- Email: [email protected]
Paleozoic Yellow Sea Transform Fault: Its Role in the Tectonic History of Korea and Adjacent Regions
588
RODINIA, GONDWANA AND ASIA
by transcurrent regimes, with NE or ENE directions, suggesting oblique collision systems. An attempt was done to determine the mean orientation of the principal horizontal compressive stresses for each belt, considering either the frontal or oblique convergence character of each one. In the Ribeira and Borborema belts the tectonic fabrics are characterized by dextral ductile to ductile/brittle transcurrent shear zones, with the development of mega S/C structures and subsidiary conjugate sinistral NS shear zones. The stretching lineations are mainly ENE with subhorizontal dip, although early oblique NW lineations associated with thrusts are also observed. On the other hand in the Aracuai and Brasilia belts the tectonic pattern shows frontal thrusts with vergence to the Sao Francisco
Craton, with stretching lineations normal to the belts. The Paraguai Araguaia belt is coherent with this pattern, representing frontal collisions over the Amazon Craton, as in Africa. The Congo Belt in Africa represents a frontal collision to the Congo Craton. The Kaoko belt in Africa with sinistral transcurrent regimes could agree with this scheme as it is parallel with some sinistral NS shear zones in the Ribeira Belt, considering the usual Gondwana reconstruction. From these general observations, it is possible to propose a picture with WNW - ESE to NW - SE directions of principal compressive stress, and we suggest that this represents the mean displacement vectors, in a coherent kinematic picture for the amalgamation of this Gondwana sector, with WNW - ESE to NW - SE main directions of closure.
Textural and Mineralogical Characteristics of the Beach Sands of Tamil Nadu, Southern India C.G. Chandrasekaran, K.V. Muralidharan and K. Joshi Nirmal Kumar Department of Geology, Presidency College, Chennai, India _
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A study of beach sands occurring along the coast between Kovalam and Mammallapuram of Chengelpet district in Tamil Nadu was undertaken in order to understand their texture, mineralogy and provenance, covering a distance of about 25 km along the coast. The sands have wide distribution from medium or fine grained, and are moderately well sorted, largely mesokurtic and negatively skewed. The sands have largely characteristics induced by fluvial deposition in coastal regions. The shape of the grains varies from angular to sub-rounded forms
indicating both far-off and nearby sources. The heavy minerals are represented by abundant garnet, ilmenite, magnetite, biotite, muscovite and traces of tourmaline, apatite, zircon, rutile and chlorite. The population of light and heavy minerals suggests involvement of varied nature of source consisting of igneous, sedimentary and metamorphic rocks. The rivers like Araniyar, Korteliyar, Adayar and Palar, flowing through the Archaean have washed down the sediments to the coastal regions thereby enriching the heavies in the coast.
Paleozoic Yellow Sea Transform Fault: Its Role in the Tectonic History of Korea and Adjacent Regions Ki-Hong Chang and Sun-Ok Park Department of Geology, Kyungpook National University, Taegu, Korea, E-mail: [email protected]
The recent recognition of the Paleozoic continents of the SinoKorea and the Yangzi with the Permo-Triassic Dabie-Sulu collision belt in between have raised the question of the eastward extension of the collision zone. Over the Korean Peninsula, neither the eastern extension of the Sulu UHP metamorphic belt nor any other plate boundary have been detected. Reviews show that whole of the Korean Peninsula is obviously SinoKorean (e.g., Lan et al., 1995) except some allochthons derived from South China. It thus became necessary to envision under the Yellow Sea an angular equivalent of the Paleozoic South China Block (Chang, 1995, 1997) called the ‘Yellow-Sea Promontory’ (YSP) (Chang, 2000). Various recent assumptions that a part of the Korean Peninsula belongs to the South China Block have never been justified.
