新疆北部卡拉麦里晚古生代走滑构造及其叠加变形序次

大型走滑断裂构造是大陆地壳内部基本的构造变形样式,通常是大陆地壳形成的标志.卡拉麦里构造带是新疆东准地区构造演化研究的重要构造单元.前人的研究认为卡拉麦里构造带是板块碰撞形成的缝合带.本文结合野外考察、构造分析和年代学工作认为,该构造带主要反映了走滑构造带的特点.在遥感影像上,卡拉麦里构造带呈断续的线状延伸特征.地震剖面上,卡拉麦里断裂带主断面产状近于直立向下延伸至基底,与一般张性断层、压性逆冲断层所显示的上陡下缓的铲状特征截然不同.野外考察显示,该构造带发育密集而陡立劈理,主断面附近劈理面倾角近于直立,在相对较浅层次的地层上,劈理面成花状散开,体现花状构造的特点.卡拉麦里构造带内的石炭系、泥盆系地层以及蛇绿岩系受到强烈改造,超糜棱岩化、糜棱岩化、千枚岩化现象普遍.糜棱岩中,硅质岩透镜体拖尾指示右旋走滑特征,与同构造岩脉次级张裂面指示的结果相一致.结合前人研究资料以及地层变形证据,可以推断构造带活动时限为270～260Ma.因此,卡拉麦里构造带是一条在晚古生代-早中生代活动的右旋剪切走滑构造带,准东地区与卡拉麦里构造带相关的缝合带确认,必须以卡拉麦里走滑构造带性质的准确厘定为基础.卡拉麦里构造二叠纪时期的走滑活动性质的确定,指示新疆北部二叠纪大陆地壳已经形成,而且,新疆北部后期叠加构造变形序次研究也显示具有大区域上的共性,指示新疆北部二叠纪以来进入基本统一大陆内部构造演化阶段.     

蒙阴盆地早白垩世火山岩地球化学特征及其岩石成因

蒙阴盆地早白垩世火山岩主要出露于青山群八亩地组和方戈庄组中。火山岩SiO₂含量为53.71%~69.08%,主要为安山质岩石和流纹岩,以钙碱性系列为主(σ平均3.42);富集Rb、Ba等大离子亲石元素和轻稀土元素,相对亏损Nb、Ta、P、Ti等高场强元素和重稀土元素;具有富集的Sr-Nd-Pb同位素组成(⁸⁷Sr/⁸⁶Sr(t)=0.7051~0.7110,ε_Nd(t)=-5.16~-16.4)。根据MgO含量和Mg^﹟值,可将安山质火山岩划分为高镁(Mg^﹟>60)和低镁(Mg^﹟<60)两个系列。高镁安山质岩石的MgO、Cr、Ni及不相容元素的含量明显高于低镁安山质岩石,且具有相对高的⁸⁷Sr/⁸⁶Sr(t)和较低的ε_Nd(t)值,Sr-Nd同位素组成趋向于EMⅡ型富集地幔端元。低镁安山质岩石地球化学特征类似于埃达克岩,其同位素组成介于EMⅠ型富集地幔端元与华北麻粒岩相下地壳之间。流纹岩具有较低的MgO、Cr、Ni含量和明显的负Eu、Sr异常,同位素组成类似于扬子中、上地壳。研究表明,蒙阴盆地高镁安山质岩石由曾遭受俯冲扬子陆壳熔体改造的华北岩石圈地幔部分熔融形成,且岩浆在上升 过程中经历了华北下地壳物质一定程度的混染或混合作用;低镁安山质岩石主要由华北下地壳部分熔融形成;流纹岩为岩石圈伸展减薄背景下仰冲至华北克拉通之上的扬子中、上地壳部分熔融的产物。地质现象显示,郯庐断裂带的伸展活动控制着蒙阴断陷盆地的发育,与蒙阴盆地早白垩世火山岩的成因有着密切的联系,在华北克拉通破坏中可能起到了重要的作用。     

安徽铜陵地区中生代侵入岩成因及成矿意义

安徽铜陵矿集区是我国最著名的铜、金、铁产地之一,成矿与岩浆作用关系密切.本次对铜陵地区中生代侵入岩进行了系统的矿物学、岩石学和元素地球化学研究.结果表明:①本区岩浆岩主要为辉石(二长)闪长岩( SiO2≤55％)、石英(二长)闪长岩(SiO255％～65％)和花岗闪长岩(SiO2≥65％)三种岩石组合,其矿物成分主要为...     

