合肥盆地钻井地层的同位素测年与地层划分   总被引：3，自引：0，他引：3  

徐春华  朱光  刘国生  谢成龙  王勇生  李长城 《安徽地质》2005,15(4):251-255

合肥盆地内部中、新界地层大面积被第四系覆盖，其地层的时代与划分主要依赖已有的6口深井地层资料。由于缺乏可靠的化石记录，这6口深井地层时代与划分一直存在着很大的分歧，制约了对该盆地的油气勘探与远景评价。本文利用这6口深井泥岩类岩屑中自生伊利石，在其结晶度分析基础上，进行了K-Ar同位素测年，成功地获得了不同深度上的地层形成时代。据此地层年龄，文中对这6口深井所钻遇的地层进行了重新的划分。  相似文献   

K-Ar Ages of Granitic Magmatism and Related Pegmatite Formation at the Umanotani-Shiroyama Mine, Shimane Prefecture, SW Japan and Their Bearings on Cooling History     

Shouji Kihara    Kenichi Hoshino    Makoto Watanabe    Hirotsugu Nishido  Shunso Ishihara 《Resource Geology》2005,55(2):123-129

Abstract. The Umanotani-Shiroyama pegmatite deposits, the largest producer of K-feldspar and quartz in Japan, are of typical granitic pegmatite. Ilmenite-series biotite granite and granite porphyry, hosting the ore deposits, and biotites separated from these rocks yielded K-Ar ages ranging from 89.0 to 81.4 Ma and 95.2 to 93.7 Ma, respectively. Muscovite and K-feldspar separated from the ore zone yielded K-Ar ages with the range of 96.2 to 93.1 Ma and 87.3 to 80.7 Ma, respectively. Muscovites from quartz-muscovite veins in the ore zone and in the granite porphyry yielded K-Ar ages of 90.4 and 76.3 Ma, respectively. K-feldspar is much younger in age than coexisting muscovite. It is noted that the K-Ar ages of biotite separates and the whole-rock ages are identical to those of muscovite and K-feldspar in the ore zone, respectively. These time relations, as well as field occurrence, indicate that the formation of the pegmatite deposits at the Umanotani-Shiroyama mine is closely related in space and time to a series of granitic magmatism of ilmenite-series nature. Using closure temperatures of the K-Ar system for biotite and K-feldspar (microcline), cooling rate of the pegmatite deposits is estimated to be about 82C/m.y. at the beginning, but slowed down to about 15C/m.y. in the later period.  相似文献   

Prolonged postcollisional shoshonitic magmatism in the southern Svecofennian domain – a case study of the Åva granite–lamprophyre ring complex     

Olav Eklund  Alexey Shebanov 《Lithos》2005,80(1-4):229-247

The Åva ring complex is one of four Paleoproterozoic postcollisional shoshonitic ring complexes in southwestern Finland. It is composed of ring dykes of K-feldspar megacryst-bearing granite, mingled in places with a shoshonitic monzonite, and lamprophyre dykes crosscutting all the rocks in a radial pattern. A survey was undertaken to trace the magma chamber beneath the ring complex to date it and measure some intensive parameters to clarify the crystallisation conditions at depth before the granite was emplaced in the upper crust. Mineral separates were extracted from the core zones of K-feldspar megacrysts in the granite, heavy mineral fractions (including zircons) from these separates were used for P-T assessment and age determinations, and the results were compared to data obtained from bulk rock samples. It appears that magma differentiation took place in a midcrustal magma chamber (at 4 to 7 kbar) possibly 30 Ma before the emplacement of the ring complex in the upper crust (deep assemblage 1790 Ma, shallow assemblage 1760 Ma). Relatively high activity of the alkalies and a low oxygen fugacity characterised the midcrustal chamber. The juvenile Svecofennian crust was invaded by shoshonitic magmas from an enriched lithospheric mantle over a long period of time. Some of these magmas were stored and differentiated in the middle crust before transportation to the upper crust. The results also show that coarse-grained granites may provide evidence for several magmatic evolutionary episodes, e.g., differentiation and crystallisation in different environments prior to final emplacement.  相似文献   

