Pub Date : 2024-11-03DOI: 10.1016/j.jseaes.2024.106396
Hangtao Yu , Chuang Xu , Hui Zhang , Pengbo Qin , Jun Wang
The Parker-Oldenburg method is a commonly used classical interface inversion method for Moho topographic inversion. However, this method is excessively reliant on two hyperparameters − the Moho density contrast and the average Moho depth. Due to the failure to take into account the effect of non-linear terms and computational inefficiencies, this previous method leads to a significant bias in the hyperparameters estimation, which renders it impossible to invert the finer Moho topography. To address this issue, we propose a new method that utilizes the genetic algorithm to estimate more accurate hyperparameters. Synthetic test results illustrate that the differences of the estimated Moho density contrast and average Moho depth from our method and the true values are only 0.044 g/cm3 and 0.729 km, respectively. Compared with the improved Bott’s method, the errors were reduced by 12.28 % and 2.23 %, respectively. To further illustrate the effectiveness of our method, we apply this method to the Southwestern Sub-basin of the South China Sea, where the Moho density contrast and average Moho depth are determined to be 0.61 g/cm3 and 19.18 km, respectively by imposing seismic data constraints. The Moho topography is then inverted based on these determinations, revealing that the Moho topography ranges from 6.3 km to 24.9 km in the study area and exhibits pronounced undulations. Compared to other Moho topography models, our Moho topography is more accurate.
{"title":"Moho topographic inversion of the South China Sea based on genetic algorithm","authors":"Hangtao Yu , Chuang Xu , Hui Zhang , Pengbo Qin , Jun Wang","doi":"10.1016/j.jseaes.2024.106396","DOIUrl":"10.1016/j.jseaes.2024.106396","url":null,"abstract":"<div><div>The Parker-Oldenburg method is a commonly used classical interface inversion method for Moho topographic inversion. However, this method is excessively reliant on two hyperparameters − the Moho density contrast and the average Moho depth. Due to the failure to take into account the effect of non-linear terms and computational inefficiencies, this previous method leads to a significant bias in the hyperparameters estimation, which renders it impossible to invert the finer Moho topography. To address this issue, we propose a new method that utilizes the genetic algorithm to estimate more accurate hyperparameters. Synthetic test results illustrate that the differences of the estimated Moho density contrast and average Moho depth from our method and the true values are only 0.044 g/cm<sup>3</sup> and 0.729 km, respectively. Compared with the improved Bott’s method, the errors were reduced by 12.28 % and 2.23 %, respectively. To further illustrate the effectiveness of our method, we apply this method to the Southwestern Sub-basin of the South China Sea, where the Moho density contrast and average Moho depth are determined to be 0.61 g/cm<sup>3</sup> and 19.18 km, respectively by imposing seismic data constraints. The Moho topography is then inverted based on these determinations, revealing that the Moho topography ranges from 6.3 km to 24.9 km in the study area and exhibits pronounced undulations. Compared to other Moho topography models, our Moho topography is more accurate.</div></div>","PeriodicalId":50253,"journal":{"name":"Journal of Asian Earth Sciences","volume":"277 ","pages":"Article 106396"},"PeriodicalIF":2.7,"publicationDate":"2024-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593066","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-11-03DOI: 10.1016/j.jseaes.2024.106395
Wen-Bin Xue, Shao-Cong Lai, Yu Zhu, Jiang-Feng Qin, Ren-Zhi Zhu, Min Liu, Hang Yang
Granites may contain critical information about composition and reworking of continental crust and are widely used to investigate continental crust evolution. Extensive Neoproterozoic granites in the northern Yangtze Block are significant to the Neoproterozoic continental evolution of the Yangtze Block. We investigated the petrology, mineralogy, whole-rock geochemistry, and zircon U–Pb–Hf isotopes of the Neoproterozoic Wuduhe biotite granites and Xiabaoping K-feldspar granites of the Huangling batholith in the northern Yangtze Block to determine their source characteristics and geological implications for the northern Yangtze Block. The Wuduhe biotite granites yielded zircon U–Pb ages of ca. 818–815 Ma. They displayed high SiO2 contents (70.19–74.23 wt%) and Na2O/K2O ratios (1.38–3.35) but low MgO (0.37–0.90 wt%) and CaO (1.49–2.97 wt%) contents, representing calc-alkaline Na-rich I-type granites. They exhibited enriched whole-rock εNd(t) (−19.8 to − 18.8) and zircon εHf(t) values (−41.3 to − 24.2), and had low CaO/Na2O (0.34–0.63), Al2O3/TiO2 (46.6–89.7), Rb/Ba (0.02–0.08), and Rb/Sr (0.04–0.12) ratios, as well as low zircon saturation temperatures (739 − 770 °C), indicating derivation from Na-rich metabasalts of the Archean Kongling complex. The Xiabaoping K-feldspar granites had zircon U − Pb crystallization ages of ca. 816–812 Ma. They displayed high SiO2 (70.82–74.80 wt%), K2O (4.41–6.35 wt%), and Al2O3 (13.46–16.31 wt%) contents, suggesting A2-type affinities. They showed enriched zircon εHf(t) (−44.3 to − 18.4) and whole-rock εNd(t) values (−23.4 to − 18.4) and high zircon saturation temperatures (869–912 °C), indicating formation by anhydrous melting of K-rich felsic rocks from the Archean Kongling complex. The geochemical diversity of these granites from the Huangling batholith was primarily controlled by source heterogeneity of the Kongling complex and distinct melting temperatures. We infer that the northern Yangtze Block underwent significant remelting of ancient continental crust in a subduction background during the Neoproterozoic, induced by continuous upwelling of mantle-derived mafic magmas.
