The Southwestern Laurentia large igneous province (SWLLIP) comprises voluminous, widespread ca 1.1 Ga magmatism in the southwestern United States and northern Mexico. The timing and tempo of SWLLIP magmatism and its relationship to other late Mesoproterozoic igneous provinces have been unclear due to difficulties in dating mafic rocks at high precision. New precise U-Pb zircon dates for comagmatic felsic segregations within mafic rocks reveal distinct magmatic episodes at ca. 1098 Ma (represented by massive sills in Death Valley, California, the Grand Canyon, and central Arizona) and ca. 1083 Ma (represented by the Cardenas Basalts in the Grand Canyon and a sill in the Dead Mountains, California). The ca. 1098 Ma magmatic pulse was short-lived, lasting 0.25−0.24+0.67 m.y., and voluminous and widespread, evidenced by the ≥100 m sills in Death Valley, the Grand Canyon, and central Arizona, consistent with decompression melting of an upwelling mantle plume. The ca. 1083 Ma magmatism may have been generated by a secondary plume pulse or post-plume lithosphere extension.The ca. 1098 Ma pulse of magmatism in southwestern Laurentia occurred ~2 m.y. prior to an anomalous renewal of voluminous melt generation in the Midcontinent Rift of central Laurentia that is recorded by the ca. 1096 Ma Duluth Complex layered mafic intrusions. Rates of lateral plume spread predicted by mantle plume lubrication theory support a model where a plume derived from the deep mantle impinged near southwestern Laurentia, then spread to thinned Midcontinent Rift lithosphere over ~2 m.y. to elevate mantle temperatures and generate melt. This geodynamic hypothesis reconciles the close temporal relationships between voluminous magmatism across Laurentia and provides an explanation for that anomalous renewal of high magmatic flux within the protracted magmatic history of the Midcontinent Rift.The Southwestern Laurentia large igneous province (SWLLIP) comprises >750,000 km2 of ca. 1.1 Ga mafic dikes, sills, and lava flows and minor felsic rocks across the southwestern United States and northern Mexico (Howard, 1991; Bright et al., 2014). Thick (≥100 m) sills intrude Mesoproterozoic strata of the Pahrump Group in the Death Valley, California, region (Wright et al., 1967), the Unkar Group of the Grand Canyon Supergroup (Timmons et al., 2012), and the Apache Group of central Arizona (Wrucke, 1990). A variety of radioisotope chronometers have previously been applied to date SWLLIP mafic rocks (see the compilation of Bright et al., 2014), but inherent difficulties in precise and accurate dating of ancient mafic rocks have hindered an understanding of the tempo of SWLLIP magmatism and its correlation to other tectonic and magmatic events of Laurentia, such as the Midcontinent Rift (MCR).The