The Dabie-Sulu UHP orogen trends as if it extends eastward to the Inijingang Zone, but it has not been possible to trace its extension there or elsewhere in Korea. It has therefore been constrained to envision a localized end Permian-Triassic collision of YSP against the Sino-Korea through the ‘Yellow-Sea Transform Fault’ (YSTF) lying off the western part of the Korean Peninsula. Dextral YSTF could allow the YSP part of the South China Block to encroach during the Paleozoic and collide against the Sino-KoreanSulu (Shandong Peninsula) during the end Permian. Triassic, leaving the western Korean Peninsula free from a direct influence of the subduction-related collision. YSTF, extant prior to the Sulu collision, possibly goes back in history earlier than the late Paleozoic. The combined YSTF and the Triassic sinistral
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Gondwana Research, K 4, No. 4, 2001
RODINIA, GONDWANA AND ASIA
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Fig.1.
Location of YSTF (Yellow Sea transform fault) and YSP (Yellow Sea promontory) relative to South China Block. Note contrasty pre-Cretaceous accretions on both sides of YSTF, which was cut by sinistral faults.
Tanlu Fault should have formed the YSP which underwent a Permo-Triassic collision. The initial collision of YSP and the Sino-Korean Craton apparently effected mineral parageneses as reflected in the distribution of ca. 250 Ma monazite CHIME signatures, which is confined to a triangular area of the West Korea. After a sustained collisional phase in the Sulu belt, the final UHP-metamorphism occurred there at about 210 Ma (Ames, 1993), which was coeval with the genesis of the syn-kinematic gneissose granite that now occurs in SW Korea, the U-Pb zircon age of which is 212 Ma (Kim et al., 1993).The coincidence of UHP metamorphism and the emplacement of the foliated granite suggest that the latter was a side effect of the UHP-metamorphism. The 250-210 Ma orogenic phase coincided with the nonmarine sedimentation of the flysch-like Hwanggangni Formation, which in turn was succeeded by sedimentation of the late Triassic-early Jurassic molasse-type Daedong Synthem. These orogenic sedimentations were significantly concentrated overwest Korea. The Jurassic plutonism including the earliest Jurassic granodiorite were generally post-orogenic. As a side effect of the convergent collision at 250-210 Ma, an east-directed escape tectonics must have occurred coevally with the Sulu collision of the YSP, as YSP was the eastern extremity of the Tethyan collisional zone. A broad transpressional fault zone, formed along the dextral contact of YSP and the Korea block, show an eastward bulging curvature due to the escape tectonics. Very probably, the eastward bulging curvature of the Korean Peninsula was also formed due to the same escape tectonics. Since the escape tectonics of YSP was both laterally eastward and vertically upward, the contact zone of YSP and Korea, the above-mentioned transpressional fault zone might have been
Gondwana Research, V. 4, No. 4, 2001
589
disrupted and overthrust eastward. Apparently, the Hwanggangni Formation was deposited in a foreland basin in front of the eastward advancing Triassic nappe. Succeeding Jurassic eastward overthrusting was largely caused by vertical tectonics that dominated the Sulu-YSF? The combined Triassic escape tectonics and Jurassic vertical tectonics of the YSP formed the nappe pile now occurring as the Okchon orogen. The Triassic olistostromes with late Precambrian isotope ages found in the Okchon Nappe were derived from YSP The transform nature of YSTF is supported by the absence of the northward on-land continuation of YSTF and the absence of geology that indicates or suggests the presence of subduction or collision zones below the eastern Yellow Sea floor. It seems certain that it was a transform fault that extended southwards beyond the Yellow Sea. Very probably, the pre-Jurassic accretionary belt of Japan was truncated by YSTF, which passed off the southwest side of the Kyushu Island. Apparently, the preJurassic accretions on both sides of YSTF were drastically different, particularly in the volume of the accretionary prisms, as revealed by the abrupt morphological difference in the belt between the Japanese Islands and the Ryukyu Islands. Mid-Paleozoic isotope dates in Sulu and Okchon anm suggest a Devonian collision of the Yangzi against the Sino-Korea (Zhu et al., 1994; Zhang et al., 1997). Similar late Precambrian collisions appear also extant. YSTF can therefore be considered as an ancient major fault of global relevance that has been repeatedly reactivated in the Paleozoic and even in the late Precambrian. The older age assigned for YSTF in this study enhances its importance in models on Rodinia assembly during the late Precambrian.
