کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
9535985 | 1356936 | 2005 | 13 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Geochemical and Nd isotopic compositions of 3.8Â Ga meta-quartz dioritic and trondhjemitic rocks from the Anshan area and their geological significance
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موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
زمین شناسی
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چکیده انگلیسی
The 3.8 Ga meta-quartz dioritic rocks discovered recently in the Anshan area show relatively high âREE contents and low (La/Yb)n ratios, with tDM of 3.50-4.16 Ga and ÉNd (3.8 Ga) of â1.24 to 4.51. Slightly older 3.8 Ga trondhjemitic rocks have been found in two locations in the Anshan area. One is the Baijiafen gneiss, which crops out near Baijiafen village and is characterized by relatively high SiO2 and Na2O, low MgO, âFeO and CaO, rather low âREE contents and low (La/Yb)n ratios. The other is the Dongshan banded gneiss located in the Dongshan Scenic Park in Anshan City, which has a similar chemical composition to the Baijiafen gneiss, except for slightly higher MgO, âFeO, CaO and âREE concentrations. All the 3.8 Ga trondhjemitic rocks exhibit large variations in Nd isotopic compositions, with tDM and ÉNd (3.8 Ga) of 3.07-3.87 Ga and 0.82-12.23 for the Baijiafen gneiss, and 2.82 to 3.40 Ga and 7.37-12.44 for the Dongshan banded gneiss, respectively. It is suggested that the 3.8 Ga trondhjemitic rocks from the Anshan area were formed by partial melting of intermediate to acidic continental material, and not basaltic material. TTG rocks of early Archean age are generally low in âREE contents and (La/Yb)n ratios compared with those of late Archean age. The regular variations of REE patterns with time may reflect thermal evolution of the primitive Earth. In the early stages, the Earth had higher geothermal gradients (>30 °C/km). After about 3.5-3.6 Ga, its geothermal gradient dropped into the garnet stability field.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Asian Earth Sciences - Volume 24, Issue 5, February 2005, Pages 563-575
Journal: Journal of Asian Earth Sciences - Volume 24, Issue 5, February 2005, Pages 563-575
نویسندگان
Yusheng Wan, Dunyi Liu, Biao Song, Jishan Wu, Chonghui Yang, Zongqing Zhang, Yuansheng Geng,