temporal resolution achieved by modern high-precision U-Pb zircon geochronology underpins the defining traits of large igneous provinces (LIPs), namely punctuated (<1 m.y.) episodes of high magmatic flux (Ernst et al., 2021; Kasbohm et al., 2021). While paucity of zircon in mafic rocks typically precludes U-Pb zircon dating, caches of zircon are often hosted in late-stage felsic differentiates (Krogh et al., 1987) or can be obtained using novel rock-digestion and mineral separation methods that concentrate zircon micro-inclusions (Oliveira et al., 2022). We present new precise ages for SWLLIP rocks in California and Arizona obtained from zircon crystals extracted from a basalt flow and localized felsic segregations in mafic sills (Fig. 1). These new ages are then used to explore a geodynamic connection between voluminous magmatic pulses in two Late Mesoproterozoic (Stenian) LIPs, the SWLLIP and the MCR.We measured U-Pb dates for zircon crystals by chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS; Mattinson, 2005). Preparation, analytical, and data-reduction methods and data for all individual U-Pb analyses are provided in the Supplemental Material1. Weighted mean ages interpreted from concordant 206Pb/238U zircon dates are reported herein and in Figure 2 with 95% confidence analytical uncertainties, and in Table 1 with mean square of weighted deviates (MSWD) values, additional sources of uncertainty, and sample descriptions. Discordant dates were excluded from age calculations but have implications for interpreting previously published, lower-precision data sets (discussed below and in the Supplemental Material).Felsic segregations from three diabase sills intruding the Crystal Spring Formation in the Death Valley region gave ages of 1097.91 ± 0.29 Ma, 1098.27 ± 0.27 Ma, and 1098.09 ± 0.91 Ma (Fig. 2). A felsic segregation in a sill in Salt River Canyon, Arizona, gave an age of 1097.97 ± 0.12 Ma. In the Grand Canyon, felsic segregations from two sills gave ages of 1098.09 ± 0.34 Ma and 1098.16 ± 0.59 Ma, and the sampled Cardenas Basalt gave an age of 1082.18 ± 1.25 Ma. A felsic zone within a diabase sill in the Dead Mountains of California, within the Colorado River trough (Fig. 1; see also fig. 4B in Howard, 1991) gave an age of 1082.60 ± 0.30 Ma.Both ca. 1098 Ma and ca. 1083 Ma episodes of SWLLIP magmatism are expressed in the Unkar Group of the Grand Canyon Supergroup. Previously, sills in the Grand Canyon were considered coeval feeders of the Cardenas Basalt (Timmons et al., 2012). Our new ages indicate that sills intruding the Bass and Hakatai Formations in western Grand Canyon (Fig. 1) were emplaced at ca. 1098 Ma, while the Cardenas Basalt erupted at ca. 1083 Ma. The Cardenas Basalt flows are conformable with the Dox Formation, making