Mineral resources prediction and assessment is one of the most important tasks in geosciences.Geochemical anomalies,as direct indicators of the presence of mineralization,have played a significant role in the search o...Mineral resources prediction and assessment is one of the most important tasks in geosciences.Geochemical anomalies,as direct indicators of the presence of mineralization,have played a significant role in the search of mineral deposits in the past several decades.In the near future,it may be possible to recognize subtle geochemical anomalies through the use of processing of geochemical exploration data using advanced approaches such as the spectrum-area multifractal model.In addition,negative geochemical anomalies can be used to locate mineralization.However,compared to positive geochemical anomalies,there has been limited research on negative geochemical anomalies in geochemical prospecting.In this study,two case studies are presented to demonstrate the identification of subtle geochemical anomalies and the significance of negative geochemical anomalies.Meanwhile,the opportunities and challenges in evaluating subtle geochemical anomalies associated with mineralization,and benefits of mapping of negative anomalies are discussed.展开更多
Two suites of mafic dykes,T1193-A and T1194-A,outcrop in Gyangze area,southeast Xizang.They are in the area of Comei LIP and have indistinguishable field occurrences with two other dykes in Gyangze,T0902 dyke with 137...Two suites of mafic dykes,T1193-A and T1194-A,outcrop in Gyangze area,southeast Xizang.They are in the area of Comei LIP and have indistinguishable field occurrences with two other dykes in Gyangze,T0902 dyke with 137.7±1.3 Ma zircon age and T0907 dyke with 142±1.4 Ma zircon age reported by Wang YY et al.(2016),indicating coeval formation time.Taking all the four diabase dykes into consideration,two different types,OIB-type and weak enriched-type,can be summarized.The“OIB-type”samples,including T1193-A and T0907 dykes,show OIB-like geochemical features and have initial Sr-Nd isotopic values similar with most mafic products in Comei Large Igneous Provinces(LIP),suggesting that they represent melts directly generated from the Kerguelen mantle plume.The“weak enriched-type”samples,including T1194-A and T0902 dykes,have REEs and trace element patterns showing withinplate affinity but have obvious Nb-Ta-Ti negative anomalies.They show uniform lowerεNd(t)values(−6‒−2)and higher 87Sr/86Sr(t)values(0.706‒0.709)independent of their MgO variation,indicating one enriched mantle source.Considering their closely spatial and temporal relationship with the widespread Comei LIP magmatic products in Tethyan Himalaya,these“weak enriched-type”samples are consistent with mixing of melts from mantle plume and the above ancient Tethyan Himalaya subcontinental lithospheric mantle(SCLM)in different proportions.These weak enriched mafic rocks in Comei LIP form one special rock group and most likely suggest large scale hot mantle plume-continental lithosphere interaction.This process may lead to strong modification of the Tethyan Himalaya lithosphere in the Early Cretaceous.展开更多
The S wave velocity structure of the earth below Eastern Southeast Asia has been investigated by analyzing the seismogram from surface wave to multiple depth waves in the time domain and three Cartesian components sim...The S wave velocity structure of the earth below Eastern Southeast Asia has been investigated by analyzing the seismogram from surface wave to multiple depth waves in the time domain and three Cartesian components simultaneously.The wave passes across the front area of subduction zone between the Philippine plate and the Asian plate.The main data are waveform comparisons,instead of the arrival times.The synthetic seismogram is calculated using the GEMINI method.The synthetic seismogram constructed by PREMAN global earth model deviates greatly from the measured one.To solve this problem,corrections are needed for the β speed structure.Corrections cover the gradient change of β_h,which turns from negative to positive in upper mantle layers as in the PREMAN,change of earth crust depth and change of zero order coefficients of β velocity function in all earth mantle layers.So,the fitting is obtained,as well as the arrival time or the waveform of Love and Rayleigh surface waves,the S wave and the repetitive depth waves ScS_2 and ScS_3.This result reveals that the Southeast Asia,being stretched due to tectonic release,has a mantle in some parts with negative anomaly of S wave velocity and vertical anisotropy in all earth mantle layers.展开更多
