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Geochemistry of the Adang Volcanics in Western Sulawesi: Unveiling the tectonic evolution of the opening of the Makassar Strait 西苏拉威西阿当火山地球化学:揭示望加锡海峡开口的构造演化
IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2025-02-19 DOI: 10.1016/j.sesci.2025.100228
Shaban Godang , Sugeng Purwo Saputro , Huan Li , Awang Harun Satyana , Weerapan Srichan
The Makassar Strait, located in central Indonesia, serves as a divider between Western and Eastern Indonesia and remains a subject of ongoing debate regarding its formation. Two primary theories have been proposed: (1) the Makassar Strait opening established a mid-ocean ridge (MOR) and led to a double subduction, and (2) it was formed through intracontinental rifting accompanied by mantle-plume magmatism. In this study, we present findings on the Adang Volcanic Complexes in Western Sulawesi, situated on the eastern side of the Makassar Strait, which have exposures of the Middle to Late Miocene age interspersed with crystalline limestone and carbonate rocks, indicating a correlation with a marine environment. The rocks investigated in this study are predominantly low-silica mafic rock, mainly composed of leucite/pseudoleucite-bearing trachytic tuff, agglomerate volcanic breccia, lavas, peralkaline dykes, and multiple mafic and leucitic intrusions. Geochemical analysis of the 12 drill core samples of leucite-bearing Adang Volcanics reveals their alkaline nature, characterized by high TiO2 relative to Al2O3 [TiO2 > (−1.1610 + 0.1935 × Al2O3)]. The samples also display geochemical signatures of Nb/Zr > 0.0627, Th/Nb > 0.67, a high ratio of Nb/Y (>0.6561) with an enrichment of light rare earth elements (LREE; La/Yb > 20), low Nb/La <0.6, and a low negative Tantalum anomaly (δTa 0.36–0.41), suggesting the magmatism was generated from the tectonics of continental extension stretching rather than subduction arc-related or mature continental rifts, where the magmatism was triggered by decompression melting during the extensional processes. Furthermore, the magmatism is thought to originate from partial melting of enriched subcontinental lithospheric mantle (SCLM), which is uncorrelated with the source of asthenospheric mantle. We propose that the formation process of the Adang Volcano is a product of the tectonic processes of the Makassar Strait opening in Central Indonesia during the Paleogene to the Early Neogene era.
望加锡海峡位于印度尼西亚中部,是印度尼西亚西部和东部的分水岭,关于它的形成一直是争论的主题。提出了两种主要理论:(1)望加锡海峡的开口形成了洋中脊(MOR)并导致了双俯冲;(2)望加锡海峡的开口是在地幔柱岩浆作用下通过陆内裂谷作用形成的。本文介绍了位于望加锡海峡东侧的西苏拉威西岛阿当火山群的发现,该火山群暴露于中新世中晚期,夹杂着结晶灰岩和碳酸盐岩,表明其与海洋环境有关。研究的岩石以低硅质基性岩为主,主要由含亮晶石/伪亮晶石的粗粒凝灰岩、粒状火山角砾岩、熔岩、过碱性岩脉以及多重基性和亮晶石侵入体组成。对阿当火山12个含白晶石岩心样品的地球化学分析表明,阿当火山岩心具有碱性,其特征是TiO2相对于Al2O3含量较高[TiO2 >;(−1.1610 + 0.1935 × Al2O3)]。样品还具有Nb/Zr >的地球化学特征;0.0627, Th/Nb >;0.67, Nb/Y比值高(>0.6561),富集轻稀土元素(LREE);洛杉矶/ Yb比;低Nb/La <;0.6,低钽负异常(δTa 0.36 ~ 0.41),表明岩浆活动产生于大陆伸展伸展构造,而非俯冲弧相关或成熟大陆裂谷,岩浆活动是由伸展过程中的减压熔融引发的。此外,岩浆活动被认为起源于富集的次大陆岩石圈地幔(SCLM)的部分熔融,而与软流圈地幔的来源无关。我们认为,阿当火山的形成过程是古近纪至新近纪早期印尼中部望加锡海峡开放的构造过程的产物。
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引用次数: 0
Multiproxy analysis of paleoredox conditions, paleoproductivity and organic matter enrichment in Cretaceous mudrocks of Bombe-Ediki and environs in the Douala sub-basin 杜阿拉次盆地Bombe-Ediki及其周围白垩系泥岩古氧化还原条件、古生产力及有机质富集多指标分析
IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2025-02-18 DOI: 10.1016/j.sesci.2024.100210
Ngong Roger Ngia , Elie Fosso Menkem , Christopher Fuanya , Christopher M. Agyingi
The formation and preservation conditions of organic matter-rich mudrocks in the Edki-Mabonji and Mbalangi-Bombe area of the Northwestern section of Douala sub-basin, Cameroon, can play an important role in the accumulation of hydrocarbon. This study integrated detailed geochemical techniques such as total organic carbon content (TOC), Total sulfur (TS), stable isotopes (δ13Corg. and δ34S), elemental geochemistry, and Scanning electron microscope (SEM) to reconstruct marine paleoredox conditions, paleoweathering conditions and primary productivity thereby, promoting the understanding of the sedimentary model of organic matter accumulation