{"title":"Generation of Neoproterozoic granites of the Huangling batholith in the northern Yangtze Block, South China: Implications for the evolution of the Precambrian continental crust","authors":"Wen-Bin Xue, Shao-Cong Lai, Yu Zhu, Jiang-Feng Qin, Ren-Zhi Zhu, Min Liu, Hang Yang","doi":"10.1016/j.jseaes.2024.106395","DOIUrl":"10.1016/j.jseaes.2024.106395","url":null,"abstract":"<div><div>Granites may contain critical information about composition and reworking of continental crust and are widely used to investigate continental crust evolution. Extensive Neoproterozoic granites in the northern Yangtze Block are significant to the Neoproterozoic continental evolution of the Yangtze Block. We investigated the petrology, mineralogy, whole-rock geochemistry, and zircon U–Pb–Hf isotopes of the Neoproterozoic Wuduhe biotite granites and Xiabaoping K-feldspar granites of the Huangling batholith in the northern Yangtze Block to determine their source characteristics and geological implications for the northern Yangtze Block. The Wuduhe biotite granites yielded zircon U–Pb ages of ca. 818–815 Ma. They displayed high SiO<sub>2</sub> contents (70.19–74.23 wt%) and Na<sub>2</sub>O/K<sub>2</sub>O ratios (1.38–3.35) but low MgO (0.37–0.90 wt%) and CaO (1.49–2.97 wt%) contents, representing calc-alkaline Na-rich I-type granites. They exhibited enriched whole-rock εNd(t) (−19.8 to − 18.8) and zircon εHf(t) values (−41.3 to − 24.2), and had low CaO/Na<sub>2</sub>O (0.34–0.63), Al<sub>2</sub>O<sub>3</sub>/TiO<sub>2</sub> (46.6–89.7), Rb/Ba (0.02–0.08), and Rb/Sr (0.04–0.12) ratios, as well as low zircon saturation temperatures (739 − 770 °C), indicating derivation from Na-rich metabasalts of the Archean Kongling complex. The Xiabaoping K-feldspar granites had zircon U − Pb crystallization ages of ca. 816–812 Ma. They displayed high SiO<sub>2</sub> (70.82–74.80 wt%), K<sub>2</sub>O (4.41–6.35 wt%), and Al<sub>2</sub>O<sub>3</sub> (13.46–16.31 wt%) contents, suggesting A<sub>2</sub>-type affinities. They showed enriched zircon εHf(t) (−44.3 to − 18.4) and whole-rock εNd(t) values (−23.4 to − 18.4) and high zircon saturation temperatures (869–912 °C), indicating formation by anhydrous melting of K-rich felsic rocks from the Archean Kongling complex. The geochemical diversity of these granites from the Huangling batholith was primarily controlled by source heterogeneity of the Kongling complex and distinct melting temperatures. We infer that the northern Yangtze Block underwent significant remelting of ancient continental crust in a subduction background during the Neoproterozoic, induced by continuous upwelling of mantle-derived mafic magmas.</div></div>","PeriodicalId":50253,"journal":{"name":"Journal of Asian Earth Sciences","volume":"277 ","pages":"Article 106395"},"PeriodicalIF":2.7,"publicationDate":"2024-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142656889","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Trans-crustal, northerly dipping, arcuate Singhbhum Shear Zone (SSZ) constituting the interface of Proterozoic North Singhbhum Mobile Belt (NSMB) and Singhbhum Craton (SC) is established over a strike length of about ∼200 km from Baharagorato Chakradharpur in the west beyond which it bifurcates around the wedge shaped Chakradharpur granite. Based on geological mapping and meso to micro scale structural analysis, present work examines the SSZ’s southeastern extension beyond Baharagora, indicating its southward continuation for about 50 km to Dubukidihi within the NSMB lithopackage. Bangriposi Shear Zone (BSZ) which defines the terrane boundary between the SC and NSMB in this sector, splays towards north as Bangriposi West Shear Zone (BWSZ) and both transects the Dhanjori Basin longitudinally. BSZ and BWSZ are interpreted to be cogenetic with SSZ. NSMB in this area comprises of pelitic and psamopelitic rocks intruded by mafic–ultramafic magmatism and granitoids. Considering a north to south compression regime during accretion of NSMB with SC, the study area, which forms the interface between the craton and mobile belt, is at an acute to obtuse angle with the direction of overall stress field. It is marked by several high strain zones characterized by N-S shear band cleavages with moderate easterly dips, and northerly pitching stretching/mineral lineation. Consistent westerly vergent folds on mylonitic plane and orientation of stretching lineation indicates top to WSW movement in the shear zones. Tectonically interleaved mafic–ultramafic schist within the Romapahari granite are sites of copper mineralization with enhanced nickel concentration pointing towards future exploration sites for epigenetic copper, uranium mineralization which is so characteristic of SSZ.
