Volcanic events‐related hydrothermal dolomitisation and silicification controlled by intra‐cratonic strike‐slip fault systems: Insights from the northern slope of the Tazhong Uplift, Tarim Basin, China

Abstract

Ordovician carbonate rocks on the northern slope of the Tazhong Uplift in the Tarim Basin are modified to varying degrees by hydrothermal fluids related to multiple tectonic-thermal events, but the nature, origin and circulation mechanisms of such hydrothermal fluids remain debated. In this article, in situ rare-earth elements and yttrium (REE + Y) concentrations, previously published geochemical datasets and petrographic investigations are integrated to develop a thermo-tectonic evolution model to improve understanding of silicification and dolomitisation occurring in the interior of the craton basin. δ 30 Si values, REE + Y ratios and fluid mixing models using modern black smoker fluid and seawater indicate that magma-sourced hydrothermal fluids, rather than basinal brine heated by magmatism, are responsible for the precipitation of cherts. Petrological and geochemical evidence suggests that deep-seated, ultramafic-derived hydrothermal fluids and/or magmatic fluids associated with Permian volcanism may have been involved in the formation of hydrothermal dolomites in the study area. Accompanying formation and reactivation of the strike-slip faults on the northern slope of the Tazhong Uplift, small volumes of hydrothermal fluids might have been triggered by seismic pumping. The early formed strike-slip fault systems may also have served as conduits for the subsequent large-scale transport of deep-seated, ultramafic-derived thermal fluids and/or Permian magmatic fluids, along which fluids were transported upwards at high flow rates. Carbonation of ultramafic rocks through interaction with deep-seated hydrothermal fluids rich in CO 2 may have served as a magnesium and silica source for dolomitisation and silicification. Trans-tensional troughs on NNE-trending strike-slip faults with positive flower structure are favourable locations for dolomitisation and silicification.

Structural diagenesis of deep carbonate rocks controlled by intra‐cratonic strike‐slip faulting: An example in the Shunbei area of the Tarim Basin, NW China

“…In addition to exhibiting PAAS‐normalized REE + Y patterns characteristic of normal marine carbonate rocks (i.e., positive La and Y anomalies and a negative Ce anomaly), DC1 also exhibited a positive Eu anomaly and MREE enrichment. Such an PAAS‐normalized REE pattern is similar to those of ultramafic‐hosted hydrothermal fluid (Figure 4d; Douville et al, 2002; Wei et al, 2021). DC1 had an extremely high Fe content and high Mn, Sr, and Ba contents (Figure 5).…”

“…Furthermore, CC4 was characterized by dark yellow (Figure 3j,n) CL, which may have been occurred during the slow subsidence stage when the physical and chemical diagenetic conditions were relatively stable. Douville et al, 2002;Wei et al, 2021). DC1 had an extremely high Fe content and high Mn, Sr, and Ba contents (Figure 5).…”

“…For example, Wang, Wang, Gu, et al (2019) and Yang et al (2021) considered that the mineral‐forming fluid was mainly formation water with a seawater origin, while Li et al (2019) proposed that the reservoir was mainly affected by the ascent of deeply‐buried diagenetic hydrocarbon‐generating fluids. In addition, deep burial and complex multi‐phase structural motions have led to a lack of consensus regarding the timing of fluid flow in this area (Wei et al, 2021). For example, some researchers have proposed that local hydrothermal fluid alteration was caused by Permian volcanism (Chen et al, 2016), while others have linked this alteration to the continuous activity of Devonian strike‐slip faults (Lu et al, 2017).…”

Hydrothermal silicification and hypogene dissolution of an exhumed Neoproterozoic carbonate sequence in Brazil: Insights from fluid inclusion microthermometry and silicon‐oxygen isotopes

“…It is important to note that the behaviour of silica during the diagenetic evolution of carbonate sediments is more complex than the simple paragenetic sequence listed above. Various sediment‐water interactions may act as either silica sinks or sources, for example: biodegradation of organic matter (Bennett et al, 1988), transformation of clay minerals, devitrification of volcanic ash (Siever, 1962; Siever & Woodford, 1973), or circulation of hydrothermal fluids (Wei et al, 2021). Chert with a predominantly volcanic silica source is recognizable by its high alkali, Al and Ti contents, ghosts of volcanic glass shards and associated volcaniclastic sediments (Maliva & Siever, 1989; Pollock, 1987).…”

“…Solutional voids and karstic vugs are commonly found in quartzites and silicified (cherty) carbonates in many hydrocarbon reservoirs in sedimentary basins, such as North Slope in Alaska (e.g. Shanmugan & Higgins, 1988), offshore Brazil (De Luca et al, 2017; Fernández‐Ibáñez, Jones, et al, 2022; Lima et al, 2020) and Tarim Basin in China (Dong et al, 2018; Wei et al, 2021; You et al, 2018).…”