Introductory geoscience courses enroll hundreds of thousands of students a year, most of whom do not major in the geosciences. For many, including future K–12 teachers, an introductory course is the only place they will encounter Earth science at the college level. New standards for K–12 science education have profound implications for teacher preparation, particularly in Earth science. The new standards call for taking a systems approach, highlighting how humans interact with Earth, making use of science and engineering practices, and engaging students in discourse. Analysis of responses to the National Geoscience Faculty Survey (n = 813 in 2004; n = 994 in 2009; n = 972 in 2012; and n = 1074 in 2016) and data from 152 syllabi suggest that a systems approach is not widespread and human interactions with Earth are not emphasized, and that most instructors engage students in mostly low cognitive-level practices. While the use of discourse practices has increased over time, these and other active learning components are not yet widely included in students’ grades. These results suggest that courses are not currently well-aligned with teacher needs. However, instructors have access to many research-based instructional resources to support them in making changes that will help all students— including future teachers. INTRODUCTION Several hundred thousand students enroll annually in introductory geoscience courses at institutes of higher education (Martinez and Baker, 2006). Fewer than 4000 students a year graduate with undergraduate degrees in geoscience (Wilson, 2016), however, which means that these courses serve a very large population of students that major in anything other than the geosciences. Few science majors require their students to take a geoscience course—it is not common for biology (Cheesman et al., 2007), nor recommended as a cognate for chemistry (ACS-CPT, 2015). In most cases, therefore, students enroll in geoscience courses to fulfill a general education requirement (Gilbert et al., 2012). Within this audience is a group of students that will become K–12 teachers, as most traditional teacher preparation programs do not include specific science content courses as part of their curricula (NRC, 2010). In the current teaching workforce, 64% of middle school teachers and 42% of high school teachers assigned to teach Earth science took no geoscience courses beyond introductory (Banilower et al., 2013). One critical purpose that introductory geoscience courses serve, therefore, is providing future teachers with their primary collegelevel Earth-science experience. While it is easy to lament the numbers, teacher preparation is part of a complex system influenced by state certification, district needs and requirements, university degree requirements, and many other components (NRC, 2010). Within this complex system, disciplinary departments at institutes of higher education often play the role of content providers. Given this role, how well
1GSA数据库项目2019217，包括方法、额外调查结果和下一代科学标准的选定组成部分，可在线访问www.geosociety.org/datarepository/2019。海洋、陆地和生命——这一方法已经被提倡了20多年（例如，Ireton等人，1996），但一直被缓慢采用。该系统也包括人类：例如，学生不再足以描述资源的全球分布。在新标准中，PE要求学生将这种分布与人类活动联系起来，并评估资源开采对环境的影响（表S1[见脚注1]）。从教育学角度讲，整合这三个维度需要“学生积极参与科学和工程实践，以加深他们对交叉概念和学科核心思想的理解”（NRC，2012b，第217页）。这句话的结构是有目的的：积极参与实践是第一位的，会导致更深的理解。实践描述了使用数据作为开发解释的基础，这些解释通过积极的话语进行了修改和完善（表S2[见脚注1]）。在地球科学中，PE将重点从识别和描述地球材料和地貌转移到分析地球科学数据，以构建解释、做出决策和评估解决方案（表S1[见脚注1]）。这些变化共同导致Wysession（2014）断言，“NGSS为美国近240年历史上教育公民了解地球科学的复杂和关键问题提供了迄今为止最好的机会。“这对地球科学界来说是一个令人兴奋的发展，但如果没有教育系统所有组成部分的深思熟虑，这一发展将无法完全实现。因为教师学习教学的一种强有力的方式是通过观察，模仿他们作为学习者所经历的教学策略（Windschtl和Stroupe，2017），所以实现变革的一个关键杠杆点是未来教师学习的科学课程。在地球科学方面，我们有两个丰富的数据集，可以用来评估地球科学入门课程与框架愿景的一致程度。国家地球科学学院调查（NAGT，2018）于2004年、2009年、2012年和2016年进行。最初的调查是在框架之前制定的，但基于相同的基础文件。在四届政府中，3853份答复涉及介绍性课程。第二组数据来自由On the Cutting Edge（Manduca et al.，2010）领导的专业发展机会参与者，他们将教学大纲上传到数字存储库，并在那里公开（SERC，2002）。GSA数据库中描述了这两个数据集的分析方法（见脚注1）。
{"title":"The Role of Introductory Geoscience Courses in Preparing Teachers—And All Students— For the Future: Are We Making the Grade?","authors":"A. Egger","doi":"10.1130/GSATG393A.1","DOIUrl":"https://doi.org/10.1130/GSATG393A.1","url":null,"abstract":"Introductory geoscience courses enroll hundreds of thousands of students a year, most of whom do not major in the geosciences. For many, including future K–12 teachers, an introductory course is the only place they will encounter Earth science at the college level. New standards for K–12 science education have profound implications for teacher preparation, particularly in Earth science. The new standards call for taking a systems approach, highlighting how humans interact with Earth, making use of science and engineering practices, and engaging students