Geology topics

Haibo Zou

Publications and source records attributed to Haibo Zou.

3 recordsLinked to original sources

USGS2026

Elemental and isotope geochemistry of Smackover Formation brines in Alabama and Arkansas: Implications for fluid mixing and water-rock interaction

This study investigates the geochemical characteristics of brines within the Upper Jurassic Smackover Formation in Alabama and Arkansas through elemental and isotopic analyses and geochemical modeling to reveal the extent and nature of fluid mixing and water-rock interactions. Smackover Formation brines exhibit Na-Cl-Ca hydrogeochemical facies and sulfate depletion relative to seawater. Lower sulfate concentrations, coupled with high H 2 S concentrations in some brines (0-364 mg/L) at temperatures >80°C, suggest that thermochemical sulfate reduction occurred. Cl/Br and Na/Br ratios indicate that salinity was controlled by the mixing of meteoric water with evaporated seawater that had reached halite saturation, rather than by halite dissolution. The δ 18 O and δ 2 H values of the brines also suggest mixing between meteoric water and evaporated seawater that had reached gypsum and halite saturation. Geochemical modeling of seawater evaporation predicts a Cl-Na or Cl-Mg facies after halite saturation, contrasting with the observed Cl-Ca dominance of the Smackover Formation brines. The Ca-enriched brines may have evolved from Cl-Mg-dominated evaporated seawater through dolomitization of limestone. The 87 Sr/ 86 Sr ratios range from 0.70740 to 0.71048, higher than the average of Jurassic seawater (0.707). The non-linear relationship between 87 Sr/ 86 Sr and 1000/Sr suggests alteration of brine geochemistry by fluid mixing or by inputs from Sr and 87 Sr-enriched rock sources. Lithium concentrations are positively correlated with 87 Sr/ 86 Sr ratios and TDS in brines enriched in these constituents. These correlations suggest deeper-seated geogenic sources and have implications for Li exploration in the northern Gulf Coast basin. Normal faults associated with the pre-Jurassic topography may have provided potential pathways for brine migration into the Smackover Formation under the influence of overpressure or thermohaline convection in the Gulf Coast.

Alabama↗

USGS2021

Zircon surface crystallization ages for the extremely reduced magmatic products of the Millennium Eruption, Changbaishan Volcano (China/North Korea)

The Millennium Eruption (ME) of Changbaishan volcano (Baitoushan, Paektu) at 946 CE (Common Era) is one of the largest explosive eruptions on Earth during Holocene times. We date unpolished zircon crystal faces from diverse ME products collected from the southern side of Changbaishan volcano where the ME pumice and welded and non-welded pyroclastic flow deposits (PFD) are better exposed. All zircons from a pumice sample of the southern caldera rim and the youngest (Group 1) zircons from a welded pumiceous PFD sample yield an isochron crystallization age of 0.7 ± 1.8 ka (2σ). Zircons from the welded pumiceous PFD sample yield additional two age groups at ~10 ka and ~ 100 ka. Zircons from a non-welded charcoal-containing PFD have only one age population at 100 ka. Our work shows that different eruption products from ME have different zircon surface age distributions and may tap different levels of a zoned felsic magma chamber. In addition, the results indicate that ion microprobe U-Th dating of zircon crystal surfaces from ME pumices can effectively date the Millennium eruption age. Previously reported zircon U-series ages for Qixangzhan eruption (12.2 ± 1.1 ka, 2σ) and Yuanchi eruption (7.3 ± 1.8 ka, 2σ) at Changbaishan are also likely to date their respective eruption ages. The occurrence of 100 ka zircons in welded and non-welded PFDs reveals an important magmatic event for the Changbaishan volcano. Zircon and Fe-rich clinopyroxene crystallized at similar temperature at 770–750 °C, indicative of early zircon crystallization in peralkaline magmas. Another important result is the extremely low oxygen fugacity (fO 2 = ΔFMQ-2) of the Changbaishan samples. Minerals in ME magmas were crystallized under some of the most reducing magmatic environments on Earth. Highly reducing conditions of magmas from Changbaishan supports a continental rift setting and argues against significant involvements of subduction-related oxidizing fluids during magma genesis.

Changbaishan Volcano↗

USGS2020

Timescales of magmatic processes in post-collisional potassic lavas, northwestern Tibet

Post-collisional potassic volcanic rocks on the Tibetan Plateau are widespread, but geologically young (<375 ka) volcanism suitable for 238 U- 230 Th geochronology is rare on the plateau. The geologically young Ashikule volcanic field from northern Tibet offers an excellent opportunity for studying high-resolution timescales of magmatism in continental collision zones. Here we report U-Th crystallization ages of zircons from Ashishan volcano and Wulukeshan volcano within the Ashikule volcanic field. In this study, we have identified 3 pulses of zircon crystallization at circa 70 ka, 105 ka, and 290 ka for Ashishan volcanic rocks and 1 pulse of zircon crystallization at circa 115 ka for Wulukeshan. Comparison of high-resolution zircon crystallization ages of 70 ka and 105 ka with respective eruption ages indicate that the zircon crystal residence time for the Ashishan volcano is short (<5 kyr). The presence of 290-ka zircon in a different Ashishan lava flow suggests the 270-ka volcanic pulse previously reported for other volcanoes in Ashikule volcanic field also occurred at Ashishan. The zircon crystallization age of ~115 ka for Wulukeshan volcano suggests that Wulukeshan volcano erupted later than previously inferred. Similar zircon age spectrums of ~105–115 ka for Ashishan and Wulukeshan volcanoes suggest a common interconnected subsurface magma reservoir for these two young volcanoes during Pleistocene time. Our new high-resolution U-Th zircon age data reveal that post-collisional potassic magmas below northern Tibet erupted soon after their formation (<5 kyr), in spite of their passage through thick continental crust. The high abundance (~60%) of geologically old (>375 ka) zircons demands for crystal-scale isotope studies of the widespread post-collisional lavas in continental collision zones, as the complexities cannot be resolved by bulk analysis methods alone.

LITHOS↗