EXAMPLES OF "ACTIVIZING REGION" IN THE CHINESE PLATFORM WITH SPECIAL REFERENCE TO THE "CATHAYSLA" PROBLEM
Chan Kuo-ta Central-southern Mining and Metallurgical Institute
Ⅰ. The Yinshan district as an example of "activizing region" in the Chinese platform One of the most typical localities that show clearly the phenomenon of"activization of platform" (активи. зация платформы) is the Yinshan region, aneast western mountain range on the border between the North-China plain andthe Mongolian plateau. It has long been recognized as a platform because ofthe presence of a folded foundation Pre-Sinian in age. However, owing to thefacts that Mesozoic crustal movements and magmatic activities are importantwithin this area, some geologists including G Schoenmann, hold that it is ageosynclinal region. It is Ю. М Шейманн who first noticed the phenomenon of activizationappearing in the Chinese platform. В. М. Синицын in his "Строенив и развитиекитайской платформы" indicates that some of the mountain ranges includingYinshan, which have been formerly referred to the folding belts developingfrom geosynclines, are in fact the internal structures of the Chinese platform. In this paper the writer after the opinion of В. М. Синицын, assigns theYinshan area as one of the "activizing regions" in the Chinese platform, andgives more detailed descriptions and discussions mainly on the point of thehistory of its stratigraphic development. Really it is a fact that the Yinshan region has an old folded foundationwhich is composed of metamorphic complex including chiefly gneisses, schists,and old granitic intrusions apparently Pre-Sinian in age. Since the formationof this folded foundation during the Luliang movement (=Goto-Karelian mo-vement), the old land of the Yinshan region has "activized" or "resurrected"several times. As early as in the Sinian period, a depression prolonging in E-Wdirection happened on its southern border, where Sinian limestone 900 metresin thickness and in some places up to 9,620 metres was so deposited. During a long time of the Palaeozoic era, the Yinshan old land was in the poriod ofdenudation except some Cambrian marine limestones only 144 metres in thick-ness deposited in the western part. At the end of the Palaeozoic era, local acti-vization with the formation of continental basin-deposits of Permian age, up to1,380 metres in thickness, as found in the Tachingshan area again happened.In the middle Mesozoic era, the Yinshan region came to a period of strongactivity. Structural depressions duo to "Процесс аркогенеза" occurred universallywithin the whole area and magmatie activities in large magnitude associatedthis crustal movement, so that a great sequence of freshwater basin-depositswith intercalations of volcanic beds, up to 8,000 metres in total thickness wereformed. During the formation of these strata, especially at the end of Mesozoic,interruptions of depositon happened frequently, folds and thrusts were abund-antly formed, and intrusive bodies of "young granite" were produced hereand there. In the Tertiary period, the Yinshan region was violently faulted, andvolcanic activities still happened, producing the basalt lava flow spreading ina wide area. The activity of the Yinshan old land has not ceased even to-dayas shown by the facte that its whole area is in the process of uplift and by thepresence of an earthquake zone known in the historical time. Ⅱ. To what Geotectonic Unit does the Southeastern Coastal Region of China Belong? On the Southeastern coast of China there is a district where geotectoniccharacteristics have never been recognized clearly. It is A. W. Grabau who firstreferred it to an old land named "Cathaysia". J. S. Lee holds the same opinion.In his geotectonic map of China, B. M. Синицын also assigns this region to aplatform and marks it as a part of his "Южно-китайский платформенный массив".However, there is still another opinion opposed to this. A. C. Хоминтовский, forinstance, renders recently this district to a geosynclinal region and proposes thename "Minche Pacific folding zone" for it. H. T. Yang and T. Y. Yu agreewith him. In the year 1954, the writer in his compilation-work connected with thegeology of Fukien and Kwangtung, found that the geotectonic characteristics ofthe southeastern coastal region of China are not only unagreeable with thosefound in a common platform on the one hand, but also contrasting, with thoseof a geosynclinal region on the other. In fact, it cannot be referred suitably toany geotectonic unit except to the intermediate type as shown by the history ofits geological development. Apparently it is an "activizing" or "resurrected" platform. During the Pre-Sinian crustal movement (the Luliang movement), a foldedfoundation composed of old gneisses, schists, and phyllites was completely for-med. Obviously this is a part of the broad old land of Southern China. In the earlier stage of the