in discourse. Analysis of responses to the National Geoscience Faculty Survey (n = 813 in 2004; n = 994 in 2009; n = 972 in 2012; and n = 1074 in 2016) and data from 152 syllabi suggest that a systems approach is not widespread and human interactions with Earth are not emphasized, and that most instructors engage students in mostly low cognitive-level practices. While the use of discourse practices has increased over time, these and other active learning components are not yet widely included in students’ grades. These results suggest that courses are not currently well-aligned with teacher needs. However, instructors have access to many research-based instructional resources to support them in making changes that will help all students— including future teachers. INTRODUCTION Several hundred thousand students enroll annually in introductory geoscience courses at institutes of higher education (Martinez and Baker, 2006). Fewer than 4000 students a year graduate with undergraduate degrees in geoscience (Wilson, 2016), however, which means that these courses serve a very large population of students that major in anything other than the geosciences. Few science majors require their students to take a geoscience course—it is not common for biology (Cheesman et al., 2007), nor recommended as a cognate for chemistry (ACS-CPT, 2015). In most cases, therefore, students enroll in geoscience courses to fulfill a general education requirement (Gilbert et al., 2012). Within this audience is a group of students that will become K–12 teachers, as most traditional teacher preparation programs do not include specific science content courses as part of their curricula (NRC, 2010). In the current teaching workforce, 64% of middle school teachers and 42% of high school teachers assigned to teach Earth science took no geoscience courses beyond introductory (Banilower et al., 2013). One critical purpose that introductory geoscience courses serve, therefore, is providing future teachers with their primary collegelevel Earth-science experience. While it is easy to lament the numbers, teacher preparation is part of a complex system influenced by state certification, district needs and requirements, university degree requirements, and many other components (NRC, 2010). Within this complex system, disciplinary departments at institutes of higher education often play the role of content providers. Given this role, how well","PeriodicalId":35784,"journal":{"name":"GSA Today","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43929399","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}
Pub Date : 2019-09-23DOI: 10.1130/ABS/2019AM-337465
A. Chapman, Ojashvi Rautela, J. Shields, M. Ducea, J. Saleeby
Continental arc lower crust and underlying mantle wedge assemblages native to the Mojave Desert were dislodged, transported eastward during Laramide shallow-angle subduction, and attached to the base of the Colorado Plateau transition zone (central Arizona, USA) and further inboard. We identify here two late Oligocene xenolith localities from the transition zone (Camp Creek and Chino Valley) that likely contain remnants of the missing Mojave lithosphere. Geochemical, isotopic, and thermobarometric data from garnet clinopyroxenite, the dominant xenolith type at both studied localities, strongly suggest a continental arc residue (“arclogite”) rather than a lower plate subduction (“eclogite”) origin. Zircon grains extracted from these nodules yield a bimodal age distribution with peaks at ca. 75 and 150 Ma, overlapping ages of continental arc magmas emplaced into the Mojave Desert (the southern California batholith) and suggesting a consanguineous relationship. In contrast, Mesozoic and early Cenozoic igneous rocks from SW Arizona, with age peaks at ca. 60 and 170 Ma, do not provide as close a match. In light of these results, we suggest that a mafic keel to the southern California batholith: (1) formed in two discrete (Late Jurassic and Late Cretaceous) pulses; (2) was transported along the Moho ~500 km eastward along the leading edge of the shallowly subducting Farallon plate; and (3) was affixed to the base of the crust in central Arizona. Titanite U-Pb and garnet Sm-Nd ages spanning ca. 60–30 Ma suggest that displaced arclogite remained at >600 °C for tens of millions of years following its dispersal and until entrainment in host latite. The lack of arclogite and abundance of spinel peridotite xenoliths in ca. 15 Ma and younger volcanic host rocks and the presence of a vertical high-seismicvelocity anomaly beneath the western Colorado Plateau suggest that arclogite has been foundering into the mantle and being replaced by upwelling asthenosphere since the early Miocene.