and enrichment in mudrocks in the study areas. Elemental compositions and their ratios suggest that the mudrocks were dominantly derived from a source area mainly consisting of felsic igneous rock with more silica (granitic rock) than an average granodiorite. Paleoweathering proxies suggest that during sediment production, the source area experienced mostly moderate chemical weathering as a result of variation in climate and sea-level changes. The proxies to reconstruct paleoredox conditions demonstrates fluctuating redox variations from mildly suboxic-to dominantly anoxic, most probably sulphidic benthic conditions, which describes anoxic organicmudrocks sandwiched between the oxygenated sandstone/claystone strata. Paleoproductivity parameters like biogenic barium (Babio), TOC, Porg/Al, Cu/Al and S/13Corg ratios, and δ34Spy, δ34SOS, δ13Corg suggest that the deposition of the mudrocks was with a high primary productivity. Consequently, the conceptual model of organic matter accumulation and enrichment reveals that moderate-to high primary productivity, suboxic-to dominantly anoxic sulphidic bottom water, organo–mineral complexes, bacterial sulfate reduction (BSR) and deposition of claystone capping bed isolating the benthic sediments influenced the accumulation and preservation of organic matter at shortened exposure duration in dominantly anoxic deeper water setting.
喀麦隆杜阿拉次盆地西北段Edki-Mabonji和Mbalangi-Bombe地区富有机质泥岩的形成和保存条件对油气聚集具有重要作用。本研究综合了详细的地球化学技术,如总有机碳含量(TOC)、总硫(TS)、稳定同位素(δ13Corg)等。通过元素地球化学、扫描电镜(SEM)等手段重建海相古氧化还原条件、古风化条件和初级生产力,促进对研究区泥岩有机质聚集富集的沉积模式的认识。元素组成及比值表明,泥岩主要来源于以长英质火成岩为主,硅质(花岗质)多于花岗闪长岩的源区。古风化指标表明,在沉积物形成过程中,由于气候变化和海平面变化,源区主要经历了中度化学风化。重建古氧化还原条件的指标显示,从轻度缺氧到主要缺氧的氧化还原变化,最可能是硫化氢底栖环境,这描述了夹在含氧砂岩/粘土岩地层之间的缺氧有机泥岩。生物钡(Babio)、TOC、Porg/Al、Cu/Al和S/13Corg比值以及δ34Spy、δ34SOS、δ13Corg等古生产力参数表明,该泥岩沉积具有较高的初级生产力。因此,有机质聚集富集的概念模型表明,在以缺氧为主的深水环境中,中高初级生产力、亚缺氧至主要缺氧的硫化物底水、有机矿物复合体、细菌硫酸盐还原(BSR)和隔离底栖沉积物的粘土岩盖层沉积影响了有机质在较短暴露时间内的聚集和保存。
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引用次数: 0
Reactive transport modeling: A powerful tool for assessing the interactions between biogeochemical and hydrogeological processes 反应输运模型:评估生物地球化学和水文地质过程之间相互作用的有力工具
IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2025-02-18 DOI: 10.1016/j.sesci.2024.100212
Jing Sun
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引用次数: 0
Dissolution behavior of feldspar in oxalic acid at 40–100 °C: Implications for Al enrichment during chemical weathering 长石在40-100℃草酸中的溶解行为:化学风化过程中Al富集的意义
IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2025-02-18 DOI: 10.1016/j.sesci.2024.100201
Xin Huang , Feng Guo , Xing Ding , Liang Zhao , Feng Zhang , Yaqian Wen
The dissolution behavior of feldspar is fundamental to understand geological processes such as surface mass cycling, chemical weathering, mineral deposition and global climate change. In this study, we select oxalic acid – one of the most popular organic acids in nature as a buffer solution to simulate the chemical weathering process of feldspar under natural environments. A total of 34 fluid–feldspar reaction experiments are performed to investigate the effects of temperature, pH, and specific surface area (SSA) on the dissolution mechanism of feldspar. Based on PHREEQC modelling of saturation index of secondary minerals, we obtain the overall dissolution rate of feldspar, which is predominantly influenced by pH and temperature, with SSA exerting a secondary effect. The dissolution rates of Na, K, Ca and Si show a positive correlation with temperature and SSA, whereas that of Al exhibits a negative correlation with SSA and a weak correlation with temperature. Based on chemical reaction kinetics, the reaction order of feldspar dissolution in oxalic acid is estimated to be approximately 0.47, suggesting that the dissolution rate of feldspar is primarily controlled by a desorption process. Our new experimental results reveal that the anomalous Al dissolution behavior, which are likely due to the formation of aluminum complexes on the feldspar surface, have potentially significant for understanding the Al enrichment mechanism during the chemical weathering of the continental crust.
