The petrogenesis and emplacement of the New Hampshire plutonic suite
The petrogenesis and emplacement of the New Hampshire plutonic suite
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新罕布什尔州深成岩组的岩石成因和侵位
DOI：
10.2475/ajs.303.5.447
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发表时间：
2003
影响因子：
2.9
通讯作者：
M. Dorais
中科院分区：
文献类型：
--
作者：
M. Dorais
与新英格兰阿卡迪亚造山运动有关的一个长期问题是，造山运动是否涉及在没有岩浆和/或来自地幔和/或下地壳的异常热量的情况下，在中地壳内部进行质量和能量的重新分配。几个封闭系统模型表明，新罕布什尔深部岩浆套件（NHPS）主要是由于中缅因地体（CMT）的变质沉积岩在地壳中部水平的部分原位熔融而形成的。地壳增厚模式、沿滑脱的剪切加热以及富铀变质沉积岩的存在被认为是深熔的热源。这些模型虽然适用于许多NHPS岩体，但在解释整个NHPS时存在以下几个困难：1)同构造伯利恒、金斯曼和斯波尔丁段的CaO-和Na - 2o含量过高，不可能来自暴露的变质岩；深层偏砾岩可能是部分NHPS烃源岩的主要来源，而不是含金属的spulding Tonalite和其他基性较强的NHPS烃源岩；2)部分NHPS δ 18o、Nd和Sr同位素值超出了CMT和Bronson Hill地体变质沉积岩的范围，需要更原始的幔状成分；3) Kinsman和Spaulding岩浆的温度高于与地壳增厚相关的区域变质作用的温度，大于850℃；(4) spulding Tonalite的Winnipesaukee岩体的岩浆绿绿岩和角闪石地球压力测量表明，在≥6 kbar的初始压力下，岩内结晶作用比推断出的同种CMT地元沉积岩与下伏基底之间的脱脱作用更深。这些数据表明，虽然NHPS中含有大量来自CMT变质沉积岩的成分，但含金属的斯波尔丁岩、金斯曼地区的基性岩、佛蒙特州东北部、缅因州西部和新罕布什尔州东南部的基性岩，提供了与封闭的地壳中部系统过程相关的热量和质量的证据。
A longstanding problem associated with the Acadian orogeny in New England is whether or not the orogeny involved a redistrubution of mass and energy within the midcrust without the addition of magmas and/or anomalous heatfrom the mantle and/or lower crust. Several closed system models suggest the New Hampshire Plutonic Suite (NHPS) resulted from essentially in situ partial melting of the metasedimentary rocks of the Central Maine terrane (CMT) at midcrustal levels. Crustal thickening models, shear heating along the decollement, and the presence of U-enriched metasedimentary rocks have been suggested as heat sources for anatexis. While applicable to numerous NHPS plutons, there are several difficulties with these models as explanations for the NHPS as a whole: 1) the syntectonic Bethlehem, Kinsman, and Spaulding members are too CaO- and Na 2 O-rich to have been derived from the exposed metapelites; deeper seated metagraywackes may account for some of the NHPS source rocks but not for the metaluminous Spaulding Tonalite and other more mafic NHPS rocks; 2) some NHPS δ 1 8 O, Nd, and Sr isotopic values are outside the range of CMT and Bronson Hill terrane metasedimentary rocks, requiring a more primitive mantle-like component; 3) the temperatures of the Kinsman and the Spaulding magmas were higher than those attained during regional metamorphism associated with crustal thickening, greater than 850°C; 4) magmatic epidote and hornblende geobarometry for the Winnipesaukee pluton of the Spaulding Tonalite suggest intratelluric crystallization, initially at pressures ≥ 6 Kbars, deeper than the inferred decollement between the allochthonous CMT terrane metasedimentary rocks and underlying basement. These data suggest that while the NHPS contains a significant component from the CMT metasedimentary rocks, the metaluminous Spaulding rocks, mafic enclaves in the Kinsman, and mafic rocks in northeastern Vermont, western Maine and southeastern New Hampshire provide evidence of heat and mass beyond that associated with closed, midcrustal system processes.