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Lower Eocene sedimentary succession and microfossil biostratigraphy in the central northern Caucasus basin 北高加索盆地中部下始新世沉积演替与微化石生物地层学
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2020-01-29 DOI: 10.1344/geologicaacta2020.18.1
E. Shcherbinina, A. Iakovleva, Y. Gavrilov, O. Golovanova, N. Muzylev
The lower Eocene sediments from the classical Paleogene section exposed along the Kheu River, northern Caucasus, southern Russia are here studied. This ca. 50m thick succession is lithologically contrasting: the lower and upper parts are composed by soft marls separated by a thick Radiolaria-rich unit of non-calcareous and low-calcareous mudstones with intercalations of compact cherty layers. According to nannofossil and dinocyst biostratigraphy, the unique intercalation of Total Organic Carbon (TOC)-rich sediment (sapropelitic bed) in the lower part of the lower Eocene correspond to the Paleocene-Eocene Thermal Maximum (PETM) and a series of sapropelitic interlayers in the upper marly part of the lower Eocene succession correlates with the Early Eocene Climatic Optimum (EECO). The study of nannofossil and dinocyst assemblages enabled detailed zonal subdivision and first-order calibration of nannofossil and dinocyst bio-events during this time-span. The studied interval of the section embraces the complete succession of nannofossil zones NP9-NP13 of Martini, 1971, CP8-CP11 of Okada and Bukry, 1980 and CNP11-CNE5 of Agnini et al., 2014. By means of dinocyst stratigraphy, the succession of Apectodinium hyperacanthum, Axiodinium augustum, Deflandrea oebisfeldensis, Dracodinium astra, Stenodinium meckelfeldense, Dracodinium varielongitudum, Ochetodinium romanum/Samlandia chlamydophora and Areosphaeridium diktyoplokum zones are identified in the Ypresian part of the Kheu section.
本文对俄罗斯南部高加索北部Kheu河沿岸暴露的古近纪经典剖面始新世下部沉积物进行了研究。这个约50米厚的层序在岩性上形成对比:下部和上部由软泥灰岩组成,中间隔着一层富含放射虫的厚的非钙质和低钙质泥岩单元,中间嵌有致密的硅质层。根据纳米化石和恐龙囊生物地层学,下始新统下部独特的富总有机碳(TOC)沉积物(腐泥质层)夹层与古新统—始新统极热期(PETM)相对应,下始新统上部灰岩层的一系列腐泥质夹层与早始新统气候最适期(EECO)相对应。通过对纳米化石和恐龙囊组合的研究,可以对这段时间内的纳米化石和恐龙囊生物事件进行详细的分区划分和一级校准。剖面研究层序包括1971年Martini的NP9-NP13、1980年Okada和Bukry的CP8-CP11、2014年Agnini等的CNP11-CNE5等纳米化石带的完整演替。利用生物囊层序,在Kheu剖面上确定了Apectodinium hyperacanthum、Axiodinium augustum、Deflandrea oebisfeldensis、Dracodinium astra、Stenodinium meckelfeldense、Dracodinium varielongitudum、Ochetodinium romanum/Samlandia chlamydophora和Areosphaeridium diktyoplokum带的演替。
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引用次数: 4
MORB-derived amphibolites in the Paleozoic basement of the Aluminé Igneous-Metamorphic Complex,. 铝质火成岩变质杂岩古生代基底中morb衍生角闪岩。
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2019-11-08 DOI: 10.1344/geologicaacta2019.17.10
I. Urraza, S. Delpino, L. E. Grecco
Amphibolites included in the metapelitic sequence and as xenoliths in intrusive magmatic rocks outcropping in the southern sector of the Alumine Igneous-Metamorphic Complex (AIMC), Neuquen, Argentina, are studied in detail in order to determine their origin and their subsequent metamorphic evolution. Field evidence and wholerock geochemistry indicate that these rocks were derived from a Mid-Ocean Ridge Basalt (MORB)-type protolith, and were accreted as tectonic slices into the metapelitic sequence that mainly formed the basal accretionary prism associated with a pre-Andean SW-NE subduction setting. Phase relationships, geochemistry of mineral assemblages and geothermobarometry indicate the presence of at least two metamorphic events (M 1 1.9−3.9kbar, 677−745oC and M 2 6.4kbar, 723oC) framed in a counterclockwise P-T path, comparable to those previously determined for the metapelitic country-rocks and metatroctolites outcropping in the same sector of the AIMC. Based on regional correlations and the agreement in the petrological, geochemical, geochronological and structural characteristics, we suggest that the MORB-derived Norquinco amphibolites and neighboring aluminous metasedimentary basement rocks of the AIMC belong to the eastern prolongation of the Western Series of the Coastal Accretionary Complex of Central Chile in west-central Argentina territory.
