Reconstructing carbonate alteration histories in orogenic sedimentary basins: Xigaze forearc, southern Tibet
Reconstructing carbonate alteration histories in orogenic sedimentary basins: Xigaze forearc, southern Tibet
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DOI：
10.1016/j.gca.2019.02.005
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发表时间：
2019-04
影响因子：
5
通讯作者：
M. Ingalls
中科院分区：
文献类型：
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作者：
M. Ingalls
碳酸盐聚集同位素测温法（T（Δ 47））和氧稳定同位素记录（δ 18 O）为碳酸盐矿物形成温度和古沃茨同位素组成提供了重要的制约，可用于重建过去的气候、构造以及生态和环境变化。这些代用指标的可靠使用要求岩石记录中的碳酸盐矿物在通常复杂的沉积后热历史中保留主要同位素组成。新的碳酸盐成块同位素测温和沉积学数据与现有的热年代学和同位素交换反应模型相结合，提供了独特的制约因素的特提斯海相碳酸盐岩（甲腊子组，措尖顶群）的碳，氧同位素的蚀变历史日喀则弧前，藏南。在结构和同位素数据的框架下，模拟了埋藏早期和晚期蚀变对埋藏至海拔4km的海相岩石Δ 47和δ 18 O值的影响< 6 km and uplifted to>。蚀变产物被认为是在两个研究得很好的机制框架：水-岩石重结晶和13 C单键18 O键在高温下的固态重排。建议的蚀变模式如下：（1）浅层、早期成岩作用，水的成分和温度与地层沃茨相似，用微晶石填充原生孔隙;（2）高温、岩石缓冲的水-岩交换和> 3-4 km深度的部分固态重排;（3）近地表、折返路径上的低温水-岩交换。单个样品中Δ 47的不均匀性（0.456 ~ 0.721）要求在退变质路径（高温至低温、低水岩比）上有显著的差异蚀变，在退变质路径上，原生成分和在早期埋藏成岩作用期间继承的成分与现代大气降水值叠加。通常假定低T（Δ 47）值记录沉积环境的原始温度。然而，甲腊子组中T（Δ 47）值较低的样品经历了广泛的高温水岩蚀变，因此，需要一种机制来增加退变质通道上的13 C单键18 O键有序性，同时保留许多原始生物成因结构和泥晶结构。这一研究突出了造山带沉积盆地碳酸盐岩晚期低温蚀变在陆地古环境和大地构造研究中的潜在意义。这项研究还提供了一个例子框架相结合的观测和分析数据，以重建一个埋藏的沉积包的碳酸盐岩蚀变史。
Carbonate clumped isotope thermometry (T (Δ 47)) and the oxygen stable isotope record (δ 18 O) provide critical constraints on the temperature of carbonate mineral formation and isotopic composition of ancient waters used in reconstructions of past climate, tectonics, and ecological and environmental change. The robust use of these proxies requires that carbonate minerals in the rock record retain primary isotopic compositions through often complex post-depositional thermal histories. New carbonate clumped isotope thermometry and sedimentology data are paired with existing thermochronology and isotope exchange reaction modeling to provide unique constraints on the alteration history of the carbon and oxygen isotopes in Tethyan marine carbonates (Jialazi Fm, Tso Jianding Group) of the Xigaze forearc, southern Tibet. Within the framework of the textural and isotopic data, the effects of early and late burial alteration on Δ 47 and δ 18 O values of marine rocks that were buried to< 6 km and uplifted to> 4 km above sea level are modeled. The alteration products are considered within two well-studied mechanistic frameworks: water-rock recrystallization and solid-state reordering of 13 Csingle bond 18 O bonds at high temperature. The proposed alteration model is as follows:(1) shallow, early diagenesis with water of similar composition and temperature to formation waters infills primary porespace with microspar;(2) high-temperature, rock-buffered water-rock exchange and partial solid-state reordering at> 3–4 km depth; and (3) near-surface, low-temperature water-rock exchange on the exhumation pathway. The Δ 47 heterogeneity within individual samples (0.456 to 0.721) requires significant differential alteration on the retrograde path (high to low temperature, low water-rock ratio) in which primary compositions and compositions inherited during early burial diagenesis are overprinted with modern meteoric values. A low T (Δ 47) value is often assumed to record the primary temperature of the depositional environment. However, samples yielding low T (Δ 47) values in the Jialazi Fm have undergone extensive high-temperature water-rock alteration, and therefore, require a mechanism for increasing 13 Csingle bond 18 O bond ordering on the retrograde pathway while preserving many primary biogenic structures and micritic textures. This study highlights the potential significance of late-stage, low-temperature alteration of carbonates derived from orogenic sedimentary basins for studies of terrestrial paleoenvironments and tectonics. This study also provides an example framework for combining observational and analytical data to reconstruct a carbonate alteration history of a buried sedimentary package.