长石的溶解行为是理解地表物质循环、化学风化、矿物沉积和全球气候变化等地质过程的基础。在本研究中,我们选择自然界中最常见的有机酸之一草酸作为缓冲溶液,模拟长石在自然环境下的化学风化过程。通过34个流体-长石反应实验,探讨了温度、pH和比表面积对长石溶解机理的影响。基于PHREEQC次生矿物饱和指数模型,得到了长石的总溶解速率,其主要受pH和温度的影响,SSA起次要作用。Na、K、Ca和Si的溶解速率与温度和SSA呈正相关,而Al的溶解速率与SSA呈负相关,与温度呈弱相关。根据化学反应动力学,估计长石在草酸中的溶解反应级数约为0.47,表明长石的溶解速率主要受解吸过程控制。我们的新实验结果表明,铝的异常溶解行为可能是由于铝配合物在长石表面的形成,这对理解大陆地壳化学风化过程中铝的富集机制具有潜在的重要意义。
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引用次数: 0
Damage analysis of rocks with different properties under cyclic splitting action 循环劈裂作用下不同性质岩石的损伤分析
IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2025-02-18 DOI: 10.1016/j.sesci.2024.100180
ZhiYong Xu , WenQiang Ao , Yi Liu
In underground construction operations, there are different types of rocks in repeated loading and unloading environments. For this reason, in this paper, two rock samples—slate and metamorphic sandstone, which contain different properties, were subjected to cyclic splitting experiments and were analyzed for damage using scanning electron microscopy, acoustic emission (AE) and stress–strain. It can be seen that the internal grains of the slate are angular and distributed in a directional arrangement, and the metamorphic sandstone has a large difference in size and shape between the grains, and it is a small-sized nodular step-like; Slate is dominated by damage forms of single shear and conjugate shear composite damage forms, with sudden changes in cumulative energy occurring just prior to the peak stress in each cyclic phase, and in metamorphic sandstone at the location of the peak stress in each cyclic phase, and the total energy of the loading phase accounts for more than 90 per cent of the entire cycle phase; Dissipation energy und obtained damage value D in the cyclic loading process, there is an obvious turning point when a large damage, and the later stages of loading damage will be more serious when the slope of slate is significantly larger than the metamorphic sandstone, the trend of change in the value of damage D is more obvious, the difference in slope between the two is nearly double, and it is more representative of the pattern of changes in the rock damage process.
