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Multivariate examination of the sediment-deficient southeast Australian continental shelf 缺乏沉积物的东南澳大利亚大陆架的多元检验
1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-10-18 DOI: 10.1130/b37019.1
Adam R. Nordsvan, N. Ryan McKenzie, Cody L. Colleps, Alexander Koch, Nicole S. Khan
Continental shelves are the most morphologically variable element within the source-to-sink system owing to the numerous processes that influence their formation. A recent multivariate analysis of a global compilation of modern continental shelf data showed that much of the variability is related to tectonic setting, the degree to which the shelf has been glaciated, and carbonate production. While these factors play first-order roles in determining the morphology of shelves, other controlling mechanisms such as siliciclastic sediment supply, wave and tidal energy, bedrock lithology, and sea-level fluctuations are not as well understood. Here, we report findings from a detailed investigation of the southeast Australian shelf that explored how sediment distribution, wave energy, and bedrock lithology influence shelf morphology. The high-resolution analysis suggests that the southeast Australian shelf has 11 distinct shelf types. No strong relationships exist between the shelf attributes or shelf type with their onshore catchments. However, a substantial section boundary correlates with a bedrock contact between the Sydney Basin in the south and the New England Orogen to the north. South of this boundary, we propose that the shelf morphology reflects transgression with low sediment supply, whereas to the north, the morphology reflects transgression with higher sediment input. Although several factors contributed to this difference in shelf morphology, we suggest that sediment distribution and retention due to the active wave climate during the most recent transgression likely played a vital role.
由于影响陆架形成的众多过程,陆架是源-汇系统中形态变化最大的元素。最近对现代大陆架数据的全球汇编进行的一项多变量分析表明,这种变化很大程度上与构造环境、大陆架被冰川覆盖的程度和碳酸盐生产有关。虽然这些因素在决定陆架形态方面起着一级作用,但其他控制机制,如硅质沉积物供应、波浪和潮汐能、基岩岩性和海平面波动等,还没有得到很好的了解。在这里,我们报告了对澳大利亚东南部大陆架的详细调查结果,探讨了沉积物分布、波浪能和基岩岩性如何影响大陆架形态。高分辨率分析表明,澳大利亚东南部的大陆架有11种不同的大陆架类型。大陆架属性或大陆架类型与其陆上集水区之间不存在很强的关系。然而,一个实质性的剖面边界与南部的悉尼盆地和北部的新英格兰造山带之间的基岩接触有关。在该边界以南,陆架形态反映了低沉积物供给的海侵,而在北部,陆架形态反映了高沉积物输入的海侵。虽然有几个因素导致了陆架形态的差异,但我们认为最近一次海侵期间活跃的波浪气候导致的沉积物分布和滞留可能起了至关重要的作用。
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引用次数: 0
Tracking multiple stages of serpentinization processes of the Yarlung Zangbo Suture Zone peridotites in southern Tibet: Implications for the tectonic evolution of the Neotethyan oceanic lithosphere 藏南雅鲁藏布江缝合带橄榄岩多阶段蛇纹石化过程的追踪:对新特提斯洋岩石圈构造演化的启示
1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-10-16 DOI: 10.1130/b36875.1
Qi Zhao, Yi Yan, Yildirim Dilek, Touping Peng, Yuxiang Zhu, Zuofei Zhu
Serpentinites are key repositories of fluid-mobile elements (FMEs) in subduction zones and record significant information about the origin and geodynamic evolution of oceanic lithosphere. Here, we report on the structural textures and mineralogical compositions of different types of serpentinites collected from the central segment of the Yarlung Zangbo Suture Zone in southern Tibet and present their bulk-rock and mineral chemistry, and Sr isotopic compositions. The main textures include massive, scaly, and gouge serpentinites exposed in the Ngamring and Sangsang ophiolites. Bulk-rock Al2O3/SiO2 and spinel Cr# values suggest that the Ngamring serpentinites originally formed in an abyssal setting, whereas the Sangsang serpentinites developed initially in a forearc mantle. Both serpentinite assemblages were subsequently incorporated into a subduction plate interface as subducted serpentinites. Massive serpentinites preserve the geochemical fingerprint of original serpentinized fluids in mid-oceanic ridge to forearc settings, whereas sheared serpentinites with scaly and gouge textures are reset in their Sr isotopic compositions and FME ratios (i.e., Cs/U, Li/U, and Rb/U) due to their reactions with slab-derived fluids. Scaly and gouge types of the Ngamring serpentinites have lower 87Sr/86Sr values (87Sr/86Sr = 0.7081−0.7082) and higher alkali element−U ratios (i.e., Cs/U, Li/U, and Rb/U) than those of the massive serpentinite types (87Sr/86Sr = 0.7091−0.7096), which indicates that they interacted with fluids at a slab interface after their initial seafloor serpentinization. In contrast, the massive Sangsang serpentinites display lower 87Sr/86Sr values (87Sr/86Sr = 0.7041−0.7043, similar to those of the Yarlung Zangbo ophiolites) and higher alkali element−U ratios than those of the sheared serpentinites (87Sr/86Sr = 0.7063−0.7087). These findings point to the significant role of the increased influx of subducted sediment-derived fluids within subduction shear zones in further affecting the serpentinization fingerprint. This study demonstrates that serpentinites with different textural, geochemical, and isotopic features within the same suture zone may represent the serpentinization products in different tectonic environments during the seafloor spreading, subduction initiation, and subduction zone evolution of oceanic lithosphere.