三塘湖盆地马朗凹陷石炭系火山岩系油气成藏主控因素及模式

三塘湖盆地马朗凹陷石炭系主要发育两套烃源岩,分别为哈尔加乌组上段和哈尔加乌组下段,油气藏形成的源控作用十分明显。通过烃源岩和原油地球化学的分析以及油源对比,发现不同类型原油的形成与分布严格受控于对应源岩的分布范围。分析表明,马朗凹陷石炭系火山岩系油气成藏的主控因素是优质烃源岩、强充注油源断裂和有利火山岩相带的合理配置。根据烃源岩与储层的配置关系,石炭系油气藏的形成可以概括为两种模式:一种为风化壳型成藏模式,油气聚集在石炭系火山岩顶部受风化淋漓作用改造的优质储层中,其中的油气来自下部烃源岩,运移通道为与烃源岩相沟通的油源断裂;另一种模式为内幕型成藏模式,储层为流体溶蚀改造的储层,其中聚集的油气来自邻近火山喷发间歇期沉积的炭质泥岩。     

松辽盆地昌德地区营城组火成岩气藏储层特征及其控制因素

松辽盆地昌德地区火山岩储层以酸性岩为主,主要岩石类型为熔结凝灰岩和凝灰岩,与国内其他含油气盆地的火山岩储层明显不同。宏观上岩性较致密,岩心观察仅见构造裂缝和溶蚀孔,局部见溶蚀洞,显微镜下观察储集空间类型多样,发育粒内溶孔、晶内熔孔、晶间微孔、构造微裂缝、炸裂缝和收缩缝等。火山岩厚度普遍较薄,其中芳深9井区火山岩厚度最大,最厚仅为75m。从岩相类型看,芳深9井附近为爆发相,其他地区为溢流相。研究区火山岩为低孔低渗储层,岩性和岩相与物性关系密切,同时控制着原生孔隙的形成。后期的成岩改造,包括构造活动、溶蚀作用等决定了次生孔隙的发育程度,构造运动产生的裂缝是该区储层得以改善的主要因素,而后期充填作用破坏了储层的储集性能。火山口附近爆发相与溢流相的叠合区是天然气勘探的有利目标。     

中国古亚洲域沉积盆地火山岩油气藏储层特征比较及其差异分析

在中国古亚洲域沉积盆地火山岩储层母岩年代和岩性、储集空间类型以及火山岩岩相综合分析的基础上,探讨了火山岩油气藏的储层特征及其差异性。研究表明,中国古亚洲域火山岩储层的母岩发育年代西早东晚,西部的准噶尔、三塘湖和吐哈盆地发育晚古生代海相、海陆交互相的中基性安山岩、玄武岩及火山碎屑岩;东部的松辽、二连和海拉尔盆地发育中生代陆相中酸性流纹岩、安山岩。火山岩原生储集空间包括气孔、孔洞以及冷凝收缩裂缝等;次生储集空间包括各种溶蚀孔及构造裂缝、风化裂缝等。火山岩岩相可分喷出相、火山通道相、次火山相和火山沉积相。其中中基性岩类多以溢流相开始,相序类型为溢流相、爆发相/火山沉积相;中酸性岩类多以爆发相或火山通道相发端,主要相序为爆发相、溢流相/侵出相。溢流相一般发育原生气孔、构造缝;爆发相多为粒间孔,而侵出相以角砾间孔和原生裂缝为主。火山岩储层的差异受多因素影响,包括岩性岩相、喷发环境以及后期构造、成岩作用等。前者奠定火山岩储层形成与分布的基础和储集空间的发育程度;后者则改造储层的储渗性能。     

Mesozoic collision-related magmatism and crust–mantle interaction along the Anhui segment of the Yangtze River Valley,east-central China