在地下施工作业中,反复加载和卸载环境中存在不同类型的岩石。为此,本文对具有不同性质的板岩和变质砂岩进行了循环劈裂实验,并利用扫描电镜、声发射和应力应变分析了其损伤特征。可以看出,板岩内部颗粒呈角状,呈定向排列,变质砂岩颗粒大小形状差异较大,为小型节状阶梯状;板岩以单剪切和共轭剪切复合损伤形式为主,累积能量突变发生在各循环阶段应力峰值前,变质砂岩在各循环阶段应力峰值位置,加载阶段总能量占整个循环阶段的90%以上;耗散能量和获得的伤害值D在循环加载过程中,有一个明显的转折点,当大量伤害,和加载的后期破坏时将更严重的石板的斜率明显大于变质砂岩,损伤D的值变化的趋势更加明显,两者之间的斜率差近一倍,并更具代表性岩石破坏模式的变化过程。
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引用次数: 0
Fate of the last drops of serpentinizing fluid: Crystallization of unusual minerals 最后几滴蛇纹石液体的命运:不寻常矿物的结晶
IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-12-06 DOI: 10.1016/j.sesci.2024.100213
Xi Liu, Xinhao Sui, Xinjian Bao, Mingyue He
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引用次数: 0
Petrogenesis of post-collisional mesozonal enderbite in the Proterozoic Chhotanagpur Gneissic Complex, Eastern India: Implications of slab-break-off 印度东部新生代 Chhotanagpur 片麻岩群碰撞后中生代内闪长岩的岩石成因:板块断裂的影响
IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-11-22 DOI: 10.1016/j.sesci.2024.100217
Poulami Roy, Bapi Goswami, Ankita Basak, Chittaranjan Bhattacharyya
Collisional orogeny produces large volumes of tonalitic melts at two stages: first, during the oceanic subduction below the continent (continental arc), and again, during the post-collisional stage. In a polydeformed and polymetamorphosed terrain, it would be challenging to distinguish between arc tonalites and post-collisional tonalites (and their metamorphosed equivalents, enderbites). The Chhotanagpur Gneissic Complex (CGC) belongs to the EW to ENE-WSW tending, 1500 km long Grenvillian collisional belt amalgamating the North and South Indian cratonic blocks. We discuss the field disposition, petrography, mineral chemistry, geochemistry, the physical condition of crystallization and metamorphism, and the petrogenetic model of enderbites from the CGC. Enderbites sporadically occur as cm-to-dm-thick leucosomal bands in migmatitic gneisses (migmatitic enderbites) and as small stock-sized plutons (massive enderbites) intruding migmatitic gneisses. Both of these types intruded before the end of the regional deformation. Both the massive and migmatitic enderbites predominantly contain plagioclase, quartz, biotite (with a higher abundance in the migmatitic type), minor orthopyroxene, clinopyroxene, hornblende, K-feldspar, and accessories such as opaque minerals, apatite, and zircon. Garnets rarely occur in migmatitic enderbites. Thermodynamic modeling suggests a low liquidus temperature (∼750 °C), intermediate pressure of emplacement (∼5.5 kb), moderate oxygen fugacity (ΔQFM = +1 to +2), and low water (∼4.0 wt%) of the parental tonalite magma. The two enderbite types have been derived from two distinct crustal (amphibolites) sources by water-fluxed partial melting at <10 kb pressure, shallower than the garnet stability field. About 20–40 % of batch-melting of shoshonitic basaltic sources yielded migmatitic enderbites, while about 40–70 % of batch-melting of within-plate basaltic sources produced massive enderbites. Discrimination diagrams display a post-collision tectonic setting of these enderbites. The migmatitic enderbites and magma of enderbite plutons formed during regional anatexis due to thermal relaxation in the lower crust after attaining peak pressure during the decompressive phase of regional granulite facies metamorphism (1000–950 Ma) related to slab breakoff at the post-collisional stage of the orogeny. Mantle-derived magmas formed by adiabatic decompression in the upper mantle supplied the heat.