蛇纹岩是俯冲带流体活动元素(FMEs)的重要储存库,记录了海洋岩石圈起源和地球动力学演化的重要信息。本文报道了藏南雅鲁藏布缝合带中段不同类型蛇纹岩的构造结构和矿物学组成,并给出了它们的体岩矿物化学和Sr同位素组成。其主要结构为出露在甘陵和桑桑蛇绿岩中的块状、鳞状和泥状蛇纹岩。大块岩石的Al2O3/SiO2和尖晶石Cr#值表明,nggamring蛇纹岩最初形成于深海环境,而Sangsang蛇纹岩最初发育于弧前地幔。两种蛇纹岩组合随后作为俯冲蛇纹岩合并到俯冲板块界面中。块状蛇纹岩保留了洋中脊至弧前背景下原始蛇纹岩流体的地球化学指纹,而具有鳞状和泥质结构的剪切蛇纹岩由于与板源流体的反应,其Sr同位素组成和FME比值(即Cs/U、Li/U和Rb/U)被重置。与块状蛇纹岩类型(87Sr/86Sr = 0.7091 ~ 0.7096)相比,鳞状蛇纹岩和泥状蛇纹岩的87Sr/86Sr值(87Sr/86Sr = 0.7081 ~ 0.7082)较低,碱元素- U比值(Cs/U、Li/U、Rb/U)较高,表明它们在海底初始蛇纹岩化后,在板块界面与流体相互作用。而块状桑桑蛇纹岩的87Sr/86Sr值(87Sr/86Sr = 0.7041 ~ 0.7043,与雅鲁藏布蛇绿岩相似)低于剪切蛇纹岩(87Sr/86Sr = 0.7063 ~ 0.7087),碱元素- U比值较高。这些发现表明,俯冲剪切带内俯冲沉积流体的增加流入对蛇纹岩化指纹的进一步影响具有重要作用。研究表明,同一缝合带内具有不同结构、地球化学和同位素特征的蛇纹岩,可能是海洋岩石圈海底扩张、俯冲起始和俯冲带演化过程中不同构造环境下的蛇纹岩化产物。
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引用次数: 0
Slab breakoff diorite porphyries derived from two cratons in a continental subduction zone, Sulu orogen, China 苏鲁造山带大陆俯冲带两个克拉通的板块断裂闪长斑岩
1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-10-16 DOI: 10.1130/b36964.1
Peng Feng, Lu Wang, Timothy Kusky, Zhe Chen, Wei Hu, Xiandeng Yang
Syncollisional magmatism plays an important but underappreciated role in continental crust growth and maturation. However, the origin of syncollisional intermediate magmas in continental subduction zones is controversial, with some models suggesting they form by arc-related processes, and others indicating they form by later slab breakoff−induced melting. Diorite porphyry dikes intruding granitic gneiss in the Paleo-Tethyan Sulu ultrahigh-pressure (UHP) continental collisional orogen have inherited zircon grains with 206Pb/238U ages of ca. 749−238 Ma, and magmatic zircons with weighted mean ages of 216−215 Ma, falling within the well-constrained time range (ca. 235−208 Ma) tracking exhumation of the Sulu UHP rocks from UHP peak conditions to amphibolite facies; they are thus syncollisional. The dikes have high Cr (330−402 ppm), Ni (84.5−103 ppm), and Mg# (64−66) values, showing a mantle origin. The porphyries have relatively high Sm/Yb, Nb/Y, La/Yb, and Gd/Yb ratios, representing a classic signature of slab breakoff magmatism. Together with the arc-like trace-element patterns and enriched Sr-Nd isotope compositions, ages, and εHf(t) values (−19.5 to −17.0) of magmatic zircons and their tectonic setting, we propose a syncollisional slab breakoff model in which the melts were initially generated from asthenospheric upwelling in the gap created when the oceanic slab attached to the Yangtze craton detached underneath the North China craton during Late Triassic collision following Paleo-Tethys Ocean closure. The diorite porphyry dikes have consistent Sr-Nd isotope compositions and spatiotemporal relationships with the nearby Shidao gabbro-syenite-granite complex, for which the tectonic affinity is controversial. Thus, we argue that the diorite porphyries and Shidao complex were sourced from two cratons, including the enriched subcontinental lithospheric mantle of the North China craton, which interacted with abundant felsic melts derived from the sinking slab breaking away from the subducted crust of the Yangtze continental-ocean transitional margin. This study sheds new light on crustal recycling versus continental growth in collisional orogens and implies that considerable syncollisional intermediate magmas can be generated by slab breakoff in continental subduction zones, representing hybrid additions to continental growth that are different and more evolved than arc magmas and have a composition similar to that of the bulk continental crust.
