从中国东部前寒武纪岩系发育论中国东部大地构造分区

GEOTECTONIC UNITS OF EASTERN CHINA, AS SPECIALLY VIEWED FROM THE DEVELOPMENT OF THE PRE-CAMBRIAN SYSTEMS OF THE SAME REGION

一.论前寒武纪划分的原则及命名关于寒武纪以前地质时代及地质层系的名词问题,作者在1948年曾予论述,已经通行的用法是把前寒武纪划分为两个阶段。前一阶段称为太古代(Archaeozoic)及太古界(Archaean);后一阶段称为元古代及元古界(Proterozoic)。

Ⅰ. Principles of classification and nomenclature of the Pre-Cambrian After a brief review of the history of nomenclature and classificationof the Pre-Cambrian, special emphasis is laid on the profound unconformitybetween the universally metamorphosed basement complex and the generallynon-metamorphosed sediments below the fossiliferous Lower Cambrian. Thefinal consolidation of the broad continental platforms with wide shelf areasand the consequent formation of wide spread shallow sea sediments mark anew period in the historical development of the earth crust, and are of firstimportance in the classification of geologic eras. Broad shallow sea conditionsare indispensable to animals for their adaptation to bottom life, and naturallyfor preservation as fossils. Thus the profound change in structural conditionsof the earth crust is equally important to animal evolution. On thesegrounds, the author agrees with Grabau and others in regarding theSinian, which forms the non-metamorphosed mantle of old platforms, as thefirst system of the Palaeozoic, and proposes the following scheme of classi-fication of the Pre-Cambrian.Lower Palaeozoic-Sinian (Jungalgonkium and Eokambrium of European authors) Proterozoic (Altalgonkium)Cryptozoic Archaeozoic(Archaean)Ⅱ. A Brief review of the classification of the Pre-Cambrian of ChinaIn North China, a fourfold classification of the Pre-Cambrian is proposed. 4. The Sinian System-non-metamorphosed sediments forming. the mantleof the old Sino-Korean Platform. --Luliang Movement-- 3. The Huto System-generally weakly yet universally metamorphosedsediments and volcanic series. --Heikotaling Movement- 2. The Wutai System-deeply metamorphosed sedimentaries and volcanicseries with the characteristic Anshan type of layered magnetite ores. 1. The Taishan System-old gneiss and gneissic granites. The interrelations of these four systems as established in the provincesShansi, Shantung, Honan and Liaoning are briefly discussed. The Taishanand the Wutai are usually inseparable, and, up to present, we know onlythat the Wutai system lies on an old granite with selimentary contact nearShenyang. Thus no clear stratigraphic boundaries of the Taishan System canbe given at the present. In South China, the Pre-Cambrian is divided into three systems. 3. The Sinian System-non-metamorphosed sediments with glacial depositsin the middle part. 2. The Kunyang System-probably corresponding to the Huto System ofNorth China, and 1. The old gneiss and schists. The Kunyang System is by far the most wide-spread basement rocksbelow the non-metamorphosed sediments in South China. In the annexed tables the different systems are correlated with theirpossible equivalents of other continents (Tables Ⅰ and Ⅱ). Ⅲ. Palaeogeography and sedimentation of the Sinian Period, with notes onthe reconstruction of certain palaeogeographical features of Pre-Sinian time Stratigraphic details of the Sinian System are referred to cited biblio-graphy. The broad palaeogeographic features are outlined, and their far-reaching effect on and special role in later geological development are em- phasized. On the Sino-Korean Platform, the Sinian sediments were deposited on apeneplained surface, and occur in three types. 1. In the Yenshan trough was accumulated more than 6,000 m ofclastic and calcareous sediments. These sediments were not folded until latein the Mesozoic era. 2. On the Shansi Plateau no more than 100 m of continental sands wasformed, flanking the hilly areas of Luliang, Wutai and Chungtiao. 