GSA Bulletin最新文献

{"title":"Long-lived (>100 m.y.) postcollisional exhumation and cooling in the Paleoproterozoic Trans−North China orogen: Evidence from phase equilibria modeling and monazite petrochronology of granulite-facies metapelites in the Fuping Complex","authors":"Li Tang, M. Santosh, R. Palin, Lihui Jia, H. Cao, Yuan‐Ming Sheng","doi":"10.1130/b36623.1","DOIUrl":"https://doi.org/10.1130/b36623.1","url":null,"abstract":"Long-lived collisional orogens that formed over tens to hundreds of millions of years are common in the geologic record. The Trans−North China orogen marks the collision between the Eastern and Western blocks of the North China craton, and it preserves metamorphic rocks with ages between 1.98 Ga and 1.80 Ga. These units allow detailed assessment of the time scale and duration of crustal thickening, exhumation, and cooling associated with a major Proterozoic orogeny. In this study, we present integrated petrography, mineral chemistry, phase equilibria modeling, and texturally controlled in situ mass spectrometry of monazite U-Th-Pb and trace-element analyses performed on a suite of orthopyroxene-bearing pelitic granulites and garnet-biotite gneisses from the Fuping Complex within the Trans−North China orogen. These rocks record clockwise pressure-temperature (P-T) paths involving granulite-facies peak conditions of 9.9−11.0 kbar and 850−880 °C for pelitic granulites, and 10.9−11.6 kbar and 860−880 °C for garnet-biotite gneisses, followed by postpeak decompression to ∼8−9 kbar and later cooling, with final solidification of melt at <840 °C. Four monazite populations were identified in these samples. Group I grains are irregular and elongated and occur in contact with or embay garnet. They have high rare earth element (REE) and Y contents and metamorphic ages of 1.90−1.86 Ga, which correspond to the breakdown of garnet during postpeak decompression. Most monazite grains crystallized from melt are represented by groups II + III + IV and are associated with orthopyroxene, biotite, plagioclase, and quartz in the matrix. They have crystallization ages between 1.86 Ga and 1.76 Ga and relatively low REE and Y concentrations. These data imply a long-lived (>100 m.y.) postcollisional exhumation and cooling involving decompression from 10−12 kbar to ∼9 kbar during 1.90−1.86 Ga, followed by retrograde cooling from 1.86 to 1.76 Ga under prolonged residence in the middle to lower crust. Initial collision and peak metamorphism occurred before 1.90 Ga, ultimately leading to the final cratonization of the North China craton and its incorporation into the Columbia supercontinent.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131387952","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":"Tracing high-pressure metamorphism in the eastern Himalayan syntaxis using detrital zircon and monazite from modern stream sediments","authors":"Yunxuan Zhang, Liang Guo, Hongfei Zhang, N. Harris, Wangchun Xu, Zhenbing She, Tao Luo","doi":"10.1130/b36556.1","DOIUrl":"https://doi.org/10.1130/b36556.1","url":null,"abstract":"The timing of high-pressure (HP) metamorphism in the eastern Himalayan syntaxis is important for understanding the India-Asia collisional processes, but it remains elusive. To reveal the metamorphic history of the eastern Himalayan syntaxis, we performed a study of geochronology, trace elements, and mineral inclusions of detrital zircon and monazite from modern stream sediments in the eastern Himalayan syntaxis. Detrital zircon comprise magmatic and metamorphic domains with different zoning. Inherited magmatic zircon domains have high Th/U, low (Dy/Yb)N, and retain ages of 1798−360 Ma. Metamorphic zircon domains with low Th/U, high (Dy/Yb)N, and inclusions of garnet, kyanite, and/or clinopyroxene probably formed under HP conditions. They yield age groups of 49−35 Ma, 33−17 Ma, and 12−7 Ma. The low Th/U and low (Dy/Yb)N metamorphic zircon domains probably formed during retrogression and yield age groups of 27−16 Ma and 10−6 Ma. Detrital monazite yield age distributions similar to those of the low (Dy/Yb)N metamorphic zircon except for the 821−402 Ma inherited cores. The (Dy/Yb)N of 31.6−5.7 Ma monazite decreases with increasing Y content, which indicates that it likely formed under the retrograde stage during garnet breakdown. Based on the oldest metamorphic ages, the initial India-Asia collision occurred no later than 50−44 Ma in the eastern Himalayan syntaxis. The multimodal age patterns of the metamorphic zircon and monazite indicate that the Indian continent underwent multistage HP and retrograde metamorphism in the eastern Himalayan syntaxis. The nearly contemporaneous HP and retrograde metamorphism indicate that the Indian continent continued subducting while the earlier HP metamorphic slices detached and exhumed.