苏鲁地体胡家林和梭罗树三叠纪变质超基性岩U-Pb、Lu-Hf和O同位素地球化学研究     

龚冰  郑永飞  陈斌  吴元保 《地球学报》2005,26(Z1):67-69

胡家林超基性岩单矿物氧同位素组成基本上接近正常地幔值（石榴石4.7‰~5.4‰)。梭罗树超基性岩及其共生榴辉岩具有氧同位素正异常（超基性岩中石榴石9.8‰~10.4‰;榴辉岩中石榴石9.0‰~12.1‰)，指示超基性岩和榴辉岩原岩可能在板块俯冲之前，在浅层或地表环境中经历过蛇绿岩套顶部相似的低温热液蚀变。胡家林超基性岩样品中的变质锆石年龄227.2±2.4 Ma，可能代表俯冲板块经峰期超高压变质后，折返初期从金刚石榴辉岩相降压至柯石英榴辉岩相过程中流体活动和错石结晶的年龄。梭罗树超基性岩样品中变质锆石的一组变质年龄240.4±2.4 Ma代表了板块俯冲至超高压峰期变质之前流体活动过程中锆石的结晶年龄，而另一组变质年龄217.1±3.3 Ma代表了板块折返过程中高压榴辉岩相重结晶条件下的锆石结晶年龄。从变质锆石到重结晶锆石，其Th/U和176Lu/177Hf呈现出相似的变化趋势，可能指示了变质作用对锆石中的U-Th-Pb同位素体系和Lu-Hf同位素体系产生相似的地球化学效应。梭罗树超基性岩可能来源于俯冲地壳内部的“残留地幔”。胡家林超基性岩重结晶锆石中继承的放射成因铅或者来源于俯冲地壳与仰冲盘底部石榴辉石岩相地幔发生的壳幔相互作用而导致碎屑锆石的重结晶；或者来源于超基性岩岩浆在板块俯冲前，通过底侵作用上升侵位与地壳物质发生混染形成岩浆锆石，这种岩浆错石在超高压变质过程中经历了重结晶。  相似文献   

Geochronologic Constraints on the Magmatic Underplating of the Gangdisê Belt in the India-Eurasia Collision: Evidence of SHRIMP II Zircon U-Pb Dating     

DONG Guochen  MO Xuanxue  ZHAO Zhidan  GUO Tieying  WANG Liangliang  CHEN Tao 《《地质学报》英文版》2005,(6)

  相似文献   

大兴安岭南部二叠系—三叠系界线及沉积环境演化     

陈树旺  郑月娟  张健  张海华  张德军  苏飞  黄欣  公繁浩  甄甄 《中国地质》2020,47(3):821-838

北方陆相二叠系—三叠系界线研究是界线地层研究的重要问题之一,对采自内蒙古巴林右旗幸福之路组二段建组剖面的安山质岩屑晶屑凝灰岩开展锆石LA-ICP-MS U-Pb测年,结果为(255.5±1.1)Ma,火山岩上部多个层位粉砂质泥岩中发现孢粉化石,计17属20种,时代为晚二叠世—早三叠世,推断幸福之路组的时代为晚二叠世—早三叠世,大兴安岭地区二叠系—三叠系界线在幸福之路组内部,二者为整合接触。幸福之路组以红层做为划分标志,岩性为正常沉积碎屑岩夹火山岩,见大量泥灰岩夹层、钙质结核及干裂现象,反映了炎热、干燥及强氧化条件的气候环境,大兴安岭地区晚二叠世晚期(幸福之路组二段下部)就已出现反映干旱气候的红层沉积,与相邻的华北及新疆准噶尔盆地相似。  相似文献   

From extension to shortening: Dating the onset of the Brasiliano Orogeny in eastern Borborema Province (NE Brazil)     

