成煤構造環(huán)境外文翻譯

1、<p>　　Coal-Producing Tectonic Environments</p><p>　　This final chapter in the investigation of coal sedimentation is concerned with depositional aspects of the highest order of magnitude, namely, the in

2、fluence of the crustal setting on peat accumulation. This is a broad and complex field which draws on information, gathered from many different disciplines of the earth sciences. Some of these are currently evolving quit

3、e rapidly, while others re in a “mopping up” stage, insensu Kuhn (1970) and Walker (1973), following recent scientific revolutions</p><p>　　Plate tectonics has created its own nomenclature, of which only the

4、 essential terms will be used here. They will be supplemented by terms which are either descriptive, and therefore independent of geotectonic theory, or which have stood the test of time because they are useful in spite

5、of their generic association with now obsolete concepts. For example, the expressions “mio-” and “eugeosynclinal assemblage” have been kept here as reference term for shallow water marine (mainly shelf), and ocean</p&

6、gt;<p>　　1 Early Examples of a Tectonic Classification of Coalfields</p><p>　　Large-scale coal formation can take place only in actively subsiding regions, for example in sedimentary basins. It is pos

7、sible therefore to characterise the geotectonic environment occupied by a coal measure sequence in a manner similar to that which is applied to other sedimentary environments. Stutzer (1920) and Stille (1926) were among

8、the first to recognise the genetic links between tectonism and the formation of coal. Stille, in particular, referred to the striking difference in terms of b</p><p>　　Later it was shown by von Bubnoff (1937

9、) that the distribution of the world reserves of coal is also related to the geotectonic setting of coalfields. His conclusions are summarized in Table 9.2, which indicates that of all coal deposits known up to 1937, som

10、e 71% developed in former tectonically very active environments, particularly in the molasses foredeeps which develop adjacent to orogenic belts and receive much of the weathered debris washed down from the uplands.</

11、p><p>　　Table 9.1. Stille’s (1926) comparison (slightly modified) between some characteristics of coal measures formed in tectonically mobile and cratonised parts of Europe, respectively</p><p>　　

12、Table 9.2. The distribution of world reserves of coal in reference to the geotectonic setting of coalfields. (After von Bubnoff 1937)</p><p>　　The concentration of coal in the regions associated with orogen

13、ic belts is even more highlighted when the lateral extent of the deposits is considered. Coalfields situated within or on the shelf margins of cratons cover a wider area than the comparatively narrow foredeeps, but its a

14、real restriction is compensated by the frequency of coal seams occurring in a thick stack of coal measures. As will be discussed later, this is related to the substantial and prolonged subsidence that the continental <

15、;/p><p>　　The continental shelf environment, being less mobile, has produced fewer coal deposits than the orogenic domain. In this context it is important to define the term shelf. To the geographer, the shelf

16、region is usually that part of the sea which extends between the strand-line and the continental slope. However, as von Bubnoff (1948a) noted, the position of the strandline is quite incidental depending on crustal movem

17、ents and relative sea level positions.From the geological viewpoint, it appears </p><p>　　Intracratonic coalfields and those formed in intramontanc basins are frequently limnic in character, i.e. they have n

18、o hydrological connection to the sea, because they have been formed in land-locked basins above the then prevailing sea level. A spectacular modern example of intramontane peat formation occurs in the reed marshes on the

19、 shores of Lake Titicaca, 3810m above sea level in the South American Andes. Compared with their paralic counterparts limnic coalfields have small size and unstabl</p><p>　　The last group of coalfields menti

20、oned in Table 9.2 occurs in the interior of continental areas. They owe their existence to a variety of events including epeirogenic sagging of continental crust and continental rifting. Many peat and coal deposits forme

21、d on consolidated basement have no tectonic origin at all, but are the result of paludification related to differential subsidence. Examples are subsidence due to salt migration and leaching in the subsurface, or the for

22、mation of sinks isolated c</p><p>　　The tectonic setting of a coalfield exerts a strong influence on the type of coal that is formed within its boundaries. Hacquebard et al. (1967), Mackowsky (1968), Shibaok

23、a and Smyth (1975), Hunt (1982) and others have demonstrated that coal composition varies more in large paralic deposits than in limnic setting, because of the larger variety of factors influencing extensive continental

24、shelf or foredeep environments. Moreover, coals formed in rapidly subsiding foreland basins are more likely t</p><p>　　2 Basin Formation as Part of Plate Tectonics</p><p>　　The theory of plate t

