Pub Date : 2024-12-13DOI: 10.1016/j.chemgeo.2024.122563
Chen Chen, Christina Yan Wang, Saihong Yang, İbrahim Uysal
Platinum-group minerals (PGMs) in podiform chromitites usually occur in the interior and/or edge of chromite. However, the origin of PGMs in podiform chromitites has long been a matter of debate. Here we examined sub-micro to nanoscale textural features, morphologies, and compositions of PGMs from the disseminated, banded, massive and nodular chromitites in the Kızıldağ ophiolite in southern Türkiye, and found both primary and secondary PGMs. The aim of this study is to reveal the transformation processes from primary to secondary PGMs, thereby taking a thorough examination of the origin of these PGMs. Primary PGMs include laurite and Os-Ir alloy, which are prevalent in all samples. They are typically enclosed within or located at the edge of chromite, and formed either prior to or contemporaneously with the crystallization of chromite at temperature of 1100–1200 °C and logƒS<ce:inf loc="post">2</ce:inf> values of -2 to -1. In contrast, PGE-bearing pentlandite are commonly present at the edge of chromite, corresponding to an increase of <ce:italic>f</ce:italic>S<ce:inf loc="post">2</ce:inf> with the progressive crystallization of chromite. These primary PGMs and PGE-bearing pentlandite in the intergranular space of chromite are susceptible to alter and transform into secondary PGMs and base metal mineral assemblages, which include Os-Ru nanophases (Os-Ru nanoparticle and OsRu<ce:inf loc="post">3</ce:inf> nanoalloy) + awaruite (FeNi<ce:inf loc="post">3</ce:inf>) + trevorite (Fe<ce:inf loc="post">2</ce:inf>NiO<ce:inf loc="post">4</ce:inf>) in nodular chromitite, Os-rich laurite + Os-Ir(Ru) alloy/oxide + pentlandite + millerite (NiS) in banded and massive chromitite, and Ru(Ir) oxide + heazlewoodite (Ni<ce:inf loc="post">3</ce:inf>S<ce:inf loc="post">2</ce:inf>) in disseminated chromitite. The development of these diverse assemblages can be attributed to the degrees of serpentinization of chromitites. The nodular chromitite underwent weak serpentinization and had low water/rock ratios (<∼1), <ce:italic>f</ce:italic>S<ce:inf loc="post">2</ce:inf> and <ce:italic>f</ce:italic>O<ce:inf loc="post">2</ce:inf>, leading to the conversion of IPGE (Os, Ir and Ru)-bearing pentlandite into Os-Ru nanoparticle- and OsRu<ce:inf loc="post">3</ce:inf> nanoalloy-bearing awaruite. The massive and disseminated chromitites had high water/rock ratios and high <ce:italic>f</ce:italic>S<ce:inf loc="post">2</ce:inf> and <ce:italic>f</ce:italic>O<ce:inf loc="post">2</ce:inf> relative to those of the nodular chromitite during serpentinization, and consequently the corresponding pentlandite was transformed into heazlewoodite and/or millerite associated with S loss. Meanwhile, Ir, Os and possibly Ru were released from laurite to form Os-Ir(Ru) alloy/oxide at the edge of laurite. Our observation highlights that primary PGMs and pentlandite in the chromitites of the Kızıldağ ophiolite have been modified under different physical-chemical conditions during serpentinization, resu
{"title":"Hydrothermal origin of platinum-group minerals during serpentinization of the podiform chromitites from the Kızıldağ ophiolite in southern Türkiye","authors":"Chen Chen, Christina Yan Wang, Saihong Yang, İbrahim Uysal","doi":"10.1016/j.chemgeo.2024.122563","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2024.122563","url":null,"abstract":"Platinum-group minerals (PGMs) in podiform chromitites usually occur in the interior and/or edge of chromite. However, the origin of PGMs in podiform chromitites has long been a matter of debate. Here we examined sub-micro to nanoscale textural features, morphologies, and compositions of PGMs from the disseminated, banded, massive and nodular chromitites in the Kızıldağ ophiolite in southern Türkiye, and found both primary and secondary PGMs. The aim of this study is to reveal the transformation processes from primary to secondary PGMs, thereby taking a thorough examination of the origin of these PGMs. Primary PGMs include laurite and Os-Ir alloy, which are prevalent in all samples. They are typically enclosed within or located at the edge of chromite, and formed either prior to or contemporaneously with the crystallization of chromite at temperature of 1100–1200 °C and logƒS<ce:inf loc=\"post\">2</ce:inf> values of -2 to -1. In contrast, PGE-bearing pentlandite are commonly present at the edge of chromite, corresponding to an increase of <ce:italic>f</ce:italic>S<ce:inf loc=\"post\">2</ce:inf> with the progressive crystallization of chromite. These primary PGMs and PGE-bearing pentlandite in the intergranular space of chromite are susceptible to alter and transform into secondary PGMs and base metal mineral assemblages, which include Os-Ru nanophases (Os-Ru nanoparticle and OsRu<ce:inf loc=\"post\">3</ce:inf> nanoalloy) + awaruite (FeNi<ce:inf loc=\"post\">3</ce:inf>) + trevorite (Fe<ce:inf loc=\"post\">2</ce:inf>NiO<ce:inf loc=\"post\">4</ce:inf>) in nodular chromitite, Os-rich laurite + Os-Ir(Ru) alloy/oxide + pentlandite + millerite (NiS) in banded and massive chromitite, and Ru(Ir) oxide + heazlewoodite (Ni<ce:inf loc=\"post\">3</ce:inf>S<ce:inf