Rapid exhumation of the northern Jiaobei Terrane, North China Craton in the Early Cretaceous: insights from Al-in-hornblende barometry and U-Pb geochronology

The Guojialing and Aishan plutons in the northern Jiaobei Terrane represent the magmatic products of the.lithospheric thinning of the North China Craton in the Early Cretaceous. The exhumation history of the terrane in.response to the thinning process and its effect on the formation and preservation of coeval gold deposits remain.poorly constrained. Granodiorites from the Guojialing pluton and monzogranites from the Aishan pluton contain.zircon grains with U-Pb ages of ca. 130 Ma and ca. 116 Ma, respectively. Using the Al-in-hornblende barometry,.the Guojialing and Aishan plutons had crystallization pressures of 3.2–5.4 kbar (∼12 km) and 1.5–2.6 kbar.(∼5 km), respectively. Using the hornblende-plagioclase thermometry, the Guojialing and Aishan plutons had.crystallization temperatures of 628–697 °C and 702–745 °C, respectively. Fluid inclusion microthermometric.data show that auriferous quartz veins in the Daliuhang deposit formed at temperatures between 243 and 322 °C.at a depth of 7–11 km which was similar to the emplacement depth of the Aishan pluton. These thermobarometric.and geochronological data reveal ∼7 km uplift between 130 Ma and 116 Ma, but negligible exhumation.for the gold deposits after its formation until 116 Ma. Combining previous results, we envisage that the exhumation.magnitude of the Guojialing intrusions were nearly the same in the wide area with slight differences.between the core and margin of a single pluton. Numerous gold deposits in the Jiaobei Terrane formed during or.after the late stage of rapid exhumation of granitoids, and were uplifted with similar depths to the Aishan pluton.since ca. 116 Ma. The rapid exhumation of the Guojialing pluton was with the regional extension, and might be.genetically associated with the intensive delamination of destabilized lithospheric root and dense residues.

胶北地体北部的郭家岭和艾山岩体代表了华北克拉通早白垩世岩石圈减薄的岩浆产物。该地体响应减薄过程的剥露历史及其对同时期金矿床形成和保存的影响仍受到很大限制。郭家岭岩体的花岗闪长岩和艾山岩体的二长花岗岩所含锆石的U - Pb年龄分别约为130 Ma和116 Ma。利用角闪石中铝压力计，郭家岭和艾山岩体的结晶压力分别为3.2 - 5.4 kbar（约12 km）和1.5 - 2.6 kbar（约5 km）。利用角闪石 - 斜长石温度计，郭家岭和艾山岩体的结晶温度分别为628 - 697°C和702 - 745°C。流体包裹体显微测温数据显示，大柳行矿床含金黄铁矿石英脉形成于243 - 322°C，深度为7 - 11 km，与艾山岩体的侵位深度相似。这些温压和年代学数据表明，在130 Ma到116 Ma之间抬升了约7 km，但金矿床在116 Ma之前形成后剥露可忽略不计。结合先前的研究结果，我们设想郭家岭侵入体在大面积内的剥露幅度几乎相同，单个岩体的核部和边缘之间略有差异。胶北地体众多金矿床形成于花岗岩类快速剥露后期或之后，并且自约116 Ma以来与艾山岩体以相似的深度被抬升。郭家岭岩体的快速剥露与区域伸展有关，可能与不稳定岩石圈地幔根的强烈拆沉和致密残余物在成因上相关。