shallow mantle have subducted to a depth of over 100 km and have then been exhumed to the surface. During the subsequent greenschist-facies and amphibole- facies metamorphism,the chromium spinels lost some Cr,Mg and Al,but gained relatively more Fe.
2006, 31(4): 488-496.
Abstract:
We report an unusual garnet pyroxenite, as a nodule enclosed within kyanite eclogites from Rongcheng, northeastern Sulu UHP metamorphic belt. Apart from its unusual texture, high degrees of various minerals (garnet, titanite, and Fe-Ti oxides) and solid exsolution within garnet or clinopyroxene, this nodule has unusual major and trace element geochemistry as shown by (1) low SiO2 (42.5%-43.1%), extremely high CaO (21.4%-21.9%), and high CaO/Al2O3 ratio (1.46-1.64); (2) high TiO2 (1.77%-1.89%), Zr (to 150 μg/g), V (359-419 μg/g), Nb (to 8 μg/g), and Y (17.7-23.1 μg/g) contents; (3) LREE-enriched, and nepherine normative; and (4) low Cr, Ni, and Co. Previous study on the mineral chemistry and texture relationships between different generations of minerals has suggested that it was formed as a cumulative clinopyroxene magacryst with high Ca-tschermakite component (31%-34%) from a gabbroic magma at p= (15-22) ×105 kPa, and T > 1 100 ℃. Major and trace element geochemistry on this nodule and its host kyanite eclogite suggest that the precursor of the Rongcheng pyroxenite was derived either from an ultramafic magma highly fractionated by accumulation of olivines or from an ultra-calcic basic magma that had lost some K2O and Na2O. No matter which was responsible for the formation of its precursor, both require a melting event and magma differentiation to occur at a pressure and temperature greater than 15×10-5 kPa and 1 300 ℃, respectively. This contribution suggests that protoliths for some of the eclogites within the Sulu UHP metamorphic belt formed in a tectonic environment distinct from those of Neoproterozoic age.
We report an unusual garnet pyroxenite, as a nodule enclosed within kyanite eclogites from Rongcheng, northeastern Sulu UHP metamorphic belt. Apart from its unusual texture, high degrees of various minerals (garnet, titanite, and Fe-Ti oxides) and solid exsolution within garnet or clinopyroxene, this nodule has unusual major and trace element geochemistry as shown by (1) low SiO2 (42.5%-43.1%), extremely high CaO (21.4%-21.9%), and high CaO/Al2O3 ratio (1.46-1.64); (2) high TiO2 (1.77%-1.89%), Zr (to 150 μg/g), V (359-419 μg/g), Nb (to 8 μg/g), and Y (17.7-23.1 μg/g) contents; (3) LREE-enriched, and nepherine normative; and (4) low Cr, Ni, and Co. Previous study on the mineral chemistry and texture relationships between different generations of minerals has suggested that it was formed as a cumulative clinopyroxene magacryst with high Ca-tschermakite component (31%-34%) from a gabbroic magma at p= (15-22) ×105 kPa, and T > 1 100 ℃. Major and trace element geochemistry on this nodule and its host kyanite eclogite suggest that the precursor of the Rongcheng pyroxenite was derived either from an ultramafic magma highly fractionated by accumulation of olivines or from an ultra-calcic basic magma that had lost some K2O and Na2O. No matter which was responsible for the formation of its precursor, both require a melting event and magma differentiation to occur at a pressure and temperature greater than 15×10-5 kPa and 1 300 ℃, respectively. This contribution suggests that protoliths for some of the eclogites within the Sulu UHP metamorphic belt formed in a tectonic environment distinct from those of Neoproterozoic age.
2006, 31(4): 497-504.
