GSA Bulletin最新文献

{"title":"Geochemistry and geochronology of the Bay of Islands metamorphic sole, Newfoundland, Canada: Protoliths and implications for subduction initiation","authors":"François Fournier-Roy, C. Guilmette, K. Larson, Antoine Godet, M. Soret, C. V. van Staal, J. Bédard","doi":"10.1130/b36662.1","DOIUrl":"https://doi.org/10.1130/b36662.1","url":null,"abstract":"The Bay of Islands complex, Newfoundland, Canada, represents a fossil subduction system that was obducted onto the Laurentian margin during the Taconic Orogeny. We present whole-rock geochemistry and geochronology for the Bay of Islands metamorphic sole from the Table Mountain and North Arm Mountain massifs. The Bay of Islands metamorphic sole can be subdivided into three units: a high metamorphic-grade Grt-Cpx amphibolite and Grt-Cpx granulite unit, a medium metamorphic-grade common amphibolite unit, and a medium metamorphic-grade metasedimentary-dominated unit. Based on their major and trace element contents, two types of protoliths can be inferred for the Bay of Islands sole metabasites: cumulate gabbroic protoliths with high Mg numbers and depleted trace element contents, and basaltic protoliths with trace element contents defining a normal mid-oceanic-ridge basalt (N-MORB) affinity. Titanite in situ U-Pb analyses of two common amphibolite samples yield dates of 486 ± 7 Ma and 484 ± 4 Ma, which are interpreted as a metamorphic age (ca. 485 Ma). One sample from the metasedimentary unit yields detrital zircon dates that range from Archean to Ordovician, with the youngest dates defining the most dominant peak at ca. 490 Ma. This youngest peak is consistent with an arc-related source that may be linked with arc magmatism of the upper plate during the Taconic Orogeny. These observations suggest that (1) the subduction responsible for the formation of the Bay of Islands complex nucleated in an oceanic domain before ca. 485 Ma; and (2) the sediments that form the metasedimentary unit were partly sourced from the upper plate and were deposited on the lower plate while subduction was active.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114172763","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Estimating paleotidal constituents from Pliocene “tidal gauges”—an example from the paleo-Orinoco Delta, Trinidad","authors":"Si Chen, E. Kvale, R. Steel, C. Olariu, Jinyu Zhang","doi":"10.1130/b36619.1","DOIUrl":"https://doi.org/10.1130/b36619.1","url":null,"abstract":"The Neogene Orinoco Delta is one of the typical river deltas where both the records of modern and ancient tidal processes can be studied. A ∼5 m.y./>10-km-thick succession on the island of Trinidad contains remnants of paleo-Orinoco deltaic deposition preserving both tide- and wave-influenced delta lobes within the same time intervals, just like the modern Orinoco Delta that has both wave-dominated and tidal-dominated lobes. The tide-influenced delta lobes and estuaries preserve some spectacular tidal bedding signals, including tidal rhythmites. The tidal record encoded within the tidal rhythmites is preserved well enough that the primary tidal constituents responsible for the tidal currents that deposited the rhythmic facies can be inferred.\u0000 Lower to upper Pliocene tidal rhythmites were examined in two main paleo-Orinoco sub-environments: (1) estuarine and delta lobe deposits of Morne L’Enfer Formation at Erin Bay, and (2) abandoned tidal channels associated with tide-influenced delta-front deposits from the Telemaque Sandstone Member of the Manzanilla Formation at Matura Bay. Both wave- and river-current signals are also present in most of the study areas.\u0000 Tidal constituent analysis of unusually well-preserved paleo-Orinoco tidal rhythmites reveals a hierarchy of tidal signals that include semidiurnal, diurnal, fortnightly (neap−spring), monthly (perigee−apogee), semi-yearly, and possibly seasonal and yearly cycles that span thickness intervals ranging from millimeters to meters.\u0000 The tidal constituents were dominated by, in decreasing importance, M2, S2, and likely K1 rather than O1. The modern tidal data clearly show that K1 is more important in terms of tide-generating potential than O1, as was likely so in the Pliocene. In both the rock and modern records, N2 is more significant than O1, P1, and K2 in terms of tide-generating potential. The comparison between the constituent analysis of the ancient tidal record and the modern tidal measurements reveals their similarities in tidal patterns and constituent types. From this, we deduce that the tidal constituents responsible for the Pliocene Orinoco Delta tides were mixed semidiurnal tidal cycles similar to those found today in Trinidad (Atlantic type of synodically dominated) rather than the Caribbean (tropically dominated) type.