{"title":"Fate of the lower lithosphere during shallow-angle subduction: The Laramide example","authors":"A. Chapman, Ojashvi Rautela, J. Shields, M. Ducea, J. Saleeby","doi":"10.1130/ABS/2019AM-337465","DOIUrl":"https://doi.org/10.1130/ABS/2019AM-337465","url":null,"abstract":"Continental arc lower crust and underlying mantle wedge assemblages native to the Mojave Desert were dislodged, transported eastward during Laramide shallow-angle subduction, and attached to the base of the Colorado Plateau transition zone (central Arizona, USA) and further inboard. We identify here two late Oligocene xenolith localities from the transition zone (Camp Creek and Chino Valley) that likely contain remnants of the missing Mojave lithosphere. Geochemical, isotopic, and thermobarometric data from garnet clinopyroxenite, the dominant xenolith type at both studied localities, strongly suggest a continental arc residue (“arclogite”) rather than a lower plate subduction (“eclogite”) origin. Zircon grains extracted from these nodules yield a bimodal age distribution with peaks at ca. 75 and 150 Ma, overlapping ages of continental arc magmas emplaced into the Mojave Desert (the southern California batholith) and suggesting a consanguineous relationship. In contrast, Mesozoic and early Cenozoic igneous rocks from SW Arizona, with age peaks at ca. 60 and 170 Ma, do not provide as close a match. In light of these results, we suggest that a mafic keel to the southern California batholith: (1) formed in two discrete (Late Jurassic and Late Cretaceous) pulses; (2) was transported along the Moho ~500 km eastward along the leading edge of the shallowly subducting Farallon plate; and (3) was affixed to the base of the crust in central Arizona. Titanite U-Pb and garnet Sm-Nd ages spanning ca. 60–30 Ma suggest that displaced arclogite remained at >600 °C for tens of millions of years following its dispersal and until entrainment in host latite. The lack of arclogite and abundance of spinel peridotite xenoliths in ca. 15 Ma and younger volcanic host rocks and the presence of a vertical high-seismicvelocity anomaly beneath the western Colorado Plateau suggest that arclogite has been foundering into the mantle and being replaced by upwelling asthenosphere since the early Miocene.","PeriodicalId":35784,"journal":{"name":"GSA Today","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46708297","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}
K. Klepeis, L. Webb, H. Blatchford, J. Schwartz, R. Jongens, R. Turnbull, H. Stowell
A new multidisciplinary project in southwest New Zealand that combines geological and geophysical data shows how and why deep lithospheric dis‐ placements were transferred vertically through the upper plate of an incipient ocean-continent subduction zone. A key discovery includes two zones of steep, downward-curving reverse faults that uplifted and imbricated large slices of Cretaceous lower, middle, and upper crust in the Late Miocene. Geochemical and structural analyses combined with 40Ar/39Ar geochronology and published images from seismic tomography suggest that the reverse faults formed at 8–7 Ma as a consequence of a deep (~100 km) collision between subducting oceanic lithosphere and previously subducted material. This collision localized shortening and reactivated two crustalscale shear zones from the upper mantle to Earth’s surface. The event, which is summarized in a new lithosphericscale profile, is helping us answer some long-standing questions about the origin of Fiordland’s unique lower-crustal exposures and what they tell us about how inherited structures can transfer motion vertically through the lithosphere as subduction initiates. INTRODUCTION In southwest New Zealand, oceanic lithosphere of the Australian Plate subducts obliquely beneath continental lithosphere of the Pacific Plate at the Puysegur Trench (Fig. 1A). Northeast of the trench, the subducted slab rotates and steepens to vertical below Fiordland, where it joins the Alpine fault (Reyners et al., 2017), an ~850 km transform that has accumulated some 480 km of horizontal displacement since ca. 25 Ma (Sutherland and Norris, 1995). This region has generated great interest among geologists, in part because it is one of only a few places where the surface tectonic record of an incipient ocean-continent sub‐ duction zone can be observed directly (Mao et al., 2017). It also represents Earth’s deepest exposed example of an Andean-style continental arc (Ducea et al., 2015). Here, we use this unique setting to explore how Fiordland’s surface and crust responded to events that occurred deep within the lithospheric mantle since subduction began in the Early Miocene. Over the past few years, our under‐ standing of the vertical links that develop within the lithosphere has benefitted from improvements in our ability to extract information from the rock record. Innovative approaches to studying fault zones that combine geochemistry and high-precision geochronology with structural analyses, for example, have enhanced our capacity to relate deformation histories to other processes across a wide range of scales (e.g., Haines et al., 2016; Schwartz et al., 2016; Williams et al., 2017). At the same time, new methods in global teleseismic tomography are revealing the geometry and extent of material that was subducted into the mantle millions of years ago in unprecedented detail (Wu et al., 2016; Reyners et al., 2017). These imaged slabs can be integrated with surface geology and plate kinem