本文详细研究了阿根廷Neuquen铝质火成岩-变质杂岩(AIMC)南段露头侵入岩浆岩中的角闪岩及其变质演化过程。现场证据和整体岩石地球化学特征表明,这些岩石起源于中洋脊玄武岩(MORB)型原岩,并作为构造片沉积到变质岩序列中,变质岩序列主要形成与前安第斯山脉西南向ne俯冲背景相关的基底增生棱镜。相关系、矿物组合的地球化学特征和地温压特征表明,在逆时针的P-T路径上至少存在两个变质事件(m1 1.9 ~ 3.9kbar, 677 ~ 745oC)和m2 6.4kbar, 723oC),与之前在AIMC同一区域露头的变质岩和变质岩相类似。基于区域对比和岩石学、地球化学、年代学和构造特征的一致性,我们认为morb衍生的Norquinco角闪岩与邻近的AIMC铝质变质沉积基底岩属于阿根廷中西部智利中部海岸沉积杂岩西系的东延。
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引用次数: 1
Morphology, biostratigraphy, and evolution of PliocenePleistocene diatoms Proboscia barboi... 上新世晚更新世硅藻的形态、生物地层学和演化。。。
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2019-10-21 DOI: 10.1344/105.000005518
J. Andrade, P. Legoinha, Z. Stroynowski, F. Abrantes
Proboscia barboi and Proboscia curvirostris are two important diatom biostratigraphic markers from the high latitudes of the North Pacific and North Atlantic Oceans, dating back to the Pliocene-Pleistocene time. This study analyzes the biostratigraphic events and describes the morphology of P. barboi and P. curvirostris , particularly the morphologic variations of the latter species, based on observations of samples of Core U1340A from the IODP Expedition 323 in the Bering Sea. In Site U1340, the First Occurrence of P. curvirostris is observed at 1.52Ma and its First Common Occurrence at 1.39Ma, where morphologic variations were found abundantly. The Last Occurrence of P. curvirostris was found at 0.33Ma, while P. barboi ’s Last Occurrence is found at 0.67Ma. Based on the morphological similarity and known biostratigraphic distribution, previous authors have assumed that P. curvirostris descends from P. barboi , although this hypothesis is still in debate. At 1.39Ma P. curvirostris shows an increased size and thickness, which is typical of P. barboi , and some specimens display an incipient structure characteristic of P. curvirostris - the secondary spine. This morphology is intermediate between the two species and suggests an evolutionary transition from P. barboi to P. curvirostris . However, P. curvirostris already existed since 1.9Ma in the subarctic indicating that its speciation happened much earlier than 1.39Ma. Furthermore, since P. barboi co-occurs with P. curvirostris in the North Pacific, this evolutionary process was cladogenetic. Besides being evidence for a phylogenetic relationship, the abundant occurrence of intermediate forms at 1.39Ma may constitute a bioevent for a short time interval in the Bering Sea.