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"154 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121234191","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Transition from breccia pipe to stratabound mineralization in Mississippi Valley-type hydrothermal systems: The Nayongzhi Zn-Pb deposit, world-class Sichuan−Yunnan−Guizhou triangle, South China","authors":"","doi":"10.1130/b36630.1","DOIUrl":"https://doi.org/10.1130/b36630.1","url":null,"abstract":"Unraveling the time-space evolution of Mississippi Valley-type (MVT) hydrothermal systems is critically important for understanding ore genesis and exploration. We studied a complete mineral system from conduit-filling to tail-end facies in the world-class Sichuan−Yunnan−Guizhou triangle, South China, via field geology, mineralogy, fluid inclusions, and in situ sulfide S-Pb isotopes to propose an integrated model for the evolution of MVT hydrothermal systems. Geological mapping shows that the mineralization transitions from breccia pipe to stratabound style: high-grade ores occur mainly as open-space infill associated with F12 fault (fluid conduit), while low-grade evaporite-related replacement ores developed distal from the fault. The δ34S value in hydrothermal sulfides shows a wide range (+3.6‰ to +27.9‰), with significant intragrain variation (up to +12.8‰), which suggests a mixture of 34S-rich sulfur produced by thermochemical sulfate reduction of evaporite within the ore host and 32S-rich sedimentary/diagenetic pyrite. In situ sulfide Pb ratios decrease away from the F12 fault, which indicates that metals were sourced from different degrees of mixing between the Proterozoic metamorphic basement and wall rocks. Fluid-inclusion microthermometric data identify two distinct fluids: a hotter (>155 °C), more saline (>18 wt% NaCl equivalent), and metal-rich fluid with a cooler (<90 °C), low-salinity (<4 wt% NaCl equivalent), and reduced sulfur-rich fluid. The mixing of two fluids was responsible for precipitating the high-grade ores near the F12 fault, and the acid-producing (H+) process created new space for stratabound ore distal to the fault. This study highlights that fluid mixing is critical for efficient sulfide accumulation, and the metal zoning pattern provides guidelines for exploration.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"117 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121395180","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tectonic and stratigraphic evolution of the late Paleozoic Darwin Basin, eastern California, USA, and implications for the onset of subduction along the southwestern Cordilleran margin of Laurentia","authors":"Lochlan Vaughn, R. Leary, M. Read","doi":"10.1130/b36664.1","DOIUrl":"https://doi.org/10.1130/b36664.1","url":null,"abstract":"The Darwin Basin, eastern California, USA, represents a key sedimentary record of tectonics along the southwestern margin of Laurentia for the late Pennsylvanian and Cisuralian (Early Permian). The basin formed when the subsidence rate of the southwestern margin of the Bird Spring Shelf abruptly increased, resulting in the deposition of deep-water facies in areas that had been shelf or littoral environments since the Neoproterozoic. We present new sedimentologic, stratigraphic, conodont biostratigraphic, and subsidence analyses of Darwin Basin strata that document the Pennsylvanian−Permian evolution of the Darwin Basin. We argue that the Darwin Basin evolved in two phases: (1) a Pennsylvanian to mid-Cisuralian foreland basin phase that co-occurred with transpressional deformation of the southwestern margin of Laurentia and was characterized by unconformity development, deposition of coarse-grained carbonate slope-apron facies, syndepositional deformation, and the development of complex basin-floor bathymetry; and (2) a mid-Cisuralian to Guadalupian (middle Permian) phase that preceded and co-occurred with the onset of arc magmatism outboard of the Darwin Basin and is characterized by rapid, uniform subsidence of the entire basin, burial of paleobathymetric highs, and the end of syndepositional deformation. We propose that the transition between these phases may represent a local response to the initiation of the North American Cordilleran subduction zone to the west of the Darwin Basin. We argue that the onset of rapid mid-Cisuralian subsidence documented within the Darwin Basin provides an estimated date of subduction zone initiation that is consistent with previous estimates of the timing of this event, the arc magmatic record, and Cenozoic subduction zone analogs.