新西兰西南部的一个新的多学科项目结合了地质和地球物理数据，展示了深层岩石圈沉积是如何以及为什么通过早期海洋-大陆俯冲带的上部板块垂直转移的。一项关键发现包括两个陡峭、向下弯曲的反向断层带，它们在中新世晚期抬升和叠瓦了白垩纪下地壳、中地壳和上地壳的大片。地球化学和结构分析，结合40Ar/39Ar地质年代学和已发表的地震层析成像图像，表明逆断层形成于8–7 Ma，是俯冲海洋岩石圈和先前俯冲物质之间深度（约100 km）碰撞的结果。这次碰撞局部缩短并重新激活了从上地幔到地球表面的两个地壳尺度剪切带。这一事件在一个新的岩石圈尺度剖面中得到了总结，它帮助我们回答了一些长期存在的问题，即峡湾独特的下地壳暴露的起源，以及它们告诉我们，随着俯冲的开始，继承的结构如何通过岩石圈垂直转移运动。引言在新西兰西南部，澳大利亚板块的海洋岩石圈在间歇泉海沟斜向俯冲在太平洋板块的大陆岩石圈之下（图1A）。在海沟东北部，俯冲板块在Fiordland下方旋转并变陡至垂直，在那里它与阿尔卑斯断层汇合（Reyners et al.，2017），这是一个约850公里的转换，自约25 Ma以来，已经积累了约480公里的水平位移（Sutherland和Norris，1995）。该地区引起了地质学家的极大兴趣，部分原因是它是少数几个可以直接观察到早期海洋-大陆俯冲带表面构造记录的地方之一（Mao et al.，2017）。它还代表了地球上最深的安第斯式大陆弧（Ducea et al.，2015）。在这里，我们利用这个独特的环境来探索自中新世早期俯冲开始以来，峡湾的表面和地壳是如何对岩石圈地幔深处发生的事件做出反应的。在过去的几年里，我们对岩石圈内形成的垂直联系的了解得益于我们从岩石记录中提取信息的能力的提高。例如，将地球化学和高精度地质年代学与结构分析相结合的断层带研究创新方法，增强了我们将变形历史与其他过程在大范围内联系起来的能力（例如，Haines等人，2016；Schwartz等人，2016年；Williams等人，2017）。与此同时，全球远程地震层析成像的新方法正在以前所未有的细节揭示数百万年前被俯冲到地幔中的物质的几何形状和范围（Wu et al.，2016；Reyners等人，2017）。这些成像的板块可以与地表地质和板块运动学相结合，以揭示以前隐藏的构造历史。这些创新和许多其他创新共同提供了新的机会，以确定随着俯冲带的形成和发展，地表构造记录如何与地幔中发生的过程联系起来（例如，刘，2015；刘等人，2017；Kisling和Schlunegger，2018）。在这篇文章中，我们将结构、地球化学和地质年代数据与地震层析成像获得的上地幔图像相结合，重建了峡湾地区新生代晚期的构造史。这些结果为大陆边缘俯冲开始的过程提供了新的见解，包括覆盖板块内垂直运动的原因和后果。
{"title":"Deep Slab Collision during Miocene Subduction Causes Uplift along Crustal-Scale Reverse Faults in Fiordland, New Zealand","authors":"K. Klepeis, L. Webb, H. Blatchford, J. Schwartz, R. Jongens, R. Turnbull, H. Stowell","doi":"10.1130/GSATG399A.1","DOIUrl":"https://doi.org/10.1130/GSATG399A.1","url":null,"abstract":"A new multidisciplinary project in southwest New Zealand that combines geological and geophysical data shows how and why deep lithospheric dis‐ placements were transferred vertically through the upper plate of an incipient ocean-continent subduction zone. A key discovery includes two zones of steep, downward-curving reverse faults that uplifted and imbricated large slices of Cretaceous lower, middle, and upper crust in the Late Miocene. Geochemical and structural analyses combined with 40Ar/39Ar geochronology and published images from seismic tomography suggest that the reverse faults formed at 8–7 Ma as a consequence of a deep (~100 km) collision between subducting oceanic lithosphere and previously subducted material. This collision localized shortening and reactivated two crustalscale shear zones from the upper mantle to Earth’s surface. The event, which is summarized in a new lithosphericscale profile, is helping us answer some long-standing questions about the origin of Fiordland’s unique lower-crustal exposures and what they tell us about how inherited structures can transfer motion vertically through the lithosphere as subduction initiates. INTRODUCTION In southwest New Zealand, oceanic lithosphere of the Australian Plate subducts obliquely beneath continental lithosphere of the Pacific Plate at the Puysegur Trench (Fig. 1A). Northeast of the trench, the subducted slab rotates and steepens to vertical below Fiordland, where it joins the Alpine fault (Reyners et al., 2017), an ~850 km transform that has accumulated some 480 km of horizontal displacement since ca. 25 Ma (Sutherland and Norris, 1995). This region has generated great interest among geologists, in part because it is one of only a few places where the surface tectonic record of an incipient ocean-continent sub‐ duction zone can be observed directly (Mao et al., 2017). It also represents Earth’s deepest exposed example of an Andean-style continental arc (Ducea et al., 2015). Here, we use this unique setting to explore how Fiordland’s surface and crust responded to events that occurred deep within the lithospheric mantle since subduction began in the Early Miocene. Over the past few years, our under‐ standing of the vertical links that develop within the lithosphere has benefitted from improvements in our ability to extract information from the rock record. Innovative approaches to studying fault zones that combine geochemistry and high-precision geochronology with structural analyses, for example, have enhanced our capacity to relate deformation histories to other processes across a wide range of scales (e.g., Haines et al., 2016; Schwartz et al., 2016; Williams et al., 2017). At the same time, new methods in global teleseismic tomography are revealing the geometry and extent of material that was subducted into the mantle millions of years ago in unprecedented detail (Wu et al., 2016; Reyners et al., 2017). These imaged slabs can be integrated with surface geology and plate kinem","PeriodicalId":35784,"journal":{"name":"GSA Today","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43788907","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}