References Ames, L. (1993) Time of collision of the Sino-Koreanand Yangtze cratons: U-Pb zircon dating of coesite bearing eclogite. Geology, v. 21, pp. 339-342. Chang, K.-H. (1995) Aspects of geologic history of Korea. J. Geol. SOC. Korea, v. 31, pp. 72-90. Chang, K.-H. (1997) Korean peninsula. In: Moores and Fairbridge, (Eds.), Encyclopedia of European and Asian Regional Geology. Chapman and Hall, pp. 465-473. Chang, K.-H. (2000) Paleozoic Yellow-SeaTransform Fault and Mesozoic Korea. Geosci. J., v. 4, Spec. Edition, pp. 4-6. Kim, C.B., Kim, Y.J. and Tbrek, A. (1993) U-Pb age of Mesozoic granites in Tamyang-Kochang area, S Korea. 48th Assembly of Geol. SOC. Korea. (Abst.) p. 13 Lan, C.-Y., Lee, T., Zhou, X.-K. and Kwon, S.-T. (1995) Nd isotopic study of Precambrian basement of South Korea: evidence for Early Archean crust? Geology, v. 23, pp. 249-252. Zhang, H.-E, Gao, S., Zhang, B.-R., Luo, T.-C. and Lin, W.-L. (1997) Pb isotopes of granitoids suggest Devonian accretion of Yangtze (South China) craton to North China craton. Geology, v. 25, pp. 10151018. Zhu, G., Xu, J., Fitches, W.R. and Fletcher, C.J.N. (1994) Isotope ages of the Penglai Group in the Jiaobei belt and their geotectonic implications. Acta Geol. Sinica, v. 7, pp. 417-433.
RODINIA, GONDWANA AND ASIA
by transcurrent regimes, with NE or ENE directions, suggesting oblique collision systems. An attempt was done to determine the mean orientation of the principal horizontal compressive stresses for each belt, considering either the frontal or oblique convergence character of each one. In the Ribeira and Borborema belts the tectonic fabrics are characterized by dextral ductile to ductile/brittle transcurrent shear zones, with the development of mega S/C structures and subsidiary conjugate sinistral NS shear zones. The stretching lineations are mainly ENE with subhorizontal dip, although early oblique NW lineations associated with thrusts are also observed. On the other hand in the Aracuai and Brasilia belts the tectonic pattern shows frontal thrusts with vergence to the Sao Francisco
Craton, with stretching lineations normal to the belts. The Paraguai Araguaia belt is coherent with this pattern, representing frontal collisions over the Amazon Craton, as in Africa. The Congo Belt in Africa represents a frontal collision to the Congo Craton. The Kaoko belt in Africa with sinistral transcurrent regimes could agree with this scheme as it is parallel with some sinistral NS shear zones in the Ribeira Belt, considering the usual Gondwana reconstruction. From these general observations, it is possible to propose a picture with WNW - ESE to NW - SE directions of principal compressive stress, and we suggest that this represents the mean displacement vectors, in a coherent kinematic picture for the amalgamation of this Gondwana sector, with WNW - ESE to NW - SE main directions of closure.