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133295429","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Opening of the Sumdo Paleo-Tethys Ocean and rifting of the Lhasa terrane from Gondwana: Insights from early Carboniferous magmatism in southern Tibet","authors":"Bin Wang, Chao-Ming Xie, C. Yakymchuk, Yongsheng Dong, Yuhang Song, Meng-long Duan","doi":"10.1130/b36761.1","DOIUrl":"https://doi.org/10.1130/b36761.1","url":null,"abstract":"The late Paleozoic tectonic evolution of the Lhasa terrane and opening of the Sumdo Paleo-Tethys Ocean remain controversial due to limited data and the ambiguous tectonic significance of Paleozoic magmatism in the southern Lhasa subterrane. Here, we explore the petrogenesis of meta-basalt from the Tangjia area and meta-gabbro from the Sumdo area to provide new constraints on the evolution of the Lhasa terrane. The geochemical characteristics of meta-gabbro are similar to those of oceanic island basalt and have positive whole-rock εNd(t) values (+0.08 to +1.03) and zircon εHf(t) values (+3.4 to +4.9), which suggests that they originated from asthenospheric mantle with minor contributions from lithospheric mantle in an intracontinental rift setting. The meta-basalt yields positive whole-rock εNd(t) values (+6.47 to +6.60) and zircon εHf(t) values (+14.2 to +15.2) and has enriched mid-oceanic-ridge−like geochemical characteristics; we suggest that the meta-basalt was sourced from the depleted mantle and interacted with enriched components in an initial oceanic basin setting. Zircon U−Pb geochronology of meta-basalt and meta-gabbro yielded crystallization ages of ca. 338 Ma and ca. 345 Ma, respectively. We suggest that the Sumdo Paleo-Tethys Ocean opened in the early Carboniferous. Negative buoyancy of Paleo-Tethys oceanic slab during subduction toward Eurasia drove the opening of the Sumdo Paleo-Tethys Ocean. Given that the Sumdo Paleo-Tethys Ocean was a limited oceanic basin, the Lhasa terrane was not completely separated from the northern margin of Gondwana before the Permian.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126510778","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Gold mineralized diorite beneath the Linglong ore field, North China craton: New insights into the origin of decratonization-related gold deposits","authors":"Zhanke Li, Jian-wei Li, Huashan Sun, Xin-Fu Zhao, A. Tomkins, D. Selby, P. Robinson, Xiao-Dong Deng, Zaicong Wang, Zhongxin Yuan, Shao-Rui Zhao","doi":"10.1130/b36658.1","DOIUrl":"https://doi.org/10.1130/b36658.1","url":null,"abstract":"Gold deposits in Precambrian cratons were mostly generated during the formation and stabilization of the cratons, but the North China craton is unusual in that its gold deposits were mainly formed ∼1.7 b.y. after its stabilization. A magmatic-hydrothermal origin or mantle-derived fluid source has been proposed for the giant gold deposits of the Jiaodong District in the eastern North China craton, but direct evidence is sparse, and the mineralization processes remain controversial. Here, we present the results of a comprehensive geological, geochronological, and geochemical study of the gold mineralized Xiejia diorite beneath the Linglong ore field at Jiaodong to link the gold mineralization to underlying magmatism. Magmatic zircon and titanite grains from the Xiejia diorite have laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) U-Pb ages of 121.3 ± 0.9 Ma to 120.8 ± 1.1 Ma and 121.7 ± 3.9 Ma, respectively, which are indistinguishable from the time of gold deposition throughout the Jiaodong District as constrained by previous studies. The diorite has a shoshonitic composition and is characterized by strong enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) along with significant depletion in high field strength elements (HFSEs) and heavy rare earth elements (HREEs). Samples of the diorite have high initial 87Sr/86Sr ratios, but low εNd(t) and ɛHf(t) values and low Pb isotope ratios. These geochemical characteristics are akin to those of contemporaneous mafic dikes in most gold mines at Jiaodong, indicating that the Xiejia diorite was most likely derived from an enriched lithospheric mantle source. The upper part of the diorite intrusion is pervasively altered and mineralized, containing an average of 0.32 g/t Au, but locally up to 7.59 g/t. Hydrothermal titanite from the mineralized diorite has a LA-ICP-MS U-Pb age of 122.3 ± 4.3 Ma, which is consistent with the gold-bearing pyrite Re-Os isochron age of 122.5 ± 6.7 Ma. Ore-related sericite aggregates from the Dongfeng gold deposit above the Xiejia diorite have a 40Ar/39Ar plateau age of 122.6 ± 1.3 Ma. Pyrite from the mineralized diorite yielded δ34SCDT values of 2.1‰−9.7‰, which are comparable with those of pyrite (δ34SCDT = 5.8‰−8.1‰, where CDT indicates the Canyon Diablo troilite standard) from gold ores of Dongfeng. Pyrite grains from both groups also have similar Pb isotope compositions. The S and Pb isotope data are consistent with values of mafic dikes that are spatially and temporally associated with gold veins in the Linglong ore field. The results presented here thus indicate a possible genetic link between gold mineralization in the Xiejia diorite and underlying magma presumably represented by the Xiejia diorite. The auriferous fluids exsolved from