25、ectonics, although primarily concerned with horizontal movements of the relatively rigid lithospheric plates (crust and uppermost mantle) over the softer asthenosphere (mantle), has also provided an explanation for the v

26、ertical movements that lead to subsidence and basin formation. The following crustal movements can be distinguished (after Dickinson 1974 and Fischer 1975):</p><p>　　Change in crustal thickness. According to

27、 the principle of isostasy thick low-density continental crust floats higher on heavy mantle material than thin high-density oceanic crust. For example, an isostatically compensated continental crust of 50 km thickness e

28、xtends 4 km above the sea, whereas a 6-km-thin oceanic crust is covered by approximately 5 km of water (Holmes, 1965). Plate tectonics provides several mechanisms for both crustal thickening and thinning. The latter, whi

29、ch is of immediate </p><p>　　Change in thermal regime. Convection currents in the plastic asthenosphere are responsible not only for horizontal plate movements but also for some vertical crustal motions whic

30、h are independent of ceustal thickness. Upwelling magma from the mantle may cause uplift by forming heat bulges in the overlying crust, and new oceanic crust is formed where such mantle material is extruded along mid-oce

31、anic rift zones. The latter are elevated above the sea floor because of thermal expansion of the affec</p><p>　　Loading affects. When sediments accumulate on an isostatically compensated crust the additional

32、 load will create a disequilibrium which will be balanced by subsidence. This means that, whatever the initial cause for the creation of a depositional site, once sediments are beginning to accumulate, their weight and c

33、ompaction are in some measure responsible for the deposition of additional sediments. This, to some extent self-prepetuating process is particularly well shown by the flexural bending u</p><p>　　As has been

34、discussed before, additional causes of sediment and coal formation are provided by subsurface salt migration and leaching, and eustatic sea-level changes, in particular by their interaction with crustal movements, which

35、produce a variety of sedimentary responses in different tectonic domains. For example, rifting of oceanic crust has depositional consequences quite different from the separation of continental crust. The rifting of conti

36、nental crust may lead to coal formation, but the</p><p>　　A plate-tectonic interpretation of the main crustal elements in reference to their ability to provide suitable sites for the formation of coal is sum

37、marized in Fig.9.1. This interpretation is based on the notion that the creation of new lithospheric crust along mid-oceanic rifts and the lateral movement of the lithospheric slabs towards subductionzones, where oceanic

38、 crust is consumed, produce three types of plate junctures. These are (after Dickinson 1974):</p><p>　　1. Divergent plate edges, where plate separation takes place and the developing gap is filled by upwelli

39、ng mantle material welding new oceanic crust to the separating plates.</p><p>　　2. Convergent plate edges, where old crust is subducted into the mantle underneath the leading edge of the overriding plate.<

40、;/p><p>　　3. Transform plate edges, where adjacent plates are laterally displace by movement along strike-slip faults.</p><p>　　Fig.9.1. The geotectonic setting of coalfields in reference to Curray

41、’s (1975) plate-tectonic subdivisions of the earth. The identification of countries is by international country code.</p><p>　　The tectonic subdivisions of coalfields used by von Bubnoff (1937) in Table 9.2

42、can be broadly accommodated within the plate tectonic framework of Fig.9.1. The fore-and many intradeeps are part of plate convergence complexes, which in view of their overwhelming quantitative, i.e. economic importance

43、, will be discussed first. The midplate continental margin is the setting of shelf deposits, whereas the cratonic and rift valley settings refer to the interior of consolidated areas.</p><p>　　3 Coalfields S

44、ituated Near Convergent Plate Edges</p><p>　　The relationships between tectonic setting and coal content of a region inferred from Tables 9.1 and 9.2 suggest that coal can form more frequently in geological

45、environments capable of offering a larger number and variety of crustal movements per unit time than less mobile areas. As mentioned above, this is a reature of foredeeps, which have been prolific coal producers in the p

46、at. Mountain chains consisting of folded and often metamorphosed rocks are formed as linear and often arcuate welts al</p><p>　　Subduction of oceanic crust beneatn oceanic crust (Fig. 9.2A). It is unlikely t

47、hat this situation will lead to significant coalfield formation because of the considerable water cover of the sea floor. Oceanic crust emerges above water only where it has been thickened by magmatic injection and may t

