共查询到19条相似文献,搜索用时 104 毫秒
1.
前寒武纪基性岩墙群的地球化学特征与岩石成因讨论 总被引:8,自引:0,他引:8
基性岩墙群广泛出现在全世界前寒武纪地盾中,它的发育往往与区域性伸展构造环境有关,并可能与地幔柱有密切联系,前寒武纪出现的基性岩墙群以拉斑玄武质占绝对优势(〉80%),但在新太古代一古元古代高Mg的苏长质组分和苦橄质岩石也占重要位置,碱性岩类则相当稀少,而在新元古代碱性岩墙则变得重要,基性岩墙群总体以富集LPEE和大离子亲石元素为特征,其中在苏长岩中更为富集,基性岩墙群的岩浆有多种来源,其中苏长质岩浆主要来源于太古宙的陆下岩石圈,而拉斑玄武质岩浆多来源于主要由主体地幔组分(PREMA)构成的是幔柱,地壳混染总体说来不是造成基性岩墙同位素及地球化学特征的主要机制。 相似文献
2.
阿尔泰造山带南缘中泥盆世苦橄岩及其大地构造和岩石学意义 总被引:21,自引:1,他引:21
阿尔泰造山带南缘中泥盆世苦橄岩位于北塔山组地层的下部, 其上依次为玄武岩和安山岩.3种岩性共同的特点是贫钛、富铁, 具Nb和Ta的负异常以及高场强元素的丰度与MORB相当, 具有典型的岛弧火山岩系的特点, 是准噶尔洋板块向南西俯冲的结果.苦橄岩和玄武岩的Zr/Nb和Sm/Nd比值与MORB相当, 表明其源区为亏损的MORB源.然而玄武岩的Ti/V和Zr/Sm比值均高于苦橄岩, 而且玄武岩的稀土元素配分曲线呈平缓型, 而苦橄岩则显示出低的稀土总量以及弱富集轻稀土型, 指示了玄武岩是被从俯冲的洋壳释放的流体交代的含角闪石的尖晶石橄榄岩的地幔源区低程度部分熔融形成的, 苦橄岩则是在高温条件下被流体交代过的石榴石橄榄岩高程度熔融的产物.安山岩则可能是榴辉岩部分熔融形成的. 相似文献
3.
藏南江孜—哲古一带广泛分布有北西向和近东西向产出的基性—中基性岩墙群,它们是新特提斯洋晚期发生大规模扩张的产物。本文对这些基性岩脉进行了较为系统的元素地球化学和Pb-Sr-Nd同位素研究。元素地球化学研究表明,该岩体略为富集LREE,Eu的亏损不明显,表明岩浆结晶分异作用较弱;LILE的富集和HFSE的亏损均不明显,所有样品均以相对富集Ta、Ce和亏损La、Y和Yb为特点。铅同位素206Pb/204Pb比值和207Pb/204Pb比值变化范围较小,分别为18.330~18.717和15.504~15.674;而208Pb/204Pb值和μ值相对变化较大,分别为37.664~39.156和9.296~9.931;初始87Sr/86Sr值变化范围较大,为0.7044~0.7105;岩石的εNd(t)值变化范围为-4.49~ 6.77,绝大多数为正值。微量元素地球化学和Nd-Sr-Pb同位素研究结果表明,藏南地区基性岩墙群可能是由来自亏损地幔源的岩浆与来自富集地幔源(EM)的岩浆混合的产物,其快速侵位造成岩浆分异作用较差,而岩浆的不均匀混合导致LILE富集与HFSE亏损均不明显,并产生较大的初始87Sr/86Sr比... 相似文献
4.
5.
6.
野外地质调查发现在阿尔泰南缘额尔齐斯构造带东段、额尔齐斯活动断裂与富蕴-锡泊渡断裂之间发育了一套未变形的酸性岩墙群.岩墙群侵位于海西期片麻岩化花岗岩和上石炭统深变质的额尔齐斯组岩层中,薄片鉴定和岩石地球化学分析确定为具有细晶结构的流纹斑岩.岩石的SiO2含量为70.9%~75.38%,K2O+Na2O含量为7.55%~8.99%;大部分样品Na2O>K2O,里特曼指数值为1.8~2.5之间,Al2O3=12.80%~14.53%,A/CNK=0.9~1.1,NK/A=0.7~0.9,具有准铝质-弱过铝质、低镁、高钾钠、低钙和锶、高(Fe)mol/(Mg)mol特点,具A型花岗岩类特点,属于亚碱性脉岩.岩石轻稀土富集,大离子亲石元素相对富集,具有明显的中等负铕异常,壳源特征明显.锆石U-Pb二次粒子微探针测年显示岩墙群形成于277~286Ma.推断岩墙是阿尔泰海西期造山运动结束后,在拉张构造环境下的地壳局部熔融产物. 相似文献
7.