Peridotites from the southern Mariana forearc were sampled on the landward trench slope of the Izu-Bonin-Mariana (IBM) subduction zone by dredging.These mantle wedge peridotites underwent hydration by fluid derived fr...Peridotites from the southern Mariana forearc were sampled on the landward trench slope of the Izu-Bonin-Mariana (IBM) subduction zone by dredging.These mantle wedge peridotites underwent hydration by fluid derived from a dehydrated descending slab,and later interacted with seawater after emplacement at or near the seafloor.This study investigates how these two different rock-fluid interaction processes influenced trace element distribution in the southern Mariana forearc peridotites.We measured trace element concentrations of peridotites from the southern Mariana forearc.The southern Mariana forearc peridotites are characterized by a distinct seawater-like REE pattern with an obvious negative Ce anomaly,and La shows good correlation with other REEs (except Ce).In addition,there is a great enrichment of U,Pb,Sr and Li elements,which show a distinct positive anomaly relative to adjacent elements in the multi-element diagram.For the seawater-like REE pattern,we infer that REEs are mainly influenced by seawater during peridotite-seawater interactions after their emplacement at or near the seafloor,by serpentinization or by marine weathering.Furthermore,the anomalous behavior of Ce,compared with other rare earth elements in these samples,may indicate that they have undergone reactions involving Ce (IV) when the peridotites interacted with seawater.Positive U,Pb,Sr and Li anomalies are inferred to be related to seawater and/or fluids released during dehydration of the subducting slab.展开更多
The study of burnt rocks is beneficial to the discussion on the tectonic movement, paleoclimate and paleogeography that coal seams are subjected to after they were formed. In order to obtain the basic data on the feat...The study of burnt rocks is beneficial to the discussion on the tectonic movement, paleoclimate and paleogeography that coal seams are subjected to after they were formed. In order to obtain the basic data on the features of the burnt rocks, a systematic study of petrology and REE geochemistry on burnt rocks in Shenmu, Northern Shaanxi Province has been done, using the methods of SEM, EDS, susceptibility measurements and ICP-MS. The burnt rocks are divided into two series in the section： the melted rocks and the baked rocks. SEM and EDS analyses reveal that all the minerals show burnt and melted traces, and there are no clay minerals except illite found in the burnt rocks. Susceptibility measurements reveal that the burnt rocks have abnormally high susceptibility values, whereas a geochemical analysis shows that the REE distribution pattern of burnt rocks is similar to that of sedimentary rocks （initial rocks）. In the longitudinal section, with increasing degree of burning （from baked rocks to melted rocks）, the ∑REE gradually decreases, and the total REE of melted rocks is obviously lower than that of baked rocks. Besides, the melted rocks show apparent negative Ce anomalies, while the baked rocks show no anomaly of Ce, and sometimes even show positive anomalies.展开更多
Cerium is one of multivalent rear earth elements, which can transfer from trivalence to tretavalence at oxidizing environment. This process may cause variable degrees of fractionation of Ce from other trivalent rear e...Cerium is one of multivalent rear earth elements, which can transfer from trivalence to tretavalence at oxidizing environment. This process may cause variable degrees of fractionation of Ce from other trivalent rear earth elements, and thus may provide specific insight into the geological processes associated with marked redoxomorphism. Multiple geochemical tracing of Sr-Nd-Ce isotopes are performed on the felsic and mafic intrusives of the Neoproterozoic（~800 Ma） Huangling complex located at the eastern Three Gorges, South China. The intrusive rocks exclusively show various extents of negative Ce anomalies. On the εCe-εNd plot, most samples from the mafic intrusions scatter within the second quadrant, whereas those from the felsic intrusions within the fourth Quadrant. Both of the two groups exhibit relatively large range of ？Ce（t） variation but limited ？Nd（t） range, which cause a deviation from the ＂crustal array＂ and reveal a decoupled Nd-Ce isotope correlation. The intermediate-felsic suite have varied Ce/Ce＊ ratios but broadly proximate εCe（t） values, indicating that their negative Ce anomalies were generated during the magmatism; on the contrary, a positive correlation between εCe（t） and Ce/Ce＊ is observed for the intermediate-mafic suite, an indication of an origin of post-magmatic alteration or metamorphism for their Ce anomalies. Calculation of model age, the occurrence age of negative Ce anomalies（TCe） for the intermediate-mafic samples infers that the alteration events took place 〉350 Ma. Data showed that negative Ce anomalies of the felsic intrusions may reflect an increase of oxygen fugacity during magma ascending, rather than an inheritance from their source rocks. This explanation implies that the Neoproterozoic magmatism occurred at the continental nucleus of the Yangtze block were developing at a geodynamic context of rapidly regional uplifting.展开更多
Total platinum-group elements （PGEs） abundances in basalts from the spreading axis of Mariana Trough ranged from 0.418 × 10^9 to 1. 022 × 10^-9, and primitive mantle-normalized PGE patterns are of positive...Total platinum-group elements （PGEs） abundances in basalts from the spreading axis of Mariana Trough ranged from 0.418 × 10^9 to 1. 022 × 10^-9, and primitive mantle-normalized PGE patterns are of positive slope showing the relative enrichment of PPGE （ platinum, palladium, rhodium） and gold relative to IPGE. Compared with other mantle-originated rocks, these basalts have lower PGE contents and wider ranges of primitive mantle-normalized ratios of palladium content to iridium one, palladium content to platinum one and palladium content to gold one exhibiting relative platinum and iridium depletion. Characteristics of PGE patterns indicated that the studied Mariana Trough basalts originated from low partial melting, and the MORB mantle beneath the spreading center had been contaminated by the are-island mantle. In the aspect of trace elements, Mariana Trough basalts showed the enrichment of LILE, lead and LREE, indicating that they had been influenced by subduetion compositions. All these demonstrated that Mariana Trough basalts are products of partial melting from a mixed mantle （ the contamination of MORB mantle by are-island mantle）.展开更多