S. Fortner, C. Manduca, L. Guertin, David W. Szymanski, J. Villalobos
{"title":"Teaching for Earth Resilience: A Strategy for Increased Diversity and Equity","authors":"S. Fortner, C. Manduca, L. Guertin, David W. Szymanski, J. Villalobos","doi":"10.1130/GSATG388GW.1","DOIUrl":"https://doi.org/10.1130/GSATG388GW.1","url":null,"abstract":"","PeriodicalId":35784,"journal":{"name":"GSA Today","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45438939","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}
The southern U.S. continental margin records a history spanning ca. 1.2 Ga, including two Wilson cycles. However, due to a thick sediment cover, the paucity of significant local seismicity, and, until recently, sparse instrumentation, details of this passive margin’s tectonomagmatic evolution remain disputed. This paper compares recent S-wave tomography and crustal thickness models based on USArray data to help establish a framework for geodynamic interpretation. Large-scale patterns of crustal velocity anomalies, corresponding to major regional features such as the Ouachita orogenic front and the Precambrian margin, are generally consistent between the models. The spatial extent of smaller-scale tectonic features, such as the Sabine Uplift and Wiggins block, remains poorly resolved. An inverse relationship between crustal thickness and Bouguer gravity across the continental margin is observed. This model comparison highlights the need for additional P-wave tomography studies and targeted, higher density station deployments to better constrain tectonic features. INTRODUCTION The southern U.S. margin (Fig. 1) ranges from the stable Laurentia craton beneath Oklahoma to a stretched and thinned passive margin to oceanic lithosphere in the deep Gulf of Mexico, recording within it a geologic history that includes two complete Wilson cycles (Thomas, 2006). Due to its extensive hydrocarbon reserves, the southern U.S. has been the focus of intensive seismic exploration. However, until recently, studies of its deep structure trailed those of other U.S. continental margins. The result is that the tectonomagmatic evolution of the southern U.S. margin remains poorly understood. The primary contributing factors to this status quo are (1) the presence of a thick sediment cover that obscures crustal structure through most of the region, (2) the paucity of significant local seismicity, and, until recently, (3) sparse seismic instrumentation in the region. Earthscope’s USArray temporarily densified the set of broadband seismographs available for studies of the region’s lithosphere (http://www.usarray.org/ researchers/obs/transportable). Approximately 435 stations occupied a total of 1830 locations in the continental U.S., for two years each, at a nominal spacing of 70 km. In USArray’s wake, there has been a surge in the number of continental-scale tomographic studies presenting snapshots of the compressional and shear wave velocities of the region’s crust and upper mantle. Although the volume of seismic data available for studies of the region has increased dramatically and sampling of the subsurface has improved as well, the presence of a thick layer of sediments and relatively low levels of seismicity (with the exception of Oklahoma) continue to challenge efforts to image the lithosphere. The collection of models for the southern U.S. region represents the state-of-theart of seismic tomography: a broad range of approaches, the inclusion of various types of data,
{"title":"Synoptic View of Lithospheric S-Wave Velocity Structure in the Southern United States: A Comparison of 3D Seismic Tomographic Models","authors":"A. Netto, J. Pulliam, P. Persaud","doi":"10.1130/GSATG387A.1","DOIUrl":"https://doi.org/10.1130/GSATG387A.1","url":null,"abstract":"The southern U.S. continental margin records a history spanning ca. 1.2 Ga, including two Wilson cycles. However, due to a thick sediment cover, the paucity of significant local seismicity, and, until recently, sparse instrumentation, details of this passive margin’s tectonomagmatic evolution remain disputed. This paper compares recent S-wave tomography and crustal thickness models based on USArray data to help establish a framework for geodynamic interpretation. Large-scale patterns of crustal velocity anomalies, corresponding to major regional features such as the Ouachita orogenic front and the Precambrian margin, are generally consistent between the models. The spatial extent of smaller-scale tectonic features, such as the Sabine Uplift and Wiggins block, remains poorly resolved. An inverse relationship between crustal thickness and Bouguer gravity across the continental margin is observed. This model comparison highlights the