同碰撞岩浆作用在大陆地壳生长和成熟过程中起着重要但未被充分认识的作用。然而,关于大陆俯冲带同碰撞中间岩浆的起源仍有争议,一些模型认为它们是由弧相关过程形成的,而另一些模型认为它们是由后来的板块断裂引起的熔融形成的。古特提斯苏鲁超高压(UHP)大陆碰撞造山带中侵入花岗质片麻岩的闪长斑岩岩脉继承了206Pb/238U年龄约为749 ~ 238 Ma的锆石颗粒和加权平均年龄为216 ~ 215 Ma的岩浆锆石,这些锆石的年龄在苏鲁超高压岩石从超高压峰值条件到角闪岩相的挖掘过程中有很好的限定时间范围(约235 ~ 208 Ma);因此它们是共碰撞的。岩脉中Cr (330 ~ 402ppm)、Ni (84.5 ~ 103ppm)和Mg#(64 ~ 66)值较高,显示地幔成因。斑岩具有较高的Sm/Yb、Nb/Y、La/Yb和Gd/Yb比值,是典型的板块断裂岩浆活动特征。结合岩浆锆石的弧形微量元素模式和富集的Sr-Nd同位素组成、年龄和εHf(t)值(- 19.5 ~ - 17.0)及其构造背景,我们提出了一种同碰撞板块断裂模型,该模型认为,在古特提斯洋闭合后的晚三叠世碰撞中,附属于扬子克拉通的大洋板块在华北克拉通下方分离时形成的缺口中,软流圈上升流最初产生了熔融体。闪长斑岩岩脉与附近石岛辉长-正长-花岗岩杂岩具有一致的Sr-Nd同位素组成和时空关系,其构造亲和性存在争议。因此,我们认为闪长斑岩和石岛杂岩来源于两个克拉通,其中包括华北克拉通富集的次大陆岩石圈地幔,它们与扬子陆-洋过渡边缘俯冲地壳分离的下沉板块产生的丰富的长英质熔体相互作用。该研究揭示了碰撞造山带地壳再循环与大陆生长的新关系,并表明大陆俯冲带的板块断裂可产生相当数量的同碰撞中间岩浆,代表了与弧岩浆不同且更演化的大陆生长的混合补充,其组成与大块大陆地壳相似。
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引用次数: 0
Growth and evolution of Neoarchean−Paleoproterozoic crust in the NW Wyoming Province: Evidence from zircon U-Pb age and Lu-Hf isotopes of the Montana metasedimentary terrane 怀俄明西北部新太古代-古元古代地壳生长演化:蒙大拿变质沉积岩锆石U-Pb年龄和Lu-Hf同位素证据
1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-10-13 DOI: 10.1130/b37160.1
Tsai-Wei Chen, Jeffrey D. Vervoort, Julia A. Baldwin
The Montana metasedimentary terrane in the northern Wyoming Province provides valuable insight into crustal formation and reworking processes along the cratonic margin and offers a unique opportunity to decipher the complex Neoarchean−Paleoproterozoic terrane assembly in southwestern Laurentia. We report new zircon U-Pb dates and Hf isotopes from seven metaigneous samples in the northwestern Montana metasedimentary terrane. The internal textures of zircon in this study are complex; some lack inherited cores and metamorphic overgrowths, while others exhibit core-rim relationships. Based on the cathodoluminescence (CL) features, we interpret these grains to be magmatic populations. These data demonstrate discrete igneous pulses at 2.7 Ga, 2.4 Ga, and 1.7 Ga, which indicate significant crustal formation intervals in the Montana metasedimentary terrane. Zircons at 2.7 Ga have positive εHf values (+2.4 to +0.9) that indicate a depleted mantle source. Most 2.4 Ga and 1.7 Ga samples have negative εHf values (−1.6 to −15.5), which indicate significant contributions from preexisting crust. Two 1.7 Ga samples, however, have near-chondritic εHf values (+0.4 to +0.3) that indicate larger juvenile contributions. The time-integrated Hf isotope trend suggests that the Paleoproterozoic zircons were produced from a mixture of older crust and juvenile mantle inputs. Additionally, the isotopic age fingerprint of the Montana metasedimentary terrane suggests that it differs from northern-bounding terranes. Viewed more broadly, the 2.7 Ga and 1.7 Ga age peaks that the Montana metasedimentary terrane shares with the global zircon age spectrum suggest that the drivers of these events in the Montana metasedimentary terrane were common throughout the Earth and may be associated with the assembly of supercontinents Kenorland and Nuna.
