IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-10-11 DOI: 10.1016/j.lithos.2024.107834

Yu-Sheng Zhu , Jin-Hui Yang , Jin-Feng Sun , Jing-Yuan Chen , Lei Xu , Rui Li , Bao-Quan Zhou

Aluminous A-type granites are not typically associated with mantle-derived rocks. Their generation is usually linked to crustal melting with mantle-derived magmas primarily acting as a heat source. However, the Triassic Bolinchuan A-type granites on Liaodong Peninsula, northeastern China, coexist with a large mantle-derived alkaline igneous complex, indicating a close genetic relationship that provides new insights into the petrogenesis of aluminous A-type granites. The Bolinchuan granites were formed during 230–226 Ma, coeval with syenites in the alkaline complex (230–224 Ma). The granites are metaluminous to weakly peraluminous, but have relatively high alkali contents (8.61–9.40 wt%). Their high Ga/Al ratios, elevated Nb, Zr, Ce, and Y contents, and high magmatic temperatures (>875 °C) indicate an affinity with aluminous A-type granites. However, the Bolinchuan granites have relatively high MgO contents at intermediate SiO₂ contents, with Mg# values of up to 47; these features are inconsistent with the melting of only crustal rocks. Instead, these granites contain mineral phases similar to those of the syenites and exhibit major and trace element trends that are continuous with those of the syenites. Their geochemical features include enrichments in large-ion lithophile elements (e.g., Ba and Sr), depletions in high-field-strength elements (e.g., Nb and Ta) and heavy rare earth elements, and small negative Eu anomalies, which are also consistent with the features of the associated syenites. Furthermore, the granites and their accessory minerals have high initial ⁸⁷Sr/⁸⁶Sr ratios, and low ε_Nd(t) and ε_Hf(t) values, which are similar to the syenites, apart from being slightly less isotopically enriched. These geochemical and isotopic features suggest the Bolinchuan granites formed from the syenitic magmas by fractional crystallization of alkali feldspar, amphibole, and apatite, in combination with the addition of ∼30 % juvenile crust-derived materials, as indicated by modeling. Our study reveals that differentiation of mantle-derived alkaline magmas can generate magmas parental to aluminous A-type granites. As such, the mantle not only provides the heat for the formation of aluminous A-type granites, but can also be the main source of the magmas.

铝质A型花岗岩通常与地幔衍生岩无关。它们的生成通常与地壳熔融有关，而地幔岩浆则是主要的热源。然而，位于中国东北辽东半岛的三叠纪博林川A型花岗岩与一个大型地幔源碱性火成岩复合体共存，表明两者之间存在密切的遗传关系，这为铝质A型花岗岩的岩石成因提供了新的见解。博林川花岗岩形成于230-226Ma期间，与碱性复合体中的正长岩（230-224Ma）共生。花岗岩为金属铝质至弱过铝质，但碱含量相对较高（8.61-9.40 wt%）。这些花岗岩的镓/铝比率高，铌、锆、铈和钇含量高，岩浆温度高（875 °C），表明它们与铝质 A 型花岗岩有亲缘关系。然而，波林川花岗岩在二氧化硅含量中等的情况下，氧化镁含量相对较高，Mg#值高达47；这些特征与仅熔融地壳岩石的情况不符。相反，这些花岗岩含有与正长岩相似的矿物相，并表现出与正长岩连续的主要元素和微量元素趋势。它们的地球化学特征包括大离子亲岩元素（如 Ba 和 Sr）的富集、高场强元素（如 Nb 和 Ta）和重稀土元素的贫化，以及小的负 Eu 异常，这与相关正长岩的特征也是一致的。此外，花岗岩及其附属矿物的初始 87Sr/86Sr 比值较高，εNd(t) 和 εHf(t)值较低，除了同位素富集程度稍低外，与正长岩相似。这些地球化学和同位素特征表明，博林川花岗岩是由正长岩岩浆经碱性长石、闪长石和磷灰石的分块结晶形成的，同时还加入了30%的幼壳衍生物质。我们的研究揭示了地幔衍生碱性岩浆的分化可生成铝质A型花岗岩的母岩。因此，地幔不仅为A型铝质花岗岩的形成提供热量，而且也可能是岩浆的主要来源。

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引用次数: 0

Constraints of in-situ elemental compositions and U–Pb ages of cassiterite on the origin of the Cretaceous Gejiu and Dulong tin deposits, SW China: Implications for the linkage of tin belts in SE Asia 锡石原位元素组成和U-Pb年龄对中国西南部白垩纪地久和独龙锡矿床成因的制约：对东南亚锡矿带联系的影响

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-10-10 DOI: 10.1016/j.lithos.2024.107832