their 1082.18 ± 1.25 Ma age a new chronostratigraphic constraint for the Unkar Group.Discrepancies between our data and the previous 1094 ± 2 Ma to 1080 ± 3 Ma ages for SWLLIP mafic rocks established from U-Pb dating of baddeleyite (Bright et al., 2014) demonstrate the importance of high-precision data and Pb-loss mitigation offered by zircon CA-ID-TIMS geochronology for accurately dating LIPs. Baddeleyite is not amenable to chemical abrasion (Rioux et al., 2010) and has been shown to often yield anomalously young dates, likely due to Pb loss, in studies measuring U-Pb dates of both zircon and baddeleyite (Gaynor et al., 2022). While closed-system U-Pb decay is evaluated by agreement between 206Pb/238U and 207Pb/235U dates within analytical uncertainty (i.e., “concordance”), the apparently concordant, low-precision baddeleyite analyses for SWLLIP mafic rocks also encompass ca. 1098 Ma and ca. 1083 Ma discordia trajectories defined by our more precise CA-ID-TIMS zircon data for samples K12-132L and MM2021-CA1, respectively (Fig. 2; Fig. S2 in the Supplemental Material). Consequently, the range of ages reported by Bright et al. (2014) likely stem from inaccurate 206Pb/238U dates due to unmitigated Pb loss that is hidden by large analytical uncertainties. Concordia upper-intercept regressions for baddeleyite data reported by Bright et al. (2014) yield ages of 1104.6 ± 59.9 Ma, 1085.4 ± 12.9 Ma, 1113.8 ± 43.0 Ma, and 1091.3 ± 17.9 Ma (±95% confidence; Fig. S3), which are unable to resolve whether these sills were emplaced at ca. 1098 Ma, ca. 1083 Ma, or during another unknown episode of magmatism in southwestern Laurentia.High-precision U-Pb zircon geochronology of Stenian (1.2–1.0 Ga) mafic rocks in California and Arizona significantly refines the timing of SWLLIP magmatism and its relationship to other Laurentian tectonic and magmatic events. The 0.75–1.5 × 106 km2 extent of the SWLLIP (Bright et al., 2014; Ernst et al., 2021) based on the regional distribution of ca. 1.1 Ga mafic and felsic rocks in southwestern Laurentia (Fig. 3) was previously interpreted to have been emplaced over ~20 m.y. (see the compilation of Bright et al., 2014). Our more precise ages reveal punctuated magmatic episodes at ca. 1098 Ma and ca. 1083 Ma. Published εNd data sets are consistent with two distinct pulses of mafic magmatism in the SWLLIP, as sills in Death Valley, the Grand Canyon, and western and central Arizona have εNd values of +3 to +5 (Hammond and Wooden, 1990) while the Cardenas Basalts have lower εNd values of +0.5 to +2 (Larson et al., 1994), as do sills in western and central Arizona, and southwestern New Mexico (Bright et al., 2014). With no clear spatial trends in εNd values (Hammond and Wooden, 1990), we hypothesize that isotopic differences reflect