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116726749","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":"Immiscible two-phase model for air blasts created during natural avalanches","authors":"Jianbo Fei, Z. Liu, Y. Jie","doi":"10.1130/b36411.1","DOIUrl":"https://doi.org/10.1130/b36411.1","url":null,"abstract":"An immiscible two-phase model based on the incompressible Navier-Stokes (N-S) equations is used to simulate the air blast generated by an avalanche. For simplicity, the avalanche is treated as an assembly of monodisperse spherical grains and described as a continuous media. The constitutive law of local µ(I) rheology is introduced to model the moving granular material. The motion of the avalanche and the induced air blast fits into a unified framework that combines the N-S−type governing equations with a µ(I)-rheology−based kinematic viscosity and a constant viscosity. The avalanche-air interface is treated using the volume-of-fluid method. A numerical program was developed on the open-source platform OpenFOAM specifically for this model to simulate the entire evolutionary process of the avalanche as well as the air blast generated. The model was validated by comparing the results of numerical simulations with those from inclined-plane laboratory experiments. With terrain input from the Shuttle Radar Topography Mission data, the model was further applied to simulate the air blast generated in two natural avalanches, namely, the Baige and Wenjia valley avalanches fo China, which occurred in 2008 and 2018, respectively. The simulation results were found to be consistent with field observations following a statistical analysis of the properties of the air blast including flow speed and area of impact of the above-mentioned natural events.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"93 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123100708","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":"Location and shape of the Lhasa terrane prior to India-Asia collision","authors":"W. Bian, Suo Wang, Yong Yao, Xianwei Jiao, Wenxiao Peng, Tianshui Yang, Shihong Zhang, Huaichun Wu, Haiyan Li, Chenglong Deng","doi":"10.1130/b36647.1","DOIUrl":"https://doi.org/10.1130/b36647.1","url":null,"abstract":"The precollisional location and shape of the Lhasa terrane are crucial for constraining the closure of the Neo-Tethys Ocean and the ensuing India-Asia collision; however, estimation of these features of the Lhasa terrane remains highly controversial. Here, we carried out a new paleomagnetic investigation on the Lower Cretaceous Duoni Formation red beds in the central-eastern Lhasa terrane. The tilt-corrected site-mean direction is declination (Ds) = 339.0°, inclination (Is) = 26.8°, ks = 78.4, and α95 = 2.3° (k—precision parameter; α95—the radius that the mean direction lies within 95% confidence; s—stratigraphic coordinates) (N = 50), corresponding to a paleopole at 64.2°N, 324.2°E, with A95 = 1.9° (A95—the radius that the mean pole lies within 95% confidence). These new paleomagnetic data pass a positive fold test and indicate that the studied area was located at 14.3 ± 1.9°N during the Early Cretaceous. No significant inclination shallowing is present in the Lower Cretaceous Duoni Formation red beds. Our new results, combined with previously published reliable Cretaceous paleomagnetic results, show that the Lhasa terrane was located at a paleolatitude of ∼22.9°N to 10.1°N from west to east and was oriented at ∼298°−296° prior to India-Asia collision.