Zhi Zhang , Jie-Hua Yang , Rui-Zhong Hu , Bin Fu , Qian Hu , Mei-Fu Zhou

The western Yunnan tin belts in SW China and the southern Myanmar tin belt in SE Asia are traditionally thought to be part of the SE Asian tin metallogenic province. However, the tectonic setting of the Youjiang tin belt in SW China and its genetic relationship to the other tin belts are poorly documented. In this belt, the giant Gejiu and Dulong tin deposits are typical of skarn-type deposits and both contain contact and distal skarn orebodies. Tin ores of distal orebodies in these two deposits are composed of cassiterite, sulfide and calcite. In both deposits, most cassiterite grains from these ores are rich in Fe and W and depleted in Nb and Ta. They have ²³⁸U/²⁰⁶Pb ages between 81.4 and 84.1 Ma, similar to hosting granitic plutons. Two generations of cassiterite with distinctly different microtextures and trace elemental compositions can be recognized. The first generation (Cst-I) is compositionally and texturally homogeneous, but the second generation (Cst-II) displays distinctly oscillatory zoning. Cst-II contains Nb, W, and U lower, and Fe, Ta, Zr and chalcophile elements (Ga, Ge, In, and Sb) higher than Cst-I. These textural and compositional variations reflect the potential involvement of meteoric water in the magmatic-hydrothermal system. In this system, ore-forming fluids were evolved to more alkaline and oxidized to facilitate the precipitation of cassiterite. Our study indicates that these two deposits in the Youjiang tin belt have mineralization styles similar to those in the adjacent western Yunnan and southern Myanmar tin belts and all these tin belts belong to the SE Asian metallogenic provinces. A westward-younging trend of tin mineralization in these three belts can be explained by the rollback of the subducted Neo-Tethyan oceanic slab. This setting is different from the one related to the subduction of the Paleo-Pacific plate.

中国西南部的云南西部锡矿带和东南亚的缅甸南部锡矿带历来被认为是东南亚锡金属成矿省的一部分。然而，中国西南部右江锡矿带的构造背景及其与其他锡矿带的成因关系却鲜有记载。在该锡矿带中，巨大的革九锡矿床和独龙锡矿床是典型的矽卡岩型矿床，均含有接触矽卡岩矿体和远端矽卡岩矿体。这两个矿床远端矿体的锡矿石由锡石、硫化物和方解石组成。在这两个矿床中，这些矿石中的锡石颗粒大多富含铁和钨，而铌和钽含量较低。它们的 238U/206Pb 年龄介于 81.4 至 84.1 Ma 之间，与寄主花岗岩柱岩相似。可以识别出两代锡石，它们的微观结构和微量元素组成截然不同。第一代（Cst-I）在成分和质地上是均匀的，但第二代（Cst-II）则显示出明显的振荡分带。与 Cst-I 相比，Cst-II 的 Nb、W 和 U 含量较低，而 Fe、Ta、Zr 和亲钙元素（Ga、Ge、In 和 Sb）含量较高。这些纹理和成分的变化反映了岩浆-热液系统中可能有陨石水的参与。在这一系统中，成矿流体被演化成碱性和氧化性更强的流体，从而促进了锡石的沉淀。我们的研究表明，右江锡矿带的这两个矿床与邻近的云南西部锡矿带和缅甸南部锡矿带的成矿方式相似，这些锡矿带都属于东南亚成矿省。这三个锡矿带的锡矿化呈西向年轻化趋势，可解释为新泰西洋板块俯冲后退。这种环境与古太平洋板块的俯冲环境不同。

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引用次数: 0

Petrogenesis of the Zenong Group volcanics in the central Lhasa subterrane, Tibet: Geodynamic implications of the scissor-like southward subduction of the Shiquanhe-Jiali Tethyan Ocean 西藏拉萨中部次地层泽农群火山岩成岩学说：狮泉河-嘉黎四叠纪剪状南向俯冲的地球动力学影响

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-10-10 DOI: 10.1016/j.lithos.2024.107831

Jia-jia Yu , Wei Chen , Ju-Xing Tang , Cheng-Yang Wang , Xu-Dong Ma , Qing-Ping Liu , Meng-Xiang Di , Chang Liu