loc=\"post\">2</ce:inf>) in disseminated chromitite. The development of these diverse assemblages can be attributed to the degrees of serpentinization of chromitites. The nodular chromitite underwent weak serpentinization and had low water/rock ratios (<∼1), <ce:italic>f</ce:italic>S<ce:inf loc=\"post\">2</ce:inf> and <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf>, leading to the conversion of IPGE (Os, Ir and Ru)-bearing pentlandite into Os-Ru nanoparticle- and OsRu<ce:inf loc=\"post\">3</ce:inf> nanoalloy-bearing awaruite. The massive and disseminated chromitites had high water/rock ratios and high <ce:italic>f</ce:italic>S<ce:inf loc=\"post\">2</ce:inf> and <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> relative to those of the nodular chromitite during serpentinization, and consequently the corresponding pentlandite was transformed into heazlewoodite and/or millerite associated with S loss. Meanwhile, Ir, Os and possibly Ru were released from laurite to form Os-Ir(Ru) alloy/oxide at the edge of laurite. Our observation highlights that primary PGMs and pentlandite in the chromitites of the Kızıldağ ophiolite have been modified under different physical-chemical conditions during serpentinization, resu","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"99 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142857929","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-12DOI: 10.1016/j.chemgeo.2024.122562
Tao Luo, Mufei Li, Xiaodong Deng, Jiarun Tu, Hongtao Shen, Tom Kapitany, Beining Hu, Wen Zhang, Zhaochu Hu
Allanite, a member of the epidote supergroup, is widely distributed across various rock types. The U-Th-Pb geochronology of allanite can provide critical time constraints for investigating igneous rock formation, metamorphic events, and hydrothermal mineralization processes. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) offers high spatial resolution for in-situ U-Th-Pb dating of allanite with the advantage of avoiding compositional zoning and inclusions. However, current allanite reference materials for LA-ICP-MS U-Th-Pb dating often contain high and variable common Pb contents, limiting their effectiveness as primary calibration standards. This study introduces two new allanite reference materials (AMK and ASP) with low common Pb content. Allanite AMK and ASP exhibit f206 values (the proportion of common 206Pb in the total measured 206Pb) below 0.8 % and 5.5 %, respectively. AMK contains 140 ± 41.9 μg g−1 (1σ) of U and 306 ± 145 μg g−1 (1σ) of Th, while ASP contains 261 ± 143 μg g−1 (1σ) of U and 130 ± 102 μg g−1 (1σ) of Th. ID-TIMS analysis yielded a weighted mean 207Pb/206Pb age of 1533.6 ± 1.9 Ma (2σ, MSWD = 5.1, n = 6) for AMK and a weighted mean 206Pb/238U age of 335.86 ± 0.52 Ma (2σ, MSWD = 5.9, n = 8) for ASP. To mitigate the impact of common Pb in primary reference materials, two 207Pb method-based calibrating procedures (VizualAge_UcomPbine software correction and a ‘two-step’ calibration strategy) were performed to the commonly used Tara allanite standard. While accurate allanite UPb ages can be obtained with both calibration strategies, analytical precision was reduced due to uncertainty propagated from the common Pb correction. Furthermore, a simple and robust allanite LA-ICP-MS U-Th-Pb dating method was established by calibrating against allanite AMK without prior common Pb correction. We propose allanite AMK as an effective primary reference material for LA-ICP-MS U-Th-Pb dating, while ASP serves as a suitable secondary reference material due to its very low common Pb content. Our results confirm no significant matrix effects during LA-ICP-MS analyses of allanites across a wide range of Th contents (from 0.03 to 21,900 μg g−1) and FeO content variations (from 12.8 to 14.6 wt%).
褐帘石是绿帘石超群的一员，广泛分布于各种岩石类型中。allanite的U-Th-Pb年代学可以为研究火成岩形成、变质事件和热液成矿过程提供关键的时间约束。激光烧蚀电感耦合等离子体质谱（LA-ICP-MS）为allanite的原位U-Th-Pb定年提供了高空间分辨率，避免了成分分带和包裹体。然而，目前用于LA-ICP-MS U-Th-Pb定年的allanite参考物质通常含有高且多变的普通Pb含量，限制了其作为主要校准标准的有效性。本研究介绍了两种常见铅含量较低的allanite标准物质AMK和ASP。Allanite AMK和ASP的f206值（普通206Pb占总测量206Pb的比例）分别低于0.8%和5.5%。AMK含有140±41.9 μg−1 （1σ）的U和306±145 μg−1 （1σ）的Th， ASP含有261±143 μg−1 （1σ）的U和130±102 μg−1 （1σ）的Th。ID-TIMS分析结果显示，AMK的207Pb/206Pb年龄加权平均值为1533.6±1.9 Ma (2σ, MSWD = 5.1, n = 6)， ASP的206Pb/238U年龄加权平均值为335.86±0.52 Ma （2σ, MSWD = 5.9, n = 8）。为了减轻主要参考物质中常见Pb的影响，对常用的Tara allanite标准品进行了两种基于207Pb方法的校准程序（vizualage_ucompine软件校正和“两步”校准策略）。虽然两种校准策略都可以获得准确的蓝纹岩UPb年龄，但由于普通Pb校正传播的不确定性，降低了分析精度。此外，建立了一种简单可靠的LA-ICP-MS U-Th-Pb定年方法，该方法通过对allanite AMK进行校准而无需事先进行常见的Pb校正。我们建议allanite AMK作为LA-ICP-MS U-Th-Pb定年的有效主要参考物质，而ASP由于其常见的Pb含量非常低，可以作为合适的次级参考物质。我们的研究结果证实，在LA-ICP-MS分析中，在广泛的Th含量（0.03至21,900 μg−1）和FeO含量（12.8至14.6 wt%）变化范围内，allanites没有明显的基质效应。
