Lower Cretaceous Xigaze ophiolites formed in the Gangdese forearc : Evidence from paleomagnetism, sediment provenance, and stratigraphy
Lower Cretaceous Xigaze ophiolites formed in the Gangdese forearc : Evidence from paleomagnetism, sediment provenance, and stratigraphy
复制标题
DOI：
10.1016/j.epsl.2015.01.032
复制
发表时间：
2015-04
影响因子：
5.3
通讯作者：
Wentao Huang;D. Hinsbergen;M. Maffione;D. Orme;G. Dupont‐Nivet;C. Guilmette;L. Ding;Zhaojie Guo;P. Kapp
中科院分区：
文献类型：
--
作者：
Wentao Huang;D. Hinsbergen;M. Maffione;D. Orme;G. Dupont‐Nivet;C. Guilmette;L. Ding;Zhaojie Guo;P. Kapp
摘要藏南印度-亚洲缝合带出露下白垩统日喀则蛇绿岩、放射虫硅质岩和与时间相当的亚洲源碎屑弧前沉积岩（日喀则群）。这些蛇绿岩被解释为形成于西藏下方的北倾俯冲带的弧前，该俯冲带产生了大约15-20° N的冈底斯岩浆弧，或者形成于亚赤道洋内俯冲带的弧前。为了更好地确定蛇绿岩的纬度范围，我们对浅成蛇绿岩放射虫岩（冲堆和白囊剖面）和不整合覆盖在蛇绿岩地幔单元上的日喀则群浊积岩（桑桑剖面）进行了古地磁、年代学和地层学的综合研究。对崇堆剖面凝灰质层和桑桑剖面日喀则群砂岩的碎屑锆石U-Pb年代学研究表明，崇堆剖面的最大沉积年龄分别为116.5± 3.1Ma和128.8± 3.4Ma，日喀则群具有亚洲物源的特征。古地磁分析，结合岩石磁学实验，表明显着的倾斜相关的研究岩石内的剩磁“变浅”。用两种独立的方法对桑桑剖面的古地磁方向进行了倾斜变浅校正，得到了一致的平均古纬度值，分别为16.2° N [13° N，20.9° N]和16.8° N [11.1° N，23.3° N]。这些结果与最近对西藏南部冈底斯弧的古纬度估计没有区别。崇堆和白囊剖面的放射岩具有低的古地磁倾角，表明古纬度处于亚赤道，但这些岩石中的古地磁方向分布强烈表明压实作用导致的低倾角偏置。研究结果表明，日喀则蛇绿岩的扩张作用发生在冈底斯弧前，并形成了弧前地层的基底。
Abstract The India–Asia suture zone of southern Tibet exposes Lower Cretaceous Xigaze ophiolites and radiolarian cherts, and time-equivalent Asian-derived clastic forearc sedimentary rocks (Xigaze Group). These ophiolites have been interpreted to have formed in the forearc of the north-dipping subduction zone below Tibet that produced the Gangdese magmatic arc around 15–20° N, or in the forearc of a sub-equatorial intra-oceanic subduction zone. To better constrain the latitude of the ophiolites, we carried out an integrated paleomagnetic, geochronologic and stratigraphical study on epi-ophiolitic radiolarites (Chongdui and Bainang sections), and Xigaze Group turbiditic sandstones unconformably overlying the ophiolite's mantle units (Sangsang section). Detrital zircon U–Pb geochronology of tuffaceous layers from the Chongdui section and sandstones of the Xigaze Group at the Sangsang section provides maximum depositional ages of 116.5±3.1 Ma and 128.8±3.4 Ma, respectively, for the Chongdui section and an Asian provenance signature for the Xigaze Group. Paleomagnetic analyses, integrated with rock magnetic experiments, indicate significant compaction-related inclination ‘shallowing’of the remanence within the studied rocks. Two independent methods are applied for the inclination shallowing correction of the paleomagnetic directions from the Sangsang section, yielding consistent mean paleolatitudes of 16.2° N [13° N, 20.9° N] and 16.8° N [11.1° N, 23.3° N], respectively. These results are indistinguishable from recent paleolatitude estimates for the Gangdese arc in southern Tibet. Radiolarites from the Chongdui and Bainang sections yield low paleomagnetic inclinations that would suggest a sub-equatorial paleolatitude, but the distribution of the paleomagnetic directions in these rocks strongly suggests a low inclination bias by compaction. Our data indicate that spreading of the Xigaze ophiolite occurred in the Gangdese forearc, and formed the basement of the forearc strata.