48、hen produce isolated small coal occurrences. However, as long as only oceanic crust is involved, the lack of a strong nearby sediment source leaves the adjacent ocean basin starved and too deep for pea</p><p&g

49、t;　　Subduction of oceanic crust underneath continental crust (Fig.9.2B). There are several past and present examples of extensive coal formation associated with this type of plate convergence. The main coalfields formed

50、in the process occupy retroarc basins (Dickinson 1974) filled with thick sedimentary successions. The beginning of sedimentation is probably related to extensional tectonics in the backarc area, at a time when subduction

51、 is still in process. However, during and following the accretio</p><p>　　Partial subduction of continental crust beneath continental crust (Fig.9.2C). This type represents an example of continental collisio

52、n. Because of its thickness and low density, continental crust can only partially be subducted which leads to tectonic stacking and overlap of the two plate margins. The conditions of coal formations in a retroarc basin

53、are the same as in (2) for the overriding plate. In addition, at least two loci of potential peat accumulation are contributed by the consumed plat</p><p>　　Fig.9.2 A-C. Three possibilities of plate converge

54、nce. Continental crust; ocanic crust;volcanics; ??? molasses sediments;??? marine sediments</p><p><b>　　中文：</b></p><p><b>　　成煤構造環(huán)境</b></p><p>　　在已知的煤沉積過程中，這種

55、最終階段是與影響泥炭堆積外在的呈最高狀態(tài)的重要的沉積因素相聯系的。這是一個寬廣且復雜的領域，它吸收了聚集地球科學許多不同學科的知識。一部分領域已經相當迅速的普遍展開，而其他的一些在跟隨最近的科學革命處于一個結束期。在20世紀70年代早期的地槽假說被板塊構造理論所替代就是后者中的一個例子。即使在經過20年后，這種新的模式仍處于被改進或裝備于概念的子集，同時在地形分析中被列為通用的重點的過程中。因此，在這個時期對于被選擇的題目做一個決定性的

56、陳述是不可能的，但是，只是描述關于現代大地構造因素方面的煤田分類是可以建立的。這種現代化目標的實現是充滿困難的，因為要從占優(yōu)勢的全球構造學靜止地槽的觀點變?yōu)楝F代的，大量的活動論解釋使得一些煤田的構造分類變得復雜。當許多煤田的構造情況，例如那些前淵或陸前盆地已經相對改變一點，建立在內部或山間的槽即造山的山脈上的煤田裝置，如果沒有仔細的學習是不能被適當的分派下去。根據該地槽的概念，幾乎所有的這些內淵，連同前淵和后淵 ，他們的超級造山帶對口，

57、被視為一組穩(wěn)定地塊的一部分，其中伴隨著 “有機終端地槽構造” 的發(fā)展（Aubouin 1965</p><p>　　板塊構造已創(chuàng)造了自己的名稱，其中只有基本術語將被用于在這里。他們對輔助術語有的只是描述性的，因此獨立的大地構造理論中，有的經受了時間的考驗，因為他們在通用的而現在已經過時的概念中是有用的。舉例來說，詞“ 中新世 ”和“ 優(yōu)地槽組合”一直在用，涉及到淺海（主要是大陸架），和深海結核，濁積巖和蛇綠巖套，

58、分別作為參考。此外，提到“ 冒地向斜 ” ， 冒地槽已在北美文獻中成為一個標準的原地術語，沉積階地邊緣超覆了大陸邊緣。同樣沉積物的構造特征，如“ 同造山期的”復理石和“后期的同褶皺到造山期（沒有褶皺作用)”的穩(wěn)定地塊，分別地，仍然可以用在一個板塊構造背景下，沒有不必要的混淆他們的相對精確的定義。尤其是在討論煤田位于聚合的板塊邊緣，穩(wěn)定地塊的概念用在造成破壞該隆起造山帶是十分有益的。由于在先前的討論，也不是本章的目的給予詳細說明了一大批例

59、子，但要選擇幾個典型的涉及了本質和結構的煤田，以各自的板塊構造建立。</p><p>　　1一個早期的煤田構造分類的例子</p><p>　　大型煤田的形成可以發(fā)生的地方，只有在活躍的下陷地區(qū)，例如在沉積盆地。因此，用一個煤系序列表征大地構造環(huán)境的方式表示其他適用的沉積環(huán)境是有可能的。Stutzer (1920) 和 Stille (1926)第一次確認構造與成煤之間的成因關系。Still