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115201559","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":"Morphometric constraints on the formation of new terrestrial analogs for planetary pits","authors":"R. Naor, A. Mushkin, I. Halevy","doi":"10.1130/b36523.1","DOIUrl":"https://doi.org/10.1130/b36523.1","url":null,"abstract":"The origin of geological depressions abounding on Mars and other planetary bodies remains poorly understood, partially due to the limited variability in the geological settings of existing terrestrial analogs. Here, we present a new terrestrial analog that is located at the northwestern margin of the Levantine volcanic field of Harrat Ash−Shaam along the Dead Sea Transform. The analog site consists of tens of geological depressions (locally named “juba”) that morphologically resemble Martian bowl-shaped pits and occur within a Pleistocene basaltic plateau that overlies Meso-Cenozoic carbonates. To constrain plausible formation mechanisms for the juba depressions, we carried out detailed field mapping and morphometric analyses using a 0.25 m/pixel digital terrain model (DTM) derived from airborne light detection and ranging (LiDAR) survey covering 34 km2 of the study area, and centimeter-scale, ground-based LiDAR scans of selected juba depressions. We show that variable magnitudes of slope asymmetry between north- and south-facing walls within the juba depressions, along with different degrees of sediment infilling, provide effective proxies for the relative geomorphic maturity of these landforms, and in turn indicate asynchronous formation of the juba depressions after the Pleistocene emplacement of the Harrat Ash−Shaam basalts in the study area. Our findings preclude formation of the juba depressions by phreatomagmatic explosions and instead point toward collapse into missing subsurface volume. In a broader context, we propose that the morphometric analyses developed herein to distinguish between plausible juba formation mechanisms in the Harrat Ash−Shaam volcanic field can be extended to better constrain the formation mechanisms of similar pit features on Mars and other planetary bodies.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122185297","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":"Tectonically controlled drainage fragmentation in the southwestern Great Basin, USA","authors":"B. Lutz, J. Knott, F. Phillips, M. Heizler, K.A. Heitkamp, Jr., E. Griffie, G. Axen, J. Calzia","doi":"10.1130/b36563.1","DOIUrl":"https://doi.org/10.1130/b36563.1","url":null,"abstract":"The area now occupied by the Great Basin, western USA, contained paleo-fluvial systems that predated the modern-day endorheic (closed) basins. The areal extent of these paleo-fluvial systems within the southwestern Great Basin is known mainly from isolated remnants preserved in the modern mountain ranges. We document the age, extent, and tectonic disruption of Mio-Pliocene fluvial systems of the southwestern Great Basin. Synthesis of new field observations, geochemistry, and geochronology with existing studies defines two latest Miocene to Pliocene east-southeast flowing drainages that predated the modern endorheic basins. The drainage network was ultimately fragmented in Pliocene time (ca. 3.5-4 Ma). Fragmentation of the drainage network led to lake formation, drying of lakes, and the formation of isolated springs. The rapid environmental changes initiated by faulting and volcanism isolated previously interbreeding populations of spring-dwelling taxa and have caused divergent evolution since Pliocene time. Modern endemism within the region’s springs is thus a direct consequence of intraplate tectonism.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"276 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131614733","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":"Intense metamorphism-generated radiogenic Sr regulated Cenozoic water Sr isotope evolution on the NE Tibetan Plateau: A perspective on Qilian orogen denudation and Asian eolian transport","authors":"Yibo Yang, A. Galy, Rongsheng Yang, Yudong Liu, Weilin Zhang, X. Ruan, X. Fang, Zhangdong Jin, B. Song, M. Yan, Guibin Zhang, K. Cao, T. Shen, Ziqiang Mao, Fuli Wu, Fei Zhang","doi":"10.1130/b36525.1","DOIUrl":"https://doi.org/10.1130/b36525.1","url":null,"abstract":"The India-Asia collision reactivated the early Paleozoic Qilian orogen with an intense metamorphic belt that promoted the release of metamorphism-generated radiogenic Sr into the drainage systems on the NE Tibetan Plateau. This metamorphic impact on the regional dissolved Sr cycle is well observed at the recent−modern scale, but its onset and evolutionary histories are unclear. We present the first basin-scale 52−5 Ma regional dissolved Sr isotopic record in water on the NE Tibetan