3. In the Hohuai Basin and elsewhere, the Sinian displays a more stablefacies, with a lower clastic and an upper calcareous series. Apart from these belts of sedimentation, there were the Liaotung-Shan-tung Shield on the east, the Huaiyang Shield on the south, and the InnerMongolian Axis on the north. The Ordos-Shensi area probably also stoodabove the sea-level (Plate Ⅰ). In South China, the Pre-Sinian surface of deposition was more rugged.The lower Sinian is represented by intermontane and piedmont clastics, theupper Sinian by tillites followed by shale; and siliceous limestones. The scopeof Sinian deposition is essentially confined to the western part of SouthChina, and Southeastern China as a whole was at that time above the sea-level. In Southwestern China, the most strongly subsiding belts were easternYunnan (east of the Kangtian Shield), northwestern Hunan (west of theHsuehfeng Shield), and southern Anhwei (between the Poyang Shield andthe Huaiyang Shield), all these shields being land supplying detritus fordeposition at that time. Widely spread sandstones occur in the Kwangsi region, comparable withthose in the Shansi region of North China. The Szechwan-Kweichow Shelfrepresents the inner, most stable portion of Southwestern China (Plate Ⅰ).The Sinian formations and the probable structures of the floor on whichthey lie are schematically shown in the accompanied sections. If we plot the outcrops of the Huto System on the map, we shall find them distributed in more or less clearly defined elongated belts, and thesebelts coincide in a general way with the shield areas of the Sinian Period.Thus, in North China, the Huto rocks occur all along the Shantung-LiaotungPeninsula and in the Huaiyang Mountains, form small massifs on the ShansiPlateau, and are perhaps also represented in the Inner Mongolian Axis.These belts may eventually represent geosynclines in the Huto Period, whichencompass still older nuclei, and which formed mountainous regions as aresult of the Luliang orogenic Movement. The old nuclear regions became onthe contrary low-lying lands receiving deposition in Sinian time. In South China, the Huto sediments occur in a meridional belt coincid-ing with the Kangtian Shield in the west, and in a huge are stretching fromsouthern Kwangsi to Fukien via Hunan and Kiangsi, delimiting the easternboundary of Sinian deposition in Southwestern China. The Szechwan-Kwei-chow region was probably composed of Pre-Huto rocks and show similarphenomena in Sinian times to the Ordos-Shensi region in North China. In Plate Ⅱ the distribution of the Huto rocks is shown. and the follow-ing tectonic elements in the Huto Period are recognized.North China: The Shantung-Liaotung Geosyncline. The Huaiyang Geosyncline. The Shansi Geosyncline. The Inner Mongolian (?) Geosyncline. The Ordos-Shensi Nucleus. The Ho-Huai Nucleus.South China: The Kangtian Geosyncline. The Protocathaysian Geosyncline The Szechwan-Kweichow nucleus. The Proto-Southeast Oldland. Ⅳ. The Geotectonic units of Eastern China and their characteristics The tectonic classification of China recently proposed by Chinese andSoviet geologists are briefly mentioned. Based on the structural characters of the foundation floor and of later geological developments, the more stableportion composing the greater part of eastern China, the Chinese Platform,as called by B. M. may be divided into (i) The Sino-KoreanPlatform, (ii) the Southwest Platform, (iii) the Southeast Mincheh OldLand with the inner-lying Hsiang-Kuei Parageosyncline. The geosynclinalbelts to the north and west of the Chinese Platform are also briefly discussed. As shown on Plate Ⅲ, the geotectonic units recognized are as follows:(Ⅰ) The Sino-Korean platform (Ⅰa) The Huaiyang Shield-the most typical shield area in China. (Ⅰb) The Tsinling Axis. (Ⅰc) The Central Shantung Shield-flooded by the Cambrian and Or-dovician seas and again partly covered by Carboniferous ingres-sions, transitional between the true shield and shelf. (Ⅰd) The Alashan Shield. (Ⅰe) The Tachingshan Shield-also flooded by Sinian and possibly Cam-brian seas. (Ⅰf) The Jehol Shield-with immense volcanic eruptions and numerousgranite intrusions, being a typical "resurrected" shield in NorthChina. (Ⅰd-Ⅰe) Form the Inner Mongolian Axis of Huang. (Ⅰg) The Shantung-Liaotung Shield-also a resurrected shield. (Ⅰh) The Ordos-Shensi Shelf. (Ⅰi) The Hohuai Shelf. (Ⅰj) The Shansi Shelf-composed of various small massives and basins,a heterogeneous shield. (Ⅰk) The Kuanchung Subsiding Belt-between the Shensi-Ordos shelfand the Tsinling Geosyncline. (Ⅰl) Huainan Subsiding Belt-north of the Huaiyang shield. (Ⅰm) The Holan Subsiding Belt-between the Alashan shield and theOrdos-Shensi shelf. (Ⅰn) The Yenshan Parageosyncline-the mobilest unit on the Sino-Korean Platform, having undergone a folding and weak dynamo-meta- morphism in late Mesozoic time.