{"title":"Southeastern extension of Singhbhum Shear Zone, Eastern Indian Shield: A detailed appraisal","authors":"Maya Tripathi, Itishree Chinara, J.P. Mohakul, Saptarshi Mallick","doi":"10.1016/j.jseaes.2024.106391","DOIUrl":"10.1016/j.jseaes.2024.106391","url":null,"abstract":"<div><div>Trans-crustal, northerly dipping, arcuate Singhbhum Shear Zone (SSZ) constituting the interface of Proterozoic North Singhbhum Mobile Belt (NSMB) and Singhbhum Craton (SC) is established over a strike length of about ∼200 km from Baharagorato Chakradharpur in the west beyond which it bifurcates around the wedge shaped Chakradharpur granite. Based on geological mapping and meso to micro scale structural analysis, present work examines the SSZ’s southeastern extension beyond Baharagora, indicating its southward continuation for about 50 km to Dubukidihi within the NSMB lithopackage. Bangriposi Shear Zone (BSZ) which defines the terrane boundary between the SC and NSMB in this sector, splays towards north as Bangriposi West Shear Zone (BWSZ) and both transects the Dhanjori Basin longitudinally. BSZ and BWSZ are interpreted to be cogenetic with SSZ. NSMB in this area comprises of pelitic and psamopelitic rocks intruded by mafic–ultramafic magmatism and granitoids. Considering a north to south compression regime during accretion of NSMB with SC, the study area, which forms the interface between the craton and mobile belt, is at an acute to obtuse angle with the direction of overall stress field. It is marked by several high strain zones characterized by N-S shear band cleavages with moderate easterly dips, and northerly pitching stretching/mineral lineation. Consistent westerly vergent folds on mylonitic plane and orientation of stretching lineation indicates top to WSW movement in the shear zones. Tectonically interleaved mafic–ultramafic schist within the Romapahari granite are sites of copper mineralization with enhanced nickel concentration pointing towards future exploration sites for epigenetic copper, uranium mineralization which is so characteristic of SSZ.</div></div>","PeriodicalId":50253,"journal":{"name":"Journal of Asian Earth Sciences","volume":"277 ","pages":"Article 106391"},"PeriodicalIF":2.7,"publicationDate":"2024-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142656882","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-11-01DOI: 10.1016/j.jseaes.2024.106392
Yasaman Ahmadi, Hamzeh Mehrabi, Mohammad Hasani, Mohsen Ranjbaran
Mixed siliciclastic–carbonate reservoirs, such as the Asmari Formation in the Zagros Basin, present significant heterogeneities that influence hydrocarbon exploration and production. This study examines the depositional and diagenetic heterogeneities of the Asmari Formation in the northwest Persian Gulf through a multi-methodological approach, including petrographic analysis, petrophysical measurements, core CT-scanning, X-ray diffraction, and sieve analysis. The primary goal is to identify the origins, scales, and predictability of these heterogeneities within a sequence stratigraphic framework to enhance reservoir characterization. Facies analysis reveals depositional environments ranging from sabkha to shoreface, peritidal, lagoonal, and shoal settings, with carbonate sedimentation interrupted by clastic influxes associated with sea-level fluctuations. Diagenetic processes, including dolomitization, dissolution, cementation, and fracturing, were identified through petrographic analysis, highlighting their effects on reservoir quality. To quantify these heterogeneities and delineate reservoir flow units, methods such as Winland classification, hydraulic flow unit (HFU) analysis, and Lorenz zonation were applied. Results show that depositional heterogeneities, predominantly driven by sea-level changes, range from small to large scales and can be predicted within a sequence stratigraphic context. Diagenetic modifications substantially affect porosity and permeability, with dolomitization improving reservoir potential, while compaction and cementation tend to reduce it. Fracturing, particularly in the lower Asmari carbonates, enhances permeability. The study concludes that accurately recognizing and modeling reservoir heterogeneities in three dimensions can significantly improve exploration and development strategies in the Persian Gulf. A better understanding of the spatial distribution of high-quality reservoir zones and impermeable baffle layers will facilitate more precise well placement, optimize hydrocarbon recovery, and mitigate exploration risks.