The S-wave velocity across the earth structure under Indonesia for Indonesia earthquakes has been investigated through seismogram analysis, simultaneously in the time domain and three Cartesian components. The data we...The S-wave velocity across the earth structure under Indonesia for Indonesia earthquakes has been investigated through seismogram analysis, simultaneously in the time domain and three Cartesian components. The data were recorded at DAV observational station, the Philippines. The main data set is the seismogram comparison between the measured and synthetic seismogram, instead of travel time data, as commonly used in other seismological research. The synthetic seismogram is calculated using the GEMINI method, which is equivalent to Mode Summation. The above seismogram comparison shows that the global earth mantle of PREMAN gives a deviating synthetic seismogram and has earlier arrival times than those of the measurement. The gradient of βh in the upper mantle layers is altered into a positive, rather than negative slope as stated in the PREMAN model, and negative corrections are imposed to the zero order of the polynomiars coefficients in all earth mantle layers. The excellent fitting, as well as travel time or waveform, is obtained from the surface waves of Love and Rayleigh, surface wave to the S and SS mantle waves as well as the core reflected waves. This result expresses that part of the earth mantle, due to a collision between India and Asia tectonic released zones, has a negative anomaly in S-wave velocity and vertical anisotropy in all of the earth mantle layers.展开更多
In the north Indian Ocean (NIO), maps of sea level anomaly from satellite altimetry were analysed from January-1995 to December-2000. The study attempted to trace the trajectories of the individual mesoscale anomalies...In the north Indian Ocean (NIO), maps of sea level anomaly from satellite altimetry were analysed from January-1995 to December-2000. The study attempted to trace the trajectories of the individual mesoscale anomalies manually and to understand seasonal changes in terms of phase speed. Mesoscale anomalies are detected as concentric circular shapes and diameters of ~90 km to 600 km and the minimum 30 days life cycle. Relatively higher eddy kinetic energy was noticed in the northwestern region of the NIO. Individual mesoscale anomalies, namely positive (warm, anticyclonic eddies) and negative (cold, cyclonic eddies) showing travelling direction westward in the NIO basins. In autumn, the number of negative anomalies detected is more than positive anomalies and vice versa during summer. The westward propagating positive (negative) anomalies in the Arabian Sea start appearing in winter (spring) along (away from) the west coast of India and west of 65°E;individual anomalies move to the west in spring/summer/autumn and collide along Somalia’s & Arabian coast. A group of positive (negative) anomalies trajectories appears as a tail at the southern tip of India are located west of the Laccadive ridge in winter (summer to autumn) associated with LH (LL). The Bay of Bengal (BB) trajectories show southwestward in northern BB, westward in central BB and northwestward in southern BB;individual anomalies are appearing along the west coast of Andaman & Nicobar ridge. The zonal phase speed decreases away from the equator, and the magnitude varies longitudinally in each season in the form of a wave-like pattern propagating westward from autumn to summer;the life cycle of the wave is almost 365 days (a year). The theoretical phase speed of the first mode of the baroclinic Rossby waves is quite similar to that of averaged zonal speed. Therefore mesoscale anomalies (eddies) are embedded into the large waves like phenomenon (Rossby waves), responsible for creating high variability and EKE in the region of NIO along the western boundaries.展开更多
基金supported by the National Natural Science Foundation of China(No.41772344)。
文摘Mineral resources prediction and assessment is one of the most important tasks in geosciences.Geochemical anomalies,as direct indicators of the presence of mineralization,have played a significant role in the search of mineral deposits in the past several decades.In the near future,it may be possible to recognize subtle geochemical anomalies through the use of processing of geochemical exploration data using advanced approaches such as the spectrum-area multifractal model.In addition,negative geochemical anomalies can be used to locate mineralization.However,compared to positive geochemical anomalies,there has been limited research on negative geochemical anomalies in geochemical prospecting.In this study,two case studies are presented to demonstrate the identification of subtle geochemical anomalies and the significance of negative geochemical anomalies.Meanwhile,the opportunities and challenges in evaluating subtle geochemical anomalies associated with mineralization,and benefits of mapping of negative anomalies are discussed.
