Petrogenesis of Triassic Intrusions, SW Maine: Forerunners of WMMS Igneous Activity

缅因州西南部三叠纪侵入岩的岩石成因：WMMS 火成岩活动的先驱

• 批准号: 8817184
• 负责人: Wallace Bothner
• 金额: $ 5万
• 依托单位: University of New Hampshire
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1989
• 资助国家: 美国
• 起止时间: 1989-01-01 至 1991-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8817184&HistoricalAwards=false
• 关键词: Petrogenesis; Triassic; Intrusions; SW; Maine

Anorogeneic igneous activity during the Mesozoic in New England was a long-lived and petrologically varied magmatic event. Three major pulses of magmatism are recognized: (1) an early Triassic phase, (2) a spatially restricted and voluminous Jurassic pulse, and (3) a regionally extensive Cretaceous phase. Modern petrologic investigations have concentrated on two later phases; petrogenetic conclusions vary from simple crustal anatexis to combined crustal assimilation and fractional crystallization (AFC) of mafic, mantle-derived magmas. In contrast, the earliest phase of activity, the Triassic event, has been petrochemically ignored. Exposed only in SW Maine, this activity is primarily represented by the Mt. Agamenticus complex (alkaline syenite to granite) and the Abbott Mountain stock (syenite). Using modern petrochemical techniques and geochronology (phase petrology, major, trace, and rare earth element geochemistry, Sr, Pb, and Nd isotope geochemistry, and 40Ar/39Ar isotope geochronology) the proposed research will carefully characterize these intrusions and develop comprehensive petrogenetic solutions. Preliminary results suggest that crustal anatexis and not AFC of mafic magmas is important in the genesis of these plutons. If so, then this Triassic magmatic event may be similar to the later Jurassic pulse and can be considered the forerunner of that activity. Comparison of petrogenetic models developed for all of the Mesozoic igneous events should increase our understanding of the evolution of this 'anorogenic' magmatism and provide better constraints on the nature of the tectono/thermal activity that was is ultimate cause.

新英格兰中生代厌造火成岩活动是一个寿命长、岩石学变化大的岩浆活动。确定了三个主要的岩浆活动脉冲：(1)早三叠纪期，(2)空间受限且体积庞大的侏罗纪期，(3)区域广泛的白垩纪期。现代岩石学研究集中在两个后期阶段；岩石成因的结论从简单的地壳深熔作用到基性幔源岩浆的地壳同化和分离结晶（AFC）联合作用。相比之下，最早的活动阶段，即三叠纪事件，在岩石化学上被忽略了。该活动仅在缅因州西南部暴露，主要代表为Agamenticus山杂岩（碱性正长岩到花岗岩）和Abbott山群（正长岩）。利用现代石油化工技术和地质年代学（相岩石学、主要元素、微量元素和稀土元素地球化学、Sr、Pb和Nd同位素地球化学以及40Ar/39Ar同位素地球年代学）对这些侵入岩进行详细描述，并制定全面的岩石成因解决方案。初步结果表明，这些岩体的成因主要是地壳的深熔作用，而不是岩浆的亚铁作用。如果是这样，那么这个三叠纪岩浆事件可能与侏罗纪晚期的脉冲相似，可以被认为是那次活动的先驱。对所有中生代火成岩事件的岩石成因模型进行比较，将增加我们对这种“造山”岩浆活动演化的理解，并更好地约束构造/热活动的性质，而构造/热活动是最终原因。