{"title":"Allanite U-Th-Pb geochronology by laser ablation inductively coupled plasma mass spectrometry: Evaluation and development of reference materials with low common Pb","authors":"Tao Luo, Mufei Li, Xiaodong Deng, Jiarun Tu, Hongtao Shen, Tom Kapitany, Beining Hu, Wen Zhang, Zhaochu Hu","doi":"10.1016/j.chemgeo.2024.122562","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2024.122562","url":null,"abstract":"Allanite, a member of the epidote supergroup, is widely distributed across various rock types. The U-Th-Pb geochronology of allanite can provide critical time constraints for investigating igneous rock formation, metamorphic events, and hydrothermal mineralization processes. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) offers high spatial resolution for <ce:italic>in-situ</ce:italic> U-Th-Pb dating of allanite with the advantage of avoiding compositional zoning and inclusions. However, current allanite reference materials for LA-ICP-MS U-Th-Pb dating often contain high and variable common Pb contents, limiting their effectiveness as primary calibration standards. This study introduces two new allanite reference materials (AMK and ASP) with low common Pb content. Allanite AMK and ASP exhibit <ce:italic>f</ce:italic><ce:inf loc=\"post\"><ce:italic>206</ce:italic></ce:inf> values (the proportion of common <ce:sup loc=\"post\">206</ce:sup>Pb in the total measured <ce:sup loc=\"post\">206</ce:sup>Pb) below 0.8 % and 5.5 %, respectively. AMK contains 140 ± 41.9 μg g<ce:sup loc=\"post\">−1</ce:sup> (1σ) of U and 306 ± 145 μg g<ce:sup loc=\"post\">−1</ce:sup> (1σ) of Th, while ASP contains 261 ± 143 μg g<ce:sup loc=\"post\">−1</ce:sup> (1σ) of U and 130 ± 102 μg g<ce:sup loc=\"post\">−1</ce:sup> (1σ) of Th. ID-TIMS analysis yielded a weighted mean <ce:sup loc=\"post\">207</ce:sup>Pb/<ce:sup loc=\"post\">206</ce:sup>Pb age of 1533.6 ± 1.9 Ma (2σ, MSWD = 5.1, <ce:italic>n</ce:italic> = 6) for AMK and a weighted mean <ce:sup loc=\"post\">206</ce:sup>Pb/<ce:sup loc=\"post\">238</ce:sup>U age of 335.86 ± 0.52 Ma (2σ, MSWD = 5.9, <ce:italic>n</ce:italic> = 8) for ASP. To mitigate the impact of common Pb in primary reference materials, two <ce:sup loc=\"post\">207</ce:sup>Pb method-based calibrating procedures (VizualAge_UcomPbine software correction and a ‘two-step’ calibration strategy) were performed to the commonly used Tara allanite standard. While accurate allanite U<ce:glyph name=\"sbnd\"></ce:glyph>Pb ages can be obtained with both calibration strategies, analytical precision was reduced due to uncertainty propagated from the common Pb correction. Furthermore, a simple and robust allanite LA-ICP-MS U-Th-Pb dating method was established by calibrating against allanite AMK without prior common Pb correction. We propose allanite AMK as an effective primary reference material for LA-ICP-MS U-Th-Pb dating, while ASP serves as a suitable secondary reference material due to its very low common Pb content. Our results confirm no significant matrix effects during LA-ICP-MS analyses of allanites across a wide range of Th contents (from 0.03 to 21,900 μg g<ce:sup loc=\"post\">−1</ce:sup>) and FeO content variations (from 12.8 to 14.6 wt%).","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"115 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142912324","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
To interpret data collected from high-pressure (P)–temperature (T) experiments simulating geological processes, pressure information during these experiments is crucial. Traditionally, the Raman shifts of the quartz 464-cm−1 band are commonly used as a hydrostatic-pressure calibrant in such experiments, particularly in those performed using hydrothermal diamond-anvil cells (HDACs). In this study, we conducted experiments using HDAC and a Raman spectrometer to investigate the sensitivity of the quartz 128-cm−1 Raman band to changes in P and T. We found that the Raman shift of this band exhibits higher sensitivity to changes in P and T than the 464-cm−1 band at Ts above 200 °C. Changes in the Raman shift of the 128-cm−1 band with Ps and Ts are 9–16 cm−1/GPa and ~ (50–40) × 10−3 cm−1/°C, respectively, at 200–700 °C and < 1.0 GPa; the corresponding values for the 464-cm−1 band are ~9 cm−1/GPa and ~14 × 10−3 cm−1/°C, respectively. The experimental data of Ps, Ts, and the Raman shifts of the quartz 128 cm−1 band relative to that at 0.1 MPa and 23 °C (∆ω128) were fitted into an equation to express their relation:
{"title":"Pressure sensor based on the Raman shift of the 128-cm−1 band of quartz for pressure measurements in hydrothermal diamond-anvil cells","authors":"Jiankang Li, I-Ming Chou, Xian Wang, Yongchao Liu, Ziheng Han, Jie Gao","doi":"10.1016/j.chemgeo.2024.122558","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2024.122558","url":null,"abstract":"To interpret data collected from high-pressure (<ce:italic>P</ce:italic>)–temperature (<ce:italic>T</ce:italic>) experiments simulating geological processes, pressure information during these experiments is crucial. Traditionally, the Raman shifts of the quartz 464-cm<ce:sup loc=\"post\">−1</ce:sup> band are commonly used as a hydrostatic-pressure calibrant in such experiments, particularly in those performed using hydrothermal diamond-anvil cells (HDACs). In this study, we conducted experiments using HDAC and a Raman spectrometer to investigate the sensitivity of the quartz 128-cm<ce:sup loc=\"post\">−1</ce:sup> Raman band to changes in <ce:italic>P</ce:italic> and <ce:italic>T</ce:italic>. We found that the Raman shift of this band exhibits higher sensitivity to changes in <ce:italic>P</ce:italic> and <ce:italic>T</ce:italic> than the 464-cm<ce:sup loc=\"post\">−1</ce:sup> band at <ce:italic>T</ce:italic>s