The widespread Mesozoic volcanics in the central Lhasa subterrane have been a subject of debate concerning their genetic mechanisms. Leveraging geochronology, element geochemistry, and Hf isotopes, we have systematically investigated the origin and dynamic mechanisms of the Zenong Group volcanics in the Bengnazangbu and western Dangreyongcuo areas in the east-middle part of the central Lhasa subterrane. Comprising primarily of andesites, dacites, and rhyolites, the Zenong Group volcanics display distinct geochemical signatures. In the Dangreyongcuo and Bengnazangbu areas, the andesite, dacite, and rhyolites show medium to high-K calc-alkaline characteristics. These rocks share similarities in trace element distribution, exhibiting enrichment in Rb, U, Th, Pb, and K, but depletion in Nb, Ta, Ti, Ba, and Sr. These characteristics accord with the typical composition of arc volcanic rocks. Zircon UPb dating has revealed that the volcanic rocks in the Dangreyongcuo and Bengnazangbu areas have ages of 127–126 Ma and 112–103 Ma, respectively. Further, the distribution of zircon UPb ages suggests a west-east younging trend both in the Zenong Group and the Shiquanhe-Jiali suture zone. The ε_Hf(t) values of andesite, dacite, and rhyolite are all below the chondrite standard line, ranging from 0 to −15, and the crustal model ages range from 2.0 to 1.2 Ga. Our data, combined with the geological setting, whole-rock geochemistry, Hf isotopes, and geochronology, suggest that the Zenong Group volcanic rocks are the result of the mixing of mantle wedge melts formed by the subduction of the Shiquanhe-Jiali Ocean with the lower crust of the Lhasa terrane, and undergoing fractional crystallization of amphibole ad plagioclase. And we believe that the Shiquanhe-Jiali Ocean was sequentially closed from west to east in a scissor-like fashion during southward subduction.

拉萨中部次地层中生代火山岩分布广泛，其成因机制一直备受争议。我们利用地质年代学、元素地球化学和Hf同位素等手段，系统研究了拉萨中亚热带东-中段蚌那藏布和当惹雍错西部地区增荣组火山岩的成因和动力机制。增荣组火山岩主要由安山岩、白云岩和流纹岩组成，显示出独特的地球化学特征。在当惹雍错和蚌那藏布地区，安山岩、辉绿岩和流纹岩显示出中高K钙碱性特征。这些岩石的微量元素分布具有相似性，Rb、U、Th、Pb 和 K 元素富集，而 Nb、Ta、Ti、Ba 和 Sr 元素贫化。锆石UPb年代测定显示，当惹荣措和本那藏布地区火山岩的年龄分别为127-126Ma和112-103Ma。此外，锆石UPb年龄的分布表明，在禅农组和石泉河-嘉黎缝合带中，锆石UPb年龄呈西东向年轻化趋势。安山岩、闪长岩和流纹岩的εHf(t)值均低于软玉标准线，在0至-15之间，地壳模型年龄在2.0至1.2 Ga之间。我们的数据与地质环境、全岩地球化学、Hf同位素和地质年代相结合，表明禅农群火山岩是石泉河-嘉黎洋俯冲形成的地幔楔熔体与拉萨地层下部地壳混合，并经历闪长石和斜长石分块结晶的结果。我们认为，在向南俯冲的过程中，石泉河-嘉黎洋是自西向东以剪刀状的方式依次闭合的。

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引用次数: 0

Timing of the subduction initiation and ophiolite emplacement of the inner Tauride Ocean: Insight from the Pınarbaşı ophiolite in Central Türkiye 内金牛座洋的俯冲起始和蛇绿混杂岩形成的时间：从图尔基耶中部的皮纳尔巴希蛇绿混杂岩获得的启示

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-10-09 DOI: 10.1016/j.lithos.2024.107833

Rahmi Melih Çörtük , Ömer Faruk Çelik , Mutlu Özkan , Joshua H.F.L. Davies , Andrea Marzoli

Late Cretaceous ophiolites are widespread in southern Türkiye, including the Tauride Belt Ophiolites and the Central Anatolian Ophiolites. Here, we report new geological, geochemical, geochronological, and zircon isotopic data from ophiolitic rocks of the Pınarbaşı ophiolite (Eastern Tauride Belt). The Pınarbaşı ophiolite forms incomplete sequences, with its mantle section dominated by serpentinized harzburgite and chromitites, while the crustal section comprises ultramafic and mafic cumulates. Whole-rock and mineral chemistry data suggest a supra-subduction zone origin. LA-ICP-MS zircon U-Pb age of 88.2 ± 0.4 Ma (MSWD = 0.84) was obtained from a plagiogranite dyke cutting serpentinized peridotite of the Pınarbaşı ophiolite. Another, U-Pb zircon crystallization age of 96.8 ± 0.6 Ma (MSWD = 1.53) was obtained from a plagiogranite dyke within the mélange of the Pınarbaşı ophiolite. Hafnium isotope compositions of these zircons (εHf(t) = +26.4 to +3.1) suggest a depleted to slightly enriched mantle source. The formation ages of the crustal rocks (gabbro, plagiogranite, and dolerite) of the Cretaceous ophiolites in the Tauride Belt from this and previous ophiolite occurrences, suggest that supra-subduction zone ophiolites in the Inner Tauride Ocean formed during the period ∼101–87 Ma. On the other hand, the peak metamorphism of the metamorphic sole rocks is reported to have occurred around ∼104 Ma. According to all available petrogenetic and geochronological data, it is considered that the supra-subduction zone crust developed shortly (∼ 3–4 Myr) after the initiation of intra-oceanic subduction and this lasted ∼10–15 Myr.