大别造山带位于华北板块与扬子板块交界,出露众多中生代中酸性岩体。文章选取新县花岗岩体为研究对象,通过详细的野外地质调查、锆石U-Pb 同位素定年,以及元素和同位素地球化学测试,研究其地质和地球化学组成特征。结果表明,新县岩体主体为二长花岗岩,按照其结晶粒度可分为三个岩石单元,形成于133~129 Ma 之间,并保存有古元古代继承锆石。岩石具有富硅和富碱特征,属于(弱) 过铝质高钾钙碱性系列,亏损Ba、Sr 等大离子亲石元素和P、Ti 等高场强元素,无显著的Nb-Ta 亏损。在稀土元素配分模式图中,具有富集轻稀土、亏损中稀土、弱富集重稀土元素等特征,并具有明显的Eu 负异常,表明岩浆源区可能为角闪石稳定区域,而非加厚下地壳的石榴子石稳定区,推测岩浆形成于加厚地壳的伸展减薄环境。其全岩εNd(t)值为-20.8~-18.4,二阶段模式年龄值为2.61~2.43 Ga,表明岩浆源区主要由古老的地壳物质构成,如崆岭群和陡岭群。对比新县岩体与邻区千鹅冲、宝安寨等Mo 矿床赋矿岩石可以看出,两者具有相似的地球化学组成特征,暗示着存在密切的成因联系,或属于同源岩浆不同演化阶段的产物。 相似文献
8.
9.
东昆仑造山带中灶火地区镁铁质岩墙群以闪长玢岩为主,含少量闪斜煌斑岩、辉绿玢岩及辉绿岩,LA-ICPMS锆石U-Pb年代学指示该套岩墙群结晶侵位年龄为(249±1)Ma。稀土元素含量整体较高,富集轻稀土元素(∑REE=99.9×10-6~173.9×10-6,(La/Yb)N=3.5~9.3);微量元素表现出富集大离子亲石元素(LILE),亏损高场强元素(HFSE)的特征;源区分析表明,镁铁质岩浆为俯冲洋壳析出的流体交代富集地幔的结果,且在岩石成因中部分熔融起到主导作用,地壳混染和分离结晶作用对岩浆成分分异起到的作用有限。构造环境分析表明,岩石的形成与俯冲作用有关,结合区域构造演化认为镁铁质岩墙群的成因为:早三叠世,在古特提斯洋向北俯冲的环境下,俯冲板片释放的流体交代富集地幔,诱发地幔部分熔融形成镁铁质岩浆,受弧后伸展的动力学背景影响,岩浆最终上升侵位形成镁铁质岩墙群。 相似文献
10.
11.
The Tongbai orogenic belt has an overall antiformal geometry and the hinge of the antiform is sub-horizontal and trends NW–SE. The Tongbai complex (TBC) in the core of the antiform is bounded by the S-dipping Yindian–Malong shear zone in the south, the sub-horizontal Taibaiding shear zone at the top and the N-dipping Hongyihe–Tongbai shear zone in the north. The three shear zones have dextral, top-to-NW and sinistral movement, respectively. They are parts of a single shear zone, termed the Tongbai shear zone, that has a uniform top-to-NW sense of shear. Three samples of deformed granitoid (mylonite or protomylonite) from the shear zone have U–Pb zircon ages of 145 ± 6 Ma, 142 ± 2 Ma and 131 ± 6 Ma, respectively. An L-tectonite in the TBC yielded a metamorphic age of 137 ± 8 Ma and a migmatite an age of 137 ± 1 Ma. The Tongbai shear zone is intruded by undeformed Early Cretaceous granite and dykes and deformation in the shear zone is constrained to ca. 140–135 Ma, synchronous with metamorphism and migmatization in the TBC. Early Cretaceous magma emplacement and the associated uplift modified the TBC into a gentle antiform and the uplift may have continued to ca. 102–85 Ma. Similar geometry and kinematics have been documented in the Dabie orogenic belt to the east, which suggests that the Central Orogenic Belt in China probably experienced a uniform orogen-parallel extension and top-to-NW shearing in the ductile lithosphere in the Early Cretaceous. 相似文献
12.