above 200 °C. Changes in the Raman shift of the 128-cm<ce:sup loc=\"post\">−1</ce:sup> band with <ce:italic>P</ce:italic>s and <ce:italic>T</ce:italic>s are 9–16 cm<ce:sup loc=\"post\">−1</ce:sup>/GPa and ~ (50–40) × 10<ce:sup loc=\"post\">−3</ce:sup> cm<ce:sup loc=\"post\">−1</ce:sup>/°C, respectively, at 200–700 °C and < 1.0 GPa; the corresponding values for the 464-cm<ce:sup loc=\"post\">−1</ce:sup> band are ~9 cm<ce:sup loc=\"post\">−1</ce:sup>/GPa and ~14 × 10<ce:sup loc=\"post\">−3</ce:sup> cm<ce:sup loc=\"post\">−1</ce:sup>/°C, respectively. The experimental data of <ce:italic>P</ce:italic>s, <ce:italic>T</ce:italic>s, and the Raman shifts of the quartz 128 cm<ce:sup loc=\"post\">−1</ce:sup> band relative to that at 0.1 MPa and 23 °C (<ce:italic>∆ω</ce:italic><ce:inf loc=\"post\">128</ce:inf>) were fitted into an equation to express their relation:","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"90 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858004","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-10DOI: 10.1016/j.chemgeo.2024.122560
Xian Chen, Zhengzhe Fan
The role of tectonic setting in new continental crust formation remains enigmatic. A key to solve this issue is to determine which tectonic setting(s) are involved in the generation of new continental crust through time. Modern mantle-derived magmas that formed in intracontinental extension settings (U/Pb = ∼0.28–0.37) and in subduction settings (U/Pb = ∼0.1–0.16) have distinct mean U/Pb ratios. When shifting from subduction to intracontinental extension settings, the mean U/Pb ratios of new crust should define an increasing trend with time, whereas a decreasing trend will be observed when the converse transition is observed. Here we calculate U/Pb ratios of new crust [(U/Pb)jc] of the Songliao Block from East Asia to determine the tectonic settings of new crust formation. Our results show that (U/Pb)jc ratios have a decreasing trend from ∼1.55 to ∼1.2 Ga, followed by an increasing trend from ∼1.2 to ∼0.8 Ga, and changed to a decreasing trend again between ∼0.8 and ∼ 0.6 Ga. This implies that new crust formation of the microcontinent in a subduction setting during the middle-late Mesoproterozoic and the middle-late Neoproterozoic, however, in an intracontinental extension setting in the late Mesoproterozoic-early Neoproterozoic. Our method may provide a potential avenue to explore the regimes of new continental crust formation.
{"title":"Evaluating the role of tectonic setting in new continental crust formation by U/Pb ratios","authors":"Xian Chen, Zhengzhe Fan","doi":"10.1016/j.chemgeo.2024.122560","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2024.122560","url":null,"abstract":"The role of tectonic setting in new continental crust formation remains enigmatic. A key to solve this issue is to determine which tectonic setting(s) are involved in the generation of new continental crust through time. Modern mantle-derived magmas that formed in intracontinental extension settings (U/Pb = ∼0.28–0.37) and in subduction settings (U/Pb = ∼0.1–0.16) have distinct mean U/Pb ratios. When shifting from subduction to intracontinental extension settings, the mean U/Pb ratios of new crust should define an increasing trend with time, whereas a decreasing trend will be observed when the converse transition is observed. Here we calculate U/Pb ratios of new crust [(U/Pb)<ce:inf loc=\"post\">jc</ce:inf>] of the Songliao Block from East Asia to determine the tectonic settings of new crust formation. Our results show that (U/Pb)<ce:inf loc=\"post\">jc</ce:inf> ratios have a decreasing trend from ∼1.55 to ∼1.2 Ga, followed by an increasing trend from ∼1.2 to ∼0.8 Ga, and changed to a decreasing trend again between ∼0.8 and ∼ 0.6 Ga. This implies that new crust formation of the microcontinent in a subduction setting during the middle-late Mesoproterozoic and the middle-late Neoproterozoic, however, in an intracontinental extension setting in the late Mesoproterozoic-early Neoproterozoic. Our method may provide a potential avenue to explore the regimes of new continental crust formation.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"201 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858008","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-10DOI: 10.1016/j.chemgeo.2024.122561
Michele Cassetta, Emanuele De Bona, Alessia Sambugaro, Francesco Enrichi, Nicola Daldosso, Beatrice Giannetta, Claudio Zaccone, Mattia Biesuz, Vincenzo M. Sglavo, Renat Almeev, Luca Nodari, Daniele Giordano, Gino Mariotto
The incorporation of iron into peralkaline silicate glasses significantly impacts their structural and thermal properties. Here we investigate how addition of iron influences the network connectivity (short- and medium-range order) and glass transition temperature (Tg) with particular regard to the iron speciation and the Fe2+ and Fe3+ coordination state. We also found a sort of tipping point in iron concentration beyond which the short-range structures evolve linearly with density while the medium-range structure deviates from linearity. This behavior seems related to a re-enrichment of tetrahedral units triggered by iron self-compensation effect explaining the observed jump in Tg.