晚白垩世蛇绿岩广泛分布于土耳其南部，包括陶里德带蛇绿岩和中安纳托利亚蛇绿岩。在此，我们报告了来自Pınarbaşı蛇绿混杂岩（东陶里德带）的新地质、地球化学、地质年代和锆石同位素数据。Pınarbaşı蛇绿混杂岩形成了不完整的序列，其地幔部分主要是蛇绿岩化的哈兹堡岩和铬铁矿，而地壳部分则由超基性岩和黑云母积岩组成。整块岩石和矿物化学数据表明其起源于超俯冲带。从切割 Pınarbaşı 蛇绿岩蛇绿岩化橄榄岩的斜长花岗岩岩体中获得的 LA-ICP-MS 锆石 U-Pb 年龄为 88.2 ± 0.4 Ma (MSWD = 0.84)。另一个U-Pb锆石结晶年龄为96.8 ± 0.6 Ma (MSWD = 1.53)，是从Pınarbaşı蛇绿混杂岩中的一个斜长花岗岩岩体中获得的。这些锆石的铪同位素组成（εHf(t) = +26.4 至 +3.1）表明其地幔来源从贫化到略微富化。金牛座带白垩世蛇绿岩的地壳岩石（辉长岩、长花岗岩和辉绿岩）的形成年龄，从这次和以前的蛇绿岩发生情况来看，表明内金牛座洋的超俯冲带蛇绿岩形成于101-87Ma之间。另一方面，据报道，变质底岩的变质高峰期约发生在 ∼104 Ma。根据现有的岩石成因学和地质年代学数据，认为超俯冲带地壳是在洋内俯冲开始后不久（3-4 Myr）形成的，并持续了 10-15 Myr。

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引用次数: 0

Constraints of upper crust magmatic processes on the formation of Saindak porphyry Cu deposit: Insights from mineral geochemistry 上地壳岩浆过程对赛因达克斑岩铜矿床形成的制约：矿物地球化学的启示

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-10-09 DOI: 10.1016/j.lithos.2024.107829

Lu Wang , Zi-xuan Wang , Yuan-chuan Zheng , Zeng-qian Hou , Zhu-sen Yang , Chang-da Wu , Xin Li

Upper crustal magmatic processes play a crucial role in linking the magmatic and hydrothermal systems of porphyry deposits, ultimately controlling the generation of ore-forming fluids. Understanding these processes within a magma chamber is essential for deciphering the formation of porphyry deposits. The Saindak deposit, a large porphyry Cu system in the western Chagai belt, features coeval ore-forming and barren magma pulses, providing key insights into the characterization of porphyry systems. In this study, detailed petrographic observations and geochemical analyses of amphibole, plagioclase, and apatite were conducted to unravel the magmatic evolution at Saindak. Based on textural relationships and crystallization sequences, three distinct populations of amphibole in the ore-forming magma were identified. These amphiboles record the entire fractional crystallization process of magma that initially emplaced at a depth of ∼5 km to the connected magma system at ∼2 km. The study of amphibole and apatite reveals that the fertile magma underwent large-scale fluid exsolution in an open system. The simultaneous and rapid depletion of Cu, Cl, S, and H₂O in the magma indicates that Cl and S were highly partitioned into the exsolved fluid phase. These elements formed complexes, which effectively concentrated metals in the fluid. Conversely, the barren magma was characterized by either low metal content or limited fluid exsolution within the magma chamber. Overall, we reconstruct the upper crustal magmatic processes at Saindak and conclude that efficient extraction of Cu through fluid exsolution is the key to porphyry deposit formation.

上地壳岩浆过程在连接斑岩矿床的岩浆和热液系统方面起着至关重要的作用，最终控制着成矿流体的生成。了解岩浆腔内的这些过程对于破解斑岩矿床的形成至关重要。Saindak 矿床是查盖带西部的一个大型斑岩铜矿床系统，其特征是矿石形成和贫瘠岩浆脉冲同时发生，这为斑岩系统的特征描述提供了重要启示。本研究对闪石、斜长石和磷灰石进行了详细的岩相观察和地球化学分析，以揭示赛因达克的岩浆演化过程。根据纹理关系和结晶序列，确定了成矿岩浆中三种不同的闪石群。这些闪石记录了岩浆从最初在 5 千米深处喷出到在 2 千米深处连接岩浆系统的整个分块结晶过程。对闪石和磷灰石的研究表明，肥沃的岩浆在一个开放系统中经历了大规模的流体溶解。岩浆中 Cu、Cl、S 和 H2O 的同时快速消耗表明，Cl 和 S 被高度分配到了外溶流体相中。这些元素形成了络合物，有效地浓缩了流体中的金属。相反，贫瘠岩浆的特点是金属含量低或岩浆腔内流体溶出有限。总之，我们重建了赛因达克的上地壳岩浆过程，并得出结论：通过流体溶出有效提取铜是斑岩矿床形成的关键。