tapping of different mantle reservoirs during temporally distinct pulses of magmatism. Felsic magmatism may have occurred with each pulse of mafic magmatism, as indicated by populations of ca. 1098 Ma ages for granitoids in central Texas and ca. 1083 Ma ages for granitoids in southwestern New Mexico and northern Mexico (Fig. 3), but existing ages for Stenian felsic rocks in southwestern Laurentia are based on discordant, pre–chemical abrasion U-Pb zircon analyses and should be reassessed by U-Pb zircon CA-ID-TIMS dating to more robustly establish their age and relationships to SWLLIP mafic magmatism.A prevailing hypothesis for the formation of the SWLLIP is that a mantle plume pooled under thin southwestern Laurentia lithosphere (Howard, 1991; Bright et al., 2014). Voluminous melt production is evident in the SWLLIP’s initial ca. 1098 Ma pulse by numerous sills that exceed thicknesses of 100 m in portions of Death Valley (Wright et al., 1967), the Grand Canyon (Timmons et al., 2012), and in central Arizona (Smith and Silver, 1975), and likely more within the extensive network of Stenian sills imaged in the Arizona subsurface (Litak and Hauser, 1992) and associated lavas that have likely been removed by erosion. Our data suggest that the ca. 1098 Ma pulse was rapid, lasting 0.25−0.24+0.67 m.y. (median ± 95% credible interval of pair-wise Monte Carlo resampling of ca. 1098 Ma ages and uncertainties), and thus consistent with voluminous, widespread, and rapidly emplaced mafic rocks characteristic of plume-related LIPs (see Ernst et al., 2021).The ca. 1083 Ma episode of SWLLIP mafic magmatism may have been generated by a secondary pulse caused by a separation of the plume head at the lower–upper mantle boundary (Bercovici and Mahoney, 1994) or from regional extension and/or delamination due to thermomechanical alteration of the lithosphere during plume-lithosphere interaction (Black et al., 2021). The regional extension hypothesis is consistent with interflow sediments in the Cardenas Basalts that suggest subsidence and sedimentation coeval with ca. 1083 Ma Cardenas Basalts eruption(s), and with the bimodal nature of ca. 1086–1080 Ma magmatism throughout southwestern Laurentia (Fig. 3).The precise U-Pb zircon CA-ID-TIMS geochronology on the SWLLIP presented here can be compared with that of the MCR (i.e., Keweenawan LIP) to assess hypothesized geodynamic relationships between these two LIPs (e.g., Bright et al., 2014; Swanson-Hysell et al., 2021). Our new ages reveal that ca. 1098 Ma SWLLIP magmatism was coeval with protracted MCR magmatism in central Laurentia, overlapping with the beginning of the MCR’s “main magmatic stage” (Vervoort et a., 2007), but a ca. 1083 Ma SWLLIP episode postdated known MCR magmatism. While mechanisms for the initiation of