60、e，尤其是提到突出差異而言，歐洲盆地充填中煤層的平均厚度和的比例關系與總煤系厚度的聯系，在這之間存在的石炭紀和第三紀煤的數量。他歸因于這樣的相似性，以對比程度的地殼的流動性，在歐洲的兩個主要成煤期受影響地區(qū)。他的結果總結在表9 .1.中。即使在第三系褐色和石炭系瀝青煤壓實比率之間的不同的計算（在較小程度壓實適用于跨煤層沉積物）的對比是相當顯著的。后來結果表明，由von Bubnoff (1937)表示，分布世界各地的煤的儲量是與煤田的大

61、地構造環(huán)境有關的。他的結論的摘要列于表9.2 ，這表明在1937年所有的煤炭儲量都已經知道，約71 ％的是發(fā)展構造非?；钴S的環(huán)境，特別是在穩(wěn)定地塊盆地前淵發(fā)展來 的，其中毗鄰造山帶和從高地來的接收的許多風化碎片。</p><p>　　表9.1 . Stille’s（1926）一些比較（略作修改）</p><p>　　分述在構造移動盆地和歐洲部分克拉通盆地特征煤的數量</p>

62、<p>　　表9.2 .分布在世界儲備煤中提到了大地構造環(huán)境的煤田。 （von Bubnoff 1937 之后）</p><p>　　側向范圍的沉積被認為在與造山帶相關的地區(qū)的煤的聚集中更是突出的。煤田位于沙洲的邊緣或沙洲內古陸核的涵蓋了更廣闊的領域較相對狹窄的前淵 ，但其地域的限制，是補償的頻率煤層發(fā)生在一個一定數量厚的煤層。正如我們將在所后面討論的，這是涉及到大量的和長期沉陷的被認為在大陸邊緣受到附

63、近俯沖的復雜的，作為一個造山帶是與板塊邊緣共生的。這是不足為奇的，因此,在北美，歐洲，亞洲和南部大陸von Bubnoff (1937) 還發(fā)現一個山脈與成煤之間的相近關系。當然，那兒已知的山脈與煤的沉積是沒有關系的。但是，往往他們的缺失是與影響植物來源有關的。例如，所有的前泥盆紀造山帶發(fā)生的時候,植物界仍然不能滿足作為生產泥炭的作用。大陸架的環(huán)境，缺少移動性，比造山作用產生的煤炭沉積少。在這方面是定義大陸架這個術語是很重要的。對于

64、地理學來說，大陸架地區(qū)向海的部分通常在股線和大陸斜坡之間延伸。不過，由于von Bubnoff (1948a)指出，濱線的位置是相當偶然的，決定于地殼運動和海平面位置.從地質的角度來看，大陸架定義的擴大似乎是有用的，因此時間的因素可以忽略。大陸架地區(qū)可能被視為邊緣的那些地區(qū)，但大陸的完整</p><p>　　克拉通內的煤田和那些形成于山間盆地的煤田在特征上經常是湖泊相的，即它們對于海洋來說沒有水文學的意義，因為他

65、們在后來的海平面之上已經形成堵塞的內陸盆地。一個引人注目的現代的例子， 山脈之間內泥炭的形成是發(fā)生在南美安第斯山脈高于海平面3810米蘆葦沼澤對海岸的的湖。與他們相比，在沉積基底的水平面之上近海成因的相對湖泊成因煤田有規(guī)模小和不穩(wěn)定的特征。然而，如上文所示，術語內淵可能包括一個復雜系列的沉積環(huán)境，其中一些可能會與造山帶現在發(fā)生的完全無關。</p><p>　　最后一批在表9.2提到的煤田發(fā)生在內部的大陸地區(qū)。他們

66、應該歸功于各種各樣的活動，包括造陸下陷大陸地殼和大陸裂谷。許多泥炭和煤炭沉積的形成是基于沒有構造的起源在所有，但泥炭化的結果是與不同的沉降有關的。這些例子是由于沉積物在地下遷移和過濾后沉淀，或下沉的孤立煤田的形成是由于該陸表的湖泊。大部分的這些煤田是湖泊相的 ，但罕見的海侵可能發(fā)生在他們的發(fā)展過程中。</p><p>　　在形成其邊界過程中,煤田的構造環(huán)境有著重要的影響力。Hacquebard 等 (1967),