barboi和Proboscia curvirostris是北大太平洋和北大西洋高纬度地区两种重要的硅藻生物地层标志,可追溯到上新世-更新世。本文利用IODP 323科考队在白令海U1340A岩芯样品的观测资料,分析了P. barboi和P. curvirostris的生物地层事件,描述了P. barboi和P. curvirostris的形态,特别是后者的形态变化。在U1340遗址,P. curvirostris在1.52Ma处首次出现,在1.39Ma处首次出现,形态变异较多。P. curvirostris在0.33Ma最后出现,P. barboi在0.67Ma最后出现。基于形态相似性和已知的生物地层分布,前人认为P. curvirostris起源于P. barboi,尽管这一假设仍存在争议。在1.39Ma处,P. curvirostris的尺寸和厚度增加,这是典型的P. barboi,一些标本显示P. curvirostris的早期结构特征-次级脊柱。这种形态介于两个物种之间,表明从barboi P.到P. curvirostris的进化过渡。然而,P. curvirostris早在1.9Ma就已经存在于亚北极地区,表明其形成时间远早于1.39Ma。此外,由于P. barboi与P. curvirostris在北太平洋共同发生,这一进化过程是枝发生的。除了作为系统发育关系的证据外,在1.39Ma大量出现的中间形式可能构成白令海短时间间隔的生物事件。
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引用次数: 1
Audiomagnetotelluric survey at the Bañitos-Gollete geothermal area, main Andes Cordillera of San Juan, Argentina. 阿根廷圣胡安主要安第斯山脉科迪勒拉的巴尼托斯-戈利特地热区的大地电磁测深。
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2019-07-30 DOI: 10.1344/GEOLOGICAACTA2019.17.8
H. Barcelona, G. Peri, D. Winocur, A. Favetto
The present research explores the Bañitos-Gollete geothermal field located in the Frontal Andes Cordillera over the Pampean flat-slab. We carried out an audiomagnetotelluric survey in order to define the underground geoelectrical structure and to understand the link between the geothermal fluid flow path and the main geological structures. 2-D audiomagnetotelluric models suggest that the deep-rooted N-S fault system controls the geothermal flow path. We propose a conductive heat-driven system, taking into consideration the geologic setting and the supposed low geothermal gradient of this tectonic environment. The mature Na-Cl waters from Gollete and an estimated reservoir temperature of ~140ºC are consistent with this conceptual model. Further investigations are required to assess the geothermal potential of the study area, and the present work likely represents only the first but necessary step in the exploration process.
本研究探索了位于潘潘平原上安第斯山脉前缘科迪勒拉的Bañitos-Gollete地热田。为明确地下电性构造,了解地热流体流动路径与主要地质构造的联系,开展了大地电磁测量。二维音频大地电磁模型表明,深根的南北向断裂系统控制着地热流动路径。考虑到该构造环境的地质背景和假定的低地温梯度,我们提出了一个传导性热驱动系统。Gollete的成熟Na-Cl水和估计的储层温度为~140ºC,与该概念模型一致。需要进一步的调查来评估研究地区的地热潜力,目前的工作可能只是勘探过程中的第一步,但却是必要的一步。
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引用次数: 0
Langhian rays (Chondrichthyes, Batomorphii) from Brielas, Lower Tagus Basin, Portugal. 来自葡萄牙下塔霍盆地Brielas的Langhian射线(软骨鱼类,Batomophi)。
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2019-07-23 DOI: 10.1344/geologicaacta2019.17.7
P. Fialho, A. Balbino, M. Antunes
The Langhian Vc unit of Brielas section (Caparica road, Almada), in the marine Miocene of the Lower Tagus Basin (West Portugal), is rich in batoid species. In this study, batoids are represented by 149 isolated fossil teeth and a single fossil dental plate collected from a bulk sample of washed and sorted sediment. A total of 12 species belonging to the orders Rhinopristiformes, Rajiformes, Torpediniformes and Myliobatiformes were identified. All genera and some species are known to have extant representatives. Aetobatus cappettai Antunes and Balbino, 2006, is described now from Langhian material which suggests it is older than previously supposed. The biogeographic ranges, environmental constraints and behaviour of the species described in this study point out to an infralittoral environment characterized by the dominance of warm water conditions, where episodic upwelling contributed to the occurrence of different types of batoids coexisting in the same habitat.