位于怀俄明州北部的蒙大拿变质沉积岩为研究克拉通边缘的地壳形成和改造过程提供了宝贵的见解,并为破译Laurentia西南部复杂的新太古代-古元古代地层组合提供了独特的机会。本文报道了美国蒙大拿州西北部7个变质岩样品的锆石U-Pb测年和Hf同位素。本研究的锆石内部结构复杂;有些缺乏遗传岩心和变质过度生长,而另一些则表现出岩心-边缘关系。根据阴极发光(CL)特征,我们认为这些颗粒为岩浆群。这些数据显示了2.7 Ga、2.4 Ga和1.7 Ga的离散火成岩脉冲,这表明蒙大拿变质沉积地体中存在明显的地壳形成间隔。2.7 Ga锆石εHf值为正(+2.4 ~ +0.9),表明地幔源为衰竭。大部分2.4 Ga和1.7 Ga样品的εHf值为负(- 1.6 ~ - 15.5),表明前人地壳对样品的贡献较大。然而,两个1.7 Ga样品的εHf值(+0.4至+0.3)接近球粒体,表明幼体的贡献较大。时间积分的Hf同位素趋势表明,古元古代锆石是由较老的地壳和较年轻的地幔混合输入产生的。此外,蒙大拿元沉积地体的同位素年龄指纹表明其与北界地体不同。从更广泛的角度来看,蒙大拿变质沉积岩的2.7 Ga和1.7 Ga年龄峰值与全球锆石年龄谱共享,表明蒙大拿变质沉积岩这些事件的驱动因素在整个地球上是共同的,可能与Kenorland和Nuna超大陆的组合有关。
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引用次数: 0
Mid-Cretaceous to early Eocene Neo-Tethyan subduction records in West Sulawesi, Indonesia 印度尼西亚西苏拉威西中白垩世至始新世早期新特提斯俯冲记录
1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-10-13 DOI: 10.1130/b37038.1
Xiaoran Zhang, Sun-Lin Chung, Chia-Yu Tien, Adi Maulana, Musri Mawaleda, Hao-Yang Lee, Ping-Ping Liu, Jinyu Xi
Situated in the heart of the Indonesian archipelago, Sulawesi records well-developed Cenozoic magmatism, yet its Cretaceous magmatic evolution remains enigmatic. Here, we report new U-Pb-Hf isotopic data of detrital zircons from West Sulawesi, Indonesia to constrain its Cretaceous to Eocene magmatic tempo. Detrital zircons aged at ca. 105−80 Ma and ca. 70−45 Ma occur as the most dominant age populations and show high positive εHf(t) values, indicating derivation from juvenile sources with limited continental crustal contamination. Our new data, combined with available results, support the existence of an Andean-type continental margin in West Sulawesi during mid-Cretaceous to early Eocene times. Importantly, the magmatic tempo of West Sulawesi is also consistent with those of southern Lhasa (Tibet) and Sumatra (Indonesia), but contrasts with those of Paleo-Pacific subduction-related arcs in SE China, SE Vietnam, East Malaysia, and NW Borneo. Therefore, we put forward that West Sulawesi may be the southeasternmost component of the Neo-Tethyan arc system that spreads over 7500 km, from southern Tibet to SE Sundaland. Such a huge arc system with concurrent magmatic flare-ups and lulls in South Asia may have played a significant role in global-scale plate reorganization.