Plateau by analyzing well-dated basin fluvial-lacustrine sediments in the Xining, Linxia, and Tianshui Basins. The Xining Basin displays an increase in basin water 87Sr/86Sr ratio and a decrease in the sediment εNd values at ca. 25 Ma. This Sr-Nd isotope-deduced provenance change coincides with the reorganization of drainage and erosion regimes that is suggested by an evident rise in the youngest peak and the lag time of detrital apatite fission-track ages from Cenozoic sedimentary basins surrounding the Qilian orogen. The Qilian-sourced eolian dust during ca. 9−8 Ma significantly elevated the river and lake water 87Sr/86Sr ratios in the downwind Linxia and Tianshui Basins, which is consistent with the expansion of the Asian dust system. Our results suggest that large-scale denudation of the Qilian orogen in response to the India-Asia collision initiated in the late Oligocene. Given the remarkable hydrological impact of the Cenozoic reactivation of the Qilian orogen, our study highlights the potentially important role of continental collision−formed metamorphic belts in regulating past regional and even seawater Sr isotope evolution.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"69 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128854608","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":"Validation of earthquake ground-motion models in southern California, USA, using precariously balanced rocks","authors":"A. H. Rood, D. Rood, G. Balco, P. Stafford, L. G. Ludwig, K. Kendrick, K. Wilcken","doi":"10.1130/b36484.1","DOIUrl":"https://doi.org/10.1130/b36484.1","url":null,"abstract":"Accurate estimates of earthquake ground shaking rely on uncertain ground-motion models derived from limited instrumental recordings of historical earthquakes. A critical issue is that there is currently no method to empirically validate the resultant ground-motion estimates of these models at the timescale of rare, large earthquakes; this lack of validation causes great uncertainty in ground-motion estimates. Here, we address this issue and validate ground-motion estimates for southern California utilizing the unexceeded ground motions recorded by 20 precariously balanced rocks. We used cosmogenic 10Be exposure dating to model the age of the precariously balanced rocks, which ranged from ca. 1 ka to ca. 50 ka, and calculated their probability of toppling at different ground-motion levels. With this rock data, we then validated the earthquake ground motions estimated by the Uniform California Earthquake Rupture Forecast, Version 3 (UCERF3) seismic-source characterization and the Next Generation Attenuation (NGA)-West2 ground-motion models. We found that no ground-motion model estimated levels of earthquake ground shaking consistent with the observed continued existence of all 20 precariously balanced rocks. The ground-motion model I14 estimated ground-motion levels that were inconsistent with the most rocks; therefore, I14 was invalidated and removed. At a 2475 year mean return period, the removal of this invalid ground-motion model resulted in a 2−7% reduction in the mean and a 10−36% reduction in the 5th−95th fractile uncertainty of the ground-motion estimates. Our findings demonstrate the value of empirical data from precariously balanced rocks as a validation tool for removing invalid ground-motion models and, in turn, reducing the uncertainty in earthquake ground-motion estimates.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117243206","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":"Juxtaposition of different-grade metamorphic rocks in an ancient orogen: Evidence from the Chengde Complex of the Trans-North China Orogen, North China Craton","authors":"H. C. Zhang, Guochun Zhao, Chao Wang, N. Xu, Jinlong Yao","doi":"10.1130/b36575.1","DOIUrl":"https://doi.org/10.1130/b36575.1","url":null,"abstract":"Juxtaposition of different-grade metamorphic slices is a typical feature of Phanerozoic orogens but is relatively scarce in Precambrian orogens. Here, we focus on the Chengde Complex at the northern segment of the late Paleoproterozoic Trans-North China Orogen, the North China Craton as a case, to explore how different-grade orogeny-related metamorphism was juxtaposed in Precambrian orogens. The Trans-North China Orogen is a typical Precambrian collisional orogen and records abundant information about the Paleoproterozoic orogeny. High-pressure (HP) mafic granulite and two types of amphibolite samples were collected from the Chengde Complex, and we conducted a combined study involving litho-structural assemblage investigation, metamorphic petrology, and geochronology to decipher their metamorphic P-T−t history.