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引用次数: 0

Spatio-temporal evolution of the Paleo-Tethys in western Yunnan: Insights from mafic rocks in the Lancang tectonic belt 云南西部古太古宙的时空演化：澜沧构造带岩浆岩的启示

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-10-05 DOI: 10.1016/j.lithos.2024.107830

Ya Cui , Yuejun Wang , Renjie Zhou , Yang Wang , Teresa Ubide , Xin Qian , Cheng Wang , Xin Wang

The Sanjiang orogenic belt in the southeastern Tibetan Plateau provides an excellent record of the Paleo-Tethys tectonic evolution. This study introduces new constraints on the spatio-temporal evolution of the Paleo-Tethys through zircon UPb ages, in-situ LuHf isotope data, and analyses of whole-rock major oxides, trace elements, and Sr-Nd-Pb isotopic compositions from Late Paleozoic mafic rocks in the Lancang tectonic belt. The mafic rocks from the Xiaoheijiang, Banpo, and Yakou areas were dated to approximately 281–267 Ma, 295–292 Ma, and 293–291 Ma, respectively. The Xiaoheijiang mafic rocks exhibit geochemical signatures resembling those of fore-arc basalt, characterized by low (La/Sm)_N, relatively flat rare earth element (REE)-normalized patterns, positive ε_Nd(t) (+5.6 to +10.1), and zircon in-situ ε_Hf(t) values (+10.0 to +14.9). These features indicate an origin from a depleted mantle source with minor contributions from slab-derived components. The Banpo and Yakou mafic rocks display geochemical affinities to back-arc basin basalt, similar to the Okinawa Trough back-arc basin basalt. Their ε_Nd(t) values range from +5.6 to +9.9 and ε_Hf(t) values from +9.5 to +15.0, suggesting derivation from a mantle wedge source modified by slab-derived fluids or melts. In combination with available geochronological data concerning the Paleo-Tethys evolution along the Lancang tectonic belt, our findings support the hypothesis that the slow-speed, low-angle subduction of the Paleo-Tethys Ocean led to the formation of a forearc accretionary complex. The slab-derived fluids metasomatized the mantle wedge as subduction depth and angle increased, facilitating the development of the Lincang arc magmatism and the opening of the Banpo-Yakou back-arc basin. Continuous subduction promoted slab retreat under gravitational forces, inducing the upwelling of depleted mantle and the forming of forearc magmas.

青藏高原东南部的三江造山带为古泰西构造演化提供了极好的记录。本研究通过对澜沧江造山带晚古生代岩浆岩的锆石UPb年龄、原位LuHf同位素数据以及全岩主要氧化物、微量元素和Sr-Nd-Pb同位素组成的分析，对古生代特提斯构造演化的时空关系提出了新的约束。小黑江、半坡和崖口地区岩浆岩的年代分别约为281-267Ma、295-292Ma和293-291Ma。小黑江岩浆岩的地球化学特征与前弧玄武岩相似，表现为低(La/Sm)N、相对平坦的稀土元素（REE）归一化模式、正εNd(t)值（+5.6至+10.1）和锆石原位εHf(t)值（+10.0至+14.9）。这些特征表明，它们的成因来自贫化地幔源，并有少量板块成因成分。Banpo和Yakou岩浆岩显示出与后弧盆玄武岩的地球化学亲缘关系，类似于冲绳海槽后弧盆玄武岩。它们的εNd(t)值在+5.6到+9.9之间，εHf(t)值在+9.5到+15.0之间，这表明它们来自经板块衍生流体或熔体修饰的地幔楔源。结合澜沧构造带沿线古特提斯演化的现有地质年代数据，我们的发现支持了古特提斯洋低速、低角度俯冲导致弧前增生复合体形成的假说。随着俯冲深度和角度的增加，板块衍生流体使地幔楔变质，促进了临沧弧岩浆活动的发展和半坡-雅口后弧盆地的形成。持续的俯冲促进了板块在重力作用下的后退，诱发了贫化地幔的上涌和前弧岩浆的形成。

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引用次数: 0

Supergene formation of sulfur-rich, tochilinite-bearing serpentinites in the Oman ophiolite 阿曼蛇绿岩中富含硫磺、含托起石的蛇绿岩的超成因形成

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-10-03 DOI: 10.1016/j.lithos.2024.107828

James Andrew Leong , Juan Carlos de Obeso , Thomas Sharp , Everett Shock , Peter Kelemen