need for additional P-wave tomography studies and targeted, higher density station deployments to better constrain tectonic features. INTRODUCTION The southern U.S. margin (Fig. 1) ranges from the stable Laurentia craton beneath Oklahoma to a stretched and thinned passive margin to oceanic lithosphere in the deep Gulf of Mexico, recording within it a geologic history that includes two complete Wilson cycles (Thomas, 2006). Due to its extensive hydrocarbon reserves, the southern U.S. has been the focus of intensive seismic exploration. However, until recently, studies of its deep structure trailed those of other U.S. continental margins. The result is that the tectonomagmatic evolution of the southern U.S. margin remains poorly understood. The primary contributing factors to this status quo are (1) the presence of a thick sediment cover that obscures crustal structure through most of the region, (2) the paucity of significant local seismicity, and, until recently, (3) sparse seismic instrumentation in the region. Earthscope’s USArray temporarily densified the set of broadband seismographs available for studies of the region’s lithosphere (http://www.usarray.org/ researchers/obs/transportable). Approximately 435 stations occupied a total of 1830 locations in the continental U.S., for two years each, at a nominal spacing of 70 km. In USArray’s wake, there has been a surge in the number of continental-scale tomographic studies presenting snapshots of the compressional and shear wave velocities of the region’s crust and upper mantle. Although the volume of seismic data available for studies of the region has increased dramatically and sampling of the subsurface has improved as well, the presence of a thick layer of sediments and relatively low levels of seismicity (with the exception of Oklahoma) continue to challenge efforts to image the lithosphere. The collection of models for the southern U.S. region represents the state-of-theart of seismic tomography: a broad range of approaches, the inclusion of various types of data,","PeriodicalId":35784,"journal":{"name":"GSA Today","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44388107","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}
Nickel production is vital to modern economic development. Of the different ore types, supergene Ni-laterite production, as open-cast mining exploitation, is on the rise and surpassing the more conventional hypogene sulfide type. This trend will likely continue. Assessing the global resource of Ni laterite is therefore of crucial importance. Compilation of scientific publications shows that the main producers and occurrences are concentrated in a few countries in Southeast Asia (New Caledonia, Indonesia, the Philippines) and the Caribbean region (Cuba and the Dominican Republic). In these regions a common geological background appears, characterized by large obducted ophiolites in tectonically active settings, subject to weathering during the Neogene. The neoformed mineralogy of such surficial deposits is well documented. A model is proposed, based on the knowledge gained on Ni-laterite deposits in New Caledonia, that could be applied to similar geological settings worldwide. This model states that in accretionary terranes, vertical motions during weathering control both ore
{"title":"Nickel-Bearing Laterite Deposits in Accretionary Context and the Case of New Caledonia: From the Large-Scale Structure of Earth to Our Everyday Appliances","authors":"P. Maurizot, B. Sevin, M. Iseppi, Tanguy Giband","doi":"10.1130/GSATG364A.1","DOIUrl":"https://doi.org/10.1130/GSATG364A.1","url":null,"abstract":"Nickel production is vital to modern economic development. Of the different ore types, supergene Ni-laterite production, as open-cast mining exploitation, is on the rise and surpassing the more conventional hypogene sulfide type. This trend will likely continue. Assessing the global resource of Ni laterite is therefore of crucial importance. Compilation of scientific publications shows that the main producers and occurrences are concentrated in a few countries in Southeast Asia (New Caledonia, Indonesia, the Philippines) and the Caribbean region (Cuba and the Dominican Republic). In these regions a common geological background appears, characterized by large obducted ophiolites in tectonically active settings, subject to weathering during the Neogene. The neoformed mineralogy of such surficial deposits is well documented. A model is proposed, based on the knowledge gained on Ni-laterite deposits in New Caledonia, that could be applied to similar geological settings worldwide. This model states that in accretionary terranes, vertical motions during weathering control both ore","PeriodicalId":35784,"journal":{"name":"GSA Today","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41614341","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}