Brielas段(Almada Caparica路)的Langhian Vc单元位于下塔霍盆地(葡萄牙西部)的海洋中新世,富含蝙蝠类物种。在这项研究中,蝙蝠牙由149颗分离的牙齿化石和一块从洗涤和分类沉积物的大量样本中收集的牙齿化石板代表。共鉴定出12种,隶属于鼻形目、Rajiformes目、Torpediques目和Myliobatformes目。已知所有属和某些物种都有现存的代表。Aetobatus cappettai Antunes和Balbino,2006年,现在根据Langhian的材料进行了描述,这表明它比以前认为的要古老。本研究中描述的物种的生物地理范围、环境制约因素和行为表明,近海环境以温水条件为主,其中偶发性上升流导致不同类型的蝙蝠类动物共存于同一栖息地。
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引用次数: 5
Evaluation of the Relative Tectonic Activity of the Adıyaman fault within the Arabian-Anatolian. 阿拉伯-安纳托利亚Adıyaman断裂相对构造活动评价。
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2019-06-18 DOI: 10.1344/GEOLOGICAACTA2019.17.6
A. Khalifa, Z. Çakır, L. Owen, S. Kaya
The left-lateral strike-slip Adiyaman fault is located in eastern Turkey within the plate boundary deformation zone between Arabia and Anatolia. The Adiyaman fault is a major splay from the East Anatolian Fault (EAF), one of the most important tectonic structures in the Eastern Mediterranean region. These faults are consequence of the collision between the Arabian and Anatolian plates and the resulting westward tectonic escape of Anatolia. Although the EAF has been intensively studied since its discovery in the late 1960s, little is known about the Adiyaman fault and its tectonic activity. In this study, we extract geomorphic indices including mountain-front sinuosity (Smf), valley floor width-to-height ratio (Vf), stream length-gradient (SL), catchment Asymmetry Factor (AF) and hypsometric integrals and curves (HI and HC) to evaluate the relative tectonic activity of the Adiyaman fault. These three geomorphic indices (AF, HI, and HC) are averaged to define an index for Relative Tectonic Activity (RTA) that allows the Adiyaman fault to be divided into categories of low, moderate and high RTA. The results confirm that the Adiyaman fault is an active fault with high to moderate Quaternary tectonic activity. However, this fault is of minor importance on accommodating plate boundary deformation, as evidenced by the recent crustal motions determined by GPS studies. Nevertheless, it is worthwhile to note that the Adiyaman fault still poses a significant seismic hazard for the region despite its relatively moderate tectonic activity.
左旋走滑阿迪亚曼断层位于土耳其东部,位于阿拉伯-安纳托利亚板块边界变形带内。阿迪亚曼断裂是东安纳托利亚断裂(EAF)的一个主要分支,东安纳托利亚断裂是东地中海地区最重要的构造构造之一。这些断层是阿拉伯板块和安纳托利亚板块碰撞的结果,安纳托利亚板块向西伸展。尽管自20世纪60年代末发现东太平洋断裂带以来,人们对它进行了深入的研究,但对阿迪亚曼断层及其构造活动知之甚少。本文通过提取山前曲度(Smf)、谷底宽高比(Vf)、河流长度梯度(SL)、流域不对称系数(AF)和等高积分曲线(HI和HC)等地貌指标,对阿迪亚曼断裂的相对构造活度进行评价。将这3个地貌指数(AF、HI和HC)取平均,得到一个相对构造活动性指数(RTA),并据此划分阿迪亚曼断层的低、中、高构造活动性。结果表明,阿迪亚曼断裂是一条第四纪构造活动高至中度的活动断裂。然而,这条断层对容纳板块边界变形的重要性不大,最近由GPS研究确定的地壳运动证明了这一点。然而,值得注意的是,尽管阿迪亚曼断层的构造活动相对温和,但它仍然对该地区构成重大的地震危险。
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引用次数: 13
Tourmaline records hydrothermal events related to Zn-Pb mineralization around the Murguía diapi. 电气石记录了Murguía底辟周围与Zn-Pb矿化有关的热液事件。
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2019-06-05 DOI: 10.1344/GEOLOGICAACTA2019.17.5
R. Galdos, Angels Canals i Sabaté, E. López, Joaquín Moreno
The chemical composition of tourmaline has been used as a host environment register as well as a potential exploration tool for mineral deposits. In this study, the textural and chemical composition of tourmalines associated with Zn-Pb mineralizations around the Murguia diapir (Basque Cantabrian Basin, N Spain) are examined to verify if they record the mineralizing events in the area. Petrographically, tourmalines have been differentiated between inherited and authigenic. Colorless authigenic tourmalines are present as halos partially around green and pleochroic detrital grains or as individual crystals. Inherited and authigenic tourmalines are also chemically distinct. Authigenic tourmalines show different X-site occupancies, a Mg/(Mg+Fe) ratio above 0.77, and are aluminum rich and plot to the right of the povondraite-oxidravite join, above the schorl-dravite join. Inherited tourmalines plot within the alkaline (Na+K) group field, and have a Mg/(Mg+Fe) ratio below 0.77. These data suggest that authigenic tourmalines grew under reducing conditions, compatible with the hydrothermal event responsible for the ore deposition and caprock formation during the diapir ascent.