Abstract:
The Neoproterozoic granitoids in Wulian region are located north of the Wulian fault. They have undergone strong dynamic deformation but are slightly metamorphosed (green-schist facies). The granitoids are mainly biotite-syenogranitic in composition with minor quartz syenitic. The initial 87Sr/86 Sr ratios (ISr) are wide, ranging from 0.697 306 to 0.753 765. This may partially be ascribed to the inhomogeneity of magma source material or multi-source mixing with different proportions. Secondary disturbed after the granitic body's intrusion and concretion may also play a role, to some degree. The εNd (750 Ma) values of the granitoids are all lower than 0 and with wide ranges (-3.1 to-24.3), and the model ages (TDM) of two stages ranges from 1.7 to 3.4 Ga. This indicates that the parental magma of the Neoproterozoic granitoids in the Wulian region was primarily derived from crustal materials but with the mixed features of multi-sources. Therefore, the Neoproterozoic granitoids in Wulian have most probably been generated by partial melting of Archaean TTG gneisses (major tonalitic component thereinto) at pressures of about 0.8 Gpa (i.e. within the middle or the lower crust), and the addition of different proportions of mantle-derived juvenile materials. The addition of mantle-derived materials has been an important influence on the genesis of the Neoproterozoic granitoids in the Wulian region.
The Neoproterozoic granitoids in Wulian region are located north of the Wulian fault. They have undergone strong dynamic deformation but are slightly metamorphosed (green-schist facies). The granitoids are mainly biotite-syenogranitic in composition with minor quartz syenitic. The initial 87Sr/86 Sr ratios (ISr) are wide, ranging from 0.697 306 to 0.753 765. This may partially be ascribed to the inhomogeneity of magma source material or multi-source mixing with different proportions. Secondary disturbed after the granitic body's intrusion and concretion may also play a role, to some degree. The εNd (750 Ma) values of the granitoids are all lower than 0 and with wide ranges (-3.1 to-24.3), and the model ages (TDM) of two stages ranges from 1.7 to 3.4 Ga. This indicates that the parental magma of the Neoproterozoic granitoids in the Wulian region was primarily derived from crustal materials but with the mixed features of multi-sources. Therefore, the Neoproterozoic granitoids in Wulian have most probably been generated by partial melting of Archaean TTG gneisses (major tonalitic component thereinto) at pressures of about 0.8 Gpa (i.e. within the middle or the lower crust), and the addition of different proportions of mantle-derived juvenile materials. The addition of mantle-derived materials has been an important influence on the genesis of the Neoproterozoic granitoids in the Wulian region.
2006, 31(4): 505-512.
Abstract:
The breakouts began to occur under the depth of 1 200 m in the main borehole of Chinese Continental Scientific Drilling (CCSD), 143 breakout images are collected from acoustic borehole televiewer data between 1 216 m and 5 047 m. The average orientation of breakouts is 319.5°±3.5°. The average orientation of maximum horizontal stress is 49.5°±3.5°. Using breakout parameters measured from borehole breakouts (depth and width of breakout) and rock cohesion and inner friction angle determined from triaxial rock compression and deformation tests, the magnitudes of principal stress are calculated at 52 different depths from 1 269 m to 5 047 m. Overburden stress is calculated using the density logging data. The magnitude of maximum principal stress is determined using acoustic emissions. A comparison of measurement results of acoustic emission and borehole breakouts is carried out, and the results from the two methods are in good agreement. According to the orientations and magnitudes of three principal stresses, stress state (SH > Sv > Sh) in the area of CCSD indicates the strike-slip stress regime and is coincident with the strike-slip stress field observed from earthquake focal plane mechanisms.
The breakouts began to occur under the depth of 1 200 m in the main borehole of Chinese Continental Scientific Drilling (CCSD), 143 breakout images are collected from acoustic borehole televiewer data between 1 216 m and 5 047 m. The average orientation of breakouts is 319.5°±3.5°. The average orientation of maximum horizontal stress is 49.5°±3.5°. Using breakout parameters measured from borehole breakouts (depth and width of breakout) and rock cohesion and inner friction angle determined from triaxial rock compression and deformation tests, the magnitudes of principal stress are calculated at 52 different depths from 1 269 m to 5 047 m. Overburden stress is calculated using the density logging data. The magnitude of maximum principal stress is determined using acoustic emissions. A comparison of measurement results of acoustic emission and borehole breakouts is carried out, and the results from the two methods are in good agreement. According to the orientations and magnitudes of three principal stresses, stress state (SH > Sv > Sh) in the area of CCSD indicates the strike-slip stress regime and is coincident with the strike-slip stress field observed from earthquake focal plane mechanisms.
2006, 31(4): 513-519.
