【作者】 吴小奇；

【导师】 刘德良；

【作者基本信息】 中国科学技术大学 ， 地球化学， 2010， 博士

【摘要】 本论文选取位于新疆北部卡拉麦里缝合带南侧陆东—五彩湾地区为典型研究区,通过对巴塔玛依内山组火山岩地质地球化学研究,主要包括岩石类型、岩相学、元素和同位素地球化学、孔渗性能等的分析,来确定该区早石炭世的构造背景和火山岩油气成藏的主控因素,进而探讨卡拉麦里缝合带后碰撞期火山活动的机制和时限,以及后碰撞构造岩浆作用对火山岩油气成藏的控制作用。陆东—五彩湾地区石炭系火山岩分布广泛,且具有明显的区域性差异。通过岩芯观察及岩石薄片鉴定,将该地区石炭系火山岩分为四大类型：火山熔岩类、火山碎屑岩类、火山熔结碎屑岩类和火山沉积岩类；并从岩相角度将区内火山岩划分为火山爆发相、火山溢流相、火山爆发—溢流过渡相和火山沉积相。在喷发间断中,相应发育了沉凝灰岩、凝灰质粉砂岩、泥质岩等。火山岩系列早期主要为基性,后期向酸性演化。火山活动以溢流式喷发为主,间以爆发式喷发,爆发相火山碎屑岩多沿断裂分布,即火山爆发中心沿主要断裂带分布。在主量元素特征上,陆东—五彩湾地区石炭系火山岩的全碱含量较高,主要为钙碱性系列,另有少量样品为低钾拉斑系列,酸性火山岩主要落入高钾钙碱性系列。从总体上看,陆东—五彩湾地区石炭系火山熔岩以中基性为主,另有少量酸性熔岩。在Harker图解上,MgO与其他主量元素表现出一定的相关性,反映出结晶分异的特征。Mg#介于38～57,表现出演化岩浆的特征。在稀土元素特征上,陆东—五彩湾地区中基性火山岩样品具有较高的稀土元素含量,在稀土元素球粒陨石标准化图上轻稀土相对富集,略有重稀土分馏。在不相容元素特征方面,这些火山岩样品在不相容元素原始地幔标准化图上表现出大离子亲石元素(LILE)和轻稀土(LREE)相对富集、高场强元素(HFSE)和重稀土(HREE)相对亏损的特征,但HFSE的含量相对较高。在同位素特征上,陆东—五彩湾地区石炭系火山岩样品的87Sr／86Sr初始比值介于0.70278-0.70365,143Nd／144Nd初始比值介于0.512517～0.512648,εNd(t)值为+5.69～+8.24,表明火山岩源于亏损的源区。尽管陆东—五彩湾地区石炭系火山岩表现出板内岩浆和岛弧岩浆的部分特征,但这些火山岩不是形成于板内或岛弧环境,而是后碰撞期的产物,其具有与典型后碰撞期火山岩一致的地球化学特征,如较高的TiO2、Zr、Nb含量和Zr／Y、Nb／Y比值等。卡拉麦里缝合带早石炭世中期～早二叠世发育大规模的火山活动,从西向东依次在准噶尔盆地陆梁隆起中部、陆东—五彩湾地区和三塘湖盆地发育较厚的火山岩,前人对其分别进行了研究,但对其构造背景的认识较为混乱,本论文中综合了前人的数据进行了重新分析。总体看来,卡拉麦里缝合带两侧火山岩均形成于后碰撞期伸展背景,在火山喷发时没有同期的洋壳消减作用。卡拉麦里洋盆关闭并发生两侧陆块碰撞时,表现出明显的软碰撞的特征,两侧陆块处于未紧密拼合的状态。岩石圈增厚有限,但由于重力失衡和强烈的地幔对流作用,发生强烈的壳幔相互作用,导致卡拉麦里缝合带后碰撞期发育强烈的火山活动。火山岩的源区主要为亏损的地幔物质和新生大陆下地壳。应当注意的是,尽管地幔对流作用很可能是卡拉麦里缝合带两侧后碰撞期火山活动的主要深部动力学机制,但也不排除在部分地区、部分时段其他机制如残余洋壳的部分熔融、加厚岩石圈深熔等也会导致火山活动。卡拉麦里缝合带两侧的陆块在发生软碰撞后,先后经历了早石炭世中晚期(C12-3)伸展(裂陷)—晚石炭世早中期(C21-2)挤压(隆升)、晚石炭世晚期(C23)至早二叠世(P1)伸展(裂陷)—中晚二叠世(P2-P3)挤压(隆升)这两个伸展—挤压旋回,表现出明显的软碰撞后陆—陆叠覆造山多旋回的特征,在每个旋回的伸展阶段都发生了大规模的火山活动,且随着时间的推移,火山活动的主体有从西向东逐渐迁移的趋势,这指示卡拉麦里缝合带很可能是从西向东逐渐发展进入后碰撞期的,也表明卡拉麦里洋盆可能是从西向东逐渐关闭的。因此,卡拉麦里缝合带与整个北疆地区一致,同样具有明显的继承性、旋回性、阶段性和方向性。火山岩油气藏是近年来准噶尔盆地油气勘探的重点之一。陆东—五彩湾地区石炭系火山岩原生孔隙的发育程度较低,主要原生孔隙类型有气孔和气管、晶内孔、晶间孔、粒间孔、冷凝收缩缝；次生孔隙的形成往往叠加复合于原生孔隙,从而改善了火山岩的储集性能；次生孔隙比原生孔隙发育,对油气的储集意义较大,其主要类型为溶蚀孔缝和构造裂缝；原生孔隙、次生孔隙的发育以及储集空间的组合类型均具有明显的区域性差异。陆东—五彩湾地区石炭系火山岩的储集物性受埋藏压实作用影响较小,与岩性岩相紧密相关,后期的风化淋滤、热液流体、构造活动、火山喷发环境均明显影响火山岩的储集性能。火山岩储集空间的形成和演化经历了原生孔隙发育、断裂构造改造、抬升风化淋滤、深埋热液作用、油气充注等几个发展阶段,且后期过程对前期过程形成的储集空间有明显的改造作用。整体上看,构造作用和风化及次生溶蚀作用都比较强烈的地区其火山岩的孔渗性能最佳。陆东—五彩湾地区石炭系火山岩的储集物性具有明显的区域性差异,储集物性较好的火山岩多分布于石炭系顶面风化壳。从总体上看,研究区火山岩油气成藏的有利因素有：紧邻石炭系和二叠系烃源岩的生烃凹陷；火岩储层物性较好；上覆致密的泥岩和粉砂质泥岩、风化壳顶部黏土层、异常高压岩层均具有很好的封盖性能；断裂和不整合面是油气垂向和侧向运移的有利通道；继承性的古隆起和正反转构造是油气运移的有利指向区。陆东—五彩湾地区石炭系火山岩油气藏除少部分为火山岩内幕油气藏外,主要表现出与不整合面相关的特性。其成藏模式主要有：新生古储型和自生自储型两大类。近年来的油气勘探表明,卡拉麦里缝合带两侧后碰撞火山岩中赋存了大量的油气资源,已发现了石西油田、克拉美丽气田和三塘湖油田等规模较大的油气田,而卡拉麦里缝合带后碰撞构造岩浆作用对油气成藏具有明显的控制作用：后碰撞期幔源岩浆底垫作用和火山活动促进了有机质的热演化；岩浆活动和岩浆岩可以直接参与烃类的形成,研究区石炭系烃源岩的分布明显受到后碰撞地质背景和火山活动的控制；致密火山岩和火山岩风化壳顶部黏土层在油气聚集成藏过程中会起到良好的封盖作用。火成岩油气藏的成藏机理、勘探开发等方面与常规油气藏的特点不同,有必要加强相关研究和工作投入。深化火山岩油气藏乃至基岩油气藏的成藏机理研究和勘探开发,以开拓火山岩油气藏新的领域,是油气勘探的迫切需求,这不仅有利于我们搞清楚火山岩中油气赋存和成藏的规律,而且也有利于油气产量的稳步提高。尽管本论文以卡拉麦里缝合带为例就后碰撞构造岩浆作用对火山岩油气藏的控制进行了分析,然而论构造岩浆作用对火成岩油气藏的控制作用而言,目前的研究仍然非常薄弱,十分必要在后续的工作加以强化。更多还原