碰撞造山作用在两个阶段产生了大量的辉绿岩熔体:首先是在大陆(大陆弧)下方的大洋俯冲过程中,其次是在碰撞后阶段。在一个多变形和多变质的地形中,要区分弧状英安岩和碰撞后英安岩(及其变质的等同物--内斜英安岩)是非常困难的。乔塔纳格布尔片麻岩群(CGC)属于东-西向东-西-西南走向,长 1500 千米的格勒维利碰撞带,将北印度和南印度的板块合并在一起。我们讨论了来自CGC的enderbites的野外布局、岩石学、矿物化学、地球化学、结晶和变质的物理条件以及岩石成因模型。内闪长岩以厘米至分米厚的白云母带形式零星出现在偏闪片麻岩中(偏闪长岩内闪长岩),以及以侵入偏闪片麻岩的小型块状岩体(块状内闪长岩)形式出现。这两种类型都是在区域变形结束之前侵入的。块状内闪长岩和偏闪长岩都主要含有斜长石、石英、斜长石(偏闪长岩中含量较高)、少量正长石、霞石、角闪石、K长石以及不透明矿物、磷灰石和锆石等附属物。石榴石很少出现在偏闪内斜岩中。热力学模型表明,母体英安岩岩浆的液态温度较低(∼750 °C),成岩压力中等(∼5.5 kb),富氧能力适中(ΔQFM = +1 至 +2),含水量较低(∼4.0 wt%)。两种内闪长岩类型分别来自两种不同的地壳(闪长岩)来源,在比石榴石稳定场更浅的<10 kb压力下通过水通量部分熔融而形成。大约20-40%的斜长岩玄武岩源批量熔融产生了偏闪长岩内闪长岩,而大约40-70%的板内玄武岩源批量熔融产生了块状内闪长岩。判别图显示了这些内斜岩的碰撞后构造背景。在区域花岗岩面变质作用的减压阶段(1000-950Ma),由于下地壳的热松弛,在区域性厌氧过程中形成了偏闪长岩内闪长岩和内闪长岩柱岩浆,这与造山运动后碰撞阶段的板块断裂有关。上地幔绝热减压形成的地幔源岩浆提供了热量。
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引用次数: 0
Late Ordovician amphibolites in the Taoxinghu area of central Qiangtang, northern Tibet, and their tectonic significance 藏北羌塘中部陶兴湖地区的晚奥陶世闪长岩及其构造意义
IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-11-06 DOI: 10.1016/j.sesci.2024.100216
Shuangfei Han , Xijun Liu , Haodong Wei , Yaoming Wei , Yao Xiao , Zhiguo Zhang
The early Paleozoic tectonic evolution of the Qinghai-Tibetan Plateau remains not fully understood. The Longmu Co-Shuanghu Suture Zone within the Qiangtang block of northern Qinghai-Tibetan Plateau, records important evidence of the early Paleozoic evolutionary history of the plateau. In this study, we investigated early Paleozoic amphibolites exposed in the Taoxinghu area of central Qiangtang, using zircon U–Pb dating, mineral chemistry, whole-rock geochemistry, and zircon Hf–O isotopes. The objective was to identify the characteristics of the protoliths and the metamorphic processes. Two types of zircons with different characteristics occur in the amphibolites, yielding zircon U–Pb ages of 490 and 440 Ma attained using kernel density estimation, which represent the ages of the protolith and subsequent metamorphism, respectively. The amphibolites have SiO2 (42.4–55.7 wt.%), and Al2O3 (14.4–18.7 wt.%) and MgO (3.62–8.80 wt.%) contents. Their geochemical characteristics show large ion lithophile elements enriched and high field strength elements depleted. The zircon U–Pb age and rock geochemical data suggest the protoliths of the amphibolites were late Cambrian supra-subduction zone-type ophiolites that organized in association with Proto-Tethyan subduction. The subsequent Late Ordovician metamorphic event might be associated with the collision between continental blocks after oceanic closure. We favor that amphibolites provide essential constraints on the early Paleozoic tectonic evolutionary history of the Qinghai-Tibetan Plateau.
青藏高原早古生代的构造演化尚未完全清楚。青藏高原北部羌塘断块内的龙木-双湖断裂带,记录了青藏高原早古生代演化历史的重要证据。本研究利用锆石U-Pb定年、矿物化学、全岩地球化学和锆石Hf-O同位素等手段,对羌塘中部陶兴湖地区出露的早古生代闪长岩进行了研究。目的是查明原岩的特征和变质过程。在闪长岩中发现了两种具有不同特征的锆石,利用核密度估计法得出的锆石U-Pb年龄分别为490 Ma和440 Ma,分别代表了原岩和随后的变质过程的年龄。闪长岩的二氧化硅(42.4-55.7 wt.%)、氧化铝(14.4-18.7 wt.%)和氧化镁(3.62-8.80 wt.%)含量较高。其地球化学特征表现为大离子亲岩元素富集和高场强元素贫化。锆石U-Pb年龄和岩石地球化学数据表明,闪长岩的原岩是晚寒武纪超俯冲带型蛇绿岩,与原泰西俯冲带相关联。随后的晚奥陶世变质事件可能与大洋关闭后大陆块之间的碰撞有关。我们认为,闪长岩为青藏高原早期古生代构造演化史提供了重要的约束条件。
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引用次数: 0