Abstract:
Magnetic susceptibility (κ) and density (ρ) were measured at 5.7 m depth intervals on drill cores from the main hole of the Chinese Continental Scientific Drilling (CCSD) Project. We analyzed the data by discriminant analysis employing SPSS 10.0 for Windows to test whether the lithology can be distinguished by petrophysical parameters. The density and magnetic susceptibility of the CCSD 100-2 000 m main hole are mainly controlled by the lithology. Lithology discriminant functions were constructed by means of the Enter Independents Together method. The results show that the total discriminant rate is 84.8%, while the rates of the serpentinized peridotite, orthogneiss, paragneiss, eclogite, amphibolite and retrograded eclogite are 100%, 87.1%, 89.7%, 89.6%, 96.7% and 63.7%, respectively. This research confirms that the petrophysical parameters of magnetic susceptibility and density can provide quantity constraints for the lithology discrimination of ultrahigh-pressure (UHP) rocks. Furthermore, it throws some light on the lithology determination, and may be useful in improving the interpretations of geophysical surveying and well logging.
Magnetic susceptibility (κ) and density (ρ) were measured at 5.7 m depth intervals on drill cores from the main hole of the Chinese Continental Scientific Drilling (CCSD) Project. We analyzed the data by discriminant analysis employing SPSS 10.0 for Windows to test whether the lithology can be distinguished by petrophysical parameters. The density and magnetic susceptibility of the CCSD 100-2 000 m main hole are mainly controlled by the lithology. Lithology discriminant functions were constructed by means of the Enter Independents Together method. The results show that the total discriminant rate is 84.8%, while the rates of the serpentinized peridotite, orthogneiss, paragneiss, eclogite, amphibolite and retrograded eclogite are 100%, 87.1%, 89.7%, 89.6%, 96.7% and 63.7%, respectively. This research confirms that the petrophysical parameters of magnetic susceptibility and density can provide quantity constraints for the lithology discrimination of ultrahigh-pressure (UHP) rocks. Furthermore, it throws some light on the lithology determination, and may be useful in improving the interpretations of geophysical surveying and well logging.
Mineralization of High-Pressure and Ultrahigh-Pressure Metamorphic Belt in Northern Jiangsu Province
2006, 31(4): 520-526.
Abstract:
Many deposits occur in the high-pressure and ultrahigh-pressure belt, northern Jiangsu Province, China. Diamond, rutile, kyanite, and marble metallogenic series, and phosphorus, quartz, and kyanite metallogenic series are presented on the basis of regional petrology, structural geology, metallogeny and mineralization age in northern Jiangsu Province. The former was formed when a huge amount of material from the Yangtze plate was subducted northwards beneath the North China plate. The latter is associated with the exhumation of the high-pressure and ultrahigh-pressure belt. The paper also discusses the existence of the Yanshanian gold, silver, and polymetallic metallogenic series. Its formation is related to the Yanshanian post-exhumation extension event.
Many deposits occur in the high-pressure and ultrahigh-pressure belt, northern Jiangsu Province, China. Diamond, rutile, kyanite, and marble metallogenic series, and phosphorus, quartz, and kyanite metallogenic series are presented on the basis of regional petrology, structural geology, metallogeny and mineralization age in northern Jiangsu Province. The former was formed when a huge amount of material from the Yangtze plate was subducted northwards beneath the North China plate. The latter is associated with the exhumation of the high-pressure and ultrahigh-pressure belt. The paper also discusses the existence of the Yanshanian gold, silver, and polymetallic metallogenic series. Its formation is related to the Yanshanian post-exhumation extension event.
2006, 31(4): 527-532.
Abstract:
This article analyzes attitude characteristics of foliation, miniature faults with striation and striation of miniature faults, and kinematic characters of brittle and ductile shear zone. The results indicate that: (1) The dip angles of eclogite-type foliations are obviously steeper than the angles of gneiss-type foliations, because the strength of the former is higher than the latter, so deformation of both is different in compressional process; the main part of ductile deformation is shearing along foliation; attitude of the main part of miniature faults with striation is identical with foliation, part of it is accompanied by other miniature faults which are conjugate with the former. (2) The main part of brittle and ductile deformation shears in an ESE-WNW direction, with a small part shearing in a near S-N direction. The movement direction of faults in brittle and ductile deformation is the same, but in structures conserved now, the main part of the ductile deformation is dominated by the ESE-WNW thrust shear sense, part of it is ductile shearing of SN direction; the main part of brittle deformations is dominated by the WNW-ESE normal shear sense. (3) The tectonic stress field of main hole is divided initially into four periods, the main structure reserved now was coming from compressional tectonic stress field in an ESE-WNW direction.