that magma and migrated upward along the Potouqing fault to form the Dongfeng gold deposit above the Xiejia diorite. The mineralized diorite thus links shallow gold mineralization t","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"152 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121392589","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tracking isotopic sources of immiscible melts at the enigmatic magnetite-(apatite) deposit at El Laco, Chile, using Pb isotopes","authors":"D. Pietruszka, J. Hanchar, F. Tornos, M. Whitehouse, F. Velasco","doi":"10.1130/b36506.1","DOIUrl":"https://doi.org/10.1130/b36506.1","url":null,"abstract":"The long-standing controversy about the origin of magnetite-(apatite) mineral deposits pertains to how they form. The Pleistocene El Laco deposit in northern Chile is a critical location because the host andesite contains immiscible melt inclusions trapped in plagioclase and clinopyroxene phenocrysts that reveal the involvement of immiscible melts in the evolution of the El Laco Volcanic System hosting the magnetite-(apatite) mineralization. We present results from the first-ever whole-rock and in situ Pb isotope investigation at El Laco, which provides a better understanding of the relationships between immiscible melts preserved in the melt inclusions, the magnetite ore, and the host andesite, and helps identify sources of the ore metals by analyzing potential sources of crustal lead. Our study reveals that the phenocrysts and the melt inclusions contain homogenous Pb isotope compositions that overlap with the host andesite, which confirms that they are coeval and cogenetic. The magnetite ore, however, has significantly more primitive 206Pb/204Pb ratios, which points to Pb isotopic disequilibrium between the magnetite ore and host andesite. Model ages of 367−167 Ma for the magnetite ore suggest that the Pb was inherited from a U−Th-depleted reservoir that could be represented by sedimentary rocks found in the basement of the Andean Cordillera under El Laco, for example, the Palaeozoic P-rich ironstones sequence. These results are consistent with the major role of crustal contamination in the formation of magnetite-(apatite) mineralization elsewhere and suggest that the magnetite ore crystallized from immiscible Fe-rich melts contaminated by the underlying sedimentary sequences.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116127691","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mineralization and genesis of the orogenic gold system in the Kalamaili area, East Junggar, Xinjiang, northwestern China","authors":"Xue-xiang Gu, Yong‐Mei Zhang, Zhanling Ge, Weizhi Chen","doi":"10.1130/b36650.1","DOIUrl":"https://doi.org/10.1130/b36650.1","url":null,"abstract":"There are many lode gold deposits and occurrences in the Kalamaili area of the East Junggar, northwestern China. However, little is known about the specifics of ore geology and geochemistry of these gold deposits because of very limited exploration and research work in this region. Field geology, fluid inclusions, stable isotopes, trace elements in quartz, and hydrothermal zircon U-Pb dating are combined in this study to constrain the nature and source of ore fluids, the timing of mineralization, and the mechanism of gold precipitation in Kalamaili. The gold deposits are confined to a narrow zone between two regional NW- to NWW-trending shear zones and are structurally controlled by secondary, high-angle faults of the shears. The orebodies occur in the Middle Devonian and Lower Carboniferous, zeolite to lower greenschist facies clastic sedimentary and pyroclastic rocks. Gold mineralization occurs as auriferous quartz-sulfide ± tourmaline veins/veinlets and disseminated ores in the immediate altered wall rocks. The ore mineralogy is relatively simple and dominated by quartz with minor to trace amounts of sulfides (pyrite and arsenopyrite), sericite, calcite, and native gold. Quartz of various generations contains three types of fluid inclusions, including predominant H2O-CO2-NaCl inclusions and subordinate H2O-NaCl inclusions and CO2 ± CH4 ± N2 inclusions. The mineralizing fluid is uniformly characterized by a medium to high homogenization temperature (mostly 240−330 °C), low salinity (typically <6 wt% NaCl equivalent), reduced, and CO2-rich-H2O-NaCl ± CH4 fluid. The hydrogen and oxygen isotope data (δ18OH2O = +5.6‰ to +14.3‰, δDH2O = −99‰ to −62‰) indicate a metamorphic origin for the mineralizing fluid. The majority of sulfide δ34S values range between 0‰ and +10‰, indicative of a largely sedimentary rock reservoir of sulfur in the ore-forming fluids. Geochemically, the auriferous quartz is characterized by low concentrations of most trace elements including Ti, Al, Li, Ge, and Sb. Laser ablation−inductively coupled plasma−mass spectrometry U-Pb isotope dating of hydrothermal zircons from the auriferous quartz vein yielded a weighted mean 206Pb/238U age of ca. 313 Ma. Phase separation of ore fluids and fluid-rock interaction are suggested as key mechanisms for the gold precipitation. Integrated geological and geochemical evidence indicates that formation of the orogenic gold system in Kalamaili is related to the transition from compressional to transcurrent deformation during the Late Carboniferous. Target gold exploration in this region should focus on the northeast side of the Kalamaili fault zone, where there exist suitable structural and stratigraphic trap sites with high fluid flux and potential gold mineralization.