【Abstract】 Ludong-Wucaiwan area, to the south of Kalamaili suture zone in north Xinjiang, was selected to study in this dissertation. Through geological and geochemical study of volcanic rocks in Batamayineishan Formation, including rock types, lithofacies, elemental and isotopic geochemistry, and the reservoir quality, the author has analysed the tectonic setting at early Carboniferous and the major controlling factors of volcanic reservoirs, and further discussed the mechanism and duration of post-collisional volcanism around Kalamaili suture zone, as well as the controlling on volcanic reservoirs by post-collisional tectono-magmatism.Carboniferous volcanic rocks were widespread and regionally different in Ludong-Wucaiwan area. After the observation of cores and slides, the volcanic rocks were divided into four types:lavas, volcaniclastic rocks, welded pyroclastic rocks, and volcanogenitic sedimentary rocks. The corresponding lithofacies were explosive facies, extrusive facies, transient facies between explosive and extrusive, and volcanogenitic sedimentary facies. Sedimentary tuff, tuffaceous siltstone and pelyte developed at the intervals of eruptions. The volcanic rocks generally evolved from basic to acidic. The volcanism was mainly extrusive eprutions, as well as explosive ones accidently. The explosive centers distributed along the major faults, since the explosive volcaniclastic rocks distributed mostly along them.According to the major elements, the Carboniferous volcanic rocks from Ludong-Wuwaican area had relatively high contents of total alkali, and were mainly belong to calc-alkaline series, while several samples were low-K tholeiitic series, and the acidic rocks were mainly high-K calc-alkaline series. The lavas were mainly intermediate-mafic, with several acidic. The MgO contents were interrelated with those of other major elements in Harker diagrams, indicating the characteristics of fractional crystallization. The Mg# values (38～57) indicated the characteristics of evolved magmas.As to the characteristics of rare Earth elements(REE), the intermediate-mafic samples had relatively high REE contents, and LREEs were relatively enriched in chondrite normalized REE patterns, with slight fractionation of HREEs. LILEs and LREEs of these volcanic samples were enriched while HFSEs and HREEs were relatively depleted in primitive mantle normalized incompatible element diagrams, but the contents of HFSEs were relatively high. These volcanic rocks were from depleted source, since the initial 87Sr/86Sr and 143Nd/144Nd ratios andεNd(t) values were 0.70278～0.70365,0.512517～0.512648 and+5.69～+8.24 respectively.Although the volcanic rocks from Ludong-Wucaiwan area indicated some characteristics of intraplate and island arc magmas, they were produced in post-collisional setting rather than intraplate or island arc, since the geochemical characteristics were identical with those of post-collisional lavas, such as high TiO2, Zr, Nb contents and Zr/Y, Nb/Y ratios.Extensive volcanism developed around Kalamaili suture zone from the middle stage of early Carboniferous to early Permian, and massive volcanic rocks were produced along the suture zone from central Luliang uprise in the west, Ludong-Wucaiwan area in the middle, and Santanghu basin in the east. Previous data from other authors was re-analysed