This article analyzes attitude characteristics of foliation, miniature faults with striation and striation of miniature faults, and kinematic characters of brittle and ductile shear zone. The results indicate that: (1) The dip angles of eclogite-type foliations are obviously steeper than the angles of gneiss-type foliations, because the strength of the former is higher than the latter, so deformation of both is different in compressional process; the main part of ductile deformation is shearing along foliation; attitude of the main part of miniature faults with striation is identical with foliation, part of it is accompanied by other miniature faults which are conjugate with the former. (2) The main part of brittle and ductile deformation shears in an ESE-WNW direction, with a small part shearing in a near S-N direction. The movement direction of faults in brittle and ductile deformation is the same, but in structures conserved now, the main part of the ductile deformation is dominated by the ESE-WNW thrust shear sense, part of it is ductile shearing of SN direction; the main part of brittle deformations is dominated by the WNW-ESE normal shear sense. (3) The tectonic stress field of main hole is divided initially into four periods, the main structure reserved now was coming from compressional tectonic stress field in an ESE-WNW direction.
2006, 31(4): 533-538.
Abstract:
The study of rutile's mineral geochemistry can provide important information for the investigation of petrology and the geodynamics of a subduction zone. Rutile-bearing eclogite (eclogitic-rutile deposit) in Sulu UHPM terrane and the > 5 000 m deep CCSD main hole provide a good opportunity for the geochemical investigation of rutile. Preliminary research has shown that eclogites of different occurrences and different types in Sulu UHPM terrane and CCSD main hole have different trace element contents, which indicate that trace elements in rutile can serve as a practical tool for provenance tracing of eclogite and for estimation of rutile mineralization temperature. Pb isotope composition of 3 rutile samples showed two abrupt changes during step-leaching analysis, which may be a reflection of tectonic condition variation during the growth history of rutile, and have potential use in tracing the process of continental subduction-exhumation. Further detailed studies on the geochemistry of rutile are needed to provide new knowledge on the geodynamics of the subduction-exhumation of Sulu terrane, and on the eclogitic rutile deposit.
The study of rutile's mineral geochemistry can provide important information for the investigation of petrology and the geodynamics of a subduction zone. Rutile-bearing eclogite (eclogitic-rutile deposit) in Sulu UHPM terrane and the > 5 000 m deep CCSD main hole provide a good opportunity for the geochemical investigation of rutile. Preliminary research has shown that eclogites of different occurrences and different types in Sulu UHPM terrane and CCSD main hole have different trace element contents, which indicate that trace elements in rutile can serve as a practical tool for provenance tracing of eclogite and for estimation of rutile mineralization temperature. Pb isotope composition of 3 rutile samples showed two abrupt changes during step-leaching analysis, which may be a reflection of tectonic condition variation during the growth history of rutile, and have potential use in tracing the process of continental subduction-exhumation. Further detailed studies on the geochemistry of rutile are needed to provide new knowledge on the geodynamics of the subduction-exhumation of Sulu terrane, and on the eclogitic rutile deposit.
2006, 31(4): 539-550.
Abstract:
The pre-pilot hole of the Chinese Continental Scientific Drilling (CCSD-PP2) is located at the UHP metamorphic supracrustal slice of northern Sulu. The rock types in CCSD-PP2 are garnet-amphibolite (amphibolite), orthogneisses, paragneisses and eclogite. The main mineral assemblage of the garnet-amphibolite from the first part in CCSD-PP2 is amphibole, garnet, biotite and albite, which resulted from retrograde metamorphism. The geochemical data show the chemical compositions of the garnet-amphibolite are consistent with so-called normal eclogite, the compositions and partition pattern of REE from garnet-amphibolote are similar to eclogite from the main hole, and there are some differences in trace element and geochemical discriminating figures between the garnet-amphibolite from CCSD-PP2 and eclogite from the main hole, which demonstrates that their protoliths are within plate basalts, and the differences are caused by the characteristics of the protolith and fluid introduction during eclogite retrograde metamorphism. Coesite and omphacite inclusions in zircons were discovered both from garnet-amphibolite and orthogneiss, closely below the garnet-amphibolite. There is similar petrological and geochemical characteristics between PP2 and main hole orthogneiss. The SiO2 content in garnet-amphibolite increases gradually toward the contacts with orthogneisses. All the lines of evidence show that the garnet-amphibolite and orthogneisses experienced subduction into the upper mantle and strong retrogressive metamorphism during exhumation, and there were compositional exchanges, to a certain extent, between them.