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128678741","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Early Cretaceous (late Barremian−Early Albian) expanding aeolian activity in East Asia: Evidence from the stratigraphic evolution of aeolian deposition in the Baiyin-Jingyuan Basin, northern China","authors":"Fei Wang, Zaijun Li, Xiaoyun Sun, Jie Zhao, Yuxin Fan, D. Xia, R. Ayyamperumal, Baofeng Li","doi":"10.1130/b36747.1","DOIUrl":"https://doi.org/10.1130/b36747.1","url":null,"abstract":"Cretaceous aeolian deposition is important for understanding variations of the tropical−subtropical atmospheric circulation under the greenhouse background. Nevertheless, detailed records revealing the response of aeolian deposition to rising atmospheric CO2 are still lacking. To shed light on their linkage, we examined the Early Cretaceous stratigraphic evolution of the Hekou Group in the Baiyin-Jingyuan Basin, northern China, using multiple methods. The results indicate that the lower Hekou Group is characterized by a transition from submerged alluvial to shallow lacustrine deposition. Overlying these facies is loess-like deposition without bedding, distinguished by grain-size distribution, surface microtextures, and geochemical analysis, which is followed by palustrine deposition. In the palustrine deposition, aeolian sand-dune and sand-sheet deposition can be identified, which gradually developed upward in the Hekou Group, with intercalated wet interdunes, damp interdunes, and pebble-sand sheetflood beds. Finally, aeolian sand dunes and sand sheets dominated the upper Hekou Group. Overall, the upward-changing facies indicated the development of aeolian deposition from an aqueous environment, revealing a long-term paleoclimatic shift from semi-humid, semi-arid to extremely arid, which reflects the expanded aeolian activity in East Asia during the Early Cretaceous. Furthermore, various records were combined to investigate the expanding aeolian activity in East Asia, which indicates a west−east-trending arid belt that was wider than the modern counterpart during the late Barremian−Early Aptian and late Aptian−Early Albian, respectively. These stepwise expansions of aeolian activity were mainly driven by rising atmospheric CO2, which strengthened the subsiding branches of Hadley circulation and the subtropical high, eventually leading to intensified aridification.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114889167","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hot orogenesis in the Paleoproterozoic: Insights from granitic gneiss domes within the Jiao-Liao-Ji belt, North China craton","authors":"Jian Zhang, Chengwei Yang, Lifu Zhao, Cheng Zhang, Hongxiang Yang, Tianjiao Lu, Jia Feng, Ran Hao, Xiaoyu Chen, Junlai Liu","doi":"10.1130/b36661.1","DOIUrl":"https://doi.org/10.1130/b36661.1","url":null,"abstract":"As a part of the Columbia supercontinent, the North China craton is an ideal object for studying the evolution of supercontinent assembly and the mechanism of orogenesis in the Paleoproterozoic. The Jiao-Liao-Ji belt, located in the eastern part of the North China craton, provides important clues for our understanding of Paleoproterozoic orogenic processes. A series of Paleoproterozoic granitic gneiss domes is preserved in the Liaodong segment of the Jiao-Liao-Ji belt. These domes are cored by the Liaoji granitic gneisses (emplaced at 2250−2150 Ma) and mantled by metamorphosed volcanic-sedimentary rocks (deposited at 2200−1940 Ma). Combining multiple lines of evidence from mesostructures and microstructures, kinematics, magnetic fabrics, and crystallographic fabrics, we suggest that the granitic gneiss domes reflect inhomogeneous shearing of the middle to lower crust during Paleoproterozoic orogenic processes. Intensive layer-paralleling shearing characterized subhorizontal flow during nearly E-W−oriented compression. As a hot orogen formed in the Paleoproterozoic, the orogenic deformation in the Jiao-Liao-Ji belt was characterized by extensive doming due to dominant subhorizontal flow and subsidiary vertical flow in the middle to lower crust.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-04-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130241908","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}