No other international scientific collaboration has contributed as much to our knowledge of Earth processes as scientific ocean drilling (SOD). These contributions include geophysical surveys, core samples, borehole well logs, and sub-seafloor observatories. After more than half a century, involving thousands of scientists from around the world, SOD has been instrumental in developing three geoscience revolutions: (1) plate tectonics, (2) paleoceanography, and (3) the deep marine biosphere. Without SOD, it is unlikely that our current understanding of Earth processes could have developed. Building upon prior scientific results, the current science plan is guided by four interlinked themes: Planetary Dynamics, Climate and Ocean Change, Biosphere Frontiers, and Earth in Motion. SOD has also been a leader in international collaborations and the open sharing of samples, data, and information. Results from SOD expeditions are open access and available online. Almost 2.5 million samples have been taken from over 360 km of core located in three repositories. Today about half the members of scientific teams, including co-chief scientists, are women. This program is needed in the future for geoscientists to continue exploring our planet to understand how it functions and to create predictive models. INTRODUCTION Scientific ocean drilling (SOD) celebrated its 50th birthday in 2018. As of December 2018, 283 expeditions (formerly called legs) have been completed and >1600 sites have been drilled (see Fig. S1 in the GSA Data Repository1). These sites represent <0.0005% of the ocean floor, yet have provided essential information about plate tectonics, ocean chemistry, evolution, life in harsh environments, and climate change. Scientists from across the world have benefited from and contributed to the program. Geophysical site survey data, cores, and associated information are available to the global scientific community to study and sample. More than 1000 international scientists, ranging in age from early career to retired, are proponents on active proposals for upcoming drilling. This article, by no means comprehensive, highlights parts of the history and a few major discoveries of SOD. More complete histories are available in Ocean Drilling: Accomplishments and Challenges (National Research Council, 2011), Earth and Life Processes Discovered from Subseafloor Environments: A Decade of Science Achieved by the Integrated Ocean Drilling Program (IODP) (Stein et al., 2014), and Koppers et al. (2019). GSA Data Repository Table S1 (see footnote 1) provides URLs to detailed, preliminary information for all SOD expeditions and legs, including co-chief scientists, sites cored, and year.
{"title":"Holes in the Bottom of the Sea: History, Revolutions, and Future Opportunities","authors":"S. O’Connell","doi":"10.1130/gsatg380a.1","DOIUrl":"https://doi.org/10.1130/gsatg380a.1","url":null,"abstract":"No other international scientific collaboration has contributed as much to our knowledge of Earth processes as scientific ocean drilling (SOD). These contributions include geophysical surveys, core samples, borehole well logs, and sub-seafloor observatories. After more than half a century, involving thousands of scientists from around the world, SOD has been instrumental in developing three geoscience revolutions: (1) plate tectonics, (2) paleoceanography, and (3) the deep marine biosphere. Without SOD, it is unlikely that our current understanding of Earth processes could have developed. Building upon prior scientific results, the current science plan is guided by four interlinked themes: Planetary Dynamics, Climate and Ocean Change, Biosphere Frontiers, and Earth in Motion. SOD has also been a leader in international collaborations and the open sharing of samples, data, and information. Results from SOD expeditions are open access and available online. Almost 2.5 million samples have been taken from over 360 km of core located in three repositories. Today about half the members of scientific teams, including co-chief scientists, are women. This program is needed in the future for geoscientists to continue exploring our planet to understand how it functions and to create predictive models. INTRODUCTION Scientific ocean drilling (SOD) celebrated its 50th birthday in 2018. As of December 2018, 283 expeditions (formerly called legs) have been completed and >1600 sites have been drilled (see Fig. S1 in the GSA Data Repository1). These sites represent <0.0005% of the ocean floor, yet have provided essential information about plate tectonics, ocean chemistry, evolution, life in harsh environments, and climate change. Scientists from across the world have benefited from and contributed to the program. Geophysical site survey data, cores, and associated information are available to the global scientific community to study and sample. More than 1000 international scientists, ranging in age from early career to retired, are proponents on active proposals for upcoming drilling. This article, by no means comprehensive, highlights parts of the history and a few major discoveries of SOD. More complete histories are available in Ocean Drilling: Accomplishments and Challenges (National Research Council, 2011), Earth and Life Processes Discovered from Subseafloor Environments: A Decade of Science Achieved by the Integrated Ocean Drilling Program (IODP) (Stein et al., 2014), and Koppers et al. (2019). GSA Data Repository Table S1 (see footnote 1) provides URLs to detailed, preliminary information for all SOD expeditions and legs, including co-chief scientists, sites cored, and year.","PeriodicalId":35784,"journal":{"name":"GSA Today","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49127515","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}