{"title":"Depositional and diagenetic heterogeneities in sequence stratigraphic framework of a mixed carbonate-siliciclastic reservoir: A case study from Oligocene–Miocene Asmari Formation in the Persian Gulf","authors":"Yasaman Ahmadi, Hamzeh Mehrabi, Mohammad Hasani, Mohsen Ranjbaran","doi":"10.1016/j.jseaes.2024.106392","DOIUrl":"10.1016/j.jseaes.2024.106392","url":null,"abstract":"<div><div>Mixed siliciclastic–carbonate reservoirs, such as the Asmari Formation in the Zagros Basin, present significant heterogeneities that influence hydrocarbon exploration and production. This study examines the depositional and diagenetic heterogeneities of the Asmari Formation in the northwest Persian Gulf through a multi-methodological approach, including petrographic analysis, petrophysical measurements, core CT-scanning, X-ray diffraction, and sieve analysis. The primary goal is to identify the origins, scales, and predictability of these heterogeneities within a sequence stratigraphic framework to enhance reservoir characterization. Facies analysis reveals depositional environments ranging from sabkha to shoreface, peritidal, lagoonal, and shoal settings, with carbonate sedimentation interrupted by clastic influxes associated with sea-level fluctuations. Diagenetic processes, including dolomitization, dissolution, cementation, and fracturing, were identified through petrographic analysis, highlighting their effects on reservoir quality. To quantify these heterogeneities and delineate reservoir flow units, methods such as Winland classification, hydraulic flow unit (HFU) analysis, and Lorenz zonation were applied. Results show that depositional heterogeneities, predominantly driven by sea-level changes, range from small to large scales and can be predicted within a sequence stratigraphic context. Diagenetic modifications substantially affect porosity and permeability, with dolomitization improving reservoir potential, while compaction and cementation tend to reduce it. Fracturing, particularly in the lower Asmari carbonates, enhances permeability. The study concludes that accurately recognizing and modeling reservoir heterogeneities in three dimensions can significantly improve exploration and development strategies in the Persian Gulf. A better understanding of the spatial distribution of high-quality reservoir zones and impermeable baffle layers will facilitate more precise well placement, optimize hydrocarbon recovery, and mitigate exploration risks.</div></div>","PeriodicalId":50253,"journal":{"name":"Journal of Asian Earth Sciences","volume":"277 ","pages":"Article 106392"},"PeriodicalIF":2.7,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593064","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-10-31DOI: 10.1016/j.jseaes.2024.106373
Biju John , Yogendra Singh , C.P Rajendran
Far from the plate boundaries, the seismogenic zones within the cratonic areas of Indian land mass had remained largely undetected. The moderate earthquakes in such areas have proved to be hugely damaging because of their infrequency and consequent lack of societal preparedness. As the subtle geological expressions of tectonism make identifying hazardous zones in cratonic areas difficult, it is important to develop locally appropriate geological criteria to isolate potential seismic source zones. Although seismically induced liquefaction preserved in the sedimentary sections is useful as an earthquake proxy, its scope remains underestimated in cratonic regions. Here we offer a field-based methodological approach to mapping liquefaction features from such an area, located south of the Bharathapuzha River in the southwestern part of the Indian craton. We used the field data to constrain the near-field earthquake potential. The earthquake-induced soil liquefaction, in the form of sand dikes and sills, was identified within an area of roughly 100 km2, and the available data suggest two episodes of liquefaction – the one between 2.0 ka and 2.5 ka, and a later event around 0.78 ka BP. The spatial distribution and the dimension of the soil liquefaction features, in an area known for the occasional spurt in minor earthquakes in recent times, are suggestive of a potential seismic source in the region that can generate earthquakes of moment magnitudes (Mw) ranging from 5.5 to 6.5. Thus the present observation is a vital input for constraining the region’s seismic hazard and the methodology developed here can be used in other areas of unknown potential.
在远离板块边界的地方，印度陆地板块内的地震带在很大程度上仍未被发现。在这些地区发生的中度地震已被证明具有巨大的破坏性，因为这些地震并不频繁发生，而且社会缺乏相应的防范措施。由于构造运动的地质表现形式十分微妙，因此很难确定板块构造地区的危险区，因此必须制定适合当地的地质标准，以隔离潜在的震源区。虽然保存在沉积剖面中的地震诱发液化可作为地震的代用指标，但在板块构造地区，其范围仍被低估。在此，我们提供了一种基于实地的方法，用于绘制印度克拉通西南部巴拉塔普扎河以南地区的液化特征图。我们利用实地数据对近场地震潜力进行了约束。我们在大约 100 平方公里的区域内发现了由地震引起的土壤液化，其形式为砂堤和砂岩，现有数据表明发生过两次液化--一次在 2.0 ka 到 2.5 ka 之间，另一次发生在公元前 0.78 ka 左右。土壤液化特征的空间分布和规模，在一个近代偶尔发生小地震的地区，表明该地区有一个潜在的地震源，可以产生矩震级（Mw）在 5.5 到 6.5 之间的地震。因此，目前的观测结果对于确定该地区的地震危险性至关重要，这里开发的方法也可用于其他潜力未知的地区。
{"title":"Sedimentary records of liquefaction from central Kerala (southwestern India), as earthquake indicators in a cratonic area","authors":"Biju John , Yogendra Singh , C.P Rajendran","doi":"10.1016/j.jseaes.2024.106373","DOIUrl":"10.1016/j.jseaes.2024.106373","url":null,"abstract":"<div><div>Far from the plate boundaries, the seismogenic zones within the cratonic areas of Indian land mass had remained largely undetected. The moderate earthquakes in such areas have proved to be hugely damaging because of their infrequency and consequent lack of societal preparedness. As the subtle geological expressions of tectonism make identifying hazardous zones in cratonic areas difficult, it is important to develop locally appropriate geological criteria to isolate potential seismic source zones. Although seismically induced liquefaction preserved in the sedimentary sections is useful as an earthquake proxy, its scope remains underestimated in cratonic regions. Here we offer a field-based methodological approach to mapping liquefaction features from such an area, located south of the Bharathapuzha River in the southwestern part of the Indian craton. We used the field data to constrain the near-field earthquake potential. The earthquake-induced soil liquefaction, in the form of sand dikes and sills, was identified within an area of roughly 100 km<sup>2</sup>, and the available data suggest two episodes of liquefaction – the one between 2.0 ka and 2.5 ka, and a later event around 0.78 ka BP. The spatial distribution and the dimension of the soil liquefaction features, in an area known for the occasional spurt in minor earthquakes in recent times, are suggestive of a potential seismic source in the region that can generate earthquakes of moment magnitudes (M<sub>w</sub>) ranging from 5.5 to 6.5.