the MCR are debated (cf. Nicholson and Shirey, 1990; Stein et al., 2015), magmatism within the rift basin occurred from ca. 1109 Ma to ca. 1084 Ma (Swanson-Hysell et al., 2019) with intervals of high melt volumes requiring mantle temperatures in excess of ambient Mesoproterozoic mantle (Hutchinson et al., 1990; Gunawardana et al., 2022) and geochemical signatures consistent with the influence of an enriched mantle source (Nicholson and Shirey, 1990; Shirey, 1997).A persistent question regarding the history of the MCR is: what caused renewal of voluminous magmatism at ca. 1096 Ma that produced the massive Duluth Complex layered mafic intrusion (one of the largest mafic intrusive complexes on Earth) and comagmatic lavas after a period of relative magmatic dormancy (Vervoort et al., 2007), and after Laurentia had drifted >3000 km since the rift’s initiation (Swanson-Hysell et al., 2019, 2021)? Swanson-Hysell et al. (2021) suggested that distal plumes could have been funneled to the thinned lithosphere under the MCR via “upside-down drainage” (terminology of Sleep, 1997); however, the previous chronology of the SWLLIP was too imprecise to test this hypothesis.The voluminous, punctuated, initial pulse of magmatism in southwestern Laurentia, constrained by ages between 1098.27 ± 0.27 Ma and 1097.91 ± 0.29 Ma, occurred ~2 m.y. prior to the 1096.19 ± 0.19 Ma to 1095.69 ± 0.18 Ma emplacement of the Duluth Complex (Swanson-Hysell et al., 2021), and buoyant plume heads can spread ~2000 km during impingement with the lithosphere (Campbell and Griffiths, 1990). Interactions of buoyant plumes with continental lithosphere may be complex (Duvernay et al., 2022), but time-dependent spreading velocities can be estimated by plume lubrication theory (Sleep, 1997). Figure 3C shows analytical results from the model of Sleep (1997) that predict radial spreading velocities for impinging mantle plumes derived from the core-mantle boundary (CMB) and from the mantle transition zone (MTZ), with upper-mantle plume head diameters of 1000 km and 300 km, respectively (Campbell and Griffiths, 1990). The solutions show dramatically decreasing lateral velocity with time due to diminishing buoyancy from flattening and thinning during spreading of a plume head (e.g., Griffiths and Campbell, 1991), but demonstrate that a 1000-km-diameter plume could spread ~1600 km (~2100 km total radius) in 2 m.y., consistent with the location of the Duluth Complex relative to the SWLLIP and the time lag in magmatism revealed by the precise geochronology. The slower spreading velocities associated with a smaller plume head (<550 km over 2 m.y.) could not reasonably advect plume material from the SWLLIP to the MCR over ~2 m.y. Laurentia’s ~30 cm/yr drift during this time (Swanson-Hysell et al., 2019) would