Textural and Mineralogical Characteristics of the Beach Sands of Tamil Nadu, Southern India C.G. Chandrasekaran, K.V. Muralidharan and K. Joshi Nirmal Kumar Department of Geology, Presidency College, Chennai, India _
-
_
I
_
-
-
- I _ _ _ I _
I
_
_
_
~
-~
” _
A study of beach sands occurring along the coast between Kovalam and Mammallapuram of Chengelpet district in Tamil Nadu was undertaken in order to understand their texture, mineralogy and provenance, covering a distance of about 25 km along the coast. The sands have wide distribution from medium or fine grained, and are moderately well sorted, largely mesokurtic and negatively skewed. The sands have largely characteristics induced by fluvial deposition in coastal regions. The shape of the grains varies from angular to sub-rounded forms
indicating both far-off and nearby sources. The heavy minerals are represented by abundant garnet, ilmenite, magnetite, biotite, muscovite and traces of tourmaline, apatite, zircon, rutile and chlorite. The population of light and heavy minerals suggests involvement of varied nature of source consisting of igneous, sedimentary and metamorphic rocks. The rivers like Araniyar, Korteliyar, Adayar and Palar, flowing through the Archaean have washed down the sediments to the coastal regions thereby enriching the heavies in the coast.
Paleozoic Yellow Sea Transform Fault: Its Role in the Tectonic History of Korea and Adjacent Regions Ki-Hong Chang and Sun-Ok Park Department of Geology, Kyungpook National University, Taegu, Korea, E-mail: [email protected]
The recent recognition of the Paleozoic continents of the SinoKorea and the Yangzi with the Permo-Triassic Dabie-Sulu collision belt in between have raised the question of the eastward extension of the collision zone. Over the Korean Peninsula, neither the eastern extension of the Sulu UHP metamorphic belt nor any other plate boundary have been detected. Reviews show that whole of the Korean Peninsula is obviously SinoKorean (e.g., Lan et al., 1995) except some allochthons derived from South China. It thus became necessary to envision under the Yellow Sea an angular equivalent of the Paleozoic South China Block (Chang, 1995, 1997) called the ‘Yellow-Sea Promontory’ (YSP) (Chang, 2000). Various recent assumptions that a part of the Korean Peninsula belongs to the South China Block have never been justified.
The Dabie-Sulu UHP orogen trends as if it extends eastward to the Inijingang Zone, but it has not been possible to trace its extension there or elsewhere in Korea. It has therefore been constrained to envision a localized end Permian-Triassic collision of YSP against the Sino-Korea through the ‘Yellow-Sea Transform Fault’ (YSTF) lying off the western part of the Korean Peninsula. Dextral YSTF could allow the YSP part of the South China Block to encroach during the Paleozoic and collide against the Sino-KoreanSulu (Shandong Peninsula) during the end Permian. Triassic, leaving the western Korean Peninsula free from a direct influence of the subduction-related collision. YSTF, extant prior to the Sulu collision, possibly goes back in history earlier than the late Paleozoic. The combined YSTF and the Triassic sinistral
-
Gondwana Research, K 4, No. 4, 2001
RODINIA, GONDWANA AND ASIA
.---
Fig.1.
Location of YSTF (Yellow Sea transform fault) and YSP (Yellow Sea promontory) relative to South China Block. Note contrasty pre-Cretaceous accretions on both sides of YSTF, which was cut by sinistral faults.