<!--> <!-->Thus the present observation is a vital input for constraining the region’s seismic hazard and the methodology developed here can be used in other areas of unknown potential.</div></div>","PeriodicalId":50253,"journal":{"name":"Journal of Asian Earth Sciences","volume":"277 ","pages":"Article 106373"},"PeriodicalIF":2.7,"publicationDate":"2024-10-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593065","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-10-30DOI: 10.1016/j.jseaes.2024.106394
Tao Ruan , Zhong–Jie Bai , Wei–Guang Zhu , Shi-Ji Zheng
The petrogenesis of the Luobusa mantle peridotites (Southern Tibet) has remained unclear. Here, a suit of the Luobusa peridotites is presented to trace their petrogenetic history. These peridotites contain protogranular lherzolites, porphyroclastic harzburgites and equigranular harzburgites, which span most compositional spectrum of global mid-ocean ridge peridotites (MORP) and supra-subduction zone peridotites (SSZP). The petrogenesis of these peridotites was linked to a two-stage mantle evolution from the MOR to the SSZ. The lherzolites are least refractory with comparable compositions to the MORP such as high whole-rock Al2O3 (0.90–1.72 wt%) and low spinel Cr# (20–40), which represent mantle residues after 8–16 % near-fractional melting of a depleted MORB mantle (DMM) source beneath anhydrous MOR. The porphyroclastic harzburgites are highly depleted with an SSZP affinity indicated by extremely low whole-rock Al2O3 (<0.50 wt%) and high spinel Cr# (57–65). They represent residual mantle wedge fluxed by the slab-fluids above a subduction zone after subduction initiation. Their trace element compositions of clinopyroxenes are consistent with the additional 8–12 % flux melting of a depleted harzburgite source that previously experienced ∼ 10 % depletion of an initial DMM source. The equigranular harzburgites are characterized by the enrichments of Na, Cr, Ti and MREE in amphiboles and clinopyroxenes and Ti in spinels, which might result from the metasomatism of a slab-derived eclogite melt. Therefore, the heterogeneous Luobusa mantle peridotites in this study recorded a multi-stage tectonic evolution from the MOR to the SSZ.
罗布莎地幔橄榄岩（西藏南部）的岩石成因一直不清楚。本文介绍了罗布莎橄榄岩的岩石成因，以追溯其岩石成因的历史。这些橄榄岩包含原花岗岩、斑岩和等花岗岩，涵盖了全球洋中脊橄榄岩（MORP）和超俯冲带橄榄岩（SSZP）的大部分成分谱。这些橄榄岩的岩石成因与从 MOR 到 SSZ 的两阶段地幔演化有关。蛭沸石的耐火度最低，其成分与MORP相当，如全岩Al2O3含量高（0.90-1.72 wt%），尖晶石Cr#含量低（20-40），是无水MOR下的贫MORB地幔（DMM）源经过8-16%的近分熔后的地幔残留物。斑状碎屑哈兹堡垒岩具有极高的贫化程度，全岩Al2O3含量极低（<0.50 wt%），尖晶石Cr#含量较高（57-65），显示出与SSZP的亲和性。它们代表了俯冲开始后由俯冲带上方的板块流体通入的残余地幔楔。它们的倩辉石痕量元素组成与贫化的哈兹堡岩源额外的8-12%通量熔融相一致，而之前的初始DMM源经历了10%的贫化。等粒状哈兹堡垒岩的特征是闪长岩和闪长辉石中富含Na、Cr、Ti和MREE，尖晶石中富含Ti，这可能是板块衍生的辉绿岩熔体的变质作用所致。因此，本研究中的异质罗布莎地幔橄榄岩记录了从MOR到SSZ的多阶段构造演化。
{"title":"Multi-stage partial melting and melt metasomatism in the formation of the Luobusa ophiolite (Southern Tibet)","authors":"Tao Ruan , Zhong–Jie Bai , Wei–Guang Zhu , Shi-Ji Zheng","doi":"10.1016/j.jseaes.2024.106394","DOIUrl":"10.1016/j.jseaes.2024.106394","url":null,"abstract":"<div><div>The petrogenesis of the Luobusa mantle peridotites (Southern Tibet) has remained unclear. Here, a suit of the Luobusa peridotites is presented to trace their petrogenetic history. These peridotites contain protogranular lherzolites, porphyroclastic harzburgites and equigranular harzburgites, which span most compositional spectrum of global mid-ocean ridge peridotites (MORP) and supra-subduction zone peridotites (SSZP). The petrogenesis of these peridotites was linked to a two-stage mantle evolution from the MOR to the SSZ. The lherzolites are least refractory with comparable compositions to the MORP such as high whole-rock Al<sub>2</sub>O<sub>3</sub> (0.90–1.72 wt%) and low spinel Cr<sup>#</sup> (20–40), which represent mantle residues after 8–16 % near-fractional melting of a depleted MORB mantle (DMM) source beneath anhydrous MOR. The porphyroclastic harzburgites are highly depleted with an SSZP affinity indicated by extremely low whole-rock Al<sub>2</sub>O<sub>3</sub> (<0.50 wt%) and high spinel Cr<sup>#</sup> (57–65). They represent residual mantle wedge fluxed by the slab-fluids above a subduction zone after subduction initiation. Their trace element compositions of clinopyroxenes are consistent with the additional 8–12 % flux melting of a depleted harzburgite source that previously experienced ∼ 10 % depletion of an initial DMM source. The equigranular harzburgites are characterized by the enrichments of Na, Cr, Ti and MREE in amphiboles and clinopyroxenes and Ti in spinels, which might result from the metasomatism of a slab-derived eclogite melt. Therefore, the heterogeneous Luobusa mantle peridotites in this study recorded a multi-stage tectonic evolution from the MOR to the SSZ.</div></div>","PeriodicalId":50253,"journal":{"name":"Journal of Asian Earth Sciences","volume":"277 ","pages":"Article 106394"},"PeriodicalIF":2.7,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593067","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The reservoir characteristics of giant oil fields in the Persian Gulf are poorly described in the geological literature due to their economic importance to host nations. The Berriasian–Early Valanginian, Lower Fahliyan Formation hosts several giant oil fields in the Persian Gulf, Iran, and in this study, sedimentary microfacies (MF), reservoir characteristics, petrophysics, rock types, and electrofacies of one of these fields are presented. Five MFs are defined and interpreted as representing deposition in lagoon, shoal, and mid shelf settings. MFs deposited in high-energy shoal settings have the best reservoir properties and mainly comprise grainstones and packstones; diagenetic alteration of these MFs reduces reservoir quality. MFs from lagoon and mid-outer shelf settings mainly consist of wackestone with poorer reservoir quality.