The pre-pilot hole of the Chinese Continental Scientific Drilling (CCSD-PP2) is located at the UHP metamorphic supracrustal slice of northern Sulu. The rock types in CCSD-PP2 are garnet-amphibolite (amphibolite), orthogneisses, paragneisses and eclogite. The main mineral assemblage of the garnet-amphibolite from the first part in CCSD-PP2 is amphibole, garnet, biotite and albite, which resulted from retrograde metamorphism. The geochemical data show the chemical compositions of the garnet-amphibolite are consistent with so-called normal eclogite, the compositions and partition pattern of REE from garnet-amphibolote are similar to eclogite from the main hole, and there are some differences in trace element and geochemical discriminating figures between the garnet-amphibolite from CCSD-PP2 and eclogite from the main hole, which demonstrates that their protoliths are within plate basalts, and the differences are caused by the characteristics of the protolith and fluid introduction during eclogite retrograde metamorphism. Coesite and omphacite inclusions in zircons were discovered both from garnet-amphibolite and orthogneiss, closely below the garnet-amphibolite. There is similar petrological and geochemical characteristics between PP2 and main hole orthogneiss. The SiO2 content in garnet-amphibolite increases gradually toward the contacts with orthogneisses. All the lines of evidence show that the garnet-amphibolite and orthogneisses experienced subduction into the upper mantle and strong retrogressive metamorphism during exhumation, and there were compositional exchanges, to a certain extent, between them.
2006, 31(4): 551-556.
Abstract:
A variety of veins were discovered during the observation and identification of rocks from the main hole of CCSD (the China Continental Scientific Drilling Project), which is located at the eclogite area in North Jiangsu. These veins can be divided into four series:① related to the UHP/HP stage; ② related to the decompression and partial melting stage; ③ related to the retrograde metamorphism stage; ④ related to the late exhumation stage. Especially, large numbers of REE-mineral-rich veins were found at depths of 3578.5-4006m. These veins from the CCSD main hole were widely distributed and some were closely related to mineralization. In genesis, they may be the result of geological fluid metasomatism on a large scale.
A variety of veins were discovered during the observation and identification of rocks from the main hole of CCSD (the China Continental Scientific Drilling Project), which is located at the eclogite area in North Jiangsu. These veins can be divided into four series:① related to the UHP/HP stage; ② related to the decompression and partial melting stage; ③ related to the retrograde metamorphism stage; ④ related to the late exhumation stage. Especially, large numbers of REE-mineral-rich veins were found at depths of 3578.5-4006m. These veins from the CCSD main hole were widely distributed and some were closely related to mineralization. In genesis, they may be the result of geological fluid metasomatism on a large scale.
2006, 31(4): 557-563.
Abstract:
Observation is the basis of geoscientific research. A significant project in the development of geoscientific study is the improvement of the signal to noise ratio in the heavily ambient noise of industrialization and urban expansion. Observation in a deep borehole is one way to restrain the noise. Recently, scientific drilling and the long-term multi-component geophysical observations in deep boreholes have been speedily developed on the continent as well as in the ocean. Many observations and studies have been reported. In the present analysis, we provide an overview of geophysical observation achievements in deep boreholes worldwide. A plan for observation in the borehole in Donghai, Jiangsu of the Chinese Continent Scientific Drilling (CCSD) project is discussed and the bright future for the deep borehole geophysical observation is clarified. The long-tem borehole observatory in Donghai will be the first noiseless multi-geophysical observatory in China. The observatory is a significant study base for researching the inner earth. The deep borehole observation will enrich geoscientific knowledge and benefit areas such as resource prospecting, environmental protection and disaster prevention.