《Journal of South American Earth Sciences》2015

In pre-drift reconstructions, the central and southern parts of the Borborema Province, northeastern Brazil, belong to a large Brasiliano-Pan-African orogenic realm situated to the north of the São Francisco-Congo Craton. In order to better understand the timing and geodynamic setting under which this orogenic system developed, a structural, geochemical and geochronological study was conducted across the east Pernambuco shear zone (EPSZ) system, which separates the Pernambuco-Alagoas Domain (PEAL) from the Central Domain. A sample of the Pinhões orthogneiss (GE-1), in the Central Domain, one sample of a syenitic orthogneiss (CA-34) wrapped by the EPSZ, and one sample of orthogneiss named Altinho (CA-40), in the northern portion of the PEAL, were dated by LA-ICP-MS. The Pinhões orthogneiss yielded an age of 869 ± 9 Ma, interpreted as the emplacement age of the protolith during a late Tonian magmatic episode. Samples CA-40 and CA-34 yielded ²⁰⁶Pb/²³⁸U weighted mean ages of 652 ± 6 Ma and 636 ± 3 Ma, respectively, which are interpreted as dating emplacement and crystallization of the magmatic protoliths. However, it is also possible that these rocks were formed during the same magmatic event in view of the identical ages of 646 ± 13 Ma and 646 ± 11 Ma, respectively, given by the less precise upper intercept of the discordia lines. The metaluminous and magnesian nature of the Altinho orthogneiss is akin to the calc-alkalic suite. However, some samples plot in the intraplate field in tectonic discrimination diagrams and the Nd T_DM model age of 1.36 Ga is unlike that of juvenile magmas in convergent settings. The Altinho orthogneiss is quite similar in terms of trace elements geochemistry to the syenitic orthogneiss, which has a clearer intraplate affinity, and the dated samples have identical initial Sr isotope ratios (0.7047). Therefore, emplacement in an extensional setting is preferred over a convergent one. Two samples of paragneisses (SB-1 and BB-9) from the PEAL were also dated. The ages of the youngest zircon grains in sample BB-9 (655–642 Ma) overlap the crystallization age of the Altinho orthogneiss, implying that sedimentation is younger than or, at best, synchronous with magmatism. The age of low Th/U grains in samples CA-34 (615 ± 8 Ma) and SB-1 (587 ± 12 Ma) are related to a subsequent metamorphic overprint, which is loosely constrained between 580 and 620 Ma. These observations, combined with evidence provided by previous studies, suggest that the change from an extensional to a contracional setting occurred at ca. 640–630 Ma. In contrast with most collisional orogens, where a long period of oceanic subduction precedes collision, the inferred tectonic evolution suggests that the Brasiliano Orogeny resulted from inversion of continental and/or proto oceanic rifts.  相似文献   

The Bastar craton,central India: A window to Archean – Paleoproterozoic crustal evolution     

《Gondwana Research》2020

The Bastar craton in central India, surrounded by cratonic blocks and Paleoproterozoic to Neoproterozoic orogenic belts, is a window to investigate the Archean-Paleoproterozoic crustal evolution and tectonic processes. Here we propose a new tectonic classification of the craton into the Western Bastar Craton (WBC), Eastern Bastar Craton (EBC), and the intervening Central Bastar Orogen (CBO). We present petrologic, geochemical and zircon U-Pb, REE and Lu-Hf data from a suite of rocks from the CBO and along the eastern margin of the WBC Including: (1) volcanic successions comprising meta-andesite and fine-grained amphibolite, representing arc-related volcanics along a convergent margin; (2) ferruginous sandstone, in association with rhyolite, representing a volcano-sedimentary succession, deposited in an active trench; and (3) metamorphosed mafic-ultramafic suite including gabbro, pyroxenite and dunite invaded by trondhjemite representing the section of sub-arc mantle and arc root adjacent to a long-lasting subduction system. Petrologic studies indicate that the mafic-ultramafic suite crystallized from an island arc tholeiitic parental magma in a suprasubduction zone environment. The chondrite-normalized and primitive mantle normalized diagrams of the mafic and ultramafic rocks suggest derivation from MORB magma. The mixed characters from N-MORB to E-MORB of the studied samples are consistent with subduction modification of a MORB related magma, involving partial melting of the metasomatized mantle wedge. Our zircon U-Pb age data suggest that the cratonic nuclei was constructed as early as Paleoarchean. We present evidence for active subduction and arc magmatism through Mesoarchean to Neoarchean and early Paleoproterozoic, with the trench remaining open until at least 2.3 Ga. Two major crust building events are recognized in the Bastar craton: during Mesoarchean (recycled Paleoarchean subduction-related as well as juvenile/depleted mantle components) and Neoarchean (accretion of juvenile oceanic crust, arc magmatism including granite batholiths and related porphyry mineralization). The final cratonization occurred during latest Paleoproterozoic, followed by collisional assembly of the craton and its incorporation within the Peninsular Indian mosaic during Mesoproterozoic. In the global supercontinent context, the craton preserves the history of Ur, the earliest supercontinent, followed by the Paleo-Mesoproterozoic Columbia, as well as minor thermal imprints of the Neoproterozoic Rodinia and associated Grenvillian orogeny.  相似文献   