Cluster analysis applied to well-log characteristics to define electrofacies. Electrofacies are then compared to effective porosity and integrated with the capillary pressure plots to define reservoir rock types. The resulting rock types were correlated to electrofacies and MFs. Here, in most cases, high reservoir quality rock types (RT3 and RT4) correlate well to high porosity and permeability electrofacies (EF1 and EF2) and grain-supported sedimentary microfacies (MF3 and MF4) and vice versa, but in some rare cases, the best reservoir rock types do not correlate to depositional facies due to the complex pattern of heterogeneity in pore types and spatial distribution that reveals considerable impact of diagenesis in the reservoir. This study reinforces the importance of accounting for diagenetic effects (particularly destructive digenetic phenomena which impact permeability) in reservoir rock typing.
{"title":"Reservoir characterization of the Fahliyan Formation in Dorood Oilfield, Persian Gulf","authors":"Maziyar Nazemi , Hassan Valinasab , Ali Kadkhodaie‐Ilkhchi , Bahman Golchin , Hamid Hassanzadeh","doi":"10.1016/j.jseaes.2024.106393","DOIUrl":"10.1016/j.jseaes.2024.106393","url":null,"abstract":"<div><div>The reservoir characteristics of giant oil fields in the Persian Gulf are poorly described in the geological literature due to their economic importance to host nations. The Berriasian–Early Valanginian, Lower Fahliyan Formation hosts several giant oil fields in the Persian Gulf, Iran, and in this study, sedimentary microfacies (MF), reservoir characteristics, petrophysics, rock types, and electrofacies of one of these fields are presented. Five MFs are defined and interpreted as representing deposition in lagoon, shoal, and mid shelf settings. MFs deposited in high-energy shoal settings have the best reservoir properties and mainly comprise grainstones and packstones; diagenetic alteration of these MFs reduces reservoir quality. MFs from lagoon and mid-outer shelf settings mainly consist of wackestone with poorer reservoir quality.</div><div>Cluster analysis applied to well-log characteristics to define electrofacies. Electrofacies are then compared to effective porosity and integrated with the capillary pressure plots to define reservoir rock types. The resulting rock types were correlated to electrofacies and MFs. Here, in most cases, high reservoir quality rock types (RT3 and RT4) correlate well to high porosity and permeability electrofacies (EF1 and EF2) and grain-supported sedimentary microfacies (MF3 and MF4) and vice versa, but in some rare cases, the best reservoir rock types do not correlate to depositional facies due to the complex pattern of heterogeneity in pore types and spatial distribution that reveals considerable impact of diagenesis in the reservoir. This study reinforces the importance of accounting for diagenetic effects (particularly destructive digenetic phenomena which impact permeability) in reservoir rock typing.</div></div>","PeriodicalId":50253,"journal":{"name":"Journal of Asian Earth Sciences","volume":"277 ","pages":"Article 106393"},"PeriodicalIF":2.7,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142656880","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-10-30DOI: 10.1016/j.jseaes.2024.106388
Sheng-Nan Ma , Zhong-Qi Quentin Yue
This paper presents a refined approach for evaluating the geometrical, physical, and chemical properties of weathered soil particles and illustrates it with a completely decomposed tuff (CDT) soil. This refined evaluation approach consists of two parts. Part I separates soil into 25 sub-groups of gravel, sand, silt, and clay particles from 14 mm to less than 0.0008 mm by washing and sieving. Part II applies laboratory tests to examine the refined geometrical, physical, and chemical properties of each sub-group of materials. These laboratory tests include the dynamic and static image analysis for particle shape evaluation, the Atterberg limits test for plasticity evaluation, the falling head permeability test for hydraulic conductivity evaluation, the energy dispersive X-ray spectrometer (EDS) test and X-ray fluorescence spectrometer (XRF) test for elemental composition evaluation, and the X-ray diffractometer (XRD) test for mineral composition evaluation. The quantitative results of these refined properties of the soil materials can be expressed as a function of the particle size. The characteristics of each sub-group of particles together determine the properties of the soil mixture. This refined evaluation approach provides a new insight for examining the properties of weathered soils and their weathering degrees.