{"title":"Fe-dependent structural evolution of peralkaline soda aluminosilicate glasses: Iron speciation vs. glass transition","authors":"Michele Cassetta, Emanuele De Bona, Alessia Sambugaro, Francesco Enrichi, Nicola Daldosso, Beatrice Giannetta, Claudio Zaccone, Mattia Biesuz, Vincenzo M. Sglavo, Renat Almeev, Luca Nodari, Daniele Giordano, Gino Mariotto","doi":"10.1016/j.chemgeo.2024.122561","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2024.122561","url":null,"abstract":"The incorporation of iron into peralkaline silicate glasses significantly impacts their structural and thermal properties. Here we investigate how addition of iron influences the network connectivity (short- and medium-range order) and glass transition temperature (<ce:italic>T</ce:italic><ce:inf loc=\"post\"><ce:italic>g</ce:italic></ce:inf>) with particular regard to the iron speciation and the Fe<ce:sup loc=\"post\">2+</ce:sup> and Fe<ce:sup loc=\"post\">3+</ce:sup> coordination state. We also found a sort of tipping point in iron concentration beyond which the short-range structures evolve linearly with density while the medium-range structure deviates from linearity. This behavior seems related to a re-enrichment of tetrahedral units triggered by iron self-compensation effect explaining the observed jump in <ce:italic>T</ce:italic><ce:inf loc=\"post\"><ce:italic>g</ce:italic></ce:inf>.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"23 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858003","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Sandium (Sc) has gained strategic importance due to its diverse applications. Magmatic ultramafic-hosted deposits are emerging as significant Sc reservoirs, not only for their direct reserves but also as precursors for laterite-hosted Sc deposits. However, the processes controlling Sc enrichment in magmatic systems remain poorly understood. This study reveals the discovery of a potentially significant Sc mineralization within an ultramafic complex of the Shangzhuang P–REE deposit, situated in the Lajishan region of western China. The ultramafic complex comprises fluorapatite-rich biotite clinopyroxenite and calcite-amphibole-K-feldspar-rich clinopyroxenite hosted in biotite clinopyroxenite. Whole-rock concentrations of Sc range from 35.9 to 134 ppm in these three rocks mentioned, while clinopyroxenes in the complex exhibit Sc concentrations ranging from 56 to 203 ppm. Zircon U<ce:glyph name="sbnd"></ce:glyph>Pb dating on three ultramafic clinopyroxenites yield consistent crystallization ages of 465 ± 2 Ma, indicating an Ordovician magmatic and Sc mineralization event coinciding with the subduction stage of the Proto-Tethys Ocean beneath the central Qilian block. Field observations, consistent ages, narrow range of Hf and Sr isotope data (zircon ε<ce:inf loc="post">Hf</ce:inf>(t): +3.2 − +13.5; clinopyroxene <ce:sup loc="post">87</ce:sup>Sr/<ce:sup loc="post">86</ce:sup>Sr: 0.704534–0.705715), and decreasing Mg<ce:sup loc="post">#</ce:sup> trend observed in both clinopyroxene-bearing whole-rock and clinopyroxene single-grain samples from the three ultramafic rocks suggest a common magmatic origin with varying degrees of fractional crystallization and crystal accumulation within an evolved magmatic system. The parent magma likely originated from a potassium-Sc-REE-rich basaltic composition. This magma was primarily sourced from carbonated phlogopite-garnet lherzolite lithospheric mantle, but had been modified by carbonate-rich fluids derived from subducted oceanic sediments during the subduction of the Proto-Tethys Ocean. The comprehension of multistage growth processes in clinopyroxene effectively signifies the extent of magmatic differentiation and points to the involvement of magma sources in the formation of Sc deposits. Significant fluctuations of Sc concentration within clinopyroxene can be attributed to variable magma compositions. Enrichment of phosphate and fluorine effectively promotes Sc migration during magma evolution, while partition coefficient of Sc into clinopyroxene may be significantly higher in a P-F-rich magma, which causes Sc to concentrate in the apatite-rich biotite clinopyroxenite. The relatively high amount of Sc in the parent magma may be related to its initial enrichment in the carbonated fertile mantle. These compositions likely result from different amounts of phosphate and fluorine in the subduction-related fluid percolating through ultramafic mantle rocks. This study significantly advances our understanding of intric
{"title":"Scandium mineralization during ultramafic-mafic magmatism in the subduction zone","authors":"Xin Chen, Hans-Peter Schertl, Junaid Khan, Pengjie Cai, Dongyang Lian, Jinshou Wang, Chengtao Yu, Hao Lin, Xiaojia Jiang","doi":"10.1016/j.chemgeo.2024.122556","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2024.122556","url":null,"abstract":"Sandium (Sc) has gained strategic importance due to its diverse applications. Magmatic ultramafic-hosted deposits are emerging as significant Sc reservoirs, not only for their direct reserves but also as precursors for laterite-hosted Sc deposits. However, the processes controlling Sc enrichment in magmatic systems remain poorly understood. This study reveals the discovery of a potentially significant Sc mineralization within an ultramafic complex of the Shangzhuang P–REE deposit, situated in the Lajishan region of western China. The ultramafic complex comprises fluorapatite-rich biotite clinopyroxenite and calcite-amphibole-K-feldspar-rich clinopyroxenite hosted in biotite clinopyroxenite. Whole-rock concentrations of Sc range from 35.9 to 134 ppm in these three rocks mentioned, while clinopyroxenes in the complex exhibit Sc concentrations ranging from 56 to 203 ppm. Zircon U<ce:glyph name=\"sbnd\"></ce:glyph>Pb dating on three ultramafic clinopyroxenites yield consistent crystallization ages of 465 ± 2 Ma, indicating an Ordovician magmatic and Sc mineralization event coinciding with the subduction stage of the Proto-Tethys Ocean beneath the central Qilian block. Field observations, consistent ages, narrow range of Hf and Sr isotope data (zircon ε<ce:inf loc=\"post\">Hf</ce:inf>(t): +3.2 − +13.5; clinopyroxene <ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr: 0.704534–0.705715), and decreasing Mg<ce:sup loc=\"post\">#</ce:sup> trend observed in both clinopyroxene-bearing whole-rock and clinopyroxene single-grain samples from the three ultramafic rocks suggest a common magmatic origin with varying degrees of fractional crystallization and crystal accumulation within an evolved magmatic system. The parent magma likely originated from a potassium-Sc-REE-rich basaltic composition. This magma was primarily sourced from carbonated phlogopite-garnet lherzolite lithospheric mantle, but had been modified by carbonate-rich fluids derived from subducted oceanic sediments during the subduction of the Proto-Tethys Ocean. The comprehension of multistage growth processes in clinopyroxene effectively signifies the extent of magmatic differentiation and points to the involvement of magma sources in the formation of Sc deposits. Significant fluctuations of Sc concentration within clinopyroxene can be attributed to variable magma compositions. Enrichment of phosphate and fluorine effectively promotes Sc migration during magma evolution, while partition coefficient of Sc into clinopyroxene may be significantly higher in a P-F-rich magma, which causes Sc to concentrate in the apatite-rich biotite clinopyroxenite. The relatively high amount of Sc in the parent magma may be related to its initial enrichment in the carbonated fertile mantle. These compositions likely result from different amounts of phosphate and fluorine in the subduction-related fluid percolating through ultramafic mantle rocks. This study significantly advances our understanding of intric","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"63 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142887307","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-10DOI: 10.1016/j.chemgeo.2024.122559
Céline Baudouin, Hugo Moreira, Charles Le Losq, Max Wilke, Fleurice Parat
Hanang is a volcano in the southern part of the east branch of the East African Rift (North Tanzania Divergence) and represents volcanism at the early stage of continental break-up. Hanang volcanism is characterized by CO2-alkaline-rich magmas and silicate‑carbonate immiscibility process at crustal level. This study describes microscale iron (Fe) and Sulfur (S) K-edge X-ray absorption near edge structure (μXANES) spectroscopy measurements on nepheline-hosted melt inclusions (MI) preserved in Hanang lavas. For the first time, the μXANES method has been used on melt inclusions composed of both silicate glass and carbonate phase. Silicate glasses from Hanang display relatively high Fe3+/ΣFe ratio (Fe3+/ΣFe = 0.31, indicative of oxidized conditions) and very low S6+/ΣS ratio (S6+/ΣS = 0.05–0.07, indicative of reduced conditions). The discrepancy of the oxidation state measured from iron and sulfur and thus, the redox conditions (fO2) inferred from these two values, either suggests that the oxidation state is affected by post entrapment processes, such as re-equilibration with the host-mineral or the immiscibility process with carbonate liquid, or it suggests a significantly different relation of Fe and S oxidation state to fO2 in this chemical system. The Fe3+/ΣFe in melt inclusions yields magma redox conditions (fO2) at around ∆FMQ + 1.4 for phonolitic liquid composition from evolved differentiation and immiscibility process between silicate melt and carbonatite (≤850C°). Sulfur speciation decoupling is attributed to silicate‑carbonate immiscibility, and as such, low S6+/ΣS does not provide primary redox conditions in this system. Hanang lavas at the early stage of East African Rift have one of the most oxidizing conditions, related to the presence of carbonate-rich alkaline magmatic system associated with carbonatites.