R. Flowers, J. Arrowsmith, V. McConnell, J. Metcalf, T. Rittenour, B. Schoene
Rebecca M. Flowers, Dept. of Geological Sciences, University of Colorado Boulder, Boulder, Colorado 80309, USA; J Ramón Arrowsmith, Arizona State University, School of Earth & Space Exploration, Tempe, Arizona 85287, USA; Vicki McConnell, Geological Society of America, 3300 Penrose Place, Boulder, Colorado 80301, USA; James R. Metcalf, Dept. of Geological Sciences, University of Colorado Boulder, Boulder, Colorado 80309, USA; Tammy Rittenour, Dept. of Geology, Utah State University, Logan, Utah 84322, USA; and Blair Schoene, Dept. of Geosciences, Princeton University, Princeton, New Jersey 08544, USA
美国科罗拉多大学博尔德分校地质科学系Rebecca M. Flowers，美国科罗拉多州博尔德80309;J Ramón亚利桑那州立大学地球与空间探索学院阿罗史密斯，美国亚利桑那州坦佩85287;Vicki McConnell，美国地质学会，3300 Penrose Place, Boulder, Colorado 80301, USA;James R. Metcalf，美国科罗拉多大学博尔德分校地质科学系，美国科罗拉多州博尔德80309;Tammy Rittenour，犹他州立大学地质系，美国犹他州洛根84322;普林斯顿大学地球科学系Blair Schoene，美国新泽西州普林斯顿08544
{"title":"The AGeS2 (Awards for Geochronology Student research 2) Program: Supporting Community Geochronology Needs and Interdisciplinary Science","authors":"R. Flowers, J. Arrowsmith, V. McConnell, J. Metcalf, T. Rittenour, B. Schoene","doi":"10.1130/GSATG392GW.1","DOIUrl":"https://doi.org/10.1130/GSATG392GW.1","url":null,"abstract":"Rebecca M. Flowers, Dept. of Geological Sciences, University of Colorado Boulder, Boulder, Colorado 80309, USA; J Ramón Arrowsmith, Arizona State University, School of Earth & Space Exploration, Tempe, Arizona 85287, USA; Vicki McConnell, Geological Society of America, 3300 Penrose Place, Boulder, Colorado 80301, USA; James R. Metcalf, Dept. of Geological Sciences, University of Colorado Boulder, Boulder, Colorado 80309, USA; Tammy Rittenour, Dept. of Geology, Utah State University, Logan, Utah 84322, USA; and Blair Schoene, Dept. of Geosciences, Princeton University, Princeton, New Jersey 08544, USA","PeriodicalId":35784,"journal":{"name":"GSA Today","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45850972","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":"Navigating “Me, too” in the Geosciences","authors":"R. Gries","doi":"10.1130/GSAT18PRSADR.1","DOIUrl":"https://doi.org/10.1130/GSAT18PRSADR.1","url":null,"abstract":"","PeriodicalId":35784,"journal":{"name":"GSA Today","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48170270","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}
3D is a task that most people, including geologists, find difficult. Geoscience educators and students often find fieldbased exercises the most effective medium for understanding complex geological concepts and visualizing relationships in 3D (e.g., Elkins and Elkins, 2007). Unfortunately, field-based training is not available to everyone. Traditional barriers to this field-based training include physical disabilities, lack of financial resources, and geographical restrictions. Recent advances in data acquisition and processing have the potential to circumvent these traditional barriers to access and open up a vast number of field sites to a diverse range of people.
{"title":"eRock: An Open-Access Repository of Virtual Outcrops for Geoscience Education","authors":"A. Cawood, C. Bond","doi":"10.1130/GSATG373GW.1","DOIUrl":"https://doi.org/10.1130/GSATG373GW.1","url":null,"abstract":"3D is a task that most people, including geologists, find difficult. Geoscience educators and students often find fieldbased exercises the most effective medium for understanding complex geological concepts and visualizing relationships in 3D (e.g., Elkins and Elkins, 2007). Unfortunately, field-based training is not available to everyone. Traditional barriers to this field-based training include physical disabilities, lack of financial resources, and geographical restrictions. Recent advances in data acquisition and processing have the potential to circumvent these traditional barriers to access and open up a vast number of field sites to a diverse range of people.","PeriodicalId":35784,"journal":{"name":"GSA Today","volume":" ","pages":""},"PeriodicalIF":0.0,"publicationDate":"2019-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42863469","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：