in this dissertation since the previous understandings were confused. In general, these volcanic rocks were all produced in post-collisional period, without any contemporary subduction of oceanic crust.The collision of bilateral landmasses around Kalamaili oceanic basin was soft-collision, and the bilateral landmasses were subsequently untightly connected. Although the lithosphere was finitely thickened, the gravitational unbalance and extensive mantle convection could cause intense crust-manlte interaction and further extensive volcanism along Kalamaili suture zone in post-collisional period. The sources of volcanic rocks were depleted mantle materials and juvenile continental crust. Although mantle convection could be the major mechanism of this volcanism, several other mechanisms such as partial melting of residual oceanic crust, anatexis of thickened lithosphere could also cause post-collisional volcanism in specific regions and times.The bilateral landmasses around Kalamaili suture zone had experienced two extension-compression cycles after the soft-collision, extension (rift) at C13～C21 and compression (uprise) at C21-2, and extension (rift) at C23-P1 and compression (uprise) at P2-P3, indicating the characteristics of continent-continent superposition orogeny after soft-collision, and extensive volcanism developed at extension stage of each cycle. The principal volcanism migrated from west to east, indicating that the Kalamaili suture zone gradually evolved into post-collisional period from west to east, which reflected that the oceanic basin might be closed gradually from west to east. Therefore, Kalamaili suture zone shared the same characteristics with total north Xinjiang as successive, cyclic, periodical and orientational.The oil and gas exploration of Junggar basin has focused on volcanic reservoirs in recent years. The primary pores of Carboniferous volcanic rocks in Ludong-Wucaiwan area, including gas pores and pipes, intra-crystal pores, inter-crystal pores, inter-grain pores, condensational shrinking fissures, were less developed than the secondary pores, which included solution pores and fissures and tectonic fissures, and were more significative to oil and gas reservoirs. The superposition of secondary pores on primary ones significantly improved the reservoir quality of volcanic rocks, and the development of primary and secondary pores and the assemble types of reservoir pore space were regionally different.The reservoir quality of volcanic rocks in Ludong-Wucaiwan area was affected by weathering and leaching, hydrothermal fluids, tectonism and environment of eruption rather than burial and welding, and was closely related to the lithologies and lithofacies. The formation and evolvement of volcanic reservoir space had experienced the following stages:the development of primary pores, the modification by faults, weathering and leaching by uprising, deep-buried hydrothermal activities, the filling of oil and gas. The latter stages could modify the reservoir space produced by the early stages. In general, the more intensive of