67、 Mackowsky (1968), Shibaoka and Smyth (1975), Hunt (1982)和其他人已經表明，煤的組成在很大程度上近海相比湖泊相呈現更大的不同，因為大量的不同因素影響寬廣的大陸架或前淵盆地環(huán)境。此外，煤的形成在迅速下沉前陸盆地更可能有高含量的微鏡煤，微亮煤和灰分比煤形成的穩(wěn)定的邊緣上，或在慢慢下沉克拉通盆地。這些煤很可能是豐富的暗煤為主的微惰性煤。</p><p>　　2盆地

68、形成作為板塊構造理論的一部分</p><p>　　板塊構造理論，雖然主要關注相對剛性巖石圈板塊（地殼與上地幔頂部在柔和的軟流圈（地幔）的橫向變動，但也提供了一個導致沉降和盆地的形成的垂直運動的解釋。接下來的地殼運動，可以劃分為(在Dickinson 1974 and Fischer 1975之后):</p><p>　　地殼厚度的變化 根據該原則，均衡厚的低密度大陸地殼的漂浮物重的地幔物

69、質比薄的高密度大洋地殼高。舉例來說，一個海平面之上均衡的大陸地殼50公里的厚度延伸4公里，而6公里的薄大洋地殼涵蓋的約5公里的水(Holmes, 1965) 。板塊構造提供了若干機制，為雙方的地殼增厚和變薄。后者，這是對的切身利益，在這里，往往是體現在地區(qū)的大陸裂谷，如在早期階段板分離地殼沿裂谷帶衰減由伸展步斷層，從而形成迅速下沉地塹和半地塹。剝蝕的均衡的地殼隆起部分同樣導致隨后的沉降。由于地殼增厚的隆起是有一些這方面的原因，因為它造成

70、的潛在來源地區(qū)煤系沉積物。這一點特別重要，在前淵盆地，在附近的造山帶其中盆地的形成往往是加上隆起。大部分隆起的例子是由于地殼增厚是與要么巖漿進入地殼要么板塊碰撞有關。</p><p>　　熱度的改變 傳送氣流的塑膠軟流圈不僅負責水平板運動，但也為一些地殼垂直的運動提供獨立的空間厚度。上涌的巖漿從地幔隆起在覆地殼可能會導致形成熱膨脹，而新的大洋地殼形成是地幔物質沿中旬大洋裂谷區(qū)擠壓。后者則是高架以上的海床，由于熱

71、膨脹受影響的地殼變的寒冷和密集隨著年齡和距離逐漸崛起形成壩頂。熱隆起地區(qū)內或沿緣大陸板塊受到剝蝕變薄，加劇他們在熱化階段的沉陷。</p><p>　　充填影響 當沉積物的積累到一個均衡補償的地殼而有額外負荷時，通過下沉將創(chuàng)造一個不平衡。這意味著，無論最初的出現一個沉積地點的原因是什么，一旦沉積物開始積累，額外的沉積物的重量和壓實在一定程度上造成沉積。這一點，在一定程度上自我穩(wěn)定過程中，尤其是以及所表現出的抗彎彎

72、曲荷載作用下的大陸架邊緣(Walcott 1972) 。其他常見的大地構造的負載引起的沉降和沉積的造山帶前淵邊緣是在相鄰的褶皺帶向下彎曲下的,在重量超過逆沖巖席下造成的(Price 1973; Laubscher 1978; Beaumont 1981; Quinlan and Beaumont 1984)。額外的負荷的向下彎曲的地殼是所提供的大量的沉積物中產生的穩(wěn)定地塊盆地，在褶皺帶和運入發(fā)展中的前淵盆地 。</p>&

73、lt;p>　　正如已經討論過，額外的原因，沉積物和煤的形成所提供的地下鹽遷移和浸出，及海平面海平面變化，特別是通過他們的相互影響與地殼運動，產生了各種沉積反應在不同的構造域。舉例來說，裂谷海洋地殼與從分離的大陸地殼沉積的后果相當不同。張裂大陸地殼可能會導致煤的形成，但裂谷的大洋地殼是不太可能導致形成的煤。影響大地構造環(huán)境的煤田就泥炭積累和煤的組成的調查，需要一個對地球主要地殼元素與他們的主要運動認識。</p><