基金supported by National Science Foundation of China(42102059 and 92055202)the China Geological Survey(DD20221817 and DD20190057)+1 种基金the basic scientific research funding in CAGS(J2204)the Second Tibetan Plateau Scientific Expedition and Research(2019QZKK0702).
文摘Two suites of mafic dykes,T1193-A and T1194-A,outcrop in Gyangze area,southeast Xizang.They are in the area of Comei LIP and have indistinguishable field occurrences with two other dykes in Gyangze,T0902 dyke with 137.7±1.3 Ma zircon age and T0907 dyke with 142±1.4 Ma zircon age reported by Wang YY et al.(2016),indicating coeval formation time.Taking all the four diabase dykes into consideration,two different types,OIB-type and weak enriched-type,can be summarized.The“OIB-type”samples,including T1193-A and T0907 dykes,show OIB-like geochemical features and have initial Sr-Nd isotopic values similar with most mafic products in Comei Large Igneous Provinces(LIP),suggesting that they represent melts directly generated from the Kerguelen mantle plume.The“weak enriched-type”samples,including T1194-A and T0902 dykes,have REEs and trace element patterns showing withinplate affinity but have obvious Nb-Ta-Ti negative anomalies.They show uniform lowerεNd(t)values(−6‒−2)and higher 87Sr/86Sr(t)values(0.706‒0.709)independent of their MgO variation,indicating one enriched mantle source.Considering their closely spatial and temporal relationship with the widespread Comei LIP magmatic products in Tethyan Himalaya,these“weak enriched-type”samples are consistent with mixing of melts from mantle plume and the above ancient Tethyan Himalaya subcontinental lithospheric mantle(SCLM)in different proportions.These weak enriched mafic rocks in Comei LIP form one special rock group and most likely suggest large scale hot mantle plume-continental lithosphere interaction.This process may lead to strong modification of the Tethyan Himalaya lithosphere in the Early Cretaceous.
基金This research is funded by the DanaHibah Penelitian Dasar of DIKTI (Grant Fund of the Basic Research from Higher Education Agency) with grant number 019/SP3/PP/DP2M/Ⅱ/2006
文摘The S wave velocity structure of the earth below Eastern Southeast Asia has been investigated by analyzing the seismogram from surface wave to multiple depth waves in the time domain and three Cartesian components simultaneously.The wave passes across the front area of subduction zone between the Philippine plate and the Asian plate.The main data are waveform comparisons,instead of the arrival times.The synthetic seismogram is calculated using the GEMINI method.The synthetic seismogram constructed by PREMAN global earth model deviates greatly from the measured one.To solve this problem,corrections are needed for the β speed structure.Corrections cover the gradient change of β_h,which turns from negative to positive in upper mantle layers as in the PREMAN,change of earth crust depth and change of zero order coefficients of β velocity function in all earth mantle layers.So,the fitting is obtained,as well as the arrival time or the waveform of Love and Rayleigh surface waves,the S wave and the repetitive depth waves ScS_2 and ScS_3.This result reveals that the Southeast Asia,being stretched due to tectonic release,has a mantle in some parts with negative anomaly of S wave velocity and vertical anisotropy in all earth mantle layers.