{"title":"Redox conditions in a carbonatite-alkaline complex: Deciphering Fe- and S-XANES in melt inclusions with silicate‑carbonate immiscibility","authors":"Céline Baudouin, Hugo Moreira, Charles Le Losq, Max Wilke, Fleurice Parat","doi":"10.1016/j.chemgeo.2024.122559","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2024.122559","url":null,"abstract":"Hanang is a volcano in the southern part of the east branch of the East African Rift (North Tanzania Divergence) and represents volcanism at the early stage of continental break-up. Hanang volcanism is characterized by CO<ce:inf loc=\"post\">2</ce:inf>-alkaline-rich magmas and silicate‑carbonate immiscibility process at crustal level. This study describes microscale iron (Fe) and Sulfur (S) K-edge X-ray absorption near edge structure (μXANES) spectroscopy measurements on nepheline-hosted melt inclusions (MI) preserved in Hanang lavas. For the first time, the μXANES method has been used on melt inclusions composed of both silicate glass and carbonate phase. Silicate glasses from Hanang display relatively high Fe<ce:sup loc=\"post\">3+</ce:sup>/ΣFe ratio (Fe<ce:sup loc=\"post\">3+</ce:sup>/ΣFe = 0.31, indicative of oxidized conditions) and very low S<ce:sup loc=\"post\">6+</ce:sup>/ΣS ratio (S<ce:sup loc=\"post\">6+</ce:sup>/ΣS = 0.05–0.07, indicative of reduced conditions). The discrepancy of the oxidation state measured from iron and sulfur and thus, the redox conditions (<ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf>) inferred from these two values, either suggests that the oxidation state is affected by post entrapment processes, such as re-equilibration with the host-mineral or the immiscibility process with carbonate liquid, or it suggests a significantly different relation of Fe and S oxidation state to <ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf> in this chemical system. The Fe<ce:sup loc=\"post\">3+</ce:sup>/ΣFe in melt inclusions yields magma redox conditions (<ce:italic>f</ce:italic>O<ce:inf loc=\"post\">2</ce:inf>) at around ∆FMQ + 1.4 for phonolitic liquid composition from evolved differentiation and immiscibility process between silicate melt and carbonatite (≤850C°). Sulfur speciation decoupling is attributed to silicate‑carbonate immiscibility, and as such, low S<ce:sup loc=\"post\">6+</ce:sup>/ΣS does not provide primary redox conditions in this system. Hanang lavas at the early stage of East African Rift have one of the most oxidizing conditions, related to the presence of carbonate-rich alkaline magmatic system associated with carbonatites.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"78 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858005","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-09DOI: 10.1016/j.chemgeo.2024.122555
Peixin Zhang, Minfang Yang, Jing Lu, Zhongfeng Jiang, Lei Wang, Yuanyuan Zhu, Wenjing Guo, Zejing Li, Zhibiao Shi, Pan Wang, Kai Zhou, Xiaotao Xu, Longyi Shao, Jason Hilton
The Permian-Triassic mass extinction (PTME) is the most severe biological crisis in Earth history and is closely linked to massive contemporaneous volcanism. However, there is currently limited evidence of Mercury (Hg) enrichment directly from volcanic sources in terrestrial strata, necessitating evidence from different regions and latitudes to confirm the relationship between volcanism and changes in terrestrial environments and biotas. To explore this connection, we conducted a comprehensive analysis integrating astronomical cycles to provide a temporal framework, Hg concentrations, and Hg isotopes from terrestrial strata in the Yiyang Coalfield, located in the southern North China Plate (NCP). Our high-resolution astronomical timescale reveals that in the low latitude NCP the PTME commenced on land with the end-Permian Terrestrial Collapse (EPTC) which preceded the marine mass extinction by approximately 270 kyr and was latitudinally diachronous. The EPTC commenced in high-to-mid latitudes (75–30°S), then approximately 100–430 kyr later spread through different mid-to-low latitude regions (60–20°N) into equatorial paleolatitudes (10°N–0°). Hg isotopic results show that the initial Hg enrichment peak during the EPTC originated from terrestrial weathering and wildfire combustion rather than directly from volcanism, whereas the three subsequent Hg enrichment peaks over a 500 kyr interval following the EPTC originated directly from volcanism. This temporal coupling suggests that terrestrial ecosystems exhibited greater sensitivity and a more rapid response to global warming than marine ecosystems. Stratigraphic correlations show the early eruptive phase of the Siberian Traps Large Igneous Province (STLIP) led to gradual collapse of terrestrial ecosystems from high to low latitudes as they responded to increasingly warmer and more stressed conditions. The main eruptive phase of the STLIP, potentially augmented by contemporaneous widespread volcanism, may have ultimately led to the final collapse of terrestrial ecosystems and marine extinctions.
