摘要
冷泉碳酸盐岩是海底冷泉流体活动的重要标志,其地球化学特征记录了过去流体活动的信息。西藏岗巴地区晚白垩世沉积地层中发育有冷泉碳酸盐岩,为了探究其形成的流体来源及沉积环境,开展了野外观察、岩石学、矿物学、地球化学研究。该区岗巴剖面冷泉碳酸盐岩以结核状产于灰黑色页岩中,碳酸盐矿物主要为泥微晶方解石,含少量草莓状黄铁矿,δ13CV-PDB为-17.0‰^-7.2‰,表明碳源可能与甲烷渗漏冷泉活动有关。稀土元素分布模式呈中稀土富集特征,经La校正后显示无Ce异常,指示了冷泉碳酸盐岩形成于弱缺氧的沉积环境中。西藏岗巴地区碳酸盐岩结核的发现及其地质地球化学特征是该地区晚白垩世冷泉甲烷渗漏活动发育的有力证据,对古冷泉流体来源及沉积环境特征的探讨将为恢复古冷泉活动提供重要线索。
Hydrocarbon-seep carbonates are a good geological archive of past fluid venting. We present field observations, petrographic and mineralogical analyses, stable carbon and oxygen isotope data, and rare earth element （REE） compositions to trace the fluid source and sedimentary environment of seep carbonates found within the Late Cretaceous marine mudstone in the Gamba area of Tibet. The carbonates occur as lenticular nodules within shales in outcrops. Petrographically, the carbonate minerals are predominantly composed of calcite. Moderately negative δ^13CV-PDB values, ranging from -17.0‰ to -7.2‰, suggest that the seep carbonates were possibly deposited from methane-seep fluids. Furthermore, the original REE＋Y patterns of the carbonate minerals exhibit middle REE enrichment, with no Ce anomalies after La anomaly corrections, indicating a weakly reduced environment. The discovery and geochemical characteristics of carbonate nodules in the Gamba area of Tibet provide strong evidence of methane leakage from the Late Cretaceous cold seeps in this region. The discussion on the source and sedimentary environment of cold seeps will provide important clues to reconstruct ancient cold seep activities.
出处
《地球化学》
CAS
CSCD
北大核心
2018年第2期217-227,共11页
Geochimica
基金
国家自然科学基金(41502113)