Reappraising the eruptive history of the Alchichica Maar Volcano (Mexico) based on Sr–Nd isotopes: Understanding the role of the magma source region on the growth of small-volume volcanoes 根据钍钕同位素重新评估阿尔奇希卡马火山(墨西哥)的喷发历史:了解岩浆源区域对小体积火山生长的作用
IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-10-19 DOI: 10.1016/j.sesci.2024.100214
Boris Chako-Tchamabé , Bodo Weber , Merlin Gountié Dedzo , Jules Tamen , Jhoanna Silis-Esquivel , Karoly Nemeth
Alchichica Maar is in the eastern sector of the Trans-Mexican Volcanic Belt, where volcanics range from basalts to rhyolites, with 87Sr/86Sr and 143Nd/144Nd values between 0.70293 to 0.70447 (εSr = −21.1 to −4.5) and 0.512733 to 0.512949 (εNd = +3.4 to +6.2), respectively. In this study, Nd and Sr isotopic data and new major and trace elements compositions are provided for the lava flow, the scoria cone, and the phreatomagmatic deposits composing Alchichica Maar Volcano. These results are used in combination with published data to reexamine its eruptive history, though to be formed by more than one eruptive event. The cogeneticy of the magmas that fed the eruptions of these deposits is examined to infer the role of the deep magma source region and post-magmatic alterations on the construction of the Alchichica Maar magmatic system. Alchichica samples present 87Sr/86Sr values between 0.70387 and 0.70447 (εSr = −9.0 to −0.4) and 143Nd/144Nd values from 0.512749 to 0.512773 (εNd = +2.0 to +2.8). While the 87Sr/86Sr values suggest a slight increment in radiogenic 87Sr from the pre-maar lower lava flow to the upper maar eruptions indicative of magma contamination within the upper crust and by hydrodynamic mingling during the phreatomagmatic phases, the slight variation in Nd isotopes suggest an overall homogeneous source where small batches of magmas formed episodically to feed monogenetic eruptions, which subsequently yielded the pre-maar lava flow, the pre-maar surge, the scoria cone, and the maar units. This study reinforces the idea that an already “tapped” source region of a monogenetic volcano may become fertile again, and new eruptions can occur from near or old vent sites. It also highlights the hazardous potential of small-volume volcanoes.
Alchichica Maar 火山位于跨墨西哥火山带的东部,火山岩从玄武岩到流纹岩,87Sr/86Sr 和 143Nd/144Nd 值分别介于 0.70293 至 0.70447 之间(εSr = -21.1 至 -4.5)和 0.512733 至 0.512949 之间(εNd = +3.4 至 +6.2)。本研究提供了组成阿尔奇希卡马火山的熔岩流、灼烧锥和岩浆沉积物的钕和锶同位素数据以及新的主要和微量元素组成。这些结果与已公布的数据相结合,重新审视了火山的喷发历史,尽管它是由一次以上的喷发事件形成的。研究了这些矿床喷发所产生的岩浆的成因,以推断深部岩浆源区域和岩浆后变化对阿尔奇希卡火山岩浆系统的形成所起的作用。Alchichica 样品的 87Sr/86Sr 值介于 0.70387 和 0.70447 之间(εSr = -9.0 至 -0.4),143Nd/144Nd 值介于 0.512749 和 0.512773 之间(εNd = +2.0 至 +2.8)。虽然 87Sr/86Sr 值表明,从岩浆喷发前的下部熔岩流到岩浆喷发的上部,放射性 87Sr 值略有增加,这表明岩浆在上地壳内受到污染,并在岩浆喷发阶段通过水动力混合而受到污染、钕同位素的微小差异表明,岩浆源总体上是均质的,小批岩浆偶发形成,为单源喷发提供了养分,随后产生了玛珥前熔岩流、玛珥前涌流、焦岩锥和玛珥单元。这项研究加强了这样一种观点,即已经 "挖掘 "过的单源火山源区可能会再次变得肥沃,新的喷发可能会从附近或旧的喷口地点发生。它还突出了小体积火山的危险潜力。
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引用次数: 0
Petrology of the Pan-African high-K alkali-calcic Bocaranga plutonic complex in the Adamawa-Yadé domain (Central African Republic): Nature, origin and contribution to geodynamic reconstruction of the Central African fold belt 阿达马瓦-亚代地区(中非共和国)泛非高 K 碱钙质博卡兰加岩浆复合体的岩石学:性质、起源及对中非褶皱带地球动力学重建的贡献
IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2024-10-11 DOI: 10.1016/j.sesci.2024.100211