苏拉威西岛位于印度尼西亚群岛的中心,记录了发育良好的新生代岩浆活动,但其白垩纪岩浆演化仍然是一个谜。本文报道了印度尼西亚西苏拉威西地区碎屑锆石的U-Pb-Hf同位素数据,以限制其白垩纪至始新世的岩浆速度。年龄约为105 ~ 80 Ma和70 ~ 45 Ma的碎屑锆石是最主要的年龄群,εHf(t)值较高,表明其来源为幼年,大陆地壳污染有限。我们的新数据,结合现有的结果,支持在白垩纪中期到始新世早期在西苏拉威西存在安第斯型大陆边缘。重要的是,西苏拉威西的岩浆速度与拉萨南部(西藏)和苏门答腊(印度尼西亚)的岩浆速度一致,但与中国东南部、越南东南部、东马来西亚和西北婆罗洲的古太平洋俯冲相关弧形成对比。因此,我们认为西苏拉威西可能是新特提斯弧体系的最东南部分,该体系从西藏南部延伸至巽他兰东南部,全长7500公里。南亚这样一个巨大的弧形体系与同时发生的岩浆爆发和平静可能在全球范围的板块重组中发挥了重要作用。
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引用次数: 0
The Manhattan project: Isotope geochemistry and detrital zircon geochronology of schists in New York City, USA 曼哈顿计划:美国纽约市片岩的同位素地球化学和碎屑锆石年代学
1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-10-13 DOI: 10.1130/b37024.1
Steven J. Jaret, Nicholas D. Tailby, Keiji G. Hammond, E. Troy Rasbury, Kathleen Wooton, Denton S. Ebel, Terry Plank, E. DiPadova, Victoria Yuan, Riley Smith, Noa Jaffe, Lisa M. Smith, Lynsey Spaeth
The geology of New York City (USA) consists primarily of metasedimentary rocks that were deformed during the series of orogenies between ca. 470 Ma and ca. 300 Ma that culminated in the amalgamation of Pangea. The rocks in New York City play a key role in understanding the tectonic history of these orogenies because they lie at a critical location at the boundary between the Northern and Southern Appalachian Mountains. The primary question addressed here is where these metasedimentary rocks originated prior to the assembly of Pangea. Through detrital zircon and whole-rock Nd isotope analyses, we show that all the metasedimentary rocks of New York City, mapped as the Manhattan Schist and the Hartland Group, are primarily derived from Laurentia as indicated by detrital zircon populations dominated by 1200−900 Ma grains and εNd values between −7 and −13. The results presented here do not necessitate an exclusively Laurentian source for the detrital material found in New York City, but the data strongly suggests protoliths represent sedimentary units that are primarily derived from the Laurentian margin. Another important result from this study is the limited contributions from any rift volcanics and/or Gondwanan material(s). There is some subtle variability across our zircon sample suite, but there is no convincing evidence for major changes in bulk provenance signal that would be consistent with derivation from vastly different continental sources for these rocks. The shared provenance signal observed here is counter to the previous suggestions that a major terrane boundary, often called Cameron’s Line, exists in New York City, separating Laurentian rocks from those of a Gondwanan affinity.
