A comparative analysis of Raman shifts of quartz inclusions in garnet was made along two traverses across the Connecticut Valley Trough (CVT) in western New England, USA, to examine the regional trends of quartz inclusion in garnet (QuiG) Raman barometry pressure results and to compare this method with conventional thermobarometry and the method of intersecting garnet core isopleths. Overall, Raman shifts of quartz inclusions ranged from 1·2 to 3·5 cm^–1 over all field areas and displayed a south to north decrease, matching the overall decrease in mapped metamorphic grade. Raman shifts of quartz inclusions typically did not show systematic variation with respect to their radial position within a garnet crystal, and indicate that garnet probably grew at nearly isothermal and isobaric pressure–temperature (P–T) conditions. The P–T conditions inferred from conventional thermobarometry were in the range of ∼500–575 °C and ∼7·4–10·3 kbar over the sample suite and are in good agreement with previous published thermobarometry throughout the CVT. These P–T results are broadly consistent with QuiG barometry and also suggest that garnet grew isothermally and isobarically at near peak P–T conditions. However, P–T conditions and P–T paths inferred using either garnet core thermobarometry or garnet core intersecting isopleths yield results that are internally inconsistent and generally disagree with the pressure results from QuiG barometry. Garnet core isopleth intersections consistently plotted between the nominal garnet-in curve on mineral assemblage diagrams and the P–T conditions constrained by QuiG isomekes for the majority of the sample suite. Additionally, most samples’ P–T results from QuiG barometry and rim thermobarometry show marked disagreement from those derived from garnet core thermobarometry, compared with the minority that showed agreement within uncertainty. Pressures calculated from QuiG barometry ranged from 8·5 to 9·5 kbar along the traverses in western Massachusetts (MA) and central Vermont (VT) and from 6·5 to 7·5 kbar in northern VT indicating an increase in peak burial of 3–6 km from north to south. Along the western end of the central VT traverse, there are differences in measured Raman shifts and inferred peak pressures of up to 1 kbar across the Richardson Memorial Contact (RMC), indicating a possible fault contact with minor post-peak metamorphic shortening of up to ∼3 km. In contrast, along an east–west traverse in the vicinity of the Goshen Dome, MA, there was little observed variation in Raman shifts across the contact. By contrast, QuiG barometry clearly indicates significant discontinuities in peak pressure east of the Strafford Dome in central VT. This supports the interpretation that post-peak metamorphic shortening was necessary to juxtapose upper staurolite–kyanite zone rocks next to lower garnet zone pelites. Overall, it is concluded that garnet core thermobarometry and garnet core isopleths may provide unreliable results for the P–T conditions of garnet nucleation and inferred P–T paths during garnet growth unless independently verified. The consistency of QuiG results with rim thermobarometry indicates that peak metamorphic conditions previously reported for the CVT using garnet rim thermobarometry are robust and that variation in QuiG barometry results is a valuable tool to analyze structural features within a metamorphic terrane.

中文翻译：

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美国佛蒙特州和马萨诸塞州康涅狄格谷海槽的区域石英包裹体气压计以及与常规热气压计和相交等值线的比较

沿美国新英格兰西部康涅狄格河谷槽（CVT）的两个导线对石榴石中石英夹杂物的拉曼位移进行了比较分析，以检验石榴石（QuiG）中石英夹杂物的区域趋势拉曼气压测量结果，并将这种方法与常规热压法和石榴石芯等值线相交的方法进行比较。总体而言，石英包裹体的拉曼位移在所有场区的范围从1·2到3·5 cm ^–1，并显示出从南到北的减小，与映射的变质坡度的总体减小相匹配。石英夹杂物的拉曼位移通常并未显示出其在石榴石晶体中的径向位置的系统变化，这表明石榴石可能在几乎等温和等压-温度下生长（P – T）条件。从常规热压法推断出的P – T条件在整个样品套件中在〜500–575°C和〜7·4–10·3 kbar的范围内，并且与先前在整个CVT中公开的热压法相吻合。这些P – T结果与QuiG气压测量大致一致，也表明石榴石在P – T峰值附近等温和等压生长。但是，P – T条件和P – T使用石榴石岩心热压法或石榴石岩心相交等深线推断的路径产生的结果在内部不一致，并且通常与QuiG气压计的压力结果不一致。石榴石等值线的交点始终一致地绘制在矿物组合图上的标称石榴石插入曲线与大多数样品套件中受QuiG等规图约束的P – T条件之间。此外，大多数样本的P – TQuiG气压法和边缘热压法得出的结果与石榴石岩心热压法得出的结果明显不同，相比之下，在不确定性范围内显示出一致的少数人。由QuiG气压计算得出的压力沿马萨诸塞州西部（MA）和佛蒙特州中部（VT）的横移范围为8·5至9·5 kbar，北部VT的范围为6·5至7·5 kbar，表明最大埋葬量从北到南3至6公里。沿着中心VT导线的西端，在测量的拉曼位移和理查森纪念接触（RMC）上推断的最高1 kbar的峰值压力存在差异，这表明可能发生故障接触，且峰后变质缩短了小至约3公里 相比之下，沿着马萨诸塞州歌珊巨蛋附近的东西走向，几乎没有观察到整个接触中拉曼位移的变化。相比之下，QuiG气压表清楚地表明，VT中部斯特拉福德穹顶以东的峰值压力明显不连续。这支持了这样的解释，即峰后变质缩短对于将下部的石榴石区的贝利特石并列于上的辉石-蓝晶石区的岩石并置是必要的。总体而言，得出的结论是，石榴石岩心热压法和石榴石岩心等值线可能会提供不可靠的结果。石榴石成核的P – T条件以及在石榴石生长过程中推断的P – T路径，除非经过独立验证。QuiG结果与边缘热压法的一致性表明，以前使用石榴石边缘热压法为CVT报告的峰值变质条件是可靠的，并且QuiG气压法结果的变化是分析变质地层内结构特征的有价值的工具。