电气石的化学成分已被用作宿主环境登记册以及潜在的矿床勘探工具。在本研究中,对Murguia底辟(西班牙北部巴斯克-坎塔布里安盆地)周围与Zn-Pb矿化有关的电气石的结构和化学成分进行了检查,以验证它们是否记录了该地区的矿化事件。从岩石学角度来看,电气石已被区分为继承电气石和自生电气石。无色自生电气石以光环的形式存在,部分围绕绿色和多色碎屑颗粒,或以单个晶体的形式存在。继承电气石和自生电气石的化学性质也不同。自生电气石显示出不同的X位占有率,Mg/(Mg+Fe)比高于0.77,并且富含铝,并且在火山灰岩-氧化镁石连接的右侧,在火山灰石连接的上方绘制。继承电气石在碱性(Na+K)组域内绘图,并且具有低于0.77的Mg/(Mg+Fe)比。这些数据表明,自生电气石在还原条件下生长,与底辟上升过程中导致矿石沉积和盖层形成的热液事件相兼容。
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引用次数: 0
The importance of coastal geomorphological setting as a controlling factor on microtextural... 海岸带地貌环境对微结构的影响是一个重要的控制因素。
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2019-05-27 DOI: 10.1344/GEOLOGICAACTA2019.17.4
Pedro J. M. Costa, D. Silva, L. Figueirinhas, J. Lario
Quartz grains collected from Arauco and Mataquito (central Chile) after the 2010 Maule tsunami presented an overwhelming dominance of dissolution textures. The analysis of superficial imprints proved that some grains were mechanically impacted before deposition. However, the percentage of grains with fresh surfaces and percussion marks was significantly lower than average values from other tsunami deposits elsewhere in the world. In this work, we discuss the reasons for such results in the context of the geomorphological setting of the areas analyzed and its influence on the microtextural signatures observed. The data presented in this study evidences a geographic dependence in the type of microtextures in the areas analyzed. For example, in Arauco the abundance of dissolution textures decreases rapidly towards the center of the embayment and increases towards the rocky headlands of its westernmost sector. By contrast, an increase of mechanical marks (e.g. fresh surfaces) is observed in the central region of the Arauco’s embayment. Similarly, in Mataquito, dissolution features are more abundant in the headlands or small capes, while there is a higher presence of mechanical marks in sandy embayments. The results of this study demonstrate the importance of the geomorphological context as a controlling factor in the intensity of mechanical imprints on the surface of quartz grains transported by tsunamis and deposited in the inner shelf and coastal areas. Therefore, our results suggest that without a detailed geomorphological contextualization microtextural discrimination can lead to misleading interpretations. Hence, there is a need for more microtextural analysis on tsunami deposits in order to assess the variability in the geographic distribution and intensity of microtextures imprinted on the surface of quartz grains deposited during a tsunami event.