Mass transfer processes between fluids and ultramafic rocks produce subsurface environments encompassing a wide range of redox conditions. A notable locality where an extensive range of redox conditions is observed in one location is Hole BA1B, a ∼ 400 m borehole drilled by the Oman Drilling Project. A sulfur-enriched serpentinite zone, containing up to 0.6 wt% S, occurs between shallow oxidized serpentinites (<30 m) and deep partially serpentinized harzburgite (>150 m). All three alteration zones are predominantly composed of serpentine. However, microanalysis of samples from the sulfur-enriched zone shows that mesh textures after olivine are composed of serpentine, brucite, and tochilinite mixtures, yielding optically black thin-section samples that characterize this sulfidic zone. It is proposed that sulfur accumulates in this zone via a process similar to those found in supergene ore deposits. Reaction-path models show that at shallow conditions open to atmospheric input, sulfur is mobilized via oxidative weathering of serpentinized dunite and harzburgite. Sulfate-bearing fluids percolate deeper and react with host rocks in a system closed to atmospheric input. As fluids become more reduced, dissolved sulfate is precipitated as sulfide minerals yielding rocks with ∼0.4 wt% S, like those observed in Hole BA1B. Despite enrichment of S in the sulfidic zone in Hole BA1B, Ni and Co contents are uniform throughout all three layers in the borehole. This is consistent with model results which show that Ni (and, by analogy, Co) is less mobile than S, and can be hosted in serpentine and NiFe alloys in addition to sulfides. The sulfur enrichment process may occur abiotically. However, sulfide enrichment via microbial reduction of sulfate and other sulfur species can also facilitate the formation of the sulfidic zone. Bioenergetic calculations show that abundant energy is available for sulfur reducing microbes, consistent with previous work demonstrating the presence of active, sulfate-reducing microorganisms in Hole BA1B and other nearby boreholes. This suggests that the observed sulfur enrichment is an ongoing process. Overall, this work shows that variable redox conditions are attained as fluids percolate and react with serpentinized ultramafic rocks at variable extents of interaction between aquifer fluids, host ultramafic rocks, and the atmosphere.

流体和超基性岩之间的传质过程产生了包含多种氧化还原条件的地下环境。阿曼钻探项目钻探的一个长约 400 米的钻孔 BA1B 是在同一地点观测到多种氧化还原条件的一个显著地点。在浅层氧化蛇绿岩（30 米）和深层部分蛇绿岩化的哈兹堡岩（150 米）之间有一个富含硫的蛇绿岩区，S 含量高达 0.6 wt%。这三个蚀变带都主要由蛇纹石组成。然而，对硫富集区样品的显微分析表明，橄榄石之后的网状纹理是由蛇纹石、青金石和托氏石混合物组成的，产生的光学黑色薄片样品是这一硫化物区的特征。据推测，硫在这一区域的积累过程与超生矿床中的过程类似。反应路径模型显示，在大气输入的浅层条件下，硫是通过蛇纹石化的云英岩和哈兹堡垒岩的氧化风化作用而被动员起来的。含硫流体渗入更深的地方，在一个封闭的大气输入系统中与主岩发生反应。随着流体变得更加还原，溶解的硫酸盐以硫化物矿物的形式沉淀下来，形成S含量在0.4 wt%以下的岩石，如在BA1B孔观察到的岩石。尽管BA1B钻孔的硫酸盐化带富含S，但钻孔中所有三层的Ni和Co含量是一致的。这与模型结果是一致的，模型结果表明，镍（以及类比的钴）的流动性比硫小，除了硫化物之外，还可能赋存于蛇纹石和镍铁合金中。硫的富集过程可能是非生物发生的。不过，通过微生物还原硫酸盐和其他硫种来富集硫化物，也可促进硫化物区的形成。生物能计算显示，硫还原微生物可以获得丰富的能量，这与之前的研究结果一致，即在 BA1B 孔和附近的其他钻孔中存在活跃的硫酸盐还原微生物。这表明观测到的硫富集是一个持续的过程。总之，这项工作表明，在含水层流体、寄主超基性岩和大气之间的相互作用程度不同的情况下，流体渗入并与蛇纹岩化超基性岩发生反应时，会产生不同的氧化还原条件。

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引用次数: 0

Metamorphism and geochronology of the Foping gneiss dome: Insights into Early Triassic collision of the Qinling Orogen, Central China 佛坪片麻岩穹隆的变质作用和地质年代：华中秦岭造山带早三叠世碰撞的启示

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-10-03 DOI: 10.1016/j.lithos.2024.107827