have displaced the MCR ~600 km eastward during 2 m.y. of plume spreading; however, this movement is only significant relative to the rates of plume spreading after ~0.8 m.y., when a spreading plume under this scenario would have already been channelized into the MCR (e.g., Sleep 1997).New ages for SWLLIP mafic rocks established by CA-ID-TIMS U-Pb zircon dating of comagmatic felsic segregations refine the timing of the SWLLIP and resolve temporally distinct ca. 1098 Ma and ca. 1083 Ma magmatic episodes. Geochronology of the ca. 1098 Ma primary magmatism of the SWLLIP and the ca. 1096 Ma pulse of magmatism in the MCR is consistent with predicted lateral plume spreading rates beneath continental lithosphere. We present a plume-spreading relationship between SWLLIP and MCR magmatism as a hypothesis to be tested by future geochronological studies integrated with geochemical data and advanced geodynamic modeling. Our study reinforces how high-precision U-Pb zircon geochronology lays a foundation for defining and correlating ancient magmatic episodes and yields the temporal resolution needed to test complex interactions between plume magmatism and continental lithosphere.We thank Bruce Buffett for insight into plume lubrication theory, and the crews of several Grand Canyon–Colorado River Field Forums for field and logistical support. Permits from the U.S. National Park Service in Death Valley and Grand Canyon National Parks and funding from National Science Foundation (grants EAR1954583, EAR1847277, and EAR1735889) enabled this research. Reviews from C. Stein, J. Kasbohm, R. Ernst, and two anonymous reviewers improved this manuscript.

中文翻译：

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高精度 U-Pb 地质年代学将西南劳伦大陆大型火成岩省和中大陆裂谷的岩浆作用联系起来

西南劳伦西亚大型火成岩省 (SWLLIP) 包括美国西南部和墨西哥北部大量、广泛的约 1.1 Ga 岩浆活动。由于难以高精度地测定镁铁质岩石的年代，SWLLIP 岩浆活动的时间和速度及其与其他中元古代晚期火成岩省的关系尚不清楚。新的精确 U-Pb 锆石定年法揭示了镁铁质岩石内共岩浆长英质偏析的独特岩浆事件。1098 Ma（以加利福尼亚州死亡谷、大峡谷和亚利桑那州中部的巨大岩台为代表）1083 Ma（以大峡谷的卡德纳斯玄武岩和加利福尼亚州死亡山脉的岩台为代表）。约。1098 Ma 岩浆脉冲是短暂的，持续 0.25−0.24+0.67 my，而且数量大且分布广泛，死亡谷、大峡谷和亚利桑那州中部≥100 m 的岩床证明了这一点，这与上升的地幔柱的减压熔融一致。约。1083 Ma 岩浆作用可能是由二次羽流脉冲或羽流后岩石圈延伸产生的。1098 Ma 劳伦西亚西南部的岩浆活动脉冲发生在约 2 my 之前，在劳伦西亚中部大陆裂谷中大量熔体生成的异常更新之前，这一现象由大约 1098 Ma 记录。1096 Ma Duluth 杂岩层状镁铁质侵入体。地幔羽流润滑理论预测的羽流横向扩散速率支持这样一个模型：来自深层地幔的羽流撞击劳伦西亚西南部附近，然后在约 2 m 的时间内扩散到变薄的中大陆裂谷岩石圈，以提高地幔温度并产生熔化。这一地球动力学假说调和了整个劳伦西亚大量岩浆活动之间的密切时间关系，并为中部大陆裂谷长期岩浆历史中高岩浆通量的异常更新提供了解释。西南劳伦大陆大型火成岩省（SWLLIP）由约 750,000 平方公里的面积组成。 。1.1 美国西南部和墨西哥北部的镁铁质岩脉、岩基、熔岩流和小型长英质岩石（Howard，1991；Bright 等，2014）。厚（≥100 m）的岩床侵入了加利福尼亚州死亡谷地区 Pahrump 群的中元古代地层（Wright 等，1967）、大峡谷超群的 Unkar 群（Timmons 等，2012）和亚利桑那州中部的阿帕奇集团（Wrucke，1990）。此前已有多种放射性同位素测年仪用于对SWLLIP镁铁质岩石进行测年（参见Bright等人，2014年的汇编），但对古代镁铁质岩石进行精确和准确测年所固有的困难阻碍了对SWLLIP岩浆活动速度和速度的理解。它与劳伦大陆其他构造和岩浆事件的相关性，例如中大陆裂谷 (MCR)。