(Ⅱ) The Southwest Platform(Ⅱa) The Kangtian Shield.(Ⅱb) The Hsuehfeng Shield.(Ⅱc) The Poyang Shield. These three form the Proto-Kiangnania of Huang.(Ⅱd) The Hokou Shield.(Ⅱe) The Szechwan-Kweichow Shelf.(Ⅱf) The Hupeh Shelf-a heterogeneous shelf.(Ⅱg) The Kwangsi Shelf-also a heterogeneous shelf.(Ⅱh) The East-Yunnan Subsiding Belt-east of the Kangtian shield.(Ⅱi) The Central Kwangsi Subsiding Belt and(Ⅱj) The west Hunan Subsiding Belt-bothbordering the Hsuehfeng Shield.(Ⅱk) The South-Anhuei Subsiding-Belt between the Poyang Shield and the Huaiyang Shield.(Ⅲa) The Mincheh Old Land or resurrected Shielde-ssentially occupying the greater portion of the Cathaysia of Grabau, which, up to the end of Triassic, had Leen a typical shield, for most of the time supplying detritus, having only received continental deposits and suffered temporary marine inundations in late Palaeozoic and early Triassic. The late Mesozoic saw immense eruptions of lavas and repeated intrusions of granites. Typical Pacific type of "orogeny" without much folding, comparable with the Jehol and the Shan- tung-Liaotung Shields in North China.(Ⅲb) The Hunan-Kwangsi Parageosyncline-beginning to subside in the Cambrian, affected by the Caledonian, the Indo-Sinian and the Yenshan Movements, typical of Poly-cyclic orogenesis as mentioned by Huang.(Ⅳ) Geosynclinal Regions (Ⅳa) The Lungchung "Zwichengebirge". (Ⅳb) The Hannan "Zwichengebirge". (Ⅳc) The Lungmenshan Parageosyncline-main folding of Yenshan Phase. (Ⅳd) The Heishan Fore-Deep in front of the Nanshan Geosyncline. (Ⅳe) The Tsinling Geosyncline-mainly Hercynian, with a southern rim of Caledonian folding. (Ⅳf) The Nanshan Geosyncline-the Bretonic Phase of a main folding, with a southern fringe of Caledonian folding, adjoining the Lung- chung "Zwichengebirge". (Ⅳg) The Mongolian Geosyncline-mainly Hercynian, probably a geo- synclinal "region", rather than a single geosyncline. (Ⅳh) The West-Yunnan Geosyncline-main folding probably of the Yen- shan phase. (Ⅳi) The Taiwan Geosyncline-main folding of the Himalayan Phase. With regard to the characteristic features of the tectonic building-up ofeastern China, three points may be mentioned: 1. Within the region of the Platforms, the shields are of a comparativelysmaller size. They usually bear an incomplete sedimentary cover and areintruded by younger granites. None of them is typical in the strict sense ofthe word. 2. The shelf areas usually receive considerably large thickness of sedi-ments. They are mobile and often show comparatively strong folding. No ty-pical shelf as exemplified by the eastern Baltic shelf is known. 3. Within the platforms, there usually occur subsiding belts along theinner side of the shields, comparable in structural features with the transi-tional zone between the geosyncline and the shelf areas. Ⅴ. Proposed systematic nomenclature in Geotectonics (in Chinese)In view of the confused translation and usage of geotectonic terms in late years, a simplified scheme of classification of the different orders ofgeotectonic units is given in tabular form. Nothing is now in the table. It is pointed out that, It should not beused. as a pigeon-hole scheme. The geotectonic elements, as they occur innature, are varied. Thus a second order shelf may be entirely enclosed bygeosynelines and become a huge intermontane basin (as exemplified by theTarim). There can be every grade of transition between a shield on theplatform and a zwichengebirge in the geosynelinal region The TsinlingAxis, Which forms the southwestern corner of the Sino-Korean Platform, ac-tually passess without interruption into the Lungchung zwichenge??rge, andthe active shields forming the border of a platform might equally be lookedupon as a composing part of the neighbouring geosyncline.