基金Supported by the Pilot Project of Knowledge Innovation Project,Chinese Academy of Sciences (Nos.KZCX2-YW-211, KZCX3-SW-223)the National Natural Science Foundation of China (No.40830849)the Special Foundation for the Eleventh Five-Year Plan of COMRA (No.DYXM-115-02-1-03)
文摘Peridotites from the southern Mariana forearc were sampled on the landward trench slope of the Izu-Bonin-Mariana (IBM) subduction zone by dredging.These mantle wedge peridotites underwent hydration by fluid derived from a dehydrated descending slab,and later interacted with seawater after emplacement at or near the seafloor.This study investigates how these two different rock-fluid interaction processes influenced trace element distribution in the southern Mariana forearc peridotites.We measured trace element concentrations of peridotites from the southern Mariana forearc.The southern Mariana forearc peridotites are characterized by a distinct seawater-like REE pattern with an obvious negative Ce anomaly,and La shows good correlation with other REEs (except Ce).In addition,there is a great enrichment of U,Pb,Sr and Li elements,which show a distinct positive anomaly relative to adjacent elements in the multi-element diagram.For the seawater-like REE pattern,we infer that REEs are mainly influenced by seawater during peridotite-seawater interactions after their emplacement at or near the seafloor,by serpentinization or by marine weathering.Furthermore,the anomalous behavior of Ce,compared with other rare earth elements in these samples,may indicate that they have undergone reactions involving Ce (IV) when the peridotites interacted with seawater.Positive U,Pb,Sr and Li anomalies are inferred to be related to seawater and/or fluids released during dehydration of the subducting slab.
文摘The study of burnt rocks is beneficial to the discussion on the tectonic movement, paleoclimate and paleogeography that coal seams are subjected to after they were formed. In order to obtain the basic data on the features of the burnt rocks, a systematic study of petrology and REE geochemistry on burnt rocks in Shenmu, Northern Shaanxi Province has been done, using the methods of SEM, EDS, susceptibility measurements and ICP-MS. The burnt rocks are divided into two series in the section： the melted rocks and the baked rocks. SEM and EDS analyses reveal that all the minerals show burnt and melted traces, and there are no clay minerals except illite found in the burnt rocks. Susceptibility measurements reveal that the burnt rocks have abnormally high susceptibility values, whereas a geochemical analysis shows that the REE distribution pattern of burnt rocks is similar to that of sedimentary rocks （initial rocks）. In the longitudinal section, with increasing degree of burning （from baked rocks to melted rocks）, the ∑REE gradually decreases, and the total REE of melted rocks is obviously lower than that of baked rocks. Besides, the melted rocks show apparent negative Ce anomalies, while the baked rocks show no anomaly of Ce, and sometimes even show positive anomalies.
基金supported by the National Natural Science Foundation of China (Nos. 41373037, 41173048, 41503025)
文摘Cerium is one of multivalent rear earth elements, which can transfer from trivalence to tretavalence at oxidizing environment. This process may cause variable degrees of fractionation of Ce from other trivalent rear earth elements, and thus may provide specific insight into the geological processes associated with marked redoxomorphism. Multiple geochemical tracing of Sr-Nd-Ce isotopes are performed on the felsic and mafic intrusives of the Neoproterozoic（~800 Ma） Huangling complex located at the eastern Three Gorges, South China. The intrusive rocks exclusively show various extents of negative Ce anomalies. On the εCe-εNd plot, most samples from the mafic intrusions scatter within the second quadrant, whereas those from the felsic intrusions within the fourth Quadrant. Both of the two groups exhibit relatively large range of ？Ce（t） variation but limited ？Nd（t） range, which cause a deviation from the ＂crustal array＂ and reveal a decoupled Nd-Ce isotope correlation. The intermediate-felsic suite have varied Ce/Ce＊ ratios but broadly proximate εCe（t） values, indicating that their negative Ce anomalies were generated during the magmatism; on the contrary, a positive correlation between εCe（t） and Ce/Ce＊ is observed for the intermediate-mafic suite, an indication of an origin of post-magmatic alteration or metamorphism for their Ce anomalies. Calculation of model age, the occurrence age of negative Ce anomalies（TCe） for the intermediate-mafic samples infers that the alteration events took place 〉350 Ma. Data showed that negative Ce anomalies of the felsic intrusions may reflect an increase of oxygen fugacity during magma ascending, rather than an inheritance from their source rocks. This explanation implies that the Neoproterozoic magmatism occurred at the continental nucleus of the Yangtze block were developing at a geodynamic context of rapidly regional uplifting.