现代高精度 U-Pb 锆石地质年代学实现的时间分辨率支撑了大型火成岩省 (LIP) 的定义特征，即间断的 (< 1 我的 ）高岩浆通量事件（Ernst 等人，2021 年；Kasbohm 等人，2021 年）。虽然镁铁质岩石中锆石含量很少，通常无法进行 U-Pb 锆石定年，但锆石储量通常存在于晚期长英质分异物中（Krogh 等，1987），或者可以使用新的岩石消化和矿物分离方法来获得，这些方法集中了锆石微包裹体（Oliveira 等人，2022）。我们提出了加利福尼亚州和亚利桑那州 SWLLIP 岩石的新精确年龄，这些岩石是从玄武岩流中提取的锆石晶体和基性基岩中的局部长英质偏析中获得的（图 1）。然后，这些新年龄被用来探索两个晚中元古代 (Stenian) LIP（SWLLIP 和 MCR）中大量岩浆脉冲之间的地球动力学联系。我们通过化学磨损-同位素稀释-热电离质谱法测量了锆石晶体的 U-Pb 年代。 （CA-ID-TIMS；Mattinson，2005）。补充材料1中提供了所有单独 U-Pb 分析的制备、分析和数据缩减方法以及数据。本文和图 2 报告了根据一致的 206Pb/238U 锆石日期解释的加权平均年龄，具有 95% 置信度分析不确定性，表 1 具有加权偏差均方 (MSWD) 值、其他不确定性来源和样品描述。不一致的日期被排除在年龄计算之外，但对解释先前发布的低精度数据集有影响（在下面和补充材料中讨论）。从侵入死亡谷地区水晶泉地层的三个辉绿岩基岩中进行的长英质分离得出的年龄为 1097.91 ± 0.29 Ma、1098.27 ± 0.27 Ma 和 1098.09 ± 0.91 Ma（图 2）。亚利桑那州盐河峡谷岩台中的长英质偏析给出的年龄为 1097.97 ± 0.12 Ma。在大峡谷中，两个岩台的长英质偏析给出的年龄为 1098.09 ± 0.34 Ma 和 1098.16 ± 0.59 Ma，而采样的卡德纳斯玄武岩给出的年龄为 1082.18 ± 1.25 Ma。加利福尼亚死亡山脉、科罗拉多河槽内的辉绿岩岩台内的长英质带（图 1；也参见 Howard，1991 年的图 4B）给出的年龄为 1082.60 ± 0.30 Ma。1098 马和约。1083 Ma 的 SWLLIP 岩浆活动在大峡谷超群的 Unkar 群中表现出来。此前，大峡谷的岩台被认为是同时代的卡德纳斯玄武岩的供给源（Timmons 等，2012）。我们的新年龄表明，侵入大峡谷西部巴斯和哈卡泰地层的岩床（图 1）位于大约 10 世纪 10 年代。1098 Ma，而卡德纳斯玄武岩在大约 1098 Ma 喷发。第1083章 Cardenas 玄武岩流与 Dox 地层一致，使其 1082.18 ± 1.25 Ma 年龄成为 Unkar 群的新年代地层约束。我们的数据与之前建立的 SWLLIP 镁铁质岩石 1094 ± 2 Ma 至 1080 ± 3 Ma 年龄之间存在差异斜锆石的 U-Pb 定年（Bright 等人，2014）证明了锆石 CA-ID-TIMS 地质年代学提供的高精度数据和 Pb 损失缓解对于准确测定 LIP 年代的重要性。斜锆石不适合化学磨损（Rioux 等人，2010），并且在测量锆石和斜锆石 U-Pb 年代的研究中，已证明经常会产生异常年轻的年代，可能是由于 Pb 损失所致（Gaynor 等人， 2022）。虽然封闭系统 U-Pb 衰变是通过分析不确定性范围内 206Pb/238U 和 207Pb/235U 日期之间的一致性来评估的（即“一致性”），但对 SWLLIP 镁铁岩的明显一致的低精度斜锆石分析也涵盖了约 206Pb/238U 和 207Pb/235U 日期之间的一致性。1098 马和约。1083 Ma 不和谐轨迹由我们更精确的 CA-ID-TIMS 锆石数据分别为样品 K12-132L 和 MM2021-CA1 定义（图 2；补充材料中的图 S2）。因此，Bright 等人报告的年龄范围。(2014) 可能源于不准确的 206Pb/238U 日期，这是由于巨大的分析不确定性掩盖了未缓解的 Pb 损失。Bright 等人报告的斜锆石数据的 Concordia 上截距回归。(2014) 的屈服年龄为 1104.6 ± 59.9 Ma、1085.4 ± 12.9 Ma、1113.8 ± 43.0 Ma 和 1091.3 ± 17.9 Ma（±95% 置信度；图 S3），无法确定这些岩台是否位于约 1000 Ma。1098 Ma，约。1083 Ma，或在劳伦西亚西南部另一次未知的岩浆活动期间。加利福尼亚州和亚利桑那州 Stenian (1.2–1.0 Ga) 基性岩的高精度 U-Pb 锆石年代学显着完善了 SWLLIP 岩浆活动的时间及其与其他劳伦斯构造的关系和岩浆事件。SWLLIP 的 0.75–1.5 × 106 km2 范围（Bright 等，2014；Ernst 等，2021）基于大约 劳伦西亚西南部的 1.1 Ga 镁铁质和长英质岩石（图 3）先前被解释为已就位超过约 20 my（参见 Bright 等人，2014 年的汇编）。我们更精确的年龄揭示了大约在大约 10 世纪间断断续续的岩浆活动。1098 马和约。第1083章 已发表的 εNd 数据集与 SWLLIP 中两个不同的镁铁质岩浆作用脉冲一致，因为死亡谷、大峡谷以及亚利桑那州西部和中部的岩台的 εNd 值为 +3 至 +5（Hammond 和 Wooden，1990），而卡德纳斯玄武岩的 εNd 值较低，为 +0.5 至 +2（Larson 等人，1994 年），亚利桑那州西部和中部以及新墨西哥州西南部的岩床也是如此（Bright 等人，2014 年）。由于 εNd 值没有明显的空间趋势（Hammond 和 Wooden，1990），我们假设同位素差异反映了在时间上不同的岩浆脉冲期间对不同地幔储层的开采。长英质岩浆活动可能伴随着每一次镁铁质岩浆活动的脉冲而发生，如大约 1000 多个镁铁质岩浆活动的数量所表明的那样。得克萨斯州中部和大约 1098 Ma 的花岗岩年龄 新墨西哥州西南部和墨西哥北部花岗岩类的 1083 Ma 年龄（图 3），但劳伦西亚西南部 Stenian 长英质岩石的现有年龄是基于不一致的，化学磨损前 U-Pb 锆石分析，应通过 U-Pb 锆石 CA-ID-TIMS 测年重新评估，以更可靠地确定其年龄以及与 SWLLIP 镁铁质岩浆作用的关系。SWLLIP 形成的一个普遍假设是地幔羽流聚集在劳伦西亚西南部薄层岩石圈下（Howard，1991；Bright 等人，2014）。在 SWLLIP 的初始阶段，大量熔体产量显而易见。