纽约市(美国)的地质主要由变质沉积岩组成,这些变质沉积岩是在大约470 Ma至300 Ma之间的一系列造山运动中变形的,这些造山运动以盘古大陆的合并为高潮。纽约市的岩石在了解这些造山运动的构造历史中起着关键作用,因为它们位于南北阿巴拉契亚山脉边界的关键位置。这里要解决的主要问题是这些变质沉积岩在盘古大陆形成之前起源于哪里。通过碎屑锆石和全岩Nd同位素分析,我们发现纽约市所有的变质沉积岩(绘制为曼哈顿片岩和哈特兰群)主要来源于Laurentia,碎屑锆石种群以1200 ~ 900 Ma颗粒为主,εNd值在- 7 ~ - 13之间。这里提出的结果并不意味着在纽约市发现的碎屑物质的唯一来源是劳伦特,但数据强烈表明,原岩代表了主要来自劳伦特边缘的沉积单元。这项研究的另一个重要结果是任何裂谷火山和/或冈瓦纳物质的贡献有限。在我们的锆石样品组中有一些微妙的变化,但没有令人信服的证据表明,总体物源信号发生了重大变化,这与这些岩石来自不同大陆来源的衍生相一致。这里观察到的共同物源信号与之前的建议相反,即在纽约市存在一个主要的地层边界,通常被称为卡梅伦线,将劳伦岩石与冈瓦纳岩石分离开来。
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引用次数: 0
Revised chronology of the middle−upper Cenozoic succession in the Tuotuohe Basin, central-northern Tibetan Plateau, and its paleoelevation implications 青藏高原中北部沱沱河盆地中、上新生代演替的订正年代学及其古高程意义
1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-10-12 DOI: 10.1130/b36965.1
Leyi Li, Hong Chang, Alex Farnsworth, Nathan A. Niemi, Peter D. Clift, Xiaoke Qiang, Chunsheng Jin, Jimin Sun, Chong Guan, Peng Zhang, Hongxuan Lu, Weiguo Liu, Balázs Bradák, Lu Peng, Yunfa Miao, Zhisheng An
Currently, the climatic implications associated with the Cenozoic tectonic history and growth mechanisms of the Tibetan Plateau lack consensus and remain controversial. This is due in part to chronological uncertainties and few paleoelevation records distributed in the central to northern Tibetan Plateau, which we address here with the development of a robust chronology (using magnetostratigraphy, biostratigraphy, detrital zircons, and regional radiochronologic dating) and a paleoelevation reconstruction for the Tuotuohe Basin (central-northern Tibet). We refined the age of the Tuotuohe Formation (37−33 Ma), Yaxicuo Formation (33−23.6 Ma), and Wudaoliang Formation (23.6−19.7 Ma). We estimated early Oligocene (ca. 29 Ma) paleotemperatures of the Tuotuohe Basin from 11 °C to 16.1 °C, which correspond to paleoelevations of 2.9 km (±0.4 km) when the relative humidity is 64% and 2.5 km (±0.5 km) when this value is 75%, using various methods including ostracod assemblages, gastropods, charophytes, branched glycerol dialkyl glycerol tetraether analysis, regional empirical formulas, and climate model simulation. Paleoelevation data and existing geological evidence in the vicinity indicate that late Eocene to late Oligocene uplift was associated with upper-crustal shortening. Since the middle Miocene, uplift has been associated with convective removal of lithospheric mantle and/or lower-crustal flow beneath the Hoh Xil Basin.
目前,与青藏高原新生代构造史和生长机制相关的气候意义缺乏共识,仍存在争议。这部分是由于年代学的不确定性和青藏高原中北部分布的古高程记录很少,我们在这里通过发展一个强大的年代学(利用磁地层学、生物地层学、碎屑锆石和区域放射性年代学)和沱沱河盆地(西藏中北部)的古高程重建来解决这个问题。对沱沱河组(37 ~ 33 Ma)、雅溪错组(33 ~ 23.6 Ma)和五道梁组(23.6 ~ 19.7 Ma)的年龄进行了细化。本文采用介形虫组合、腹足类、轮生类、支链甘油二烷基甘油四乙基分析、区域经验公式和气候模式模拟等方法,估算了沱沱河盆地早渐新世(约29 Ma)古温度值为11 ~ 16.1℃,相对湿度为64%时对应的古海拔高度为2.9 km(±0.4 km),相对湿度为75%时对应的古海拔高度为2.5 km(±0.5 km)。古高程资料和附近已有的地质证据表明,晚始新世至晚渐新世隆升与地壳上部缩短有关。中新世中期以来,可可西里盆地的隆升与岩石圈地幔的对流移除和(或)下地壳流动有关。
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引用次数: 0
Origin of composite Ni-Cu sulfide- and Fe-Ti oxide-bearing mafic-ultramafic intrusions in the Central Asian Orogenic Belt, China: Role of externally derived crustal organic carbon in controlling mineralization of post-collisional mafic magmatism 中亚造山带含Ni-Cu硫化物和Fe-Ti氧化物复合基性-超基性岩体的成因:外源地壳有机碳在控制碰撞后基性岩浆成矿作用中的作用
1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-10-12 DOI: 10.1130/b36851.1
Yonghua Cao, Christina Yan Wang, Bo Wei