基金This study was supported by the National Natural Science Foundation of China under contract No. 40273025the National High Technology Research and Development of China under contract No. 2006AA09Z219+1 种基金the Key Laboratory of Marine Sedimentology and Environmental Geology, the State 0ceanic Administrationthe National Basic Research Program of China under contract No. G2000078503.
文摘Total platinum-group elements （PGEs） abundances in basalts from the spreading axis of Mariana Trough ranged from 0.418 × 10^9 to 1. 022 × 10^-9, and primitive mantle-normalized PGE patterns are of positive slope showing the relative enrichment of PPGE （ platinum, palladium, rhodium） and gold relative to IPGE. Compared with other mantle-originated rocks, these basalts have lower PGE contents and wider ranges of primitive mantle-normalized ratios of palladium content to iridium one, palladium content to platinum one and palladium content to gold one exhibiting relative platinum and iridium depletion. Characteristics of PGE patterns indicated that the studied Mariana Trough basalts originated from low partial melting, and the MORB mantle beneath the spreading center had been contaminated by the are-island mantle. In the aspect of trace elements, Mariana Trough basalts showed the enrichment of LILE, lead and LREE, indicating that they had been influenced by subduetion compositions. All these demonstrated that Mariana Trough basalts are products of partial melting from a mixed mantle （ the contamination of MORB mantle by are-island mantle）.
文摘The S-wave velocity across the earth structure under Indonesia for Indonesia earthquakes has been investigated through seismogram analysis, simultaneously in the time domain and three Cartesian components. The data were recorded at DAV observational station, the Philippines. The main data set is the seismogram comparison between the measured and synthetic seismogram, instead of travel time data, as commonly used in other seismological research. The synthetic seismogram is calculated using the GEMINI method, which is equivalent to Mode Summation. The above seismogram comparison shows that the global earth mantle of PREMAN gives a deviating synthetic seismogram and has earlier arrival times than those of the measurement. The gradient of βh in the upper mantle layers is altered into a positive, rather than negative slope as stated in the PREMAN model, and negative corrections are imposed to the zero order of the polynomiars coefficients in all earth mantle layers. The excellent fitting, as well as travel time or waveform, is obtained from the surface waves of Love and Rayleigh, surface wave to the S and SS mantle waves as well as the core reflected waves. This result expresses that part of the earth mantle, due to a collision between India and Asia tectonic released zones, has a negative anomaly in S-wave velocity and vertical anisotropy in all of the earth mantle layers.
文摘In the north Indian Ocean (NIO), maps of sea level anomaly from satellite altimetry were analysed from January-1995 to December-2000. The study attempted to trace the trajectories of the individual mesoscale anomalies manually and to understand seasonal changes in terms of phase speed. Mesoscale anomalies are detected as concentric circular shapes and diameters of ~90 km to 600 km and the minimum 30 days life cycle. Relatively higher eddy kinetic energy was noticed in the northwestern region of the NIO. Individual mesoscale anomalies, namely positive (warm, anticyclonic eddies) and negative (cold, cyclonic eddies) showing travelling direction westward in the NIO basins. In autumn, the number of negative anomalies detected is more than positive anomalies and vice versa during summer. The westward propagating positive (negative) anomalies in the Arabian Sea start appearing in winter (spring) along (away from) the west coast of India and west of 65°E;individual anomalies move to the west in spring/summer/autumn and collide along Somalia’s & Arabian coast. A group of positive (negative) anomalies trajectories appears as a tail at the southern tip of India are located west of the Laccadive ridge in winter (summer to autumn) associated with LH (LL). The Bay of Bengal (BB) trajectories show southwestward in northern BB, westward in central BB and northwestward in southern BB;individual anomalies are appearing along the west coast of Andaman & Nicobar ridge. The zonal phase speed decreases away from the equator, and the magnitude varies longitudinally in each season in the form of a wave-like pattern propagating westward from autumn to summer;the life cycle of the wave is almost 365 days (a year). The theoretical phase speed of the first mode of the baroclinic Rossby waves is quite similar to that of averaged zonal speed. Therefore mesoscale anomalies (eddies) are embedded into the large waves like phenomenon (Rossby waves), responsible for creating high variability and EKE in the region of NIO along the western boundaries.
