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

综合古地磁/地质年代学研究需要在东南部新英格兰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。比如：1.据报道，新元古代，但以前未注明日期的布莱顿火山夹层从四个地理上分开的部分在罗克斯伯里砾岩有最大年龄约587 Ma，490 Ma，438 Ma和362 Ma的基础上1-4颗粒锆石馏分。 据报道，奥陶纪昆西花岗岩（基于上截距年龄437 + 23 Ma）已产出志留纪-泥盆纪锆石（单颗粒分析，207 Pb/ 206 Pb年龄约为410 Ma）。 据报道，波士顿盆地西部630 + 15 Ma的Dedham花岗岩的三个单颗粒锆石分析结果表明，207 Pb/ 206 Pb年龄的加权平均值约为610 Ma。先前报道的新元古代阿瓦隆极形成罗克斯伯里砾岩是来自志留纪或更年轻的岩石。新元古代岩石形成于低中纬度，而不是以前报道的中高纬度，其年代为610 ~ 570 Ma。该建议寻求资金，以继续开展工作，澄清波士顿地区的地层和构造关系，作为完成5或6个年代确定的古磁极的基础。这些极点将限制修订后的解释古纬度东南部新英格兰阿瓦隆区在新元古代弧岩浆活动，它的位置在假设的“雪球”地球气候事件和时间中古生代增生到北美。将在阿瓦隆弧岩（包括Dedham花岗岩和马塔潘火山杂岩）、新元古代地层（包括剑桥泥质岩和冰海沉积物（包括罗克斯伯里砾岩的Scquantum段））的21个新地点收集定向古地磁岩心，在“布赖顿”火山岩和其他几个年龄不确定或限制不严的地层中，（包括据报道的梅德福岩脉和卡夫岛岩床的侏罗纪侵入岩）。其中12个地点还将用于支持地质年代学，10个地点用于地球化学。

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.