Observation is the basis of geoscientific research. A significant project in the development of geoscientific study is the improvement of the signal to noise ratio in the heavily ambient noise of industrialization and urban expansion. Observation in a deep borehole is one way to restrain the noise. Recently, scientific drilling and the long-term multi-component geophysical observations in deep boreholes have been speedily developed on the continent as well as in the ocean. Many observations and studies have been reported. In the present analysis, we provide an overview of geophysical observation achievements in deep boreholes worldwide. A plan for observation in the borehole in Donghai, Jiangsu of the Chinese Continent Scientific Drilling (CCSD) project is discussed and the bright future for the deep borehole geophysical observation is clarified. The long-tem borehole observatory in Donghai will be the first noiseless multi-geophysical observatory in China. The observatory is a significant study base for researching the inner earth. The deep borehole observation will enrich geoscientific knowledge and benefit areas such as resource prospecting, environmental protection and disaster prevention.
2006, 31(4): 564-568.
Abstract:
The relationship between thermal conductivity and ultrasonic velocity has been analyzed by using 655 samples from scientific boreholes drilled in Donghai, eastern China. The samples are classified into 4 different types: fresh eclogite, retrograde eclogite, orthogneiss and paragneiss. We established equations that enabled us to predict thermal conductivity from measuring the P-wave velocity of each type of rock. The regression analysis of thermal conductivity vs. ultrasonic velocity yields a correlation coefficient of about 0.7 for eclogite and 0.5-0.4 for gneiss. The result shows that the linear equation is sufficient to describe the relationship between thermal conductivity and ultrasonic velocity. For verifying these equations, we chose several typical lithology units of the CCSD mainhole to estimate thermal conductivity from P-wave velocity. The calculated values are consistent with the measured average value of thermal conductivity, which means these equations can be used to infer thermal conductivity for underground rocks through P-wave velocity in the Donghai region or similar area. These results are of great significance for thermal conductivity selection in thermal structure analysis or heat flow calculations.
The relationship between thermal conductivity and ultrasonic velocity has been analyzed by using 655 samples from scientific boreholes drilled in Donghai, eastern China. The samples are classified into 4 different types: fresh eclogite, retrograde eclogite, orthogneiss and paragneiss. We established equations that enabled us to predict thermal conductivity from measuring the P-wave velocity of each type of rock. The regression analysis of thermal conductivity vs. ultrasonic velocity yields a correlation coefficient of about 0.7 for eclogite and 0.5-0.4 for gneiss. The result shows that the linear equation is sufficient to describe the relationship between thermal conductivity and ultrasonic velocity. For verifying these equations, we chose several typical lithology units of the CCSD mainhole to estimate thermal conductivity from P-wave velocity. The calculated values are consistent with the measured average value of thermal conductivity, which means these equations can be used to infer thermal conductivity for underground rocks through P-wave velocity in the Donghai region or similar area. These results are of great significance for thermal conductivity selection in thermal structure analysis or heat flow calculations.
2006, 31(4): 569-574.
Abstract:
The main aim of this paper is to analyze reflectors in the pilot hole of CCSD (China Continental Scientific Drilling). The lithology of the metamorphite in the CCSD pilot hole can be identified by logging curves and geo-logging data. The wave impedance can be calculated by using acoustic (AC) and density log (DEN) curves. By comparing the acoustic wave impedance with the VSP (vertical seismic profile), the reflectors of the CCSD pilot hole have been analyzed. The results indicate that reflected waves are primarily produced by the wave impedance properties of the lithology (such as the wave impedance difference between eclogite and paragneiss or between eclogite and ultrabasic serpentinite, etc) and the fracture. The fractures are mainly the ductile shear zones. If the fracture thickness is less than 1m, reflectors cannot be produced. The study provides significant data concerning the interpretation of seismic reflection signals in the earth's crust.