Tanlu Fault should have formed the YSP which underwent a Permo-Triassic collision. The initial collision of YSP and the Sino-Korean Craton apparently effected mineral parageneses as reflected in the distribution of ca. 250 Ma monazite CHIME signatures, which is confined to a triangular area of the West Korea. After a sustained collisional phase in the Sulu belt, the final UHP-metamorphism occurred there at about 210 Ma (Ames, 1993), which was coeval with the genesis of the syn-kinematic gneissose granite that now occurs in SW Korea, the U-Pb zircon age of which is 212 Ma (Kim et al., 1993).The coincidence of UHP metamorphism and the emplacement of the foliated granite suggest that the latter was a side effect of the UHP-metamorphism. The 250-210 Ma orogenic phase coincided with the nonmarine sedimentation of the flysch-like Hwanggangni Formation, which in turn was succeeded by sedimentation of the late Triassic-early Jurassic molasse-type Daedong Synthem. These orogenic sedimentations were significantly concentrated overwest Korea. The Jurassic plutonism including the earliest Jurassic granodiorite were generally post-orogenic. As a side effect of the convergent collision at 250-210 Ma, an east-directed escape tectonics must have occurred coevally with the Sulu collision of the YSP, as YSP was the eastern extremity of the Tethyan collisional zone. A broad transpressional fault zone, formed along the dextral contact of YSP and the Korea block, show an eastward bulging curvature due to the escape tectonics. Very probably, the eastward bulging curvature of the Korean Peninsula was also formed due to the same escape tectonics. Since the escape tectonics of YSP was both laterally eastward and vertically upward, the contact zone of YSP and Korea, the above-mentioned transpressional fault zone might have been
Gondwana Research, V. 4, No. 4, 2001
589
disrupted and overthrust eastward. Apparently, the Hwanggangni Formation was deposited in a foreland basin in front of the eastward advancing Triassic nappe. Succeeding Jurassic eastward overthrusting was largely caused by vertical tectonics that dominated the Sulu-YSF? The combined Triassic escape tectonics and Jurassic vertical tectonics of the YSP formed the nappe pile now occurring as the Okchon orogen. The Triassic olistostromes with late Precambrian isotope ages found in the Okchon Nappe were derived from YSP The transform nature of YSTF is supported by the absence of the northward on-land continuation of YSTF and the absence of geology that indicates or suggests the presence of subduction or collision zones below the eastern Yellow Sea floor. It seems certain that it was a transform fault that extended southwards beyond the Yellow Sea. Very probably, the pre-Jurassic accretionary belt of Japan was truncated by YSTF, which passed off the southwest side of the Kyushu Island. Apparently, the preJurassic accretions on both sides of YSTF were drastically different, particularly in the volume of the accretionary prisms, as revealed by the abrupt morphological difference in the belt between the Japanese Islands and the Ryukyu Islands. Mid-Paleozoic isotope dates in Sulu and Okchon anm suggest a Devonian collision of the Yangzi against the Sino-Korea (Zhu et al., 1994; Zhang et al., 1997). Similar late Precambrian collisions appear also extant. YSTF can therefore be considered as an ancient major fault of global relevance that has been repeatedly reactivated in the Paleozoic and even in the late Precambrian. The older age assigned for YSTF in this study enhances its importance in models on Rodinia assembly during the late Precambrian.
References Ames, L. (1993) Time of collision of the Sino-Koreanand Yangtze cratons: U-Pb zircon dating of coesite bearing eclogite. Geology, v. 21, pp. 339-342. Chang, K.-H. (1995) Aspects of geologic history of Korea. J. Geol. SOC. Korea, v. 31, pp. 72-90. Chang, K.-H. (1997) Korean peninsula. In: Moores and Fairbridge, (Eds.), Encyclopedia of European and Asian Regional Geology. Chapman and Hall, pp. 465-473. Chang, K.-H. (2000) Paleozoic Yellow-SeaTransform Fault and Mesozoic Korea. Geosci. J., v. 4, Spec. Edition, pp. 4-6. Kim, C.B., Kim, Y.J. and Tbrek, A. (1993) U-Pb age of Mesozoic granites in Tamyang-Kochang area, S Korea. 48th Assembly of Geol. SOC. Korea. (Abst.) p. 13 Lan, C.-Y., Lee, T., Zhou, X.-K. and Kwon, S.-T. (1995) Nd isotopic study of Precambrian basement of South Korea: evidence for Early Archean crust? Geology, v. 23, pp. 249-252. Zhang, H.-E, Gao, S., Zhang, B.-R., Luo, T.-C. and Lin, W.-L. (1997) Pb isotopes of granitoids suggest Devonian accretion of Yangtze (South China) craton to North China craton. Geology, v. 25, pp. 10151018. Zhu, G., Xu, J., Fitches, W.R. and Fletcher, C.J.N. (1994) Isotope ages of the Penglai Group in the Jiaobei belt and their geotectonic implications. Acta Geol. Sinica, v. 7, pp. 417-433.