Rodrigue Martial Topien , Jules Tcheumenak Kouémo , José Kpéou , Gaetan Moloto-A-Kenguemba , Maurice Kwékam
The Bocaranga plutonic complex belongs to the northwestern extension Adamawa-Yadé Domain of the Central African Fold Belt (CAFB) in the Central African Republic (CAR). Six petrographical units are recorded in the Bocaranga plutonic complex: (i) a coarse-grained biotite granite, (ii) hornblende-biotite granite, (iii) fine-grained biotite granite, and (iv) two micas granite emplaced in Pan-African metamorphic basement rocks composed of (v) gneisses and (vi) amphibolites. Their chemical compositions are similar to quartz monzonites, monzogranite, syenogranite and alkali granite, respectively. The pluton rocks are metaluminous to weakly peraluminous I-type granitoids, hornblende-biotite granite are magnesian and high-K alkaline, while grained biotite granite and fine-grained biotite granite are ferroan, alkalic-calcic and shoshonitic, whereas the two micas granite are weakly to strongly peraluminous and calc-alkaline. The evolution of the major elements (Al2O3 and CaO) and some trace elements (Sr) suggest that fractional crystallization controlled by plagioclase is the main magma differenciation process which influenced the magmatic evolution in this plutonic complex. However, the presence of gneiss xenoliths and mafic enclaves within the plutonic complex, combined to the geochemical data, indicate that the Bocaranga plutonic complex is most likely the result of mixing between mantle- and crust-derived magmas, with high crustal implication for coarse-grained biotite granite, fine-grained biotite granite and two micas granite and high mantle one for hornblende-biotite granite. High U–Th content displays by two-mica granite the high REE content display by all the plutonic rocks indicate that these rocks appear to be respectively favourable for mineralisation in the aforemention elements, thus indicating that the Bocaranga area may represents a potential exploration target for U–Th and REE deposits. The Bocaranga plutonic complex is a synkinematic pluton whose emplacement is synchronuous to the D2 ductile deformation phase related to linear lithospheric delamination along the MBéré Shear Zone around 620-550 Ma during the late-to post-collisional history the Pan-African orogeny. Such granitic plutons are common in the Orogenic Belt of Central Africa and the Brasiliano Belt.
博卡兰加岩浆岩复合体属于中非共和国中部非洲褶皱带(CAFB)的西北延伸阿达马瓦-亚代域(Adamawa-Yadé Domain)。博卡兰加岩浆岩群中有六个岩相单元:(i) 粗粒生物花岗岩,(ii) 角闪石-生物花岗岩,(iii) 细粒生物花岗岩,(iv) 两种云母花岗岩,它们被安放在由(v) 片麻岩和(vi) 闪长岩组成的泛非变质基底岩中。它们的化学成分分别类似于石英独居岩、独居岩、正长岩和碱性花岗岩。深成岩为金属铝质至弱过铝质的 I 型花岗岩,角闪石-黑云母花岗岩为镁质和高 K 碱性,粒状黑云母花岗岩和细粒黑云母花岗岩为铁质、碱性-钙质和霰石质,而两种云母花岗岩为弱至强过铝质和钙碱性。主要元素(Al2O3 和 CaO)和一些微量元素(Sr)的演化表明,由斜长石控制的碎裂结晶是影响这个岩浆复合体岩浆演化的主要岩浆分异过程。然而,该深成岩复合体中存在片麻岩异长岩和黑云母飞地,再加上地球化学数据,表明 Bocaranga 深成岩复合体很可能是地幔和地壳岩浆混合的结果,粗粒生物花岗岩、细粒生物花岗岩和两种云母花岗岩具有较高的地壳影响,而角闪石-生物花岗岩则具有较高的地幔影响。双云母花岗岩显示的高铀-钍含量和所有深成岩显示的高稀土元素含量表明,这些岩石似乎分别有利于上述元素的成矿,从而表明博卡兰加地区可能是铀-钍和稀土元素矿床的潜在勘探目标。博卡兰加岩浆岩复合体是一种同源岩浆岩,其形成与泛非造山运动晚期至碰撞后历史时期约 620-550 马年沿 MBéré 剪切带的线性岩石圈分层相关的 D2 延展变形阶段同步。这种花岗岩柱岩在中非造山带和巴西利亚诺带很常见。
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Solid Earth Sciences
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