Composite Ni-Cu sulfide- and Fe-Ti oxide-bearing mafic-ultramafic intrusions have been discovered in convergent margin settings worldwide, but their origins remain enigmatic. Permian Kebu mafic-ultramafic intrusion in the Central Asian Orogenic Belt hosts both Ni-Cu sulfide and Fe-Ti oxide mineralization and formed in a post-collisional, Andean-style arc setting. The Ni-Cu sulfide- and Fe-Ti oxide-bearing rocks in the intrusion have similarly arc-like trace element patterns on the primitive mantle−normalized trace element diagram and negative εNd(t) values (−16 to −5), which indicate that the parental magma of the intrusion may have been derived from the enriched, metasomatized lithospheric mantle. The magma oxygen fugacity (fO2) was calculated to be FMQ+1.3∼FMQ+2.0, which can be attributed to the evolution of hydrated parental magma derived from the metasomatized lithospheric mantle. Also, the rocks all have negative δ13C values (−28.5‰ to −20‰), which indicates incorporation of external-derived crustal organic carbon into magmas. However, the Ni-Cu sulfide-bearing rocks contain more high-temperature carbon than the Fe-Ti oxide-bearing rocks. Modeling results based on alphaMELTS show that the magmas forming the Ni-Cu sulfide-bearing rocks may have assimilated more organic carbon than those that formed the Fe-Ti oxide-bearing rocks. Based on the estimated amounts of organic carbon in the two types of rocks, we deduced that initially oxidized magma pulses may have been reduced in variable degrees, leading to the formation of composite Ni-Cu sulfide and Fe-Ti oxide mineralization in one intrusive body. Mafic magmas in subduction-related, convergent margin settings are commonly highly oxidized due to metasomatism of the mantle wedge by slab-derived fluids/melts, and this may explain why the mafic-ultramafic intrusions associated with composite Ni-Cu sulfide and Fe-Ti oxide mineralization often occur in convergent margin settings.
含Ni-Cu硫化物和Fe-Ti氧化物的复合镁铁质-超镁铁质侵入体已在世界范围内的辐合边缘环境中被发现,但其起源仍然是一个谜。中亚造山带二叠系克布基性-超镁铁质岩体在碰撞后的安第斯弧环境中形成,同时具有镍铜硫化物和铁钛氧化物矿化作用。在原始地幔归一化微量元素图和负的εNd(t)值(- 16 ~ - 5)上,侵入岩中含Ni-Cu硫化物和Fe-Ti氧化物的岩石具有相似的弧形微量元素模式,表明侵入岩的母岩浆可能来源于富集交代的岩石圈地幔。岩浆氧逸度(fO2)值为FMQ+1.3 ~ FMQ+2.0,这与岩石圈地幔交代的水合母岩浆演化有关。岩石δ13C值均为负(- 28.5‰~ - 20‰),表明岩浆中存在外源的地壳有机碳。含镍铜硫化物的岩石比含铁钛氧化物的岩石含有更多的高温碳。基于alphamelt的模拟结果表明,形成含镍铜硫化物岩石的岩浆可能比形成含铁钛氧化物岩石的岩浆吸收了更多的有机碳。根据对两类岩石有机碳含量的估算,推测初始氧化岩浆脉冲可能发生了不同程度的减少,从而在同一侵入体内形成了镍铜硫化物和铁钛氧化物复合矿化。在俯冲相关的辐合边缘环境中,由于地幔楔的交代作用,基性岩浆通常被板块衍生的流体/熔体高度氧化,这可以解释为什么与复合镍铜硫化物和铁钛氧化物成矿相关的基性-超基性侵入常发生在辐合边缘环境中。
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引用次数: 0
Genesis of the Samba Cu deposit of the Central African Copperbelt in Zambia: Constraints from geochemistry and geochronology 赞比亚中非铜带桑巴铜矿的成因:地球化学和地质年代学的制约
1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-10-11 DOI: 10.1130/b37146.1
Yong Zhang, Shouyu Zhou, Xiaolei Wu, Qiaofan Hu
The Samba Cu deposit is located in pre-Katangan Supergroup basement metavolcanic rocks of the Central African Copperbelt in Zambia. To better understand the formation of the Cu deposit, we use geochronologic, geochemical, and S isotopic data obtained for the deposit’s host rocks and sulfide minerals. Laser ablation−inductively coupled plasma−mass spectrometric (LA-ICP-MS) dating of zircon from host rocks, including quartz-sericite schist and biotite-sericite-chlorite schist, yields ages of 1967 ± 17 Ma and 1960 ± 20 Ma, which are interpreted as the crystallization ages of the original volcanic rocks. Re-Os analyses of molybdenite intergrown with chalcopyrite constrain sulfide deposition to 548.1 ± 7.5 Ma and 524.1 ± 7.3 Ma, which correspond to the timing of the Cu mineralization. LA-ICP-MS U-Pb analyses of metamorphic rutile from the biotite-sericite-chlorite schist yield a U-Pb age of 508.3 ± 6.6 Ma, which is interpreted to represent the age of regional metamorphism. The new data suggest that the Cu mineralization at Samba was synchronous with the Lufilian orogeny.
