近日，美国雪城大学Jay Thomas团队报道了解耦的独居石与石榴石岩石年代学揭示美国纽约市曼哈顿片岩的短时高温阿卡迪安期变质作用。这一研究成果于2025年11月24日发表在《地质学》杂志上。

美国纽约州南部的曼哈顿岩带（由古老岩石组成的带状区域）位于北美最大的人口密集区之一，但其构造-变质历史仍鲜为人知。

研究组对纽约市中央公园采集的曼哈顿片岩样本进行了独居石U-Pb测年、石榴石Sm-Nd测年以及石榴石扩散年代学研究。包裹在石榴石和基质中的独居石给出约4.38亿年的²⁰⁶Pb/²³⁸U年龄，但其中一个基质颗粒显示明显更年轻的约3.91亿年年龄；所有分析的独居石稀土元素组成均一致。石榴石给出了稳健的约3.86亿年等时线年龄，用于约束石榴石在近峰期变质条件下的生长时间。

1毫米级石榴石中锰含量的环带保留表明，约3.86亿年时近峰期变质条件持续时间小于5百万年。曼哈顿片岩记录了多期变质历史：约4.38亿年时发生塔康期绿片岩相变质作用（由残余独居石记录），随后约3.86亿年时发生短时阿卡迪安期蓝晶石相变质作用（由石榴石及主要造岩组合记录）。这些结果与涉及中地壳局部、间歇性加热的构造模型一致，而非渐进且广泛存在的加热-冷却过程。该研究展示了结合副矿物与主要矿物年代学研究可获得的精细构造-变质认识。

附：英文原文

Title: Decoupled monazite and garnet petrochronology reveals short-duration, high-temperature Acadian metamorphism in the Manhattan Schist, New York City, USA

Author: Adrian E. Castro, Daniel R. Viete, Stephanie Walker, Steven J. Jaret, Isabella Brunet, Katherine Morin, Dana C. Brenner, Supratik Roy, Ethan F. Baxter, Oliver M. Wolfe, Jay Thomas

Issue&Volume: 2025-11-24

Abstract: The Manhattan Prong (a belt of ancient rock in southern New York, USA) underlies one of the largest population bases in North America yet its tectonometamorphic history remains poorly understood. We performed monazite U-Pb and garnet Sm-Nd petrochronology in association with garnet diffusion chronometry on a sample of the Manhattan Schist from Central Park, New York City. Monazite included in both garnet and matrix yielded a 206Pb/238U date of ca. 438 Ma, though one matrix grain yielded a distinctly younger date of ca. 391 Ma; all monazite analyzed showed identical rare earth element compositions. Garnet yielded a robust isochron date of ca. 386 Ma, interpreted to constrain the timing of garnet growth at near-peak metamorphic conditions. Retention of manganese zoning in 1-mm-scale garnet requires that near-peak metamorphic conditions at ca. 386 Ma persisted for <5 m.y. The Manhattan Schist records a polymetamorphic history involving Taconic greenschist-facies metamorphism at ca. 438 Ma, recorded by relict monazite, then short-lived Acadian kyanite-grade metamorphism at ca. 386 Ma, recorded by garnet and the major rock-forming assemblage. These results are consistent with tectonic models that involve localized, episodic heating of the middle crust, rather than gradual and more pervasive processes of heating and cooling. Our study is an example of the nuanced tectonometamorphic understanding that can be gained by combining accessory and major phase petrochronology.

DOI: 10.1130/G53777.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G53777.1/718833/Decoupled-monazite-and-garnet-petrochronology