桐柏造山带南北两侧的殷店—马垅剪切带和鸿仪河—桐柏剪切带是分割核部杂岩和高压变质岩石单元的两条重要界限带,通过对其详细的野外观察、显微构造分析、石英C轴组构EBSD(Electron Backscattered Diffraction)分析,发现这两条剪切带有统一的几何学、运动学特征,剪切运动学特征具有对称性,反映了二者可能是同一条剪切带,拥有近EW向伸展的运动特征。一体化的剪切带是一条覆盖于桐柏杂岩之上的拆离剪切带,总体表现为上盘NWW向运动,下部发育大量枢纽近EW向的鞘褶皱和压缩型应变的L型构造岩(L tectonites),剪切带内部则以压扁型应变为主发育大量的S-L构造岩(即糜棱岩系列岩石)。现今桐柏造山带内大量近EW向的线性构造可能源自于平行造山带伸展的构造活动。这种上盘NWW方向剪切拆离的地质特征在大别造山带广泛发育,反映了中国中东部的秦岭—桐柏—大别—苏鲁造山带在早白垩世可能发生过中—下地壳近EW向伸展的构造演化。 相似文献
13.
桐柏造山带在形成和演化过程中产生了多条韧性剪切带, 本文选取其中大河-固县剪切带和殷店-马垅剪切带作为研究对象, 分析其构造变形特征, 并利用数学法和图解法, 分别计算出两条韧性剪切带的位移量; 对殷店-马垅剪切带尝试用同构造变形石英脉的ESR测年来确定剪切带的活动年龄, 其结果与前人在该地区所获得的年龄十分吻合。大河-固县剪切带具右旋剪切的运动学特征, 运动学涡度Wk明显大于0.75, 指示以简单剪切为主, 位移量为857~867 m。殷店-马垅剪切带同样为右行剪切, 其位移量为1 081~1 113 m, 石英ESR测年结果140.6~131.5 Ma, 表明桐柏造山带碰撞后的构造变形以剪切活动为主, 活动年龄在早白垩世时期。 相似文献
14.
桐柏杂岩的南北边界的剪切带分别是殷店-马垅韧性剪切带和晓天-磨子潭韧性剪切带,这两条韧性剪切带内都发育杆状构造,且杆状构造具有层状结构,层与层之间通过一种特殊的滑脱面结合。由于晓天-磨子潭韧性剪切带相对于殷店-马垅剪切带位置明显更靠近商丹断裂带,早期商丹断裂带的活动在岩石中留下的变形痕迹导致了后期晓天-磨子潭韧性剪切带的变形程度要略强于殷店-马垅剪切带。这两条剪切带都是以简单剪切为主的剪切带,变质条件也相似,都属于角闪岩相变质,处于中-下地壳流变层位置。U-Pb同位素测年结果显示,晓天-磨子潭韧性剪切带的活动年龄为171~142Ma,殷店-马垅韧性剪切带的活动年龄为164~137Ma,两条剪切带的主活动期都在中-晚侏罗世,在早白垩世随着岩浆活动的峰期到来慢慢减弱停止。桐柏造山带在印支晚期碰撞挤压背景下的向东挤出不是一个整体的挤出,而是有层次的差异挤出,挤出的同时层与层之间会发生滑动,滑脱面类似滑动的润滑剂,酷似"管状流动"的构造。在晓天-磨子潭韧性剪切带和殷店-马垅韧性剪切带的牵引作用下,整个桐柏造山带由西向东发生管状流动。 相似文献
15.
阿尔金南缘构造带西段辉绿岩墙群的地球化学特征及构造环境 总被引:5,自引:0,他引:5
对阿尔金南缘构造带西段辉绿岩墙群的岩石学和地球化学的详细研究表明,该区辉绿岩墙群为拉斑系列岩石,其主量元素以中等TiO2(1.19%~1.59%)、高MgO(5.51%~7.88%)、贫K2O(0.04%~0.84%)和P2O5(0.10%~0.20%)、Na2OK2O为特征;高场强元素(HFSE)丰度特征显示其为E-MORB型或过渡型玄武岩质岩石;稀土元素总量相对较高,轻重稀土元素分馏不显著[(La/Yb)N=1.93~3.61,LREE/HREE=3.01~4.10],在球粒陨石标准化配分模式图上呈略富集型.结合玄武岩构造环境判别图解综合分析推测,它们可能形成于一种裂谷向MORB环境过渡的构造环境,即初始小洋盆构造环境. 相似文献
16.