SILLS软件在单个萤石流体包裹体LA-ICP-MS微量元素分析数据处理中的应用     

李阳  邹灏  刘行  蒋修未  李蝶 《岩矿测试》2020,39(2):300-310

近年来激光剥蚀电感耦合等离子体质谱(LA-ICP-MS)应用于单个流体包裹体成分定量分析已成为研究流体包裹体的最佳手段之一。该实验过程和数据处理比较复杂,目前国内外采用的数据分析软件为一款基于MATLAB的SILLS软件,该软件主要是对矿物(锆石)、流体包裹体以及熔体包裹体LA-ICP-MS分析结果进行处理。本文以萤石流体包裹体LA-ICP-MS分析为例,阐述了样品制备与流体包裹体的优选方法,对流体包裹体片厚度以及单个流体包裹体的选取要求作了详细描述,对仪器参数设置、内外标样选取和剥蚀方法等进行了说明。基于SILLS软件采用尖峰消除的方法对待处理数据进行校正,对不同种类型的波峰进行峰宽的选取。在元素比值校正和等效盐度计算过程中,由于被测样品是萤石,Ca元素具有较高的背景值,选择以Na作为流体包裹体的内标元素,以Ca作为寄主矿物的内标元素对寄主矿物浓度进行计算,同时提出以电价平衡代替质量平衡进行等效盐度计算。以上方案提高了LA-ICP-MS分析单个萤石流体包裹体的准确性,有助于解释成矿流体来源和矿床成因等问题。  相似文献   

华北板块北缘中段二叠纪岩浆岩年代学、地球化学及锆石Hf同位素测试数据集          下载免费PDF全文

王文龙  刘洋  赵利刚  滕飞  杨泽黎 《中国地质》2020,47(S1):32-39

华北板块北缘中段位于华北板块与白乃庙弧的结合处，以赤峰-白云鄂博断裂为界，南、北归属不同的大地构造单元，并且具有不同的基底属性。二叠纪岩浆岩在华北板块北缘广泛分布，断裂带两侧均有出露，源区组成十分复杂，制约着对其岩石成因及构造背景的深刻认识。本文通过对横跨赤峰–白云鄂博断裂的“北柳图庙幅等4幅区调”和“乌兰布拉格幅等2幅区调”2个项目的1∶50 000区调工作，共计6个1∶50 000图幅内的二叠纪岩浆岩的年代学、地球化学及锆石Hf同位素测试数据进行整合、分析，为进一步研究华北板块北缘中段二叠纪岩浆岩的源区及构造-岩浆演化过程提供详实的数据支撑。区内二叠纪侵入岩广泛出露，岩石类型以花岗闪长岩、（石英）闪长岩及二长花岗岩为主，并含有少量的正长花岗岩。二叠纪火山岩主要分布在断裂带以南，岩性包括安山质、英安质及少量流纹质火山岩。锆石U–Pb测年表明工作区内二叠纪岩浆岩的形成时代主要为中–晚二叠世，断裂带南北两侧的岩浆岩具有截然不同的锆石Hf同位素特征，总体而言，南侧相对富集，北侧相对亏损。本数据集包括3个.xls类型文件（Zircon U–Pb dating data.xls，Zircon Hf isotope data.xls，Whole-rock geochemistry data.xls），分别记录了104件样品的地球化学数据、16件样品的锆石U–Pb测年数据和12件样品的锆石Hf同位素数据。本数据集测试样品主要在中国地质调查局天津地质调查中心实验测试中心完成，数据质量可靠。  相似文献