2010年Maule海啸后,在Arauco和Mataquito(智利中部)采集的石英颗粒显示出压倒性的溶解结构优势。表面印迹分析证明,部分颗粒在沉积前受到了机械冲击。然而,具有新鲜表面和冲击痕迹的颗粒的百分比明显低于世界其他地方海啸沉积物的平均值。在这项工作中,我们在分析地区的地貌环境及其对观察到的微结构特征的影响的背景下讨论了产生这种结果的原因。本研究中提供的数据证明了所分析地区微纹理类型的地理依赖性。例如,在阿劳科,溶解结构的丰度在靠近海湾中心的地方迅速减少,而在靠近其最西端的岩石岬角的地方增加。相比之下,在阿劳科洞穴的中心区域观察到机械痕迹(如新鲜表面)的增加。同样,在Mataquito,溶解特征在海岬或小岬角更为丰富,而在沙质河口则有更多的机械痕迹。本研究的结果表明,在海啸运输并沉积在内陆架和沿海地区的石英颗粒表面的机械印记强度中,地貌环境是一个重要的控制因素。因此,我们的研究结果表明,如果没有详细的地貌背景化,微纹理区分可能会导致误导性的解释。因此,有必要对海啸沉积物进行更多的微结构分析,以评估海啸事件期间沉积的石英颗粒表面微结构的地理分布和强度的变化。
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引用次数: 6
Late-Variscan multistage hydrothermal processes unveiled by chemical ages coupled with compositiona. 晚期瓦里斯坎多阶段热液过程揭示了化学年龄与成分的耦合。
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2019-01-31 DOI: 10.1344/GEOLOGICAACTA2019.17.1
S. Timón-Sánchez, F. López-Moro, R. Romer, D. Rhede, A. Fernández-Fernández, C. Moro-Benito
The scheelite skarn from Los Santos and the W-Au veins from El Cabaco district, located in the Spanish Central System Batholith (SCSB), are some of the best-known tungsten ore deposits in Spain. Uraninite is an accessory mineral in both deposits, which underwent several hydrothermal flow events. Chemical and textural characteristics, as well as electron microprobe U-Th-Pb uraninite chemical data from the different stages of the skarn and the vein-type mineralizations, are presented here. Based on these data the uraninite was able to be classified into two groups. Group I uraninite has an octahedral habit and occurs as inclusions in K-feldspar relicts of the leucogranite related to Los Santos skarn formation. It shows high Th (6.95 to 8.51wt.% ThO 2 ) and high Rare Earth Elements (REEs) contents (0.55 to 1.38wt.% ∑REE 2 O 3 ). Group II uraninite occurs i) associated to El Cabaco granite, in a greenish selvage-style greisen and its reddish envelope and in the mineralized rimming quartz veins and ii) in Los Santos high-temperature endoskarn and anorthite skarn, where it is associated with U-rich mica. This uraninite type has lower Th and ∑REE 2 O 3 contents than Group-I uraninite. The mineral chemistry and the assemblage and textural relationships suggest that Group-I uraninite is magmatic and the attained U-Th-Pb chemical age of 300±4Ma is interpreted as the magmatic age of the skarn-forming aplite granites in the western part of the SCSB. Group-II uraninite includes two events: i) hydrothermal uraninite, which yields an age of 295±2Ma, dates a strong alkali mobilization and early tungsten deposition and ii) a later hydrothermal process, around 287±4Ma, that resulted in sulfides and late scheelite precipitation and widespread silicification. Finally, the gold deposition is younger than this silicification according to textural criteria. Therefore, W-Au deposits in the western part of the SCSB were formed by superposition of several processes that took place some 15Ma after the skarn-forming granite crystallized. Comparable W, W-Au and U deposits in the Variscan orogenic belt show a similar timing of hydrothermal events, suggesting that the hydrothermal history was controlled by large-scale Late-Variscan tectonic processes.