{"title":"Terrestrial mercury anomalies across the Permian-Triassic transition in North China linked to volcanism","authors":"Peixin Zhang, Minfang Yang, Jing Lu, Zhongfeng Jiang, Lei Wang, Yuanyuan Zhu, Wenjing Guo, Zejing Li, Zhibiao Shi, Pan Wang, Kai Zhou, Xiaotao Xu, Longyi Shao, Jason Hilton","doi":"10.1016/j.chemgeo.2024.122555","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2024.122555","url":null,"abstract":"The Permian-Triassic mass extinction (PTME) is the most severe biological crisis in Earth history and is closely linked to massive contemporaneous volcanism. However, there is currently limited evidence of Mercury (Hg) enrichment directly from volcanic sources in terrestrial strata, necessitating evidence from different regions and latitudes to confirm the relationship between volcanism and changes in terrestrial environments and biotas. To explore this connection, we conducted a comprehensive analysis integrating astronomical cycles to provide a temporal framework, Hg concentrations, and Hg isotopes from terrestrial strata in the Yiyang Coalfield, located in the southern North China Plate (NCP). Our high-resolution astronomical timescale reveals that in the low latitude NCP the PTME commenced on land with the end-Permian Terrestrial Collapse (EPTC) which preceded the marine mass extinction by approximately 270 kyr and was latitudinally diachronous. The EPTC commenced in high-to-mid latitudes (75–30°S), then approximately 100–430 kyr later spread through different mid-to-low latitude regions (60–20°N) into equatorial paleolatitudes (10°N–0°). Hg isotopic results show that the initial Hg enrichment peak during the EPTC originated from terrestrial weathering and wildfire combustion rather than directly from volcanism, whereas the three subsequent Hg enrichment peaks over a 500 kyr interval following the EPTC originated directly from volcanism. This temporal coupling suggests that terrestrial ecosystems exhibited greater sensitivity and a more rapid response to global warming than marine ecosystems. Stratigraphic correlations show the early eruptive phase of the Siberian Traps Large Igneous Province (STLIP) led to gradual collapse of terrestrial ecosystems from high to low latitudes as they responded to increasingly warmer and more stressed conditions. The main eruptive phase of the STLIP, potentially augmented by contemporaneous widespread volcanism, may have ultimately led to the final collapse of terrestrial ecosystems and marine extinctions.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"23 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858006","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-09DOI: 10.1016/j.chemgeo.2024.122524
Jing Zhao, Xuewan Wu, Wei Zhang, Zhifeng Wan, Yifei Dong, Xi Xiao, Yang Wu, Xiaoyu Wu, Junxi Feng, Qianyong Liang
Cold seep carbonates are commonly used to record the nature of seepage, including fluid sources, diagenetic environments, and variations in seepage activity. However, the relationship between diagenetic environments and trace element enrichment in dynamic environments is poorly understood. Pipe-morphology cold seep carbonates form from outside to inside in methane seeps and record variations in elements and isotopes over time, which can be used to reconstruct diagenetic environments and fluid dynamics. In this work, we analysed the mineral compositions, carbon and oxygen (CO) isotopes and major and trace element contents in different areas of pipe-morphology cold seep carbonate collected from the Qiongdongnan Basin in different growth directions. The cold seep carbonate exhibits changes from high-magnesian calcite (HMC) to aragonite and then to HMC, indicating that it has undergone changes in the sedimentary environment inside the fluid migration pathway. On the basis of these findings, the formation of this pipe-morphology cold seep carbonate is divided into three stages. The low δ13C values (from −36.13 ‰ to −32.18 ‰) indicate anaerobic oxidation of methane during carbonate formation. The response of δ13C to changes in the methane flux is not obvious. The gradual increase in δ18O from the outer to the inner portions suggests that the methane flux affected δ18O. The samples have relatively high enrichment factors (EFs) of molybdenum (Mo) and high molybdenum/uranium (Mo/U) ratios. The UEF values show an increasing trend from the outer to the inner portions, whereas the changes in MoEF, CdEF and VEF are not obvious. However, MoEF, CdEF, and VEF all have good correlations with Mn/Al and Fe/Al, indicating that the particulate shuttle process significantly impacts the enrichment of Mo, Cd, and V. We concluded that the enrichment of U is influenced by the methane flux, whereas the enrichment of Mo, Cd and V is unrelated to methane dynamics. This study provides insights into the behaviour of the methane flux and seawater, redox-sensitive trace element contents and changes in the sedimentary environment and plays an essential role in understanding the activities of cold seeps in dynamic environments.