Palaeozoic era, the whole area of this region wasexposed in the air and under denudation. Hence, no deposit of any kind wasformed. After the Caledonian movement, depressions happened in the western partof this region, where the Devonian-Lower carboniferous continental deposit, theNanching series consisting mainly of quartzite, conglomerate and shale has beenformed, but the other parts were still under denudation. These facts show thatthis region was still a land at that time. Uralian and Lower Permian limestones, known respectively as the Chuan-shan limestone and the Chihsia limestone, separated from each other by adisconformity, spread widely in this region. This indicates that the marine trans-gressions really happened in the southeastern coastal region of China. However,the thicknesses of these limestones (only 30 metres and 150 metres respectively)and their uniformity in the horizontal direction show that the sea at thosetimes was shallow, and the magnitude of subsidence of the earth crust withinthis region was small. The unnoticed lateral changing of lithological charactersof these limestones proves the same fact. Undoubtedly these limestones arenothing but the marine deposits of platform-type. From Upper Permian toTriassic, this region was under a condition of alternation of transgression andregression of the sea. Owing to the fact that the amplitude of oscillation of theearth crust of this region at that time was small, the deposits formed duringthe marine transgression were thin and interrupted again and again by disconfor-mities (or even unconformities). Sometimes continental deposits are intercalated. Since the later period of Triassic, the southeastern coastal region has neverbeen covered by the sea again. And, a new condition began to happen in LowerJurassic. Here, the old land became to "resurrected", so that a series of depres-sing belts were formed as a result of "Процесс аркогенеза". In association withthe subsidence of these depressions, continental beds with a total thicknessup to 3,000 metres were deposited. In the beds interruptions frequently occurred.Folds were abundants, although they or at least some of them were intermediatetype. At the same time, magmatic activities were significant. Itappearedfirstly in the form of volcanic eruptions as recorded by a great sequence of beds consisting of tuff and rhyolite intercalating in the continental bedsmentioned above. And then, at the end of the Mesozoic, numerous graniticbodies were produced. Coming to the Cenozoic era, this region still sufferedfrom rather strong crustal movements accompanied by basalt lava eruptions. Theactivity of the old land has not yet been ceased even to-day as marked by thepresence of a famous earthquake zone between Kwangtung and Fukien, and theabundance of hot springs which widely spread within this region. All theseshow the typical characters of an "activizing" or "resurrected" platform. Final-ly, the complexity of the types of mineral deposits found in Fukien and Kwang-tung also proves the geotectonic nature of this region. Summarizing the whole matter, we may say that the southeastern coastalregion of China was originally an old land. Although it has been agian andagain submerged by the sea, the resulting marine deposits are entirely differentfrom those of geosynclinal region. In the middle of Mesozoic, this region beganto be active violently again, producing a series of depressions or "secondarygeosynclines", in which thick continental beds were deposited, and, at the sametime, folds of intermediate type, serious volcanic eruptions and magmatic intru-sions were produced. Hence, to refer the southeastern coastal region of China toan "activizing" platform is quite strongly proved. The northwestern boundary of this "activizing" platform is generally onthe line starting from central Chekiang through central Kiangsi to the Sou-thwestern part of Kwangtung, because the history and characteristics of geolo-gical development of the Southeastern Kiangsi and Central-southern Kwangtungare quite similar to those of Fukien and Eastern Kwangtung. As to the nomination of this geotectonic unit, the writer proposes to callit "Cathaysian activizing region". This name is derived from the "Cathaysia"of A. W. Grabau but adds, according to necessity, the meaning of activizing or"resurrected" characters of this region. The so-called "Minche Pacific foldingzone" of A. C. Хоминтовский is obviously unacceptable because it entirely doesnot coincide with fact. Compared with the "aetivizing" platforms found in other parts of theworld, the Cathaysian coastal "activizing" platform has its own characteristics,especially shown by the presence of numerous, widely spread, small depressionsor "secondary geosynclines", and the acidic magmatic activities appearing on alarge scale. All these indicate that this is a special type differing from all theknown "activizing" platforms.