《China Geology》2021,4(1):56-66
The timing of the initial Indo-Asian collision is a subject of debate for a long time. Besides, the magmatic trace of the collisional process is also unclear. In the present study, the authors report Early Eocene leucocratic sill/dike swarms in the northern edge of the Nymo intrusive complex of the Gangdese belt, southern Tibet. The Nymo intrusive complex was emplaced at ca. 50 –47 Ma and surrounded by the metamorphosed Jurassic-aged Bima Formation volcano-sedimentary sequence along its northern side. At outcrops, the leucocratic sills/dikes intruded along or truncated the deformed foliations of the host Bima Formation, which has been subject to high-temperature amphibolite-facies metamorphism at ca. 50 –47 Ma. Detailed cathodoluminescence image analyses reveal that the zircon grains of the leucocratic sills/dikes have core-mantle textures. The cores yield the Jurassic ages comparable to the protolith ages of the Bima Formation. In contrast, the mantles of zircon grains yield weighted mean ages of ca. 49–47 Ma, representing the crystallization timing of these leucocratic sills/dikes. The coeval ages for the Nymo intrusive complex, the high-temperature metamorphism, and the leucocratic sills/dikes indicate that a close relationship exists among them. The authors tentatively suggest that these leucocratic sills/dikes were generated from partial melting of the Jurassic-aged Bima Formation volcanic rocks, triggered by the high heat from the magma chamber of the Nymo intrusive complex. This Early Eocene tectono-thermal event of coeval magmatism, metamorphism and partial melting was most likely formed during the Indo-Asian collisional setting.©2021 China Geology Editorial Office. 相似文献
17.
18.
河南桐柏围山城层控金银成矿带同位素地球化学 总被引:6,自引:2,他引:6
河南省桐柏山区的围山城金银成矿带包括破山特大型银矿、银洞坡大型金矿、银洞岭大型银多金属矿床及一些矿点,赋矿地层是新元古界歪头山组,矿体产状与地层产状一致,形态呈似层状、鞍状或透镜状,层控特征显著。氢-氧-碳同位素地球化学研究指示早、中阶段的成矿流体主要为变质水,晚阶段有大量大气降水加入成矿流体系统。碳-硫-铅同位素指示成矿物质来自于歪头山组地层;钾-氩同位素表明成矿作用(100~140Ma)发生在秦岭陆陆碰撞造山的高峰期之后碰撞挤压向伸展转变的背景下。综合考虑矿带的成矿流体来源、成矿物质来源以及矿床地质特征,认为围山城成矿带属典型的层控造山型金银成矿系统,形成于中生代扬子与华北板块的陆陆碰撞造山体制。 相似文献
19.
Geochemistry of the Caledonian basic volcanic rocks at the south margin of the Qinling orogenic belt, and its tectonic implications 总被引:1,自引:0,他引:1
The geochemistry of the basic volcanic rocks at the south margin of the Qinling orogenic belt(SMQOB) suggests that they were formed in an intraplate tectonic setting.The REE distribution patterns show these rocks are strongly enriched in LREE with high ∑REE, and their trace elements geochemistry is similar to that of contimental flood basalt.All the above evidence suggests that the Caledonian basic volcanic rocks in the SMQOB were tholeiitic basalts formed in an intraplate spreading-initial rift tectonic setting.The characteristics of regional geology and geochemistry indicate that there was an intraplate spreading-rift tectonic setting between the South Qingling block and the Yangtze block in the Caledonian epoch.The dynamic spreading in this district began in the Early Caledonian and then the intraplate spreadinginitial rifts were formed in the Late Caledonian.As a result of spreading of the Tethys and geodynamic processes in deep mantle ,the Mianlue-Huashan oceanic basin was formed between the Qinling block and the Yangtze block in Devonian,and the Qinling microplate was separated from the northern part of the Yangtze plate. 相似文献