tectonism and weathering as well as secondary solution, the better reservoir quality of the volcanic rocks. The reservoir quality of Carboniferous volcanic rocks in Ludong-Wucaiwan area were regionally different. Almost all the volcanic rocks with favorable reservoir quality lied in the weathered crust at the top of Carboniferous.In general, the favorable factors controlling volcanic reservoir formation for oil and gas were as follows:close to the depression of hydrocarbon generation from Carboniferous and Permian source rocks, favorable quality of volcanic reservoirs, overlying compact mudstones and silty mudstones, good capping quality of clay deposition at the top of weathered crust and ultra-high pressure of rock stratums, favorable pathway for vertical and lateral migration of oil and gas by faults and unconformities respectively, favorable pointing zones for oil and gas as successive paleo-uprise and positive reversion structures. Besides some inner-volcanic reservoirs, the majority of Carboniferous volcanic reservoirs in Ludong-Wucaiwan area were related to unconformities, and their reservoir formation models were mainly two types, new bed generating and old bed preserving reservoirs, self-generating and self-preserving reservoirs. Oil and gas exploration in recent years revealed plentiful oil and gas resources in post-collisional volcanic rocks around Kalamaili suture zone, and several large oil and gas fields were discovered, such as Shixi oil field, Kelameili gas field and Santanghu oil field. Post-collisional tectono-magmatism of Kalamaili suture zone had controlled the volcanic reservoir formation obviously:underplating of mantle-derived magmas and post-collisional volcanism had promoted the thermal evolution of organic matters; the magmatism and igneous rocks could be directly involved in the generation of hydrocarbons; the distribution of Carboniferous hydrocarbon source rocks was controlled by post-collisional setting and volcanism; compact volcanic rocks and the clay deposition at the top of weathered crust of volcanic rocks could be the favorable capping rocks in the accumulation and reservoir formation processes of oil and gas.The reservoir formation mechanism and exploration techniques of volcanic reservoirs for oil and gas were different from those of regular ones, and it’s worthy of strengthening the interrelated research and investment. Therefore, it’s urgent to deepen the study on reservoir formation mechanisms and exploration on oil and gas reservoirs in volcanic rocks even the bedrocks, and to enlarge the new fields on volcanic reservoirs for oil and gas exploration. They are favorable to both the understanding of disciplines of accumulation and reservoir formation in volcanic rocks, and the stable increase of oil and gas output.Though the controlling of post-collisional tectono-magmatism on volcanic reservoirs had been analysed in this dissertation taking Kalamaili suture zone as an example, the study on the controlling of tectono-magmatism on volcanic reservoirs were weak, and need to be strengthened in further works.更多还原