本文介绍了一种用于评估风化土壤颗粒的几何、物理和化学特性的改进方法，并以完全分解凝灰岩（CDT）土壤为例进行了说明。这种细化评估方法由两部分组成。第一部分通过冲洗和筛分将土壤分成 25 个子组，包括 14 毫米到小于 0.0008 毫米的砾石、砂、粉土和粘土颗粒。第二部分通过实验室测试来检验每个子组材料的细化几何、物理和化学特性。这些实验室测试包括用于评估颗粒形状的动态和静态图像分析、用于评估塑性的阿特伯格极限测试、用于评估水导率的水头下降渗透性测试、用于评估元素组成的能量色散 X 射线光谱仪（EDS）测试和 X 射线荧光光谱仪（XRF）测试，以及用于评估矿物组成的 X 射线衍射仪（XRD）测试。这些土壤材料细化特性的定量结果可以用粒度的函数来表示。每个子颗粒组的特性共同决定了土壤混合物的特性。这种精细评估方法为研究风化土壤的性质及其风化程度提供了新的视角。
{"title":"Refined evaluation approach for geometrical, physical and chemical properties of completely decomposed tuff soil particles","authors":"Sheng-Nan Ma , Zhong-Qi Quentin Yue","doi":"10.1016/j.jseaes.2024.106388","DOIUrl":"10.1016/j.jseaes.2024.106388","url":null,"abstract":"<div><div>This paper presents a refined approach for evaluating the geometrical, physical, and chemical properties of weathered soil particles and illustrates it with a completely decomposed tuff (CDT) soil. This refined evaluation approach consists of two parts. Part I separates soil into 25 sub-groups of gravel, sand, silt, and clay particles from 14 mm to less than 0.0008 mm by washing and sieving. Part II applies laboratory tests to examine the refined geometrical, physical, and chemical properties of each sub-group of materials. These laboratory tests include the dynamic and static image analysis for particle shape evaluation, the Atterberg limits test for plasticity evaluation, the falling head permeability test for hydraulic conductivity evaluation, the energy dispersive X-ray spectrometer (EDS) test and X-ray fluorescence spectrometer (XRF) test for elemental composition evaluation, and the X-ray diffractometer (XRD) test for mineral composition evaluation. The quantitative results of these refined properties of the soil materials can be expressed as a function of the particle size. The characteristics of each sub-group of particles together determine the properties of the soil mixture. This refined evaluation approach provides a new insight for examining the properties of weathered soils and their weathering degrees.</div></div>","PeriodicalId":50253,"journal":{"name":"Journal of Asian Earth Sciences","volume":"277 ","pages":"Article 106388"},"PeriodicalIF":2.7,"publicationDate":"2024-10-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142593063","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-10-28DOI: 10.1016/j.jseaes.2024.106379
Haibo Zou , Zipei Guo
Late Quaternary basaltic trachyandesites (SiO2 = 52.1–55.6 wt%) on the Tibetan Plateau are present at Laoguipo volcano, situated within the hydrothermally active Tengchong volcanic field (TVF) in the southeastern Tibetan Plateau. A low seismic velocity zone likely representing a magma body as the heat source for the geothermal system is detected 10–25 km below the Laoguipo volcano area and 80 % of seismic activities in TVF occur below Laoguipo and nearby Maanshan. Previously reported K-Ar ages for Laoguipo vary from Holocene to Middle Pleistocene (9 ka to 239 ka, thousand years ago) with large uncertainties. Here we use whole-rock 230Th-226Ra isotope disequilibrium and zircon 238U-230Th isotope disequilibrium to constrain the ages of Laoguipo basaltic trachyandesites. The eruption age for Laoguipo is 10.5 ± 2.5 ka. Zircon 238U-230Th isochron ages for 2 Laoguipo rocks are 55 ± 5 ka (2σ) and 61 ± 10 ka (2 σ), indicating a long magma residence time (∼45 ka) prior to eruption. Oxygen isotopes (δ18O) for Laoguipo zircons range from 6.8 to 7.8 ‰, higher than mantle-derived zircon δ18O value of 5.3 ± 0.6 ‰ (2σ). Hafnium isotopic values (εHf) for Laoguipo zircons are all negative, ranging from −13.9 to −3.7. Notably, zircon εHf values and zircon δ18O values are negatively correlated. Coupled with the sieve texture of plagioclase crystals, our data reveal that these relatively primitive mafic volcanic rocks at Laoguipo underwent an early-stage open-system magmatic processes. The young eruption age (10.5 ± 2.5 ka) and the active seismic activities suggest that Laoguipo is a potentially dangerous volcano in TVF, SE Tibet.