The main aim of this paper is to analyze reflectors in the pilot hole of CCSD (China Continental Scientific Drilling). The lithology of the metamorphite in the CCSD pilot hole can be identified by logging curves and geo-logging data. The wave impedance can be calculated by using acoustic (AC) and density log (DEN) curves. By comparing the acoustic wave impedance with the VSP (vertical seismic profile), the reflectors of the CCSD pilot hole have been analyzed. The results indicate that reflected waves are primarily produced by the wave impedance properties of the lithology (such as the wave impedance difference between eclogite and paragneiss or between eclogite and ultrabasic serpentinite, etc) and the fracture. The fractures are mainly the ductile shear zones. If the fracture thickness is less than 1m, reflectors cannot be produced. The study provides significant data concerning the interpretation of seismic reflection signals in the earth's crust.
2006, 31(4): 575-577.
Abstract:
The only main hole of the Chinese Continental Scientific Drilling (CCSD) Project, the deepest scientific drilling project of all the ICDP projects, reached its depth of over 5000m, from which more than 4400m cores were collected. Hence the scanned core image database of CCSD project is also the largest of all the databases of ICDP projects. After various samplings, some cores have been completely damaged or disappeared. To make full use of the scanned core images, an MS ACCESS database was developed, on the basis of the original DIS system. More than 8000 images (about 100gigabyte) have been efficiently and systematically managed and shared on the Internet with some user-friendly query program and interfaces using the ASP and VB techniques. This new information technology, proved by one year's trial test, can not only store permanently and efficiently the original image data, but also help geologists to study efficiently the cores for their scientific purpose.
The only main hole of the Chinese Continental Scientific Drilling (CCSD) Project, the deepest scientific drilling project of all the ICDP projects, reached its depth of over 5000m, from which more than 4400m cores were collected. Hence the scanned core image database of CCSD project is also the largest of all the databases of ICDP projects. After various samplings, some cores have been completely damaged or disappeared. To make full use of the scanned core images, an MS ACCESS database was developed, on the basis of the original DIS system. More than 8000 images (about 100gigabyte) have been efficiently and systematically managed and shared on the Internet with some user-friendly query program and interfaces using the ASP and VB techniques. This new information technology, proved by one year's trial test, can not only store permanently and efficiently the original image data, but also help geologists to study efficiently the cores for their scientific purpose.
2006, 31(4): 578-584.
Abstract:
A number of gabbric plutons discontinuously crop out along the Liulin-Dingyuan-Wangmuguan region in the Beihuaiyang tectonic belt of north Dabie. They were previously considered to have been developed in a post-orogenic extensional setting. In this paper we present new data of zircon SHRIMP dating and EPMA chemical analysis results of pyroxenes and plagioclases from the Liulin gabbro at the northern foot of Jigongshan Mountain. SHRIMP U-Pb dating on magmatic zircons yielded an age of (611±13) Ma, which is interpreted as the crystallization time of the Liulin gabbro. The date is significantly older than the immediately adjacent Upper Ordovician Dingyuan Formation, revising the contact relationship between the gabbro body and its wall rock. Pyroxene is exclusively augite with high Na2O, FeO and MnO contents, and plagioclase is low CaO andesine, which share characteristics with their counterparts from gabbros formed in an intra-plate setting and are largely different from those from gabbros associated with island arc or active continental margin. The results indicate that there may have been a continental rifting event in the north of the Dabie orogen during the late Neoproterozoic period.
A number of gabbric plutons discontinuously crop out along the Liulin-Dingyuan-Wangmuguan region in the Beihuaiyang tectonic belt of north Dabie. They were previously considered to have been developed in a post-orogenic extensional setting. In this paper we present new data of zircon SHRIMP dating and EPMA chemical analysis results of pyroxenes and plagioclases from the Liulin gabbro at the northern foot of Jigongshan Mountain. SHRIMP U-Pb dating on magmatic zircons yielded an age of (611±13) Ma, which is interpreted as the crystallization time of the Liulin gabbro. The date is significantly older than the immediately adjacent Upper Ordovician Dingyuan Formation, revising the contact relationship between the gabbro body and its wall rock. Pyroxene is exclusively augite with high Na2O, FeO and MnO contents, and plagioclase is low CaO andesine, which share characteristics with their counterparts from gabbros formed in an intra-plate setting and are largely different from those from gabbros associated with island arc or active continental margin. The results indicate that there may have been a continental rifting event in the north of the Dabie orogen during the late Neoproterozoic period.