\u0000 HP mafic granulite and amphibolite occur as enclaves or dikes within felsic gneisses. HP mafic granulite records clockwise P-T paths with isothermal decompression (ITD) segments, and the peak metamorphic P-T conditions are 13.0−14.9 kbar/790−830 °C. Peak metamorphic P-T conditions retrieved from garnet-bearing amphibolite are 8.3 kbar/675 °C, whereas peak metamorphic P-T conditions retrieved from garnet-free amphibolite are 4.0−5.5 kbar/500−510 °C. Zircon U-Pb dating of HP granulite and amphibolite yield different prograde (1914−1871 Ma), peak (1869−1816 Ma), and retrograde (ca. 1830 Ma) metamorphic ages, and all of these data indicate that these metamorphic rocks were diachronously transferred to different depths in the subduction channel and subsequently exhumed at shallower crustal levels. Therefore, we conclude that the Chengde Complex is composed of imbricate rocks with different metamorphic grades and ages, and such an unordered juxtaposition of diverse metamorphism could also be a typical feature of Precambrian orogens.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"66 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133739815","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":"Geodynamic controls in the southernmost Northern Andes magmatic arc: Trace elements and Hf-O isotopic systematics in forearc detrital zircon","authors":"C. Witt, M. Poujol, M. Chiaradia, D. Villagómez, M. Seyler, O. Averbuch, N. Bouden","doi":"10.1130/b36510.1","DOIUrl":"https://doi.org/10.1130/b36510.1","url":null,"abstract":"U-Pb dating of single detrital zircon grains by laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS) paired with Hf and O isotopic and trace-element analyses provide first-order indicators of the Late Cretaceous−Cenozoic evolution of the southern Ecuadorian magmatic arc. Detrital zircon U-Pb ages define significant clusters that are tentatively interpreted as intense arc magmatism at ca. 72 Ma, ca. 60 Ma, and ca. 43 Ma. A major accretionary event in the Late Cretaceous (75−65 Ma) is marked by a broad range of zircon isotopic values (εHf[t] > 20 and δ18O > 8‰) that suggest melting of both the lower and upper crust (most likely of continental affinity) as well as enriched mantle components. Highly fractionated signatures in trace-element patterns and Eu/Eu* combined with mantle-like δ18O and juvenile εHf values characterize zircons from 60 to 45 Ma, suggesting that the Late Cretaceous−middle Eocene arc originated from an enriched mantle and likely reflects the persistence of overthickened crust previously attributed to the main Late Cretaceous accretionary period. Subsequently, negative shifts in εHf(t) isotopic composition from 45 to 30 Ma are paired with mantle-like δ18O values as well as decreases in U/Yb and Eu/Eu*. These signatures could be attributed to magma emplacement in a thinner crust and the existence of a broad extensional magmatic arc extending from the current forearc toward areas near the craton; however, other scenarios cannot be excluded. This event was characterized by enriched mantle melt sources with residence times pointing to known crustal events (Sunsás) in the Amazonian craton. From 30 to 10 Ma, the isotopic record slightly evolved toward a depleted mantle signature with a substantial increase in fractionation. Our results combined with previously published isotopic records from detrital zircon grains found in modern rivers suggest that, for at least the last 30 m.y., the southernmost Northern Andes magmatic arc has been segmented, with the emplacement of juvenile magmas to the north and more enriched magmas related to the recycling of ancient continental crust and/or subducted sediments to the south—aspects found in other Northern Andes settings in which the continental arc was constructed in both oceanic and continental crust.","PeriodicalId":242264,"journal":{"name":"GSA Bulletin","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2022-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125145102","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}