Samba铜矿床位于赞比亚中非铜带的前加丹甘超群基底变质火山岩中。为了更好地了解铜矿床的形成,我们使用了矿床主岩和硫化物矿物的地质年代学、地球化学和S同位素数据。激光烧蚀-电感耦合等离子体-质谱法(LA-ICP-MS)测定了石英-绢云母片岩和黑云母-绢云母-绿泥石片岩中锆石的年龄,分别为1967±17 Ma和1960±20 Ma,可作为原始火山岩的结晶年龄。辉钼矿与黄铜矿共生的Re-Os分析表明,硫化物沉积时间为548.1±7.5 Ma和524.1±7.3 Ma,与铜成矿时间一致。对黑云母-绢云母-绿泥石片岩中变质金红石进行LA-ICP-MS U-Pb分析,U-Pb年龄为508.3±6.6 Ma,可解释为区域变质年龄。新资料表明,桑巴铜成矿与鲁菲连造山运动同步。
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引用次数: 0
Products and dynamics of lava-snow explosions: The 16 March 2017 explosion at Mount Etna, Italy 熔岩-雪爆炸的产物和动力学:2017年3月16日意大利埃特纳火山的爆炸
1区 地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-10-10 DOI: 10.1130/b37102.1
R. Cioni, D. Andronico, L. Cappelli, A. Aravena, P. Gabellini, A. Cristaldi, R.A. Corsaro, M. Cantarero, F. Ciancitto, E. De Beni, G. Ganci
Volcanic hazards associated with lava flows advancing on snow cover are often underrated, although sudden explosions related to different processes of lava-snow/ice contact can occur rapidly and are only preceded by small, easily underrated precursors. On 16 March 2017, during a mildly effusive and explosive eruption at Mount Etna, Italy, a slowly advancing lava lobe interacted with the snow cover to produce a sudden, brief sequence of explosions. White vapor, brown ash, and coarse material were suddenly ejected, and the products struck a group of people, injuring some of them. The proximal deposit formed a continuous mantle of ash, lapilli, and decimeter-sized bombs, while the ballistic material travelled up to 200 m from the lava edge. The deposit was estimated to have a mass of 7.1 ± 0.8 × 104 kg, which corresponds to a volume of 32.0 ± 3.6 m3 of lava being removed by the explosion. Data related to the texture and morphology of the ejected clasts were used to constrain a model of lava-snow interaction. The results suggest that the mechanism causing the explosions was the progressive build-up of pressure due to vapor accumulation under the lava flow, while no evidence was found for the occurrence of fuel-coolant interaction processes. Although these low-intensity explosions are not particularly frequent, the data set collected provides, for the first time, quantitative information about the processes involved and the associated hazard and suggests that mitigation measures should be established to prevent potentially dramatic accidents at worldwide volcanoes frequented by tourists and with fairly easy access, such as Etna.
尽管与熔岩-雪/冰接触的不同过程有关的突然爆炸可能发生得很快,而且之前只有很小的、容易被低估的前兆,但与熔岩流在积雪上移动有关的火山危险往往被低估了。2017年3月16日,意大利埃特纳火山发生了一次温和的喷发,缓慢推进的熔岩叶与积雪相互作用,产生了一系列突然而短暂的爆炸。白色蒸汽、棕色灰和粗糙的物质突然喷射出来,产品击中了一群人,其中一些人受伤。最近的沉积物形成了一个连续的地幔,由火山灰、石蜡和分米大小的炸弹组成,而弹道物质从熔岩边缘传播到了200米的地方。据估计,该矿床的质量为7.1±0.8 × 104千克,相当于32.0±3.6立方米的熔岩被爆炸带走。利用与喷出碎屑的结构和形态相关的数据来约束熔岩-雪相互作用的模型。结果表明,岩浆流下蒸汽积聚导致的压力逐渐积聚是导致爆炸的机制,而没有发现燃料-冷却剂相互作用过程的证据。虽然这些低强度的爆炸不是特别频繁,但所收集的数据集首次提供了有关所涉及的过程和相关危害的定量信息,并建议应制定缓解措施,以防止在游客经常去的、相当容易到达的世界范围火山(如埃特纳火山)发生可能发生的重大事故。
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引用次数: 0
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Geological Society of America Bulletin
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