{"title":"Geochronology and petrogenesis of basaltic trachyandesites from Laoguipo volcano (SE Tibetan Plateau): U-series and Sr-Nd-Hf-O isotope constraints","authors":"Haibo Zou , Zipei Guo","doi":"10.1016/j.jseaes.2024.106379","DOIUrl":"10.1016/j.jseaes.2024.106379","url":null,"abstract":"<div><div>Late Quaternary basaltic trachyandesites (SiO<sub>2</sub> = 52.1–55.6 wt%) on the Tibetan Plateau are present at Laoguipo volcano, situated within the hydrothermally active Tengchong volcanic field (TVF) in the southeastern Tibetan Plateau. A low seismic velocity zone likely representing a magma body as the heat source for the geothermal system is detected 10–25 km below the Laoguipo volcano area and 80 % of seismic activities in TVF occur below Laoguipo and nearby Maanshan. Previously reported K-Ar ages for Laoguipo vary from Holocene to Middle Pleistocene (9 ka to 239 ka, thousand years ago) with large uncertainties. Here we use whole-rock <sup>230</sup>Th-<sup>226</sup>Ra isotope disequilibrium and zircon <sup>238</sup>U-<sup>230</sup>Th isotope disequilibrium to constrain the ages of Laoguipo basaltic trachyandesites. The eruption age for Laoguipo is 10.5 ± 2.5 ka. Zircon <sup>238</sup>U-<sup>230</sup>Th isochron ages for 2 Laoguipo rocks are 55 ± 5 ka (2σ) and 61 ± 10 ka (2 σ), indicating a long magma residence time (∼45 ka) prior to eruption. Oxygen isotopes (δ<sup>18</sup>O) for Laoguipo zircons range from 6.8 to 7.8 ‰, higher than mantle-derived zircon δ<sup>18</sup>O value of 5.3 ± 0.6 ‰ (2σ). Hafnium isotopic values (ε<sub>Hf</sub>) for Laoguipo zircons are all negative, ranging from −13.9 to −3.7. Notably, zircon ε<sub>Hf</sub> values and zircon δ<sup>18</sup>O values are negatively correlated. Coupled with the sieve texture of plagioclase crystals, our data reveal that these relatively primitive mafic volcanic rocks at Laoguipo underwent an early-stage open-system magmatic processes. The young eruption age (10.5 ± 2.5 ka) and the active seismic activities suggest that Laoguipo is a potentially dangerous volcano in TVF, SE Tibet.</div></div>","PeriodicalId":50253,"journal":{"name":"Journal of Asian Earth Sciences","volume":"277 ","pages":"Article 106379"},"PeriodicalIF":2.7,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142560706","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-10-28DOI: 10.1016/j.jseaes.2024.106380
Li Lixia , Yan Guanzhou , Wei Xin , Gong Fangyi , Oliver Lehnert , Wu Rongchang
A diverse and abundant isolated sponge spicule assemblage of Late Ordovician age is first reported from the western margin of the Yangtze Platform in South China. The spicule assemblage was recovered from argillaceous limestone sampled for conodonts. It includes 14 types which can be split into two categories: hexactinellid spicules and demosponge spicules. The assemblage primarily comprises hexactines and their derivatives, including not only some distinctive types such as Kometia cruciformis, but also large numbers of morphotypes that are quite common and diagnostic for hexactinellids, e.g. swollen hexactines, curved hexactines, and stauractines. Demosponge spicule types are represented by tetraxons, and various desmas typical for lithistids also occur. A highly modified hexactine, Kometia cruciformis, is recovered from China for the first time. This record represents currently the only recovery of such spicules from strata outside of Australia, and is coeval to the assemblage known from the Malongulli Formation. The presence of such unique modified hexactines (Kometia) in both time-equivalent assemblages suggests that certain spicules may have potential importance in biostratigraphic correlations and palaeobiogeographical interpretations, demonstrating the dispersal of taxa and their migration along the peri-Gondwana shelf areas during the Ordovician, driven by ocean current systems. The Late Ordovician sponge spicule assemblage from the Yangtze Platform provides new perspectives for investigating phylogeny, biostratigraphy, and palaeobiogeography of Palaeozoic sponges, and promotes some understanding of macroevolution in siliceous sponges.
{"title":"Late Ordovician sponge spicules from the Yangtze Platform, South China: Biostratigraphical and palaeobiogeographical significance","authors":"Li Lixia , Yan Guanzhou , Wei Xin , Gong Fangyi , Oliver Lehnert , Wu Rongchang","doi":"10.1016/j.jseaes.2024.106380","DOIUrl":"10.1016/j.jseaes.2024.106380","url":null,"abstract":"<div><div>A diverse and abundant isolated sponge spicule assemblage of Late Ordovician age is first reported from the western margin of the Yangtze Platform in South China. The spicule assemblage was recovered from argillaceous limestone sampled for conodonts. It includes 14 types which can be split into two categories: hexactinellid spicules and demosponge spicules. The assemblage primarily comprises hexactines and their derivatives, including not only some distinctive types such as <em>Kometia cruciformis</em>, but also large numbers of morphotypes that are quite common and diagnostic for hexactinellids, e.g. swollen hexactines, curved hexactines, and stauractines. Demosponge spicule types are represented by tetraxons, and various desmas typical for lithistids also occur. A highly modified hexactine, <em>Kometia cruciformis</em>, is recovered from China for the first time. This record represents currently the only recovery of such spicules from strata outside of Australia, and is coeval to the assemblage known from the Malongulli Formation. The presence of such unique modified hexactines (<em>Kometia</em>) in both time-equivalent assemblages suggests that certain spicules may have potential importance in biostratigraphic correlations and palaeobiogeographical interpretations, demonstrating the dispersal of taxa and their migration along the <em>peri</em>-Gondwana shelf areas during the Ordovician, driven by ocean current systems. The Late Ordovician sponge spicule assemblage from the Yangtze Platform provides new perspectives for investigating phylogeny, biostratigraphy, and palaeobiogeography of Palaeozoic sponges, and promotes some understanding of macroevolution in siliceous sponges.</div></div>","PeriodicalId":50253,"journal":{"name":"Journal of Asian Earth Sciences","volume":"277 ","pages":"Article 106380"},"PeriodicalIF":2.7,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142586058","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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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