The middle segment of the Yangtze River Deep Fault Belt, located in the foreland of the Dabie orogen, contains widely exposed volcanic–intrusive complexes that formed during two episodes of magmatism (post-collisional and post-orogenic), reflecting crust–mantle interactions during the Late Jurassic (J₃) to Early Cretaceous (K₁). This article summarizes research on the Mesozoic igneous suites and xenolith suites in the area along the Yangtze River. ‘Post-collisional magmatism’ occurred during lithospheric extension at ～145–130 Ma. Its beginning and end are marked by gabbroic xenoliths and pyroxene cumulates within intrusions at Tongling, and by alkali-rich magmatic rocks. The association includes peraluminous silicic rocks and metaluminous mafic–felsic igneous suites, ranging from medium-K to high-K calc-alkaline to shoshonitic compositions. Taking the Tongling region as an example, quartz monzodiorite yields a sensitive high resolution ion microprobe (SHRIMP) zircon U–Pb age of 139.5 ± 2.9 Ma, and granodiorite yields an age of 135.5 ± 4.4 Ma. These intrusive rocks contain 52.79–66.46 wt.% SiO₂, 13.12–17.73 wt.% Al₂O₃, 1.37–4.62 wt.% MgO, 3.86–6.84 wt.% FeO^T, and 4.71–7.87 wt.% total alkalis (Na₂O?+?K₂O). ACNK values range from 0.62 to 1.20, and ANK values from 1.45 to 3.48. ‘Post-orogenic magmatism’ occurred during lithospheric delamination at ～130–120 Ma. The start of magmatism was marked by the formation of gabbro containing spinel lherzolite xenoliths in the Nanjing–Wuhu Basin (NWB), and its end was marked by the generation of feldspathoid phenocryst-bearing phonolite in the NWB and the Lujiang–Zongyang Basin (LZB), respectively. The association that formed during this episode ranges from alkaline to peralkaline. Taking the Niangniangshan Formation in the NWB as an example, the Nosite phonolite yields a whole-rock monomineral Rb–Sr isochron age of 120 ± 9 Ma, and contains 49.92–60.09 wt.% SiO₂, 17.67–20.65 wt.% Al₂O₃, 0.08–2.45 wt.% MgO, 1.32–6.62 wt.% FeO^T, and 9.24–13.92 wt.% total alkalis (Na₂O?+?K₂O). ACNK values range from 0.72 to 1.24, and ANK values from 1.03 to 1.35.

The two magmatisms correspond to two episodes of crust–mantle interaction. The first involved intensive interaction between middle–lower crust and underplated basaltic magma derived from the upper mantle lithosphere, whereas the second involved minor interaction between the middle–lower crust and basaltic magma derived from the lower lithospheric mantle.     

Statistical evaluation of tectonomagmatic discrimination diagrams for granitic rocks and proposal of new discriminant-function-based multi-dimensional diagrams for acid rocks

The four tectonic discrimination diagrams of Pearce et al. [Journal of Petrology, v. 25, p. 956–983] for granitic rocks were first evaluated using the literature cited by these authors as well as from our new database. The first diagram (Y?Nb) cannot discriminate volcanic-arc and collision settings. Both Y?Nb and Yb?Ta diagrams have an overlapping field for within-plate and ocean-ridge granitoids. The remaining two diagrams (Y?+?Nb?Rb and Yb?+?Ta?Rb) use a mobile element (Rb) in their y-axis. Although these diagrams successfully discriminate volcanic-arc and within-plate granites, they perform less well for collision tectonics. Besides, felsic or acid rocks are scarce in ocean-ridge settings, which limits the usefulness of these diagrams for this geological environment. Therefore, using an extensive database, we proposed a set of five new discriminant-function-based multi-dimensional diagrams for acid magmas from four tectonic settings (island arc, continental arc, continental rift, and collision). The very similar tectonic settings of island and continental arcs are discriminated for the first time. These diagrams are based on correct statistical treatment of compositional data, because they use natural logarithm transformation of major-element ratios and linear discriminant analysis (LDA). The use of discordant outlier-free samples prior to LDA improved the success rates by about 3–5%. Success rates of these diagrams as inferred from a testing set were between 76% and 88% for island arc, 60% and 92% for continental arc, and 72% and 84% for both continental rift and collision settings. Finally, application of these new diagrams to case studies not compiled in our initial database used for constructing these diagrams provided the following results: a collision setting for the Himalayas at about 30 Ma; an island arc setting for Quaternary acid rocks from geothermal boreholes in El Salvador; an island- or continental-arc setting for northern Italy at 35–52 Ma; a continental-arc setting for the Italy–Austria border at about 30 Ma; either a rift or a collision setting for northern Nigeria at about 164 Ma; a collision setting for central Nigeria at about 144 Ma and for the Cretaceous Masirah ophiolites of Oman; and an island arc setting for the Cretaceous Semail ophiolites of Oman. In spite of the relative mobility of major elements, these applications suggest utility of the new discrimination diagrams for all four tectonic settings.     