Jiali You, Zhao Yang, Longlong Gou, Yunpeng Dong, Xiaohui Shi, Dengfeng He

The Foping gneiss dome, which outcrops in the narrowest part of the Qinling Orogen, contains high-grade metamorphic rocks that record the collision between the North China Block (NCB) and South China Block (SCB). Herein, petrography, mineral chemistry, phase equilibria modeling and UPb geochronology are used to constrain the collision events responsible for the high-grade metamorphism and exhumation of the Foping gneiss dome. The pelitic and mafic granulites sampled from the dome reveal peak metamorphism at P/T conditions of 6.2–7.4 kbar/ 805–855 °C, and document clockwise P-T-t paths with retrograde metamorphism of amphibolite-facies at 3.4–4.7 kbar/ 605–715 °C. While the pelitic schist from the rim of this dome witnessed peak metamorphism at P/T conditions of 4.9–5.1 kbar/ 590–605 °C and retrograde metamorphism at 3.5–3.7 kbar/ 510–520 °C. UPb dating of zircon and monazite confirm ages of ∼247–240 Ma for peak metamorphism with granulite-facies, ages of ∼208–198 Ma for retrograde metamorphism. The two metamorphic stages may record the transition from crustal thickening to dome exhumation, and the age of peak metamorphism probably marks the timing of the collision between the NCB and SCB along the Qinling Orogen in the Early Triassic. The collision probably terminated in the Late Triassic. The new discovery of the Triassic metamorphic event in the Qinling, combined with previously reported collision event of the Dabie Orogen to the east, supports the idea that the continental collision between the NCB and SCB along the Qinling-Dabie Orogen was synchronous.

出露于秦岭造山带最狭窄处的佛坪片麻岩穹隆含有高品位变质岩，记录了华北地块（NCB）和华南地块（SCB）之间的碰撞。在这里，岩相学、矿物化学、相平衡模型和UPb地质年代学被用来约束造成佛坪片麻岩穹隆高品位变质和隆升的碰撞事件。从穹隆取样的辉长岩和黑云母花岗岩显示了在6.2-7.4千巴/805-855 °C的P-T-T条件下的峰值变质作用，并记录了顺时针P-T-T路径，以及在3.4-4.7千巴/605-715 °C的闪长岩类型逆变质作用。而该穹隆边缘的辉长岩片岩在4.9-5.1千巴/590-605 °C的P/T条件下发生了峰值变质作用，在3.5-3.7千巴/510-520 °C的条件下发生了逆变质作用。锆石和独居石的UPb年代测定证实，花岗岩变质峰值的年龄为247-240Ma，逆行变质的年龄为208-198Ma。这两个变质阶段可能记录了从地壳增厚到穹隆出露的过渡，而变质峰值的年龄可能标志着早三叠世秦岭造山带NCB和SCB碰撞的时间。碰撞可能在晚三叠世结束。秦岭三叠纪变质事件的新发现，结合之前报道的大别山以东的碰撞事件，支持了沿秦岭-大别山造山带的NCB和SCB大陆碰撞是同步进行的观点。

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引用次数: 0

The volcanic/plutonic ratio in space and time, on Earth and beyond; How efficiently do magmas reach the surface during planetary evolution? 地球及地球以外时空的火山/岩浆比例；岩浆在行星演化过程中到达地表的效率如何？

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-10-03 DOI: 10.1016/j.lithos.2024.107825

Olivier Bachmann , Christian Huber

With the recognition of multiple crustal cross sections on our planet, the advent of high-precision geochronology, and the ever-increasing application of geophysical imaging beneath volcanoes, we now know that volcanic rocks are the tip of a magmatic “heat”berg, overlying a significant igneous plumbing system that leaves many types of plutonic rocks in the crust. The ratio of volcanic to plutonic rocks in a given magmatic province (the V/P ratio) varies in space and in time as a function of several parameters controlled by the tectonic setting, geological age of the magmatic province, duration of magmatic activity, rheology of the crust, physical properties of the magma and state of the magma reservoirs. This contribution intends to explore these different parameters, in order to better constrain how the V/P ratios evolve in space and time in the course of planetary crust evolution. In particular, we stress that the efficiency of phase separation (in particular crystal / melt separation) in crustal magma reservoirs, fundamental to igneous differentiation and crust formation, is a key factor in controlling the V/P ratios. This efficiency, in turns, depends on parameters such as magma fluxes (“mantle productivity”) and chemical compositions (including volatile content), as well as the mechanical properties of the multi-phase magma and of its the crustal container. The emergence of thermo-mechanical modeling tools coupling the magma reservoir with its surrounding wall-rocks is paving the way to a more quantitative understanding of the fundamental processes that control the fate of magmas traversing through planetary crusts.