在死亡谷（Wright 等人，1967 年）、大峡谷（Timmons 等人，2012 年）以及亚利桑那州中部（Smith 和 Silver，1975 年）的部分地区，1098 Ma 脉冲通过许多厚度超过 100 m 的岩床，更可能是在亚利桑那州地下成像的广泛的斯滕尼亚基岩网络中（Litak 和 Hauser，1992）以及可能已被侵蚀去除的相关熔岩。我们的数据表明大约。1098 Ma 脉冲快速，持续 0.25−0.24+0.67 my（约 1098 Ma 年龄和不确定性的成对蒙特卡罗重采样的中值 ± 95% 可信区间），因此与大量、广泛且快速就位的镁铁质岩石一致与羽流相关的 LIP 的特征（参见 Ernst 等人，2021）。1083 Ma 的 SWLLIP 镁铁质岩浆作用可能是由下-上地幔边界处的地幔柱头分离引起的二次脉冲产生的（Bercovici 和 Mahoney，1994），或者是由于地幔热机械改变导致的区域伸展和/或分层。地幔柱与岩石圈相互作用期间的岩石圈（Black et al., 2021）。区域延伸假说与卡德纳斯玄武岩中的互流沉积物一致，表明沉降和沉积与大约 1083 Ma Cardenas 玄武岩喷发，并具有约 1083 Ma Cardenas 玄武岩喷发的双峰性质。1086–1080 Ma 整个劳伦西亚西南部的岩浆活动（图 3）。此处提供的 SWLLIP 上的精确 U-Pb 锆石 CA-ID-TIMS 地质年代学可以与 MCR（即 Keweenawan LIP）的地质年代学进行比较，以评估假设的地球动力学关系这两个 LIP 之间（例如，Bright 等人，2014 年；Swanson-Hysell 等人，2021 年）。我们的新时代揭示了大约。1098 Ma SWLLIP 岩浆活动与劳伦西亚中部的持久 MCR 岩浆活动同时期，与 MCR“主要岩浆阶段”的开始重叠（Vervoort 等，2007），但大约 1098 Ma SWLLIP 岩浆活动与劳伦西亚中部的持久 MCR 岩浆活动同时期，与 MCR 的“主要岩浆阶段”的开始重叠（Vervoort 等，2007）。1083 Ma SWLLIP 事件晚于已知的 MCR 岩浆作用。虽然 MCR 的启动机制存在争议（参见 Nicholson 和 Shirey，1990；Stein 等人，2015），但裂谷盆地内的岩浆活动发生在大约 1990 年。1109 马至约。1084 Ma（Swanson-Hysell 等，2019），具有高熔体量间隔，要求地幔温度超过周围中元古代地幔（Hutchinson 等，1990；Gunawardana 等，2022），并且地球化学特征与 1084 Ma 的影响一致。丰富的地幔来源（Nicholson 和 Shirey，1990；Shirey，1997）。关于 MCR 历史的一个持续存在的问题是：是什么导致了大约 10 年前大量岩浆活动的更新。1096 Ma，经过一段相对的岩浆休眠期（Vervoort et al., 2007），以及劳伦西亚自那时以来漂移了超过 3000 公里之后，产生了巨大的德卢斯杂岩层状镁铁质侵入体（地球上最大的镁铁质侵入杂岩体之一）和共岩浆熔岩（Vervoort 等，2007）裂痕的起始（Swanson-Hysell 等人，2019、2021）？斯旺森-海塞尔等人。(2021) 提出，远端羽流可能通过“倒置排水”流入 MCR 下变薄的岩石圈（睡眠术语，1997）；然而，先前的 SWLLIP 年表太不精确，无法验证这一假设。劳伦西亚西南部大量、间断的初始岩浆脉冲，受到年龄在 1098.27 ± 0.27 Ma 和 1097.91 ± 0.29 Ma 之间的限制，发生在大约 2 my 之前德卢斯杂岩在 1096.19 ± 0.19 Ma 到 1095.69 ± 0.18 Ma 就位（Swanson-Hysell 等，2021），并且浮力羽流头在撞击岩石圈期间可以传播约 2000 公里（Campbell 和 Griffiths，1990）。浮力羽流与大陆岩石圈的相互作用可能很复杂（Duvernay et al., 2022），但随时间变化的扩散速度可以通过羽流润滑理论来估计（Sleep, 1997）。图 3C 显示了 Sleep (1997) 模型的分析结果，该模型预测了源自地核-地幔边界 (CMB) 和地幔过渡区 (MTZ) 的撞击地幔羽流的径向扩散速度，上地幔羽流头部直径为分别为 1000 公里和 300 公里（Campbell 和 Griffiths，1990）。解决方案显示，由于羽流头部扩展期间变平和变薄而导致浮力减小，横向速度随时间急剧下降（例如，Griffiths 和 Campbell，1991），但证明直径 1000 公里的羽流可以扩展约 1600 公里（〜 2100 公里总半径）在 2 my 内，与德卢斯杂岩相对于 SWLLIP 的位置以及精确地质年代学揭示的岩浆作用时间滞后一致。与较小的羽流头（<550 km，超过 2 my）相关的较慢的扩散速度无法合理地将羽流材料从 SWLLIP 平流到 MCR，超过约 2 my Laurentia 在此期间约 30 厘米/年的漂移（Swanson-Hysell 等人） ., 2019) 将在 2 my 的羽流扩散过程中将 MCR 向东移动约 600 公里；然而，这种运动仅相对于 ~0.8 my 之后的羽流扩散速率才显着，此时这种情况下的羽流扩散已经被引导到 MCR 中（例如，Sleep 1997）。 CA 建立的 SWLLIP 镁铁质岩石的新年龄-ID-TIMS U-Pb 锆石共岩浆长英质偏析细化了 SWLLIP 的时间并解决了时间上不同的约。1098 马和约。1083马岩浆期。大约的地质年代学。1098 Ma SWLLIP 和约 1098 Ma 的原生岩浆活动 MCR 中的 1096 Ma 岩浆活动脉冲与预测的大陆岩石圈下的横向羽流扩散速率一致。我们提出了 SWLLIP 和 MCR 岩浆作用之间的羽流扩散关系作为假设，将通过未来的地质年代学研究与地球化学数据和先进的地球动力学模型相结合来检验。我们的研究强化了高精度 U-Pb 锆石地质年代学如何为定义和关联古代岩浆事件奠定基础，并产生测试羽流岩浆作用和大陆岩石圈之间复杂相互作用所需的时间分辨率。我们感谢布鲁斯·巴菲特对羽流润滑理论的见解，以及几个大峡谷-科罗拉多河现场论坛的工作人员提供现场和后勤支持。这项研究得到了美国死亡谷和大峡谷国家公园国家公园管理局的许可以及国家科学基金会的资助（拨款 EAR1954583、EAR1847277 和 EAR1735889）。C. Stein、J. Kasbohm、R. Ernst 和两位匿名审稿人的评论改进了这份手稿。