Chemical geodynamics of Western Anatolia

We report major and trace element concentrations and Nd–Sr–Pb isotopic data of 10 post-collisional volcanic domains in Western Anatolia, a seismically active part of the Alpine–Himalayan belt in the Aegean extensional province. Our objective is to provide geochemical constraints for tectono-magmatic processes shaping the late Cenozoic geodynamic evolution of Western Anatolia.

Calc-alkaline volcanic rocks occurring to the north of the Izmir–Ankara–Erzincan suture zone show arc-like trace elements and isotopes and were formed by the melting of the metasomatized Neotethyan mantle-wedge; this process was facilitated by asthenospheric upwelling resulting from slab delamination. Calc-alkaline and alkaline volcanic rocks from within the Izmir–Ankara–Erzincan suture zone also show the imprint of subduction fluids in their major and trace elements, but their isotopic compositions indicate derivation from a metasomatized lithospheric mantle followed by assimilation of ancient crust. Volcanics along the N–S-oriented Kirka–Afyon–Isparta trend were derived from the lithospheric mantle that was metasomatized by fluids from the older subduction of the African plate. Golcuk–Isparta volcanic rocks show an asthenospheric imprint; the latter was a consequence of upwelling following a tear in the subducting African lithosphere. Shoshonitic Kula volcanic rocks show very high trace element concentrations, OIB mantle-like trace elements, and Nd–Sr–Pb isotopic signatures, and were formed by partial melting of the upwelling asthenospheric mantle; this event was synchronous with the Aegean extension and possibly also with slab window formation due to ruptures in the African plate.

Inherent in the above chemical geodynamic models are the high ?_Nd(0) values (+6.4) of the end-member volcanic rocks, implying the presence of an asthenospheric source beneath Western Anatolia that is responsible for the currently observed high heat flow, low Pn wave velocities, high seismicity, and tectonic activity.     

Thermotectonic evolution of Precambrian basement rocks of the Kuruktag uplift,NE Tarim craton,China: evidence from apatite fission-track data

The Kuruktag uplift is located directly northeast of the Tarim craton in northwestern China. Neoarchaean-to-Neoproterozoic metamorphic rocks and intrusive rocks crop out widely in the uplift; thus, it is especially suited for a more complete understanding of the thermal evolution of the Tarim craton. Apatite fission-track (AFT) methods were used to study the exhumation history and cooling of these Precambrian crystalline rocks. Nine apatite-bearing samples were collected from both sides of the Xingdi fault transecting the Kuruktag uplift. Pooled ages range from 146.0 ± 13.4 to 67.6 ± 6.7 Ma, with mean track lengths between 11.79 ± 0.14 and 12.48 ± 0.10 μm. These samples can be divided into three groups based on age and structural position. Group A consists of five samples with AFT apparent ages of about 100–110 Ma and is generally associated with undeformed areas. Group B comprises three specimens with AFT apparent ages lower than 80 Ma and is mostly associated with hanging wall environments close to faults. Group C is a single apatite sample with the oldest relative apparent age, 146.0 ± 13.4 Ma. The modelled thermal history indicates four periods of exhumation in the Kuruktag uplift: late-Early Jurassic (180 Ma); Late Jurassic–Early Cretaceous (144–118 Ma); early-Late Cretaceous (94–82 Ma); and late Cenozoic (about 10 Ma). These cooling events, identified by AFT data, are assumed to reflect far-field effects from multi-stage collisions and accretions of terranes along the south Asian continental margin.