{"title":"Multistage formation and geochemical response of pipe-morphology cold seep carbonate in the Qiongdongnan Basin, northern South China Sea","authors":"Jing Zhao, Xuewan Wu, Wei Zhang, Zhifeng Wan, Yifei Dong, Xi Xiao, Yang Wu, Xiaoyu Wu, Junxi Feng, Qianyong Liang","doi":"10.1016/j.chemgeo.2024.122524","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2024.122524","url":null,"abstract":"Cold seep carbonates are commonly used to record the nature of seepage, including fluid sources, diagenetic environments, and variations in seepage activity. However, the relationship between diagenetic environments and trace element enrichment in dynamic environments is poorly understood. Pipe-morphology cold seep carbonates form from outside to inside in methane seeps and record variations in elements and isotopes over time, which can be used to reconstruct diagenetic environments and fluid dynamics. In this work, we analysed the mineral compositions, carbon and oxygen (C<ce:glyph name=\"sbnd\"></ce:glyph>O) isotopes and major and trace element contents in different areas of pipe-morphology cold seep carbonate collected from the Qiongdongnan Basin in different growth directions. The cold seep carbonate exhibits changes from high-magnesian calcite (HMC) to aragonite and then to HMC, indicating that it has undergone changes in the sedimentary environment inside the fluid migration pathway. On the basis of these findings, the formation of this pipe-morphology cold seep carbonate is divided into three stages. The low δ<ce:sup loc=\"post\">13</ce:sup>C values (from −36.13 ‰ to −32.18 ‰) indicate anaerobic oxidation of methane during carbonate formation. The response of δ<ce:sup loc=\"post\">13</ce:sup>C to changes in the methane flux is not obvious. The gradual increase in δ<ce:sup loc=\"post\">18</ce:sup>O from the outer to the inner portions suggests that the methane flux affected δ<ce:sup loc=\"post\">18</ce:sup>O. The samples have relatively high enrichment factors (EFs) of molybdenum (Mo) and high molybdenum/uranium (Mo/U) ratios. The U<ce:inf loc=\"post\">EF</ce:inf> values show an increasing trend from the outer to the inner portions, whereas the changes in Mo<ce:inf loc=\"post\">EF</ce:inf>, Cd<ce:inf loc=\"post\">EF</ce:inf> and V<ce:inf loc=\"post\">EF</ce:inf> are not obvious. However, Mo<ce:inf loc=\"post\">EF</ce:inf>, Cd<ce:inf loc=\"post\">EF</ce:inf>, and V<ce:inf loc=\"post\">EF</ce:inf> all have good correlations with Mn/Al and Fe/Al, indicating that the particulate shuttle process significantly impacts the enrichment of Mo, Cd, and V. We concluded that the enrichment of U is influenced by the methane flux, whereas the enrichment of Mo, Cd and V is unrelated to methane dynamics. This study provides insights into the behaviour of the methane flux and seawater, redox-sensitive trace element contents and changes in the sedimentary environment and plays an essential role in understanding the activities of cold seeps in dynamic environments.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"22 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815919","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-09DOI: 10.1016/j.chemgeo.2024.122551
Hunter C. Olson, Allegra Hosford Scheirer, Samantha R. Ritzer, Erik A. Sperling
Accurately reconstructing original Total Organic Carbon (TOC) in thermally mature rocks is essential for the correct application of geochemical proxies and understanding organic carbon burial through time. To reconstruct original TOC using empirical methods, it is vital to have an accurate estimate of the original Hydrogen Index (HI). The two most common methods are estimating original HI using kerogen type or using average HI values from immature rocks elsewhere in the basin. This study tests the ability to use inorganic geochemical data to reconstruct original HI using the Upper Cretaceous-Paleogene Moreno Formation from the San Joaquin Basin, California, USA as a case study. The study utilized cores from the Moreno Formation that are thermally immature, thus preserving original HI values, and that span a range in initial HI. First, inorganic geochemical data were produced (elemental abundances and iron speciation) for samples previously analyzed for organic geochemistry. These data suggest that bottom water conditions during deposition of the Moreno Formation were ferruginous (anoxic and non-sulfidic), without development of sustained euxinia (anoxic and sulfidic). Next, a random forest machine learning analysis was implemented to analyze which inorganic geochemical variables best predict HI in the Moreno Formation. The most important proxies were those for detrital input (Ti, Th), marine export productivity (Cu, Ni), and redox proxies for suboxic conditions (Se, Cr, iron speciation). Finally, the random forest framework was used to predict HI values for three main study cores based on their inorganic geochemistry. These predictions were compared stratigraphically and statistically against the measured values and the kerogen type and average HI methods for reconstructing HI and show this new method has better predictive power than approaches based on single values. This indicates strong promise for using inorganic geochemistry, which is relatively immune to thermal maturation, to reconstruct organic geochemical parameters that are modified during burial and diagenetic process.
{"title":"Prediction of organic geochemical parameters from inorganic geochemical data in the Cretaceous-Danian Moreno Formation, San Joaquin Basin, California","authors":"Hunter C. Olson, Allegra Hosford Scheirer, Samantha R. Ritzer, Erik A. Sperling","doi":"10.1016/j.chemgeo.2024.122551","DOIUrl":"https://doi.org/10.1016/j.chemgeo.2024.122551","url":null,"abstract":"Accurately reconstructing original Total Organic Carbon (TOC) in thermally mature rocks is essential for the correct application of geochemical proxies and understanding organic carbon burial through time. To reconstruct original TOC using empirical methods, it is vital to have an accurate estimate of the original Hydrogen Index (HI). The two most common methods are estimating original HI using kerogen type or using average HI values from immature rocks elsewhere in the basin. This study tests the ability to use inorganic geochemical data to reconstruct original HI using the Upper Cretaceous-Paleogene Moreno Formation from the San Joaquin Basin, California, USA as a case study. The study utilized cores from the Moreno Formation that are thermally immature, thus preserving original HI values, and that span a range in initial HI. First, inorganic geochemical data were produced (elemental abundances and iron speciation) for samples previously analyzed for organic geochemistry. These data suggest that bottom water conditions during deposition of the Moreno Formation were ferruginous (anoxic and non-sulfidic), without development of sustained euxinia (anoxic and sulfidic). Next, a random forest machine learning analysis was implemented to analyze which inorganic geochemical variables best predict HI in the Moreno Formation. The most important proxies were those for detrital input (Ti, Th), marine export productivity (Cu, Ni), and redox proxies for suboxic conditions (Se, Cr, iron speciation). Finally, the random forest framework was used to predict HI values for three main study cores based on their inorganic geochemistry. These predictions were compared stratigraphically and statistically against the measured values and the kerogen type and average HI methods for reconstructing HI and show this new method has better predictive power than approaches based on single values. This indicates strong promise for using inorganic geochemistry, which is relatively immune to thermal maturation, to reconstruct organic geochemical parameters that are modified during burial and diagenetic process.","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"54 1","pages":""},"PeriodicalIF":3.9,"publicationDate":"2024-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858007","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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