Collaborative Research: Stratigraphic Resolution as Key to Tectonic Synthesis in the Southeastern New England Avalon Zone Around Boston, Massachusetts

合作研究：地层分辨率是马萨诸塞州波士顿周围新英格兰东南部阿瓦隆带构造综合的关键

• 批准号: 0125477
• 负责人: Margaret Thompson
• 金额: $ 9.78万
• 依托单位: Wellesley College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-04-15 至 2006-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0125477&HistoricalAwards=false
• 关键词: Collaborative; Research; Stratigraphic; Resolution; Key

Integrated paleomagnetic/geochronologic study necessitates radical tectonic re-thinking in the Boston portion of the Southeastern New England Avalon Zone because new isotopic data reveal fundamental flaws in the long accepted regional stratigraphy. For example:1. Reportedly Neoproterozoic, but previously undated Brighton volcanic interbeds from four geographically separated sections in the Roxbury Conglomerate have maximum ages of approximately 587 Ma, 490 Ma, 438 Ma and 362 Ma based on 1-4 grain zircon fractions.2. Reportedly Ordovician Quincy Granite (based on an upper intercept date of 437 + 23 Ma) has yielded Siluro-Devonian zircons (single grain analyses with 207 Pb/ 206 Pb dates of approximately 410 Ma).3. Reportedly 630 + 15 Ma Dedham Granite west of the Boston Basin has yielded a weighted mean 207 Pb/ 206 Pb date of approximately 610 Ma based on three single zircon analyses.Preliminary paleopoles based on these geochronological data further suggest that:1. The previously reported Neoproterozoic Avalonian pole form the Roxbury Conglomerate is from Silurian or younger rocks.2. Reliably dated Neoproterozoic rocks formed at low-mid latitudes rather than the previously reported high-mid latitude for the 610 to ~ 570 Ma interval.This proposal seeks funding for continued work to clarify stratigraphic and structural relationships inthe Boston area as a basis for completing 5 or 6 well dated paleomagnetic poles. These poles will constrain revised interpretations of the paleolatitude of the Southeastern New England Avalon Zone during Neoproterozoic arc magmatism, its position during during hypothesized "snowball" earth climatic events and the timing of mid-Paleozoic accretion to North America. Oriented paleomagnetic cores will be collected at 21 new locations in Avalonian arc rocks including Dedham Granite and Mattapan Volcanic Complex, in overlying Neoproterozoic strata including the Cambridge Argillite and glaciomarine deposits comprising the Squantum Member of the Roxbury Conglomerate, in "Brighton" Volcanics and in several other formations of uncertain or poorly constrained age (including reportedly Jurassic intrusive rocks of the Medford dike and Calf Island sill). Twelve of these sites are also targeted for supporting geochronology and ten for geochemistry.

综合古地磁/地质年代学研究需要对新英格兰东南部阿瓦隆带的波士顿部分进行彻底的构造重新思考，因为新的同位素数据揭示了长期接受的区域地层学的根本缺陷。例如：1。据报道，根据 1-4 粒锆石分数，来自 Roxbury 砾岩四个地理上分离部分的新元古代但之前未注明日期的 Brighton 火山夹层的最大年龄约为 587 Ma、490 Ma、438 Ma 和 362 Ma。2。 据报道，奥陶纪昆西花岗岩（基于 437 + 23 Ma 的上截距日期）已产出志罗-泥盆纪锆石（单晶分析，207 Pb/ 206 Pb 日期约为 410 Ma）。3。 据报道，基于三个单锆石分析，波士顿盆地以西的 630 + 15 Ma Dedham 花岗岩得出了约 610 Ma 的加权平均 207 Pb/ 206 Pb 日期。基于这些年代学数据的初步古极点进一步表明： 1．先前报道的罗克斯伯里砾岩新元古代阿瓦隆阶极点来自志留纪或更年轻的岩石。2．可靠测年的新元古代岩石形成于中低纬度地区，而不是之前报道的 610 至 570 Ma 区间的中高纬度地区。该提案寻求资金，以继续开展澄清波士顿地区地层和结构关系的工作，作为完成 5 或 6 个测年良好的古地磁极的基础。这些极点将限制对新元古代弧岩浆作用期间新英格兰东南部阿瓦隆带的古纬度、其在假设的“雪球”地球气候事件期间的位置以及中古生代向北美吸积的时间的修订解释。将在阿瓦隆期弧岩中的 21 个新位置收集定向古磁芯，包括戴达姆花岗岩和马塔潘火山杂岩体、上覆新元古代地层，包括剑桥泥岩和包括罗克斯伯里砾岩 SQuantum 岩层在内的冰洋矿床、“布莱顿”火山岩和其他几个年龄不确定或约束较差的地层（包括 据报道是梅德福堤和小牛岛岩台的侏罗纪侵入岩）。其中十二个站点还用于支持地质年代学，十个站点用于地球化学。