随着人们对地球上多个地壳横断面的认识、高精度地质年代学的出现以及火山下地球物理成像技术的不断应用，我们现在知道，火山岩是岩浆 "热 "堡的一角，其上覆盖着一个重要的火成岩管道系统，在地壳中留下了多种类型的柱状岩石。特定岩浆岩带中火山岩与柱状岩的比例（V/P 比例）在空间和时间上都有变化，这是受构造环境、岩浆岩带的地质年代、岩浆活动持续时间、地壳流变学、岩浆物理性质和岩浆储层状态等参数控制的函数。本文旨在探讨这些不同的参数，以便更好地确定 V/P 比值在行星地壳演化过程中如何在空间和时间上演变。我们特别强调，地壳岩浆库中相分离（尤其是晶体/熔体分离）的效率是控制 V/P 比值的关键因素，是火成岩分异和地壳形成的基础。这种效率反过来又取决于岩浆通量（"地幔生产力"）和化学成分（包括挥发物含量）等参数，以及多相岩浆及其地壳容器的机械特性。将岩浆库与其周围壁岩结合起来的热力学建模工具的出现，为更定量地了解控制岩浆穿越行星地壳的命运的基本过程铺平了道路。

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引用次数: 0

New constraints on the tectonic history of the basement of the Western Cordillera and coastal forearc of Ecuador 厄瓜多尔西科迪勒拉山系和沿海前弧区基底构造史的新制约因素

IF 2.9 2区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Lithos

Pub Date : 2024-10-01 DOI: 10.1016/j.lithos.2024.107821

Richard Spikings , Sebastian Betancur , Cristian Vallejo , Massimo Chiaradia , Alexey Ulianov , Antoine de Haller , Stephen Forti , Wilfried Winkler , Bernardo Beate

The Western Cordillera and forearc of the Northern Andes (north of 5° S) are constructed from allochthonous terranes floored by oceanic crust. A paucity of accurate geochronological data from the ultramafic and mafic basement sequences of the Western Cordillera and Coastal region of Ecuador has lead to distinct differences in published tectonic models, with different allochthonous units and contrasting timelines of accretion and collision. We present new zircon UPb and groundmass ⁴⁰Ar/³⁹Ar dates of the basement units, which have been combined with new whole rock geochemical and isotopic data to constrain their tectonic histories prior to and during their accretion to South America. Ultramafic and mafic rocks with oceanic plateau affinities can be divided into two plateau sequences, where an inboard, younger plateau (85–92 Ma; Pallatanga Block) is sutured against South America, and was modified by a pre-accretionary intra-oceanic arc (Pilatón-Pujilí arc) that was terminated by the accretionary process. An older, outboard oceanic plateau sequence (∼120 Ma) forms the basement to a series of coastal blocks within the present forearc (Piñon, San Lorenzo, Pedernales and probably the Esmeraldas blocks). The outer plateau also hosts a pre-accretionary intra-oceanic arc (Pascuales – San Lorenzo arc), which remained active during and post-accretion (San Lorenzo – Rio Cala arc). Coeval changes in palaeomagnetic declination, the onset of rapid exhumation (>1 km/My) of the Early Cretaecous continental margin and sedimentation within the newly formed retro-arc foreland basin and foreland region supports a model where both oceanic plateau sequences accreted to South America in a single accretion event at 75–70 Ma. Thus, it is likely that the accreted oceanic plateau was composite, and included both the younger and older plateau sequences prior to accretion. We test an alternative model where the inner (younger) and outer (older) oceanic plateaus accrete in sequence, although this fails to account for the timing of block rotations in the forearc.

北安第斯山脉（南纬 5°以北）的西科迪勒拉山系和前弧是由大洋地壳覆盖的同生陆相构造而成的。厄瓜多尔西科迪勒拉山系和沿海地区超基性岩和基性岩基底序列缺乏准确的地质年代数据，导致已公布的构造模型存在明显差异，不同的同生单元以及增生和碰撞的时间线形成鲜明对比。我们展示了基底单元新的锆石 UPb 和地层 40Ar/39Ar 时间，并结合新的全岩地球化学和同位素数据，以确定它们在向南美洲增生之前和期间的构造历史。具有大洋高原亲缘关系的超基性岩和岩浆岩可分为两个高原序列，其中一个内侧、较年轻的高原（85-92 Ma；Pallatanga 块）与南美洲缝合，并被增生前的大洋内部弧（Pilatón-Pujilí 弧）所改变，该弧被增生过程所终止。一个更古老的外侧大洋高原序列（120Ma∼）构成了目前前弧内一系列海岸区块（皮尼翁区块、圣洛伦索区块、佩德纳莱斯区块，可能还有埃斯梅拉达斯区块）的基底。外侧高原上还有一个火山喷发前的洋内弧（帕斯瓜莱斯--圣洛伦索弧），在火山喷发期间和喷发后（圣洛伦索--里奥卡拉弧）仍很活跃。古地磁偏角的共时变化、早克里特大陆边缘开始快速掘起（>1 km/My）以及新形成的弧后前陆盆地和前陆区域内的沉积作用都支持这样一个模型，即在 75-70 Ma 的一次增生事件中，两个大洋高原序列都向南美洲增生。因此，吸积的大洋高原很可能是复合的，在吸积之前既包括较年轻的高原序列，也包括较古老的高原序列。我们测试了另一个模型，即内部（较年轻的）和外部（较老的）大洋高原依次增生，尽管这无法解释前弧区块旋转的时间。

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