74、;p>　　板塊構造解釋中主要地殼元素在參考他們有能力為形成煤提供合適的地點，總結在了圖9.1 。這種解釋是基于概念，即創(chuàng)造新的巖石圈地殼,沿中海洋的裂痕和橫向運動的巖石圈面向俯沖地區(qū)，其中大洋地殼的消滅，生產三種類型的板塊結合點。它們是(after Dickinson 1974):</p><p>　　板塊邊緣，板塊分離的發(fā)生和發(fā)展的差距，是由上涌的地幔物質焊接新的大洋地殼并向板塊分離。</p>

75、<p>　　聚合板塊邊緣，那里的舊地殼俯沖到下地幔的主要邊緣的推覆板塊。</p><p>　　轉換板塊的邊緣，毗鄰的板塊沿走滑斷層運動橫向位移。</p><p>　　Fig.9.1. The geotectonic setting of coalfields in reference to Curray’s (1975) plate-tectonic subdivisions

76、 of the earth. The identification of countries is by international country code.</p><p>　　在表9.2 von Bubnoff (1937) 所用的構造區(qū)分煤田，大致可容納在圖9.1所表示的板塊構造的框架內。前淵和許多內淵是部分板塊銜接形成，鑒于它們的壓倒性數量，即經濟上的重要性，將首先討論。大陸邊緣中部是確定大陸架的沉積，

77、而穩(wěn)定地塊和裂谷的設置是指內部的綜合領域。</p><p>　　3 聚合板塊邊緣的盆地</p><p>　　從表9.1和9.2推斷一個地區(qū)構造背景和煤的組成之間的關系表明，煤可以在地質環(huán)境的能力提供了較大量的和不同的地殼運動在單位時間內頻繁運動較缺少運動的區(qū)域容易形成。如上所述，這是一個前淵盆地，它是多產煤的小塊。山脈連接成的褶皺，往往變質巖被形成線性，往往聚合板塊邊緣的弓狀隆起伴隨一定數

78、量構造巖漿活動，所有這些似乎主要與俯沖過程相關。然而，并不是所有的前俯沖帶形成煤田，這是一個與聚合板塊性質有關的問題，即他們是否構成海洋或大陸地殼。</p><p>　　根據圖9.1和9.2 ，有三種情況：</p><p>　　俯沖的大洋地殼之上的大洋地殼（圖9.2A ）。這種情況將導致重大的煤田的形成是不可能的,因為相當多的水覆蓋了海底。只有大洋地殼露出了上水面，而且通過巖漿入侵增厚，才

79、可能產生孤立的小煤田的形成。然而，只有大洋地殼參與，附近缺乏一個強有力的沉積物來源導致鄰近的海洋盆地缺失或泥炭堆積太深。反過來說，復合島弧系統，在其中的幾個俯沖帶的運轉，同時在相反的方向和/或在其中異地地殼碎片（地形）已增益向島弧系統，可為煤的形成提供合適的條件。日本列島的一個例子，其中包含的煤田第三系年齡均在前島弧和后島弧的位置(Aihara 1986) 。弧前盆地的其他地方是未知的顯著的煤產地，因為在盆地階段構造不穩(wěn)定和后生構造作用

80、的破壞。Aihara (1986) 所描述的在Hidaka盆地中央北海道產生在3000米厚的早第三紀連續(xù)的褶皺和斷層中的煤層，是比較罕見的厚煤層的煤系序列形成和保存在了弧前環(huán)境中。</p><p>　　俯沖的大洋地殼下的大陸地殼（ 圖9.2B）。與此相關類型的板塊銜接的有幾個過去和現在的例子是有關大規(guī)模成煤的。主要煤田形成于被厚的沉積層序所充填的弧后盆地(Dickinson 1974)。沉淀的開始可能與在弧后區(qū)的

81、伸展構造相關，在俯沖仍在進行中的過程時。不過，期間和之后的弧前盆地中的異地堆積地形是受到了擠壓應力的原因，這造成它減少了在逆沖斷層下的重壓。</p><p>　　部分俯沖的大陸地殼下方的大陸地殼（圖9.2C）。這種類型代表了大陸碰撞的例子。因為它的厚度和密度低，大陸地殼只能部分被俯沖而導致的構造疊加和重疊的兩個板塊的邊緣。在弧前盆地的成煤條件在（ 2 ）中與超覆板塊是一樣的。此外，至少有兩個有潛力的泥炭堆積的場所