位于西班牙中央体系基岩(SCSB)的Los Santos白钨矿矽卡岩和El Cabaco地区的W-Au矿脉是西班牙最著名的钨矿床。铀矿是两个矿床的副矿物,均经历了多次热液流动事件。本文介绍了矽卡岩和脉状矿化不同阶段的化学和结构特征,以及电子探针U-Th-Pb铀矿化学数据。根据这些资料,可将铀矿分为两类。I类铀矿具有八面体习性,以包裹体形式赋存于与洛斯桑托斯夕卡岩形成有关的浅花岗岩的钾长石残余物中。高Th (6.95 ~ 8.51wt)。% ThO 2)和高稀土元素(ree)含量(0.55 ~ 1.38wt)。%∑ree 2 0 3)。II组铀矿产于i)与El Cabaco花岗岩伴生,呈绿色边沿型灰岩及其红色包膜,矿化边缘石英脉中;II)在Los Santos高温内矽卡岩和钙长岩矽卡岩中,与富铀云母伴生。该类铀矿具有较低的Th和∑REE 2o3含量。矿物化学、组合和结构关系表明,ⅰ群铀质岩为岩浆质,获得的U-Th-Pb化学年龄为300±4Ma,可解释为SCSB西部矽卡岩型斜长花岗岩的岩浆年龄。ii类铀矿包括两个事件:1)热液铀矿,形成时间为295±2Ma,表明其形成于强碱活化和早期钨沉积阶段;2)热液铀矿形成于287±4Ma左右,形成了硫化物和晚期白钨矿沉淀和广泛的硅化作用。最后,根据结构标准,金沉积比硅化更年轻。因此,SCSB西部的W-Au矿床是在矽卡岩形成的花岗岩结晶约15Ma后,由多个过程叠加而成的。瓦里斯坎造山带的W、W- au和U矿床具有相似的热液事件时间,表明热液历史受大规模晚瓦里斯坎构造作用的控制。
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引用次数: 7
Multiphase dolomitization in the Jutana Formation (Cambrian), Salt Range (Pakistan): evidences from field observations, microscopic studies and isotopic analysis 巴基斯坦盐岭寒武系Jutana组多相白云化:野外观测、显微研究和同位素分析证据
IF 1.5 4区 地球科学 Q3 Earth and Planetary Sciences Pub Date : 2019-01-21 DOI: 10.1344/GEOLOGICAACTA2019.17.2
S. Khan, M. Shah
Excellent dolomite exposures are observed in the eastern Salt Range (Pakistan), where the Cambrian Jutana Formation consists of two distinct units (i.e. oolitic – pisolitic unit and massive dolomite unit). Field observations revealed that the lower, oolitic-pisolitic unit mostly comprises medium to thick bedded, interlayered brown yellowish dolostone containing ooids/pisoids and faunal assemblages, and grey whitish sandstone with distinct depositional sedimentary features (i.e. trough-, herringbone- and hhummocky crossbedding). The upper massive dolostone unit consists of thick bedded to massive dolostone. These two units are separated by shale. Petrographic studies identified three dolomite types, which include: fine crystalline dolomite (Dol. I), medium-coarse crystalline dolomite (Dol. II) and fracture associated, coarse crystalline dolomite (Dol. III). Stable isotope studies indicate less depleted δ 18 O values for Dol. I (-6.44 to -3.76‰V-PDB), slightly depleted δ18O values for Dol. II (-7.73 to -5.24‰V-PDB) and more depleted δ 18 O values for Dol. III (-7.29 to -7.20‰V-PDB). The δ 13 C values of the three dolomite phases are well within the range of Cambrian sea-water signatures. Furthermore, δ 26 Mg-δ 25 Mg signatures (Dol. I; δ 26 Mg=-1.19 to -1.67, δ 25 Mg=-0.61 to -0.86 and Dol. II; δ 26 Mg=-1.34 to -1.59, δ 25 Mg=-0.70 to -0.83) indicate three phases of dolomitization in different diagenetic settings. First, an initial stage of dolomitization during the early Cambrian resulted from altered marine, Mg-rich fluids associated with the mixing zone mechanism. Second, a late stage of dolomitization was associated with burial during late Permian. A third dolomitization phase was related to post-Eocene times.
在巴基斯坦盐岭东部,寒武系朱塔纳组由两个不同的单元(即鲕粒-泥质单元和块状白云岩单元)组成。野外观测表明,下部鲕粒-鲕粒单元主要由中厚层状、层间棕黄色白云岩组成,含鲕粒/鲕粒和动物组合;灰白色砂岩具有明显的沉积特征(槽状、人字状和丘状交错层理)。上部块状白云岩单元由厚层状到块状白云岩组成。这两个单元被页岩隔开。岩石学研究确定了三种白云岩类型,包括:细晶白云岩(Dol;I)、中粗晶白云岩(Dol.;II)和与裂缝相关的粗晶白云岩(Dol。III).稳定同位素研究表明,Dol的δ 18o贫化值较少。I(-6.44 ~ -3.76‰V-PDB), δ18O值略微下降。ⅱ(-7.73 ~ -5.24‰V-PDB), δ 18o值较贫。III(-7.29 ~ -7.20‰V-PDB)。3个白云岩相的δ 13c值均在寒武系海水特征范围内。此外,δ 26 Mg-δ 25 Mg特征(Dol。我;δ 26 Mg=-1.19 ~ -1.67, δ 25 Mg=-0.61 ~ -0.86;二世;δ 26 Mg=-1.34 ~ -1.59, δ 25 Mg=-0.70 ~ -0.83)反映了不同成岩环境下白云化的三个阶段。首先,寒武纪早期白云化的初始阶段是由于海相富镁流体的蚀变与混合带机制有关。二是白云化后期与晚二叠世的埋藏有关。第三个白云化阶段与始新世后有关。
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引用次数: 8
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Geologica Acta
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